26 August 2016

Catching Some Comet Dust: Giotto II (1985)

Giotto 1 liftoff. Image credit: European Space Agency
On the overcast morning of 2 July 1985, the eleventh Ariane 1 rocket to fly lifted off from the Centre Spatial Guyanais in Kourou, French Guiana, an outpost of the European Community located a few degrees north of the equator on the northeast coast of South America. The last Ariane 1 to fly, it bore aloft Giotto, the first European Space Agency (ESA) interplanetary spacecraft. Giotto's destination was Comet Halley.

A "dirty snowball" containing materials left over from the birth of the Solar System 4.6 billion years ago, Halley needs about 76 years to revolve around the Sun once. Its elliptical orbit takes it from the cold emptiness beyond Neptune to the space between the orbits of Venus and Mercury. Halley travels around the Sun in a retrograde orbit, meaning that it orbits "backwards" relative to the eight planets and most other objects making up the Solar System.

Comet Halley has passed through the inner Solar System 30 times since its first verified recorded apparition in 240 B.C. In 837 A.D., it passed just 5.1 million kilometers from Earth; during that apparition, its dust tail must have spanned nearly half the sky, and its bright coma – the roughly spherical dust and gas cloud surrounding its icy nucleus – may have appeared as large as the full moon.

Shortly after its bright apparition in the year 1301, Italian artist Giotto di Bondone was inspired to add Comet Halley to his painting The Adoration of the Magi. The Giotto spacecraft was named for him.

Comet Halley appears near the top of Giotto di Bondone's The Adoration of the Magi. 
Throughout most of its known apparitions, Comet Halley was not understood to be one comet repeatedly passing through the inner Solar System. Not until 1705 did English polymath Edmond Halley determine that comets seen in 1531, 1607, and 1682 were probably one comet orbiting the Sun. He predicted that, if his hypothesis was correct, the comet should reappear in 1758 (which it subsequently did).

The Ariane 1's third stage injected 980-kilogram Giotto into a 198.5-by-36,000-kilometer orbit about the Earth. Thirty-two hours after launch, as it completed its third orbit, flight controllers in Darmstadt in the Federal Republic of Germany commanded drum-shaped Giotto to ignite its French-built Mage solid-propellant rocket motor. The motor burned 374 kilograms of propellant in 55 seconds to inject the spinning 2.85-meter-tall, 1.85-meter-diameter spacecraft into orbit about the Sun.
 
Two months before Giotto's launch, Americans P. Tsou (Jet Propulsion Laboratory), D. Brownlee (University of Washington), and A. Albee (California Institute of Tech) proposed in a paper in the Journal of the British Interplanetary Society that a second Giotto mission be launched to fly close by one of 13 candidate comets between 1988 and 1994. They proposed that the new spacecraft, which they dubbed Giotto II, might launch on an Ariane 3 or in the payload bay of a Space Shuttle. Giotto II's "free-return" trajectory would take it as close as 80 kilometers from the target comet's nucleus, then would return it to Earth.

Near the comet, Giotto II would expose sample collectors to the dusty cometary environment. Near Earth, it would eject a sample-return capsule based on the proven General Electric (GE) Satellite Recovery Vehicle (SRV) design. The capsule would enter Earth's atmosphere to deliver its precious cargo of comet dust to eager scientists.
 
Tsou, Brownlee, and Albee pointed out that the Mage solid-propellant motor was not required to boost Giotto into interplanetary space; that is, that the Ariane 1 could do the job itself. Giotto was, however, based on a British Aerospace-built Geos magnetospheric satellite design, which included the Mage motor. Re-testing the design without the motor would have cost time and money, so ESA elected to retain it for Giotto. After noting that the GE SRV could fit comfortably in the space reserved for the Mage, they proposed that, in Giotto II, the reentry capsule should replace the motor.

Giotto included on its aft end a "Whipple bumper" - named for its inventor, planetary astronomer Fred Whipple - to protect it from hypervelocity dust impacts. During approach to Comet Halley, the spacecraft would turn the bumper in its direction of flight. The bumper comprised a one-millimeter-thick aluminum shield plate designed to break up, vaporize, and slow impactors, a 25-centimeter empty space, and a 12-millimeter-thick Kevlar sheet to halt the partially vaporized, partially fragmented impactors that penetrated the aluminum shield.
 
In the case of Comet Halley, dust would impact the bumper at up to 68 kilometers per second. Tsou, Brownlee, and Albee noted that the 13 candidate Giotto II comets were all less dusty and would have lower dust impact velocities than Halley. Because of this, Giotto II would need less shielding than Giotto.

Comet dust would, nonetheless, create challenges for Giotto II. Tsou, Brownlee, and Albee devoted much of their paper to describing how the spacecraft might successfully capture dust for return to Earth. One proposed capture system, based on the Whipple bumper design, would use a shield made from ultrapure material to vaporize and slow impacting dust particles. The vapor from the impactor and the impacted part of the bumper would then be captured as it condensed. Scientists would disregard the bumper material when they analyzed the condensate.
 
Tsou, Brownlee, and Albee also noted that thermal blankets from the Solar Maximum Mission (SMM) satellite, launched into Earth orbit on 14 February 1980, had demonstrated that intact capture of high-velocity particles was possible. The multilayer Kapton/Mylar blankets, which were returned to Earth on board the Space Shuttle Challenger (STS 41-C, 6-13 April 1984), had been found to have collected hundreds of intact meteoroids and human-made orbital debris particles.

The three scientists described preliminary experiments in which gas guns were used to fire meteoroid and glass fragments at "underdense materials," such as polymer foams and fiber felts. The experiments suggested that such materials could capture at least partially intact comet dust particles.

Giotto's encounter with Comet Halley spanned 13-14 March 1986. At closest approach the spacecraft passed just 596 kilometers from Halley's nucleus. The comet’s 15-by-eight-by-eight-kilometer heart turned out to be extremely dark, with powerful jets of dust and gas blasting outward into space.

Artist's concept: Giotto at Halley. Image credit: European Space Agency
Halley's hot heart as imaged by ESA's Giotto spacecraft. 
The intrepid probe suffered damage from dust impacts – one large particle sheered off more than half a kilogram of its structure – but most of its instruments continued to operate after the Comet Halley flyby. ESA thus decided to steer Giotto toward another comet.

On 2 July 1990, five years to the day after its launch, Giotto flew past Earth at a distance of 16,300 kilometers, becoming the first interplanetary spacecraft to receive a gravity-assist boost from its homeworld. The gravity-assist flyby put it on course for Comet Grigg-Skjellurup, which it flew by at a distance of 200 kilometers on 10 July 1992.
 
After determining that Giotto had less than seven kilograms of hydrazine propellant left on board, ESA turned it off on 23 July 1992. The inert spacecraft flew past Earth a second time at a distance of 219,000 kilometers on 1 July 1999.
 
By that time, a comet coma sample return mission was under way with two of the Giotto II proposers playing central roles. In late 1995, Stardust became the fourth mission selected for NASA's Discovery Program of low-cost robotic missions. Brownlee and Tsou, respectively Stardust Principal Investigator and Deputy Principal Investigator, designed the mission's sample capture system.

Artist's concept of the NASA Stardust spacecraft at Wild 2. Image credit: NASA
The 380-kilogram Stardust spacecraft left Earth on a free-return trajectory on 7 February 1999, and flew past Comet Wild 2 (one of the 13 Giotto II candidates) at a distance of about 200 kilometers on 2 January 2004. Stardust captured dust particles in aerogel, a silica-based material of extremely low density that was invented in the 1930s. Tsou, Brownlee, and Albee had apparently been unaware of aerogel when they proposed Giotto II in 1985.

Stardust returned to Earth on 15 January 2006. Its sample capsule streaked through the pre-dawn sky over the U.S. West Coast before parachuting to a landing on a salt pan in Utah.

When opened on 17 January 2006 at NASA's Johnson Space Center, in the same lab that received the Apollo moon rocks, Stardust's 132 aerogel capture cells were found to contain thousands of intact dust grains captured from Wild 2. Subsequent analysis indicated that some probably formed close to other stars before our Solar System was born.
 
Sources

"Comet Coma Sample Return via Giotto II," P. Tsou, D. Brownlee, and A. Albee, Journal of the British Interplanetary Society, Volume 38, May 1985, pp. 232-239

ESA Remembers the Night of the Comet, European Space Agency, 11 March 2011 (accessed 26 August 2016)

Stardust: NASA's Comet Sample Return Mission, NASA Jet Propulsion Laboratory (accessed 26 August 2016)

12 August 2016

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 3)

The glory that is Saturn. The Cassini spacecraft was crossing the plane of the rings as it captured this image, so they are visible only as a sharp thin line running across the center of the image and a complex play of shadows on the planet's northern hemisphere. Image credit: NASA
One can hardly blame Arthur C. Clarke for stubbornly insisting that the spaceship Discovery travel to Saturn. Even with the minimal knowledge of the Saturn system we possessed in 1968, when the film and novel 2001: A Space Odyssey had its debut, it was clear that Saturn is home to some intriguing space oddities which Clarke could put to work in his narrative.

There are, of course, the rings. They make Saturn an austere work of art wrought in ice and orbital mechanics. Clarke attributed their creation to the same advanced aliens who uplifted humankind at the beginning of the book and film 2001, three or four million years before Discovery's launch.

