31 August 2015

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Image credit: NASA
On 28 July 1973, the Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off from Launch Pad 39B at Kennedy Space Center, Florida, bound for the Skylab Orbital Workshop in low-Earth orbit. Despite their mission's numerical designation, they were the second crew to visit Skylab; in a move guaranteed to generate confusion for decades to come, NASA had designated as Skylab 1 the unmanned Workshop launched on 14 May 1973, and had dubbed the first crew to visit it Skylab 2.

The Skylab 3 Apollo Command and Service Module (CSM) separated from the S-IVB second stage of its Saturn IB launch vehicle and began maneuvering to catch up with Skylab. During final approach to the Workshop, one of the four steering thruster quads on the CSM began to leak nitrogen tetroxide oxidizer from its forward-firing engine. The crew dutifully shut off the quad and used the three quads remaining to complete docking without further incident.

On 2 August, a second thruster quad began to leak, raising fears that tainted nitrogen tetroxide might have damaged both quads. If this were the case, then the Skylab 3 CSM's remaining two quads and Service Propulsion System (SPS) main engine might also have been compromised; though the individual quads and the SPS had independent plumbing, all contained oxidizer from the same batch. If the leaks continued and spread, moreover, nitrogen tetroxide might contaminate the inside of the CSM's drum-shaped Service Module, potentially damaging other spacecraft systems.

The leaks did not catch NASA off guard. As was common in the 1960s and early 1970s, NASA had considered potential Apollo and Skylab failures - however unlikely - and had planned ahead. Within hours of the second leak, The U.S. civilian space agency put into motion a variant of a plan Kenneth Kleinknecht, Skylab Program Manager, and Lawrence Williams, Apollo Spacecraft Program Office, had described less than a year earlier at the Fifth Annual Space Rescue Symposium in Vienna, Austria.

In their paper, Kleinknecht and Williams explained that Skylab would provide the first true opportunity for space rescue in the U.S. space program. One-seat Mercury and two-seat Gemini spacecraft had been too small and limited in capability to serve as rescue spacecraft. Apollo lunar CSMs were much more capable; even so, they each carried only a little more breathing oxygen, fuel cell reactants, and food than were needed to support a three-man crew for the duration of a lunar mission (about 10 days). If an Apollo CSM had become stranded in lunar orbit – by an SPS failure, say – then its crew would have perished long before NASA could have attempted a rescue.

The Skylab Orbital Workshop. The red arrow points to the Multiple Docking Adapter's radial port. Image credit: NASA
If astronauts needed to evacuate Skylab, they could board their CSM docked at Skylab's front port, undock from the Workshop, and splash down in the ocean in less than a day. If, on the other hand, a crew's CSM became unusable while they lived and worked on board Skylab, then the astronauts could await rescue.

Stranded astronauts were unlikely to run out of supplies. Kleinknecht and Williams noted that the Orbital Workshop would be launched with enough oxygen, food, water, and other supplies on board to support three men for eight months. At the time they presented their paper, NASA planned three three-man Skylab visits lasting 28, 56, and 56 days - that is, a total of a little less than five months.

NASA, meanwhile, would prepare and launch a rescue CSM with a crew of two. Skylab, Kleinknecht and Williams explained, had a second, radial docking port on its Multiple Docking Adapter. The rescue CSM would dock at the radial port to pick up the stranded crew.

They proposed that the CSM intended for the next Skylab crew should become the rescue CSM. This would presumably reduce by one the number of long-duration Skylab missions that could be flown. A fourth CSM, which would serve as the backup CSM throughout the Skylab program, would serve as the rescue CSM for Skylab 4, the third and final planned Skylab crew.

Image credit: NASA
Kleinknecht and Williams estimated that stripping out the rescue CSM's aft bulkhead lockers to make room for a "rescue kit" would require about a day. The rescue kit would include a pair of special astronaut couches, connectors and hoses for linking two additional space-suited astronauts to the rescue CSM's life support and communications systems, and an experiment-return pallet for bringing home a select few of the stranded crew's science results. The rescue CSM's two-man crew would recline in the left and right CSM couches; the three rescued Skylab crewmen would return to Earth in the center couch and in the two special couches mounted below the others in place of the lockers.

The rescue CSM would bring along a special Apollo probe-and-drogue docking unit that would enable astronauts inside Skylab to manually undock and cast off the crippled CSM. This would clear the Workshop's front port for any future CSM dockings. Kleinknecht and Williams did not explain what would happen to the unmanned CSM after it was discarded.

Though the time needed to install the rescue kit was minimal, the time needed to refurbish Pad 39B and prepare the rescue CSM and Saturn IB rocket for launch would depend upon when NASA declared that a rescue was necessary. After each Skylab Saturn IB launch, ground crews would need about 48 days to refurbish Pad 39B and prepare the next Skylab CSM and Saturn IB.

If a rescue were judged to be necessary at the beginning of the 28-day first manned Skylab mission (Skylab 2), then the mission would be extended by 20 days, making the total duration about 48 days. If a rescue were declared to be necessary late in Skylab 2 - say at the time of planned return to Earth - then preparations for the next Skylab CSM launch would be farther along, but would have started later. The rescue CSM and Saturn IB would thus need 28 days before they could lift off, bringing the total Skylab 2 mission duration to about 56 days, or double the duration planned at launch.

Activation of the Skylab rescue capability early in the Skylab 3 or Skylab 4 mission might permit a rescue before the return time planned when the stranded crew left Earth, Kleinknecht and Williams found. A failure near the planned conclusion of Skylab 3 or Skylab 4 would see a rescue CSM launched as little as 10 days after the rescue plan was activated.

Skylab rescue crewmen Vance Brand (left) and Don Lind. Though he never flew to Skylab, Brand would reach space as part of the Apollo-Soyuz Test Project in July 1975 and as Commander of Space Shuttle missions STS-5 (November 1982), STS-41-B (February 1984), and STS-35 (December 1990). Lind would reach space as a Mission Specialist on Shuttle mission STS-51-B (April-May 1985). Image credit: NASA
The 2 August 1973 failure of the second Skylab 3 CSM thruster quad unleashed a storm of activity. NASA prepared the backup Skylab CSM, not the Skylab 4 CSM, as its rescue vehicle, and tapped Skylab 3 backup crewmen Vance Brand and Don Lind to pilot it.

NASA had made other changes to Kleinknecht and Williams' rescue plan. The special probe-and-drogue docking unit for casting off the malfunctioning CSM had become a concave drogue unit that would be installed over the front port. It was launched with Skylab, not in the rescue CSM. After they installed it, the stranded astronauts would "trigger" the drogue to manually release their balky CSM. The rescue CSM would then dock at the front port, not the radial port.

Almost as soon as NASA activated the rescue plan, laboratory analysis on Earth showed that the batch from which the nitrogen tetroxide in the Skylab 3 CSM's propulsion systems had been taken was not tainted. As unlikely as it might seem, the two thruster quad malfunctions lacked a common cause.

Working in the CSM simulator in Houston, astronaut Brand demonstrated that the Skylab 3 crew could maneuver their spacecraft adequately even if they lost a third thruster quad. That is, if they were left with only one functioning quad when time came for them to return home, they could still safely deorbit their CSM.

Though rescue preparations continued as a precaution, by 10 August NASA managers had cleared the Skylab 3 crew for the full duration of their planned 59-day mission on board the Workshop. On 25 September 1973, Bean, Lousma, and Garriot returned to Earth as originally planned, in the CSM that had launched them to Skylab.

Sources

"Skylab Rescue Capability," Kenneth S. Kleinknecht and Lawrence G. Williams; paper presented at the Fifth Annual Space Rescue Symposium Organized by the Space Rescue Studies Committee of the International Academy of Astronautics, 23rd Congress of the International Astronautical Federation, Vienna, Austria, 9-12 October 1972

Skylab News Reference, NASA Office of Public Affairs, March 1973, pp. IV-6 - IV-8

"Skylab: Outpost on the Frontier of Space," T. Canby, National Geographic, October 1974, p. 460

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)

What If An Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

28 August 2015

A Forgotten Pioneer of Mars Resource Utilization (1962-1963)

Sixty-five years ago: the first rocket launch from Cape Canaveral, Florida. A captured German V-2 with an American WAC Corporal sounding rocket on top begins a low-angle flight to a downrange distance of at least 320 kilometers. Image credit: U.S. Army/NASA
Most Mars expedition plans of the 1950s and early 1960s made little use of martian resources. Apart from using the planet's atmosphere to slow landers for touchdown, either through use of parachutes or, more commonly in the time period, large wings, Mars spacecraft generally depended little on materials or conditions peculiar to Mars. This was because so little was known of the planet.

