Hubble telescope marks another milestone in space

The Hubble Space Telescope as last seen by the crew of the space shuttle Atlantis after a fifth andfinal servicing mission in 2009. NASA

Five years after a fifth and final shuttle servicing mission, the Hubble Space Telescope's instrumentsare operating in near-flawless fashion and while one of its six stabilizing gyroscopes has failed,project managers are optimistic the observatory will be able to operate through the end of thedecade, wrapping up 30 years at the apex of astronomy.

If those forecasts hold up, NASA will be able to use Hubble in concert with its successor, the $8billion James Webb Space Telescope, giving astronomers a golden opportunity to compare Hubble'svisible-light images with Webb's deep infrared views to better understand the structure andevolution of the early universe.

"Hubble's doing great," said John Grunsfeld, NASA's director of space science operations and one ofthe spacewalkers who helped service Hubble during a final visit in 2009. "We've had one gyrofailure, but that's to be expected.

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"If we can keep Hubble going through 2020, with an October 2018 James Webb Space Telescopelaunch, the scientific opportunity is tremendous. Now we can't guarantee that. It's space, it's reallyhard. [But] knock on wood, we can keep Hubble going a long time."

Matt Mountain, director of the Space Telescope Science Institute at Johns Hopkins University, isequally optimistic.

"Hubble seems to be in remarkably good condition, the gyros are holding out, the instruments areholding out far better than we anticipated," he said in an interview.

"The real issue for us, which is what's proving very exciting, is though the instruments have nowbeen up for almost five years, we're finding news ways to use them and new ways to correct theeffects of being in space," he said. "And so they're becoming even more sensitive than they were

when we went up there."

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The Space Telescope Science Institute still receives five to six times more applications for observingtime that can be honored and Grunsfeld said NASA will continue funding the observatory, at morethan $90 million per year, as long as it remains scientifically viable. NASA has spent $7.5 billion onHubble in real year dollars since the program was approved in 1977, not counting the cost of sixdedicated shuttle missions.

"When we get to 2020, if we're down to a single instrument, maybe we only have Wide Field Camera3 left and we're on the cusp of launching a wide-field survey telescope ... the science community maydecide funding isn't worth it and we ought to put it into the next-generation telescope," Grunsfeldsaid.

"If the over-subscription (rate) drops down to a much lower number, and I don't know where thatthreshold would be, and there's more pressure on James Webb or a new telescope, then we wouldput it into a senior review where it competes against those other instruments."

All that said, Grunsfeld added, "I think we'll get to 2020 with Hubble."

Hubble was launched 24 years ago, on April 24, 1990, aboard the shuttle Discovery. In what becamethe opening chapter of a space drama rivaling the "Perils of Pauline," engineers discovered itspresumably near-perfect 94.5-inch primary mirror suffered from spherical aberration, a conditionthat prevented it from bringing starlight to a sharp focus.

The shuttle Discovery, carrying the Hubble Space Telescope in its cargo bay, climbs away from theKennedy Space Center during launch April 24, 1990.

NASA

In a remarkable display of Apollo 13-style ingenuity, engineers precisely mapped the aberration anddesigned corrective optics that were installed during a December 1993 shuttle servicing mission, thefirst of five that eventually were launched.

With its razor-sharp vision restored, Hubble quickly became one of the most scientifically productive

observatories ever built, chalking up a steady string of major discoveries and sending downspectacular images that now grace everything from scholarly journals to grade school textbooks, T-shirts and posters.

"Its images have become part of our culture in our textbooks, magazines, art and even popularmovies and TV programs," Ed Weiler, former Hubble project scientist and Grunsfeld's predecessor atNASA Headquarters, said before the final shuttle visit. "Although we probably never will be able tovisit these places hair chalk or objects, Hubble actually allows our human minds and spirits to travellight years and even billions of light years to the farthest reaches of the cosmos."

