
To save on weight, a detour to the moon is the best route to Mars - jimsojim
http://news.mit.edu/2015/mars-mission-save-weight-fuel-on-moon-1015
======
Ankaios

      “This is completely against the established common wisdom
      of how to go to Mars, which is a straight shot to Mars,
      carry everything with you,” de Weck says. “The idea of
      taking a detour into the lunar system … it’s very
      unintuitive."
    

and later...

    
    
      “Assuming you can extract these resources, what do you
      do with it? Almost nobody has looked at that question.”
    

Give me a break. People discuss this sort of approach all the time. They don't
necessarily publish their conclusions, though.

~~~
avmich
They do sometimes; a lunar resources conference, in the aftermath of Apollo
missions, had discussions regarding use of Moon regolith for things like
refueling.

~~~
Ankaios
Yeah, there's loads of great analysis of lunar resource use from that era, and
propellant for use beyond the Moon is a major motivation for the current
interest in lunar polar volatiles. For them to act like the notion that lunar
resources could be valuable for trips elsewhere is a major revelation is
ridiculous.

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givan
We still use chemical propulsion almost everywhere from cars to rocket
engines, a breakthrough in propulsion systems will not only make solar system
exploration feasible but will be greatly beneficial to our society by reducing
pollution and costs.

We need the next steam engine for a new industrial revolution, space
exploration and our society depends on it.

I think that all space resources should be channeled into this, our current
approach to solar system exploration is the same as trying to explore the
world by foot, expensive an inefficient and no matter how big our ambitions
are we don't have the technology to accomplish them.

~~~
raducu
Exactly! Nuclear thermal rockets/fission-fragment rockets are the way to go,
but you can't launch them directly from Earth because of the nuclear fallout.

~~~
Gravityloss
Well, you can't use them for launch. And there's lots of other options for in-
space propulsion.

The specific impulse is "only" double that of chemical ones, and there's
potentially a large dry mass penalty.

~~~
raducu
You mean the specific impulse for nuclear thermal rockets, as far as I know
the fission fragment rockets have ISPs in the 10^5 range.

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Nexialist
You can already produce fuel on Mars itself using the Sabatier Reaction with
technology available today, you have to bring along a little hydrogen but
that's not too big of a deal.

Refueling on the moon requires an (almost pointless) web of infrastructure
that balloons the cost of a mission, and more importantly, increases the time
to carry out the mission.

Each US administration has a habit of cancelling the more ambitious NASA/JPL
projects of the previous one, so if we really want to go to mars, it has to be
a mission doable in as short a time span as possible, such as proposed by
Zubrin's Mars Direct plan.

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sandworm101
Does anyone writing these papers have any appreciation for the difficulties of
producing liquid H2 appropriate for use in manned rockets? This is some
seriously tricky stuff. Turning water into liquid H2 is one thing, making it
out of dirty moon-frost is another. A little impurity here and there and your
rocket engine becomes a bomb.

~~~
avmich
Detander - a gas liquifier - can be pretty small and lightweight even for a
big flow. Industrial hydrogen liquifiers are built routinely since 1950s if
not earlier.

If you're trying to liquify hydrogen, you'll find out that most - almost all -
impurities in the gas become liquid or solid before hydrogen becomes liquid.
That's a good way to clean hydrogen, so you won't have an odd mixture as the
result.

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Gravityloss
Asteroids are even better for resource utilization.

They might be far away in space but a lot closer by delta vee, and they can be
reached, mined and escaped with low maximum thrust, meaning very efficient
propulsion methods can be used.

This discussion just goes around in the same stupid circles for decades. We
know so many better ways of doing things, but they can not be done for
political / PR reasons.

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p4bl0
If you have one hour if front of you, I highly recommend this documentary:
[https://www.youtube.com/watch?v=tcTZvNLL0-w](https://www.youtube.com/watch?v=tcTZvNLL0-w)

In it they explain how it would be feasible to be on Mars in ten years with
current technology and not so much additional fundings.

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golergka
I've done that in KSP, seems to be working.

~~~
sandworm101
Do it in RSS, or even 64k. Stock KSP is a tiny tiny place.

~~~
runholm
Doesn't that just increase the gain of doing the refueling?

