On Aug/1/2018 at 7:59 AM, Jeff Findley wrote :
In article , says...
So start dropping comets on Mars. You're going to (eventually) need
more water than Mars has anyway. In the long run, you're going to want
to terraform the whole planet.

Have you run the numbers on that?
I kind of agree with you, but I would put that in the longer term category.

Should be some numbers he

https://forum.nasaspaceflight.com/in...?topic=38524.0

It's an often discussed topic. Essentially you need nuclear powered
rocket engines (fusion would be best, but fission would work too) so you
can go out to the Ort Cloud, find suitable objects, then use some of
their mass as reaction mass for the drive to get it to Mars. We're
likely talking many thousands of comet like objects. The advantage of
getting them from the Ort Cloud is that their volatiles haven't been
boiling off after many passes around the sun (like an actual comet).

I suspect you mean the Kuiper belt or the scattered disc. It would be
difficult to get an object from the Oort cloud to hit Mars in less than
20,000 years using technologies resembling what is known today. Of
course, who knows what technologies will be available in 1000 years.
Kuiper belt and scattered disc objects could be suitable for this
purpose. But even with closer Kuiper belt and scattered disc objects, I
consider that to be a long term project.

How fast the process would be depends on how many tugs you have at your
disposal, how big they are, and how reliable they are. We're not likely
talking near term tech here. More like something a hundred years or
more into the future.

And this just gets you an atmosphere. It wouldn't likely be breathable,
so you're still going to need engineered organisms to get rid of stuff
like CO2, methane, ammonia, and etc. and replace it with O2 and H2O.
Still, if you could bring up the pressure to about 5 psi and the
temperature to something more earth like, you could walk around on Mars
with a breathing mask and suitable clothing rather than a bulky pressure
suit.

Some launch systems that are wacky and impractical here on Earth become
feasible on Mars. For instance, if you have some kind of maglev rail on
the slope of Olympus Mons, you have the advantage of near vacuum at the
top and lower orbital/escape speeds.

Have you run the numbers on that? Is it long enough to safely launch
people?

Only back of the envelope calculations.

Olympus Mon: diameter = 624 km, height = 25 km.
So the rail could be about 313 km long.

Mars low orbit velocity = 3.36 km/s.
Mars escape velocity = 5.03 km/s.

That means to reach escape velocity you need an acceleration of 40.4
m/s^2 (4.12 g) for 124.5 seconds on that 313 km rail.
For low Mars orbit you need an acceleration of 18.03 m/s^2 (1.84 g) for
186.3 seconds.

I'm not sure I would want to experience the required acceleration to
reach escape velocity after living a long period in the lower Martian
gravity. Martian colonist would know better than us whether that is too
risky or not. But the acceleration for low Mars orbit seems to be no
problem.

The real accelerations would be a little more than that because, at
those speeds, even the thin Martian atmosphere at a height of 25 km (a
little more than a thousandth of an atmosphere) gives significant drag.
On the other hand, I didn't take into account Mars' rotational speed
(you would place the rail on the appropriate side of Olympus Mons), but
I would expect that to be less than the loss caused by drag. So the real
accelerations are higher than the above mentioned numbers. This is only BOE.

This isn't a simple thing to do. But it isn't like, for instance that
SpinLaunch bull**** for which someone is getting some funding. It is a
workable solution. A Martian colony might find another better solution.

That's not nearly as bad as I would have thought in terms of
acceleration. If you limit acceleration to 3 g, it sounds like you'd be
able to get to a high Mars orbit (with a burn at the highest point, of
course, so you don't crash back down on Mars).

The acceleration isn't bad, the difficult part is the air drag. At 4
km/s, even 1 millibar of atmosphere is problematic. It isn't in the
nutcase impossible to do category. But it is an engineering challenge.


Alain Fournier