
Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says - extarial
https://www.scientificamerican.com/article/moon-is-stepping-stone-not-alternative-to-mars-nasa-chief-says/
======
xefer
A couple of interesting points to consider when thinking about putting a base
on the Moon:

"Each Apollo mission increased the mass of the lunar atmosphere by about 30%,
and it took several weeks for the atmosphere to return to its natural state.
Highly sensitive measurement or communication instruments may be affected by
the additional atmospheric particles." [1]

"Studies have also revealed that the balance is very delicate. At present, the
solar wind sweeps the lunar atmosphere into space very efficiently, limiting
its density to that of a collisionless gas (an exosphere). If the atmosphere
were, however, a factor of just 1000 denser, this process would invert itself
and the atmosphere would remain stable for tens of thousands of years. Just
the Apollo missions to the Moon increased the atmospheric density by a factor
of 10 with rocket exhaust (mostly CHON compounds). Large scale human activity
on the Moon could push the total mass over the limit and create an artificial
atmosphere, pushing the Exobase off the surface and creating a stable, if
highly tenuous atmosphere which could threaten precisely the most important
asset that the Moon can offer us: its sterility and almost atmosphereless
nature." [2]

[1]
[http://www.tsgc.utexas.edu/tadp/1995/spects/environment.html](http://www.tsgc.utexas.edu/tadp/1995/spects/environment.html)

[2]
[https://web.archive.org/web/20050214155703/http://www.iac.es...](https://web.archive.org/web/20050214155703/http://www.iac.es/galeria/mrk/atmo_lun.html)

~~~
tomatotomato37
I'm not really convinced this is something to worry about. If the vaccuum is
this unstable it would be eventually be inflated anyway by a comet or gaseous
asteroid collision, and it's a happy coincidence that the moon hadn't lately
had a significant collisions in the period of history that we were able to get
up there and measure it.

~~~
Latteland
I agree, is there really that much value in the moon being sterile and having
no atmosphere. If it had one that was much denser, we could use aero braking.
This would be far away from that.

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davedx
Ugh.

Zubrin's 'The Case For Mars' (which on reading, it's obvious SpaceX have based
a lot of their strategy on) is categorically against going back to the Moon
and using it as a 'stepping stone'.

Zubrin's 'Mars Direct' architecture shows quite plainly that it is possible
using current technology readiness levels and funding to send a significant
scientific mission to Mars _directly_ , without the need for huge orbital
infrastructure or Moon Bases.

I had a similar feeling when SpaceX announced their #DearMoon project. I truly
hope the Moon doesn't distract them from their true goal: the timely
establishment of a permanent human presence on Mars.

We've been to the Moon. We don't _need_ to go back. We _need_ to aim higher.

~~~
martythemaniak
Depends on what the moon missions are. Building moon-specific infrastructure
(ie adapting things to 14 day long light / dark cycles, 0.3g) would be a
distraction. Using it as a close - by testing ground probably doesn't matter
except it had the upside of possible getting people excited.

For example, spacex wants to test the BFS. They could send it on a wide orbit
2 days away, or they could orbit around the moon instead. Going for the moon
is probably only slightly different (ie different orbit insertion) but other
than that it would be the same, except awesome pics/video.

~~~
njarboe
If the moon's gravity was 0.3g, that would be close enough to Mars'(0.38g)
that it would be useful as a prelude to a Mars landing/exploration/occupation.
Unfortunately the Moon's gravity is 0.17g, so not as relevant.

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fireismyflag
The moon has 1/6th of Earth's gravity and 0% of our atmospheric pressure.

Mars has 1/3rd of the gravity and 0.6% of the pressure.

Those 2 factors make them very similar to each other and the distance makes
the moon the clear candidate for a first step.

~~~
logfromblammo
Transport between bodies in space is measured by kilometers per second as
delta-V, not kilometers.

    
    
      Earth  LEO     9.3  km/s
      LEO    escape  3.22 km/s
      escape MTO     0.6  km/s
      MTO    MCO     0.9  km/s
      MCO    LMO     1.4  km/s
      LMO    Mars    4.1  km/s
                    -----
                    19.5
      
      Earth  LEO     9.3  km/s
      LEO    LLO     4.04 km/s
      LLO    Moon    1.87 km/s
                    -----
                    15.2
      
      Moon   LLO     1.87 km/s
      LLO    escape  1.40 km/s
      escape MTO     0.6  km/s
      MTO    MCO     0.9  km/s
      MCO    LMO     1.4  km/s
      LMO    Mars    4.1  km/s
                    -----
                    10.3
      
      (Earth -> Moon -> Mars = 25.5 km/s)
    

In order for the Moon to be a stepping stone, it would have to be a refueling
station where most of the mass involved ultimately comes from the Moon, rather
than Earth. As it is now, the Lunar industrial plant produces 0 Mg of rocket
fuel annually. For 30% more delta-V, a rocket from Earth can just go to Mars
directly.

~~~
Nomentatus
Thanks for the numbers.

30% of delta-V but much more than 30% more fuel used (etc) since "compound
interest" applies as you're using fuel to ship fuel out of orbit and then much
of that fuel again to change your orbit to mars, etc.

Similarly, Napoleon came up against the limits of using horses to pack hay for
horses invading Russia - compound interest; you can only do so much.

PS - that 30% assumes a path that I don't, and no solar power used to catapult
oxygen off the moon. I'd go for a Lagrange point you're ignoring.

