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|
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.
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 engine 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 the design 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.
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, hydrogen gas from the turbopumps 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).|
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.
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
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