Hubble needs regular maintenance
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Few science instruments have enjoyed the star
status of the Hubble Space Telescope (HST).
Since its launch 15 years ago, it has captured some of the
most profound - and widely distributed - images of the Universe.
Its ethereal shot of a shimmering Eagle Nebula is as likely
to be found on the side of a bus as in the pages of an astronomy
textbook.
And, like a celebrated icon, Hubble has now become the focus
of controversy.
Its future is up for grabs. And as scientists discuss how -
even whether - to service the ageing telescope and prolong its
life, the debate over using a human or a robot to do so has
grown contentious.
While the US space agency (Nasa) talks tentatively of sending
robots to service Hubble, a panel of the National Research
Council (NRC), the principal operating agency of the National
Academy of Sciences (NAS), has recently recommended that
astronauts make the repairs.
Now, another vote has been cast in favour of sending humans
to do the job.
In a statement released on Tuesday, the American Astronomical
Society (AAS), the largest professional astronomical
organisation in North America, said it endorsed the NRC
position.
Nasa, it stated, should pursue a manned mission to repair
Hubble and launch it as early as possible after the space
shuttle is ready to fly again.
The AAS called Hubble "a remarkable instrument for scientific
discovery", and supported the NRC¿s conclusion that a shuttle
mission presented the lowest risk.
Is it safe?
The NRC panel comprised a group of distinguished astronomers,
engineers, former astronauts and Nobel laureates.
Their December report concluded that an unprecedented robotic
mission might not be developed in time to save Hubble, would be
more technologically risky, and could critically damage the
telescope.
It also found that the differences between the risks faced by
a crew to service Hubble and those of a single shuttle mission
to the International Space Station (ISS) were small.
"[The NRC] came down very clearly saying that if you really
care about the space telescope, then doing the shuttle mission
is the best answer," Harvard University Astronomer and AAS
President Robert Kirshner told the BBC News website.
Congress directed Nasa to request a study from the NRC to
look into HST servicing options after Nasa cancelled what was to
be the fifth, and final, shuttle-servicing mission to the
telescope.
Nasa administrator Sean O'Keefe, citing safety concerns,
announced the decision to cancel the shuttle flight shortly
after President Bush announced his space initiative and said
that shuttle flights would be used only to service the ISS, as a
step to putting humans on the Moon and Mars.
Since then, the space agency has looked at robotic options to
repair Hubble's fading gyroscopes and batteries. The telescope
is also slated for a new camera and spectrograph. With these
repairs, Hubble's observing life could extend to 2013.
Although it recently signed a contract with a Canadian firm,
MacDonald Dettwiler (MD) Robotics, to develop a servicing robot,
Nasa has not fully committed to a robotic mission.
Hubble death
At the AAS meeting in San Diego last week, in a session
outlining the options for Hubble, Col Mark S Borkowski, Nasa
Project Manager for Hubble Robotic Servicing, said that 2005
would be used to firm up a plan.
"We have probably as many questions as you have about what is
the future of Hubble, what is the best way to maximise the
future of Hubble and what are our options," he said.
The agency is investigating the feasibility and cost of
developing a robotic mission, and also the alternative of
leaving Hubble to its fate.
Hubble needs an urgent upgrade
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While the robotic technology developed by MD Robotics was
encouraging, said Col Borkowski, it might neither justify its
estimated $175-$300m price tag, nor be viable in time to save
the telescope.
A preliminary design review of the robot is scheduled for
March, with a critical review to follow later in the year.
Ultimately, he said, Nasa would decide whether a robot
mission was worth it.
Plan B is not to service Hubble and bring it down at the end
of its observing life. In this case, a robot could also be
developed to de-orbit the instrument.
While Dr Borkowski stressed that the NRC recommendation of a
shuttle flight would be a "key input" into the ultimate decision
about repair, he also reiterated that Nasa had no plan to
conduct shuttle servicing.
