Shuttle-Era Manned Mars Flyby (1985)
By David S. F. PortreeEmail Author June 17, 2012 | 2:48 am | Categories: Beyond Apollo, Science Blogs
In the 1960s, NASA expended nearly as much study money and effort on manned Mars and Venus flyby mission planning as it did on its more widely known plans for manned Mars landings. Italian aviation and rocketry pioneer Gaetano Crocco had first described a free-return manned Mars/Venus flyby mission in 1956. Manned flyby studies within NASA began with the EMPIRE study the Marshall Space Flight Center (MSFC) Future Projects Office initiated in 1962 and culminated in the NASA-wide Planetary Joint Action Group (JAG) study of 1966-1967.
The Planetary JAG, led by the NASA Headquarters Office of Manned Space Flight, brought together engineers from MSFC, Kennedy Space Center, the Manned Spacecraft Center (MSC), and Washington, DC-based planning contractor Bellcomm. It issued a Phase I report in Oct. 1966 and continued Phase II study work in Fiscal Year (FY) 1967. The Phase I report emphasized a manned Mars flyby mission in 1975, but included Mars and Venus flyby opportunities through 1980. All would be based on hardware developed for the Apollo Program and for its planned successor, the Apollo Applications Program (AAP). The piloted flyby spacecraft would carry automated probes, including one type that would land on Mars, collect a sample of surface material (containing, it was hoped, evidence of life), and launch it back to the flyby spacecraft for immediate analysis.
According to Edward Clinton Ezell and Linda Neuman Ezell, writing in their 1984 history On Mars, MSC was largely responsible for the demise of 1960s manned flyby mission planning. On Aug. 3, 1967, the Houston-based center, home of the astronaut corps and Mission Control, distributed to 28 aerospace companies a Request for Proposal (RFP) for a manned Mars flyby spacecraft sample-returner design study. By doing this, MSC appeared to disregard warnings from Congress that no new NASA programs would be tolerated.
In the summer of 1967, NASA was preoccupied with recovery from the Jan. 27, 1967 Apollo 1 fire, which had killed astronauts Virgil Grissom, Roger Chaffee, and Ed White. Many in Congress felt that NASA had been lax in maintaining quality and safety standards, so deserved to be punished for the accident. They did not, however, wish to cut Apollo funding and endanger accomplishment of Apollo’s very public goal of a man on the moon by 1970. In addition, by Aug.1967, the Federal budget deficit for FY 1967 had reached $30 billion. Though negligible by modern standards, this was a shocking sum in 1967. The deficit was driven in large part by the cost of fighting in Indochina, which had reached more than $2 billion a month, or the entire Apollo Program budget of $25 billion every 10 months.
After learning of MSC’s RFP, long-time House Space Committee Chair and NASA supporter Joseph Karth declared angrily that “a manned mission to Mars or Venus by 1975 or 1977 is now and always has been out of the question – and anyone who persists in this kind of misallocation of resources. . .is going to be stopped.” On Aug. 16, the House cut all funding for advanced planning from NASA’s FY 1968 budget bill and slashed the budget for AAP from $455 million to $122 million. Total cuts to President Lyndon Johnson’s Jan. 1967 NASA budget request amounted to more than $500 million, or about 10% of NASA’s FY 1967 budget total.
Though he opposed the cuts, President Johnson bowed to the inevitable and signed the budget into law. The Planetary JAG and Bellcomm tied up loose ends of the manned flyby study during FY 1968, but most work on the concept ended little more than a month after the Houston center issued its ill-timed RFP.
It is ironic, then, that NASA’s next piloted Mars flyby study took place in Houston, at Johnson Space Center (JSC), as MSC had been rechristened following President Johnson’s death in Jan. 1973. Barney Roberts, of JSC’s Engineering Directorate, reported on the study to the joint NASA-Los Alamos National Laboratory (LANL) Manned Mars Missions workshop in June 1985.
Roberts explained that the NASA flyby plan aimed to counter a possible Soviet manned Mars flyby. He cited a 1984 CIA memorandum which suggested (without citing much in the way of proof) that the Soviet Union might attempt such a mission in the late 1990s to garner international prestige.
Going for a ride: piloted Mars flyby spacecraft prepares for launch from Earth orbit in the late 1990s. A = twin Orbital Transfer Vehicles (OTVs); B = twin strap-on propellant tanks; C = Command Module; D = Mission Module. Image: NASA/David S. F. Portree.
NASA’s manned Mars flyby would be based on Space Shuttle, Space Station, and Lunar Base hardware expected to be operational in the late 1990s. Space Shuttle Orbiters would deliver to NASA’s low-Earth orbit (LEO) Space Station an 18-ton Mission Module (MM) and a pair of empty expendable propellant tanks with a mass of 11.6 tons each. The MM, derived from a Space Station module, would include a 3000-pound radiation shelter, 7000 pounds of science equipment, and 2300 pounds of food and water.
The MM would be docked to a six-ton Command Module (CM) and two 5.75-ton Orbital Transfer Vehicles (OTVs). The OTVs would each include an aerobrake heat shield and two Shuttle-derived rocket engines. Roberts assumed that the CM and OTVs would be in space already as part of NASA’s Lunar Base Program. The strap-on tanks would be joined to the MM/CM stack by trunion pins similar to those used to anchor payloads in the Shuttle Orbiter payload bay, then Station astronauts would perform spacewalks to link propellant pipes and electricity and control cables.