There is also peculiar Iapetus - which Clarke called Japetus (the German spelling) - a 1500-kilometer-diameter moon very dark on one side (its leading hemisphere as it orbits Saturn) and very bright on the other. The arrangement of the dark leading and bright trailing hemispheres mean that Iapetus, Saturn's second-largest moon after Titan, is very bright to Earth-based observers when its 79-day orbit puts it on one side of Saturn and very faint roughly 40 days later, when it moves into view on the other side.

Stanley Kubrick, who directed the film 2001, co-authored its screenplay, and received co-author credit on early editions of the novel, also sought to send Discovery to Saturn, but had to settle for Jupiter. The film's overtaxed art department rebelled - Kubrick, ever the perfectionist, was given to demanding quick-turnaround changes which he subsequently threw away. Perhaps more important, a portrayal of Saturn convincing to 1968 film audiences proved too great a challenge for 2001's pioneering special-effects technology and skilled artisans. Had they known how improbable-seeming Saturn really appears, Kubrick and the production crew might have given themselves a bit of slack.

A raging storm in Saturn's northern hemisphere imaged by the Saturn-orbiting Cassini automated explorer 10 years after 2001. In 1968, observers using Earth-based telescopes believed Saturn's atmosphere to be practically featureless. Image credit: NASA
This is the third and last of a series of posts I have written this summer on real-world proposals for spacecraft and supporting infrastructure meant to emulate the spacecraft and infrastructure portrayed in the film and novel 2001. In the first installment, I described 2001's Earth-moon transport system and a 1997 NASA Lewis Research Center (now called NASA Glenn Research Center) plan to partially duplicate it using the International Space Station, nuclear-thermal rockets, and oxygen mined from the moon.

In the second installment, I described two versions of Discovery, the "hero ship" of 2001. I emphasized the film Discovery; that is, the open-cycle gas-core nuclear-fission design the film's technical consultant, Frederick Ordway, described in the British Interplanetary Society magazine Spaceflight in 1970.

This post picks up the 2001 story where my first post left off, then I will conclude the series by discussing a paper NASA Glenn researchers Craig Williams, Leonard Dudzinski, Stanley Borowski, and Albert Juhasz first presented in July 2001 and subsequently published as a NASA Technical Memorandum (TM) in March 2005. They describe a fusion-powered spacecraft meant to emulate 2001's Discovery spacecraft. They named it Discovery II.

My first post ended with United States Astronautics Agency (USAA) bureaucrat-astronauts accidentally triggering an ancient alarm system. Radio waves blast from an alien black monolith in the moon's great ray crater Tycho. The film 2001 then skips ahead 18 months, and we get our first look at Discovery, her crew, and their daily routine.

As always, Clarke fills in missing details. The novel describes a host of robotic monitors scattered across the Solar System. Each in turn detects the radio signal from the Tycho monolith. Later we learn that data from the monitors enabled scientists on Earth to determine that the signal was directed at Saturn. In the movie, the signal was, of course, beamed at Jupiter.

Fateful decisions are made at the highest level of the United States government. The ancient Tycho monolith and the signal it aimed at Saturn are to be kept secret, allegedly to prevent cultural shock and mass hysteria.

Preparations for Project Jupiter, the first piloted round-trip journey to the Solar System's largest planet, are by this time well advanced; this provides an opportunity. In search of those who received the Tycho monolith signal, the Jupiter ship Discovery will instead travel one-way to Saturn with a gravity-assist flyby at Jupiter to gain speed. I describe the development of gravity-assist spaceflight in my "The Challenge of the Planets" post series; please see the "More Information" links at the bottom of this post.

Discovery's crew of six is split up. A separately trained three-man "survey crew" will travel to Saturn in hibernation; they will thus remain safely incommunicado, ensuring that the mission's true purpose does not slip out during radio communications with Earth. Mission Commander David Bowman and his deputy, Frank Poole, will remain awake. The pair form a minimal caretaker crew during the interplanetary phase of the Saturn mission.

Bowman and Poole are told that their mission aims to expand knowledge of the Solar System and to extend space technology capabilities, and that the survey crew has been placed aboard Discovery in hibernation to conserve life support resources. Hibernation development is a major goal of their mission, for after 100 days of scientific exploration at Saturn the entire human crew is scheduled to hibernate for more than five years. Eventually, the as-yet-unbuilt spacecraft Discovery II will arrive to take them home.

The NASA Glenn Discovery II has no connection with the Discovery II crew-retrieval spacecraft of the novel 2001. Clarke barely describes the latter. I encourage readers to speculate on the shape and capabilities of the Discovery II in the 2001 universe.

The sixth member of the Discovery crew, the HAL 9000 computer, is an artificial intelligence (AI). HAL 9000 knows the true purpose of the trip to Saturn; it is, however, programmed not to tell Bowman and Poole. The secrecy order creates a terrible behavioral conundrum for HAL 9000. Deep in its programming is a directive never to distort information, yet it has been commanded to do just that. This weighs heavily on the advanced AI. HAL 9000 is an innocent being, unable to tamp down what amounts to its conscience. The conflicting directives drive HAL 9000 to neurotic behavior which exacerbates the internal conflict, leading to psychosis and murder between Jupiter and Saturn.

Following the deaths of Poole and the three hibernating crewmen, Bowman is left alone aboard Discovery with HAL 9000. For his own safety, he disconnects the AI. When he finishes, he is the only conscious being within a billion kilometers.

Mission Control belatedly tells Bowman the true purpose of Discovery's mission. He begins a program of study to prepare himself for whatever he will encounter at Saturn. Without HAL 9000 to monitor him in hibernation, his has become a true one-way mission. Increasingly intrigued (and not a little daunted) by the prospect of contact with highly advanced aliens, Bowman is, however, able to put aside thoughts of a lonely death far from home. He even sympathizes with HAL 9000's plight.

The real thing: cylindrical projection of Iapetus image mosaic. The Cassini spacecraft captured images of Iapetus during flybys at different distances and under different lighting conditions; hence some are blurred and others are sharp. The leading hemisphere is at right. Image credit: NASA
Bowman uses Discovery's telescopes to observe the Saturn system. He determines that Iapetus is his goal; the line between the dark and light hemispheres is sharp and obviously artificial. Guided by Earth-based computer control, Discovery of the book successfully fires her plasma jet propulsion system to place herself first into orbit about Saturn and then, with her last drops of hydrogen propellant, into orbit about Iapetus. Bowman then descends in a one-man space pod with the aim of landing atop a giant ("at least a mile high") black monolith standing at the exact center of the white hemisphere of Iapetus. Bowman calls it the Tycho monolith's "big brother."

The big monolith has plans for Bowman; it is, among other things, a Stargate, a space-time shortcut leading into a galactic transit system. He is soon whisked across the Milky Way Galaxy to meet an enigmatic fate. I do not feel qualified to describe the intricacies of Stargate technology, so here I will conclude my overview of the second half of the novel 2001.

Discovery II: this forward view highlights the artificial-gravity section and the spacecraft's lone docking port. Image credit: NASA
Neither did I feel qualified to describe nuclear fusion propulsion technology when I started work on this post, but I think I stand a good chance now of accurately describing the NASA Glenn nuclear-fusion spacecraft Discovery II. If, however, you detect what you believe is an error, it probably is, so please let me know so that I can correct it.                                    

In their documents, the NASA Glenn team describes Jupiter and Saturn versions of its Discovery II. As shown by their estimated weights, only minor differences distinguish the two versions; at 1690-metric-tons, the Jupiter-bound Discovery II would weigh only nine metric tons less than the Saturn-bound version. In keeping with my already-established emphasis on Saturn in this post, I have opted to focus on the Saturn version of NASA Glenn's Discovery II.

The Discovery II design was hatched while an obscure NASA study group called the Decadal Planning Team (DPT) was active. A creation of President William Clinton's Office of Management and Budget, the DPT aimed to articulate a philosophical foundation for NASA advance planning in the 21st century. It did this to prepare the way for new space initiatives during the Presidency of Clinton's Vice President and "space czar," Albert Gore.

"Go anywhere, any time" was an oft-repeated DPT slogan that seems on the face of it to apply well to NASA Glenn's Discovery II. The spacecraft's fusion rocket could in theory propel it to Saturn in 212 days when the planet was at opposition - that is, when Saturn was as close to Earth as it could be. The NASA Glenn team found that, all else being equal, a Saturn voyage at conjunction - that is, when Saturn was on the far side of the Sun and thus as distant from Earth as it could be - would last only 15% longer. Discovery II's course to Saturn in both instances would follow nearly a straight line, not the graceful rising curve of a minimum-energy Hohmann transfer.

At present, nuclear fusion occurs mainly inside stars. Human efforts toward harnessing star power since the 1940s have emphasized fusion bombs. The U.S. exploded the first such weapon in 1952; a nuclear-fission device served as the "spark plug" for triggering the fusion explosion.

Development of electricity-generating fusion reactors, by contrast, has turned out to be more difficult than once assumed. The international ITER project, based in southern France, now hopes to test a prototype commercial fusion reactor in the 2030s.

