The Case for Mars (9 page)

MAP will return an avalanche of science data that will transform our understanding of Martian geology and meteorology, atmospherics and geomorphology. Engineers and scientists will have the data at hand to help them design new missions, ident
ify sites for exobiological investigations and, perhaps, prospect for water when exploring the Martian surface. But the greatest return from MAP will be the least tangible—its impact on the intellectual life of humanity at large.

Today, nearly five hundred years since Copernicus and Kepler, Brahe and Galileo, most people still think of Earth as the only world in the universe. The other planets remain mere points of light, their wanderings through the night sky of interest to a select few. They are abstractions, notions taught in schools. The MAP cameras offer the possibility of taking humanity’s eyes to another planet in a way that has never been done before. Through the gondola’s cameras we will see Mars in its spectacular vastness—its enormous canyons, its towering mountains, its dry lake and river beds, its rocky plains and frozen fields. We will see that Mars is truly another world, no longer a notion but a possible destination. And just as the New World entranced and enticed mariners here on Earth, so can Mars entice a new generation of voyagers, a generation ready to fashion the ships and sails proper for heavenly air.

THE MARS SAMPLE RETURN MISSION

The Holy Grail of robotic Mars exploration programs is the Mars Sample Return (MSR) mission. If only those
Viking
samples had been in one of our labs, we could have subjected them to a battery of tests and examinations that would have left no doubt in interpretation of results. Well then, why not bring a sample back? Currently, NASA’s solar system exploration branch has penciled in precisely such a mission for 2005.

There are three ways this might be done. The first, and conceptually the simplest, is the brute-force method. In this case, a launch vehicle in the claof a Titan IV is used to deliver to the surface of Mars a very large payload consisting of a miniature rocket ship, massing perhaps 500 kilograms, completely fueled for an ascent from Mars and flight back to Earth. The lander also has on board a robotic rover that is dispatched to wander about (under human remote control) and collect geologic samples. The samples are then loaded aboard a capsule on the rocket vehicle. When the launch window from Mars back to Earth opens up, about a year and a half after arrival, the rocket blasts off and flies back to Earth. Upon approach to Earth eig
ht months later, the capsule separates from the rest of the rocket vehicle and performs a high-speed reentry, much in the manner of an Apollo manned capsule. Depending upon design, the capsule may be decelerated by a parachute or simply use a crushable material like balsa wood or styrofoam to cushion the landing shock when it hits the targeted desert landing area.

This brute-force mission is fairly simple conceptually, but the problem is that it is likely to be very expensive, as robotic explorations missions go. The Titan IV alone costs $400 million, and the large lander needed to carry a fully fueled ascent vehicle is also likely to be very costly. Thus, the brute force approach has always led to cost estimates that have made the mission a nonstarter. In an effort to reduce costs, several other methods have also been studied.

One of the most popular alternatives to the brute-force plan is the Mars Orbital Rendezvous, or MOR plan. In this scheme, two spacecraft are sent to Mars, each launched by a comparatively low-cost ($55 million each) Delta 2 booster. One of the launches delivers to Mars orbit an Earth return vehicle (ERV) and entry capsule, and the other delivers to the Martian surface a fully fueled Mars ascent vehicle (MAV), equipped with a rover and sample can. The rover is deployed to collect samples which are placed in the sample can. When this is completed, the MAV takes off and flies to Mars orbit where it performs an autonomous rendezvous and dock with the ERV. The sample can is then transferred from the MAV to the reentry capsule on board the ERV. The two craft then separate, the MAV to be expended and the ERV to wait in Mars orbit until the launch window back to Earth opens up, at which point it fires its engine to send it on a trans-Earth trajectory. The rest of the mission is then performed in the same manner as the brute-force approach.

The main talking point of the MOR plan is that it considerably lowers launch costs relative to the brute-force scheme. Since the MAV only has to fly to Mars orbit, and not all the way back to Earth, and moreover only has to lift the sample can and not the complete reentry system, it can be made much smaller than the ascent vehicle used in the brute-force scheme. Thus the lander required to deliver it can be made smaller, lighter, and cheaper, and a much less muscular launch vehicle can be used to send it to Mars. However
, there are major problems associated with the MOR scheme. In the first place, two separate launch vehicles are needed, which doubles the risk of launch failure causing mission failure. Also, two complete spacecraft are needed, each of which has to be designed, built, checked out, and subjected to launch environment testing (when you launch a spacecraft it is subjected to severe vibration and acoustic loads, and these must be simulated in expensive setups before launch), and each must be integrated into a launch vehicle. Basically, doing all this will double mission costs. Furthermore, the interfaces between the two spacecraft must be perfect, not only in the factory, but after launch and years of space flight and thermal cycling both in space and on the Martian surface. Guaranteeing this is a very tough design problem; in fact it probably can’t be guaranteed since it can’t be testd in advance. Finally, the autonomous rendezvous, dock, and sample transfer in Mars orbit required to do this mission is an undeveloped technology which will be very costly to develop and which
cannot be tested in advance of the mission
. This multiplies the risk associated with this already marginal mission plan still more.

