Oct 13, 2011
Studies of manned Mars missions have been conducted over the last two decades by NASA, other space agencies and non-government groups, including the Mars Society. NASA has developed a series of design reference missions to serve as guideposts toward sending a human crew to Mars, and for comparing different approaches and criteria.
NASA's vision is to combine the knowledge gained from robotic Mars missions and the experience of human lunar missions to develop a plan to send people to Mars in the 2025–2030 timeframe.
New technologies must be developed to transport the infrastructure, facilities and crew from Earth to Mars. The infrastructure and facilities also need to be developed. Advanced technology is needed to provide life support (particularly consumables) to the crew during all phases of the mission. If space exploration is about venturing to new worlds and understanding the universe in ever-increasing detail, robots will be essential in assisting the astronauts in a wide range of tasks.
Depending upon the final mission architecture adopted, a manned Mars mission will require 250 to 500 metric tons of mass to be delivered to low Earth orbit—about two to four times the amount required to support a human lunar expedition.
The development of heavy-lift launch vehicles in the Saturn V class (or more powerful) would allow a moon mission to be accomplished in a single launch and Mars missions to be done in two to four launches. The on-time requirement for the Mars launches can be greatly mitigated by adopting mission strategies in which each booster sends its own payload directly to Mars independently. The crew leaves Earth only after it has been confirmed that all the other payloads have arrived on Mars safely. Such direct injection
mission designs also eliminate the need for in-orbit assembly, and the costly orbital infrastructure required to support it.
Three types of space propulsion systems can be considered: chemical propulsion, nuclear-thermal rockets, and electric propulsion.
Chemical propulsion has already supported human lunar missions. However, the exhaust velocity obtainable by such systems is limited. Nuclear thermal rocket engines work by using a solid-core fission reactor to heat hydrogen propellant, which is passed through the engine block as a coolant and then ejected from the nozzle to produce thrust. Because such devices decouple the energy source from the motive mass, they can achieve significantly higher exhaust velocities than chemical engines. In a ground test program conducted jointly by NASA and the Atomic Energy Commission during the 1960s, nuclear thermal rocket engines were fired with thrust levels ranging from 15,000 to 250,000 pounds, and exhaust velocities of 8,500 m/s. Limited only by the temperature tolerance of reactor materials, exhaust velocities for this technology approaching 10,000 m/s appear achievable.
Electric propulsion systems accelerate a charged propellant via electrostatic or magnetohydrodynamic processes. There is thus almost no limit to the theoretical exhaust velocity of such technology and, in fact, velocities of 50,000 to 100,000 m/s—10 to 20 times those of chemical engines—have been demonstrated. The problem, however, is that electric power must be supplied to drive such units. This could be done in space using either photovoltaic or nuclear sources, but the size of such systems would be considerable.
In order to achieve Mars orbit insertion and descent to the surface, rather large accelerations are required. Until now, all Mars orbiting spacecraft have been captured into orbit using rocket propulsion. It would be highly advantageous from the point of view of reducing mission mass to accomplish this orbital capture maneuver using aero-braking (and aero-capture friction against the planet's atmosphere) in place of propellant.
Equally important will be technologies that allow the crew to make use of resources they find on Mars. Local resource utilization, if feasible, would greatly reduce the costs and difficulty in transporting necessary materials from Earth. Not having to deliver fuel, for instance, could reduce mission mass significantly. It is believed Mars is a rich source of materials from which propellants could be made. Large regions of the Martian surface have been identified from orbit as containing more than 60 percent water by weight.
Such water, now in frozen mud, could be accessed and electrolyzed to produce both oxygen and hydrogen rocket propellants. Hydrogen so obtained could also be reacted with the carbon dioxide that makes up the Martian atmosphere to produce methane and oxygen to fuel a rocket, or alternatively, methanol and oxygen for a fuel cell. Carbon dioxide, nitrogen, and water required for plant growth are plentiful on the Red Planet's surface. The rich carbon supply on Mars also suggests a possibility of local production of such essentials as plastics, lubricants, and synthetic fabrics.
Source: ASME
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