Earth-based fusion electricity-generation technology would need to advance and considerable additional investigation into almost all engineering aspects of fusion rocketry would be necessary before a fusion engine could become part of NASA's spaceflight tool kit. Nevertheless, the NASA Glenn engineers optimistically predicted that Discovery II's maiden voyage might take place 30 years after they completed their NASA TM - that is, in the year 2035.

Discovery II: this aft view highlights the spheromak fusion reactor, four slush hydrogen tanks, and magnetic rocket nozzle. Image credit: NASA
Discovery II's proposed propulsion fusion reactor would be of a modified Tokamak design. The original Tokamak, a 1970s Russian invention, was a normal torus - the proverbial doughnut - with a magnetically contained high-temperature plasma filling. Discovery II's "spheromak" propulsion reactor, by contrast, would be shaped like a cored apple. Plasma would swirl inside a relatively compact torus with an approximately "D"-shaped cross section. Because it would be compact, it would need less structure and fewer heavy components, such as electromagnets. The spheromak could thus be made much lighter than an equivalent doughnut Tokamak.

Though the NASA Glenn team took pains to make her propulsion reactor as light as possible, at an estimated 310 metric tons it was still the most massive single hardware element of the Discovery II. The reactor weight estimate did not include support systems such as the fission reactor and battery bank that would supply the electrical power necessary for fusion reactor startup.

Tokamak vs. spheromak. Image credit: Culham Centre for Fusion Energy
The NASA Glenn researchers opted for a deuterium/helium-3 (D/He-3) reactor fuel mix, partly because it is relatively well understood and partly because deuterium and helium-3 are relatively plentiful in the outer Solar System. The spacecraft would arrive at Saturn with an empty reactor fuel tank and refuel with deuterium and helium-3 mined from its icy moons and tawny cloud bands. Discovery II would "burn" 11 metric tons of D/He-3 reactor fuel to travel one-way to Saturn.

Nuclear fusion brings together atomic nuclei at high temperatures and pressures. Lightweight nuclei, such as those of various isotopes of helium and hydrogen, yield the most energy per unit, so are generally favored as reactor fuel. When atomic nuclei fuse, they release prodigious energy and create heavier elements. The heavier elements would, over time, build up in Discovery II's fusion plasma, gradually reducing the reactor's performance. In addition, some small portion of the spheromak interior walls would sputter away and mix with the swirling plasma.

Heavy element and wall debris plasma (informally known as "ash") would congregate in a "halo" against the outer wall of the plasma torus through skillful management of interlaced "toroidal" and "poloidal" magnetic fields, then a gutter-like magnetic "divertor" would vent the ash plasma from the aft end of the torus. The vented ash plasma would produce thrust.

The NASA Glenn team proposed increasing that thrust by augmenting the vented ash plasma flow with hydrogen. Contact with ash plasma and passage through a constricted "throat" would heat the hydrogen until it also became plasma. A skeletal "magnetic nozzle" would then expel the plasma mix into space to generate thrust. The divertor and magnetic nozzle would together have a mass of only six metric tons, the NASA Glenn team estimated.

Discovery II would include four cylindrical 37-meter-long propellant tanks containing a total of 861 metric tons of "slush" hydrogen. Chilling the hydrogen until it became slush using an on-board refrigeration system would increase its density, reducing the size and number of hydrogen tanks required.

Two authors of the 2001 and 2005 Discovery II documents - Borowski and Dudzinski - proposed in 1997 a different kind of propulsion plasma augmentation. I described this in the first post of this three-part series (see "More Information" below). Their system had lunar liquid oxygen, or LUNOX, augmenting hydrogen plasma expelled from a nuclear-fission reactor. The hydrogen plasma and LUNOX would burn as in a chemical-propellant rocket engine, increasing thrust and making possible 24-hour Earth-moon "commuter" flights.

To place its Discovery II fusion ship into space, the NASA Glenn team postulated the existence of a Heavy Lift Launch Vehicle (HLLV) capable of boosting 250 metric tons into a circular assembly orbit between 140 and 260 nautical miles above the Earth. They argued that 250 tons would be very near the practical maximum payload for an HLLV. Placing Discovery II components into assembly orbit would require that seven of the monster rockets launch in rapid succession. This would create challenges in the areas of HLLV assembly, pad installation, and launch operations, among others.

The Discovery spacecraft of the book and film 2001 included large-diameter propulsion and crew modules. The latter was a sphere a little over 12 meters in diameter and the former was even longer and wider. The NASA Glenn team looked upon these with skepticism; such modules would likely be too large to launch intact, so would need to be at least partly built in space by spacewalking astronauts or through complex teleoperations.

They ignored the versatile space pods portrayed in the book and film 2001, which might have made orbital assembly easier, opting instead for pre-assembled launch packages that would fit within a 10-meter-diameter, 37-meter-long streamlined HLLV payload fairing. The self-propelled launch packages would, they explained, rendezvous and dock automatically in assembly orbit.

EASE assembly experiment, 1985. Image credit: NASA
Having said that, they then contradicted themselves by describing a series of HLLV payloads that would in fact require extensive in-space assembly. The first would include Discovery II's 203-meter-long, six-metric-ton central truss. The NASA Glenn team explained that it would be based on the Experimental Assembly of Structures in EVA (EASE) Space Station truss concept tested during STS-61B spacewalks in late 1985.

The Discovery II truss, hexagonal in cross section, would comprise 58 "bays," each built from 97 separate struts, nodes, and other parts. EASE assembly occurred in the payload bay of the Space Shuttle Atlantis. Discovery II central truss assembly would apparently take place in open space.

Following truss assembly, spacewalking astronauts would install a wide variety of systems inside and outside the truss. Most obvious were 20 rectangular 25-meter-long radiator panels for cooling Discovery II's electricity-generation systems. Each would reach orbit folded like an accordion.

Most important for the six remaining HLLV flights of the assembly phase would be communications, avionics, and reaction control systems. The avionics system, linked to controllers on Earth through the communications system, would use the hydrogen-fueled reaction control system to keep the truss and its attached payloads stable in orbit so that subsequent payloads could dock with it.

The HLLV's 250-metric-ton weight limit required that the 310-metric ton reactor reach space in two launches. The NASA Glenn engineers proposed launching part of the fusion reactor - its poloidal magnetic coils - with the truss payload. This meant that spacewalking astronauts would need to piece together in space Discovery II's most complex and important hardware element.

The second HLLV payload would include the remainder of the fusion reactor and the magnetic rocket nozzle. The third - the 172-metric-ton "artificial gravity crew payload" - would comprise seven pressurized crew modules. The NASA Glenn team offered no information as to how the crew modules would join together automatically in assembly orbit. The fourth through seventh payloads would each comprise a filled slush hydrogen propellant "cryo-tank." Thrusters and avionics would permit them to maneuver into place near Discovery II's tail.
Discovery II with selected components and dimensions indicated. Click on image to enlarge. Image credit: NASA
The NASA Glenn team had Discovery II saving reactor fuel and propellant by departing the Earth-moon system from a loose, distant, "sub-parabolic" orbit, but gave no indication as to how she would reach her departure orbit from her assembly orbit. Presumably the spacecraft would be moved using space tugs.

The NASA Glenn engineers stated that an air-breathing space plane would deliver a six-to-12-person crew to a space station in low-Earth orbit. There they would board a taxi vehicle for the journey to the waiting Discovery II. They would dock with Discovery II's only docking port, located on the front of her central hub crew module, and transfer to Discovery II.

Crews returning from Saturn would park the spacecraft in sub-parabolic orbit and await retrieval. Discovery II would be designed for reuse, though how she would be refueled, resupplied, and refurbished in sub-parabolic orbit after each flight was left to the reader's imagination.

Preparation for departure, much of which could occur before the crew arrived, would require weeks. The magnets and reactor structure would need to be thoroughly cooled using liquid helium, though the chief reason for the long preparation period would be the need to charge a five-metric-ton nickel-hydrogen battery bank. A two-megawatt, 10-metric-ton auxiliary fission reactor inside the central truss would slowly charge the batteries in preparation for the roughly one-gigawatt burst of radio-frequency energy needed to start fusion in the reactor. The NASA Glenn team called this start-up technique "high harmonic fast wave heating."

D/He-3 fuel would enter the reactor rather spectacularly as one-gram, 2.2-centimeter cube-shaped "pellets" accelerated at a rate of 27,580 gravities inside a 185-meter-long electromagnetic rail-gun. How the long, complicated rail-gun would be assembled in space within the central truss was not described. The solid-deuterium/liquid-helium-3 pellets would enter the reactor moving at 10 kilometers per second, so would deeply penetrate the dense plasma torus. This would help to preserve the stability of the swirling plasma flow. Pellets would need to be injected into the reactor once per second to maintain reactor energy output.

Swirling plasma in the fusion reactor torus would at start-up torque (twist) the central truss. Discovery II's maximum acceleration would reach 1.9 milligravities as she closed in on her target planet, when her cryo-tanks would be nearly empty. This acceleration, though minute, would place strain on the central truss, as would operation of various turbines and the movement of coolant and working fluids through pipes and pumps. The reactor fuel injector would generate a four-gravity load each time it fired a pellet. The NASA Glenn team suggested that a flywheel might absorb some of the forces Discovery II would place on herself, but provided little information as to how this would function.

