The Case for Mars (10 page)

It is doubtful that any kind of program could have survived that price tag. Given its long timelines and limited set of advertised accomplishments on the road to colonizing space, which did little to arouse the enthusiasm of the space-interested public, the 90-Day Report proposal certainly could not. Unless that $450 billion number could be radically reduced, the SEI was as good as dead, a fact made clear in the ensuing months and years as Congress proceeded to zero out every SEI appropriation bill that crossed its desks.

In fact, however, there was no real inner logic underlying the 90-Day Report, nor any truly new thoughts. Rather, it was a rehash of fixed ideas that hearkened back to the forty-year-old “Die Marsprojekt,” an outline of human missions to Mars that German rocket designer Wernher von Braun and his collaborators had first worked out in the late 1940s, and then updated technically to provide the basis for NASA’s failed proposal for a humans-to-Mars Apollo follow-on program in 1969. For von Braun and his collaborators, a manned interplanetary mission was part and parcel of a hardware fabricator’s wildest dreams: the huge interplanetary spaceship (or better yet, fleets of huge interplanetary spaceships) assembled and launched from Earth-orbiting space stations. What actually occurred on the surface of Mars became an event of secondary interest. Around this fixed idea—giant space stations assembling gigantic spaceships—the unwieldy 90-Day Report team had proceeded to cast as crucial technologies every existing, planned, or wished-for NASA technology development program. In order to include everybody in the game, they designed the most complex mission architecture they possibly could—exactly the opposite of the correct way to do engineering.

DEFINING A COHERENT SPACE EXPLORATION INITIATIVE

By the end of 1989, it was thus clear to many that the mission architecture described in the 90-Day Report was incoherent. In an effort to develop a systematic critique, I produced the following memo, which I subsequently used as the introduction to each of a large series of papers about the Mars Direct plan (see, for example, reference 6). What I had to say then summarizes much of the logic that led to the development of Mars Direct, and I reproduce it here in full, with some bracketed material added for clarity:

The need currently exists for a coherent architecture for the Space Exploration Initiative (SEI). By a coherent architecture what is meant is a clear and intelligent set of objectives and a simple, robust, and cost-effective plan for accomplishing them. The objectives chosen should offer the maximum payoff, and their accomplishment should enhance our ability to achieve still more ambitious objectives in the future. The plan, in order to be simple, robust, and low cost, should not make inter-dependent missions (i.e. Lunar, Mars, and Earth orbital) that have no real need to be dependent on each other. The plan should, however, employ technology that is versatile enough to play a useful role across a wide range of objectives, so as to reduce costs through commonality of hardware. Finally, and most importantly, technologies must be chosen that maximize the effectiveness of the mission at the planetary destination. It is not enough to go to Mars; it is necessary to be able to do something useful when you get there. Zero capability missions have no value.

While the above principles may appear to be common sense, they were violated in every particular by many recent SEI studies [i.e. the 90-Day Report] and as a result, a picture has been presented of SEI that is so costly and unattractive that congressional funding of the program is very much in doubt. Such architectures have driven costs through the roof by employing totally different launch vehicles for the Moon and Mars; totally different space transfer vehicles and propulsion technologies for the Moon and Mars; totally different excursion vehicles for the Moon and Mars; a completely artificial dependence of the Mars missions on the Lunar missions; and a requirement to base the Lunar missions on a massive orbital assembly, refueling, and refitting infrastructure at Space Station Freedom. Furthermore, both the Lunar and Mars missions studied have been close to zero capability, with no serious attempt made to provide surface mobility, and with Mars explorers
spending less than 5 percent of the total Earth-Mars round trip mission transit time on the surface of the Red Planet.

Meeting the demands of coherence drives the design of the SEI architecture in certain very definite directions. To wit:

1. Simplicity and Robustness require that the Lunar and Mars missions not depend upon any LEO [low-Earth-orbit] infrastructure. In addition to being tremendously costly to develop, build, and maintain, such infrastructure is intrinsically unreliable and difficult to repair, and its use adds risk to all planetary missions based on it due to the difficulty in verifying quality control of any space-based construction. The demand for the elimination of LEO infrastructure argues in favor of using both advanced propulsion and/or indigenous propellants, both of which can contribute to reducing mission mass to the point where no on-orbit assembly is required.