The potential benefits of using martian resources to make spacecraft propellants, building materials, and life support consumables were so compelling, however, that some planners chose to incorporate them into their mission designs anyway. Chief among the anticipated benefits was a dramatic reduction in spacecraft mass if raw materials for rocket propellants could be found at Mars. Reducing mission mass meant fewer expensive, temperamental rockets would be needed to launch Mars spacecraft components and propellants into Earth orbit for assembly, which in turn meant reduced mission cost and risk.

The Working Group on Extraterrestrial Resources (WGER) was formed in early 1962. Besides NASA, the group included representatives from the U.S. Air Force, the U.S. Army, the U.S. Geological Survey, the Bureau of Mines, aerospace corporations, and universities. The group, which met throughout the 1960s, focused mainly on lunar resources. A few researchers, however, used the WGER as a forum for discussing eventual exploitation of Mars resources.

One of these bold forward-thinkers was Ernst Steinhoff, representing the RAND Corporation, a think tank created in 1946 to provide advice to the U.S. military services. RAND had performed Mars studies for the U. S. Air Force as early as 1960. Steinhoff, whose specialty was rocket guidance, came to the U.S. in 1945 with Wernher von Braun, Ernst Stuhlinger, Krafft Ehricke, and other members of the Peenemünde rocket team.

After working to launch captured, sometimes modified, V-2 missiles for the U.S. Army - the image at the top of this post shows the 24 July 1950 launch of the two-stage Bumper 8 rocket - Steinhoff went to work for U.S. industry in 1956. He joined RAND in 1961, and was instrumental in the formation of the WGER the following year. In fact, he became the WGER's first chairman.

Mars pioneer Ernst Steinhoff. Image credit: U.S. Air Force
Steinhoff summed up his Mars work in papers presented at a March 1962 meeting at NASA's Marshall Space Flight Center in Huntsville, Alabama, and at the pivotal June 1963 American Astronautical Society Symposium on the Manned Exploration of Mars in Denver. George Morgenthaler of Martin Marietta Corporation organized the Denver symposium, the first non-NASA meeting devoted to piloted Mars travel. As many as 800 engineers and scientists heard Steinhoff's paper and 25 others. It was the first time so many science and engineering professionals with an interest in Mars had come together in one place, and the last Mars meeting of its size until the 1980s.

Near the end of 1963, soon after he chaired the second annual meeting of the WGER (23-25 October 1963), Steinhoff could not pass up an offer to become Chief Scientist at the Air Force Missile Development Center at Holloman Air Force Base in Alamogordo, New Mexico. When he assumed his new responsibilities, his involvement in the WGER and his work on Mars subjects suffered. This is unfortunate, for in his Huntsville and Denver papers he anticipated and promoted mission concepts which would, with the passage of decades, emerge as highly significant in Mars exploration planning. Had he continued his work at RAND, he might have further promoted his ideas, and that might have changed the course of Mars mission planning in the 1960s and beyond.

Steinhoff's work focused on "autarchic" – that is, self-sufficient – bases on Mars and Phobos. Self-sufficiency would be achieved through mining and processing of local materials, and by equipping the base with regenerable (recycling) life support systems. The Phobos and Mars bases would support scientific research and serve as transportation "terminals" for spacecraft.

Steinhoff estimated that extraterrestrial water could supply over 90% of the logistical needs of space-faring humans. He wrote that the moon's gravity – nearly 20% as strong as Earth's – would make it an inefficient "interim space base" for fueling Mars-bound ships. Citing Clyde Tombaugh, who had written that Mars's moons were probably made of the same water-rich materials as Mars itself, Steinhoff proposed that Phobos supplant the moon as a stepping stone to Mars. Nuclear systems could cook water out of Phobos rocks, then split it into hydrogen and oxygen chemical rocket propellants.

Image of Mars captured at Mt. Wilson Observatory in 1956, the year of the last close Mars opposition at the time Steinhoff wrote his papers. Because Mars has a decidedly elliptical orbit, the Earth-Mars distance during oppositions varies over a roughly 15-year cycle. The next close opposition would occur in 1971; the next after that was in 1988; and the most recent took place in 2003. Another will take place in 2018. When Steinhoff speculated on the nature of martian resources, this was among the best images of Mars available. Image credit: Mt. Wilson Observatory/NASA
Steinhoff's early Mars expedition would include 18 astronauts and a convoy of three crew and six cargo spacecraft. They would use a conjunction-class Mars mission profile, traveling to Mars in 256 days, remaining in the Mars system for 485 days, and then returning to Earth in 256 days.

Two chemists and two geologists would prospect on Phobos for water-rich rocks. The little moon's weak gravity would enable space-suited astronauts to easily assemble "ready-to-operate" base modules shipped from Earth. Space construction workers, Steinhoff wrote, would be able to carry and connect 50-ton modules by hand. (Steinhoff apparently forgot that weightless objects retain their mass. Astronauts can move massive objects, it is true, but only through considerable exertion, and only if they have a firm footing and adequate handholds. Stopping a massive object in weightlessness requires as much effort as setting it in motion.)

Reusable winged three-man shuttles based at the Phobos terminal would provide access to Mars's surface. In common with most Mars planners of his day, Steinhoff assumed, based on the consensus view of Earth-based astronomers, that the martian atmosphere would be about 10% as dense as Earth's - that is, thick enough to support gliding shuttles requiring minimal landing propellants.

Mars's surface would be rough, Steinhoff expected, so the first gliding shuttle landing would be a difficult proposition. He proposed that early shuttles should parachute drop cargo and astronauts, then blast back to Mars orbit without landing. Among the early air-dropped cargoes would be a radio-controlled bulldozer, which astronauts on Phobos would remote-control to build a smooth, level runway for the first Mars shuttle landing. This was probably the first time anyone proposed to teleoperate equipment on Mars from orbit.

The runway would be built within 25º of the martian equator so that it could be reached with relative ease from Phobos' equatorial orbit. The first Mars surface base would be established near the runway. Inflatable modules would provide living space for early explorers. After the Mars base became operational, shuttles would rely on propellants manufactured from Mars water to return to the Phobos base.

The Mars base would use vehicles and building techniques that Steinhoff's RAND colleagues had proposed in their Air Force studies. Rocket turbine engines tailored to the martian atmosphere - which many expected would be made mostly of nitrogen, as is Earth's atmosphere - would power surface rovers, airplanes, and helicopters with low-mass inflatable parts. Astronauts would manufacture cement from martian materials, construct masonry and cinder-block buildings, and inhabit martian caves.

After the propellant needs of the Mars system were met, Phobos would become a fueling station for interplanetary spacecraft. Steinhoff estimated that enough propellant could be manufactured in just 100 days to launch a spacecraft from Phobos to 300-mile-high Earth orbit, and that Phobos propellants could cut the time required for transfer between Mars and Earth in half.

He added that "use of indigenous resources, combined with more advanced nuclear ferry systems, may . . . pave the way to intensive interplanetary exploration within the limitations of our national resources." Phobos could, for example, serve as a refueling stop for Jupiter-bound piloted spacecraft.

Sources

"Powerplants for Atmospheric and Surface Vehicles on Mars," Research Memorandum RM-2529, W. H. Krase, The RAND Corporation, 10 April 1960

"Vehicles for Exploration on Mars," Research Memorandum RM-2539, T. F. Cartaino, The Rand Corporation, 30 April 1960

"A Possible Approach to Scientific Exploration of the Planet Mars," Paper #38, Ernst A. Steinhoff, editor, From Peenemünde to Outer Space, "A Volume of Papers Commemorating the Fiftieth Birthday of Wernher von Braun," NASA Marshall Space Flight Center Technical Report, 1962, pp. 803-836

"Use of Extraterrestrial Resources for Mars Basing," Ernst A. Steinhoff, Exploration of Mars, George Morgenthaler, editor, pp. 468-500; proceedings of the American Astronautical Society Symposium on the Exploration of Mars, Denver, Colorado, 6-7 June 1963

"Manned Exploration of Mars?" Raymond Watts, Sky & Telescope, August 1963, pp. 63-67, 84

Report of the Second Annual Meeting of the Working Group on Extraterrestrial Resources on October 23-25, 1963, at the Air Force Missile Development Center, Holloman Air Force Base, Alamogordo, New Mexico, MDC-TR-63-7, no date (1965?)

