Now coasting towards Mars, the crew has a bit of work to do. The Hab is positioned in, what most would call, an ‘unusual configuration’. When the stack of components was being assembled in the Vertical Assembly Building, the Hab was placed upside down from the way it will rest on the Martian surface. The launch couches (in which the crew is strapped) are bolted to the ceiling so the crew’s backs are to the thrust. Behind them are the Falcon 9 core booster, the connecting tether, and their atmospheric drag chutes.<\/p>\n
Going up the rocket stack are: the landing rocket thrusters to help them touch down softly on Mars; an inflatable combination heat-shield and aero-brake to aid in slowing the craft as it enters the micro-thin Martian atmosphere; and finally, the retro pack of engines to slow Bolo One’s orbit allowing them to fall into the atmosphere. This upside-down configuration avoids the need to undock, rotate, and re-dock with the booster. That antiquated maneuver was used by the Apollo Service Module to extract the Lunar Excursion Module from its shroud, back in the late ’60s and early ’70s. This adaptation is just one step in eliminating un-necessary risk.<\/p>\n
After the core booster flames out and the ship is drifting on toward Mars, the crew will un-strap from their seats and experience the full effects of weightlessness. Their launch couches will then be unbolted from the ceiling and stowed away in the EVA Prep Room, until the craft nears their destination. At that time, they will be brought out and attached to the floor, this time, in preparation for landing.<\/p>\n
Floating around in the Hab is an exhilarating and potentially unsettling experience. Those who have previously ventured into space are familiar with the effects, but Carl and Jackie are rookies on this trip. Training in the ‘Vomit Comet’ (NASA’s low-Gee aircraft trainer) helps prepare for the event. Valerie was tasked with monitoring the rookies’ possible ‘stomach discomfort’ as the veterans say.<\/p>\n
After getting their ship secured and ready, the crew will release the hold down clamps on the booster and begin deploying the tether: the Anti-Gravity Assist System that Tom had been testing as he orbited the moon. The tether will be reeled out fifty meters to start with. Then, the small rockets engines mounted on the sides of the Hab will be fired to get the two pieces rotating around the center of gravity, amid the tether, like a bolo.<\/p>\n
Since the tether is attached to the top of the Hab, akin to spinning a rope attached to the handle of a filled bucket, the centrifugal force from the rotation will push the crew toward the floor, thereby simulating gravity. There are two ways to alter the amount of centrifugal force and the resultant level of gravity. One is to change the length of the tether, while keeping the spin rate constant. The other way is to keep the length of the tether the same and alter the rate of the spin. Mission planners believed that a spin rate over two revolutions per minute could cause severe dizziness. To keep the spin rate down around one rpm, the tether needed to be 910 meters from the Hab to the center of gravity.<\/p>\n
If the Hab and the booster were of the same mass, the center of gravity would be halfway between the two and the tether would then be twice that length. But, if the booster were lighter, this would require the tether to be much longer, as the center point of gravity would be closer to the Hab than to the booster, like the way a teeter-totter’s fulcrum can be shifted when one child is heavier than the other.<\/p>\n
This variable tether concept will be especially useful on the return trip to Earth. As Mars’ gravity is only about 38% that of Earth’s, the crew will lose a lot of their physical strength during the 18-month stay on the surface. If they had to make the trip home in Zero Gee, the sudden return to Earth’s gravitational strength could very likely prove fatal. Similarly, going from Mars gravity to Earth gravity, rather than a gradual introduction, is not ideal either. But, by starting off at 38% Earth Normal Gravity (ENG) when they leave Mars, and steadily increasing the gravity effect by about 2.5% per week, the crew will be able to build up their musculature to survive the change.<\/p>\n
This gradual build-up is reminiscent of the tale of ‘the farm boy and the calf’. As the story goes: on the day a new calf was born, the young farm boy picked up the calf and carried it all the way around the barn ten times. He did this five times a day until the calf grew so big he could no longer lift it. By that time, the boy could lift over 135 kilograms (nearly 300 lbs.).<\/p>\n
The crewmembers will only need to lift their own weight to move around freely, but the concept is the same. Little-by-little their gravitational weight (centrifugal force) will increase and, presumably, their physical strength. In theory, they could come home from Mars in as good of shape as when they left Earth.<\/p>\n","protected":false},"excerpt":{"rendered":"
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