The revolving crew section would also place strain on the truss. Though they noted that data concerning a healthful level of artificial gravity do not yet exist, NASA Glenn team opted to provide Discovery II's astronauts with artificial gravity one-fifth as strong as Earth gravity. Three arms 17 meters long would each connect a 5.6-meter-tall, 7.5-meter-diameter lab/hab module to a 7.5-meter-diameter central hub where weightless conditions would prevail. The artificial-gravity system would spin 3.25 times per minute. The two-deck lab/hab modules would contain accommodations for four astronauts each. Opting for separate lab/hab modules connected only through a hub would mean that the "hamster wheel" jogging routine demonstrated in the film 2001 could not occur.

All crew modules would include a layer of water between two layers of graphite epoxy hull material for radiation protection and to serve as a heat dump for crew module thermal control. The central hub would also contain a solar-flare storm shelter with augmented shielding.

Discovery II would arrive at Saturn - more accurately, Saturn sub-parabolic orbit - with nearly empty cryo-tanks. Her crew would carefully shut down her fusion reactor and begin charging her battery bank for another start-up in several weeks' time.

The NASA Glenn team offered a vague vision of how their ship might refuel for the trip home to Earth. Robotic fuel-gathering systems, perhaps suspended from balloons, might be placed into Saturn's atmosphere. They would need to process hundreds of kilograms of gas to obtain a single gram of helium-3 or deuterium and tens of thousands of tons to collect the 11 metric tons required to refuel Discovery II.

No indication was given as to how or when the refueling infrastructure would have been established. Similarly mysterious was how the collected D/He-3 would reach Discovery II.

Hydrogen propellant would be more plentiful than either deuterium or helium-3. The NASA Glenn team envisioned that Discovery II's self-propelled hydrogen cryo-tanks would separate and maneuver to an automated refueling station; meanwhile, identical full tanks would rendezvous with Discovery II and replace the depleted ones. How and when the hydrogen refueling station would have been established and how it would collect hydrogen at Saturn was left to the imagination.

Discovery II would carry no auxiliary craft, so would need vehicles pre-deployed at Saturn if her crew was meant to leave the ship and land on any of the ringed planet's many moons. The NASA Glenn team did not explain how auxiliary craft might reach Saturn ahead of Discovery II, nor how they would be maintained after they became based in Saturn's neighborhood.

Could NASA Glenn's Discovery II replicate the capabilities of 2001's Discovery? As detailed in the second part of this three-part post series, the film Discovery differed from the Discovery of Clarke's novel. The cinematic and literary spacecraft had different propulsion systems, though both relied on nuclear fission. Discovery of the film was a gas-core nuclear-thermal rocket; Discovery of the book employed electromagnetic "plasma jets" that drew electricity from a fission reactor.

Both of 2001's Discovery spacecraft - admittedly fictional, but designed with great concern for realism - could travel round-trip to Jupiter without reliance on pre-deployed assets. Both were adaptable enough that they could be diverted from Jupiter to Saturn when the need arose. That adaptability was based on advanced crew support (hibernation) and automation (HAL 9000) systems. Because of those advanced non-propulsion systems, the round-trip Jupiter mission could be re-planned as a one-way Saturn mission with eventual crew retrieval by a second spacecraft.

Though it promised fusion rocket capability, the NASA Glenn Discovery II design study is in fact incomplete. Among other things, its failure to account for the existence at Saturn of extensive pre-deployed assets essential to Discovery II's mission plan makes it hard to take seriously. Furthermore, it emphasizes propulsion to the exclusion of other potentially ground-breaking, mission-shaping technologies. For these reasons, NASA Glenn's Discovery II cannot be said to replicate the capabilities of the Discovery spacecraft portrayed in the book and film 2001: A Space Odyssey.

Saturn viewed by the Cassini spacecraft from an orbital position north of the planet's equator. The gray north polar region and peculiar spinning hexagonal polar vortex at its center are just visible. Image credit: NASA
More Information

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 1)

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 2)

The Challenge of the Planets, Part Three: Gravity

Sources (please also see Part 1 and Part 2 Sources)

Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion, NASA/TM-2005-213559, C. Williams, L. Dudzinski, S. Borowski, and A. Juhasz, NASA Glenn Research Center, March 2005

2001: A Space Odyssey, Arthur C. Clarke, New York: New American Library, October 1999, pp. 80-82, 85-101, 120-203

18 July 2016

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 2)

The good ship Discovery from the classic 1968 motion picture 2001: A Space Odyssey. From right to left, we see the pressure sphere housing the crew; a train of six propellant modules; the communications complex; four more linked propellant modules; and the propulsion module. Image credit: Turner Entertainment/Metro Goldwyn Mayer
When I set out back in June to write about a pair of plans for accomplishing the space voyages portrayed in the classic 1968 film and novel 2001: A Space Odyssey, I assumed that I could get the job done in a single post. I should have known better; not only are the plans complex, there is much to say about the film and book that inspired them. Now I plan a total of three posts, of which this is the second.

This post deviates from my original intent in another way; it does not describe a real spaceflight plan inspired by and meant explicitly to reproduce a capability portrayed in the movie or book 2001. Instead, it describes how the spaceship Discovery, the setting for much of the action in the second half of the film 2001, was intended to propel itself between planets. This will lay useful groundwork for the third and final post in this little series.

Along the way, by way of explaining the details of the cinematic Discovery's propulsion system, I will sum up the state of advanced nuclear propulsion research at NASA Lewis Research Center (LeRC) in the early 1970s. During the same period, President Richard Nixon, the Congress, and NASA itself brought down the ax on the joint NASA/Atomic Energy Commission (AEC) nuclear-thermal propulsion development program.

The novel 2001 (written by Arthur C. Clarke) and the film 2001 (based on a screenplay jointly written by director Stanley Kubrick and Clarke) differ as to how Discovery is portrayed. There are in fact two different Discovery spacecraft.

Discovery in the novel 2001: A Space Odyssey measures more than 300 feet long from its forward-mounted spherical pressure hull to its aft-pointing plasma jet propulsion units. Immediately behind the pressure hull is a cluster of four cylindrical hydrogen propellant tanks and, behind them, a complex system of cooling fins. The fins form a "V" with the broad top of the "V" facing forward and a shielded nuclear reactor at its point.

The nuclear reactor would generate electricity for "focusing electrodes" in Discovery's plasma jets. These would heat the hydrogen and expel it to generate thrust. Judging by Clarke's description, the Discovery plasma jet design was apparently based on the same principle as the jets that propelled the Aries-1B moon shuttle I discussed in my last post.

The cooling fins, which Clarke described as "[v]eined with a delicate tracery of pipes for
. . .cooling fluid," were meant to radiate excess heat from Discovery's nuclear reactor into space. They would, he wrote, "glow cherry red" when the ship's plasma jets operated at full thrust, but become "dark and cool" after the jets were switched off.

Discovery of the film 2001 lacks any sign of cooling fins. Partly this is because Kubrick worried that his audiences would wonder why a spacecraft operating in the vacuum of space would need wings, but Kubrick's evolving aesthetic vision also played a part. Ultimately, he sought a frail-looking, skeletal Discovery.

The largest single component of the cinematic Discovery is the propulsion module at its aft end, with the roughly 40-foot-diameter pressure sphere at the spacecraft's forward end coming in a close second. In between is a train of linked propellant modules, each about 20 feet long. From a certain distance, these resemble vertebrae. About halfway along Discovery's "spinal column" is a communications complex with three Earth-pointing dish antennas, one large and two small.

Sadly, we never see Discovery's engines in action in the film 2001. We might have witnessed the slender spacecraft slowly turn to point its engines forward as it approached Jupiter, then watched in wonder as they lit up to slow Discovery so that the giant world's gravity could capture it into orbit.

Discovery's engines, 700 feet behind the pressure sphere bearing the crew. Image credit: Turner Entertainment/Metro Goldwyn Mayer
The timing for such a maneuver would, however, have been awkward from a story point of view; having just lobotomized the HAL 9000 computer, the "brain and central nervous system" of his ship, it seems doubtful that David Bowman, the sole surviving member of Discovery's five-person crew, could have had enough time to prepare for and carry out a successful deceleration maneuver. Kubrick opted instead to skip the Jupiter capture maneuver and proceed directly to his film's enigmatic, mind-bending climax.

Despite never seeing it operate, we have at our disposal information about how the cinematic Discovery's propulsion system was meant to work. The individual most responsible for this was Frederick Ordway.

Ordway was born in 1927. He graduated Harvard in 1949 with a Bachelor of Science degree, then earned certificates in physics and geosciences at the Sorbonne. In 1950, while studying in Paris, he attended the first International Astronautical Congress, where he met Clarke, whose six-decade writing career was just taking off.

In the 1950s, Ordway worked for New York-based aviation companies, generally in the area of rocketry. Toward the end of the decade, at the urging of Wernher von Braun, he relocated to Huntsville, Alabama, to work at the Army Ballistic Missile Agency (ABMA). Ordway became a NASA employee in July 1960, when ABMA became the nucleus around which NASA Marshall Space Flight Center crystallized.

In 1963, Ordway published the first of more than 20 books he would author in his lifetime. Titled Conquering the Sun's Empire, it was a popular-audience vision of humankind's future in the Solar System illustrated by his friend and collaborator, the artist Harry Lange.