More Information

Clyde Tombaugh's Vision of Mars (1959)

EMPIRE Building: Ford Aeronutronic's 1962 Plan for Piloted Mars/Venus Flybys

The Challenge of the Planets: Part One - Ports of Call

24 August 2015

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

Image credit: NASA
George Mueller left private industry to become NASA's new Associate Administrator for Manned Space Flight in September 1963. He immediately asked John Disher and Adelbert Tischler, two veteran NASA engineers not directly involved in Apollo, for an independent assessment of the moon program. On 28 September, they told Mueller that it could not achieve President Kennedy's goal of a man on the moon by 1970. They estimated that NASA might be able to carry out its first manned moon landing in late 1971.

Mueller took drastic action. When he joined NASA, the Apollo flight-test plan was based on the philosophy of incremental testing, which meant that untried rocket stages would launch only dummy stages and dummy spacecraft. On 29 October 1963, Mueller informed his senior managers that Apollo test flights would henceforth use complete systems. Mueller's directive meant that, when the Saturn V S-IC first stage flew for the first time, it would be as part of a complete 363-foot-tall three-stage Saturn V. The new "all-up" approach would, it was hoped, slash the number of test flights needed before the Saturn V could launch astronauts to the moon.

George Mueller. Image credit: NASA
All-up Saturn V testing, today hailed as a visionary and heroic step, made many Apollo engineers nervous. The Saturn V was the largest rocket ever developed. It had engines of unprecedented scale and power: the F-1 engines in the 33-foot-diameter S-IC first stage, which burned RP-1 kerosene fuel and liquid oxygen, remain today the largest ever flown. The J-2 engines in the top two stages, the 33-foot-diameter S-II second stage and the 22-foot-diameter S-IVB stage, gulped down temperamental liquid hydrogen and liquid oxygen propellants. Cautious engineers could see many opportunities for trouble, and they were aware that problems they could not foresee might be the most difficult to solve. Many believed that NASA should have in place backup plans in case the Saturn V suffered development delays.

Eighteen months after Mueller's announcement, E. Harris and J. Brom, engineers with The RAND Corporation think tank, proposed one such back-up plan. Their brief report, originally classified "Secret," looked at how NASA might accomplish a manned moon landing by 1970 if the Saturn V could not be certified as safe enough to launch astronauts.

Harris and Brom's backup plan would see the Apollo Saturn V lift off without astronauts on board. It would expend its S-IC first stage and S-II second stage in turn, then its S-IVB third stage would place itself plus unmanned Apollo Command and Service Module (CSM) and Lunar Module (LM) spacecraft into parking orbit about the Earth. Because it would carry no crew, the CSM would need no Launch Escape System (LES) tower on its nose.

The astronauts would reach Earth orbit separately in a ferry CSM launched atop a two-stage Saturn IB rocket. The ferry CSM would carry a special drogue docking unit on its nose for linking up with the unmanned CSM's nose-mounted probe docking unit. The special drogue, the only new system required for RAND's backup plan, would need about one year and "perhaps several million dollars" to develop.

The top of the Apollo 13 Lunar Module Aquarius. The red arrow points to the concave drogue docking unit. Image credit: NASA
The astronauts would dock with and transfer to the lunar mission CSM in Earth orbit, then would cast off the ferry CSM. The remainder of their mission would occur as in NASA's Apollo plan (image at top of post). The astronauts would restart the S-IVB stage to perform Trans-Lunar Injection (that is, to leave Earth orbit for the moon). After S-IVB stage shutdown, they would detach the CSM from the Spacecraft Launch Adapter (SLA) shroud that linked the bottom of the CSM to the top of the S-IVB. The SLA, made up of four segments, would peel back and separate, revealing the LM. The CSM would then dock with the drogue docking unit on top of the LM and pull the moon lander free of the spent S-IVB stage.

The RAND engineers declined to recommend whether the unmanned Saturn V or the manned Saturn IB should be launched first. They noted that liquid hydrogen fuel in the Saturn V's S-IVB stage would boil and escape at a rate of 700 pounds per hour; the stage would thus need to be restarted within 4.5 hours of reaching parking orbit if it were to retain enough propellants for Trans-Lunar Injection. They noted that deletion of the 2900-pound LES would make the unmanned Saturn V that much lighter, so its S-IVB stage could be loaded with an extra 2900 pounds of liquid hydrogen; that is, enough to permit it to loiter in low-Earth orbit for nearly 10 hours. Extending the loiter time further would demand a complex and costly S-IVB stage redesign.

Launching the crew first would avoid the S-IVB stage loiter-time constraint. Harris and Brom noted that, though the Apollo lunar mission was scheduled to last only from seven to 10 days, NASA planned a 14-day Earth-orbital Gemini mission by the end of 1965 to certify that astronauts could withstand long space flights. Assuming that the Gemini flight confirmed that humans could endure 14 days in weightlessness, then the ferry CSM crew could in theory wait for from four to seven days for the unmanned Saturn V to join them in Earth orbit. Harris and Brom recommended that, if the unmanned Saturn V became delayed so that the astronauts waiting in orbit could not accomplish a lunar mission and return to Earth within 14 days of first reaching space, then they should carry out an unspecified backup Earth-orbital mission in the ferry CSM so that their flight would not be wasted.

NASA officials did not take up the Harris and Brom proposal, though for a time in 1968 they might have wished that they had. The first unmanned Saturn V test flight, Apollo 4, lifted off on 9 November 1967. In keeping with Mueller's 1963 directive, it included complete S-IC, S-II, and S-IVB stages, plus a CSM with LES. Because LM development had hit snags, a dummy LM rode inside its SLA. The eight-hour Earth-orbital mission was an unqualified success.

Troubled flight: Apollo 6 unmanned Saturn V test, 4 April 1968. Image credit: NASA
Apollo 6 was, however, another story. On 4 April 1968, two minutes into its unmanned flight, the second Saturn V to fly began to shake back and forth along its long axis. Dubbed "pogo" by engineers, the violent oscillations tore pieces off the SLA and damaged one of the S-II's five J-2 engines. Following S-II ignition, the engine under-performed and shut down prematurely, then a control logic flaw caused a healthy S-II engine to shut down. The remaining three S-II engines burned for a minute longer than planned to compensate for the two failed engines. The S-IVB's single J-2 engine then burned for 30 seconds longer than planned to reach a lopsided Earth orbit. Two orbits later, the engine refused to restart.

The pogo oscillations might have injured astronauts; the S-IVB failure would certainly have scrubbed their flight to the moon. Post-flight analysis showed, however, that the pogo and engine failures had relatively simple fixes. After intense internal debate, NASA decided in October 1968 that the third Saturn V should launch Apollo 8 astronauts Frank Borman, James Lovell, and William Anders to the moon. The giant rocket performed flawlessly, placing the Apollo 8 CSM on course for lunar orbit on 21 December 1968.

Sources

"Apollo Launch-Vehicle Man-Rating: Some Considerations and an Alternative Contingency Plan (U)," Memorandum RM-4489-NASA, E. D. Harris and J. R. Brom, The RAND Corporation, May 1965

The Apollo Spacecraft: A Chronology, Volume II, NASA SP-4009,  Mary Louise Morse & Jean Kernahan Bays, NASA Scientific and Technical Information Office, 1973, pp. 104-106

Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, NASA SP-4206, Roger Bilstein, NASA, 1980, pp. 347-363

Apollo: The Race to the Moon, Charles Murray & Catherine Bly Cox, Simon & Schuster, 1989, pp. 153-162

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)

What If An Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

21 August 2015

A 1974 Plan for a Slow Flyby of Comet Encke

So close: the CONTOUR spacecraft. Image credit: NASA
Comet Halley is often called "Humankind's Comet" because it has appeared throughout much of recorded human history and because its orbital period of about 76 years is roughly equivalent to a human lifespan. Given the often frustrating nature of spaceflight planning, Comet Encke could be nicknamed "Spaceflight's Comet." It has made the short list of targets for comet-exploring spacecraft for half a century. With one of the shortest orbital periods of any comet – just 3.3 years – and an inclination relative to the plane of the Solar System of only about 10°, Encke is among the comets most easily accessible to spacecraft. Yet despite being named the target of many proposed comet missions, Encke has never received a visitor from Earth.

Humans came closest to exploring Comet Encke a little over a decade ago. Following its launch on 3 July 2002, NASA's 775-kilogram COmet Nucleus TOUR (CONTOUR) spacecraft moved through a series of elliptical phasing orbits about the Earth designed to position it for a solid-propellant rocket motor burn on 15 August 2002. The burn would have launched it into solar orbit near the Earth. CONTOUR would then have re-encountered Earth in August 2003. The gravity-assist kick it was meant to receive from our planet would have put it on course for a Comet Encke close flyby on 12 November 2003.