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rl3
Seeing as the title could be a bit misleading, I'm glad the article clarifies:

> _Ishimatsu says the research demonstrates the importance of establishing a
> resource-producing infrastructure in space. He emphasizes that such
> infrastructure may not be necessary for a first trip to Mars. But a resource
> network in space would enable humans to make the journey repeatedly in a
> sustainable way._

In other words if we want to get to Mars ASAP, setting up lunar mining and
refueling infrastructure probably isn't the fastest way to go about that, even
if it is more mass efficient.

~~~
IndianAstronaut
I am curious as to why we just don't set that up on Mars to begin with. Set up
a manufacturing infrastructure and an agricultural base.

~~~
chisleu
Because everything you take to mars costs ~68% more fuel to get off of earth.
Getting off of Earth is much harder than getting off of the moon, which has
~86% less gravity.

If you only take enough fuel to get to the moon, then you can load up there
and enjoy a significantly easier time to get up to speed on the way to Mars.

I didn't see how much of a percentage difference it is in total fuel though,
in the article. I'm expecting it is pretty close or they would have cited it
instead of the Earth liftoff reduction.

~~~
Cshelton
Well another consideration is the additional time added to the Mars trip.
Right now, going directly from Earth, around Earth a bunch of times, then
straight to Mars will be 6-9 months one way, which I believe the opportunity
to come back would be ~2 years after arriving (I may be wrong here). So,
assuming we are doing a round trip and not one way, it's already a 3 year trip
ish? Either way, I see building a launching space station orbiting earth as
the best way. Use smaller rockets like the falcon 9, get a bunch of fuel into
orbit, build the ship from many parts and trips, then launch from Earths
orbit. Make the built ship reusable for many Mars trips. Like in the
Martian...

~~~
TeMPOraL
A fuel station in LEO may be convenient, but it will still be much cheaper to
ship fuel from the Moon than from the surface, Δv-wise. Per a handy Δv map[0],
it's about 2.5km/s (if you aerobrake) vs. almost 10km/s to lift fuel from
Earth.

[0] - [http://i.imgur.com/SqdzxzF.png](http://i.imgur.com/SqdzxzF.png)

~~~
sandworm101
Aerobrake a couple tons of liquid H2 and O2 in earth's atmosphere? Assuming it
doesn't all boil off, it would certainly make for some nice fireworks.

~~~
TeMPOraL
Add moar heatshields, eh? ;).

Also, I was thinking more about dipping in the atmo a little, doing the kind
of aerobraking the ISS has to fight all the time. You don't have to make the
entire insertion in one orbit.

~~~
sandworm101
A slow series of aerobrakes would run up against the time factor. Today's H2
storage boils off about 1% per day. So if you spend a few weeks slowing things
down gradually you quickly defeat the advantage as much of your fuel has
escaped.

~~~
TeMPOraL
Didn't consider that. Thanks!

EDIT: Maybe there are some improvements for storage available that don't make
sense on Earth given H₂ prices? A magnetic containment field, perhaps? Or
whatever chemistry shenanigans are used for hydrogen fuel cells? You would be
trading the time factor for mass and volume (the latter doesn't matter that
much in space, and could even help with aeroinsertion), but it may still add
up moneywise.

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droithomme
Interesting. This was the claim of the Bush administration, that the moon was
the route to Mars, but that program was cancelled after being ridiculed.

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Johnny555
This point is key:

"assuming the availability of resources and fuel-generating infrastructure on
the moon"

Sure, if the moon is a gas station, then stopping there to fuel up on the way
to mars makes sense. But it's making a big leap of faith that refueling
infrastructure and raw materials can be reasonably built on the moon.

~~~
TeMPOraL
ESA seems to be interested in pushing that angle. The recent announcement was
very refreshing to hear[0].

I like to imagine it's Musk radiating enthusiasm for rubbing progress into our
faces, but whatever it is, something seem to have caused a renewed interest in
manned space projects. Maybe it's just ESA and NASA stepping up their PR game.
But whatever it is, I'm thankful and have high hopes!

[0] - [http://www.space.com/29285-moon-base-european-space-
agency.h...](http://www.space.com/29285-moon-base-european-space-agency.html)

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roflchoppa
if you remove mass from the moon for fuel, does that not effect the orbit of
the moon, and with that the tides?

~~~
TeMPOraL
If you start spinning counterclockwise, you're robbing Earth of angular
momentum and shortening the day. Source:
[https://xkcd.com/162/](https://xkcd.com/162/).

The point is, Moon is big. It will be long, long time before we could do
anything there that could make a measurable difference in Moon's orbital
parameters or tidal forces it generates.

