Re: Improved lunar landing architecture


Cardman wrote:
> >
> >If accessible water is found, that would of course change things
> >dramatically.
>
> That has already been proved well enough already. What is most
> interesting is the assumed frozen water that is very close to the
> equator. This water is estimated to be as large as the North Sea,
> where they just need conclusive proof that it is really there.
>
> I doubt that you could pick a better location for a base, when they
> would just need to dig a well and to haul up ice.

That's what I meant. Relatively clean ice, rather than a 3-10% water
conent that needs hauling and heating. I agree that that is a benefit
that Mars probably has.
>
> >I was looking at the reverse - goign from Earth to Mars, and figured
> >you'd built your craft at L1 or L4/L5. Then, during the outfitting (say
> >over 1 - 2 years), use electric propulsion to put in a highly eliptical
> >orbit. Then for take off, fire the engines at perigee.
>
> I guess that is a bit outside this Mars colonization debate, but all
> ideas are still welcome.
>
> >I estimate a 440m/s kick at perigee would give an Earth Departure
> >Velocity of 3km/s.
>
> Well 3 km/s is not that much, but I did notice your mention of
> electric propulsion. So that is just the start.

I calculate 3km/s is enough for Mars intercept. The point is you get
that with only 440m/s of delta-V.

Since "Entering Space" has been quoted from, chapter 8 (page 166) deals
with gravity assist.

>
> >From Phobos, you could extend a tether both ways - almost to the
> >surface of Mars, and out to high orbit. If extending out 4,000 km, the
> >upper end would provide all the launch delta V required.
>
> Since the surface of Mars would be between 9235.6 and 9518.8 km below
> you, then your 4000 km only covers less than half the distance. Also
> it is worth noting that Phobos orbits at 2.138 km/s, which makes using
> this tether somewhat interesting if not dangerous.
>
Sorry, I meant 4,000 km out, or up, for launching to Earth. Phobos is
actually a mean of 9270 km from the centre. So 5,900km downwards, would
enable escape from Mars with a delta V of only 400m/s.

> Oh and that reminds me. Let me go make an eBay advert requesting a
> 8000 km long tether delivered to Phobos orbit.
>
It wouldn't weigh much and could be made of Spectra 2000. Just like
some fishing rods. And Mars doesn't have a large space debris problem.

> Since tether technology has not yet come anywhere close to this
> requirement yet, then this plan can fit on the shelf labeled
> "hopefully future technology".
>
I haven't run the mass equations, but I'm pretty sure this is well
within the capability of spectra. Nano tubes are not required.

> >That would allow Mars surface to transfer orbit with almost no fuel
> >required
>
> You underestimate Phobos's orbital height, and that 2.138 km/s has to
> be handled somehow.

lowering and raising cargos might cause some swinging of the tether,
but the 2.138km/s comes from Phobos. The bottom of the tether travels
at about 400m/s faster than the surface.


> >Ion enegines can only make a small difference to a Hohmann orbit,
> >unless you ahve a miraculously light weight power source.
>
> Massive engines and a medium weight power source is my plan. Getting
> that initial kick is the hard part, where it may need a little booster
> help, but after that it is cruise mode for a few months.

Massive engines need a massive power supply. Assume about 1km2 solar
array, or 1,000 tons for 100 MW. Nuclear would be heavier, as would
solar at Mars orbit.
>
> >One such source might be beamed microwave power.
>
> Not the best idea for a passenger craft. Also I am sure that even this
> kind of power source can be put on that previously mentioned shelf as
> well. These engines would require a damned lot of power.
>
Microwaves are very easily stopped. Just watch your coffee boil. You'll
still be safe.

> You may have noticed that NASA has been working on a plan to make a
> small sized nuclear reactor, which they also hope to use on their Moon
> Base. Unfortunately this technology seems difficult to prefect, which
> is why it could well take a few more years.
>
> However, here is your prefect massive ion engine power source. The
> only following issue is keeping this radioactive overheating monster
> away from everything else. That problem can be solved.
>
I still think it'll never beat chemical or nuclear thermal for short
trips of 1 month. Electric propulsion is great if you have lots of
energey. But that takes lots of time.

> So two technologies that should be here well before Mars time.
>
> >ion (or more likely plasma) engines might be a way to transfer cargo,
> >but I think they're more suited to decade long outer solar system
> >missions.
>
> You are thinking small. These baby girlie little feeble ion engines
> are no reflection on what a large engine can do. This is reflected by
> the fact of how long their fuel actually lasts. Like SMART-1 must have
> been powering away for a couple of years now.
>
> So all you have to do is to greatly increase power, enlarge your ion
> engine, then to spew out your xenon fuel as fast as possible. Since
> even NASA's large ion engine is on the small size, then about 16 of
> these in an array should do a nice job.
>
If you want something really big, go for Plasma engines. But you're
always power limited.

..

.

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