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A couple of things since the last post. Number 1, the guy who will make food that isn't food. Perhaps there wouldn't be a need to grow food, but just bring along this stuff. Number 2, the graphene posts. Perhaps the amount of mass can be reduced even further. These ideas got me thinking once again about the space hab. To recap what preceded on this subject: part 14 of the series, I decided to take some risks with the amount of shielding in place. This was necessary in order to keep the mass from getting out of hand. The goal is to keep mass to a minimum.
We may need to take some risks. There may be some wiggle room with what you can get away with.
If we go with only 50% shielding, we can make a "coffin" out of lead that's 1 cm thick, which will weigh in at 1750 lbs or so. Two of these would mass at 3500 lbs.
Now for how to keep as healthy as possible on the trip. There should be some artificial gravity. How to accomplish this?
There are other questions, but let's tackle this one first.
Given that it may be possible to obtain really lightweight "thread" to be used as a tether, the two coffins can be spun around each other at such an RPM and distance that 1 g may be obtainable without using too much mass. One problem though. It would be desirable to stop the rotation and get out of the coffins from time to time.
Perhaps the spider fab can make a tube and thread the tube in order to make it rigid. The tube needs to be strong enough to withstand the forces upon it as it slows down and speeds up. It is uncertain how much is needed for this purpose. That could impose a mass penalty, but if it does, it may have to be paid. It won't do to have the crew spending all their time in the coffins.
How to connect to the space sail? Hopefully, this won't prove to be too big of a problem. Perhaps a connection with another tether will be all that is needed. However, as the coffins begin to spin, I worry a bit that it may impose instabilities upon the entire spacecraft. It needs to spin without wobbles and such, but those may be impossible to eliminate. When there are wobbles or vibrations, these need to be isolated so that the sail is not disturbed.
As a result of this thinking, it may be desirable to keep the rotating, artificial gravity device small. There's too much of a risk that it will impose a problem. Not only that, but that the coffins won't be included. That means a very limited time in the artificial g device since the crew will be exposed during this time. The risks have to be traded off. If you want less health risk, you may impose higher mission risk. The highest priority is to get there and back safely. What kind of shape they will be in will have to play second fiddle to that.
You will need an inflatable device to give access to the artificial g device. Since the device will be small, then we can go back to the sphere design that we had before. But the sphere will be minimized in terms of mass.
The crew will come out of the coffins into a pressurized sphere. They will be connected to a rod, perhaps reinforced with the strong threads mentioned. Then they will be spun up to the highest RPM they can tolerate. They will spin for as long as they can before the radiation dosage becomes too risky, then the spinning will cease. They will go back into the coffins where they spend most of their time.
Perhaps all this adds to much health risk. Anyway, the sphere would be tethered to the sail, possibly at the mast. Therefore, there must be no torque nor vibration transmitted to the sail's mast. How this may be done isn't clear now. If it can't be done, there could be a problem. Some type of artificial g must be generated, or the trip must be kept as short as possible. This may not be convenient with this type of propulsion.
After some pause, I thought of a way to stabilize the vibrations and torque. So I hope. Just use the mass of the coffins. As the two crew members are spun up, the will rotate around a rod that connects the two coffins at each end of the sphere. There will be a second rod that the two crew members are connected to. The will spin around the axis that is created at the intersection of the two rods. It is hoped that the two crew members will weigh as much as each other to a fine degree. Whatever difference in mass will have to be compensated for somehow. Anyway, the balance will hopefully keep out vibrations. Torque is removed through a bearing system that will transmit it through the sphere and be compensated by thrusting. Hopefully, this will not prove to be too much. Changes in rotational speed could be a big problem, as forces may well be transmitted through the rods and to the sphere, which would not be good. Rotational energy should be supplied by an electrical motor. The motor could become a generator and recover the energy for the slow down.
The thought just occurred to me that artificial g may not be possible with a space sail. That means the crew members will need rehab somewhere when they get back. If there's to be no artificial g on the mission, it won't interfere with work at the asteroid. There's very little g there as well.
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