In January 1965, Clarke introduced Ordway and Lange to Kubrick, who hired them both in mid-February to provide him with technical advice. The Discovery design in the novel 2001, known informally as the "dragonfly," was based on Lange pre-production illustrations developed during early discussions between Ordway, Lange, Clarke, and Kubrick.

A major part of Ordway's contribution to 2001: A Space Odyssey involved visiting aerospace companies and NASA centers, where he interviewed experts in spaceflight-related fields and collected advance-planning documents in an effort to ensure that Kubrick's film would present a believable vision of spaceflight at the turn of the millennium. He also became a spokesperson for the film, which had aroused intense interest in the aerospace community.

25 September 1965: Frederick Ordway (left, in white) joins a few notables for a tour of the British studio where 2001: A Space Odyssey was filmed. From left to right, they are: Donald "Deke" Slayton, NASA Director of Flight Crew Operations; Arthur C. Clarke; Stanley Kubrick; and George Mueller, NASA Associate Administrator for Manned Space Flight. Image credit: The Stanley Kubrick Archives
Ordway's formal involvement with 2001 production ended after nearly two years, in December 1966, 15 months ahead of the film's world-wide release in April 1968. Ordway's time on Kubrick's payroll coincided with NASA's peak funding year.

In 1965-1966, it was still reasonable to assume that the U.S. space agency would in the 1970s, 1980s, and 1990s expand upon the achievements of the 1960s Apollo Program. Thirty-five years seemed to be plenty of time to build a giant artificial-gravity Earth-orbital space station, establish a moon base, land humans on Mars, and launch humans and intelligent, talking computers into the outer Solar System.

According to Ordway, the cinematic Discovery was meant to have a "Cavradyne" gas-core nuclear-thermal propulsion system. He described it in a 1970 Spaceflight magazine article on the spacecraft of 2001. His description subsequently appeared as design notes in a set of Discovery blueprints drawn by graphic artist Shane Johnson. Ordway himself excerpted his 1970 description of Discovery's propulsion system in a 1982 paper. I will describe the fictional Cavradyne system shortly; before that, though, I will provide for it some "real world" context.

At the time Ordway published his 1970 article, NASA and the Atomic Energy Commission (AEC) had for more than a decade worked together to develop nuclear-thermal rockets. NASA and the AEC emphasized solid-core nuclear-thermal propulsion; gas-core nuclear engines of the type envisioned for Discovery of the film were widely seen as exotic and perhaps impossible.

Nuclear rocketry had ceased to be a national priority as early as 1963-1964, when Presidents John F. Kennedy and Lyndon Baines Johnson grounded the Reactor In-Flight Test (RIFT) project, which had optimistically aimed to launch a solid-core nuclear rocket engine into Earth orbit on a Saturn V rocket in 1967. Nevertheless, many within NASA remained hopeful in 1970 that solid-core nuclear rocket stages might navigate the Earth-moon system in the mid-to-late 1970s, as described in NASA's 1969 Integrated Program Plan (IPP). I discuss the IPP elsewhere in this blog - please see the "More Information" links at the end of this post.

During the 1960s, low-level gas-core engine studies took place under the aegis of the Advanced Reactor Concepts Section at NASA Lewis Research Center (LeRC) in Cleveland, Ohio. Robert Ragsdale, chief of the Section, performed gas-core research and analysis with his LeRC colleagues and supervised small contractual studies at more than a dozen corporations and universities across the United States. It is possible that Ordway contacted Ragsdale or researchers his Section funded as he gathered information for Kubrick, though no record of such a meeting is known to exist.

A solid-core nuclear-thermal rocket, the most basic kind, can be seen as a nuclear reactor with an open-cycle cooling system. A reflector focuses neutrons radiated from solid uranium fuel elements back into the reactor core, causing nuclear fission to occur. The fuel elements grow hot. Left to themselves, they would melt catastrophically; however, a turbopump drives propellant (typically cryogenic liquid hydrogen) into the reactor. The propellant turns to hot plasma upon contact with the fuel elements and vents into space through a bell-shaped nozzle, generating thrust.

A major advantage of a nuclear-thermal rocket engine over a chemical-propellant rocket engine (for example, the Space Shuttle Main Engine) is in the area of specific impulse, or the ratio of a unit of propellant expended to a unit of thrust generated. Specific impulse, abbreviated Isp, is expressed in seconds. The best Isp attainable using liquid hydrogen/liquid oxygen chemical propellants is in the neighborhood of 450 seconds, while the best solid-core nuclear Isp is in theory roughly twice that - on the order of 800 to 1000 seconds.

Nuclear-thermal Isp is dependent on the temperature of the fuel elements. Achieving an Isp much greater than about 1000 seconds using a solid-core nuclear-thermal engine rapidly becomes infeasible because the propellant can no longer cool the fuel elements enough to prevent them from melting. Supplemental cooling - for example, coolant flowing through plumbing within the engine to pick up its excess heat and then through large cooling fins to radiate that heat into space - becomes increasingly necessary, boosting spacecraft weight. The NASA LeRC team found that, for really high Isps, the heaviest gas-core engine system would be its cooling system. Increased weight would mean more costly heavy-lift rockets to place the spacecraft's components into space for assembly as well as reduced engine performance.

Gas-core nuclear-thermal propulsion promised a way around the "temperature barrier." In a gas-core engine, uranium would take the form of an incandescent ball of plasma in which nuclear fission would take place. The uranium fuel element (the plasma ball) would operate at a temperature far above the point at which a solid-core uranium fuel element would vaporize - and that would be exactly as it should be.

Ragsdale's group emphasized open-cycle gas-core propulsion over closed-cycle gas-core propulsion. The open-cycle plasma ball would "float" in a "stagnant region" that would fill about 40% of a spherical engine chamber about a dozen feet across. Hydrogen propellant would flow around the plasma ball, be heated until it also became a plasma, and then vent through a nozzle into space.

No physical wall would separate the uranium plasma from the hydrogen, an omission meant to reduce engine mass and complexity. A thin uranium wire would feed slowly into the plasma ball to make up for the small amount of uranium plasma - about 0.25% of the propellant flow at any particular moment - that would escape the open-cycle gas-core engine with the hydrogen propellant. As the open-cycle engines was shut down, the entire uranium plasma ball, diluted by hydrogen, would gradually vent from the nozzle into space.

A closed-cycle gas-core system - sometimes called a "nuclear lightbulb" - would include a physical barrier between the uranium plasma ball and the hydrogen propellant. The barrier would add weight and complexity, and might create temperature limitations; it would, however, also prevent uranium plasma from escaping into space. Presumably it would also make engine start-up - hydrogen flow initiation for cooling followed by creation of a stable uranium plasma ball in which fission would occur - a simpler task.

Using mathematical models, Ragsdale's group studied open-cycle gas-core engines with Isps of between 1500 and 3000 seconds. These could, they determined, operate without supplemental cooling.

To reach Isps beyond 3000 seconds, the plasma ball would need to become so hot that surrounding structure would melt and fail without supplemental cooling. Even with supplemental cooling, seemingly insurmountable temperature barriers would soon be reached. For an Isp of 5000 seconds, for example, the core temperature would run at about 22,000 K (about 39,000° F, or 21,700° C); that is, about four times the temperature of the Sun's surface and well above the melting point of all known materials.

Ragsdale's group found a surprisingly simple partial solution to the melting problem. The hydrogen propellant would enter the spherical chamber containing the uranium plasma ball through pores or slots. Seeding the propellant with tungsten particles, each roughly the size of those making up cigarette smoke, would help it to absorb heat, preventing all but about 0.5% of the plasma ball's thermal radiation from reaching the inner chamber wall. The resulting increased hydrogen temperature would also mean increased engine thrust.

About 7% of the uranium plasma ball's energy would, however, emerge as gamma and neutron radiation, pass unimpeded through the hydrogen/tungsten propellant mix, and heat the chamber wall and surrounding structures. Research had found that, because of this, some level of supplemental cooling would inevitably be required to prevent destruction of the gas-core engine.

Simplified cutaway of an open-cycle gas-core nuclear rocket engine. A pressure vessel provides structural strength and a beryllium oxide (BeO) moderator absorbs neutrons radiated from the uranium plasma, limiting pressure shell and adjacent spacecraft structure heating. Coolant moves through passages in the moderator to provide supplemental cooling. After passing through the moderator, the coolant flows through a space radiator then returns to the moderator to pick up more heat. A turbopump drives hydrogen propellant through the inner, "porous" wall. Uranium enters the plasma ball in the form of a "wire" roughly the diameter of a pencil lead to make up for the small amount carried off by the hydrogen plasma, which vents into space through the nozzle at right to generate thrust. Not shown is the system for introducing tungsten particles into the hydrogen. An engine of this basic design could in theory yield Isps of between 3000 and 5000 seconds. Image credit: NASA
Citing more than a decade of research, Ragsdale predicted confidently that open-cycle gas-core nuclear-thermal propulsion would be confirmed to be feasible within just a few years. It is important to note, however, that the gas-core studies explored in this post were of necessity preliminary due to limited research funding. One consequence of this is that some study results are inconsistent and many are perhaps optimistic.

