On 2019-07-26 2:44 PM, Niklas Holsti wrote:
On 19-07-26 20:54 , David Spain wrote:

Or even
more simply, just put the spacecraft into a spin along the flight path
vector. Thus no 2nd ship required or fancy rendezvous and un-tether
maneuvers needed.

Spinning (rolling) around the long axis would give a rotational radius
of only 4.5 m, max, giving disorientating Coriolis and other effects.
The pseudogravity would be radial, 90 degrees offset from the real
longitudinal gravity when the ship stands on its rear fins. Not good, IMO.

The centrifuge in Discovery was small in radius since it had to be
contained within the pressure sphere of the hull (12.2 meters). I wonder
if AC Clarke had done the math on that?

https://en.wikipedia.org/wiki/Discovery_One

This would also allow incremental build-up of
spacecraft by joining future Starships together in LEO to make a larger
spacecraft.

I don't understand how the spin/roll is related to incremental joining
of Starships. In a Starship, one end "kicks" (the aft end) and the other
"penetrates" (the front end); they are not easily connected together to
form a larger living space. At most, one could dock two Starships
front-to-front. Can you clarify what you mean?


Yes you can dock front-to-front. If fact, what if you dock to a
habitation module like a large inflatable Bigelow module? Once in orbit
the nose of a Starship docks to an already inflated an constructed
habitation module where the diameter expands to 20-30 meters and the
circular 'decks' run parallel to each other along the inner
circumference. Now you have an artificial gravity environment where the
rate of roll is much, much less to achieve a given gravity and you get
this without needing a 2nd Starship and all the complexity of trying to
counterbalance two Starships. Of course two Starships could share this
hab module if docked at each end. The habitation module would remain in
orbit and not land but could be reused from either destination. Also if
the roll rate is small enough it might be possible to work within the
original Starship cabins under micro-gravity where the role of walls vs
floors are inverted during transit, but because the Starship cabins are
much closer to the axis of rotation there is very little gravity here.
None along the center line of the Starship.

A downside would be that this might require a 2nd Starship to attach to
the first Starship in Earth orbit to give it the boost it needs for TMI.
Depends on the mass of the hab module vs Starship's propulsion budget,
which is probably tight already. If the math works, it might be possible
that the 2nd Starship only gets the configuration into an elliptical
orbit high enough that the enhanced 1st Starship and hab can 'kick' into
Hohmann orbit at apogee after separation from 2nd Starship which can
then return to Earth. Of course there is the 'hab as a cycler' scenario
which avoids this, but puts more maneuver burden on Starship. And the
added complexity of launching and maintaining a cycler, which is NOT on
SpaceX's drawing board today (and neither is a hab I might add).

This might also require a change to the possible Mars arrival navigation
scenario in that Starship(s) would need first to slow into orbit around
their destination first in order to detach the hab module and then
descend. Rather than a direct descent trajectory. Which requires more
fuel, etc. OR you de-roll and detach just before arrival and have the
hab module have its own propulsion to place it into orbit. That puts
less on Starship but far more on the hab module, plus now you have to
figure out how to refuel it for the return if it can't contain or
preserve enough fuel for both legs of the journey. A way to help this
issue is if the hab goes up 'unfurnished'. Meaning the bulk of the
supplies for life support and habitation are brought up in Starship.
Moved into the hab during transit and then stowed back into Starship
upon arrival. It's going to be needed on the surface anyway, not wasted
hanging out in orbit. Anything that can reduce the mass of the hab is a
win in general.

The main reason I like this scheme is that it places far less burden on
changes and potential stresses to Starship itself and fancy in-space
maneuvers and configurations, over more straightforward docking and roll.

There are a TON of issues remaining to get crewed Starships to Mars. For
starters I think Elon is totally underestimating the complexity of a
working life support system that can sustain for the months needed if in
a Hohmann transfer orbit let alone once on Mars for a year or so. The
hab scheme gives you artificial gravity but doesn't simplify the life
support issue, just the opposite.

No matter how you slice it, there is complexity to artificial gravity. I
have the sneaking suspicion that EM thinks this can be short circuited
by routine exercise inside a Starship. If I can compensate for the
deleterious effects using exercise, drugs, or alcohol (lol) well...
'tight is right'. :-)

I've reflected on these issues before, which given what SpaceX is doing
vs some of the still to be resolved issues for Mars & Mars transit,
makes me think the Moon is still much less of a harsh mistress and the
hidden agenda here.

Dave