2. Low Cost requires that the same launch vehicles, space transfer vehicles and propulsion technology, and to the extent possible, excursion vehicles be used for both the Moon and Mars, as well as other destinations. Low cost also demands the elimination of LEO infrastructure, as the potential cost savings made possible by re-use of space transfer vehicles at such infrastructure are insufficient to balance the cost of the infrastructure. This can be seen by noting that the cost of such infrastructure is currently estimated to be about three orders of magnitude larger than the value of the vehicle hardware elements (engines, avionics) that it would be able to save with each space-based refit. Thus, about a thousand refitted missions would be required before such a facility broke even—a somewhat distant prospect. Low cost also demands that the most cost-effective trajectories be taken at all times (i.e. conjunction class [low energy, long surface stay] trajectories for Mars), and that an initial group of opposition class [high energy, short surface stay] Mars missions using completely different hardware from the main sequence of conjunction class missions not be undertaken.

3. High Effectiveness requires that the astronauts be endowed with three essential elements once they reach their destination. These three essentials are:

a. Time

b. Mobility

c. Power

Time is obviously required if the astronauts are t
o do any useful exploration, construction, or resource utilization experimentation on the surface of the destination planet. This clearly means that opposition class Mars missions (which involve 1.5 year flight times and 20-day surface stays) are out of the question. It also means that architectures involving Lunar or Mars orbital rendezvous (LOR, MOR) are very undesirable, for the simple reason that if the surface stay time is long, so is the orbit time. The LOR or MOR architectures are therefore left in a predicament of whether to leave someone in the mothership during the extended surface stay, exposed to cosmic rays and the rigors of zero-gravity conditions and accomplishing nothing; or leave the mothership unmanned for an extended period and have the returning crew trust to fate that it will be shipshape when they return. If it isn’t, their predicament may be hopeless. The alternative to LOR and MOR architectures are those that employ direct return to Earth from the planet’s surface. This is possible to do on a Lunar mission with all terrestrial-produced propellants, however the mission capability is greatly enhanced if Lunar produced LOX [liquid oxygen] can be used for the return. Direct return from the surface of Mars absolutely demands that indigenous propellants be used.

Mobility is absolutely required if any useful exploratory work is to be accomplished on a body the size of Mars or even the Moon. Mobility is also needed to transport natural resources from distant locations to the base where they can be processed, and is also required to enable crews to visit distant assets, such as optical and radiotelescopic arrays on the Moon. The key to mobility on both the Moon and Mars is the generation of indigenous propellants for use in both high powered ground rovers and rocket propelled flight vehicles. On the Moon the resource of choice is Lunar LOX, which can be burnt with terrestrial fuels such as hydrogen or methane. On Mars, chemical fuel and oxidizer combinations such as methane/oxygen or carbon monoxide/oxygen can be produced for both surface and flight vehicles, and, in addition, rocket thrust for flight propulsion can also be produced by using raw carbon dioxide propellant heated in a nuclear thermal rocket engine.

Power can be generated in the large amounts required for indigenous propellant production on both the Moon and Mars only by using nuclear reactors. Once indigenous propellants have been produced, they form a very convenient mechanism for storing the nuclear energy, thus providing explorers with mobile power, for example by runnin
g a 100 kWe generator off the internal combustion engine on a ground rover. The presence of a power rich environment, both at the base and at remote sites, is essential to allow the astronauts to pursue a wide variety of scientific and resource utilization activities.

We thus see that the requirements for Simplicity, Robustness, Low Cost, and High Effectiveness drive SEI toward an architecture utilizing direct launch to the Moon or Mars with a common launch and space transfer system, and direct return to Earth from the planet’s surface utilizing indigenous propellants, which are also used to provide surface mobility and mobile power.
⁶

This was the thinking process that led to the development of a radically new type of Mars mission architecture that came to be known as “Mars Direct.”

