posted 06-04-2004 06:44 PM            

I used the STS-61 flight (HST 'Hubble' servicing) and STS-110 flight (ISS ) as these were the two missions I had data for.

Both missions had the 'normal' ascent from KSC.
Both had an OMS-2 burn
Both had an NC1 OMS burn
HST mission had a small NSR burn
Both had an NC2 OMS burn
Both had an NPC (multi axis RCS ) burn
Both had an NC3 burn
Both had rendezvous operations (STS-61 with HST and STS-110 with ISS)
Both had several small station keeping burns to complete final alignments with respective targets.
STS-61 grappled the HST while STS-110 had the task of fine manoeuvring to dock with ISS.

The return to Earth scenarios were almost the same with the primary de orbit burn being the most significant part after the un docking and separation from targets .

The number values are obviously slightly different but they are not significantly different between the missions..

So where is the increased 'danger' for a HST mission versus an ISS mission ?

If any burns were to go wrong on an ISS mission (unless within just a few feet of the ISS where EVA transfer may just be an option) I do not see how much 'safer' a ISS mission would be when viewed against a HST mission ?

If any other failure mode took place (eg tile loss) , as far as I can determine any attempted repair would be the same whether an HST or ISS mission. The only advantage of an ISS mission is that the shuttle could still dock with ISS and undertake more 'leisurely' repairs.
But you still have to do EVA's to carryout repairs and you still have to fly-back with your "on orbit" un-tested repair !

The orbital parameters are different (ISS around 366 x 358 km , 91 minutes period , 51.6 degrees inclination against HST of around 570 x 564 km , 96 minute period and 28.46 degrees) but these do not affect the shuttle 'safety' to any greater degree.

Even in the last few day's several 'prominent' astronauts have signed a letter urging a crewed repair flight to the HST instead of a very technologically risky unmanned robotic mission.

If O'Keefe (and others at Capitol Hill) view a manned HST servicing mission as 'dangerous' then , in my book , as the number of burns and other factors are almost the same between a HST and ISS mission, then ISS missions ought to be classified 'dangerous' ?
But, let's hope not !

Manned space flight - with our current levels of technology - will always be fraught with an element of danger. Of course we should try to eliminate as many risks as possible and make it as safe as possible for the crew members. But, at some point, the decision has to be 'fly' otherwise manned space flight will stagnate for a long long time.

The HST is too important a science instrument to 'discard', at this stage, when a 'proven method' of repairing it already exists.

If NASA turns away from a manned repair mission to HST (after applying the current round of safety fixes to the shuttle system) history will view the administrators not as "..safety conscious, crew savers .." but probably as '..Lilly livered, turncoats..'.especially when members of their own astronaut community urge them to 'fly'.

To let HST perish without attempting a manned repair mission will be viewed by the world's communities as a failure of US science and technology and,especially, its space program. Its plans and ideas for manned flights to the Moon (again) and manned missions to Mars will just be scorned and scoffed at. After all,it will be said, they couldn't even fly to repair Hubble in earth orbit !

So,Mr O'keefe (and the other Capitol Hill administrators) ,please reconsider your decision.The public, I am certain, would be more behind you and more likely to applaud you for being able to "change your mind" and able to make a bold statement if you reversed your decision. They are more likely to believe that a strong manager is in the 'driving seat' - someone ideally poised to go out and explore and conquer the space environment. Anything less and you would become just another unidentifiable name tag.

Don't get me wrong ! I don't want the manned exploration of space undertaken in a "string-and-glue and hold your breath and hope it works" attitude. It must be made as safe as possible. There are even many opportunities where unmanned robotic missions will do a better job . That's why I support using the Moon as a "testing ground" for man-to-Mars-and-return technologies - even if takes decades to perfect..

But the HST repair mission is a 'special case' Manned repair flightsby the shuttle to HST have been done before (and done very very well) and the technology is proven. So , once again, go for it. Go do the repair. Make a song and dance about it. Shout it from the roof tops. And the world will continue to look on in awe at the Universe shown by the magnificent Hubble images and data . Images and data returned by the technology that is American.

Anything less and you will risk 'losing' a generation's interest in manned spaceflight - a generation that you need to take you on to the planets and the stars.

