How the Space Shuttle completed a final, daring Hubble repair 15 years ago

The Hubble Space Telescope continues to operate to this day in part due to the work performed 15 years ago by the crew of STS-125. Dubbed Hubble Servicing Mission 4 (HSM 4), scientists knew this would be their final chance to use the space shuttle to visit and upgrade the orbiting laboratory.

As we look back on the mission, the question remains whether or not Hubble will be visited or repaired again.

Hubble’s Blurry Start

Launched in April 1990, the Hubble Space Telescope started off with a serious defect. NASA had to announce that the billion-dollar observatory was not functioning as it should. This was due to a mirror that was precisely ground to the wrong shape — by just 1/50th the width of a human hair — a decade earlier at the Perkin-Elmer facility in Danbury, Connecticut.

Known as a “spherical aberration,” the mistake meant that all points of light would not focus at a singular point, essentially rendering the telescope nearsighted, with many images appearing blurry.

After much lauding from late-night comedians, the press, and even members of congress who originally supported the telescope, it was decided that a repair mission would be attempted to literally bring Hubble into focus.

Servicing Mission 1

Launching in 1993, STS-61 installed the Wide Field and Planetary Camera-2 (WF/PC2), which would replace the original Wide Field and Planetary Camera (WF/PC) and feature built-in corrective optics, and the Corrective Optics Space Telescope Axial Replacement (COSTAR) box which would correct the light for three axial instruments. The High Speed Photometer (HSP), which was one of four instruments mounted in boxes just above the telescope’s mirror, was sacrificed and COSTAR was installed in its place.

The repairs were a resounding success.

More Visits to Hubble

While engineers never planned for entire instruments to be removed from it, Hubble continued to get smarter and sharper. Servicing Mission 2 visited in 1997 adding the Space Telescope Imaging Spectrograph and Near Infrared Camera and the Multi-Object Spectrometer.

Astronauts Steven Smith and John Grunsfeld work inside Hubble during Servicing Mission 39 in 1999. (Credit: NASA)

Then Hubble was hit with failing gyroscopes, which help keep it pointed at its targets. Three of the six onboard the telescope had failed. That saw the launch of Servicing Mission 3A in 1999. Not only were the gyros replaced, the crew upgraded the computers and electronics in anticipation the next mission, 3B.

Three years later Columbia visited and installed the first new instrument since that second servicing mission, the Advanced Camera for Surveys, doubling the view of the wide field camera already onboard and bringing Hubble into the 21st century along with upgrading its solar panels to more effective ones.

Had Atlantis suffered major damage during her launch to the telescope, Endeavour was sat on Pad 39B, ready to launch at short notice on an ambitious rescue mission.

Uncertainty Over HSM 4

Crews had hoped for at least one more repair mission, but that was put into serious doubt following the loss of the STS-107 crew upon reentry in 2003. The shuttle was grounded while improvements to vehicle safety were made, however during that down time, President George W. Bush announced that the shuttle program would be retired in 2010.

On Jan. 6, 2004, NASA Administrator Sean O’Keefe made the decision to cancel the fifth servicing mission, labeled HSM 4, amid safety concerns after the recent disaster.

However, NASA’s next administrator, Mike Griffin, reinstated the mission after safety concerns were addressed, and Space Shuttle Atlantis would fly the STS-125 mission to Hubble. One of the risk mitigation procedures included a unique rescue mission in the event of an anomaly.

Rescue Mission

This rescue mission was called STS-400.

When the Space Shuttle fleet returned to action after the loss of Columbia, major alternations were made both to the vehicle and to the procedures – all aimed at mitigating the threats of damage to the Thermal Protection System (TPS) on the orbiter.

While engineers successfully reduced most of the foam liberations from the External Tank – the cause of the damage that mortally wounded Columbia – it was decided that an additional backup option would become the norm – using the International Space Station (ISS) as a “Safe Haven” if inspections showed major damage to the heat shield of the orbiter.

That was the pattern for all RTF (Return To Flight) missions, with on-orbit inspections of Flight Day 2 involving the Orbiter Boom Sensor System (OBSS) checking over every inch of the orbiter TPS to send huge amounts of photos and video to the Damage Assessment Team (DAT) on the ground.

The OBSS and a slide of detailed chip damage – via L2

All the OBSS imagery from its suite of sensors would then be followed up by the stunning RPM (R-bar Pitch Maneuver, popularly called the Rendezvous Pitch Maneuver) that put the orbiter into a black flip under the Station while ISS crewmembers took high-quality photos of the TPS.