Along with helping astronomers pin down the age of the universe -- 13.7 billion years -- withunprecedented precision, Hubble observations confirmed the existence of super-massive black holesand played a key role in supernova observations confirming the presence of "dark energy," amysterious force that appears to be speeding up the expansion of the universe.

More recently, Hubble has been used to search for minor planets beyond Pluto, to look for planetsorbiting other suns, to improve the accuracy of astronomical distance measurements and to studygravitational lenses created by galaxy clusters that magnify the light from even more distant, andancient, galaxies that formed shortly after the big bang.

The secret to Hubble success was NASA's ability to launch shuttle servicing missions to replaceoutdated or malfunctioning components, to repair systems that could not be replaced and to installnew, state-of-the-art instruments to keep the observatory at the forefront of astronomy.

"The spherical aberration story is one for the history books," James Jeletic, deputy project managerof Hubble operations at NASA's Goddard Space Flight Center, told CBS News. "And then theastronauts and the whole idea of the servicing, which allowed us to put new instruments on boardand things of that nature, that has worked just absolutely spectacularly."

Four years after Hubble was equipped with corrective optics, astronauts on a second servicingmission installed two new instruments -- the Space Telescope Imaging Spectrograph and the NearInfrared Camera and Multi-Object Spectrometer, or NICMOS -- replaced a fine guidance sensor, agyroscope and installed a solid-state data recorder.

After multiple gyroscope failures in the late 1990s, NASA managers decided to split a third servicingmission into two shuttle flights.

During Servicing Mission 3A, launched in December 1999, spacewalking astronauts installed a newflight computer, a second solid-state data recorder, another fine guidance sensor and a full set of sixgyroscopes. During Servicing Mission 3B, launched in March 2002, another shuttle crew installedtwo new solar arrays, the Advanced Camera for Surveys, an experimental cooling system forNICMOS and a replacement power control unit.

The Hubble Space Telescope was equipped with corrective optics during a 1993 shuttle servicingmission, counteracting a flaw in the observatory's primary mirror. Hubble has operated at theforefront of optical astronomy ever since.

NASA

Then, 11 months later, the shuttle Columbia was destroyed during re-entry by a breach in its wingleading edge heat shield. Plans for a fifth shuttle visit, Servicing Mission 4, were put on hold andeventually cancelled by then-NASA Administrator Sean O'Keefe.

He made the decision in large part because Hubble and the International Space Station were indifferent orbits and a Hubble repair crew could not reach safe haven aboard the station if theirshuttle suffered a Columbia-class problem.

But NASA and contractor engineers eventually came up with heat shield repair techniques andO'Keefe's successor, Michael Griffin, reinstated the fifth servicing mission.

During the final visit in 2009, four spacewalkers working in two-man teams carried out five back-t-

-back spacewalks, installing six new stabilizing gyroscopes, a full set of six nickel-hydrogen batterypacks, a new data computer and two new instruments, the $126 million Wide Field Camera 3 andthe $81 million Cosmic Origins Spectrograph.

The repair crew also installed an upgraded fine guidance sensor, new insulation blankets and agrapple fixture that will permit attachment of a rocket motor at some point down the road to enablea controlled re-entry when Hubble's orbit decays to the point of no return.

Grunsfeld and his crewmates also repaired two science instruments, the Space Telescope ImagingSpectrograph, which suffered a power supply failure in 2004, and the Advanced Camera for Surveys,which malfunctioned in 2007.

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Jeletic said other than a single gyro failure, the observatory is operating in near-flawless fashion fiveyears after the final shuttle crew departed.

"Batteries are fine, solar arrays are fine, all the communications equipment is fine, we don't see anyglitches with the computers, the instruments are all fine," he said. "In fact, an interesting statistic,the Advanced Camera for Surveys, which was repaired by the astronauts during the last servicingmission, that's actually now run longer on the repair than it did originally for the Wide Field Camerapart of it."

The ACS, like the repaired Space Telescope Imaging Spectrograph, no longer has any internalredundancy.

