On Jul/31/2018 at 8:59 AM, Jeff Findley wrote :
In article , says...

On Jul/27/2018 at 6:37 AM, Jeff Findley wrote :
In article ,
says...

Planetary Society Blog

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Liquid Water on Mars! Really for Real This Time (Probably)

Posted: 25 Jul 2018 09:11 AM PDT
http://www.planetary.org/blogs/emily...rs-really.html

A radar instrument on one of the oldest operational Mars orbiters has
discovered possible evidence of present-day liquid water on Mars.

This is really big news. We really, really need to explore this area to
determine how much water is there and how easy it is to get to. Water
means air to breathe and rocket fuel (CO2 from the atmosphere plus H2O
gives you liquid methane and liquid oxygen).

I should add also that using Martian water for rocket fuel is the right
thing to do at first. But once you have a well established colony you
will want to keep water for the colony. The colonist will probably want
their colony to grow. And they will want lots of water. The more water
you have the easier it is to have an attractive colony.

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.

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.

You can also significantly stretch the rail if you are willing to build
a support structure off the cliff at the base of Olympus Mons. But that
isn't an easy engineering project. But once you have a colony on Mars,
the lower gravity also puts it in the feasible category and not in the
wacky impractical category.


Alain Fournier