A thorny subject
This prompted pointed responses from some astronomers in the
audience. Rodger Thompson, a University of Arizona astronomer
and principal investigator of the Near-Infrared Camera and
Multi-Object Spectrometer, which astronauts placed on Hubble in
1997, reiterated the cogency of the NRC finding.
"I have to say that you - Nasa - have a solution in hand and
you have not taken it.
' "You¿ve created your own problem by refusing to use the
low-cost option with small incremental risk," Dr Thompson said.
"It's really up to you to reverse that, and make the decision to
do the shuttle mission."
He later told the BBC News website that Hubble was
specifically designed for shuttle servicing, and that four prior
astronaut missions to the telescope were "very successful".
Dr Kirshner also asked the panel why, given that the best bet
for saving Hubble was a shuttle mission, according to the NRC,
"there was no planning at Nasa for a shuttle mission".
"I didn't say there was no planning," said Col Borkowski, "I
said there is no plan."
If Nasa is parsing its words to both pursue a course of
action for Hubble, and deftly keep its options open, it does so
at time of great uncertainty and restructuring for the space
agency.
Nasa is shuffling priorities and funding to accommodate the
President's back-to-the-Moon initiative and is in leadership
limbo as Mr O'Keefe prepares to step down.
Nasa officials said that the decision not to pursue a shuttle
mission to service Hubble ultimately rested with Mr O'Keefe.
"A new administrator will have final decision in where we
go," said Nasa spokeswoman Susan Hendrix, of the Goddard Space
Flight Center.
Two out of three
As the clock ticks for Hubble, the observing carries on.
The telescope's science instruments are working well, with
the exception of the Space Telescope Imaging Spectrograph (STIS),
which shut down in August, said Rodger Doxsey, head of the
Hubble Mission Office at the Space Telescope Science Institute (STScI),
which operates Hubble for Nasa.
While Hubble awaits its tune-up, Nasa scientists weigh
options for battery and gyroscope conservation.
"Our goal is to get the longest lifetime that we can," said
Dr Doxsey. "We don't want to lose science waiting for the
servicing to take place."
The ultimate lifetime limiters for Hubble are its batteries,
which, like those in a mobile phone, lose their ability to
recharge over time. Without servicing, the batteries will give
out in 2007-08.
The gyroscopes keep the telescope stable, which anyone who
has tried to steady a telephoto lens can appreciate. Hubble has
six gyroscopes. Two have failed, but it needs only three to
control it.
Anticipating further failures, Nasa Goddard would test a
control mode next month for science to proceed on two gyros,
said Dr Doxsey.
Astronomers petitioning for time with Hubble must consider
the two-gyro mode in their proposals.
Robotic dexterity
Meanwhile, the plans for a robot mission are underway. The
proposed candidate, designed by MD Robotics, is a slightly
modified version of Dextre, the dexterous robot built to service
the ISS.
Looking like a human stick figure with arms akimbo and a long
grapple arm in place of legs, the robot is designed for complex
manoeuvres in space and has been tested at Goddard on a mock-up
of Hubble.
Its charge in space is to replace the telescope's batteries,
change the connectors on the gyroscopes, and install two new
instruments: the new Cosmic Origins Spectrograph, which is
sensitive to very faint UV light, such as that from
intergalactic gas in the early Universe, and the Wide Field
Camera 3, optimised for infrared, ultraviolet and visible
wavelengths.
Dr Thompson said that, although he was impressed with the
robot's performance at Goddard, an unprecedented robotic repair
of Hubble was too risky to be pursued single-mindedly.
Given that a return to flight was inevitable, he said, and
that many flights were necessary to complete construction of the
ISS, routing one to extend the life of a scientific instrument
that has already proven so valuable was reasonable.
"One flight to the Hubble Space Telescope will produce far
more science than 25 flights to the ISS," he said.
Great Hubble discoveries were still to come, agreed Dr Doxsey,
and efforts should be made to encourage them.
"We want to think twice about turning off a telescope that is
in its prime," he said.