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Old May 26th 19, 01:16 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default Two Starships in "bolas" rotation

In article , says...

On 5/21/2019 2:15 PM, Niklas Holsti wrote:

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


This very type of configuration of Starships has been discussed here
before. It is not an unrealistic approach. However I was unaware that
the SpaceX plan called for two Starships to make the journey all the way
to Mars. Two Superheavys (or whatever SpaceX is calling the BFR these
days) where planned but one of them was not a Starship destined for Mars
but a fueling pod for the Starship that was. That's the plan I remember.


This is all still very notional since Starship/Super Heavy has yet to
fly. But I do believe the plan was always for Starships to make the
journey to Mars in pairs. That would provide redundancy. Tankers are a
separate thing which are obviously needed in order to top off the
propellant tanks of Starship.

And to do this "right", IMHO, you need even more Starships. What you'd
want to do is to preposition a return Starship (or at least a propellant
production Starship which would stay on Mars) which would produce
propellant for the return trip. Once that's "full", you'd send your
crewed ship. Otherwise, there's no coming back if the crewed Starship
fails to make its own propellant once on Mars.

The only way the delta-V case for crewed Mars missions is by using in
situ propellant production.

But frankly I think Mars is a long way off. In fact the Moon is
becoming a major distraction.


Agreed.


And that actually makes sense since all this
hardware can be tested out far more easily on lunar missions.


Disagree. The hardware will be very different between the two. For
starters, the landing mode is different. Mars has a thin atmosphere
which you want to use to shed as much delta-V as possible. The moon
lacks any atmosphere. This also means that in situ propellant
production will be completely different. On Mars it will rely on CO2
from the atmosphere. On the moon, it would rely on any water which can
be produced from local resources. This means different fuels will be
produced (methane on Mars, LH2 on the moon). So even the engines will
need to be different. In fact, the difference in atmospheres drives a
lot of the engineering, so the hardware just won't be the same at all.

Second, power generation challenges are different. The long lunar night
makes for a large electricity storage requirement. Mars night is much
shorter. Mars dust storms provide a challenge for solar arrays. The
moon has no dust storms, but does have dust which can be kicked up by
human and robotic activity and then stick to surfaces via static
electric forces.

Third, spacesuits are likely to be quite different. The 1/6 gravity of
the moon allows for much more massive designs than Mars suits. This is
a huge challenge when designing practical Mars suits.

Fourth, dust challenges are different. Both bodies have dust. But the
dust is hugely different. On Mars you have dust storms and the dust can
have perclorates in it which make it toxic, so it has to be dealt with
in order to prevent humans from coming into contact with it. On the
moon, the dust has super sharp edges due to no weathering and it is
famously abrasive. It's primary health hazard would be the lungs, which
don't tolerate small particles of any origins. But lunar dust is
largely non-toxic in other respects. So even though "dust bad", the
solutions for dealing with that dust might end up being different due to
the different properties of that dust.

I'm sure I could go on, but I think I've made my point.


If you want to go to Mars, go to Mars. Going to the moon first is
largely a distraction because most of that "experience" gained will be
thrown out and nearly everything will need to be re-engineered
specifically for the Martian surface environment.

There is a
push within NASA to refocus on the Moon and a lunar base, by any means
possible. If that means contracting with private enterprise to do it, so
be it. We will have to wait and see how Starship does in this regard.


Clearly, especially since the current NASA plan of record doesn't
include Starship in any meaningful way. It still relies heavily on
SLS/Orion, so we will be limited to one crewed mission per year. That's
pretty weak sauce considering how "close" the moon is.



We are along a familiar trajectory here. Same one as was taken for
recoverable Falcon 9 stages. I think Starship will focus on P2P
suborbital trajectories first to establish launch and return procedures
that must work anyway.


Only if they can find a paying customer. Such flights without Super
Booster would be severely limited in P2P range. All P2P promotional
videos made to date show Starship being lofted by Super Booster. I
personally think we'll see Starship only flights for testing, but
nothing else.

Then a push to orbit, then a push beyond.


I personally think the "push beyond" will take a very long time. Once
Starship/Super Booster is flying to earth orbit, its primary mission
will be Starlink satellite deployment. Yes you can keep flying up to 60
Starlink satellites at a time on Falcon 9 (more polar orbits will either
have less satellites or require Falcon Heavy launches), but when the
goal is on the order of 12,000 satellites (by the mid 2020s), that's at
least 200 Falcon/Falcon Heavy launches in a few short years! If we
guess those launches cost on average $50 million each, that's $10
billion in launch costs just to get the initial constellation up and
running!

And keep in mind the lifetime of these satellites is relatively short
(from memory something like 3-5 years), so this isn't a "one time"
thing. If Starlink is successful, SpaceX will be continuously launching
its own Starlink satellites for some time to come.

SpaceX needs Starlink for the potential revenue to attract investors to
develop Starship/Super Heavy. But SpaceX also needs Starship/Super
Heavy to launch and maintain the Starlink constellation.

Mars is still Musk's ultimate goal, but Starlink will need to come first
in order to provide the massive cash flow needed to turn Starship from a
cargo launcher into a true crewed spaceship capable of performing an
actual Mars mission. IMHO, of course.

Opening
out the envelope becomes easier the further along the curve you get.
However the first part of that curve is the hardest.


Each part of the development of Starship will present its own
challenges. But getting it from development to a cargo launcher
involves the same types of challenges that Falcon development had.
They've done this before.

Going from cargo launcher to crewed Mars spacecraft involves a whole
host of other challenges that SpaceX has yet to face. That's where the
true "unknown unknowns" are hiding.

Talking more about the configuration of the two Starships on an actual
flight to Mars is a tad premature, IMHO, so I'm going to snip the rest
of the discussion, interesting as it is.

Jeff
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