Re: Improved lunar landing architecture



Cardman wrote:

I believe you would have to do the same for Mars, call the expense 1 km/sec because of Mars' thinner atmosphere and lower gravity. 


I am not so sure about that. The atmosphere on Mars is a great deal
thinner, where just going up a short distance can be compared to this
higher Earth atmosphere.


With the smaller Martian gravity, Mars' atmosphere thins more gradually.

On earth the mesosphere is where meteors (and sometimes spacecraft) burn up. This is about 80 to 100 km up. I believe the altitude is comparable on Mars.


So I do not see why you cannot take a more direct orbital route, when
going into Mars orbit. Still, I will leave that to those people who
desire to do the full calculation to see just what is the ideal flight
path.


So Hohmann insertion from Mars: 6.6 km/sec because of atmosphere. 


Good enough.


To get from Mars to Phobos takes 5.9 km/sec and to Deimos 6.36 km/sec (this includes the 1 km/sec atmosphere delta vee expense)

You might say "Wait a minute. 5.9 or 6.36 is almost the same as 6.6 km/sec. It'd take more delta vee to make a pit stop at Deimos or Phobos." 


Yes, I do say that.


However the ship from Mars to Phobos (or Deimos) need only provide air, water, etc. for a few hours. The ship from Phobos (or Deimos) to earth must provide radiation shielding, food, water and air for a 7 month journey. This ship is far more massive. It makes more sense to launch the massive interplanetary craft from Deimos or Phobos than it does from the martian surface. 


While that is true enough, you overlook the other option. As the ideal
craft, for such a long trip, is best left simply moving between HEO
and HMO, and then back again.

So that is almost exactly like your Phobos or Deimos based craft, but
now you save like 30 years on completing this unnecessary Mars orbital
infrastructure.

The only difference is that all your fuel, cargo, and people, have to
be launched directly from Mars surface. And only the additional fuel
(and a few extras) is additional to your method.


You think "the additional fuel (and a few extras)" is trivial?

The rocket equation:
Mf/Mp = e^(dV/Ve) - 1

Mf = mass fuel
Mp = mass payload
e  = approximately 2.72
dV = delta vee
Ve = Velocity exhaust.

In short your fuel requirements go up _exponentially_ with delta vee increases. And with more fuel, large fuel tanks must be added to the payload.

Zubrin advocates methane and oxygen rocket fuel made from Martian in situ resources. Exhaust velocity of Methane and oxygen IIRC is about 3 km/sec.

Launching from Mars:   e^(6.6/3) - 1 =  about 8.

You'd need eight times the fuel mass of your interplanetary hab & large fuel tank.

Launching from Deimos: e^(2.4/3) - 1 = about 1.2

Launching from Phobos: e^(1.8/3) - 1 = about .82.

Also much of your payload: oxygen, water, radiation shielding, etc. could come from the Martian Moon.


But for Mars to Earth trips it would make sense to send your interplanetary ship from Phobos or Deimos fuel depots.


Local fuel at the expense of time, money, and infrastructure.

It will also take a lot of time and money to set up rocket fuel making infrastructure on Mars.

Plus launching through an atmosphere subjects the ship to vibration, high temperatures and other stress. It would be better to launch interplanetary ships from a more benign vacuum environment.


Also I am doubting that these two moons are even moving in the right
direction for moving between them and Earth. And so you would have to
waste fuel both achieving this orbit, then more fuel getting back into
an Earth bound orbit.


Their orbits are nearly coplanar with the plane of ecliptic.

Mars' inclination is about 1.85 degrees, so there is some plane change delta vee expense. But you'll have this regardless if you launch from Mars or a Martian Moon.



Yes, a little water. And I highly doubt that it is worth going this
deep in this gravity well for these few drops.

Some Carbonaceous chondrites meteorites that hit earth are about 20% water (Hitting earth there're in a warmer neighborhood than Phobos or Deimos). And as I mentioned density of these Phobos & Deimos suggests a high water content. As you mentioned the Russian Phobos probe was thought to detect outgassing, another indication of water.

20% of 1.08e16 kg is 2.16e15 kg of water and 20% of 1.8e15 kg is 3.6e14 kg of water. That could provide reaction mass or hydrogen & oxygen fuel for a lot of interplanetary craft. 


Yes, where it sounds like a nice refuel point. The problem is that it
is a lot of extra time and infrastructure for this little gain.


Little gain? please see above paragraphs discussing the rocket equation.

Not a refuel point. The ship from Mars to Deimos would be small, only needing to accomodate passengers for a few hours.

The interplanetary craft parked at Phobos would be fully fueled from Phobos resources.


Since you already have to launch people and cargo from the Mars
surface, then you can save the billions spent on this extra
infrastructure, by simply launching fuel as well.


Which is a better way to colonize Mars?

Slavish adherence to Zubrin's Mars Direct and ignor the Moon, Phobos, Deimos and NEOs.
vs
Development of the Moon, Deimos, Phobos & NEOs would make sustained investment in Martian colonization possible. 


This could be compared with "going for the real meat" instead of
spending ages "chewing on bones".

How many decades and trillions would it take to create a self sufficient Martian colony? This investment could be sustained through several administrations and winds of public opinion? And with no return on investment?

Sounds like a good fantasy.

Achieving a return on investment from more accessable resources, though difficult, is much more plausible than getting an ROI on Martian products.

Once there is return on investment, expanding into space becomes self sustaining.

So you would be spending trillions on your cow and never getting any real meat beyond several flags and lots of footprints.


I can also say that this point in NASA's history makes for an
interesting example for your infrastructure plan. As when NASA works
on making their Moon Base, then they are going to abandon the ISS.

The only logical reason for doing this is to simply avoid the large
extra costs involved in having to keep supporting and maintaining the
ISS.

So I directly state that the more infrastructure that you have the
more NASA's support costs will go up and up. And by maintaining this
infrastructure they will cripple themselves from further expansion.


And with Martian infrastructure NASA's support costs will go down and down?


As the one thing that your Phobos and Deimos plan most overlooks is
that this is yet one more location to support with additional food,
hardware, repairs and other required resources.

I believe it would be substantially easier to establish a base on Phobos or Deimos than Mars.


And so simply going directly to Mars means that they can now focus
their available budget on where it does the most good. This means that
their current Moon to Mars plan makes a lot of sense.

As just maybe by focusing their budget on the Moon and Mars alone
(Moon drop optional), then so can they hope to make one of these two
places self-supporting. And you should well know that this is much
more likely to happen on Mars.

So in the end it makes a lot of sense to stop assing about and to run
a Mars Colony Direct plan ASAP.

Is ROI in your vocabulary? Perhaps civilizations could invest huge amounts over decades and centuries with no ROI in Pharoah's time. That time has passed.


Cardman. 


--
Hop David
http://clowder.net/hop/index.html

.

Relevant Pages

  • Re: large masses on Phobos, Diemos
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  • Re: large masses on Phobos, Diemos
    ... As you probably know the low density of Phobos and Deimos suggest icey ... If rocket fuel could be mined on Phobos, fuel needed for a round trip ... Does Stickney point towards Mars? ... This way Martian volatiles wouldn't have to be mined for Hohmann trips. ...
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  • Re: Improved lunar landing architecture
    ... >Hohmann insertion from Deimos: 2.4 km/sec ... >Hohmann insertion from Phobos: 1.8 km/sec ... >Hohmann insertion from Mars: 5.6 km/sec ... >Slavish adherence to Zubrin's Mars Direct and ignor the Moon, Phobos, ...
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