Instead, the CONTOUR spacecraft disintegrated during its Earth-departure burn. Observers visually tracked three objects where there should have been one CONTOUR. The CONTOUR Mishap Investigation Board determined that the most likely cause of the failure was an obvious-seeming design flaw: that the spacecraft's solid-propellant rocket motor, embedded at its center, produced enough heat that it weakened CONTOUR's structure, causing the spacecraft to break apart under acceleration. The Board cautioned, however, that lack of telemetry during the Earth-departure burn left open the possibility of several other causes, including rocket motor casing rupture, meteoroid or human-made space debris collision, or attitude-control failure leading to a destructive tumble.

If engineers and scientists at NASA's Goddard Space Flight Center (GSFC) had had their way, Comet Encke would have received its first visitor as early as 3 December 1980. In fact, it would have received two visitors at the same time, for they envisioned launching two spacecraft to Comet Encke on a single rocket. The Encke probes, near twins, would have flown by the comet at a relatively slow speed compared with other proposed comet spacecraft; hence, in the November 1974 NASA Technical Note they wrote to describe it, they dubbed their mission a "ballistic slow flyby."

The twin Comet Encke ballistic slow flyby spacecraft stacked within their streamlined Centaur launch shroud. The adapter would join with the top of the Centaur upper stage. Image credit: NASA
The Comet Encke probes were meant to depart Earth between 16 and 30 August 1980 atop a Titan rocket with a Centaur upper stage. Ironically, given CONTOUR's fate, the GSFC team rejected an additional solid-propellant "kick" rocket motor as too risky. The probes would travel on a curving ballistic path directly from Earth to Encke; hence the term "ballistic" in the mission's description.

Robert Farquhar led the four-person GSFC team. In 1972-1973, he had participated in GSFC's 35-member Cometary Explorer Study Group, which aimed to explore Comet Grigg-Skjellerup in April 1977 and Comet Giacobini-Zinner in February 1979 using a single 450-kilogram spinning spacecraft. The NASA-appointed Comet and Asteroid Science Advisory Committee had endorsed Cometary Explorer as the first step in a logical program of comet exploration leading to a NASA Comet Halley mission in 1985-1986.

Unfortunately, the U.S. civilian space agency, faced with rapidly declining budgets and bearing the heavy burden of Space Shuttle development, had been unable to fund Cometary Explorer. The 1980 Encke slow flyby mission would, it was hoped, put NASA comet exploration back on track to Halley.

Technicians at Cape Canaveral lower the launch shroud over the West German-U.S. Helios B solar probe spacecraft.  Image credit: NASA
Farquhar's team modeled its Comet Encke mission on the German-U.S. Helios A/Helios B Sun probe missions. Helios A left Earth in late 1974 (about a month after the GSFC group published its Technical Note, in fact). The Helios probes were designed to survive perihelion (the point in their Sun-centered orbit where they were nearest the Sun) at only 0.30 times the Earth-Sun distance, which is inside the orbit of the planet Mercury; the Encke probes would pass their cometary target as it neared perihelion at 0.34 times the Earth-Sun distance. The Helios probes would orbit in the plane of the Solar System; the Encke probes would match their target's modest orbital tilt.

The GSFC team's Encke probes, which would spin to create gyroscopic stability, would move apart immediately after they separated from their launch vehicle's Centaur stage. Farquhar's team dubbed them the "tail probe" and the "coma probe." Each would resemble the lower half of a hourglass-shaped Helios spacecraft. Solar cells on their sides would power spacecraft systems and a suite of science instruments.

If necessary, a course-correction rocket burn would take place 10 days after launch. A second burn 50 days after launch would aim the tail probe at a point in the Comet Encke's wan tail about 10,000 kilometers behind the nucleus and would aim the coma probe at a point immediately in front of the nucleus. A third, very modest, course-correction burn was scheduled for Launch +85 days. The two spacecraft would encounter Comet Encke at about Launch +102 days.

Depending on their launch date, the Comet Encke spacecraft would reach their target between 3 December and 8 December 1980 moving at between 7.6 and 9.03 kilometers per second. Comet Encke would reach perihelion on 6 December. The Encke flybys would occur at around 1000 hours Greenwich Mean Time on all days of their arrival window so that the 100-meter dish-shaped antenna at Effelsberg, West Germany – the same antenna used to communicate with the Helios probes – could receive data for as long as possible before the twin probes set below the local horizon.

Image credit: NASA
Farquhar and his colleagues envisioned that their two probes would carry slightly different science payloads. The 375-kilogram coma probe, which would linger within 1000 kilometers of the sunlit side of the nucleus for nearly 42 minutes, would include a despun platform bearing its radio dish antenna, TV camera, neutral mass spectrometer, UV spectrometer, and Lyman-alpha spectrometer. The 325-kilogram tail probe would include a despun antenna, but would lack the coma probe's despun platform and its four instruments. Both probes would include on their spinning main sections an ion mass spectrometer, a DC magnetometer, an AC magnetometer, an electron analyzer, a plasma analyzer, an electric field detector, a dust detector, and a dust composition instrument.

The GSFC team was not the only group in 1974 that planned a 1980 Comet Encke mission. The GSFC scientists and engineers made a point of comparing their mission plan with its main rivals. They explained that, in their comparison, "the primary evaluation criteria [would] be the science value and realism of attaining mission objectives."

Their plan's leading rival, a mission design advocated mainly by the Jet Propulsion Laboratory and its contractors, was based on solar-electric propulsion. Launch would take place on 17 December 1978 and a Comet Encke flyby would occur on 6 November 1980. The GSFC team noted that the mission's 30-centimeter-diameter solar-electric (ion) propulsion thruster had yet to be developed, let alone tested; nevertheless, it would be expected to operate flawlessly for 690 days. In addition, the thruster would interfere with the spacecraft's particle-and-fields instruments. Interference would not cease when the thruster was switched off.

Assuming that its untried thruster functioned as hoped, however, the solar-electric spacecraft would pass Comet Encke moving at only four kilometers per second, which constituted an advantage over GSFC's ballistic slow flyby. It would do so, however, more than a month before perihelion, when Comet Encke was still about 0.5 times the Earth-Sun distance from perihelion. At that point in its orbit, the nucleus would be relatively inactive: if past observations were any guide, Comet Encke would have almost no tail.

The ballistic slow flyby's lesser rival was a ballistic fast flyby advocated mainly by NASA Ames Research Center and its contractors. A spin-stabilized spacecraft similar to the Pioneer 10 and Pioneer 11 outer Solar System spacecraft would launch on 18 August 1980 atop a relatively cheap Atlas/Centaur rocket with a solid-propellant kick stage. After a voyage of just 92 days, the spacecraft would whiz past Comet Encke on 18 November 1980 at a blistering 20.1 kilometers per second.

Farquhar's group noted that high-speed impacts with Comet Encke dust particles could easily destroy the ballistic fast flyby spacecraft, and that its camera would likely return only motion-blurred images (assuming that it had time to locate the nucleus or any other important comet features). It would remain within 1000 kilometers of the nucleus for a mere nine minutes.

The GSFC team concluded that, compared with the solar-electric and ballistic fast flybys, the ballistic slow flyby was "superior in every respect." This assertion may well have been correct; the rivalry between the slow flyby, solar-electric, and fast flyby groups split the small community of comet exploration advocates, however, helping to ensure that no spacecraft explored Comet Encke in 1980.

Comet Encke as observed by the MESSENGER Mercury orbiter on 17 November 2013. Encke passed the planet Mercury at a distance of just 3.7 million kilometers and reached perihelion four days later. The comet will reach its next perihelion on 10 March 2017. Image credit: NASA/JHUAPL/Carnegie Institution of Washington
Sources

Mission Design for a Ballistic Slow Flyby of Comet Encke 1980, NASA Technical Note D-7726, R. Farquhar, D. McCarthy, D. Muhonen, and D. Yeomans, NASA Goddard Space Flight Center, November 1974

Comet Nucleus Tour CONTOUR Mishap Investigation Board Report, NASA, 31 May 2003

More Information

Cometary Explorer (1973)

Missions to Comet d'Arrest and Asteroid Eros in the 1970s (1966)

19 August 2015

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

238,000 miles from home - Earth as viewed by the Apollo 8 astronauts in lunar orbit, Christmas Eve 1968. Image credit: NASA
The three-man crew of Apollo 8 – Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders – was the first to leave Earth on a Saturn V rocket. They departed Cape Kennedy, Florida, on 21 December 1968, and left Earth orbit for the moon about two and a half hours later.