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Sir_Cmpwn
Another issue with this would be that a Mars vehicle would probably be big,
and to a large extent designed to never land on anything. Getting it down to
the Moon safely and back out again would be very complicated. The solution is
to do a fuel run with a smaller craft that can disengage from the main craft
several times, but then you're doing several landings and takeoffs and that's
going to shoot the risk WAY up.

I think that we would be wise to invest in a space elevator on the Moon. We
can't support one on Earth with currently understood technology, but the Moon
is different and it could be done with modern materials. A plan of this sort
would seriously reduce the cost of lunar development and increase the
viability of the plan in the article.

~~~
phire
The risk of multiple moon landings and takeoffs is really quite small as the
moon has no atmosphere.

Perhaps not mission critical small, it might be in the range of 0.1-2% risk
for each landing/takeoff cycle. So if you require 10 refuelling launches, your
total risk is 1-20%.

Say you had a large moon lander, or multiple landers that make up a robotic
fuel collection and refining system. Then you have a reusable lander-launcher
that lands, collects the fuel and delivers whatever it doesn't use for
takeoff/landing into a orbital fuel deport orbiting either the moon or earth.
Actually might be best to have your deport orbiting the moon until it's full
then send it on a slow, low-fuel, multi-month path back to earth orbit,
perhaps you meet the Mars transfer vehicle there.

If at any point the fuel transfer lander-launcher fails, you can launch a new
one from earth and push back your Mars mission. Perhaps you have multiple fuel
transfer landers as a contingency, or to increase throughput (fuel in orbit
isn't just useful for a single Mars mission)

Only once you have your fuel ready, do you launch your Mars crew.

You could do a similar setup at Mars to collect fuel for your trip and avoid
having to drag that fuel from the moon. But a Mars fuel transfer lander-launch
would be much more complex and risky, and it would be a lot harder to land the
fuel collection/refining facility.

~~~
Sir_Cmpwn
Don't forget to add the rendezvous risk. It would also be extremely difficult
to try and send it to meet the vehicle during the Mars transfer - the launch
window eventually closes, and even during the launch window the ideal
trajectories are quite different.

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greglindahl
Another way to "save on weight" is to use the lowest-cost launch from Earth,
and rendezvous in orbit. We're going to know what the risk and cost of
reusable Falcon 9 and Falcon Heavy is long before we'd start building this
lunar base. A 75% reduction in SpaceX's already low launch rates would be a
big savings.

We even have experience launching fuel to ISS on the Russian and European
unmanned supply ships.

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yCloser
I bet the author just installed Kerbal Space Program...

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LoSboccacc
Can't find paper but I wonder if he'd taken into account near future
technologies, like orbital construction (look at the IIS, that was 'built' in
orbit) and fully reusable rockets.

Anyway I do believe we need to establish a resource operation on moon just
because debugging a resource operation on mars as our first space colony would
be all too risky.

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atomicbeanie
I first read about this idea in [http://www.amazon.com/Orthogonal-Galaxy-Book-
ebook/dp/B00QD3...](http://www.amazon.com/Orthogonal-Galaxy-Book-
ebook/dp/B00QD35580/ref=sr_1_1?s=digital-
text&ie=UTF8&qid=1445001975&sr=1-1&keywords=Michael+Lewis+Galaxy)

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Armisael16
Obviously getting a chance to refuel en route is huge for saving dv - the
rocket equation is a harsh mistress. Honestly, I'm a little surprised that it
isn't more efficient to move the fuel for lunar orbit to LEO.

~~~
TeMPOraL
If you're flying prograde wrt. the Moon, you'll still be burning enough Δv to
reach the Moon, so it may seem to be more efficient to just get yourself
captured there, fuel up, and continue away.

I haven't had time to play KSP in half a year, so my intuition may be a little
off.

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jackreichert
On a similar note, I do think that best way to get a shot at better and more
investments in space would be to build a hotel on the moon.

(Maybe I should submit my blogpost about that to a journal to get academic
cred.)

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greesil
Oh wat no slingshot?

~~~
lucaspiller
Once you've refuelled on the Moon, you can do an Earth flyby (with a small
burn) to reduce the delta-v required to escape the Earth-Moon system. This is
what the Nozomi craft tried to do:

[https://en.wikipedia.org/wiki/Nozomi_%28spacecraft%29](https://en.wikipedia.org/wiki/Nozomi_%28spacecraft%29)

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foota
But what about the mass depletion to the moon!
([https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress](https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress))

