Mars in Texas
NASA's Manned Spacecraft Center (MSC) (renamed the Johnson Space Center in 1973) began as the Space Task Group (STG) at NASA Langley Research Center in Hampton, Virginia, where it was formed in late 1958 to develop and manage Project Mercury. Following Kennedy's May 1961 Moon speech, the STG's responsibilities expanded, so it needed a new home. The STG became the MSC and moved to Houston, Texas.
Maxime Faget became MSC's Assistant Director for Research and Development. He launched the first MSC piloted Mars mission study in mid-1961, but it remained in-house and at a minimal level of effort until late 1962, after Marshall kicked off EMPIRE. MSC's study was supervised by David Hammock, Chief of MSC's Spacecraft Technology Division, and Bruce Jackson, one of his branch chiefs. Chief products of MSC's study were a Mars mission profile unlike any proposed up to that time and the first detailed Mars Excursion Module (MEM) piloted Mars lander design.
Jackson and Hammock presented MSC's Mars plan at the first NASA intercenter meeting focused on interplanetary travel, the Manned Planetary Mission Technology Conference held at Lewis from 21 to 23 May 1963. The NASA Headquarters Office of Applied Research and Technology organized the meeting, which focused mainly on specific technologies, many with applications to missions other than Mars. The "Mission Examples" session, chaired by Harry Ruppe, was relegated to the afternoon session on the last day of the meeting.
Hammock and Jackson presented MSC's mission design publicly for the first time at the American Astronautical Society (AAS) Symposium on the Manned Exploration of Mars in Denver, Colorado, the first non-NASA conference devoted to piloted Mars travel. 15 George Morgenthaler of Martin Marietta Corporation in Denver organized the symposium. As many as 800 engineers and scientists heard 26 papers and a banquet address by Secretary of the Air Force Eugene Zuckert. It was the first time so many individuals from Mars-related disciplines came together in one place, and the last Mars conference as large until the 1980s. Sky & Telescope magazine reported that the "Denver symposium . . . helped narrow the gaps between engineer, biologist, and astronomer." 16
Hammock and Jackson called Mars "perhaps the most exciting target for space exploration following Apollo . . . because of the possibility of life on its surface and the ease with which men might be supported there." 17 Two of their plans used variations on the MOR mode, but the third, dubbed the Flyby-Rendezvous mode, was novel—it would accomplish a piloted Mars landing while still accruing the weight-minimization benefits of a Crocco-type flyby.
The Flyby-Rendezvous mode would use two separate spacecraft, designated Direct and Flyby. They would reach Earth orbit atop Saturn V rockets. The unpiloted Flyby craft would depart Earth orbit 50 to 100 days ahead of the piloted Direct craft on a 200-day trip to Mars. The Direct craft, which would include the MEM lander, would reach Mars ahead of the Flyby craft after a 120-day flight. The astronauts would then board the MEM and abandon the Direct craft. The MEM would land while the Direct craft flew past Mars into solar orbit. Forty days later the Flyby craft would pass Mars and begin the voyage back to Earth. The crew would lift off in the MEM ascent vehicle and set out in pursuit, boarding the Flyby craft about two days after leaving Mars. Near Earth the astronauts would separate from the Flyby spacecraft in an Earth-return capsule, enter Earth's atmosphere, and land.
One of MSC's MOR plans used aerobraking, while the other relied on propulsive braking. In aerobraking, the lifting-body-shaped Mars spacecraft would skim through Mars' upper atmosphere to use drag to slow down and enter orbit. The Mars surface explorers would separate from the orbiting ship in the MEM and land for a surface stay of 10 to 40 days. They would then lift off in the MEM ascent stage, dock with the orbiting ship, and leave Mars orbit. Earth atmosphere reentry would occur as in the Flyby-Rendezvous mode. Hammock and Jackson's propulsive-braking MOR mission resembled the aerodynamic-braking mode design, except that a chemical or nuclear propulsion stage would place the ship in Mars orbit.
Hammock and Jackson found that the chemical all-propulsive spacecraft design would weigh the most at Earth-orbit departure (1,250 tons), while the nuclear aerobraking design would weigh the least (300 tons). The Flyby-Rendezvous chemical and aerobraking chemical designs would weigh about the same (1,000 tons).
The MEM design for the Houston Center's MOR plans—the first detailed design for a piloted Mars lander—was presented in June 1964 at the next major meeting devoted to Mars exploration, the Symposium on Manned Planetary Missions at Marshall. 18 Philco (formerly Ford) Aeronutronic performed the study between May and December 1963. Franklin Dixon, the presenter, was Aeronutronic's manager for Advanced Space Systems. The design, which the company believed could land on Mars in 1975, was first described publicly in Houston in November 1964 at the American Institute of Astronautics and Aeronautics (AIAA) 3rd Manned Space Flight Conference.
Figure 1—Landing on Mars. Aeronutronic's Mars lander, a lifting body glider, relied on aerodynamic lift to minimize required propellant. The design was based on optimistic estimates of Martian atmospheric density. ("Summary Presentation: Study of a Manned Mars Excursion Module," Franklin Dixon, Proceeding of the Symposium on Manned Planetary Missions: 1963/1964 Status, NASA TM X-53049, Future Projects Office, NASA George C. Marshall Spaceflight Center, Huntsville, Alabama, June 12, 1964, p. 467.)
