sss3@ukc.ac.uk (S.S.Sturrock) (02/06/91)
Hi chaps, This week on BBC2 there was a Horizon programme about the HST titled "A small problem with the mirror". There was a discussion about how to correct the problem. The eventual method decided on was to remove one of the four experiment pods from behind the mirror and replace it with a correcting set of mirrors. While this seems to be a cost effective method, I was wondering if there were some other reason why the HST was not just recovered and the mirror replaced. Is it because the Shuttle would not be able to land safely with the added weight, or maybe it could land but would be so damaged that it could not be re-used? Thanks in advance. Shane Sturrock, Biol Lab. Canterbury, Kent, Great Britain.
eric@abode.wciu.edu (Eric C. Bennett) (02/07/91)
In article <6814@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >While this seems to be a cost effective method, I was wondering if there were >some other reason why the HST was not just recovered and the mirror replaced. >Is it because the Shuttle would not be able to land safely with the added >weight, or maybe it could land but would be so damaged that it could not >be re-used? > >Thanks in advance. I think you are probably right on both accounts. The shuttle can carry more weight into orbit than it can bring back. But, of the two above, I would say the second would be closer to the point. There would almost certainly be some damage to the HST during re-entry and landing. Also, since the HST is so large, they would have to dedicate an entire shuttle mission to putting it back into orbit. If they just go up there and fix it, they could also do other shuttle expirements, launches, etc. Eric -- Eric C. Bennett uucp: {elroy|cit-vax}!wciu!abode!eric El Monte, Ca Internet: eric@abode.wciu.edu If you can read this you aren't looking through the hubble space telescope!
jabishop@uokmax.ecn.uoknor.edu (Jonathan A Bishop) (02/07/91)
sss3@ukc.ac.uk (S.S.Sturrock) writes: >Hi chaps, >This week on BBC2 there was a Horizon programme about the HST titled "A small >problem with the mirror". There was a discussion about how to correct the >problem. The eventual method decided on was to remove one of the four >experiment pods from behind the mirror and replace it with a correcting >set of mirrors. >While this seems to be a cost effective method, I was wondering if there were >some other reason why the HST was not just recovered and the mirror replaced. >Is it because the Shuttle would not be able to land safely with the added >weight, or maybe it could land but would be so damaged that it could not >be re-used? The problem was not discovered until after the Shuttle had landed. Another Shuttle mission would have to be scheduled. Also, Hubble is considerably more delicate than other satellites which have been returned to earth aboard the Shuttle; it could become damaged, and the payload bay would not be a clean environment. All in all, it's easier to give it the spectacles. -------- jabishop@uokmax.ecn.uoknor.edu "I'm with you, LEM, though it's a shame that it had to be you. The mother ship is just a blip from your train made for two. I'm with you, boys, so please employ just a little extra care. It's on my mind, I'm left behind when I should have been there." --Jethro Tull, "For Michael Collins, Jeffrey, and Me"
p515dfi@mpirbn.mpifr-bonn.mpg.de (Daniel Fischer) (02/08/91)
In article <6814@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >..some other reason why the HST was not just recovered and the mirror replaced. >Is it because the Shuttle would not be able to land safely with the added >weight, or maybe it could land but would be so damaged that it could not >be re-used? It's not the weight issue: initially the HST was designed to be returned periodically with the STS, but this plan was dropped already many years ago. Among the reasons were the vibration loads of touch-down, but to my knowledge the principal objection was the cleanliness of the mirrors: any dirt(+) would severely compromize the UV reflectivity. Ironically this same concern has also contributed to the terrible chain of mistakes at Perkin-Elmer and NASA: they simply didn't dare to do all possible tests with the precious mirror(s) in fear of contamination. Whether this was a key factor is not clear, but the Allen Report mentions it as a contributing cause. (+) One might ask: hey, why is the STS payload bay supposed to be dirty? But then again, the last Shuttle mission had almost to be terminated because of excessive dirt in several systems... One would have to put a sack around the HST in orbit before berthing it, but even then exhaust from the OMS and RCS could hit it (question to Henry at all: how much pollution does a Shuttle typically produce in its vicinity dyring an orbital rendezvous, like when they captured LDEF a year ago? Did they find traces of the thruster exhaust on the satellite?).
