Mars Society Switzerland
Feasibility of inhabited flights to Mars
Back 3 2 6 4 5 8 7 9People often say that any exploration of Mars by means of inhabited flights is not to be considered for several decades to come. These assertions are ill-founded: Already in 1996, Dr Robert Zubrin, in his book “The Case for Mars”, launched the “Mars Direct” concept elaborated over the previous years when he was chief engineer working at Martin Marietta. This concept was built on several brilliant ideas which make these flights possible using today’s technologies. Robert Zubrin knew the problematic of the voyage to Mars very well as he was in charge of the Mars project at Martin Marietta, one of the major firms competing to provide the launchers for such enterprise when the Appolo program was being completed. Tenders had been issued by NASA. Unfortunately NASA had seen too big and, in 1993, the project was given up to the benefit of the International Space Station for budgetary reasons. In effect, applying the guidelines of Werner Von Braun, the “conquest” of Mars would have cost some 450 billion USD whereas the ISS was budgeted for “only” 50 billion (it eventually cost 100!). Von Braun thought, without any consideration for money, that the exploration should be made with a real “space train” implying assembling of many elements in Low Earth Orbit (“LEO”), a score of astronauts and the propergol which should have gone with them. The advantage of Zubrin’s architecture and consequently its feasibility, essentially relies upon points exposed below which, under the second President Bush, inspired NASA for the drafting of its first “Design Reference Mission” (“DRM”) after this President decided that exploration flights within the solar system must again make room to inhabited missions beyond LEO (“Constellation” project). With the last version, “DRA5” (see next page), we unfortunately saw a drift of the original spirit of the project (heavier load and complexification) which made it costlier and set more intricate technical challenges. This was opening the door to the cancellation of the Constellation project just decided by president Obama who, anyway, had other priority in mind. ISRU : According to Robert Zubrin, astronauts will have to “live off the land” using local resources (ISRU= In Situ Resource Utilization). On Mars there are minerals, sunlight and above all, an atmosphere. This atmosphere is very thin but it is 95% made of carbonic gas which is indeed a very interesting stuff as it can be broken easily into oxygen and, with the addition of a small quantity of (imported) hydrogen, methane and water. Methane is an excellent propergol and water can be used for a variety of purposes. It will therefore be unnecessary to bring one’s propergol to Mars for the trip back to Earth. This allows reducing by so much the load to be pulled out of Earth gravity on the way to Mars. Sequence of several direct flights to Mars : Rather than sending a spatial train to Mars to be assembled in LEO (people working in very difficult…and very costly conditions, assembling stations, flights just for servicing those stations, and so on) or sending in Space a launcher much more powerful than Saturn V…which does not exist, it is much easier to send a sequence of direct flights to Mars (one, then two flights at each launch window i.e. every 26 months) because Mars is, Earth apart, the safest place to live within the solar system (and the easiest place where to work and therefore assemble elements necessary to exploring). The first flight will carry a first Earth Return Vehicle (“ERV”), uninhabited, with, inside, a chemical unit for producing oxygen and methane, equipments for scientific exploring, a small atomic generator and a pressurized rover. After having checked that the chemical unit has indeed produced and stored enough oxygen and methane, a second flight will be sent, exact copy of the first one (including a second ERV); then, within the same launch window, a third flight. Aboard this last spaceship, there will be a team of four astronauts (not six!) and all kind of equipments needed for life and science (food for three year, a recycling unit for water and oxygen, a pressurized rover). The third flight would land in the vicinity of the first one (note that it will hold a pressurized rover in case it would land a little too far from the first one). The second flight, after a longer trajectory (more economical) than the first one, will arrive in the vicinity of Mars only after the third one and Control Commands on Earth would have the possibility to correct its landing according to the exact position of the inhabited lander. If, for practical reasons, the second flight could not be used by the team of explorers of the third one, it would be used as back up to the fourth flight (inhabited) sent during the launch window following the third one, and so on. ISRU and the sequential flights to Mars would thus allow using chemical launchers of the Saturn V type (Apollo) or Ares V (planned by the former NASA administration and cancelled by order of President Obama) that nowadays we can build (we already did forty years ago!) Artificial gravity : Microgravity during the 6 months of the trip, would be extremely debilitating for the astronauts (loss of muscular and bone masses). It has to be avoided. The solution brought forward by Robert Zubrin, is artificial gravity within the habitat, to be produced during the voyage by a centrifugal force resulting from the rotation of the couple made of the habitat and the last stage of the launcher linked together by a tether (after the latter is fully burnt …of course) and to which an impulse would be given by a small burst after the ship leaves LEO. To create Martian gravity (0.38% g), a 2 rotations per minute for a 86 meters lever arm (total length of the tether would depend of the mass of the counterweight) would be enough. This speed is acceptable to human organisms but, for more comfort, the tether could be made longer (and the rotation speed slower), thus reducing, as would be convenient and economical, the effects of gravity differences between head and feet as well as effects of the Coriolis force. Other ideas : Robert Zubrin proposed many other ideas which, together, constitute a coherent system relying on the same principles: “Live off the land” and “Mars is safer”. Thus aerocapture would allow, using the Martian atmosphere, slowing down spaceships upon their arrival in Mars vicinity, which would induce further savings in propergol; waste recycling would allow reducing the mass of embarked consumables; water could provide a convenient screen against radiations during the trip if tanks are located around the habitat; and so on… *** If exploring Mars is still a project "in limbo" forty years after exploring the Moon, it is first of all for financial, i.e. political, reasons: Governments prefer to spend for other projects the fifty-some billions dollars which would be necessary for one cycle of Mars exploration. It is also because the inhabitants of Earth have turned much more risk adverse than they were in Apollo’s time. Pierre Brisson
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