Five turns of fuel is still more than a grav deck burns...

Let's think about a more precise calculation.

The 'small habitat' in TR3057 has a width of 500 meters and so a radius of 250 meters at 120K tons, which is in the ballpark of what we are looking at. To reach a half g, you want the velocity on the outer shell to satisfy v

^{2}/r ~= 4.9 m/s

^{2}. Calculating, v = (4.9*250)

^{0.5}=35 m/s. So for a 1/10th g drive, could spin this up in ~36 seconds.

Logically you

*could* use the main drive if it was arranged in a Mammoth style and you could spin the drive axis 90 degrees, but perhaps we should just use attitude adjustment thrusters. Attitude adjustment thrusters give a rotational vector in SO at the rate of 60 degree rotation per minute per thrust point. We're looking for a rotation velocity of 480 degrees per minute, so that takes 8 thrust points which requires 40 minutes with a 1/10th g drive.

So, depending on the rules, the fuel usage varies between .8 tons in the worst case (tactical thrust with standard attitude adjustment thrusters), 0.027 tons (strategic thrust with standard attitude adjustment thrusters), .012 tons (swivel mount main drive with tactical thrust), or even .00072 tons (swivel mount main drive with strategic thrust).

If you want to go with the worst case, that costs 1.6 tons to spin up and spin down which costs a worst case of 24K c-bills according to CO. The _smallest_ grav deck (<100M radius) adds 25M to the cost of a station which suggests a breakeven after 1042 weeks if you spin up and spin down once per week. That's about 20 years and the fuel cost is a negligible additional to the stationkeeping fuel costs.

Personally, I believe the 'strategic thrust with standard attitude thrusters' fits the situation better. That would have a buyback time of 577 years.

Still kind of dubious about that working. At only 107,000 tons I can't see it being that big. Too fast of rotation with too small a radius will leave people non-functional.

The question seems to be "what is the radius"? Published figures are fairly large: 250meters for the small habitat, 100 meters for a Behemoth, 138 meters for a Mammoth. These are certainly in the ballpark of grav deck radiuses.

If thats the case then why not make it modular so that it can be assembled from 50kton sections, this allows you to have your grav deck as well as everything else, and not have to spend fuel mass, (and internal stress of the frame) by spinning up and down the station.

Modular stations have a multiplier of 50 instead of 5, so the space station cost balloons to 280M c-bills. It's definitely cheaper to just use a grav deck.