From SPACE.com
By Tariq Malik
Staff Writer
posted: 8 January 2008 5:20 p.m. ET

NASA's final shuttle flight to overhaul the Hubble Space Telescope will fly only when it is safe to do so, the agency's science chief said Tuesday.

Alan Stern, associate administrator for NASA's science mission directorate, said the agency's planned August launch to Hubble by seven astronauts aboard the Atlantis orbiter is dependent on the success of three other shuttle flights to lift off in upcoming months.

The shuttle must first haul a new European laboratory to the International Space Station (ISS). But that flight — slated to launch no earlier Jan. 24 — has been waylaid by fuel sensor system glitches since December and faces a likely slip to early February, NASA officials have said.

"Our watch word in all this is safety," Stern said during a meeting at the American Astronomical Society in Austin, Texas. "Hubble is perfectly capable of taking care of itself, and if the servicing mission needs to be in September, October, later in the year - whenever - we're going to do it the safest way we can as an agency. Safety is going to be first."

Hubble's final visitors

Targeted for an Aug. 7 launch, Atlantis and its STS-125 astronaut crew will fly the fifth servicing mission — dubbed SM-4 — to Hubble since the observatory's launch in 1990.

But the mission is not without risk.

Unlike shuttle astronauts on ISS construction flights, Hubble-bound spaceflyers will not be able to return to the space station should their spacecraft suffer major damage. Instead, another NASA shuttle is expected to be ready to launch a rescue mission within about 25 days of any serious problem aboard Atlantis, NASA officials have said.

In fact, the agency canceled the Hubble servicing mission outright after the loss of seven astronauts and the space shuttle Columbia during atmospheric reentry in 2003. An errant piece of fuel tank foam damaged the Columbia's left wing-mounted heat shield during liftoff, leading to the accident.

"The decision not to fly the Hubble servicing mission following the tragic loss of Columbia was based on an assessment of risk, given the circumstances at the time," said astronaut John Grunsfeld, lead spacewalker for the upcoming Hubble servicing mission.

Since the agency resumed shuttle flights in 2005, NASA engineers and astronauts have repeatedly proven their ability to use new inspection techniques to ensure orbiter heat shield health on seven successful missions. It was based on the success of those techniques that NASA revisited, and ultimately approved, Hubble's final servicing flight in October 2006.

"We felt that the risk of this Hubble mission is comparable to the risk of, say, an STS-115 [mission], which we flew post-Columbia," said Grunsfeld, who will make his third trip to Hubble and fifth spaceflight during the servicing flight.

Without one last servicing mission, Hubble could physically last until 2011, but this summer's flight is designed to extend its science-producing lifetime through 2013.

Planned upgrades for the orbital observatory include fresh batteries and gyroscopes; unprecedented repairs to its main camera and a spectrometer; as well as the installation of the new Wide Field Camera 2 and Cosmic Origins Spectrograph. If all goes well, the STS-125 mission would leave Hubble 90 times more powerful than the original telescope that launched in 1990.

Hubble has proven itself to be a watershed astronomical tool for researchers and the public-at-large, said Grunsfeld, a physicist. But the agency has not shirked safety to support that science, he said, as proven by the repeated delays for NASA's upcoming shuttle flight so engineers can fix a redundant, but vital, system.

"We need to fly safe, that's our number one job," said Grunsfeld. "I still believe that Hubble, and Hubble science and Hubble program ... is still something that's worth risking my life for, and I know I have a crew of six other crewmembers who believe that as well.

BTW, here are the tasks to be performed on Servicing Mission 4 (source: http://hubble.nasa.gov/missions/sm4.php ):

Install WFC3 - Wide Field Camera 3:
A high-resolution/wide-field camera with continuous coverage of wavelengths or colors of light from the ultraviolet to the near-infrared.

Install COS - Cosmic Origins Spectrograph:
The most sensitive ultraviolet spectrograph ever planned to fly on HST.

Repair STIS:
Restore the Space Telescope Imaging Spectrograph to operational status.

Repair ACS:
Restore critical scientific functionality to the Advanced Camera for Surveys.

Replace Rate Sensor Units (gyroscopes):
Complete change-out of all six gyroscopes, the heart of HST's pointing system, and HST's main wear-out items.

FGS - Fine Guidance Sensor:
Last in a series of changed-out units that allow fine pointing of HST.

Replace Batteries:
Replace the six batteries originally launched with Hubble in 1990, which are steadily losing capacity as they age.

Install Soft Capture Mechanism:
Install the Soft Capture Mechanism on the aft end of Hubble to aid autonomous rendezvous and capture of Hubble of a future mission.

New Outer Blanket Layers (NOBLs):
Install the remaining three NOBLs to thermally protect equipment bays whose thermal insulation has been degraded by the space environment.

Sounds like the SM4's crew will have plenty to do!

_________________
"There's no right way to eat a rhesus"!

Tis a shame they wont bring the noble old Hubble back when it's outlived a useful life. Very few of the space artifacts we have in museums actually went on the missions. Apart from mostly just re-entry capsules all you can see is surplus equipment and such.

Hubble belongs in a museum lest the Space Program become one of the greatest feats of mankind but leaves no trace of itself.

_________________
"Reality is that which, when you stop believing in it, doesn't go away."
--PKD

I agree, but I am not sure how they would recover Hubble.

The only way to bring Hubble back would be the way it went up, in the cargo bay of the orbiter. The solar panels would be rolled up, or if they snagged, ejected into space.

Unfortunately, unless the Smithsonian or others want to spend the BIG BUCKS to mount such a mission, it won't happen. Additionally, the human risk would be considered too great. Heck, the SM-4 wasn't going to happen until it was proven that the thermal protection system (TPS) could be thoroughly inspected and possibly repaired in space.

