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Old July 26th 19, 05:58 PM posted to sci.space.policy
Niklas Holsti
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Default Two Starships in "bolas" rotation

On 19-07-24 20:18 , wrote:
On Tuesday, May 21, 2019 at 2:15:19 PM UTC-4, Niklas Holsti wrote:
The SpaceX plans for the first Mars trips involve two Starships
making the trip at the same time. The SpaceX videos show a Starship
flying alone, in a fixed attitude (pointing away from the Sun) thus
in free fall. From other sources there is some concern that a
multi-month weightless trip may incapacitate the pilots and
passengers, for example resulting in blurred vision when they are
again subjected to acceleration or gravity. Here I propose a
possible solution: cable the two Starships together in a
nose-to-nose attitude and rotate them to provide simulated gravity
during the trip.


Do you have any numbers on this? How much propellant would be
necessary to spin up the rotation?


Assuming a 50 m radius of rotation and a desired acceleration
(pseudo-gravity) of 3 m/s/s, a rotational speed of about 12.2 m/s is
enough. So quite small compared to orbital velocities.

I think the propellant demand could be reduced by starting the rotation
with a longer radius and lower speed, and then reeling in the cable to
shorten the radius, letting conservation of angular momentum increase
the rotational speed until the desired acceleration is reached. But the
radius should be long enough to keep Coriolis effects and other
differences between real and simulated gravity comfortably small.

Would it be necessary to despin
them upon arrival, or are you going to just cut the cable and let the
two ships float off into different orbits?


Surely not "cut" the cable -- the system should be reusable :-)

At least for the first trips to Mars, the two Starships will no doubt
try to land near to each other, so they should not be put on very
different paths.

The most comfortable method is perhaps to reel out the cable slowly,
increasing the rotational radius and smoothly reducing the acceleration
to a small value, and then disconnect the Starships and correct the
paths with thrusters.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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