The First Missions to Mars

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    The basic plan for sending human crews to Mars, since at least the 1950's (see the Disneyland episode titled "Mars and Beyond"), involves sending an interplanetary ship to Mars, where it will go into orbit around the planet and then launch small rocketships to take explorers to the planetís surface. Robert Zubrinís Mars Express plan only improves the basic plan by having return rockets sent to Mars before the explorers are sent, thereby ensuring that the people get home. All of this is aimed at getting people onto the Martian surface quickly and expediently.

    NASA wants to take a more sedate approach. The first crewed missions will merely orbit the planet and return to Earth, without attempting a landing. Itís basically the same plan that NASA used for the Apollo program, with Apollo 10 making a feint at the moon without actually landing. Itís a step-by-step confidence-building approach and it does make good sense. However, the idea of people spending 16 months in orbit around Mars just taking pictures and making measurements strikes a lot of people as unworthy of the effort: after all, automated probes have been doing that job for decades. Thereís a way to fix that flaw.

    Most discussions of exploring Mars neglect two things Ė Phobos and Deimos. The size of small asteroids, the Martian moonlets should figure prominently in plans to explore Mars. It would require very little extra rocketpower for an interplanetary ship going into the right orbit around Mars to approach and land on one or the other of the two bodies.

    If the expeditions use Hohmann transfer orbits, then each expedition will take 210 days going from Earth to Mars, 496 days orbiting Mars, and 210 days returning to Earth, a total of 2.5 years. A new launch window opens once every 2.14 years (780 days) roughly, so as one expedition is coming home, the next one launches itself to Mars. That slight overlap means that each expedition will have a certain number of contingencies built into its plan, depending on information transmitted to Earth by the previous expedition: it would be impractical to wait for the previous expedition to complete its return to Earth before sending the next one.

    The first expedition will be entirely exploratory. While making observations of Mars from orbit, the explorers will spend 8 months studying one of the moons and then 8 months studying the other. They will produce detailed maps of the moons and study their structure and composition. They will be seeking water, likely underground and in the form of hydrated minerals, or, lacking that, oxide-based minerals. This is the information that mission control on Earth is waiting to receive.

    If water exists in reasonably accessible form on one or both of the moons, then the second expedition will not bring extra hydrogen. Instead, the expedition will bring extra components for the base that they are going to start building. The base will likely be built on Phobos, the larger of the moons and the one closer to Mars. The base, as first built, will consist almost entirely of laboratories and workshops. The crew will live aboard the spaceship that brought them.

    One large piece of equipment that the second expedition will bring to Phobos is a chemical processing plant. If thereís enough water to be had, part of the plant will bake it out of the moonís rocks so that it can be separated into hydrogen and oxygen. Those elements will be liquified and stored in tanks attached to the base. If water is scarce, the hydrogen can be used to reduce the oxides in the regolith. For example, under the right conditions iron oxide (rust) and hydrogen yield iron and water. If thereís no water to be had, the expedition will bring its own hydrogen and use it to reduce the oxides. In any case, the main product of the plant will be liquid oxygen, which will be stored for future use. Extra hydrogen would be a bonus.

    The third expedition will bring habitat modules to add to Camp Phobos, three communications stations, and two landers. With the habitat modules in place the crew can live in the base and not aboard their interplanetary ship. The landers will be brought with their fuel tanks full of liquid methane and carrying tanks full of liquid hydrogen. The oxygen tanks will be empty, the liquid oxygen being obtained from the Phobos base.

    Carrying cargo in pods strapped to its sides, the first lander will be sent to land on Mars on autopilot. It will set itself down at the site chosen for the first Mars base, near, we hope, a source of readily obtainable water (such as permafrost a meter or so beneath the surface). After securing itself following the landing, the lander will start up a small nuclear reactor and begin refueling itself in accordance with the Zubrin plan.

    The refueling apparatus will draw in Martian air (almost entirely carbon dioxide), mix it with hydrogen, and then, using the Sabatier process driven by nuclear heat, convert the mixture into methane and water. The methane gets liquified and put into the rocketís fuel tank and the water gets electrolyzed. The system liquifies the oxygen and puts it into the rocketís oxidizer tank and sends the hydrogen back through the Sabatier process. The process will continue until the hydrogen is used up and the landerís propellant tanks are full.

