Re: Improved lunar landing architecture

On Thu, 11 Aug 2005 13:53:02 -0700, Hop David
<hopspageHATESSPAaMmM@xxxxxxxxxxxxxxxxxxxxx> wrote:

>Cardman wrote:
>
>> And did you not say that these two moons are rather deep in this same
>> Martian gravity well to make them worthwhile? So for a smaller volume
>> of water you still have a large gravity well to face.
>
>This is getting to be a long thread. It's hard to remember who said what
>but I don't think I said that.

Yes, it is a bit hard to recall who said what. The easiest method is
just to ask.

>If you want to get from Mars to Earth, you could save a lot fuel if
>Phobos or Deimos were bases/fuel depots
>
>Hohmann insertion from Deimos: 2.4 km/sec
>Hohmann insertion from Phobos: 1.8 km/sec
>Hohmann insertion from Mars: 5.6 km/sec
>
>Launches from earth must go above the atmosphere before doing their
>orbital insertion burn. This usually costs about 2 km/sec.

Yes I noticed. Saves all that additional drag.

>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.

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.

However, simply with the one standard craft, fitted out for all these
different options, then you simply have an efficient flight rate of
these lower mass cargos.

So whenever your interplanetary craft reaches Mars orbit, then you
have all these launches from the Mars surface, where they dock,
offload, and then take the new people and cargo down to the surface.

I should also point out that while maximum fuel efficiency is
important now, then it won't be in the future. As just as soon as they
start keeping fuel in orbit, then so can you go that bit further.

>Now the trip to Mars is a much different story. In this trip the Martian
>atmosphere is an asset instead of a liability since you can use it for
>aerobraking.

Yes, our big craft could possibly do that as it goes to achieve HMO,
but that extra fuel always helps to save a lot of time.

>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.

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.

>> 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.

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".

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.

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.

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.

Cardman.
.

Relevant Pages

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