In an effort to make the MOR plan look more attractive, its advocates have taken to innovative accounting techniques, such as assigning the cost of the two required launches to separate missions. In more extreme proposals the rover would be flown out on a prior mission, so that its costs and the costs of its mission operations can be charged to someone else. In this case, the lander carrying the MAV now must satisfy the additional requirement of performing a landing with nearly pinpoint accuracy next to the rover. Once again, this cannot be tested in advance, yet it would represent a drastic improvement of the state of the art for targeting unmanned Mars landers, which currently involve landing errors of up to 100 kilometers. For the sake of novelty, apparently, some orbital rendezvous fans have also proposed moving the location of rendezvous from Martian orbit to interplanetary space. This saves propellant on the ERV, because now it does not have to capture into or blast out of Mars orbit, but it adds not only a considerable amount of propellant to the MAV, but also an untestable requirement that the MAV be able to blast off at exactly the right moment to catch and
rendezvous in deep space
with an ERV that is zooming past Mars at a speed of 5 km/s. This could be very tough to guarantee, from the point of view of MAV engineering systems alone, putting aside the possibility of bad weather on the preappointed take-off date.

So, if the brute-force plan is too costly and the MOR scheme is too risky, what’s left?

What’s left is a third plan, that I, along with engineers Jim French, Kumar Ramohali, Robert Ash, Diane Linne, and several others, have been advocating for some years now. This third plan is known as the Mars Sample Return with In-Situ Propellant Production, or MSR-ISPP.

In the MSR-ISPP plan a single Delta 2 is used to send a single
unfueled
Mars ascent vehicle (MAV) to the Martian surface together with a rover. While the rover is collecting samples, the MAV employs a small onboard chemical plant to turn gas pumped in from the Martian atmosphere into rocket propellant (I favor methane/oxygen, though carbon monoxide/oxygen has also been proposed), filling the tanks of the MAV. By the time the launch window back to Earth opens, all the propellant needed for the return flight has been made, and with the samples all collected, the MAV takes off and flies directly back to Earth, just as in the case of the brute force mission. The direct return to Earth is possible with a Delta-launched spacecraft because the Delta and its lander only had to deliver the MAV’s dry mass (perhaps 70 kilograms) to the Martian surface, instead of the much larger wet mass needed to perform the brute force mission.

The MSR-ISPP mission is by far the cheapest of the mission plans discussed, because instead of employing a Titan IV with one large spacecraft, or two Deltas with two small spacecraft, it can be flown on a single Delta with one small spacecraft. It is also much lower in risk than the MOR plan, because the “advanced technology” required, the in-situ propellant production (ISPP) plant, can be fully tested in advance in Mars simulation chambers on Earth. In addition, the ISPP unit represents a system of a much lower order of complexity (essentially nineteenth-century chemical engineering) than the avionics required for autonomous Mars orbit rendezvous, let alone deep space rendezvous. As noted earlier (and as I will discuss in more detail later), at Martin Marietta, we built and demonst
rated successful operation of a full-scale MSR-ISPP unit making both methane and oxygen for $47,000—an amount of money that would be “in the noise” in an MSR mission budget. Now it’s true that the Martin ISPP machine was a working brassboard test device, not mature flight hardware, but what needs to be understood is that
the issue of mission risk associated with a new technology is not one of maturity, it is one of testability.
Because it is testable, ISPP technology is much lower risk than the in-space rendezvous technologies required for the MOR mission. Furthermore, if it is decided to use two spacecraft on the MSR-ISPP mission, they will be identical spacecraft (and therefore cheaper than the two different spacecraft needed for the MOR mission), and, if either one makes it back, the mission is a success. In contrast, in the MOR mission, if either spacecraft fails, the mission is lost.

