The Mars Transit Vehicle

An artists depiction of what a joint SpaceX/Bigelow aerospace transit vehicle might look like. (Source: http://img03.deviantart.net/039d/i/2015/208/1/4/spacex_mars_transporter_by_euandesign-d930lb3.jpg}

The first spacecraft habitat's that go to mars will have to be a remarkable achievement in efficient use of space. The more crew compartments and services provided to the astronauts, the heavier the craft will end up being. So a long duration spacecraft, needs to be small and pragmatic enough to be affordable, yet large enough to accommodate as many of the needs of the crew as possible. The study, "Minimum Acceptable Net Habitable Volume for Long-Duration Exploration Missions" published by NASA, establishes the minimum requirements of volume for the crew of a Mars transit vehicle. Ultimately, I believe these findings will become very important in the eventual design of the spacecraft.

One of the greatest challenges to overcome will be negating the health effects of microgravity on astronauts while they are in transit. Astronauts aboard the ISS must devote a large amount of their time to exercise to avoid muscular dystrophy and deterioration of bone marrow. They regularly run on a treadmill and use resistance bands to simulate gravity. The study, assumes that the exercise equipment will be smaller than what is currently being used on the ISS. A Mars transit will be at least six months so this equipment will inevitably add volume and mass to the Mars spacecraft. Another approach is to design the spacecraft to incorporate a centrifuge, a spinning section that simulates gravity using centrifugal force. This sort of architecture would most likely increase the overall cost and size of the vehicle and it may be more efficient to simply use exercise equipment to simulate gravity.

Another important aspect of the spacecraft will be the psychological influence it will have on the astronauts. Unavoidably, being in a highly confined space for long periods of time will take a toll on the mental health of the astronauts. Everyone has experienced the feeling of confinement during long road or airplane trips. It can quickly result in frustration and an uncomfortable feeling of confinement, These limits have been pushed in space before by cosmonaut Valeri Polyakov who holds the record for continuous time spent in space at 14 months without any drastic changes in his mental health. It is vital that the astronauts have a communal area for dining and other activities in order to assure that the spacecraft is not mentally damaging. A specified work space will also have to be a requirement, allowing for a separation between the recreational and working activities of the crew.

SpaceX testing a reusable booster stage

One aspect of the vehicles design that is not analyzed in the study, is it's capacity for reusability. There are two distinct approaches to designing a deep space craft. It can be built with the same design philosophy as the Saturn V, where most of the vehicle never returns to the earth in an effort to save mass at the expense of losing hardware. Alternatively, the design can make an attempt to salvage a portion of the hardware used in the vehicle for later missions like the Space Shuttle. The current model of NASA does not currently embrace reusability. Every component of the SLS rocket, the main fuel tanks, solid rocket boosters, and second stage will drop into the ocean after launch, and those components will have to be constructed again for the next launch. This makes the cost of flying multiple missions extremely high, because each SLS will take large amounts or resources to complete. So how do you reuse a rocket stage? You either have to attach parachutes to the stage for a soft ocean landing or land the rocket propulsively on land. Led by Elon Musk, SpaceX, a private space company who was recently granted a contract to bring crew to the ISS in 2017, has been been developing rockets that have a full recoverable first stage that can boost back towards the launch site and land with a high level of accuracy. This is an extremely difficult maneuver to pull off, and SpaceX has failed to accomplish it twice. Nonetheless, SpaceX has long-term plans to build a Mars vehicle capable of being fully reusable. This would dramatically reduce the cost of traveling to mars to a fraction of the cost that NASA has proposed.

Of course this would bring new challenges to designing a habitat, because in NASA's model, the transit vehicle does not need to be brought to the surface of Mars or the Earth, with only the Orion capsule serving as the lifeboat that return the crew to the surface of Earth. Ultimately, if SpaceX achieves it's goal of building a fully reusable mars vehicle, I believe this will be a much greater accomplishment towards the future of space travel than a single expendable Mars mission.

Citation:

Whitmire, Alexandra. "Minimum Acceptable Net Habitable Volume for Long-Duration Exploration Missions." (2015). Print.