henry@zoo.toronto.edu (Henry Spencer) (02/08/91)
In article <1614@mpirbn.mpifr-bonn.mpg.de> p515dfi@mpirbn.UUCP (Daniel Fischer) writes: >... (question to Henry at all: how much pollution does a Shuttle >typically produce in its vicinity dyring an orbital rendezvous, like when >they captured LDEF a year ago? Did they find traces of the thruster exhaust >on the satellite?). I hadn't heard of anything like that, although they were relatively careful about thruster firings while in the immediate vicinity, as I recall. Hydrazine/N2O4 thrusters are moderately "clean". However, there has been enough concern about such issues, especially for space stations and the like, that at least one reusable-manned-spacecraft proposal I've seen had a small set of compressed-nitrogen thrusters for maneuvering in areas where normal rocket exhausts would be undesirable. -- "Maybe we should tell the truth?" | Henry Spencer at U of Toronto Zoology "Surely we aren't that desperate yet." | henry@zoo.toronto.edu utzoo!henry
tjc@castle.ed.ac.uk (A J Cunningham) (02/08/91)
In article <1991Feb6.214941.316@abode.wciu.edu> eric@abode.wciu.edu (Eric C. Bennett) writes: >some damage to the HST during re-entry and landing. Also, since the HST is >so large, they would have to dedicate an entire shuttle mission to putting >it back into orbit. If they just go up there and fix it, they could also >do other shuttle expirements, launches, etc. What's to stop them doing a launch and then recovering HST? Just curious. Tony -- Tony Cunningham, Edinburgh University Computing Service. tjc@castle.ed.ac.uk Thanksgiving For a National Victory (Robert Burns) Ye hypocrites, are these your pranks? To murder men and give God thanks? Desist, for shame! Proceed no further: God won't accept your thanks for murther.
dietz@cs.rochester.edu (Paul Dietz) (02/08/91)
In article <1991Feb8.075406.5464@cs.mcgill.ca> sparky@cs.mcgill.ca (James R. SMITH) writes: >Concern has been expressed about dirt and contamination in the payload >bay during reentry with the HST. Aren't we going to replace the mirror >and support components once it's down here anyway? It's never going to BE down here again. Maintenance will be on orbit. You can't replace the main mirror on orbit. One particular concern with HST, I understand, is that the UV reflectivity of the mirror is very sensitive to the presence of contaminants. Paul F. Dietz dietz@cs.rochester.edu
demers@SRC.Honeywell.COM (Robert DeMers) (02/09/91)
One of the major contaminants that is given off by the shuttle is Scotchgard. Although great for protecting the shuttle from moisture when on the ground, it's murder on sensitive optics. This is also a problem for the star trackers that will be on the space station (whenever that happens). Bob DeMers Honeywell SRC, MN65-2500 internet: demers@src.honeywell.com 3660 Technology Drive Tel: 612 782 7269 Minneapolis, MN 55418
haw30@duts.ccc.amdahl.com (Henry A Worth) (02/09/91)
>In article <6814@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes: >While this seems to be a cost effective method, I was wondering if there were >some other reason why the HST was not just recovered and the mirror replaced. >Is it because the Shuttle would not be able to land safely with the added >weight, or maybe it could land but would be so damaged that it could not >be re-used? > Two Points: 1> The Shuttle manifest is somewhat over-subscribed. With shifting priorities, inconsistent budgets, and technical problems; it is hardly certain that the HST repair flight will be flown on time -- if at all. To bring the HST back down to Earth for refurbishment would be to take a considerable risk that it would never get back into orbit. 2> There should be some consideration of cost effectivness. In the decade++ since the HST was designed there had been MAJOR advances in active/adaptive optics, mirror casting techniques (spin casting), electronics, CCD's, image processing and compression, and other technologies. The cost of two shuttle flights and a major refurbishing of the HST (the solar panels would also have to be replaced, and while we are at it we might as well replace the batteries, the troublesome tracking devices, ... ) may well EXCEED the cost to build a new, superior, space telescope (or even a series) and launch it with a commercial ELV. Another advantage is that the HST stays in orbit and continues its work. One cost-saving option would be to design the new instrument for wide-field work only -- the HST's major weaknes. This approach may even be more desirable than the planned repair mission (has anyone at NASA - or elsewhere -- run the numbers?) -- ------------------------------------------------------------------------ Henry Worth -- haw30@duts.amdahl.com No, I don't speak for Amdahl -- I'm not even sure I speak for myself.
NU128479@NDSUVM1.BITNET (02/09/91)
You talk of fixing the HST, is their any plans to build a new one? Surely, NASA learned from its' mistakes!???? I feel a new hubble would be the best alternative (it will take several years to build it though) but why spend all this money and time on fixing a crippled telescope when it won't perform as good as a new one? Or as good as it was supposed too? I know people would call it a waste of money - throwing the Hubble away - but such immense trouble and resources are going into a defective project that should just be scrapped. I am still pissed off that the mirror is defective. I know that I do not have the knowledge or experience to critically evaluate this project, but any project of this size (the Hubble) should have been evaluated from the top-down many times. I believe the "top-down" evaluation was performed by some engineer(s) with an over-estimated sense of knowledge, if performed at all. It's just not the mirror - so many things are wrong with the HST that trying its frustrating to even think how all those things could be designed wrong. I don't know whether to laugh or cry. Start over,NASA.I know you have many good people who work there, but you have serious problems with your upper management. Admit you made mistakes and do it right the next time. I would love a fully functional Hubble, and if NASA does correct the current Hubble with satisfactory results, I will be happy. But eventually NASA or some other country will launch a new improved telescope and I feel we should start on it now, instead of committing its' resources on fixing a mistake. Steve Harter.