Though its target was the moon, the Apollo 8 mission included no Lunar Module (LM). The manned lunar lander had suffered production delays; this was understandable, given that no one had ever before built a vehicle for landing humans on another world. NASA's planned mission sequence for manned Apollo missions had begun with a low-Earth orbit (LEO) test of the Command and Service Module (CSM) on Apollo 7 (11-22 October 1968). This was to have been followed in short order by an LEO test of the CSM and LM, then a CSM/LM test flight in higher Earth orbit. During the next mission in the sequence, astronauts would test the CSM and LM in lunar orbit, then the first Apollo lunar landing attempt would take place. NASA designated these five increasingly ambitious missions C, D, E, F, and G.

Putting off the next Apollo flight - the D mission - until the LM was ready might have placed in jeopardy attainment of Apollo's goal of landing a man on the moon ahead of the Soviet Union and before the end of the 1960s. Because of this, in late summer 1968, NASA began to look at a modified mission sequence. The C-prime mission, which would see the Apollo 8 CSM orbit the moon without an LM, was made public on 12 November 1968, three weeks after Apollo 7 successfully accomplished the C mission. The mission would test many CSM elements of the lunar landing mission and the world-wide system of radio dishes and transceivers NASA had created for Apollo lunar mission communications and tracking.

The C-prime mission had been the subject of intense debate at the highest levels of NASA, for it meant traveling to the moon without the backup life support and propulsion systems the LM could provide. Those in favor of launching the C-prime mission were helped by intelligence reports that the Soviet Union might launch a man around the moon during December 1968. Such a mission might steal Apollo's thunder; though it would merely swing around the moon and fall back to Earth, it would enable the Soviets to claim that they had launched a man to the moon first.

Eleven hours after launch, the Apollo 8 crew carried out a course correction. This required that they ignite the CSM's Service Propulsion System (SPS) main engine for the first time. Had the SPS not functioned as planned, the crew could have adjusted their course using the CSM's cluster of four Reaction Control System (RCS) thruster quads. The CSM would then have swung around the moon without entering orbit and fallen back to Earth.

Partial cutaway of Apollo CSM spacecraft. Image credit: NASA
The 20,500-pound-thrust SPS, an AJ-10-137 rocket engine manufactured by Aerojet, was located at the aft end of the CSM. Other AJ-10 variants had propelled Vanguard, Atlas-Able, and Thor-Able launch vehicles. The SPS burned hydrazine/UDMH fuel and nitrogen tetroxide oxidizer. Chemically inert helium gas pushed the propellants into the engine's ignition chamber. Hydrazine/UDMH and nitrogen tetroxide are hypergolic propellants; that is, they ignite on contact with each other. The resulting hot gas then vented through a large engine bell, which swiveled to help steer the CSM.

The Apollo 8 SPS performed almost perfectly during the 21 December course correction burn and during a second burn 61 hours after launch designed to help ensure that the Apollo 8 CSM would enter the orbit about the moon planned for it. Three hours later, Apollo 8 was given a "go" to enter lunar orbit. The spacecraft passed behind the moon, out of radio contact with Earth, and the crew ignited the SPS for the third time. It burned for a little more than four minutes, slowing the Apollo 8 CSM enough for the moon's gravity to capture it into orbit.

The Apollo 8 CSM orbited the moon 10 times over the next 20 hours. Then, on 25 December 1968, about 89 hours after launch, the crew ignited the SPS behind the moon to begin the journey home to Earth. The rocket motor performed flawlessly during this critically important burn, which NASA dubbed Trans-Earth Injection (TEI).

Two and a half days later, on 27 December, the CSM split into two parts. The Service Module (SM), which contained the SPS, separated from the Command Module (CM), which held the crew. The former burned up in Earth's atmosphere as planned, while the latter, protected by a heat shield, maneuvered in the upper atmosphere to reduce heating and deceleration, deployed parachutes, and splashed safely into the Pacific Ocean.

Four days after Apollo 8's triumphant return, A. Haron and R. Raymond, engineers with Bellcomm, NASA's Washington, DC-based planning contractor, completed a brief study of what might have happened had the SPS not ignited for the TEI burn. Specifically, they looked at how long a crew might survive in lunar orbit following a TEI failure.

Haron and Raymond found that the "first constraint" on the crew's endurance would be depletion of the CSM's supply of lithium hydroxide (LiOH) canisters. The square canisters were used in pairs to remove carbon dioxide exhaled by the crew from the CSM's pure oxygen atmosphere. During Apollo 8, the crew had traded a saturated LiOH canister for a fresh one every 12 hours, thus expending two per day.

The Bellcomm engineers calculated that, at that rate, the crew would use up the last of the 16 LiOH canisters launched on board the CSM 96 hours after TEI failure. They would then grow drowsy and become unconscious as carbon dioxide built up in the crew cabin. Had TEI failed on Apollo 8, Borman, Lovell, and Anders would probably have suffocated on 29 December.

Haron and Raymond noted, however, that LiOH canisters might be changed less often without harming the crew. They cited a November 1968 Manned Spacecraft Center study that had shown that LiOH canisters could absorb carbon dioxide for up to 37 hours. If a stranded Apollo CSM crew began to ration its LiOH canisters immediately after TEI failure, they would be able to stretch their survival time to 148 hours. In that case, the Apollo 8 crew would have survived until New Year's Eve – the day Haron and Raymond completed their study.

If NASA elected to include 10 additional LiOH canisters on CSMs bound for the moon, and if immediately after TEI failure the astronauts powered down the CSM so that its three fuel cells remained just barely operational, then endurance might be stretched to about two weeks, the Bellcomm team estimated. The fuel cells, manufactured by Allis Chalmers, operated by combining liquid hydrogen and liquid oxygen reactants to produce electricity and water. Electricity from the fuel cells powered the CSM through most of the mission. The crew drank the water; it was used also for cooling in the CSM's Environmental Control System (ECS) and electronics. Excess water could be dumped overboard.

Haron and Raymond looked briefly at the possibility of switching off two fuel cells to conserve reactants. If this were done, then the remaining fuel cell might operate for up to three weeks after TEI failure. However, a single fuel cell would probably not produce enough electricity to operate all CSM systems vital to the crew's continued survival, some of which were not immediately obvious. As an example, Bellcomm cited the RCS quads: the astronauts would need to use them to maneuver the CSM to keep its ECS radiators in shadow to conserve cooling water. In addition, the LiOH canister shortage would remain. "The feasibility of extending survival time to as much as three weeks cannot be confirmed at this time," Haron and Raymond wrote.

The Bellcomm study was mainly of academic interest, since a crew stranded in orbit around the moon, 238,000 miles from Earth, could not have been rescued even if they did survive for two or three weeks. NASA did not have the ability to maintain a rescue Saturn V rocket and CSM on standby.

The space agency would have cause to recall the brief Bellcomm study twice during subsequent Apollo missions. During Apollo 13 (11-17 April 1970), an oxygen tank exploded in the CSM Odyssey, badly damaging its SM. Because the explosion happened while the mission was en route to the moon, its crew, commanded by Apollo 8 astronaut James Lovell, was able to use the LM Aquarius as a lifeboat. They employed its descent engine in place of the SPS. The docked spacecraft flew behind the moon, where the crew fired the LM descent engine to adjust their course and speed their return to Earth.

On Apollo 16 (16-27 April 1972), as the CSM Casper orbited the moon, it suffered a malfunction in the system used to swivel the SPS engine bell. The LM Orion, which had already undocked in preparation for landing, stood by in lunar orbit until the SPS problem was understood, then landed several hours behind schedule.

Had it been judged necessary, NASA could have scrubbed the Apollo 16 landing. Orion would then have redocked with Casper. The astronauts could have used Orion's descent engine and (if necessary) Casper's RCS quads to perform TEI. Going ahead with the landing eliminated that option; the descent engine used most of its propellants to land on the moon, then was left behind on the surface with the rest of the LM descent stage. The LM ascent stage, with its smaller engine, returned to lunar orbit with virtually dry tanks. This left only the SPS available for TEI.

As a precaution, NASA moved up Apollo 16's TEI burn by a day in the hope that, should the SPS misbehave, the crew and engineers on Earth would have adequate time to find a solution and ensure a safe, if delayed, return to Earth. As it turned out, the Apollo 16 SPS performed a flawless TEI burn.