THE BIRTH OF MARS DIRECT

By January 1990, it was clear that the 90-Day Report was going down in flames. A retreat meeting of selected Martin Marietta management was called at the Broadmoor Hotel in Colorado Springs to discuss what to do about the situation. Because we were known within the company as the Mars “idea people,” Dr. Ben Clark, a lower level Martin manager who had been one of the four principal investigators on the 1976
Viking
mission (he had designed the X-ray florescence experiment), and I, only a senior engineer, were invited. We were by far the lowest ranking people there.

Ben and I hit the assembled executives with the idea that Martin ought to assemble a small select team and develop our own “blue sky” approach to Mars—one free from all of NASA’s current prejudices. It would be hard enough to develop a sound, cost-effective, near-term approach to a human Mars mission without having a bunch of marketeers come in and tell us that we should design the mission this wayor that so as to please some manager or group at NASA Johnson or Marshall Space Centers; our team would have to be independent of such influences. After all, it was precisely such an effort to please everyone that had allowed the 90-Day Report to get out of control.

This was a very radical proposal. The standing wisd
om among the managerial class in the aerospace industry holds that you should always play back to “the customer” (NASA or the Air Force) what they want to hear, which is to say a reiteration of their own party line. That’s clearly the easiest way to make a sale. We were proposing the opposite approach: come up with some good ideas and then tell the customer what they need to hear, whether they like it or not.

While not the most senior, the dominant figure at the meeting was Al SchallenmuUer, the newly appointed vice president of Martin Marietta Civil Space Systems, the subdivision of the company charged with responsibility for the SEI. Schallenmuller had cut his teeth as an engineer working for Kelly Johnson in Lockheed’s fabled Skunkworks. He knew that, if approached the right way, big and difficult programs could be accomplished cheap and fast. In 1976, he had been one of the key engineers on the
Viking
program. He could never refrain from talking about the thrill of seeing
Viking’s
first photograph of the Martian surface; Schallenmuller really wanted to get back to Mars. He knew that if nothing better than the 90-Day Report was on the table, there would be no program. He supported our proposal.

Thus, in February 1990, Martin Marietta formed a twelve-person “Scenario Development Team,” chaired by Al Schallenmuller, and charged with developing “broad new strategies” for human space exploration. Most of the members of the team, like Ben, me, and David Baker, a spacecraft systems engineer, were generalists. But there were a few specialists, such as Bill Willcockson, Martin’s expert on aerobraking, the use of a planetary atmosphere to decelerate spacecraft (Bill was later to play a key role in the successful aerobraking of the
Magellan
spacecraft at Venus); Al Thompson, a leader in the artificial gravity area; and Steve Price, Martin’s specialist in the design of planetary ground rovers.

The two personalities with the most strongly held ideas on Mars mission design were Ben and I, but we were in only limited agreement. We agreed that low-energy, conjunction-class missions were the way to go, that a lunar base was unnecessary to support Mars missions, and that the use of an orbital infrastructure to support on-orbit assembly was a clear minus in mission design. After that, we parted ways. Ben felt that with sufficient use of robotics
, on-orbit assembly could be accommodated by using onboard manipulators to allow the spacecraft to build itself up from a series of pieces of hardware delivered to it on-orbit. Because he was willing to assemble his spacecraft on-orbit, Ben did not have the same drive as I did to reduce mission mass. So, while he had for years maintained a significant interest in the possibilities of manufacturing propellants on Mars, he saw no need to introduce such strategies into his mission plan. Ben also did not see the need to maximize time on the surface of Mars. His crew spent a year and a half at the Red Planet, but occupied nearly all that time in orbit, with only a comparatively brief thirty-day sortie to the surface in a small landing craft. Ben used chemical propulsion, obtainable off-the-shelf from existing vendors. The result of this thinking was a relatively conventional mission (if one calls the then dominant 90-Day Report thinking conventional) involving constructing a 700-metric-tonne orbiting spacecraft, but avoiding the 90-Day Report’s costly deturs in development and construction of lunar and orbital infrastructure. Ben initially called his mission plan “Concept Six,” but later changed its name to “The Straight Arrow Approach.”