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Dixon pointed out that the chief problem facing Mars lander designers was the lack of reliable Mars atmosphere data, noting that "two orders of magnitude variations in density at a given altitude were possible when comparing Mars atmosphere models of responsible investigators." Aeronutronic settled on a Martian atmosphere comprising 94 percent nitrogen, 2 percent carbon dioxide, 4 percent argon, and traces of oxygen and water vapor, with a surface pressure of 85 millibars (about 10 percent of Earth sea-level pressure). For operation in this atmosphere, Aeronutronic proposed a "modified half-cone" lifting body with two stubby winglets.
The Aeronutronic MEM would measure about 30 feet long and 33 feet wide across its tail. The 30-ton MEM would ride to Mars on its mothership's back under a thermal/meteoroid shield which the crew would eject two hours before the Mars landing. The three-person landing party, which would consist of the captain/scientific aide, first officer/geologist, and second officer/biologist, would don space suits and enter the small flight cabin in the MEM's nose. Five minutes before planned deorbit, the MEM would separate from its mothership and retreat to a distance of 1,000 feet. There it would point its tail forward and fire its single descent engine to begin the fall toward Mars' surface.
The MEM's heat-resistant hull would be made largely from columbium, with nickel-alloy aft surfaces. Aeronutronic calculated that friction heating would drive nose temperature to 3,050 degrees Fahrenheit. At Mach 1.5, between 75,000 and 100,000 feet above Mars, a single parachute would be deployed and the MEM would assume a tail-down attitude. The engine would then ignite a second time and the parachute would separate. Aeronutronic's design included enough propellant for an estimated 60 seconds of hover before touchdown on four landing legs with crushable pads.
Aeronutronic attempted to select a MEM landing site using photographs taken by Earth-based telescopes. Theorizing that living things might follow the retreating edge of the melting polar cap in springtime, they suggested that NASA target the MEM to Cecropia at 65 degrees north latitude (this corresponds to Vastitas Borealis north of Antoniadi crater on modern Mars maps). 19 Upon landing, the astronauts would eject shields covering the MEM windows and look out over their landing site to evaluate "local hazards," including any "unfriendly life forms." 20 Mars surface access would be through a cylindrical airlock that lowered like an elevator from the MEM's tail.
Figure 2—Astronauts exploring Mars near Aeronutronic's lander would take pains to collect biological specimens before terrestrial contamination made study impossible. A large dish antenna (left) would let them share their discoveries with Earth. ("Summary Presentation: Study of a Manned Mars Excursion Module," Franklin Dixon, Proceeding of the Symposium on Manned Planetary Missions: 1963/1964 Status, NASA TM X-53049, Future Projects Office, NASA George C. Marshall Spaceflight Center, Huntsville, Alabama, June 12, 1964, p. 470.)
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Dixon stated that "biological evaluation of life forms is essential for the first purely scientific effort to allow pre-contamination studies before man alters the Mars environment," 21 implying that little effort would be made to prevent the astronauts from introducing terrestrial microorganisms. Aeronutronic listed "investigate life forms for possible nutritional value" 22 among the tasks of the Mars biology study program. The crew would explore Mars for between 10 and 40 days, spending about 16 man-hours outside the MEM each day.
Aeronutronic's MEM was envisioned as a two-stage vehicle. For return to Mars orbit, the ascent motor would fire, blasting the flight cabin free of the descent stage. Two propellant tanks would be cast off during ascent. After docking with the orbiting mothership, the MEM flight cabin would be discarded.
Figure 3—Returning to Mars orbit: Like the Apollo Lunar Module, Aeronutronic's lander design used its descent stage as a launch pad for its ascent stage. Unlike the Lunar Module, it cast off spent propellant tanks as it climbed to orbit. ("Summary Presentation: Study of a Manned Mars Excursion Module," Franklin Dixon, Proceeding of the Symposium on Manned Planetary Missions: 1963/1964 Status, NASA TM X-53049, Future Projects Office, NASA George C. Marshall Spaceflight Center, Huntsville, Alabama, June 12, 1964, p. 468.)
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UMPIRE
Every 26 months, an opportunity occurs for a short (six-month) minimum-energy transfer from Earth to Mars. In some opportunities the planet is farther from Earth than in others. This means that in some opportunities the minimum energy necessary to reach Mars is greater than in others. The most difficult Mars opportunities require about 60 percent more energy than the best opportunities. The more energy required to reach Mars, the more propellant a spacecraft must expend. Because of this, a spacecraft launched in a poor Mars opportunity will weigh more than twice as much as one launched in a good Mars opportunity.
The quality of Mars launch opportunities runs through a continuous cycle lasting about 15 years. Not surprisingly, this corresponds to the cycle of astronomically favorable oppositions described in Chapter 1. The EMPIRE studies showed that the best Mars opportunities since 1956 would occur in 1969 and 1971, just as the Apollo lunar goal was reached. Opportunities would become steadily worse after that, hitting a peak in 1975 and 1977, then would gradually improve. The next set of favorable oppositions would occur in 1984, 1986, and 1988.
The Marshall Future Projects Office contracted with General Dynamics/Fort Worth and Douglas Aircraft Company in June 1963 to "survey all the attractive mission profiles for manned Mars missions during the 1975-1985 time period, and to select the mission profiles of primary interest." The study, nicknamed "UMPIRE" ("U" stood for "unfavorable"), was summed up in a Future Projects Office internal report in September 1964. 23
General Dynamics and Douglas worked independently, but each found that the "best method of alleviating the cyclic variation of weight required in Earth orbit is to plan long (900-1100 days) missions." 24 The companies advised that "serious consideration . . . be given to the concept of the first manned landing on Mars being a long term base" rather than a short visit. 25 That is, the two companies recommended making the first Mars expedition conjunction class, not opposition class.