Sources

NASA News Press Kit, Project: Apollo 8, 15 December 1968

"Consumables Affecting Extended CSM Lifetime in Lunar Orbit," Case 320, A. Haron and R. Raymond, Bellcomm, Inc., 31 December 1968

Apollo 8: "A Most Fantastic Voyage," Lt. Gen. Sam C. Phillips, National Geographic, May 1969, pp. 593-631

Apollo 13: "Houston, We've Had a Problem," NASA EP-76, 1970

NASA Mission Report: Apollo 13, A Successful Failure, 20 May 1970

How Apollo Flew to the Moon, W. David Woods, Springer Praxis, 2008, pp. 236-238

More Information

What If an Apollo Lunar Module Ran Low on Fuel and Aborted its Moon Landing? (1966)

What If an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)

15 August 2015

Multiple Asteroid Flyby Missions (1971)

Pioneer 10/11. Image credit: NASA
Between 1 January 1801, when asteroid 1 Ceres was discovered, and March 1971, when the International Astronomical Union (IAU) held its "Physical Studies of the Minor Planets" colloquium in Tucson, Arizona, astronomers compiled a list of 1748 numbered asteroids. That they bore numbers indicated that they had each been observed more than once so that their orbital paths and positions were known.

Astronomers had spotted many thousands of other asteroids. Often they appeared as annoying streaks on photographic plates intended to capture images of objects deemed more worthy of an astronomer's attention: for example, distant galaxies. The vast majority of those asteroids were not knowingly observed again.

As the 1960s ended and the 1970s began, enthusiasm for asteroids as objects of study began to grow. In part this was because the future looked bright for robotic space exploration. No longer were automated spacecraft seen mainly as precursors for piloted moon missions.

Mars, with its two satellites Phobos and Deimos - believed to be captured asteroids - came in for special attention in NASA's 1970s robotic exploration program. Mariners 8 and 9 were scheduled for launch less than three months after the Tucson colloquium. The twin spacecraft, built by the Jet Propulsion Laboratory (JPL) in Pasadena, California, were planned to be the first Mars orbiters, though there was some concern that the Soviets might get there first.

The twin Viking spacecraft were scheduled to leave Earth for Mars in mid-1975. Each would include a Lander and an Orbiter. The Viking Landers were planned to be the first Mars soft-landers. NASA Langley Research Center (LaRC) in Hampton,Virginia, managed Viking; JPL served as contractor for the Mariner-based Viking Orbiters.

Pioneers 10 and 11 (image at top of post) were on track to become humankind's first emissaries to the Outer Solar System. To reach Jupiter (and, in the case of Pioneer 11, Saturn), they would become the first spacecraft to pass through the Asteroid Belt between Mars and Jupiter. Built by TRW and managed by NASA Ames Research Center (ARC) in Mountain View, California, they were due to launch in March 1972 and April 1973, respectively.

Most of the papers presented at the Tucson colloquium emphasized Earth-based telescope observations of asteroids, not spacecraft exploration, and in fact a consensus emerged by the colloquium's end that spacecraft exploration of asteroids would be premature. Nevertheless, among those present in Tucson was a small cadre of asteroid mission proponents. LaRC engineers David Brooks and William Hampshire, for example, described missions to multiple Main Belt asteroids.

They looked first at the simplest multiple asteroid flyby mission: one which saw a spacecraft launched on a random date into an elliptical Sun-centered orbit with a perihelion of one Astronomical Unit (AU) and an aphelion within the Asteroid Belt at three AU. An AU is equal to the mean Earth-Sun distance. They assumed that, in order to obtain useful data, the spacecraft would need to pass no more than 15,000 kilometers from an asteroid. Based on these stipulations, they calculated that a randomly launched spacecraft stood virtually no chance of exploring even one asteroid.

They added, however, that a randomly launched spacecraft stood a good chance of passing within 0.1 AU of 10 asteroids on average. While 0.1 AU (about 15 million kilometers) was too great a distance for effective exploration, this finding meant that, if the spacecraft could change its velocity, then it could shape its orbital path to pass within 15,000 kilometers of multiple asteroids.

Large velocity changes would enable exploration flybys of many asteroids, but would require costly new spacecraft development. New asteroid discoveries would also increase the number of possible flyby candidates. Brooks and Hampshire were determined, however, to show what could be accomplished with small velocity changes, spacecraft already in the development pipeline, and the 1748 asteroids numbered as of March 1971.

The Viking Orbiter, they noted, would carry enough propellants to change its velocity by 1.5 kilometers per second. They revealed that NASA ARC had studied a Pioneer 10/11-class spacecraft modified to capture into a highly elliptical Jupiter orbit. A Pioneer 10/11-class spacecraft could change its velocity by only 0.2 kilometers per second, but the hypothetical Pioneer Jupiter orbiter would up this to about one kilometer per second.

The LaRC engineers then provided detailed multiple asteroid flyby sequences for three missions. The missions were: leave Earth in the 1980-1982 period and orbit the Sun in a one-AU-by-three-AU orbit; leave Earth in late 1975 and fly past 1 Ceres; and leave Earth in 1975 and travel through the Asteroid Belt to Jupiter.

In no case would a spacecraft perform maneuvers which together would change its velocity by more than one kilometer per second. In each case, Brooks and Hampshire assumed that the spacecraft would pass 15,000 kilometers from the first asteroid it encountered because its launch vehicle put it there; that is, the propellant cost of exploring the first asteroid in any multiple asteroid sequence would count against the rocket stage that boosted the spacecraft out of Earth orbit, not the spacecraft itself.

Brooks and Hampshire found that launch from Earth into a one-by-three-AU orbit on 14 July 1981 would cause the spacecraft to pass within 0.1 AU of 15 asteroids over the course of 659 days. Unfortunately, nudging the spacecraft's path so that it would pass within 15,000 kilometers of all 15 would require a total velocity change of 41.6 kilometers per second.

Large velocity changes were necessary in part because some flybys occurred close together. The spacecraft would, for example, pass about 0.1 AU from asteroid 149 Medusa on 10 January 1982, just nine days after a 15,000-kilometer flyby of asteroid 1515 Perrotin. A velocity change of several kilometers per second would be required to bend the spacecraft's path to enable it to pass just 15,000 kilometers from 149 Medusa so soon after leaving 1515 Perrotin.

Spacing out asteroid encounters meant that a small spacecraft velocity change immediately after a close asteroid flyby could yield a large spacecraft orbit change. If mission designers opted instead to follow the 1515 Perrotin close flyby with a close flyby of 1674 Groeneveld six months later (13 June 1982), then added a 12 July 1983 close flyby of 561 Ingewelde, the total spacecraft velocity change would amount to just 0.93 kilometers per second.

The LaRC engineers identified seven three-asteroid missions and one four-asteroid mission, all launched on 14 July 1981, that would need total velocity changes of less than one kilometer per second. A multiple flyby mission to 149 Medusa, 870 Manto, and 1720 Neils would require the smallest velocity change - just 0.58 kilometers per second. The four-asteroid mission, which would explore 1515 Perrotin, 1674 Groeneveld, 561 Ingewelde, and 1720 Neils, would need a total velocity change of 0.8 kilometers per second.

Brooks and Hampshire gave less attention to their 1975 Ceres and Jupiter multiple asteroid missions. They determined that a late 1975 launch would enable close flybys of 632 Pyrrha and either 946 Poësia or 947 Monterosa en route to 1 Ceres, at 950 kilometers across the largest asteroid. The 632 Pyrrha-947 Monterosa-1 Ceres flyby sequence would need the lowest total velocity change of any of mission they studied: just 0.24 kilometers per second.

Jupiter-bound spacecraft presented two new problems, Brooks and Hampshire explained. First, they would move fast. For example, a spacecraft bound for Jupiter in 1975 targeted to pass the large (124-by-75-kilometer) asteroid 27 Euterpe would zip past at 18 kilometers per second, making data collection difficult.

In addition, a Jupiter-bound spacecraft would follow a short path through the Asteroid Belt, so would pass few asteroids. Brooks and Hampshire were able to identify only one multiple asteroid flyby opportunity for the 1975 Jupiter mission. The spacecraft would fly first past 666 Desdemona on 19 November 1975, then past 396 Aeolia on 6 April 1976. It would change its velocity by 0.52 kilometers per second. The LaRC engineers did not indicate whether any part of the velocity change would be applied to correcting the spacecraft's course to Jupiter after the 396 Aeolia flyby.

NASA would need two decades to carry out its first multiple asteroid flyby mission, and when it did the mission would resemble none of Brooks and Hampshire's scenarios. The Galileo Jupiter Orbiter grew from the NASA ARC Pioneer Jupiter Orbiter they described at the Tucson colloquium. The mission received new-start funding in 1977. Launch aboard the Space Shuttle was scheduled for January 1982.

Space Shuttle technical delays, fierce political battles over the type of upper stage that would propel Galileo to Jupiter, costly redesigns so that it could fit different upper stages, and technical problems with the Centaur-G' upper stage delayed Galileo's planned launch to May 1986. In January 1985, NASA Administrator James Beggs added to the Galileo mission the option of a flyby of the large (233-by-193-kilometer) asteroid 29 Amphitrite.