Ragsdale pointed to planned 56-day astronaut stays on board Skylab in Earth orbit when he proposed a 60-day round-trip piloted Mars mission with a spacecraft mass of 2250 tons in Earth orbit at mission start. Of this, the gas-core engine would account for from 50 to 250 tons and hydrogen propellant about 1500 tons. He noted that, if it were determined that astronauts could remain healthy for up to 80 days in space, then extending the Mars voyage duration accordingly would cut in half the quantity of hydrogen propellant the gas-core Mars spacecraft would expend during its round-trip journey.

NASA LeRC researchers envisioned 80-day gas-core "courier" Mars missions. These would travel to Mars in 40 days and then return to Earth in 40 days. The spacecraft would linger near Mars only long enough to "jettison" a forward-mounted payload.

Like so many advanced concepts, NASA LeRC gas-core propulsion never got the conceptual artwork it deserved - until now. This illustration, kindly provided by artist William Black/http://william-black.deviantart.com/, is based on a crude line drawing that appears in early 1970s NASA LeRC gas-core propulsion reports. It shows the 80-day "courier" spacecraft early in its Earth-departure burn. The NASA LeRC line drawing indicated a need for radiator fins, but did not show their shape or extent; Black has made them resemble the "V"-shaped radiator configuration of the dragonfly Discovery in the novel 2001. Doing so places them within the conical radiation shadow created by the shield at the front of the gas-core engine (see image below) so that they do not reflect radiation toward the crew. Please click on image to enlarge.
Closeup of an open-cycle gas-core nuclear-thermal rocket engine based on NASA LeRC design concepts as envisioned by artist William Black/http://william-black.deviantart.com/. The large disc at left is a shadow shield for protecting the spacecraft crew from radiation from the engine. The cage-like truss structure surrounds the uranium storage and feed system and tungsten particle feed, hydrogen feed, and coolant circulation lines. Liquid hydrogen cools the silver part of the engine bell, becoming a hot gas; it then drives turbopumps (colored gold) that pump hydrogen into the spherical gas-core engine chamber. In Black's interpretation, turbobump hydrogen gas then vents aft into space through a pair of pipes. He also includes a gimbal system for pivoting the engine off its center line and an uncooled rocket nozzle extension (colored black).
Ragsdale wrote that the Space Shuttle, with its planned ability to routinely and cheaply launch payloads to Earth orbit, would help to make possible piloted interplanetary spacecraft with gas-core engines. This observation is ironic because, in testimony before a February 1971 Congressional hearing on the future of U.S. nuclear rocketry, NASA Acting Administrator George Low had used the need to fund Shuttle development as an excuse for slashing nuclear propulsion funds in Fiscal Year 1972 to a level barely sufficient to close out the program.

In his January 1972 article, Ragsdale wrote that his group had big plans for gas-core development in the 1972-1975 period. As it turned out, however, the Nixon White House and NASA officials announced while his article was still current that they had slashed all funding for nuclear rocket research from the Fiscal Year 1973 NASA budget. NASA and the AEC backed out of the nuclear-thermal propulsion business by the end of 1973.

Now we return to the world of 2001: A Space Odyssey. Ordway's conjectural Cavradyne engine, a closed-cycle gas-core system, was a "cavity reactor only several feet across." A uranium plasma ball with a temperature of about 11,400 K (about 20,000° F, or 11,100° C) would float at the center of a graphite inner container that would pass heat but not neutrons. Hydrogen would flow between the graphite container and the inner wall of the cavity reactor outer shell, then would vent as high-temperature plasma through a nozzle into space.

Nuclear-propulsion spacecraft designs are usually shaped at least in part by the need to keep astronauts well away from sources of radioactivity. The cinematic Discovery's length of 700 feet reflected the presence - judging from the external configuration of its propulsion units - of at least three and possibly six Cavradyne engines. One can speculate that each engine was meant to have a shield at its forward end, creating overlapping radiation shadows that would encompass the pressure sphere bearing the crew.

Neither Ordway nor Clarke provided detailed performance data for their Discovery spacecraft. The voyage durations they mention do, however, imply high-performance propulsion. In a late 1965/early 1966 draft of the 2001 screenplay, for example, Discovery's trip time to Saturn with a gravity-assist at Jupiter is given as 257 days. In Clarke's novel, Discovery reaches Jupiter in about six months and then proceeds onward to Saturn. In a draft of the novel which has Jupiter as Discovery's goal, excerpted in Clarke's 1972 book The Lost Worlds of 2001, the one-way trip-time is given as 219 days. These trip times are consistent with the Earth-Mars trip times in NASA LeRC conference papers and reports.

Sources

2001: A Space Odyssey, draft screenplay by Stanley Kubrick and Arthur C. Clarke, p. c15d, 11/1965

Kubrick, Stanley, and Arthur C. Clarke, 2001: A Space Odyssey, directed by Stanley Kubrick, Metro Goldwyn Mayer, April 1968

The Lost Worlds of 2001: The Ultimate Log of the Ultimate Trip, Arthur C. Clarke, New York: Signet, January 1972, pp. 130-132

"Part B: 2001: A Space Odyssey in Retrospect," Frederick I. Ordway, III; Science Fiction and Space Futures, Eugene E. Emme, editor, AAS History Series, Volume 5, San Diego: Univelt, 1982, pp. 47-105

2001: A Space Odyssey, Arthur C. Clarke, New York: New American Library, October 1999, pp. 98-99, 105, 190-191

The 2001 File: Harry Lange and the Design of the Landmark Science Fiction Film, Christopher Frayling, London: Rare Art Press, 2015, pp. 210-211, 217, 226, 228-231

U.S.S. Discovery: Manned Nuclear Exploration Vessel (Registry XD-1) Spacecraft Interior Blueprints and Exterior Plans, Shane Johnson, no date (c. 1985), Sheets 1, 3, and 5

"Crew Radiation Dose from a Gas-Core Nuclear Rocket Plume," NASA TM X-52832, C. Masser, NASA Lewis Research Center; paper presented at the Sixteenth Annual Meeting of the American Nuclear Society in Los Angeles, California, 28 June-2 July 1970

"Gas-Core Rocket Reactors - a New Look," NASA TM X-67823, R. Ragsdale and E. Willis, NASA Lewis Research Center; paper presented at the Seventh AIAA Joint Specialist Conference in Salt Lake City, Utah, 14-18 June, 1971

"To Mars in 30 Days by Gas-Core Nuclear Rocket," R. Ragsdale, Astronautics & Aeronautics, January 1972, pp. 65-71

"Reactor Moderator, Pressure Vessel, and Heat Rejection System of an Open-Cycle Gas-Core Nuclear Rocket Concept," NASA TM X-2772, M. Taylor, C. Whitmarsh, P. Sirocky, and L. Iwanczyk, NASA Lewis Research Center, July 1973

Humans to Mars: Fifty Years of Mission Planning, 1950-2000, NASA SP-2001-4521, Monographs in Aerospace History #21, David S. F. Portree, Washington: NASA, February 2001, pp. 33-52

More Information

Could the Space Voyages in the Film and Novel 2001: A Space Odyssey Really Happen? (Part 1)

The Last Days of the Nuclear Shuttle (1971)

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

On the Moons of Mighty Jupiter (1970)

Touring Titan by Blimp & Buoy (1983)

The Challenge of the Planets, Part Three: Gravity

11 June 2016

Could the Space Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 1)

An advanced LANTR moon shuttle departs low-Earth orbit. Image credit: Pat Rawlings/NASA
The film and novel 2001: A Space Odyssey changed my life. I know, that sounds overwrought, but it's true. I was six years old in April 1968, when the classic collaboration between science fiction author Arthur C. Clarke and film director Stanley Kubrick hit movie screens around the world. By that point in my young life, I had been reading for three years. I knew that I liked science - especially geology - so a "science fiction" film sounded intriguing.

By the time the movie drew to a close, I had become a spaceflight fan and a science fiction buff. I remain so afflicted today. (I expect that the existence of this blog makes the "spaceflight fan" part kind of obvious.)

The film 2001 is enigmatic, with mostly banal dialog and an ending that left many who saw it in its first run feeling confused and even cheated. Clarke's novel fills in gaps, but its narrative differs from the cinematic narrative. For example, in the movie 2001, Jupiter is the spaceship Discovery's destination; in the book 2001, the natural wonders of the Saturn system as understood in 1968 are used to good effect. None of this ambiguity troubled me; in fact, the mysteries stoked my young imagination.

Arthur C. Clarke (left) and Stanley Kubrick on the Aries-1B moon shuttle passenger cabin set. Image credit: The Stanley Kubrick Archives
This background explains why a pair of technical papers caught my attention as the year 2001 approached and passed. Nuclear propulsion engineers at NASA's Lewis Research Center (now Glenn Research Center) in Cleveland, Ohio, authored both papers. They described ways that the piloted spaceflight capabilities portrayed in the film and book 2001 might be made reality using technology and techniques that are either already in existence or are plausibly foreseeable.

In the first paper, first published in 1997 and subsequently lightly revised, Stanley Borowski and Leonard Dudzinski looked at how a 24-hour voyage to a lunar surface base might be accomplished using Nuclear Thermal Rocket (NTR) propulsion and liquid oxygen (LOX) mined from the moon. For comparison, Apollo spacecraft needed more than three days to travel from Cape Kennedy to lunar orbit.