I'd heard that the original plan WAS to bring it back but after the first shuttle loss they deemed landing with a full cargo bay far too risky.

If you think about it, it is kind of wasteful to haul all that empty space into orbit and BACK as the shuttle is designed UNLESS you might want to someday bring something back.

_________________
"Reality is that which, when you stop believing in it, doesn't go away."
--PKD

The are cases where NASA brought an in-orbit satellite back to earth (source: http://science.ksc.nasa.gov/shuttle/tec ... sions.html )

- Retrieval of the WESTAR and Palapa B-2 communication satellites from low earth orbit (after their payload assist modules failed to fully burn) - February 1984

- Retrieval of LDEF (Long Duration Exposure Facility) in January, 1990 (the planned mission was delayed due to the loss of Challenger)

- Several free flying payloads that were retrieved during the same shuttle mission

In the past, the such missions were usually planned to deliver a payload and bring back the satellite(s) in the empty bay. But, satellites are now launched via expendable rockets (to save cost) removing that opportunity from the shuttle. Also, since the orbits for the Hubble and International Space Station are so different, they cannot merge two such missions.

Here's more info on the Hubble maintenance mission, courtesy of SPACE.com:

A Whole New View: Hubble Overhaul to Boost Telescope's Reach
By Tariq Malik, Staff Writer
posted: 23 January 2008

When astronauts overhaul the Hubble Space Telescope this summer, they will leave behind a vastly more powerful orbital observatory to scan the universe.

Set to launch aboard NASA's shuttle Atlantis on Aug. 7, the Hubble servicing mission will be the fifth - and final - sortie to upgrade the aging space telescope.

"We're not only going up to Hubble to refurbish it, but also to expand its grasp tremendously," said Alan Stern, associate administrator for NASA's science mission directorate, in a recent briefing. "We expect to make the very best discoveries of the entire two-decade plus Hubble program with the new instruments to be installed."

A deeper look

In addition to performing vital repairs, astronauts will add two new instruments to Hubble's observation platform � Wide Field Camera-3 and the Cosmic Origins Spectrograph � that will drastically boost its vision range.

"This refurbished Hubble [will be] a new telescope," said astronomer Sandra Faber of the University of California, Santa Cruz. "We estimate that at the end of this repair Hubble will be 90 times more powerful than when it was first launched."

That means that Hubble will be able to see at least 90 times more objects in deep space than it could when it was deployed in April 1990, she added.

With its ability to scan the universe at wavelengths ranging from the near-infrared, visible spectrum to the near-ultraviolet, the new Wide Field Camera-3 should allow Hubble to see objects that formed fewer than 800 million years after the beginning of the universe.

"To follow galaxy formation to times that are even earlier than this, we need a camera that can take sharp pictures efficiently at longer wavelengths," Faber said. "And that's exactly what Wide Field Camera-3 is going to do."

The new camera has better resolution than its Wide Field Planetary Camera-2 predecessor and a wider field of view than Hubble's current NICMOS spectrometer, and could reveal objects that formed when the universe was just 400 or 500 million years old, she added.

"A difference like this makes a huge difference in the structure and formation of the galaxies that we'll see," Faber said. Astronomers currently estimate that the universe is about 13.7 billion years old.

Hubble's new Cosmic Origins Spectrograph, meanwhile, will scan the universe in the ultraviolet range with about 10 times more sensitivity than the observatory's current tools.

"I believe it's the most sensitive UV spectroscopic capability ever to fly in space for astronomical purposes," said Hubble senior project scientist David Leckrone of NASA's Goddard Space Flight Center in Maryland. "It's designed, because it's so sensitive, to go as deep as possible out across the universe as fast as possible."

Researchers hope the new spectrograph will map the so-called cosmic web, the universe's large-scale structure made up of strands of galaxies that branch out in three dimensions like an astronomical spider's web.

"It is amazing to me how we've been able to reinvent the Hubble Space Telescope with each of these missions," said astronaut John Grunsfeld, who will serve as the lead spacewalker for the telescope's last overhaul.

Full power ahead

Hubble service astronauts will also replace failed gyroscopes, fine guidance sensor and aged batteries, and make unprecedented repairs to the space telescope's main camera and a vital spectrograph.

"When the astronauts leave Hubble for the last time, it will be at the apex of its capabilities," said Leckrone. "It will be the first time since 1993 that there will be five working instruments aboard."

Spacewalkers will replace Hubble's cracked thermal insulation and replace each of its 16-year-old batteries among other hardware.

They will also repair the observatory's Space Telescope Imaging Spectroscope and the Advanced Camera for Surveys (ACS), both of which were never designed to be fixed in orbit. Spacewalkers will remove more than 111 tiny screws to repair the two units.

"The good news is we're going to try and repair ACS. The bad news is we've never done it before," said Grunsfeld. "It's very tricky."

Grunsfeld and his six crewmates plan to stage five spacewalks to service Hubble during their STS-125 mission. NASA initially canceled the spaceflight following the 2003 Columbia tragedy, but later reinstated the mission after a detailed risk analysis.

The result, researchers said, is about five extra years of science for Hubble before its controlled deorbit sometime after 2020. To prepare for the space telescope's eventual demise, spacewalkers will also attach a connecting port that will allow a robotic tug to dock with Hubble.

"None of us could have imagined what this fourth-generation suite of instruments can do," said Stern, adding the 90-fold jump in observation power for Hubble will be unprecedented. "We will have the capability, literally, of approximately 100 Hubbles [circa] 1990 when this mission is done."


There's a nice video of the Hubble's initial launch and subsequent servicing missions at the following link:
Link here

Thats going to be quite the mission and good for Hubble.

Its going to be a sad day when Hubble finally meets its demise, the knowledge it has brought us is incalculable.