Destruction of the Space Shuttle Challenger on 28 January 1986 caused more delays and cancellation of the Centaur G' stage needed to boost Galileo directly to Jupiter. JPL re-planned the Galileo mission for an October 1989 launch with gravity-assist flybys of Venus and Earth (twice) and Jupiter arrival in December 1995. The new path put 29 Amphitrite far out of reach.

Following its first Earth gravity-assist, Galileo entered the Asteroid Belt and performed the first-ever asteroid flyby: a cruise past 18-by-nine-kilometer 951 Gaspra at a distance of 1604 kilometers on 29 October 1991. Galileo flew past Earth a second time to gain the final gravity-assist speed boost it needed to reach Jupiter; then, on 28 August 1993, it flew by 60-by-19-kilometer 243 Ida at a distance of 2410 kilometers, revealing that it has small moon. Dactyl, as the 1.6-by-1.4-by-1.2-kilometer satellite was named, brought to three the number of asteroids Galileo explored during its circuitous voyage to Jupiter.

Main Belt asteroid 243 Ida and its moon Dactyl, 28 August 1993. Image credit: NASA
Sources

"Multiple Asteroid Flyby Missions," David Brooks and William Hampshire, NASA SP-267, Physical Studies of the Minor Planets, Proceedings of the 12th Colloquium of the International Astronomical Union held in Tucson, Arizona, 6-10 March 1971, Tom Gehrels, editor, 1972, pp. 527-537

"Reasons for Not Having an Early Asteroid Mission," Edward Anders, NASA SP-267, Physical Studies of the Minor Planets, Proceedings of the 12th Colloquium of the International Astronomical Union held in Tucson, Arizona, 6-10 March 1971, Tom Gehrels, editor, 1972, pp. 479-485

Memorandum, Clark Chapman to various, "Notes Concerning the 'Centaur Wars' and Possible Action by the Planetary Science Community," 14 September 1982

Interoffice Memorandum GLL-JRC-84-189, Jet Propulsion Laboratory, J. R. Casani to W. E. Giberson, "Galileo Asteroid Flyby," 11 September 1984

Memorandum, T. V. Johnson, W. J. O'Neil, and C. M. Yeates to PSG/IDS, "Galileo Asteroid Encounter," Jet Propulsion Laboratory, 1 October 1984

Press Release, Public Information Office, Jet Propulsion Laboratory, "NASA Administrator James M. Beggs has approved the addition of an asteroid flyby option to the Galileo mission," 17 January 1985

Interoffice Memorandum GLL/TCC-87.238, Jet Propulsion Laboratory, T. C. Clarke to Galileo Project Science Distribution list, "Minutes of Galileo PSG Meeting of 11/21/86," 20 April 1987

Journey Into Space: The First Thirty Years of Space Exploration, Bruce Murray, W. W. Norton, 1989, pp. 180-237

Related Posts

Earth-Approaching Asteroids as Targets for Exploration (1978)

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Fun With Killer Asteroids

12 August 2015

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L4

Mariner 1 launches atop an Atlas-Agena B rocket, a missile-based workhorse of the early Space Age. Image credit: NASA
James Van Allen discovered the two Earth-circling radiation belts that bear his name in 1958. The discovery, based on data from Explorer 1 (the first U.S. satellite), Explorer 3, and Pioneer 3, was the first fundamentally new finding of the Space Age. In addition to its scientific and practical importance, it constituted a prestige victory in the Cold War space race with the Soviet Union. Time magazine put Van Allen on the cover of its 4 May 1959 issue.

The Van Allen Belts are a feature of Earth's magnetosphere. Though fascinating in its own right, the magnetosphere became a source of frustration for scientists eager to study the Sun. This is because Earth's magnetic envelope blocks solar particles, preventing detailed study of flares and other solar phenomena.

Physicist James Van Allen (center) holds aloft the backup Explorer 1 satellite and upper stage with Jet Propulsion Laboratory director William Pickering (left) and Wernher von Braun. Image credit: NASA
Van Allen chaired the National Academy of Sciences Space Science Board Summer Study in Iowa City, Iowa, between 17 June and 10 August 1962. Iowa City is home to the University of Iowa, where Van Allen was a professor. His role as chair of the two-month study pointed up its intended significance. The Summer Study was meant to chart a course for U.S. space science and to bring together under NASA sponsorship the disparate elements of the nascent space science community. It involved more than 100 scientists from many disciplines.

Among them were Leo Steg, a General Electric scientist whose specialties were missile reentry vehicles and orbital mechanics, and Eugene Shoemaker, a U.S. Geological Survey geologist noted for his study of asteroid impacts, impact and explosion craters, and the cratered lunar surface. Their collaboration on a brief report on the uses of a libration (L) point satellite illustrates the interdisciplinary intent of the Iowa City study. It was also among the earliest proposals to treat the L points as destinations that could be explored and put to good use.

The Earth-moon system contains five L points. They are features as real as the moon and the Earth. In theory, an object parked at one of these "equilibrium" points will remain there indefinitely. In practice, the Sun's gravity perturbs objects parked at the Earth-moon L points, making station-keeping necessary. The propulsive energy (and thus propellants) needed to keep station is, however, quite modest.

Steg and Shoemaker examined the possibility of placing a satellite in orbit about the L4 or L5 point of the Earth-moon system. L4 is located 60° ahead of the moon along its orbit about the Earth; L5 is 60° behind the moon along its Earth-centered orbit.

Beyond Earth's magnetosphere and nearly always in view of the Sun, either L4 or L5 would, they wrote, "be an excellent location for a satellite whose objective is to perform solar-flare observations." Even if the magnetosphere did not interfere with its observations, a solar-observation satellite in low-Earth orbit would spend up to half its time in Earth's shadow, in the night portion of its orbit, so could not monitor the Sun continuously. The L4 or L5 satellite would be eclipsed by the Earth about as often as the moon is - that is, for a few hours each year.

Schematic illustration of Earth-moon system with libration points indicated. Image credit: NASA
In keeping with his scientific discipline, Shoemaker had a geologic interest in the Earth-moon L4 and L5 points. It stemmed from a possible breakthrough made behind the Iron Curtain 14 months before the Iowa City meeting. In March-April 1961, Polish astronomer Kazimierz Kordylewski had succeeded in photographing very faint dust clouds at the Earth-moon L4 and L5 points. He had first observed them in 1956 while peering through a telescope, but had at first been unable to capture them on film. The clouds were thought to be made up of dust knocked off the moon by large asteroid impacts and captured temporarily at the L4 and L5 points.

Had it flown, Steg and Shoemaker's L point mission would have begun with an Atlas-Agena B rocket launch (image at top of post) from Cape Canaveral on 24 October 1963. After arrival in low-Earth parking orbit, the rocket's Agena upper stage would have restarted to boost a nearly 900-pound satellite toward the Earth-moon L4 point. The satellite would travel the 246,781-mile path to L4 in about 78 hours.

Steg and Shoemaker envisioned that their satellite would include a rocket engine and propellants with a total mass of 360 pounds for course corrections, injection into an elliptical orbit around the L4 point, and station-keeping. The satellite's 70-pound science payload would include a 30-pound micrometeorite collector/analyzer for study of Kordylewski cloud dust grains, thus permitting examination of possible lunar surface material without a moon landing. The remaining 40 pounds of instrumentation would be dedicated to solar-flare observations.

Fifty pounds of radio equipment would transmit the L4 satellite's findings to Earth. Steg and Shoemaker noted that their proposed satellite's unique position might enable it to serve as a useful "communication base" for future lunar missions. It might, for example, relay radio signals between Earth and part of the Farside, the lunar hemisphere that is turned always away from the Earth.

Sources

A Review of Space Research: The Report of the Summer Study conducted under the auspices of the Space Science Board of the National Academy of Sciences at the State University of Iowa, Iowa City, Iowa, 17 June-10 August 1962, Publication 1079, National Academy of Sciences – National Research Council, Washington, DC, 1962

"Dust-Cloud Moons of the Earth," J. Wesley Simpson, Physics Today, February 1967, p. 39

More Information

Earth-Approaching Asteroids as Targets for Exploration (1978)

10 August 2015

"He Who Controls the Moon Controls the Earth" (1958)

The Farside hemisphere of the moon with Earth in the background: an image captured on 16 July 2015 by NASA's telescopic EPIC camera on the National Oceanic and Atmospheric Administration's DSCOVR spacecraft at the Sun-Earth L1 point. Image credit: NASA/NOAA 
On 28 January 1958, U.S. Air Force Brigadier General Homer A. Boushey, Deputy Director of U. S. Air Force Research and Development, spoke before the Aero Club of Washington. The weekly news magazine U.S. News & World Report took note and published excerpts from his speech.