The second paper is much more ambitious, but also more speculative. It offers a design and operational scenario for a nuclear-fusion-propulsion spacecraft named Discovery II which could reach Jupiter orbit in just four months and Saturn orbit in seven. I will discuss it in my next post.

The film and book 2001 both begin with a band of man-apes who are having a tough time of it. They grub in the dust for bits of vegetation beside competing quadruped herbivores and huddle together at night listening to screeching big cats, for whom they make easy prey.

The book focuses on a hominid named Moonwatcher. Some time after an intellect-boosting encounter with an alien black monolith, he grasps the related concepts of tool-use and hunting. Soon his entire band wields bone clubs. They hunt the unsuspecting herbivores, drive off the big cats, and make war on a technologically backward rival band.

After murdering the rival band's leader, Moonwatcher of the film 2001 hurls his club triumphantly at the sky, where it becomes an Earth-orbiting satellite bearing nuclear warheads. In a heartbeat we leap over three million years of human evolution and technology advancement.

A more hopeful sign of advanced technology appears - a gleaming white space plane in Pan American Airlines livery. On board is Dr. Heywood Floyd, a high-level bureaucrat on a mission for the United States Astronautics Agency (USAA). National security, the novel 2001 explains, requires that he fly with only a pilot, co-pilot, and stewardess for company.

USAA is evidently a NASA successor organization. One can speculate that, in the 2001 timeline, a well-funded NASA worked with large commercial entities and handed off certain of its roles as, with NASA aid, those commercial entities succeeded in proving themselves capable of providing necessary spaceflight services. Along the way, NASA handed off aeronautical research (the first "A" in the acronym NASA) and became more focused on advanced spaceflight development and scientific exploration. This prompted a name change.

The Pan Am space plane deposits Floyd at a wheel-shaped artificial-gravity international space station. It is the fifth in a series, so is called Space Station V. There Floyd confronts members of a rival band - a group of Soviet scientists on their way home from the moon - and transfers to a near-spherical Aries-1B moon shuttle to begin his journey to the U.S. moon base in 150-mile-wide Clavius crater.

Aries-1B moon shuttle. Image credit: Turner Entertainment/Metro Goldwyn Mayer
In the book 2001, the 30-passenger moon shuttle's "low-thrust plasma jet" propulsion system operates for "more than 15 minutes" to begin the 25-hour voyage to the moon. Floyd, alone on board with a pilot, co-pilot, steward, stewardess, and two engineers, hears the "whistling" of the "electrified" plasma jets. He feels the acceleration they impart to the moon shuttle as a "mild" pressure pushing him down into his seat.

In their 1997 paper, Borowski and Dudzinski dubbed their moon shuttle propulsion system LANTR, which stands for "LOX-Augmented Nuclear Thermal Rocket." They envisioned that LANTR propulsion would form a critical component of a cislunar transportation infrastructure that ultimately would include multiple interdependent vehicles and a Lunar Oxygen (LUNOX) mining and refining base near the Apollo 17 landing site at Taurus-Littrow on the southeast edge of Mare Serenitatis.

LUNOX, the NASA Lewis nuclear propulsion engineers explained, was likely to become the first large-scale space commodity. The "orange soil" Apollo 17 explorer Harrison Schmitt kicked up on the flank of Shorty Crater - which, it turns out, occurs at many places on the moon - would, they estimated, make a rich feedstock for LUNOX refining: every 25 tons of the volcanic glass-rich stuff collected and processed would yield a ton of LUNOX. For comparison, about 327 tons of more typical lunar surface material would need to be mined and refined to produce a ton of LUNOX.

The LANTR architecture would evolve over time from a NASA Lewis Nuclear Thermal Rocket (NTR) architecture developed for the abortive Space Exploration Initiative (1989-1993) of President George H. W. Bush. It would not at first use LUNOX, reach the moon in a day, or include reusable vehicles.

Borowski and Dudzinski sought to reduce the cost of their Earth-to-low-Earth-orbit (LEO) launches by exploiting then-existing Space Shuttle hardware and facilities. A pair of Shuttle-Derived Launch Vehicles (for example, Shuttle-C), each capable of placing a 66-ton payload into 407-kilometer-high LEO, would suffice to launch an expendable "two-tank" NTR stage, expendable piloted lunar spacecraft, and cargo.

Shuttle-C in its most basic form: an expendable cargo canister with a two-engine Shuttle boat-tail replaces the Space Shuttle Orbiter. Image credit: NASA
The first Shuttle-C's payload, the 24-meter-long "core stage," would comprise a pair of NTR engines, attitude control and docking systems, and a 7.6-meter-diameter, 17.5-meter-long insulated, meteoroid-shielded tank with 49.3 tons of cryogenic liquid hydrogen (LH2) inside. The engines would serve as both electricity generators and rocket motors. Because they would have two roles, or "modes," Borowski and Dudzinski dubbed them Bimodal Nuclear Thermal Rocket (BNTR) engines.

The BNTR engine's basic design would resemble that of NTR engines going back to the 1950s. LH2 would serve double duty as nuclear-fission reactor coolant and rocket propellant. After passing through and cooling the reactor, the hydrogen, now hot and gaseous, would vent into space through a bell-shaped nozzle to produce thrust.

The second Shuttle-C payload would comprise a 4.6-meter-diameter, nine-meter-long tank with nine tons of LH2, an adapter for linking with the core stage, and a conical crew capsule with four astronauts on board. It would also include a second spacecraft: a 44-ton LH2/LOX chemical-propulsion Lunar Landing Vehicle (LLV) with a five-ton crew cabin and nine tons of cargo bound for the lunar surface.

The two Shuttle-C payloads would dock in LEO, forming what Borowski and Dudzinski called a Lunar Transfer Vehicle (LTV). With the LLV attached, it would measure 46 meters in length. Its twin BNTR engines would heat and expel LH2 for 47.5 minutes to place the LTV/LLV combination on course for an Earth-moon voyage lasting 84 hours.

At the end of this cislunar journey, the BNTR engines would fire a second time so that the moon's gravity could capture the LTV/LLV combination into 300-kilometer-high orbit. The crew would board the LLV and descend to the lunar surface with their nine tons of cargo, which would include equipment for mining, refining, and storing LUNOX, as well as scientific gear and lunar base components.

The crew would spend 45 days on the moon living out of the LLV. They would then pilot the LLV back to lunar orbit, transfer to the LTV capsule, cast off the spent LLV, and fire the BNTR engine pair to depart lunar orbit for an 84-hour journey to Earth.

Near Earth, the crew capsule would detach from the LTV and reenter the atmosphere directly. The remainder of the LTV would swing by Earth and fire its BNTR engines briefly to boost itself into a Sun-centered disposal orbit. In total, the LTV BNTR engines would operate for 61.4 minutes during a 54-day round-trip lunar mission.

Borowski and Dudzinski described one-way cargo missions based on their piloted architecture. Twenty-five tons of additional cargo would replace the crew cabin and propellants for boosting the LLV back to lunar orbit, bringing total cargo delivered to the moon's surface to 34 tons.

LUNOX production would ramp up with each successive expendable LTV/LLV lunar mission. In lockstep with the increasing supply of LUNOX, NASA would upgrade the cislunar transportation system, so that, after an unspecified number of flights, it would evolve into Borowski and Dudzinski's reusable LANTR architecture. The LANTR architecture would, they explained, support routine weekly 24-hour Earth-moon "commuter" flights.

By then, LUNOX production would amount to 10,878 tons per year. Of this, reusable Earth-bound LANTR LTVs would use 4888 tons, while reusable LLVs for transporting LUNOX, crews, and cargoes between the LUNOX surface base and a lunar orbit propellant depot would expend 5990 tons.

The NASA Lewis engineers assumed that 11 solar-powered, teleoperated LUNOX plants operating 35% of the time (70% of each two-week lunar daylight period) could each strip-mine and refine 25,000 tons of orange soil to produce about 1000 tons of LUNOX per year. They estimated that the orange soil area near the Apollo 17 landing site might yield up to 700 million tons of LUNOX; that is, enough to support weekly 24-hour commuter flights for the next 60,000 years.

LANTR would see the basic all-LH2 BNTR engine augmented with a system for introducing LOX into the supersonic hot hydrogen exhaust flow "downstream" of the reactor. The LOX would enable the hydrogen to burn much as it does in a conventional LOX/LH2 chemical rocket engine, dramatically increasing LANTR thrust. This, Borowski and Dudzinski wrote, would offer "big engine" performance from "smaller, more affordable, easier to test NTR engines."

To trim development cost, the LANTR LTV would structurally closely resemble the all-LH2 LTV already described. At 7.5 meters long, the LANTR LTV's forward section would measure 1.5 meters shorter than its all-LH2 counterpart. The aft section, the core stage, would be outwardly identical to its all-LH2 predecessor. As with the all-LH2 LTV, a pair of Shuttle-Cs would launch the fore and aft sections of the LANTR LTV, which would then rendezvous and dock automatically in LEO.

The LANTR LTV would then dock automatically with a propellant depot in LEO. There it would fill its large tank with 45.5 tons of LH2 and its small tank with 112.3 tons of LOX, which is much denser than LH2. The propellant depot's LOX and LH2 would all be produced on Earth and boosted into LEO on Shuttle-derived launch vehicles.

