Mars When? A View from 1966

Image: DSFPortree/NASA

In March 1966, at the height of 1960s optimism about America’s future in space, Robert Riedesel and John Wall, respectively Project Manager and Chief Engineer of the Future Systems Department at Douglas Aircraft Company, presented a paper in which they discussed the many constraints which they believed made a piloted Mars mission unlikely before 1981. Though the specifics have changed, the general constraints on mission planning they listed nearly half a century ago are the same ones planners of costly piloted space missions face today.

Their first group of constraints, those deriving from the natural phenomena in the Solar System, included the cycle of minimum-energy Mars launch opportunities and the 11-year solar activity cycle. Minimum-energy Mars launch opportunities occur about every 26 months, the Douglas engineers noted. The less energy needed to reach Mars, the fewer propellants would be required. The fewer propellants required, the fewer costly heavy-lift rockets would be needed to launch Mars spacecraft propellants and tanks into Earth orbit.

Riedesel and Wall noted that not all minimum-energy opportunities are created equal; the amount of energy required to reach Mars follows a roughly 15-year cycle because the planet has a relatively elliptical orbit about the Sun. The year 1971 would present the most favorable minimum-energy opportunity since 1956. Unfavorable opportunities would occur in 1977 and 1979, they wrote, then opportunities would improve in 1981, 1984, and 1986. The year 1988 would see the most favorable Mars launch opportunity since 1971.

The 11-year solar cycle would reach maximum intensity in 1981, then would decline to a minimum in 1986-1987. The potential for “giant” solar flares during solar maximum meant that astronauts traveling to Mars in 1981 would need a massive radiation shelter. Riedesel and Wall recommended that NASA launch its first Mars expedition in 1986, when the solar minimum and a highly favorable Earth-Mars transfer opportunity would coincide.

Some of Wall and Riedesel’s schedule constraints were based on the accumulation of spaceflight experience that they believed would be necessary before humans could make the grand leap to Mars. Before engineers could develop a piloted Mars spacecraft, they would, to cite two examples, need more data on the martian surface environment and the effects on humans of long exposure to space conditions (for example, weightlessness). Riedesel and Wall expected that planned Voyager automated Mars explorers and astronaut stays on board an Earth-orbiting space station would provide the necessary data as early as 1973. They cited Apollo spacecraft development experience when they estimated that Mars spacecraft development would require at least seven years after the needed data became available. This would mean that the first Mars expedition could set out no earlier than the 1981 launch opportunity.

Economics would also shape the piloted Mars mission schedule. Riedesel and Wall cited published Mars program cost estimates ranging from $40 billion to $100 billion. Their own estimate – $62 billion, or about 2.5 times the cost of Apollo – included the cost of automated precursor probes, an Earth-orbiting space station, a heavy-lift rocket more powerful than the Saturn V, and eight piloted test missions leading to one piloted Mars landing.

The Douglas engineers assumed that NASA’s budget would remain at its Apollo peak value of about $5 billion per year, with $3 billion of that going toward piloted spaceflight. This meant that, in the 15-year period between 1966 and their earliest piloted Mars mission opportunity in 1981, the sum available for a piloted Mars mission would total only $45 billion. It would total $60 billion if the expedition departed in 1986. They concluded that, if astronauts were to set foot on Mars in the 1980s, then either a “major increase” in the space agency’s budget or “a less expensive approach to interplanetary exploration” would be necessary.

Finally, they looked at the political issues in which any piloted Mars program would necessarily become embroiled. Although the names have changed, the politics of the Presidential election cycle vis-a-vis spaceflight have altered little since 1966. Riedesel and Wall predicted that, if President Lyndon B. Johnson won reelection in 1968, then he would have little incentive to commit funds and political capital to a piloted Mars program that would not succeed until long after he left office. The Mars program might start when Johnson’s successor took office in January 1973. The new president would, however, find no personal political benefit in championing a Mars expedition, even if he initiated it immediately after he took office. This was because it would leave Earth no earlier than the 1981 launch opportunity, which would commence 10 months after his second term ended in January 1981.

If, on the other hand, President Johnson were not reelected in 1968, then his successor could initiate the automated Mars probe and space station programs in 1969 with a good chance of seeing them succeed before his second term ended. Commitment to a piloted Mars expedition would probably have to wait until another president took office in January 1977, however. Given the time required for hardware development, this would, Riedesel and Wall estimated, postpone launch of the first U.S. piloted Mars expedition until at least 1984.

Reference:

“Scheduling Constraints on Manned Exploration of Mars,” Robert Riedesel and John Wall, A Volume of Technical Papers Presented at the AIAA/AAS Stepping Stones to Mars Meeting, pp. 99-106; paper presented in Baltimore, Maryland, March 28-30, 1966.

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