mrb1@cbnewsh.att.com (maurice.r.baker) (02/10/91)
In article <91039.210444NU128479@NDSUVM1.BITNET>, NU128479@NDSUVM1.BITNET writes: > I know that I do not have > the knowledge or experience to critically evaluate this project..... > I believe the "top-down" evaluation was performed by some > engineer(s) with an over-estimated sense of knowledge, if performed at all. ^^^^^^^^^^^ Please stop and think for a second before making a statement like this. Eval- uation of a program (like the HST) is done by many people over the project lifetime. Sure, the mirror problem shouldn't have been overlooked. But to use the word "engineer(s)" to refer to the entire group of technical, scientific, management, financial, operations research, etc., etc., etc. professionals that managed and evaluated HST construction is specious. It's attitudes and perceptions like that which make engineering the difficult, poorly understood, and largely unrespected profession that it is today. There's at least one book (don't have it here at the office, but will post the title, ISBN, etc. if anyone's interested) which chronicles the HST project up to a couple of years ago....covers the politics, personalities, finances, etc. as well as the technical considerations involved. Maybe you've read the book or seriously looked at these kinds of issues; if so, I've responded in error. If not, please try to get some facts before performing an evaluation of any project. I'd prefer to marvel at its successes in data gathering & observation to date [limited though they might be] while recognizing the need to learn from our mistakes. Maurice R. Baker Electrical Engineer AT&T Bell Labs, Holmdel homxc!jj1028 -or- jj1028 at homxc.att.com
henry@zoo.toronto.edu (Henry Spencer) (02/10/91)
In article <91039.210444NU128479@NDSUVM1.BITNET> NU128479@NDSUVM1.BITNET writes: >You talk of fixing the HST, is their any plans to build a new one? Surely, >NASA learned from its' mistakes!???? I feel a new hubble would be the best >alternative (it will take several years to build it though) but why spend >all this money and time on fixing a crippled telescope when it won't perform >as good as a new one? ... Because we'd be lucky to see HST2 in orbit before 2010, given the rate at which such large projects get funded and done these days. -- "Read the OSI protocol specifications? | Henry Spencer @ U of Toronto Zoology I can't even *lift* them!" | henry@zoo.toronto.edu utzoo!henry
steve@nuchat.sccsi.com (Steve Nuchia) (02/12/91)
In <1614@mpirbn.mpifr-bonn.mpg.de> p515dfi@mpirbn.UUCP (Daniel Fischer) writes: >(+) One might ask: hey, why is the STS payload bay supposed to be dirty? But >then again, the last Shuttle mission had almost to be terminated because of >excessive dirt in several systems... One would have to put a sack around the What I hear from my sources is that the orbiter contamination control people wanted to but were not allowed to clean the Astro-1 filters. Apparently there was some kind of turf fight over orbiter versus payload equipment. In any case they've been working very hard to clean up the payload bays and keep them clean, and to develop procedures to control the cabin contamination introduced by its occupants. There were problems initially -- apparently nobody realized that a reusable spacecraft would need to be *cleaned* -- but by the time the HST was put on board, the payload bays (all of them) were up to snuff. -- Steve Nuchia South Coast Computing Services (713) 964-2462 "Innocence is a splendid thing, only it has the misfortune not to keep very well and to be easily misled." --- Immanuel Kant, Groundwork of the Metaphysic of Morals
p515dfi@mpirbn.mpifr-bonn.mpg.de (Daniel Fischer) (02/13/91)
In article <1991Feb8.133106.15736@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: > >It [i.e.:HST]'s never going to BE down here again... Certainly not within the next 15 years, that's for sure. BUT: what will they do with HST after the nominal mission is over in 2005? Without any further STS visit it would reenter a few years later (due to a viewgraph seen at an HST news conference at ESTEC a year ago) - another Salut coming? Have there ever been plans made public on a final HST recovery or in-orbit destruction or whatever mission to end its orbital life?
sysmgr@KING.ENG.UMD.EDU (Doug Mohney) (02/14/91)
In article <1638@mpirbn.mpifr-bonn.mpg.de>, p515dfi@mpirbn.mpifr-bonn.mpg.de (Daniel Fischer) writes: >Certainly not within the next 15 years, that's for sure. BUT: what will they >do with HST after the nominal mission is over in 2005? Without any further STS >visit it would reenter a few years later (due to a viewgraph seen at an HST >news conference at ESTEC a year ago) - another Salut coming? Have there ever >been plans made public on a final HST recovery or in-orbit destruction or >whatever mission to end its orbital life? Well, they could pull it down and look at it as a long-life test article for materials in orbit. Or they could refit it with enhanced cameras and boost the orbit somehow and keep it running for another 15 years. Or bring it back and put it in the Air and Space Museum :-) Doug Mohney, Operations Manager, CAD Lab/ME, Univ. of Maryland College Park * Ray Kaplan for DECUS president * SYSMGR@CADLAB.ENG.UMD.EDU