posted 06-04-2004 06:44 PM
I thought I would look at where the implied 'danger' was in a shuttle Hubble servicing mission compared to a shuttle mission to the ISS
from the viewpoint of rocket engine firings.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