"Id much rather see us maintain the old vehicles until we get the new ones in place. We would have this continuity of accommodating the unexpected, adapting to science as it evolves and taking advantage of new technologies," McCandless said.
McCandless told SPACE.com that steps must be taken to apply on-orbit servicing effectively.
"We shouldnt go off and have a total reversion to what, for lack of better words, I call expendable satellites. Thats where you launch something and you have no access to it. So when something goes wrong, or new technology becomes available, you cant do anything about it," McCandless said.
NASA reaction
Alan Bunner, science program director for NASA Headquarters, took some issue with the concerns raised by McCandless. His views were obtained by SPACE.com in a later phone interview.
"We have a real enthusiastic astronaut corps at NASA and they do their job very well and they love it," Bunner said. "Our job at NASA Headquarters is to figure out when is the appropriate time to involve the astronauts. Thats because manned operations dont come cheap. They are not without risk and we kind of have to hold these cowboys back."
For the Compton Gamma Ray Observatory, Bunner said that NASA could not justify astronaut involvement in bringing the spacecraft back to Earth in a shuttle.
"We had no need to have that spacecraft back. By deploying it into the Earths atmosphere we solved the problem of a possible uncontrolled reentry. That was much, much cheaper and didnt involve risk to human life. Prudence, budget and safety and other factors just didnt call for us using the astronauts," Bunner said.
Bunner said that the Extreme Ultraviolet Explorer (EUVE) was not completely a recoverable spacecraft. "We werent even sure we could get up there and get EUVE in time," he said.
"EUVE is a safe mission to just let it naturally reenter," Bunner said. "Again, it just didnt make sense for us to involve astronauts retrieving a mission that had no real need to be retrieved," he said.
In the future, Bunner said, NASA will focus on a mixture of serviceable platforms and throw-away free-flying satellites. He speculated that far from Earth -- at special gravitational-balance locales called L-points -- NASA could anchor various science instruments.
"Eventually there will be a substantial business out there. Those will be staging areas where astronauts will be needed to go there and work there," Bunner said.
"I think we make the best use of astronaut skills and enthusiasm at the appropriate times," Bunner said.
Tool time for telescopes
To date, there have been three Hubble Space Telescope (HST) servicing missions: December 1993, February 1997 and December 1999.
The next visit to the HST is now slated for approximately November 1, 2001, said Russ Werneth, HST manager for spacewalks at the NASA Goddard Space Flight Center in Greenbelt, Maryland.
A follow-on and last service call by astronauts to the powerful orbiting eye in the sky is on the books for 2003. For now, 2010 is considered the end-of-the-line date for Hubble stellar staring duties.
Werneth said that 93 hours of astronaut
, helped assure success in servicing the observatory."Train and train, and re-train...thats one of the key reasons that weve been so successful in the servicing missions," Werneth said.
Rud Moe, HST servicing mission manager at NASAs Goddard center, said the ongoing enhancement of the observatory has increased its "discovery potential," he said.
"Its a real science machine," Moe said. "Were doing more and more with less and less as we go on," he said.
Moe said future servicing missions should propel HST toward the 20 year mark of successful operations. "Hopefully, we will have removed all the infant mortality from the Hubble by that time," Moe said.
New solar arrays to increase available power, along with advanced and upgraded equipment, are making Hubble all the more productive, Moe said.
"You have to add to the lessons learned for Hubble," Moe said, "not to shy away from the impossible."
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