The space shuttle Atlantis is less
than a week away from blasting off to overhaul the Hubble Space Telescope for
the fifth and final time in its nearly 20-year lifetime, but this last flight
stands out from the pack in more ways than one.
Atlantis and a crew of seven
astronauts are slated to launch
toward Hubble on May 11 at 2:01 p.m. EDT (1801 GMT) from NASA's Kennedy
Space Center in Cape Canaveral, Fla. Their mission is packed with five back-to-back
spacewalks to repair vital systems and boost Hubble's
vision into the universe.
NASA has even primed a second space
shuttle to serve
as a rescue ship in the unlikely event that Atlantis suffers critical
damage space junk and strands its crew in orbit.
Here are reader questions asked in a
recent Live Forum hosted by SPACE.com reporters, along with a few others
on the nuts and bolts of the mission:
Why does Hubble need this last
overhaul flight?
It's been seven years since NASA's
last Hubble servicing mission (STS-109 in 2002) and the space telescope was designed
to typically go only three years between overhauls. Because of the long gap,
several systems have experiences some failures and need repair. NASA had
already built new cameras, instruments and maintenance gear to support this
flight, too.
Why is this NASA's last mission to
Hubble?
Under NASA's current plan, the
agency will retire its aging three space shuttles in 2010 after completing
construction of the International Space Station. There will then no vehicle
large enough to carry new instruments to Hubble or return broken components to
Earth.
The shuttles typically carry seven
people on two-week flights. Each has a cavernous cargo bay 15 feet (4.5-meters)
wide and 60 feet (18 meters) long. NASA's shuttle replacement, the Orion Crew
Exploration Vehicle, is a smaller, capsule-based spacecraft currently designed
to launch four astronauts to the space station or on lunar missions.
Didn't NASA cancel this final
shuttle flight to Hubble? What happened?
Yes. NASA canceled Atlantis'
STS-125 mission to extend Hubble's operational life in January 2004 after a
review board found it too risky in the wake of the 2003 Columbia tragedy that
killed seven astronauts. The board directed NASA to fly only missions that kept
shuttle astronauts within reach of the International Space Station, where they
could take refuge if their spacecraft was damaged.
But the cancellation was met by
fierce opposition from the public and science community. In 2005, NASA considered
sending a robot to perform the Hubble repairs and upgrades, but ultimately
found it infeasible.
By September 2006, NASA had
successfully resumed space shuttle launches and flown the first two missions
since the Columbia accident. That success, coupled with new heat shield and
repair tools, led NASA to reconsider – and later approve – the final Hubble
servicing mission.
If it was approved, why is there a
rescue shuttle for the Hubble servicing mission?
While NASA is confident Atlantis'
mission to Hubble will go well, the agency is also prepared in case it doesn't.
Because the shuttle must fly higher and in a different inclination than the
space station to reach Hubble, it does not have enough fuel to reach both the
space telescope and orbiting lab.
Atlantis pilot Gregory C. Johnson
has said the shuttle will spend nearly half its propellant just to reach
Hubble, leaving it very little margin to return home. That is a standard
feature of all Hubble repair missions because of the telescope's high orbit
(300 miles up, whereas the space station is around 220 miles above the planet).
So, the shuttle Endeavour is already
poised on a second launch pad. NASA plans to have Endeavour and a small crew of
four astronauts ready to launch within seven days of any possible declared
emergency.
What new science will the upgrades
allow for Hubble?
Hubble can currently see distant
galaxies and stars that were forming when the universe was just 700 million
years old. The universe is currently 13.7 billion years old, and with the
upgrade during STS-125, astronomers hope Hubble will be able to see the
universe at time about 500 million years after the theoretical Big Bang that
started it all. Astronomers are hopeful the new gear will allow
Hubble to see infant galaxies among other new findings.
When would the first images from
Hubble be released?
If all goes well with the Hubble
repair mission, the first new image is expected to be released around
September. The telescope's control center at NASA's Goddard Space Flight Center
in Greenbelt, Md., plans about 10 weeks of tests and checkouts to make sure the
telescope is fully operationally.
What are the main goals for the
Atlantis' STS-125 Hubble Servicing Mission?
The following is a basic rundown of
work to be performed
during five spacewalks.
New Instruments and Gear:
- Installing the Wide Field Camera 3 (WFC3): a new and
more powerful main camera that bests its predecessors by seeing in both
ultraviolet and near infrared as well as visible light. Hubble would be
able to see 90 times more objects than it did at launch in April 1990.
This instrument will replace Hubble's current Wide Field Camera 2, which
will be brought back to Earth.
