The third servicing mission, to which four spacewalking astronauts were assigned in the summer of 1998, was projected for launch in June 2000 and should have been 'the biggie' with no fewer than six excursions to change the telescope's large solar array wings for smaller, but heavier and more rigid, electricity-generating panels, replace its computer 'brain', install gyroscopes to 'steer' Hubble and fit a new $75-million instrument called the Advanced Camera for Surveys (ACS). The latter would provide it with a wide-field survey capability from visible to near-infrared wavelengths, as well as imaging from near-ultraviolet to near-infrared.
All that changed in early 1999, when NASA became increasingly concerned by a rash of failures of the telescope's existing gyroscopes. It was thought that the failures had been triggered by wiring corrosion. Fitted with six of the devices for redundancy, at least three are needed to provide stability and pointing accuracy. In March, when the space agency hurriedly split the third Shuttle servicing mission into two halves -one in October 1999 to carry out the most critical repairs, the other some time the following year to replace the solar arrays and fit the ACS - Hubble was operating on only three gyroscopes.
After several more months of fleetwide wiring inspections in the wake of the STS-93 scare, Discovery and her seven-man crew finally set off just before Christmas and successfully staged three spacewalks to replace all six gyroscopes with new models and fit the new computer 'brain'. Hubble was, quite literally, brought back from the brink of disaster when the third servicing crew reached it: a fourth gyroscope had failed in November 1999, forcing NASA to put the telescope in 'safe mode' and suspending all astronomical observations until urgent repairs could be made.
By the time Discovery's crew returned to Earth, all that remained to be done from the 'original' third servicing mission was the replacement of the solar panels and the installation of the ACS. Additionally, it was intended that the next repair crew would fit a new 'cryocooler' to enable NICMOS to resume work. Although it would officially be the fourth Shuttle visit to the observatory, Altman's flight was actually labelled 'HST SM-3B' - or Hubble Space Telescope Servicing Mission-3B - because it represented the other 'half' of what should have been the third servicing mission.
Entirely appropriately, John Grunsfeld, who had been on board the December 1999 ('3A') mission and was one of the spacewalkers originally trained to fly 'the biggie', was reassigned as Payload Commander of 3B. He would be joined by Linnehan for three spacewalks, while physicist Jim Newman - a veteran astronaut who helped to assemble the first segments of the International Space Station in December 1998 - would work with rookie spacefarer Mike Massimino on two other excursions. By the time Columbia returned to Earth at the end of the SM-3B mission, she would have significantly improved Hubble's observing power.
For the astronauts, however, their personal Hippocratic Oath was to 'Do No Harm'. ''I think of [Hubble] as a big old beast and I'm doing surgery on it,'' said Linnehan, a veterinarian by training who previously flew two life sciences missions on Columbia. ''The one cardinal rule about surgery is you don't want to make it worse! You don't want to leave any tools or sponges inside the patient. You want to make sure everything works at least as well as it did before you went in, and hopefully a lot better.''
NASA's then-Administrator, Dan Goldin, was also keenly aware of the telescope's importance - not only to the astronomical community, but as an icon of space science for the general public. In 2001, recalled Newman, he called the four SM-3B spacewalkers to his Washington office and ''let us know that, on spaceflights, there's always risk and sometimes failure happens. [But] then he looked us in the eyes and said: 'That's not an option for you!' Hubble is very, very near and dear to a number of people, so we have been impressed with that responsibility.''
In order of priority, the most important task was replacing the observatory's central Power Control Unit (PCU) - essentially its 'heart' - followed by the installation of the ACS and a cryocooler to revive NICMOS. However, the order of the spacewalks was not dictated by priority or technical complexity, but rather by the need to create a 'best fit'. ''It's like a puzzle,'' said STS-109 Lead Flight Director Bryan Austin. ''In putting the puzzle together, the board is only so big - it fits five EVAs - and the puzzle pieces unfortunately are big and they only fit really in one way.''
The PCU replacement was most critical and caused the greatest deal of worry in the minds of both mission planners and the astronauts themselves. ''It's kinda like open-heart surgery,'' said Austin, ''except we don't have [Hubble] on a heart-lung machine.'' Many scientists associated with the telescope admitted they would be on the edge of their seats. ''It violates a long-standing policy in the space business that if something's working well, you don't turn it off and just hope it comes back on,'' said Ed Weiler. ''We're not doing that cavalierly. We fully anticipate that everything will work just fine.''
