Re: Space Policy: Why Mars should be our top priority.

On Fri, 24 Apr 2009 19:14:47 -0700, Fred J. McCall wrote:

Marvin the Martian <marvin@xxxxxxxxxxxx> wrote: :
:Energy wise & rocket wise, Mars is closer than the moon, :

You've said this before. I've pointed out that the source you gave
doesn't agree with your claim. Go add it up for yourself.

Yes, I've said it before.

You didn't point out anything.

Let's go here:
http://en.wikipedia.org/wiki/Delta-v#Delta-vs_around_the_Solar_System
From LEO to the moon surface is 4.1 km/s + 1.6 km/s.

So the KE from LEO (Low Earth Orbit) to the moon is 1/2 m v^2 = 16.24 kJ/
kg.

From LEO to Mars is 2.5 + 0.7 + 0.6 = 3.8 km/s The red arrows indicate
the opportunity to Aerobrake; using the planet's atmosphere to slow down
rather than needing rocket energy. So the KE from LEO to Mars is 7.22 kJ/
kg, less than half the energy of the trip to the moon.

For further benefit, there's the Mass ratios. Since the mass ratios go as
exp(delta V/ v_e) where delta V is the final velocity of the rocket and
v_e is the exhaust velocity of the rocket engine.
http://en.wikipedia.org/wiki/Specific_impulse

If you have a fuel/oxidizer with a specific impulse of about 360, you
have a exhaust velocity of g*I = 3.5 km/s.

So, your rocket mass ratio from LEO to the Moon

So, the KE from LEO to the moon is exp(5.7/3.5) = 5.1 This means that the
rocket to get you to the moon, when fueled, is 5.1 times the mass
actually delivered to the moon surface.

On the other hand, from LEO to Mars with the same rocket fuel is exp
(3.8/3.5) =~ 3.0 So, you can put a lot more mass on Mars than you can on
the moon with the same rocket from LEO.

What I said is true, and what you said... yeah. right.
.

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