    Meanwhile, the expeditionís crew will attach the new habitat modules to Camp Phobos and then deploy the three communication stations into areosynchronous orbit, 120 degrees apart, so that they will maintain continuous contact between Camp Phobos and Camp Ares. Observations and experiments will continue until the first lander signals that it is refueled and ready to return to Phobos.

    Then a team will board the second lander and ride it down to the Martian surface, landing close to the first lander. After ensuring that both landers are secured, the team will remove the cargo pods from both and the empty hydrogen tanks from the first, laying those latter aside for future use. From the cargo pods the team will take a small electric tractor (some assembly may be required), two modules (one habitat and one laboratory/workshop), and other equipment needed for them to build the first part of Camp Ares.

    Even before the camp is established (the team can live in their lander for a time), at least one member of the crew will search for a source of readily available water. If such can be found (and itís likely that it will), the whole project becomes easier and less expensive. Among the things taken from the cargo pods, the crew will find an apparatus for tapping that source, purifying the water, and pumping it into one of the empty hydrogen tanks.

    Before they return to Phobos the team will set out various experiments and measuring apparati which can be monitored from Earth. They will remove the nuclear reactor and propellant-production apparatus from the first lander and move it to a place near the water-storage tank (the residual heat from the reactor may be used to prevent the water in the tank from freezing). Then they will ride the first lander back to Phobos, secure it and the base, and the expedition will return to Earth. The second lander, remaining on Mars, will begin to refuel itself through its own nuclear reactor and propellant-production apparatus.

    The fourth expedition will bring hydroponic-farming modules to add to Camp Phobos, making the base essentially self-sufficient (though emergency rations will also be kept on hand). It will also bring a second, new interplanetary ship, which will go to Deimos.

    In addition to the farming modules, the first ship will bring a third lander, cargo pods for the first lander, and, if needed, a tank of methane to refuel the first lander. That last item may not be needed and it will be a major benefit to the program if it is not.

    Spectroscopic studies indicate that Phobos and Deimos look like they may have the same composition as do the meteorites called carbonaceous chondrites. If the actuality matches that indication, then the moons contain as much as 22% water by mass and a large amount of carbon in the form of organic molecules. Camp Phobos and Camp Deimos could both produce the fuel and oxidizer needed for the methane-burning rocket engines used in the Mars system.

    The second ship, going to Deimos, doesnít carry any landers, so it will bring an essentially complete base Ė the habitat modules, laboratory/workshop modules, and farming modules. It will also bring two small ferries for moving people and supplies between Phobos and Deimos.

    With the second lander already refueled, part of the Phobosian contingent will ride to Camp Ares on the third lander. They will remove the hydrogen tanks, nuclear reactor, and propellant-production plant from the second lander and add them to Camp Aresí fuel depot, which will begin filling the tanks with liquid methane and liquid oxygen. The crew will then remove the cargo from the third lander and use it to improve Camp Ares. Part of the cargo will consist of hoses and pipes that will enable the crew to refuel the third lander from the Camp Ares filling station.

    Once the third lander is refueled, a crew will come down in the first lander and both crews will use its cargo to finish building Camp Ares. In particular that means setting up hydroponic-farming modules. The crew will also refuel the first lander.

    With all three camps able to produce food, air, and water, the fourth expedition will leave them occupied by small crews when it returns to Earth. From that time onward, the camps will be occupied continuously for the duration of the project and, perhaps, beyond. Subsequent expeditions will bring fewer materials for expanding the bases and more materials, such as rovers, for exploration.

    Exploration of Mars and its moons will proceed at a steady pace. Imagine a rover, running on autopilot, driving itself to a point where a small rocket meets it. A crew from the rocket boards the rover and lives in it for several weeks as they explore a small part of Mars. Then the rocket re-intercepts the rover and takes the crew back to Camp Ares while the rover drives itself to its next assignment.

    This will be a very expensive project with no prospect of a commercial return. Thereís no profit in it. Except for a few "souvenirs of Mars", thereís nothing that can be sold on Earth. So why would any rational society undertake such a project?