Meanwhile, a Space Shuttle or a next-generation reusable piloted spacecraft would deliver to the International Space Station (ISS) 20 passengers bound for the LUNOX production base on the moon. Accommodations on board the ISS are, of course, not spacious, so the new arrivals would immediately move into a 15-ton, 4.6-meter-diameter, eight-meter-long cylindrical Passenger Transport Module (PTM) docked with the station. Even in its most advanced form, Borowski and Dudzinski wrote, their Earth-moon transportation system would be "spartan" compared with Heywood Floyd's moon shuttle; it would, for example, not employ stewards.

The 20 moon voyagers would remain inside the PTM throughout their 24-hour Earth-moon journey, so would see little change in their immediate surroundings from the time they boarded it until they entered the lunar surface base. The PTM would, nevertheless, interface with three vehicles besides the ISS during each lunar flight.

As the time for LEO departure approached, the PTM would undock from the ISS and move away using its chemical-propellant attitude-control thrusters. It would rendezvous with a LANTR LTV standing by near the LEO propellant depot at a "safe distance" from the ISS: that is, far enough away that radiation from its BNTR engines could neither harm the ISS crew nor reflect off ISS structure and harm the astronauts in the PTM. The PTM would approach and dock tail-first with the LANTR LTV, forming a 195.6-ton LANTR "commuter shuttle."

The commuter shuttle would climb away from LEO quickly (image at top of post). Acceleration to 24-hour Earth-moon transfer velocity would need only 21.2 minutes, or less than half the duration of the all-LH2 LTV burn required to achieve an 84-hour Earth-moon transfer.

During the climb away from LEO, the 20 passengers would, like Dr. Floyd in the book 2001, feel only a "mild" pressure - to be exact, 0.23 Earth gravities of acceleration at BNTR start-up, when the commuter shuttle was fully loaded with propellants, and 0.46 gravities just before BNTR engine shutdown, when about half its propellants had been expended.

Twenty-four hours after LEO departure, the BNTR engines would fire again to slow the commuter shuttle so that the moon's gravity could capture it into lunar orbit. It would rendezvous with a lunar-orbit propellant depot containing LH2 brought from Earth and LUNOX.

The PTM would undock from the commuter shuttle and link up with a waiting lunar surface-based reusable LLV, the second vehicle with which it would interface during its trip to the moon. The skeletal four-engine LLV would weigh 10.9 tons without propellants or cargo and 59.5 tons loaded with 33.6 tons of propellants and the 15-ton PTM.

In lunar orbital night: at the end of a 24-hour Earth-moon crossing, the PTM (lower left) has separated from the LANTR LTV (lower right) near the moon-orbiting propellant depot (barely visible above the LANTR LTV). A reusable LLV now moves into position to grapple the PTM and begin descent to the LUNOX production base on the moon's surface. Image credit: Pat Rawlings/NASA


The LLV would descend to the LUNOX base on four plumes of flaming Earth hydrogen and LUNOX. After touchdown, a wheeled flatbed - the third vehicle with which the passenger module would interface - would move into position beneath the PTM and detach it from the overhead LLV framework. The PTM/flatbed combination would then roll over the lunar surface from the landing field to an airlock leading into a surface habitat. After linkup with the habitat, the 20 passengers would exit the PTM to begin their duties on the moon.

In addition to moving passengers and cargo between Earth and moon and back again, the LANTR architecture would, as already indicated, move LUNOX and Earth-produced LH2. Four times per week a reusable tanker module with an empty weight of five tons loaded with 25 tons of LUNOX would ride a flatbed to a waiting automated LLV and then ascend to the moon-orbiting propellant depot. After pumping its LUNOX cargo into the propellant depot's tanks, it would return to the LUNOX base.

Welcome to the moon: in the lower right corner, a PTM rides a six-wheeled flatbed to an airlock leading into a large inflatable lunar surface habitat. Meanwhile, at upper center-right, a tanker LLV lifts off on a mission to transport LUNOX to the lunar-orbital propellant depot. Image credit: Pat Rawlings/NASA 
Borowski and Dudzinski assumed a fleet of four LANTR LTVs. Each would carry out 13 Earth-moon round-trips per year, for a total of 52 commuter flights (that is, one per week). Each LANTR LTV would in its BNTR engines hold enough fissile material to permit 44 Earth-moon round-trips, giving it an operational lifetime of 3.3 years.

A LANTR LTV near end-of-life would perform a one-way all-cargo mission before disposal into a Sun-centered orbit. One-way cargo would include Earth-produced LH2 for the propellant depot in lunar orbit. With about 23 tons of surplus LH2 in its "core stage" tank, a one-way LOX load of only 66 tons, and a potential cargo weight of about 80 tons, the LANTR LTV might deliver more than 100 tons of LH2 to lunar orbit during its final mission.

When Borowski and Dudzinski wrote their paper in 1997, existence of lunar polar ice in permanently shadowed craters, first predicted in 1961, remained uncertain. Data from a 1994 joint experiment using the Clementine lunar orbiter and NASA's Deep Space Network antennas had hinted strongly at the existence of hydrogen at the poles, but alternate explanations for the hydrogen signal existed, and an experiment using the giant Arecibo radio telescope in Puerto Rico could find no trace of lunar hydrogen.

Robotic spacecraft have since confirmed that a large quantity of water ice exists at the moon's poles - in the billions of tons. Provided that mining equipment can be designed to operate in the very cold, very dark environment of the permanently shadowed craters, the existence of water ice means that both oxygen and hydrogen await us on the moon in potentially easily processed form.

In theory, water ice-rich feedstock need only be heated to separate out the water, which would then be split into hydrogen and oxygen using electrolysis. Though this would seem to render Borowski and Dudzinski's LUNOX mining scenario irrelevant, their LANTR-based transportation system could burn LOX and LH2 derived from lunar polar ice as easily as it could Earth LH2 and LUNOX.

Early drafts of the 2001: A Space Odyssey screenplay - there were many - are replete with informative dialog. Though actors spoke some of the dialog during filming, most was replaced with classical music and sound effects in the final film.

In a late 1965/early 1966 draft of the script, the Aries-1B moon shuttle pilot and co-pilot speculate about the purpose of Heywood Floyd's unprecedented one-passenger lunar flight. The pilot remarks that the moon shuttle will return to Earth orbit without passengers because Clavius Base is under quarantine. Only Floyd will be permitted to leave the moon shuttle and no one at the base will be permitted to board it.

The co-pilot notes that moon shuttle tickets cost $10,000 one-way, so Floyd's mission will cost USAA and U.S. taxpayers about $600,000. Alas, Borowski and Dudzinski provided no estimate of the cost of reaching the moon using their infrastructure.

In the book 2001, Floyd disembarks from the Aries-1B and stops for a glass of lunar sherry - made from moon-grown algae - in the Clavius Base Administrator's office. He then attends a briefing in which he hears the latest news about the find that justified his secretive single-passenger moon flight. A black monolith found beneath the floor of Tycho crater has, he learns, nothing to do with the Chinese expedition of 1998. It was, geologists from Clavius Base have determined, deliberately buried three million years ago. It is thus the first evidence of intelligent life off the Earth.

After a moonbus ride across the rugged southern Lunar Highlands to Tycho, Floyd witnesses the beginning of a slow lunar dawn. He dons an advanced space suit - it takes only a few minutes and barely restricts his movements - then descends into the pit excavated around the monolith. Meanwhile, the Sun rises slowly over the lip of the excavation, shining its light on the monolith for the first time in three million years.

In the film 2001, Floyd joins other bureaucrats for a group photo in front of the monolith. Set against the brooding monolith, which seems to soak up all light, this very human ritual is so mundane as to be comical. As the photographer gestures repeatedly for them to move closer together - a critical part of the group-photo ritual - the monolith interrupts by emitting a powerful electronic scream.

Floyd and the others stumble around in pain and confusion as their suit radios receive the signal and blast it into their helmets. Only later do they realize that, by exposing the monolith to the Sun, they have tripped an ancient alarm.

Sources

"2001: A Space Odyssey" Revisited - The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners," AIAA-97-2956, Stanley Borowski and Leonard Dudzinski; paper presented at the 33rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit in Seattle, Washington, 6-9 July 1997

"2001: A Space Odyssey" Revisited - The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners, NASA/TM-1998-208830/REV2, Stanley Borowski and Leonard Dudzinski, NASA Glenn Research Center, June 2003

Kubrick, Stanley, and Arthur C. Clarke, 2001: A Space Odyssey, directed by Stanley Kubrick, Metro Goldwyn Mayer, April 1968

2001: A Space Odyssey, Screenplay by Stanley Kubrick and Arthur C. Clarke, pp. b35-b36a, 12/1965

2001: A Space Odyssey, Arthur C. Clarke, New York: New American Library, October 1999

The Making of Stanley Kubrick's 2001: A Space Odyssey, Piers Bizony, Taschen, 2014, p. 58-59

2001Italia.it: A Blog Devoted to 2001: A Space Odyssey, Simone Odino (accessed 12 June 2016)

More Information

The Last Days of the Nuclear Shuttle (1971)

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

Space Station Gemini (1962)

Making Propellants from Martian Air (1978)