Two Starships in "bolas" rotation

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.

Such rotating spaceship combinations have been suggested before, of
course, but it seems to me that the Starship design is uniquely apt for
this.

The two Starships would be connected by two cables (wire ropes) starting
from the outer ends of the two articulated aft fins and passing through
non-load-bearing connections ("rings", "eyelets") at the outer ends of
the two front fins. The weight (centripetal acceleration) of each
Starship would thus be carried by the outer ends of the aft fins, just
as when the Starship has landed and these fins act as two of the three
landing legs. The connection to the front fins would stabilize the
Starship in a "nose-up" position. Alternatively, a third cable could
connect to the third (dorsal) landing leg for an even closer emulation
of the landed, upright state.

The articulation (rotation) range of the fins seems (from the videos)
large enough to place the pull from the cables close to the center of
gravity of the Starship -- even if the third landing leg is not used --
so the simulated gravity would be aligned with the long axis of the
Starship, as in the landed position.

For a Mars trip, a simulated Martian gravity level could be used, giving
less stress and weaker Coriolis effects than full Earth gravity. The
same two-Starship bolas system could be used in Earth orbit to test the
long-term effects of Martian gravity levels before Mars trips are
undertaken.

There may be a thermal problem. The Starship carries cryopropellants
which must not evaporate away during the trip from Earth to Mars or vice
versa. In the SpaceX trip videos, the Starship points away from the Sun,
and is furthermore shadowed by a semi-circular fan of solar cells
unfolded at the aft end of the Starship. This prevents solar heating of
the Starship structure, which may be important to limit propellant
evaporation. In a rotating Starship pair the same shadowing is not
possible. The illumination conditions depend on the orientation of the
rotation axis.

For human comfort, it seems best for the rotation axis to point at the
Sun, which means that the direction of incoming sunlight and the
position of the Sun as seen from the Starships are constant and not
rotating. (Another nice feature of this orientation is that the
Starships could be slowly rolled around their long axes to simulate a
day-night cycle.) However, this also means that both Starships are
constantly illuminated and heated from one side, which may cause
propellant evaporation.

If the rotation axis is perpendicular to the Sun direction, the average
solar illumination of the Starships is reduced, but is still larger than
in the fixed away-from-Sun attitude. As seen from a Starship the Sun
rotates around the Starship, front to aft and back again, once per
Starship rotation. This rapid rotation of the illumination may be very
distracting to the passengers.

A lesser problem may be how to mount the solar cell fans. Their original
aft-facing position at the aft Starship end is now bad, because the fans
would not be well illuminated and would be stressed by centripetal
forces. One solution is to mount the solar cell fans on the cables, at
the center of rotation. If the rotation axis does not point at the Sun,
or if the centripetal forces are still too strong even this close to the
axis, the fans could be decoupled from the rotation by a rotating
electrical coupling at the rotation axis.

So that's the suggestion. Comments are welcome...

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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