- Adding the Cosmic Origins Spectrograph (COS): This
instrument uses the ultraviolet range to find out the temperature,
density, chemical composition and velocity of intergalactic gas and
galaxies, with ten times the sensitivity of current Hubble instruments.
This device will replace Hubble's corrective lens – COSTAR – which fixed
the blurry vision caused by the telescope's flawed main mirror. The
corrective optics are no longer required because
all of Hubble's new instruments automatically compensate for the mirror's
flaw.
- Attaching the Soft Capture and Rendezvous System: This
docking port will allow a future spacecraft, most likely robotic, to latch
onto Hubble in order to guide it to a fiery demise in Earth's atmosphere
or up to the relative safety of a graveyard – or "museum" – orbit.
Maintenance work:
- Replacing six Rate Sensor Units (RSU):
The gyroscopes help keep Hubble pointed precisely at distant stars and
galaxies for hours at a time. Hubble can technically limp by on two or
even one gyroscope, but the fresh exchange ensures that the science keeps
flowing.
- Replace one of three Fine Guidance Sensors: Hubble has
three Fine Guidance Sensors used to keep the telescope stead for
long-duration observations. They are also used
for astrometry, which studies the precise position and motion of stars.
- Replacing six Nickel Hydrogen Batteries: The suitcase
-sized batteries get swapped out for the first time in 16 years, giving
Hubble an extra lease on life for the next 5 to 10 years. The batteries
keep Hubble humming during the night portion of its orbit.
- Replacing Thermal Insulation: The multilayer insulation
on Hubble has become torn and broken by the harsh environment of space.
The new thermal blankets protect the damaged insulation and helps maintain
a steady temperature for Hubble.
Vital Repairs:
- Repairing the Space Telescope Imaging Spectrometer
(STIS): A two-sided instrument that uniquely scans across all light
wavelengths of objects such as planets, comets, stars and galaxies.
Spacewalkers will replace a failed power converter to restore one side of
the damaged device.
- Replacing the Fine Guidance Sensor (FGS): One of three
optical sensors that help Hubble lock onto targets with a system of
mirrors and lenses. The old FGS returns home after being removed from
Hubble during an earlier servicing mission.
- Fixing the Advance Camera for Surveys (ACS): A highly
efficient survey tool with a wide field of view that became damaged.
Astronauts hope to repair some of its capabilities since it failed last
year.
- Repairing the Science Instrument Command & Data
Handling Unit: This repair will restore full redundancy to Hubble's vital
data handling unit, which serves as the central relay that beams telescope
imagery and data back to Earth.
How many days will the shuttle be docked with Hubble during the mission/repair?
Atlantis will arrive at Hubble on
the third day of the 11-day mission and cast off on Flight Day 9, so it will be
attached for about a week. Five of those consecutive days include spacewalks.
How would the rescue mission work,
if needed, and how long would it last?
A
rescue mission to Atlantis – called STS-400 – would last about a week. Endeavour would launch from
Pad 39B at the Kennedy Space Center with shuttle commander Chris Ferguson,
pilot Eric Boe and spacewalkers Shane Kimbrough and
Stephen Bowen. The rescue crew consists of the same four astronauts who last
launched on Endeavour's flight deck during its most recent flight, STS-126 in
November 2008.
The astronauts would fly Endeavour
to Atlantis, and grapple the stricken ship with Endeavour's robotic arm. They
would then perform a complicated series of three spacewalks to move the seven
astronauts from the damaged Atlantis into Endeavour, with Atlantis commander
Scott Altman the last to leave.
After a day to rest, the astronauts
would perform their standard prelanding heat shield
inspection and return to Earth a day or so later.
NASA considers the need for such a
rescue mission as extremely unlikely, but wanted to have an option just in
case.
What is the greatest risk to
Atlantis' crew?
NASA officials have repeatedly said
that the STS-125 mission to Hubble faces a higher risk of severe damage from
space junk and micrometeorites. Initially, that risk was about a 1-in-185
chance, which exceeded NASA's safety rules that call for a maximum risk of a
1-in-200 chance.
Since then, NASA has found ways to
reduce the risk further by flying Atlantis in a tail-first orientation with its
payload bay facing the Earth as much as possible. The shuttle will also fire
its engines to move to a safer orbit just after releasing Hubble near the end
of its mission.
Altogether, NASA's management
efforts now set the risk at about a 1-in-229 chance of critical damage from
space junk, despite recent spikes in debris levels from a Feb. 10 satellite
collision and China's 2007 anti-satellite test. The current 1-in-229 chance
puts the risk on par with other risks associated with human spaceflight, NASA
officials have said.
