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James Oberg On Mars!



 
 
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  #1  
Old August 22nd 09, 07:05 PM posted to sci.space.history,sci.space.policy
Marvin the Martian
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Default James Oberg On Mars!

On Tue, 18 Aug 2009 19:33:45 -0400, Jonathan wrote:

"Eric Chomko" wrote in message
news:49cafe7c-dba7-4f75-90d0-

...
On Aug 17, 10:17 pm, Pat Flannery wrote:
And why it's so hard to get
the
http://thespacereview.com/article/1448/1

Pat


Lemme see, Mars at 36 million miles at its closest and the moon at 250K
miles on average, that is 36 x 4 = 144 times as far. It takes 8 days
to do a lunar mission. So, if we equate the distance to mission time,
linearly, we have a Mars mission taking 1152 days, 3 years and almost 2
months. The Mars synodic period is 780 days, or 2 years and 50 days. So
clearly we have to speed something up if we want to get the astronauts
back ASAP. And we also want to have some appreciably amount to time on
mars as well given a more than 2 years commitment to the actual mission
from launch to landing.


Eric



I thought Bolden said "Mars in 39 hours"! Or days, or whatever. What
pipe-dream was he smoking?


That was the ion engine claim.
  #2  
Old August 24th 09, 04:39 PM posted to sci.space.history,sci.space.policy
David Spain
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Default James Oberg On Mars!

Marvin the Martian wrote:
I thought Bolden said "Mars in 39 hours"! Or days, or whatever. What
pipe-dream was he smoking?


That was the ion engine claim.


I'm going to assume that aerobraking is not a possibility if you're
moving that fast, so does that figure presume some ion engine braking
as part of orbital insertion, or ion engine braking plus aerobraking?

Dave
  #3  
Old August 24th 09, 10:13 PM posted to sci.space.history,sci.space.policy
Pat Flannery
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Default James Oberg On Mars!

David Spain wrote:

I'm going to assume that aerobraking is not a possibility if you're
moving that fast, so does that figure presume some ion engine braking
as part of orbital insertion, or ion engine braking plus aerobraking?


That wasn't a ion engine, it was the superconducting VASIMR plasma
engine, which generates a lot more thrust than a ion engine.

Pat
  #4  
Old August 24th 09, 11:16 PM posted to sci.space.history,sci.space.policy
David Spain
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Default James Oberg On Mars!

Pat Flannery wrote:
That wasn't a ion engine, it was the superconducting VASIMR plasma

engine, which generates a lot more thrust than a ion engine.

Pat


OK, my bad, sorry. What's cooling those superconducting magnets?
If they aren't YtBaCuO2 it ain't liquid N. That'd be liquid H or liquid
He. I suppose you could ionize H, so it could double as a coolant for
the magnets and as a fuel source. But liquid N might be easier to deal
with with a lower ionization energy if you could use it instead or
the colder liquid O, but N would be less corrosive. Liquid O might be
more utilitarian to have around tho'. Liquid H, requires more energy
to ionize, but would yield a higher thrust. Probably rules out

Now you've got long term cryogenic fuel storage issues, but dramatically
shorter transit times I suppose.

It's a stretch, but so's any kind of Mars program, so a research
project possibly.

Woah! Take a look he

http://chemed.chem.purdue.edu/genche...ch7/ie_ea.html

I must remember to pay more attention to my atomic orbitals!
Lithium might be the best bet. Li at Atomic # 3
won't yield as good an ISP as H but look at the ionization energy!

This has got be the sweet spot for this type of engine! No cryo issues
except for magnet cooling!

So you feed it a supply of solid Li, heat it in vacuum to sublime to gas
and you're ready to go into stage 1 of VASIMIR.

Thus only need enough liquid H to cool the magnets, or maybe liquid N if using
high T superconducting magnets. Damn, do we *need* superconducting magnets?
What's the mag flux needed for this that normal electromagnets can't do?

Still need that beefy electrical power source.

Dave
 




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