Boushey warned the Aero Club of dire consequences should the Soviet Union seize control of the moon. He presented his speech four months after Soviet engineers had launched 83.6-kilogram Sputnik 1, the first artificial satellite, three months after they had launched the dog Laika on board 508.3-kilogram Sputnik 2, and three weeks after the failure of Vanguard TV-3, the first U.S. attempt to launch a satellite.

When Boushey is described in any detail, he is often portrayed as a strangelovian Cold Warrior. He is, however, better seen as an early U.S. rocketry and spaceflight proponent. He had enrolled in Stanford University to study engineering in 1929, but the Wall Street Crash of that year and consequent Great Depression intervened, so in 1932 he joined the U.S. Army Air Corps. During training at Randolph Field, Texas, he encountered a copy of U.S. rocketry pioneer Robert Goddard's seminal 1919 monograph A Method of Reaching Extreme Altitudes.
Pioneering U.S. rocketeer Homer A. Boushey.
Image credit: U.S. Air Force

Goddard had launched the world's first liquid-propellant rocket, named "Nell," on 16 March 1926, in Auburn, Massachusetts. The rocket flew 184 feet, or roughly half the length of a Saturn V moon rocket. He received funding support for his rocket experiments from the Smithsonian Institution, which published his monograph, and from the wealthy Guggenheim family. The latter's support enabled Goddard to move his experiments to the wide-open spaces of New Mexico in 1930.

Boushey completed his aeronautical engineering degree at Stanford in 1936, and joined the Aircraft Laboratory at Wright Field in Ohio. While there, he corresponded with and visited Goddard. The two men became fast friends; Goddard would become the godparent of one of Boushey's daughters.

In August 1941, Boushey served as the test-pilot for a series of U.S. government-funded rocket-assisted take-off experiments. These employed solid-propellant rocket motors to boost a single-seater Ercoupe airplane off a runway. Theodore Von Kármán of the Guggenheim Aeronautical Laboratory at California Institute of Technology led the rocket development effort. The plane's single propeller was removed for the final test on 23 August; Boushey then took off under rocket thrust alone, making him the first American to pilot an exclusively rocket-powered aircraft.

During the Second World War, Boushey commanded the first U.S. jet-powered fighter group. In the days after the Japanese capitulation, he flew over Hiroshima, allowing him to observe firsthand the devastation nuclear weapons could cause.

The first U.S. rocket plane: Army Air Corps pilot Homer Boushey takes to the air in one of a series of rocket-assisted take-off flight tests. Image credit: U.S. Air Force
In his January 1958 talk, Boushey acknowledged that there existed in the nascent U.S. space community "divided opinion as to whether or not a manned or unmanned moon base has any military significance." He then presented arguments in favor of a military lunar base.

The moon, he explained, is 239,000 miles away, a distance a rocket might cross in about two days. Boushey noted that the moon is a synchronous rotator, which means that it keeps the same face turned always toward Earth. Telescopes on the moon's Earth-facing Nearside could thus monitor military activities on the revolving Earth as they passed in and out of view. Boushey estimated that objects as small as 100 feet wide might be visible. Conversely, the Farside hemisphere (image at top of post) is always turned away from Earth. Boushey believed that this would make it an ideal location for the conduct of secret military operations beyond the reach of prying eyes in Russia.

Earth's moon, Boushey declared, could also provide "a retaliation base of unequaled advantage." If the U.S. gained control of the moon, then the Soviets would be unable to attack the United States without suffering "sure and massive destruction." They could either attack the U.S. first and endure a counter-strike from the moon about 48 hours later, or they could launch missiles at the moon first. The U.S. military lunar base would, of course, immediately detect the light and heat of the Soviet missiles' rocket exhaust and launch a retaliatory strike.

Boushey then spoke what are probably the most famous words in his speech: "[i]t has been said that 'he who controls the moon controls the earth.' Our planners must carefully evaluate this statement for, if true - and I, for one, think it is - then the U.S. must control the moon."

Seventy years ago: U.S. aircraft dropped nuclear weapons on the Japanese port cities of Hiroshima (left) and Nagasaki on 6 August and 9 August 1945. To date these remain the only nuclear weapons used in anger. Homer Boushey flew over the ruins of Hiroshima and saw the devastation there for himself. Image credit: Wikipedia
The excerpts from Boushey's speech in U.S. News & World Report contained no overt mention of the possibility that U.S. missiles might be launched from the moon preemptively; that is, that the U.S. moon base might be used to destroy the Soviet Union with little risk of retaliation. Boushey did, however, describe attributes of the moon that would make a preemptive attack feasible.

The moon's weak gravitational pull, coupled with its lack of an atmosphere, would permit missiles to be "catapulted" from their siloes, thereby avoiding use of easily detected rocket motors. Hiding the siloes on the Farside would further increase the odds that a U.S. attack would go unnoticed until warheads entered Earth's atmosphere over Soviet territory.

Building and maintaining the U.S. military lunar base would not, Boushey maintained, have to break the bank. He assumed that the moon would be found to be made of the same elements as the Earth, so that the "possibilities of construction and creation of an artificial environment [would be] virtually unlimited." Electricity from solar panels made on the moon could be stored using massive lunar-made flywheels which, once spun up by lunar-made electric motors, could spin for weeks in the absence of atmospheric friction. By using the flywheels to turn the electric motors, the latter could become generators for supplying the base with electricity during the two-week lunar night.

Boushey ended his speech by offering an alternative to lunar militarization. He pointed out that on "January 16 [1958] Secretary [of State John Foster] Dulles proposed the formation of an international commission to insure [sic] the use of outer space exclusively for peaceful purposes, and if the Soviet premier is sincere in decrying the production of ever-more-powerful weapons he will jump at the chance. In 10 years," he added, "the opportunity of jointly imposing control may have been lost."

U.S. Secretary of State Dean Rusk signs The Outer Space Treaty at the White House as President Lyndon Baines Johnson (right), British Ambassador to the United States Sir Patrick Dean (center), and Soviet Ambassador to the United States Anatoly Dobrynin (left) look on. Image Credit: United Nations
Almost exactly nine years after Boushey delivered his speech, on 27 January 1967, the U.S., the Soviet Union, and the United Kingdom signed the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies. The following October, they called upon other nations of the world to sign and ratify what had by then become known as The Outer Space Treaty. Among other far-reaching provisions, it required that the moon not be put to any military purpose. The Outer Space Treaty, which took effect on 10 October 1967, became the rock upon which the body of international space law is built.

By the time The Outer Space Treaty took effect, Boushey had been retired from the Air Force for a little more than six years. He ended his career at age 52 in July 1961 as Commander of the Air Force Arnold Engineering Development Center in Tennessee. By that time, President Dwight Eisenhower had passed over the military in favor of civilian U.S. space exploration under the aegis of NASA. Despite military support for NASA programs and some brave starts, such as the Dyna-Soar spaceplane and the Manned Orbiting Laboratory, U.S. military spaceflight would be limited mainly to unmanned surveillance satellites until the Space Shuttle era.

Soon after his retirement, Boushey became an outspoken critic of the escalating war in Indochina. Despite this, President Richard Nixon recognized his key role in U.S. astronautics by inviting him to the 13 August 1969 "Astronauts' Dinner" held in Los Angeles to celebrate the July 1969 triumph of Apollo 11, the first manned moon landing.

In 1982, while the Administration of President Ronald Reagan called for expansion and modernization of the U.S. nuclear arsenal, Boushey co-sponsored California's Nuclear Freeze ballot initiative, which passed overwhelmingly. In 1985, he joined other retired U.S. military officers in Moscow to draft an agenda for nuclear arms control. He cited his 1945 flight over Hiroshima when he declared that political leaders did not adequately grasp the destructive power of nuclear weapons. The man who had spoken out for a U.S. military moon base in 1958 spoke out against nuclear weapons to the end of his days. Boushey died in 2000 on Christmas Day at the age of 91.

Sources

"Who Controls the Moon Controls the Earth," Homer A. Boushey, U.S. News & World Report, 7 February 1958, p. 54

"Gen. Homer Boushey dies; he was a pioneer in rocket-powered aircraft," The Almanac, 3 January 2000 http://www.almanacnews.com/morgue/2001/2001_01_03.boushey.html (accessed 8/10/15)

"Homer A. Boushey," Keay Davidson, SFGate.com, 6 January 2000 http://articles.sfgate.com/2001-01-06/news/17580737_1_air-force-lunar-base-rocket (accessed 8/10/15)

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