
Wouldn't it be more viable to build a Mars Space Station on Earth's orbit? - Mikho
Wouldn&#x27;t it be more viable to build a Mars Space Station—ark—on Earth&#x27;s orbit and send it to Mars orbit at the next launch window?<p>This would save a lot of money and years of time as it won&#x27;t require building many dedicated BFRs for every payload and pack of passengers allowing to use existing SpaceX Falcon rockets to bring all required payload to the orbit continuously. It would also allow starting habitat construction near Earth that could save time between the launch windows. Later the whole thing with payload and people could be sent to Mars orbit where it would unload half-baked constructions on Mars and serve as a post between Earth and Mars.<p>While on Earth&#x27;s orbit this could attract a lot of attention, money serving for sponsors&#x27; PR, and as a tourist attraction for riches.<p>Do you think financially and from time frame consideration building the MSS could be more viable than building many BFRs to launch everything during the launch window and only then start construction on Mars?
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rbanffy
There are a couple downsides to send a single thing.

The final propulsion needs is mostly the same, so you won't pay more to push
stuff to Mars than you would to boost that stuff from LEO to a Mars transfer
trajectory. The mass and delta-v being the same, the propulsion budget is the
same.

Say, if you assemble it and then something happens and you can't slow down and
enter Mars orbit, you lost the whole thing.

If the station is assembled, it's shape won't probably work well for
atmospheric braking and would require a bit more fuel to slow down. A single
module could, conceivably, dive deeper into the atmosphere and shed more speed
with that.

Acceleration loads on the assembled thing are also to be considered. If we
decide against chemical rockets, the question is mostly moot - acceleration
will be low, but constant.

If we send multiple modules separately, we end up with a lot of propulsion
capacity that, with some clever design, can be reused for landings and orbital
ascents. You can never have too many of a single thing when you are that far
from Earth.

The upside is that it's easier to assemble everything in Earth orbit and it'd
be easy to teleoperate robots.

Having said that, I suppose an extra week living in the Earth-Mars transit
vehicle while the arriving crew assembles their home is not a big deal for
someone who already spent 3 months in transit.

edit: if we are to do that, putting a station in a cycler orbit would probably
be more interesting. That way you depart Earth with supplies and rendezvous
with your living quarters for the trip. The cycler can have the shielding to
protect astronauts on their way.

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Mikho
There is no reason for the whole station to land on Mars. Approaching Mars the
whole thing would split to start breaking. Big parts of it (bigger than a BFR)
with payloads--half-baked assembled constructions--would separate and enter
Mars atmosphere for landing. Then the station itself will be less heavy for
breaking using the gravity of Mars and its orbit for that.

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rbanffy
I think we were talking about a space station. If it ever lands, I assume it'd
be unintentional.

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Mikho
Yep. SS. Also apart from the tech stuff, it's important to consider financial
and administrative issues. Building the thing near Earth allows making it
attractive for sponsor/ad money and save construction and preparation time
starting earlier in space using Falcons. Meaning existing plan does not allow
any payload launched unless BFR is built. Not to mention spending fewer
resources to build all that BFRs required launching all payload simultaneously
during the launch window.

P.S. BTW, ISS has limited service time left. So there is a need to plan
construction of a new Space Station on Earth's orbit in any case.

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rbanffy
You don't need - and you don't even should - launch all pieces at once. You
can launch them into the same orbit so they meet at some point. It's easier to
make the parts meet in Martian orbit because the distances allow for finer
corrections over longer periods of time. It doesn't matter if some pieces
arrive months or years before others as long as they are all there when it's
time to assemble the station.

A Falcon Heavy can take about twice as much cargo as a shuttle could to the
ISS. This means the launch costs of upgrading/refurbishing the ISS, or even
replacing it, just got much lower, and the whole process requires half as many
launches (and the modules can, now, be bigger than the shuttle payload bay).

I assume the BFR should be able to take, with a non-reusable second stage,
almost a whole space station, ready for assembly. Or to carry large modules,
such as a centrifuge, so that astronauts don't need to be continually exposed
to microgravity during their entire stay in orbit.

And with the full BFR, it can return ISS modules to the ground for study or
refurbishment which, I assume, is valuable as it allows the study of
structures and materials exposed to space for decades, as well as reflight of
existing and already validated components.

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aurizon
We do build them all on earth, orbit them and send them to the Moon or Mars
etc and land/orbit them for their tasks.

A large structure - too large to launch as a complete station should be
orbited here as many separate loads and then assembled to form the station,
and then sent to Mars - as you suggest. It is not practical to send the loads
to Mars and assemble there.

Every item from earth has a huge cost. Items made from loose asteroids, the
Moon, Mars etc may well be a lot cheaper. You must bear in mind that
elements(metals, Oxygen etc) would need to be extracted and made into raw
materials suitable for whatever you want to make. That means each one would
need to be screened about the relative energy economics. Few items from
asteroids could be used as they are found.

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api
The problem with this is the delta-V requirement to actually send it to Mars.
Even with in-orbit refueling as proposed by SpaceX you'd probably require a
big rocket and/or a lot of fuel to send something really massive.

Ion rockets might be used but that would make the trip take forever and would
be very costly.

There do exist very slow low-energy transfer orbit trajectories, but AFIAK
those require you to start at various Lagrange points. So maybe it could be
done but you'd have to build it at a Lagrange point, destroying the cost
savings, and it would take forever to deliver to Mars.

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Mikho
Sending simultaneously many BFRs basically with the same payload right from
Earth I'd say would require even more fuel, lot's of investments to build that
many BFRs and then construction need to be started from scratch after the
launch on Earth and on Mars after unloading. So all the time and money will be
spent to build a huge amount of rockets.

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IntronExon
The major cost is lifting mass out of Earth’s gravity well, so if you really
want to cut costs we require sources of materials which don’t come from Earth.
Once you have this, and build your station, why send it to Mars? Keep it here,
or send it to a planet with resources we can use (a moon of Jupiter might
work).

You’d need a compelling reason to do this, since the cost from R&D to launches
would be in the trillions and take decades.

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Mikho
IIS has not so many years left to live, BTW. Space Stations as posts on orbits
are good for many practical and scientific reason.

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IntronExon
Absolutely, but to me that’s an argument for space stations in orbit around
Earth, not Mars.

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Mikho
Agree. Though one does not exclude another. Starting with a new ISS to test
ideas and tech and extending it later to SS for Mars would be logical.

