Re: Orbital Mechanics

On Thu, 30 Dec 2004, David Weinshenker wrote:
> So what's the required delta-V for a "minimal mothball orbit-raising 
> mission" - i.e., boost it to an orbital altitude such that the orbit 
> won't decay any time soon, and it can safely be powered down and 
> allowed to "go passive" pending a later full-repair mission? 

Unfortunately, that isn't really a viable option.  To make repair and
reactivation possible, you must maintain temperature control of various
areas in the interior, so that sensitive components don't go out of their
"storage" temperature range.  (Batteries are particularly intolerant of
temperature extremes.)  That means, in practice, that you must maintain
at least crude attitude control, plus solar power and battery operations.
And *that* means that various things -- notably the batteries -- continue
to use up their limited working life.  There's really no such thing as
truly passive on-orbit storage for a system like Hubble.

There is also a substantial problem with predicting just how long a low
orbit will last, as witness Skylab. 

> This would be much easier than a plane change for an 
> acceleration-sensitive object like the Hubble, since it could done 
> with a gentle continuous thrust. (I wonder if the numbers work out for 
> some sort of electric propulsion.)

Actually, the numbers work out fairly well for electric propulsion to move
Hubble to the station orbit, using off-the-shelf thrusters and solar arrays.

                                                          Henry Spencer
                                                       [email protected]