Re: Hubble tug

In sci.astro.amateur message <hOjUl.34314$ZP4.30017@xxxxxxxxxxxxxxxxxxxx
, Sat, 30 May 2009 17:02:18, Scott Smader <smader@xxxxxxxxxxx> posted:
"Chris L Peterson" <clp@xxxxxxxxxxxxxxxxxx> wrote in message
news:61i225hpsbb7p91jjtfmls4lbjia7bo02s@xxxxxxxxxx
On Sat, 30 May 2009 07:36:00 -0700, "Scott Smader" <smader@xxxxxxxxxxx>
wrote:

Hubble may be in an LEO, but it's still much(!) higher than the ISS:
Hubble: 320 nm
ISS: 190 nm

A factor that makes an insignificant difference in mission cost.

Agreed that the cost of getting to orbit dominates, but this seems an
argument to salvage what's already in orbit.


To launch into a lowish orbit requires approximately 8 km/sec, provided
by fuel supplied at ground level.

To change the orbital inclination by sixty degrees requires a velocity
change equal to the orbital velocity, and for lower inclination changes
it is approximately proportional (but slightly worse).

From memory, Hubble is at 28.5 degrees inclination, ISS is at 51.5
degrees, difference 23 degrees.

Therefore, matching inclination will require a bit over 8 * 23/60 km/s,
which is 3.2 km/s. The fuel, etc., for that must first be taken to
orbit.

Hubble weighs 11 tonnes; ATV, launched by Ariane 5, 21 tonnes. On the
pad, Ariane 5 weighs 777 tonnes - mass ratio 37. Falcon 9's mass ratio
may be a little better.

For 3.2 kps as opposed to 8 kps, mass ratio will be 37 ^ (3.2/8), which
is 4. That means to re-incline Hubble would roughly take 44 tonnes, at
Hubble, ready to light.

Allowing for overheads, that would be two or three Shuttle payloads (and
Shuttle is not allowed to lift big fuelled boosters) or a similar number
of Ariane Fives or a couple of Falcon 9 Heavies.

Check that.

There is also a difference in altitude, but that is of lesser
importance.

--
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Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
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