    If we believe that Humanityís destiny properly lies entirely on Earth, then we should not waste our resources on any such project. We simply hunker down on our home world and accept whatever Nature sends our way. That plan didnít work well for Order Dinosauria, though, to be fair, there is no indication that any of the dinosaurs had developed a civilization capable of expanding into space.

    If we believe that Humanity should spread out at least to the limits of our own solar system, then the Mars project will serve as a pay-forward investment. Its primary value lies in the experience it gives us in working and living in an interplanetary environment. In particular, we want the experience that people will gain from working on and around Phobos and Deimos. That experience will be valuable when people begin transforming asteroids into floating cities. Such transformations may actually be practiced on Phobos and Deimos, which are very much like asteroids.

    Thus the Mars project will serve as a major stepping stone to the creation of self-sufficient cities in space. Mars may turn out to be the Sumeria of interplanetary civilization.

Appendix: Astrodynamics in the Mars System

    For spacecraft moving within the Mars system, a small set of facts constitutes necessary knowledge. In flights among Mars and its moons we can reasonably assume that people will use rocket engines burning methane (natural gas) and oxygen. If the engines run with a combustion chamber pressure of 68 atmospheres, the exhaust velocity will come to 3615 meters per second (corresponding to a specific impulse of 368.6 seconds). Given a mission with a certain delta-vee, dividing that number into the delta-vee yields a number whose exponential is the mass ratio for the vehicle executing the mission.

    Mars has an equatorial radius of 3380 kilometers (more or less) and the ground at the equator moves east at 239.5 meters per second due to the planetís rotation. The surface gravity is 0.3839 times the surface gravity of Earth, which corresponds to a downward acceleration of 3.766 meters per second per second.

    The moons both follow orbits that are ellipses of very low eccentricity, which are close enough to circles that we can regard them as such for this approximation. Phobosí orbit has a radius of 9376 kilometers and an orbital speed of 2138 meters per second. Deimosí orbit has a radius of 23,463 kilometers and an orbital speed of 1351.3 meters per second. The areosynchronous orbit, the orbit where a satellite will remain above on spot on the Martian surface, has a radius of 20,416 kilometers and an orbital speed of 1446.6 meters per second.

    If we want to send a ferry from Phobos to Deimos, exploiting the efficiency of the Hohmann transfer orbit, we must first give the ferry a delta-vee of 417.17 meters per second in the prograde direction to raise the apoAreon of the ferryís orbit to the orbit of Deimos. When it reaches Deimos, the ferry adds another 329.73 meters per second in the prograde direction in order to raise the periAreon of its orbit to that of Deimos so that the ferry floats on the same orbit with Deimos and can make a soft rendezvous. To go from Deimos to Phobos, the ferry gives itself the same delta-vees in the retrograde direction in reverse order. The total delta-vee is 746.9 meters per second, so the mass ratio needed for the mission is 1.2295; that is, at the start of the mission, for every tonne of spacecraft, cargo, and crew, the ferry must carry 229.5 kilograms of propellant.

    To go from Phobos to the areosynchronous orbit requires a first delta-vee of 364.5 meters per second and a second delta-vee of 298.9 meters per second, for a total of 663.4 meters per second. The corresponding mass ratio is 1.20143, so for every tonne of dry mass, the ferry must carry 201.43 kilograms of propellant.

    To go from the areosynchronous orbit to Deimos requires a first delta-vee of 49.38 meters per second and a second delta-vee of 47.698 meters per second, for a total of 97.078 meters per second. The corresponding mass ratio is 1.0272, so for every tonne of dry mass, the ferry must start out with 27.2 kilograms of propellant.

    Going from Phobos to a landing on the Martian surface is a different proposition. Calculate, per kilogram, the difference between the gravitational potential energies of an object on Phobosí orbit and the same object on the Martian surface. To that number add the difference, per kilogram, between the kinetic energy of an object on Phobosí orbit and the kinetic energy of an object sitting on a point on the Martian equator. Claim that the sum is a pure kinetic energy and calculate the corresponding velocity. The result, 4547.8 meters per second, is the minimum delta-vee for a craft to go from Phobos to a landing on Mars. We have the corresponding mass ratio as 3.5185, which means that, for every tonne of ship, cargo, and crew, the ship must start out with 2.52 tonnes of propellant. Of course, the same mass ratio will bring a ship from the Martian surface to Phobos.


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