Phill Parker

posted 06-04-2004 07:37 PM              

The shuttle has twice demonstrated it has a propensity for catastrophic failure. Orbital insertion which does not facilitate use of ISS as a lifeboat leaves the crew with only one course of action - return to earth in the degraded vehicle regarless of the nature of the casualty and risk STS-107s fate. Access to ISS not only expands the duration of time to correct a failure, it offers resources (tools, EVA suits, Canadarm2 ect) that may not have been carried onboard the STS due to weight/space constraints. Additionally there are two potential methods of escape..a second Shuttle or multiple Soyuz runs...

More significantly, a number of ground based 6.5 meter telescopes are online/coming on line using Adaptive Optics and deformable secondary mirrors that have double the resolution of Hubble in H-band. Much larger 10-50 meter class scopes are under construction that will further improve this margin. Additionally the James Web is launched in FY11 perhaps only 3-4 years after Hubble is gone. On a cosmic time scale that time is relatively insigificant; with the possible exception of Supernova's, planetary events most of the science will still be out there waiting to be collected. I just dont see the risk/benefit payoff to justify placing additional lives in jeoporady to sustain Hubble.

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Scott Schneeweis

posted 06-04-2004 08:00 PM               

quote:

---

Originally posted by spaceuk:
If any other failure mode took place (eg tile loss) , as far as I can determine any attempted repair would be the same whether an HST or ISS mission. The only advantage of an ISS mission is that the shuttle could still dock with ISS and undertake more 'leisurely' repairs.But you still have to do EVA's to carryout repairs and you still have to fly-back with your "on orbit" un-tested repair !

---

Phil, I believe you overlooked a few key advantages the ISS provides:

• the ability to safely inspect the orbiter from all sides by performing a 'fly-around' of the station as the astronauts aboard photograph and report what they are seeing;
  
• the ability to transfer the crew off the damaged orbiter to either (a) the station or (b) another vehicle (Soyuz, shuttle) through the station, to either wait for repairs to be completed or to return to Earth as supplies for a repair are launched; and
  
• the ability to assist inspection and repair using the station's robotic arm;

But this is all academic because for better or worse, the Gehman commission found that a separate, stand-alone repair method would need to be devised for missions that did not launch to the ISS. I think it would set an even worse precedent if NASA decided it knew better then the commission and ignored a finding.

So then the question becomes whether it is worth the investment to devise a completely different repair method for a single proposed mission that would ultimately extend the already-overextended life of a satellite (albeit a very popular, very productive one).

Or is it better to apply that money (actually, less) to a robotic mission that would not only seek to accomplish the work set forth by the cancelled manned mission, but extend our abilities to repair other satellites in LEO (and possibly beyond-LEO orbit -- Spitzer anyone?) and possibly be reused several times to continue extending the life of HST? Which would we rather: the short term payoff or the long term investment?

posted 06-05-2004 12:38 AM            

The trouble is, that's not going to happen. NASA, Congress, this administration and former administrations have shown no qualms whatsoever about letting old programs die with the promise of new ones - then either never doing the new programs, or funding them so poorly that it is almost as good as not doing them. It never happened when the "spending money" was relatively plentiful - and that is certainly not the case in this time of economic tailspin.

I sincerely hope that we are retiring old programs and new ones will take their place. But the track record of prior attempts to do that over the last 30 years is one of mostly dismal failure.

Hubble is one of NASA's very, very few unqualified successes of the last 20 years. In fact, it is one of humankind's greatest successes. Read or hear an account of how they were serviced, and it is immediately evident that no robot could do the work that is needed. The "robotic servicing" option currently being looked into is I believe simply a way of waylaying the very justified criticism of one of the dumbest things NASA has ever chosen to do.

I wish I could share your positive outlook, and I sincerely hope I'll be proved wrong. But every decision made so far after the Presidential speech has been a bad one. Ask any astronaut who can speak off the record, especially those who have already been to Hubble, whether they would be willing to go again now. If they are willing, NASA should be too.

FF

P.S. The responses above also seem to advocate a point of view which I feel is the wrong track to be going down - one, in fact, which goes against every successful aerospace test craft "fix" that has ever worked. Rather than look at ways of spotting / saving a spacecraft that gets the same tile damage as Columbia - fix the real problem - foam shedding off the ET and slamming into a fragile spacecraft, a problem that never should have been tolerated - then the shuttle will be safer than it ever was on any of the many (safe and successful) prior Hubble repair missions. Don't dither with the symptoms, as bureaucracies are wont to do - cure the disease...