Shuttle-derived heavy-lift rockets would then deliver a total of 221 tons of liquid hydrogen and liquid oxygen propellants to the Space Station for loading into the flyby spacecraft’s twin tanks. The propellants would be pumped aboard just prior to departure for Mars to prevent liquid hydrogen loss through boil off. The flyby spacecraft’s mass at the start of its Earth-departure maneuver would total 358 tons.
As the launch window for the Mars flyby opportunity opened, the flyby spacecraft would move away from the LEO Space Station, then the four OTV engines would ignite and burn for about one hour to put the it on course for Mars. The only propulsive maneuver of the baseline mission, it would empty the OTV and strap-on propellant tanks. Roberts advised retaining the empty tanks to help to shield the MM and CM against meteoroids and radiation.
Roberts told the workshop that the flyby spacecraft would spend two-and-a-half hours within about 20,000 miles of Mars. Closest approach would bring it to within 160 miles of Mars’s surface. At closest approach, the spacecraft would be moving at about five miles per second.
The spacecraft would then begin its long return to Earth. Roberts provided few details of the interplanetary phases of the manned flyby mission.
As Earth grew from a bright star to a distant disk, the Mars flyby astronauts would discard the twin strap-on tanks. They would then undock one OTV by remote control and re-dock it to the front of the CM. After entering the CM and sealing the hatch leading to the MM, they would discard the MM and second OTV, then would then strap into their couches to prepare for aerobraking in Earth’s upper atmosphere and capture into Earth orbit. After the OTV/CM combination completed the aerobraking maneuver, the crew would pilot it to a docking with the Space Station.
Almost home: Piloted Mars flyby spacecraft prepares for aerobraking maneuver in Earth's atmosphere. A = OTVs; C = Command Module bearing crew; D = discarded Mission Module (attached to discarded OTV). Image: NASA/David S. F. Portree.
Roberts told the NASA/LANL workshop that Earth return would be the most problematic phase of the piloted Mars flyby mission. This was because the OTV/CM combination would encounter Earth’s upper atmosphere at a speed of 55,000 feet (10.4 miles) per second, producing reentry heating well beyond the planned capacity of the OTV’s heat shield. In addition, the crew would suffer “exorbitant” deceleration after living for a year in weightlessness.
OTV with Command Module aerobrakes in Earth's upper atmosphere. Image: NASA.
Roberts proposed a “brute-force” solution: use the OTV’s rocket motors to slow the OTV/CM to lunar-return speed of 35,000 feet (6.6 miles) per second. The braking burn would, however, increase the Mars flyby spacecraft’s total required propellant load to nearly 500 tons. He calculated that, assuming that a Shuttle-derived heavy-lift rocket could be designed to deliver cargo to LEO at a cost of $500 per pound (an optimistic assumption, as it would turn out), then Earth-braking propellant would add $250 million to his mission’s cost.
Roberts briefly considered reducing the Mars flyby spacecraft’s mass by substituting an MM derived from a five-ton Space Station logistics module for the 18-ton MM. This would mean, however, that the crew would have to spend a year in cramped quarters with no exercise or science equipment.
Planners in the 1960s had wrestled with and prevailed over the same problems of propellant mass and Earth-return speed that JSC faced in its 1985 study. Bellcomm, for example, had proposed in June 1967 that the Planetary JAG’s manned Mars flyby save propellants by assembling the flyby spacecraft in an elliptical orbit, not a circular Space Station orbit. The elliptical orbit would mean that, in effect, the flyby spacecraft would begin Earth-orbit departure even before it was assembled. In addition, returning the crew directly to Earth’s surface in a small Apollo-type capsule with a beefed-up heat shield would greatly reduce or eliminate required braking propellants and enable an aerodynamic “skip” maneuver that would reduce deceleration stress on the astronauts.
Neither of these solutions was applicable to JSC’s 1985 plan, however, because the spacecraft and modules proposed for NASA’s 1990s Shuttle/Station/Lunar Base infrastructure would not permit them. Not all of the techniques developed in the 1960s for reducing propellant requirements and Earth-return speed were hardware-dependent, however.
For example, TRW’s Space Technology Laboratory proposed as early as 1964, during EMPIRE follow-on studies, that NASA use a Venus flyby to slow spacecraft returning from Mars. This would limit Earth-Mars free-return opportunities to those that would intersect Venus on the return leg, but would also eliminate the costly end-of-mission braking burn and enable Venus exploration as a bonus. The Planetary JAG’s Oct. 1966 report described Mars-Venus and Venus-Mars-Venus flyby missions. Bellcomm confirmed in late 1966 and 1967 that opportunities for such multi-planet flybys are not rare.
Reference:
“Concept for a Manned Mars Flyby,” Barney B. Roberts; Manned Mars Missions: Working Group Papers, NASA M002, Vol. 1, NASA/LANL, June 1986, pp. 203-218; proceedings of a workshop at NASA Marshall Space Flight Center, Huntsville, Alabama, June 10-14, 1985.
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