How does the Delta V profile for this mission differ from a "normal" ISS flight?
Atlantis will launch due east from
NASA's Kennedy Space Center in Central Florida. It is destined for an orbit of
about 300 miles (482 km), or about 100 miles higher than the International
Space Station, which has an inclination – or tilt with respect to the Earth's equator
– of about 28.5 degrees. On space station missions, a space shuttle launches to
a high inclination of 51.6 along a northeasterly track to reach the outpost's
220-mile (354-km) orbit.
How much longer Hubble will
last? It seems like it's been up there forever!
It's certainly has been up there for
awhile! The mission engineers say that if everything goes according to plan and
they get the necessary repairs done, Hubble will last for at least another five
years, or through at least 2014 – possibly longer. Hubble launched aboard the
space shuttle Discovery on April 24, 1990 and celebrated its 19th birthday in
orbit last month.
What could spell the death of
Hubble?
Without the upcoming STS-125 mission, Hubble is one failure away (the data
handling unit they revived last fall) from being space
junk. With it, it has a good chance of going at least through 2014, but some of
the repaired gear will be single string only. So that can fail. Even a wayward
space rock or orbital trash could pose a real, and
unexpected threat down the road.
Is this really NASA's final service
call to Hubble or could a future spacecraft like Orion attempt some type of
flight?
From what the mission scientists said, this really is the last call. Orion
won't be in place until no earlier than 2015, and Hubble is meant to be
serviced every three years (this is the longest it has gone - seven years -
without servicing). They also haven't commissioned any new parts and those
would take awhile to build if they did want to send anything new up there.
Looking to the future, how will
Hubble be decommissioned? Will they capture it and return it to Earth when it
is finally ready to be taken offline? Or, is it a situation where as long as
it's healthy, it will stay in service like the Mars rovers?
NASA originally discussed plans to
return Hubble to Earth at the end of its mission, but with the shuttle fleet
retiring that's not in the cards now. Lead STS-125 spacewalker John Grunsfeld has said even if NASA wanted to, Hubble may now
be too big and heavy (with all the added hardware over the last 19 years) to
fit in a shuttle payload bay.
During the STS-125 mission,
spacewalkers will attach a soft docking mechanism, a docking port for a future
robotic spacecraft that - at the end of Hubble's mission - could latch on and
then steer the school bus-sized space telescope into a controlled re-entry. A sort of space cremation, most likely over the Pacific Ocean.
Grunsfeld said the jury is still out on this.
NASA could also attach a motor and boost it into a graveyard, or museum orbit.
NASA hopes Hubble will last well
beyond 2014, but the STS-125 mission should extend its mission at least that
much.
Will the Atlantis crew return any
keepsakes of Hubble for the Smithsonian Air and Space Museum?
On this mission, the astronauts are
actually going to bring back the Wide Field Planetary Camera 2 and NASA
scientists are hoping it'll be up in the National Air & Space Museum before
too long.
Among the other items returning to
Earth aboard Atlantis is the COSTAR, the corrective optics that served as
Hubble's first contact lens to correct its blurry vision after its initial
launch. All of Hubble's new instruments automatically compensate for the mirror
defect that caused the blurry vision.
In terms of the decommissioning,
isn't it true that the robotic vehicle that would use the soft-docking
mechanism for Hubble is not even built yet?
Yes. Right now, NASA's plan is to
use a generic soft-docking mechanism, one it has developed for spacecraft like
Orion and others at the International Space Station. The robotic craft
envisioned to steer Hubble down to its death or a
graveyard orbit is not yet built.
How much will the mission to Hubble
cost?
According to Ed Weiler,
NASA's science mission directorate chief, this last Hubble servicing mission is
expected to cost about $1.1 billion. That is an increase from the estimated
$900 million price tag NASA initially announced in 2006 when the agency
committed to the STS-125 mission. The cost has swelled due to the last few
years of delays.
Can NASA save money and risk by
building a new space telescope to replace Hubble instead of flying the
servicing mission?
Weiler has said that while the cost of the
mission is one that can be criticized, even attempting to build a new space
telescope would face the same scrutiny later on because cost overages would
most assuredly follow then too.
Hubble was initially slated to cost
about $400 million, but by the time of its 1990 launch it had increased to
several times that. To date, NASA has spent about $10 billion to build Hubble
and keep it operating in space for the last 19 years.
However, a
future space telescope - like a daughter of Hubble - would cost much more,
be larger and require a new launch vehicle (like NASA's heavy-lift Ares V) that
does not yet exist.