PPS - you've assumed Mars, not, say, near-earth asteroids or trojans with a
very different, far lower delta-V. Vastly different problem.

~~~
logfromblammo
Going directly from low orbit to a transfer orbit to the second body will
usually save some delta-V over going to escape orbit first and then going to
transfer orbit. I didn't have the numbers for low lunar orbit to Mars transfer
orbit, so I changed the Earth to Mars path for a fairer comparison.

I didn't forget the Lagrange libration points, but decided not to include them
because they were not relevant to the parent comment, and they would still
require some mechanism to get propellant mass up to them. They're currently
almost empty, and won't be very useful until the Moon itself has launch
capacity to get water up there. Again, I was mainly responding to the parent
post.

The rocket equation is indeed a bear. As delta-V scales linearly, fuel
requirements scale up exponentially. One way to manage it is to use stages.
Another is to refuel and assemble vehicles higher up in the gravity well. As
it happens, shipping tanks of fuel and propellant up to LEO separately means
that missions to Mars starting fully fueled from LEO would require only 0.9
km/s more than missions starting from the lunar surface. Measuring by delta-V,
LEO is at about the halfway point for an Earth-Mars mission.

But it's also worth noting that the surface of the Moon is closer to LEO than
the surface of the Earth. Shipping fuel and propellant from the Moon to LEO,
to rendezvous with and refuel a vehicle coming up from Earth, is even cheaper
than shipping up the resupply mass from Earth.

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lostmsu
I profoundly disagree. IMHO, the destination is open space, not another
planet, and the gravity well on the Moon is waaay easier to overcome.

~~~
sp332
What's interesting about open space? To me it's the _stuff_ in space that
makes interesting destinations.

~~~
monocasa
There's a lot of stuff in space that isn't in a deep gravity well of a
spherical body. For instance mining asteroids enough to have a self sustaining
manufacturing base at micro-g could allow for the earths manufacturing and
power generation needs to be met somewhere that's not on the Earth, decreasing
pollution.

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jakamau
Asking from a point of ignorance, but are there major paradigm changes that
are possible by having a "drydock" on/near the moon? Why is this seen as a
major waste by critics?

\- Are we largely constrained in our ship design since everything has to be
structurally capable of handling launch and re-entry from earth's gravity
well?

\- How would our ship designs change if they were just meant to transport
heavy loads and never actually re-enter a major gravity well? Similar to the
Gateway hand-off mentioned in the article

\- Wouldn't asteroid mining, resource harvesting be easier from a semi-
permanent base that's still reasonably close to earth?

\- Doesn't "Moon Base" just sound really freakin' cool?

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tarruda
Interesting related video from Kurzgesagt released 1 week ago:
[https://youtu.be/NtQkz0aRDe8](https://youtu.be/NtQkz0aRDe8)

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ArchTypical
If you can't make a base on the moon, why risk trying to make one on Mars?
It's impractical from a risk perspective.

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cheeko1234
Robert Walker on Quora is a prolific writer regarding this.

[https://www.quora.com/profile/Robert-
Walker-5](https://www.quora.com/profile/Robert-Walker-5)

Specific answer to why moon first:

[http://qr.ae/TUGvkb](http://qr.ae/TUGvkb)

~~~
tomp
I find his answer entirely unconvincing.

> I think we are best not rushing into space, there’s no hurry about that.
> Let’s find out about space first, explore, learn, learn about our own
> capabilities too, [...]

Exactly the same argument can be made _then_.

> [...] have settlements in space when and where they are acutally needed, as
> the needs arise.

By then it will be too late. The idea is that we _learn by doing_.

> All this is hugely expensive and Earth would have to foot the bill. Because
> there is no way that they are going to turn a profit on Mars.

All this is hugely expensive and UK would have to foot the bill. Because there
is no way that they are going to turn a profit in America.

> Not many peopole could afford a $200,000 spacsesuit.

"640K ought to be enough for anybody"

The most convincing part of his argument is weeks-long Martian dust storms.

------
yazr
How "self sustaining" will a Mars base ever be ?

So let assume they can make oxygen, water, maybe even calories. Great. Self
supporting base.

But other than that. Everything will have to be trucked in. Pipes, electrical
wires, valves, medical supplies, antennas, plastics, etc.

Will any of these be manufactured on-site in say 2050 ?!

~~~
ng12
I'm far from an expert on either chemistry or manufacturing, but there's
credible arguments that almost everything you need can be obtained locally:
[http://canada.marssociety.org/winnipeg/plastics.html](http://canada.marssociety.org/winnipeg/plastics.html)

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zwieback
Human space flight - what a waste of resources. Send robots for the next 100
years.

~~~
cuboidGoat
By the end of this century I suspect there will be more than a million people
living off earth, with the majority in orbitals.

In about 200 years or so, I wouldn't be at all surprised if there were more
people off earth than on it.

~~~
chr1
What would be the incentive for living off earth for such a large number of
people?

I really wish for you to be right, but with population growth slowing down,
and possibility of building floating cities or terraforming Sahara, building
large orbital stations or going to mars in large numbers may be economically
not viable, unless we invent something radically new.

~~~
Kim_Bruning
Same incentive as everywhere. They get paid. ;-)

Even the most automated of robotic factories on earth still have a number of
humans in an oversight role, where they make themselves quite useful.

The same would be true of any space industry. People would be hired on for a
tour in space, and they'd be paid sufficient salary to make it worth their
while.

~~~
cuboidGoat
And when you are up there, you will want to stay up if you can, as each dip
into the well costs you a ton of money.

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nonbel
Everyone just wants NASA to do something cool. The probes are ok, but pictures
of rocks are getting boring. This requires risks...

And sadly, I would expect the end result of this sentiment to be fewer probes
rather than cooler projects.

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sunstone
So, baby steps. :)

~~~
rripken
If that's the case isn't the next step a base on Phobos or Deimos?

~~~
superkuh
Yep. You need less change in velocity to get to their surface than to land on
the Moon.

