Chair Force Engineer

Friday, March 09, 2007

TeamVision (Part 5 of 5)

In Era 5, TeamVision lays out the opening steps for opening the solar system to human spaceflight. It doesn’t begin with a Mars landing, but the asteroids and the Martian moons are targets for precursor missions that will lead to Mars.

One thing I noticed in the proposal is an Orion configuration which places a habitat module between the Command Module and Service Module. My guess is that, like in Manned Orbiting Laboratory, the astronauts will transfer between the CM and habitat by way of a hatch in the heat shield. While this may seem like a vulnerability during re-entry, the reflight of the Gemini 2 capsule demonstrated that the hatch would fuse closed during the plunge to earth.

Artificial gravity is provided for the astronauts on their trip to the vicinity of Mars. While NASA continues research into the effects of weightlessness on the human body, it’s clear from what we do know that weightlessness is generally a bad thing over long periods of time. While Robert Zubrin and others have suggested spinning the spacecraft (tethered to the booster) at a rate that would provide the 0.38g of the Mars environment, TeamVision recommends a higher level of artificial gravity due to the stresses created by EVA’s in bulky space suits. The higher level of artificial gravity creates more demands on the spacecraft and tether system. There’s debate on whether a tether is reliable enough to use in this application without snapping, or if a heavier truss would be better. I think that if shape-memory composites can be successfully demonstrated, they’d be an ideal candidate for the truss. In any event, artificial gravity should be tested in low earth orbit before it makes the flight to Mars.

The Mars expedition would be launched using two launches of the Jupiter III, plus lunar LOX that would be transferred to the spacecraft at EML1. The first launch would be an unmanned cargo lander. The second would be a manned spacecraft, which would occur roughly two years later.

The cargo lander would reach Mars by way of a flyby trajectory that took it past Venus. I wonder if TeamVision accounted for the extreme thermal shifting that will occur between the Venus vicinity and Mars vicinity. The thought of performing a Venus flyby was enough to frighten Robert Zubrin.

In any event, the cargo lander would deliver a Mars Ascent Vehicle (MAV,) supplies, and a pressurized rover to the red planet. It would utilize Martian carbon dioxide in a Sabatier reactor to produce methane propellant for the ascent to Mars orbit once the surface mission is complete.

The manned crew follows a faster, fuel-intensive trajectory which requires 180 days to reach Mars. Separate in-space & surface habitats will be their housing (based on the lunar habitat, but optimized for the unique environments they’ll be exposed to.) The surface habitat will use an optimal combination of propulsion and parachutes to make a soft landing with a human crew. No discussion is made about crew visibility during descent, but the idea used for the “direct ascent” moon lander should apply. The crew will spend 619 days on Mars before climbing in the MAV and docking with the space habitat and its attached propulsion stage. Artificial gravity is provided on the outbound leg of the journey. I was a bit concerned that no discussion was made about how the return capsule will deal with the speed of a re-entry at earth from the speeds necessitated by the trajectory from Mars.

I also get a bit uneasy when hearing about a reliance on aerobraking for capturing into Mars orbit. Mission planners count on saving a lot of propellant mass by braking with atmospheric friction. But aerobraking has never been used for a purely non-propulsive capture into orbit around a planet before. I’d like to see it tested before we proceed down that route. Then again, I’d shudder to think of how big these Mars ships would be if aerobraking weren’t used. As TeamVision admits, “Understanding the degree to which aerobraking can be utilized will be a driving Mars mission parameter.”

TeamVision even gives attention to the "and beyond" part of NASA's “Moon, Mars and beyond” mantra. Proposed missions for Era 6 include building a “Monty Burns Sun-Shield” to counteract Global Warming, the mining of Lunar Helium-3 (an unlikely prospect in the near term,) and asteroid protection.

In Era 5, TeamVision lays out a good architecture for a chemically-propelled trip to Mars and back. Some of the Mars Direct ideas, like artificial gravity and in-situ resource utilization, are implemented. It begs the question of whether the Sun-Mars L1 point should be used as a waystation in the same way that Earth-Moon L1 is a waystation for flights to the moon and back.

That being said, I think the lack of nuclear propulsion is a real drawback to the exploration of Mars. While the TeamVision Era 5 proposal gets us to Mars with chemicals, it’s like sailing the ocean with sailboats, when steam-powered ships are being held back only by the political whims of the people back home. Nuclear propulsion greatly reduces the mass that must be launched to Mars, although it will not benefit from the production of lunar LOX. Development of nuclear-thermal and nuclear-electric rockets will force us to invest a lot of money and political capital, but the payoff is too enticing to refuse.

As an overall, integrated plan, I truly appreciate TeamVision's effort to get the vision back on track. TeamVision has a clear path for exploring both the moon and Mars, whereas NASA hasn't publicly discussed what comes after we land on the moon. TeamVision also has a cost-effective way to develop lunar-specific hardware in a shorter period of time than NASA does. (By adopting direct landing & ascent, and developing Jupiter I instead of Ares I, TeamVision gets a foot in the lunar doorway before the next administration rolls into Washington.) Perhaps the most enduring contribution of the TeamVision report is a rational discussion of the lunar crew size and the strong argument that NASA's current crew size is twice what it needs to be.

The implications of a smaller crew are huge. If the two astronauts ride in a Gemini-sized capsule, they can make a direct landing & ascent with a Saturn V-class booster. The smaller capsule could also make the "Direct Launcher" concept work, by reducing the mass that must be put in low earth orbit (due to the lower-than-anticipated Isp of the RS-68 Regen engines.) Finally, it could enable an all-EELV (a.k.a. "Less Pork") approach, akin to the "Early Lunar Access" proposal of 1992.

Stephen Metschan, who wrote the TeamVision report, referred to it as a "Voice in the Wilderness" akin to John Houbolt's advocacy of Lunar Orbit Rendezvous. While today's NASA will probably be undone by its closed-mindedness, TeamVision's voice in the wilderness is saying a lot of inspiring things to the future generations who will succeed in exploring the solar system.

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