# Hubble Orbit

I heard the decision this morning to drop the Hubble Space Telescope into the Pacific Ocean. I wondered what the required delta v would be to move the Hubble into a "safe" service orbit nearer the ISS. The rescue options that have been most public have been either a robitic service mission or an unacceptably dangerous shuttle mission. By moving the Hubble into a closer orbit with the ISS a "safe" manned mission could probably be developed.
What I am proposing is an unmanned maneuvering rocket similar to the ISS re-supply vehicles could be modified to move the Hubble into an orbit where it could be serviced from the ISS using the Shuttle.
By the time I figured this out myself Hubble would be in the bottom of the Pacific.

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pervect
Staff Emeritus
I don't have any numbers, but I can observe offhand that it will probably be rather expensive, because the orbital plane of the ISS is significantly different than that of the Hubble.

ISS has a 352 km perigee and a 364 km apogge, with a 51.6 degree inclination

Hubble has a higher orbit (around 600 km), but a 28.5 degree inclination.

I have done some very simlpistic calculations and I get something on the order of 5 k/sec delta v. Almost all the energy is used in changing the orbital inclination. Changing the orbital height seems to require only 0.13 k/sec. I must have missed something. If the required energy is really this much it looks like moving the 11,000 kg. Hubble into the ISS orbit is going to be impossible.

Well if the problem could be opened up to international input, and a plan were created, then things like funding, labor, risk, and future, could be assessed.

pervect
Staff Emeritus
If you don't boost the Hubble into a higher elliptical orbit first, I calculate will take at least 3km/sec to change the angular momentum enough to do the plane change.

You probably can improve on this some by boosting to an eccentric elliptical orbit, then doing the plane change maneuver at a higher altitude, then burning back to the desired lower altitude ISS orbit.

pervect
Staff Emeritus
With a specific impulse of 452 seconds in vacuum the effective exhaust velocity of the space shuttle main engine is 4.4 km/sec. This means that a mass ratio of 1:1 would provide 4.4 km/sec of delta-v. If we imagine that the space shuttle could be refuelled in space (this would probably take a development project to implement assuming it's feasible at all), we could get 4.4km sec delta-v if we could launch an amount of fuel equal to the end-of-mission weight of the shuttle into a rendevous orbit. Unfortunately this would be around 100,000 kg of fuel :-(.

A current shuttle payload is around 24,000 kg of fuel - one shuttle payload would give a delta v of 4.4km/sec*ln(124/100) = 950m/second, not even close to being enough.

http://www.astronautix.com/lvs/shuttle.htm

for some of the shuttle figures (which are approximate, another web site had 104,000 kg as the "end of mission" weight, though I don't recall the URL

Someone else is apparently also interested in the same problem (could be a poster here under another name, too, I suppose)

http://edhiker.home.comcast.net/ShuttleOrbitCalc.html [Broken]

I recall that there was a SF story by Geoffrey Landis with an ingeneous solution for an emergency orbital plane change using the shuttle. Unfortunately, it requires an intact shuttle. The idea was to take advantage of aerodynamic lift to do some of the plane-change, by flying the shuttle multiple times through the atmosphere.

A neat idea, of uncertain practicality with a fully intact shuttle - but not something you want to do if the shuttle's heat tiles have been damaged by stuff hitting them on liftoff.

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pervect
Staff Emeritus
I ran across another link today on the feasibility of the Hubble plane change.

http://www.aura-astronomy.org/nv/hubble.pdf [Broken]

They also get a 3 km/sec number for the delta v, doing a more througouh analysis of an actual Hoffman transfer orbit - but unfortunately they don't analyze the problem of the lowest energy transfer (which would probably involve kicking the Hubble into an elliptical orbit first, then doing the plane change).

Moving the Hubble itself makes a lot more sense than trying to put together a rescue fuel package for the Shuttle, because the Hubble is a lot lighter than the Shuttle, about 10x lighter.

Unfortunately, it's also fairly fragile, one not only has to do the orbital transfer but not break the Hubble in the process. The equipment powerful enough to do the job that's "off the shelf" would exceed Hubble's structal limits.

One of the more interesting ideas is to use a solar powered electric thruster to do the orbital change, though this would take about 3 years during which time the Hubble probably couldn't operate.

Another complication is that lowering the Hubble's altitude to that of the ISS might impair its operation, while leaving the Hubble at a higher altitude would run into a problem of differing rates of orbital precession. They calculate that precession of the Hubble at its current altitude (but the new inclination) would still allow service visits, it's just that they'd have definite limited time windows and only occur once every two years.

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Thanks Pervect. My original but apparently not unique idea was to realign the Hubble orbit with the ISS using ion propulsion, service it at the station using the shuttle then boosting it into a higher orbit in the same plane. It just seems a shame to drop it into the Pacific. The rebuild parts are already made and ready to go up. There is no guarantee that the replacement(s) will ever get launched. There is an ion propulsion unit at Orbitalrecovery.com that has a thrust of 270 newton meters this is with an ISP around 3800. Three years seems a long time but is is better that destruction in my opinion.

I took a look at the link. Thanks again. They seem to be worried about the ablity of an ion engine to operate long enough to do the job. The copy of the one used on the Deep Sace One ran for over 24,000 hours. If they boosted it into a higher orbit would they get a larger percentage of time in sunlight to power the engine. It seems possible to do this and I am glad to see that there are some people thinking about ways to save the Hubble.
I am not an astronomer just someone who has been hooked on space since before the Mercury flights. Am I correct in understanding that they got the 3 year transfer with a one newton thruster?

pervect
Staff Emeritus