Hubble Service Mission

It seems that the idea of a robotic mission to hubble is now not a likely event from what I read recently, see link

http://www4.nationalacademies.org/news. ... enDocument

My understanding is one of the main objections to a manned mission to hubble is that the ISS cannot act as a "Safe Haven" for the shuttle crew should the orbiter develope a problem. This is due to Hubble being in a different orbit to the ISS and the shuttle not being able to change orbits.

Any mission to hubble by an orbiter would not require it to fill its cargo bay completely with equipment, why not fit an additional fuel tank in the cargo bay to allow the orbiter to make the orbital adjustment. If it was to difficult interface an additional fuel tank to the orbiter's existing systems might it not be possible to deploy a separate engine with its own fuel tank to make the adjustment.

I'm not sure how much additional weight this would add to the orbiter but I would have thought even an increase of 15,000kg would still make the service mission feasible. The cost and lead times of engineering such a mission is probably less than the proposed robotic mission.

A bonus of this approach is that a deployable separate propulsion system could also aid development of small space tugs that might be used to assemble larger structures in orbit such as a stack of Bigelow's inflatables.

Another point is that NASA will have to have some form of mission to hubble so that it can be deorbited safely, at present they have little or no control over hubble's reentry. Hubble is to large to burn up completely in the Earth's atmosphere and large pieces are likely to reach the Earh's surface, if this happened in densely populated areas this could have dire consequences.

What do you think, is this possible?

Thinking some more about the above, the difference between the orbital heights of the ISS and hubble is about 180km, I dont know know the angle between them or whether the ISS passes directly below hubble.

The orbiter could fire its forward facing OM rockets to reduce height then speed up again by firing its main engines or possibly one of them if they can be operated separately.

If an extra fuel tank is taken in the cargo hold, it might be possible to manouvre it using the robot arm so that it mates with the existing connectors for the external tank. This would reduce the amount of modifications needed to the orbiter and a video camera mounted on the "cargo tank" could be used to guide it into position. I'm not sure whether it would be possible to connect another fuel tank to the external tank ports while in space but they obviously separate so it might not be a difficult proposition.

The fuel for the required , high angle orbital plane change would be massive, lugging 120,000+ pounds of what had at that point been written off as junk (a failed space shuttle). What would it take to talk Rutan (or a Rutan clone) into making a lightweight fiberglass Apollo or Mercury style capsule (more than one if needed) to get a minimum service crew down to F-22 bailout altitude, where standard equipment works? These will easily fit into the shuttle bay, and have future uses (lifeboats for Bigelow).