"It's amazing. It truly is," Jeletic said. "Given all the things that can fail, a lot of people were hopingfor one or two years of continued work with it. Now we've gotten over five."

Likewise, the Space Telescope Imaging Spectrograph, which also is operating in "single-string"mode, is still going strong.

"It shares the load in spectroscopy with COS (Cosmic Origins Spectrograph)," Jeletic said. "COS getsa little bit more work, but STIS gets its fair share."

The only other instrument issues have been transitory space radiation-triggered single-event upsets"where a particle came down and hit some part of the computer circuitry and caused a bit to flip."

"You reset the electronics and you're back in business," Jeletic said. "So no damage or anything like

that, and we were back up and running in less than 30 hours. So that's a no brainer. We get those ondifferent parts of the spacecraft, that's not unusual."

Neither is shrinkage caused by a phenomenon known as desorption, in which atoms and moleculesmaking up a spacecraft's components can slowly migrate to the surrounding environment. As aresult, the telescope's structure has actually shrunk ever so slightly over the years. One of Hubble'sFine Guidance Sensors, while still operating normally, is suffering from a slightly reduced aperture.

"We see that, for example, with the optical telescope assembly, which is the structure that holds themirrors," Jeletic said. "Every so often, every two or three years, we'll actually do a secondary mirrormove to pull it back into focus. Similarly, with the Fine Guidance Sensors, there's still some of thatgoing on. Nothing that we can't manage right now, just watching that trend."

The only other issue of any significance is the March 7 loss of a gyroscope, apparently due to thefailure of a hair-thin flex wire that carried current to the unit. The gyro had operated for more than50,000 hours when it failed, a near record.

Three of the six gyros installed in 2009, including the one that in March, used an older style flexwire design while hair chalk three incorporated silver-coated "enhanced" flex wires to improvedurability. In an unrelated event, another gyro was put in powered-down reserve because of "noise"in its circuitry. Engineers have since uploaded software to compensate and the gyro is consideredfully operational.

In any case, Hubble normally operates with just three gyroscopes with the others in reserve,powered off but ready for use if needed. The gyro with the noise issue is one of the two currentlyheld in reserve.

Jeletic said the loss of one gyro poses no issues for Hubble, especially given that engineers havedeveloped software that would permit science operations to continue with two gyros or even withone.

"They're all ready to roll," Jeletic said of the software packages. "The two-gyro [software] was thefirst one, we actually used that before the previous servicing mission and then the one gyro we'veimplemented and tested as well. That's ready to go."

While engineers could improve Hubble's life expectancy by putting more gyros in reserve now, threeare required to maximize the observatory's science return.

"We want to optimize that situation and get as much science back as we can while all theinstruments are truly working," Jeletic said. "So we're going to stay in three-gyro mode. If thatchanges, if all the sudden we've lost two instruments or something, we may take another look atthat. Or, if we end up losing gyros over time and we're down to two gyros, then we will automaticallyjump to the one-gyro mode and put one in reserve. That's the game plan."

Predicted failures of Hubble's science instruments and subsystems give NASA managers optimismthe spacecraft will remain scientifically viable through the end of the decade. As the above chartsindicate, engineers believe there's a better than 80 percent chance the telescope can reach 2020without any major failures.

NASA

Operating Hubble much beyond 2020 will be technically and politically problematic. And no matterwhat happens, the telescope will continue slowly but surely losing altitude because of atmosphericdrag, a phenomenon that depends in large part on the 11-year solar cycle and how much the suncauses the atmosphere to heat up and expand.

Based on an average solar cycle, the latest projections show atmospheric friction will cause Hubbleto fall back to Earth around 2036. In a worst-case scenario, re-entry could come as early as 2027.

NASA still plans to attach a small rocket motor to the base of the telescope at some point to makesure it can be guided to a safe entry, one that will ensure surviving debris falls into the ocean.

But planning for Hubble's re-entry is many years away. In the near term, as a recent senior-levelNASA management review concluded, "Hubble is operating at or near the highest level ofperformance and scientific productivity in its history."

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