As we will see, using in-situ produced propellant is also the only way to make human exploration of Mars affordable. As far as MSR mission planning is concerned, that should be decisive in determining strategy. The MSR mission’s value will be greatly increased if it can be used to demonstrate the key technology needed for human flights to Mars. Consider this: the MSR mission will only be able to return a kilogram or so of samples gathered from the surface of Mars within at best a few kilometers of the landing site. Since it is unlikely that there is life today on the Martian surface, the search for Martian biology will largely be a search for fossils. Small robotic rovers with their limited range and long communication time delay (up to 40 minutes due to speed limitations of radio signals) in Earth-Mars command sequence data transmission are a very poor tool for conducting such a search. If you doubt that, consider parachuting rovers such as
Sojourner
or
Marsokhod
into the Rockies. It is likely that the next ice age would arrive before one of them found a dinosaur fossil. Fossil searches require mobility, agility, and the ability to use intuition to immediately follow up very subtle clues. Human investigators—rock hounds—are required.

If Mars is to be made to give up its secrets, “people who do not shrink from the dreary vastness of space” will have to go there themselves.

3: FINDING A PLAN

MARS THE HARD WAY

On July 20, 1989, President George Bush stood on the steps of the National Air and Space Museum in Washington, D.C. Behind him, within the cool halls of the museum, rested artifacts from America’s greatest space explorations, among them a gumdrop-shaped spacecraft named
Columbia
, the Apollo 11 command module. The men who rode the
Columbia
home from lunar orbit—Neil Armstrong, Mike Collins, and Buzz Aldrin, the Apollo 11 crew—now flanked Bush as the president prepared to announce a bold new venture in space on this the twentieth anniversary of humanity’s first landing on the Moon.

Bush spoke of the challenges and allure of space exploration, of committing the nation to a sustained program of human exploration of the solar system and even of the permanent settlement of space. This was heady stuff, even if it did come twenty years after the United States’ astronauts first stepped off of Earth’s surface and onto another world. He continued, speaking of the need for more than a ten-year plan, of a “long-range, continuing” commitment to space exploration. Then he proclaimed his program: “Fst, for the coming decade—for the 1990s—Space Station Freedom. . . . And next—
for the new century—back to the Moon. . . . And then—a journey into tomorrow—a journey to another planet—a manned mission to Mars.”

Thus was born the program which came to be known as the Space Exploration Initiative, or SEI. It was a good start, but it was all downhill from there.

In response to the speech, a sprawling NASA team representing all the centers in the agency, supported by all the major aerospace contractors, went off to figure out how Bush’s program could be realized. The team returned three months later with a document entitled “Report of the 90-Day Study on Human Exploration of the Moon and Mars,” which soon became known simply as “The 90-Day Report.” Before humans could go to Mars, the report said, the nation would need a space infrastructure buildup of thirty years, and the largest and most costly U.S. government program since World War II.

NASA would build the previously envisioned Space Station, but triple its size with the addition of “dual keels” containing large hangars for the construction of interplanetary spaceships. A plethora of additional orbital facilities would be built too: free-flying orbital cryogenic propellant depots; checkout docks; crew construction shacks; and so forth. This huge and complex array of facilities would be used to construct and service trans-lunar spaceships (which themselves would require three heavy-lift vehicles plus one Space Shuttle launch each for their deployment). Those who recalled the single launch required for each Apollo mission scratched their heads and thought, “It wasn’t this hard to get to the Moon the last time. …” Over the course of a decade, these lunar spaceships would haul to the Moon all the supplies and equipment necessary to build up a massive lunar base complex. Together with the orbital facilities, the lunar base would then provide the basis for building truly huge—1,000 tonnes plus—“Battlestar Galactica”-class spaceships for, finally, voyages to Mars. These trans-Mars space cruisers would employ propulsion and other technologies totally new and different from the lunar craft, and thus require vast new development expenditures as well as additional infrastructure beyond those needed to support the lunar missions. Initial Mars missions would require about eighteen months in transit (round trip) with a one-month stay in Mars orbit. As for actually landing on Mars, a small craft would descend to th
e surface and support a small crew of explorers for two weeks or so, thereby enabling a “flags and footprints” (and little else) human Mars mission to occur. The trans-Mars spaceships would fly out huge and return to Earth orbit tiny, having dropped bits and pieces—fuel tanks, excursion vehicles, aeroshields—in the course of each mission, thereby imposing a massive expense on each “flags and footprints” exercise that followed. The 90-Day Report did not include a published cost estimate; however, cost estimates for the program were generated that eventually leaked to the press. The bottom line: $450 billion.