[FPSPACE] Tethers in LEO

[David Anderman]

It appears that a couple of issues are being confused here, let me try to
unravel this:

1) Optimal artificial gravity levels for long term spaceflight: if it were
easy or desirable to create artificial gravity via a tether at 1/6 g
(lunar gravity), one simply test bed would be at the Moon. I have been
told that if the optimal "g" force were greater than 1/6 g, then
astronauts could walk around the Moon wearing weights.

However, the question is if there is an artificial gravity force LESS than
1/6 g. Using a tether to provide 1/6 g requires high rotation rates and
accompanying coriolis effects that astronauts won't enjoy.

How does NASA plan to test if LESS than 1/6 g is 'good enough' for Mars
missions?

2) Tethers in LEO. These are great in theory, but not in practice near
51.6 degrees inclinations, 400 km altitude. The problem is that tethers
break, especially when at altitudes where there is more debris raining
down from higher orbits. If you think of the problems that could be caused
by a snapped tether in orbit at that altitude and that inclination, you
may be able to visualize part of the problem. The other issue is that a
tether rotating to create artificial gravity around 1/6 could have an
angular momentum on the order of 100 m/s, close to re-entry velocities at
400 km altitude. I am not suggesting a horror scenario where the tether
breaks in just the right way that some spacecraft accidentally re-enters,
but most spacecraft have a tough time correcting an out of plane manuever
of that magnitude.

Tethers out in cislunar space don't have the debris problem, there is a
better chance to recover from breakage if there is a break, and there is
less out there to be damaged from a broken 'runaway' tether,

DWA



>> -----Original Message-----
>> From: fpspace-bounces at friends-partners.org
>> On Behalf Of David Anderman
>> Sent: Thursday, July 29, 2004 1:03 AM
>> Subject: [FPSPACE] Tethers in LEO
>>
>> So far, the objections to Lunar Express seem minor and
>> workable compared with the harsh reality that our mission
>> planners for the Big Mars Mission may not have the partial
>> gravity data that they need for 10 to 15 years.
>
>  I gather that nobody knows just yet if lunar gravity is
>  acceptable long-term.  Therefore it seems prudent to
>  throw one's surplus million-dollar bucket in that
>  direction, rather than conduct tests with a revolving
>  Soyuz with a radius much too small for such a test.
>
>  If lunar gravity turns out insufficient for human beings,
>  then it adds to the worries Mars Mission planners face
>  en route. OTOH if lunar gravity ( plus exercise ) keeps
>  you fit as a fiddle, then Martian gravity is bound to be
>  even safer. The long sojourn on Mars envisaged by Zubrin's
>  Mars Direct ( and maybe also by the Bush Initiative ) will
>  then be valuable prior to the return voyage.
>
>  What you people should do therefore, is land your aged
>  spaceship on the Moon and challenge NASA to keep its
>  astronauts alive thereafter! You might also strike a deal
>  with NASA beforehand that they will keep your crew supplied
>  with burgers, pepsi, fresh mountain air, Washington DC
>  newspapers and/or toilet paper for as long as your crew
>  cares to stay alive. In return for biomedical data, of course.
>
>  Odds are that sooner or later the Bush Moon Initiative will
>  bail your little flock out and offer them a triumphant free
>  return to Earth. How the IRS will look upon such 'retornados'
>  is not for me to contemplate though.
>
> --
> Jens Kieffer-Olsen
> Slagelse, Denmark
>
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