If the procedure failed, added Linnehan, ''Hubble is dead.'' Nevertheless, replacing the troublesome unit was essential: a series of potentially devastating failures after 12 years of orbital wear and tear had rendered it a health risk to the telescope. Its job was to route electrical power from the solar arrays to the scientific instruments, control systems and batteries. The risk was that, in order to replace it, the spacewalkers had to totally power down Hubble to protect themselves from electrocution while they worked. They would then have barely eight hours to complete the delicate operation before thermal extremes inflicted permanent damage.
By the autumn of 2001, the plan was to replace the telescope's two solar arrays on the first and second spacewalks. This would enable the new arrays' attached diode controller boxes to better manage the electrical system while Hubble was fully shut down for the PCU changeout; then, on the third spacewalk, Grunsfeld and Linnehan would conduct the critical operation. Unfortunately for them, the 73-kg device had not been designed to be replaced and was wired into the electrical system by 36 closely spaced, hard-to-reach connectors that had to be removed one at a time by the two fully suited men.
It would be busy, with very little margin or time for error. ''We're book-keeping just a couple of minutes for connector mate [and] connector de-mate,'' said Austin before the flight. ''So multiply that times 36: that's a lot of time, and if you're off by 30 seconds - times 36 of those - that's about 15 minutes or so! Things can add up real easily if you start to run into problems.''
Of course, there would be no point in fitting the new camera and NICMOS cryocooler if Hubble did not come back to life after its heart surgery; consequently they were shifted onto the fourth and fifth spacewalks. For a year and a half before Columbia finally lifted off, Grunsfeld, Linnehan, Newman and Massimino meticulously practised each of their tasks in the water tank at JSC, wearing training versions of the spacesuits they would use and working on full-scale Hubble mockups in full-size payload bays. For every hour of their 30 hours of spacewalks, they spent at least 12 hours underwater . . .
''Do we think we can do it all?'' asked Anne Kinney, NASA's Director of Astronomy and Physics, before the launch. ''Yes, we do. We wouldn't plan it if we didn't think that. But it is very ambitious. It's not easy. We'll worry all the way.''
The flight would run for 11 days and its target launch date had already slipped to November 2001 because of the longer-than-expected time needed to fix Columbia's wiring at Palmdale. Despite the achievements of earlier servicing missions, many within NASA looked at SM-3B as the most complicated of the four and few could
have felt the pressure more than Scott Altman. A seasoned Shuttle pilot with two missions under his belt - including Neurolab in the spring of 1998 - he was now saddled not only with the burden of command, but also with the most exacting flying challenge of his career.
''As the Commander,'' he told a CNN interviewer shortly before launch, ''going through the whole training flow, your focus really widens out and you are responsible for much more [than as a Pilot]. I guess it's the mantle of command. You think about how training is going, how the crew is doing together, what our performance is like in the sim[ulator]s and then try to coordinate all that and produce a polished product.''
Joining Altman, Carey, Grunsfeld, Linnehan, Newman and Massimino to round out the seven-member crew was petite Mission Specialist Nancy Currie, whose duties were divided between acting as flight engineer during ascent and re-entry and deftly operating the RMS. Before the launch, she described herself as having ''a quarterback attitude with a magic touch.'' It was her job to help Altman and Carey to monitor the Shuttle's displays and subsystems. ''I'm kinda 'quarterbacking' to make sure everybody's in the right procedure, on the right page, adjusting or helping with any switch throws as necessary,'' she told an interviewer before launch.
''I'm flying with some very large guys on this crew, so my seating height is quite a bit lower than them. There are actually some things I can see in the cockpit that they can't see. I can look up and verify switch positions and actually direct their hand to certain switches.'' As one of the few active US Army officers in the astronaut corps, Currie was making her fourth Shuttle flight; she had also been on board the first International Space Station assembly mission, manipulating the RMS to precisely attach the Unity node onto the Russian-built Zarya control module.
Her experience with the mechanical arm was beneficial on STS-109, as she was required to not only use it to pull Hubble out of space and anchor it into Columbia's payload bay - and redeploy it later in the mission - but also to move her colleagues around as they undertook nearly 30 hours' worth of gruelling spacewalks. ''In terms of masses, the Russian [module] was slightly more massive [than Hubble],'' she said before the launch, ''so I'm familiar with moving large masses; and essentially the slower you go [with the RMS], the better off you are. That's kinda my trademark and I take a lot of grief [in the Astronaut Office] for going very slowly. It's kind of a joke of who can fly the slowest, and definitely I think I win that prize! But what I found is the slower you move, then the less problems you have, say, with oscillations in the arm [and] the controllability of the arm. When you say 'Stop', the payload stops, and because of the upgrades we've made to the arm [since 1996] and really tremendously increased the capability, [it] flies exceptionally smoothly, even with a massive payload like [Hubble].''
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