This maneuver was also a new inclusion for Return To Flight and also required the mission to be to the ISS.

The orbiter would then dock with the ISS and, providing the DAT cleared the orbiter from any damage concerns, one final inspection would take place shortly after undocking in order to provide the final green light to return home.

At any point during the mission timeline, the observation of major damage would have resulted in a call to evaluate repairs or opt to use the ISS as “Safe Haven” – an option still available to the crew even after undocking, per a contingency return to the ISS if issues had been found during “Final Inspections” with the OBSS.

Shuttle managers always had this option during ISS missions, with the next orbiter set to launch placed into a point of her processing flow that would allow a change of call signs.

Had the call to take up “Safe Haven” been made, the next orbiter would move to her “LON” (Launch On Need) call sign, assigned as Contingency Shuttle Crew Support (CSCS) on the manifests, abandoning its primary mission flow and moving to the pad as a rescue vehicle, launching with a subset of four from her assigned crew.

For example, the Atlantis STS-122 mission had Endeavour on LON standby as STS-323. Once Atlantis was cleared for return, Endeavour reverted back to her primary STS-123 mission flow.

The Shuttle (FAWG) Manifest ahead of STS-125 – via L2 (Note, the plans changed for the latter flights

Incidentally, the fate of the damaged orbiter during such a contingency was mostly based on programming that would have ordered the orbiter to undock and conduct a destructive, tail-first, re-entry over the Pacific Ocean.

However, there were options to allow the orbiter to make an uncrewed landing via a box of tricks to carry out some of the crew inputs, such as lowering the landing gear. It was always unlikely to be used during a Safe Haven/LON event, given the concerns a damaged orbiter would not survive re-entry.

The Autonomous Orbiter Rapid Prototype (AORP) was a modification that matured to full RCO (Remote Control Orbiter), allowing the orbiter to complete the final landing procedures requiring human intervention. It would have required crewmembers on the ISS to install a box into the flight deck over certain “human intervention” switches.

All of the remaining Shuttle missions were dedicated to finishing the assembly of the ISS, allowing this key backup of “Safe Haven” to be implemented until the end of the program. There was a plan to return to Hubble one final time, but NASA Administrator Sean O’Keefe canceled this mission due to the fallout from the Columbia disaster.

However, with Hubble in desperate need of upgrades and repairs, pressure from the science community and then lawmakers – notably Senator Barbara Mikulski – successfully gained support from O’Keefe’s replacement, Mike Griffin, who reinstated the mission.

That led to a major review within NASA, given that this mission would not have the support of “Safe Haven” and actually included additional risks for the orbiter. It would have to push its propellant reserves to reach the higher orbit of Hubble and also increase the risk of being hit by MMOD (Micro-Meteoroid Orbiting Debris).

After much deliberation, the solution was to have another Shuttle on the adjacent pad, ready to launch at short notice to rush to the aid of Atlantis’ crew.

As the Shuttle manifest started to align, Atlantis was awarded STS-125’s servicing mission to Hubble and Endeavour was next in line to launch and thus gained the STS-400 rescue mission supporting role.

The “unofficial” STS-400 patches used within NASA via NSF and CollectSPACE

Normally, with “Safe Haven” in play, the crew of the damaged orbiter could reside in the ISS for several months until the next Shuttle could be launched to return them to Earth. However, with no”Safe Haven,” Atlantis would go through two stages of power-down procedures to stretch consumables to around four weeks in “lifeboat” mode.

If unrepairable damage is detected during the FD-2 TPS inspections and a decision is made to conduct an immediate Group C+ power-down, Atlantis could act as a life raft for her Flight Crew for just over 24 days if needed.

Similarly, should un-repairable damage be detected on FD-10 during the late inspections, and the decision made to move immediately into Group C+ power-down, Atlantis could act as a life raft for an additional 16.5 days, with the STS-400 rescue mission arriving No Earlier Than 15 days 16 hours after the damage was detected.

While a ‘P-t-P’ (Pad to Pad) option was available, the turnaround was classed as “too tight to be viable.” Thus, NASA opted to hold back the full handover date of Pad 39B to the Constellation Program in preparation for the Ares I-X test launch until after the stand-down was given during STS-125. Endeavour was the last Shuttle to reside on Pad 39B.

Atlantis and Endeavour on the KSC pads – via L2

The dual flows for Atlantis and Endeavour saw the latter play musical chairs during their processing flows before both taking up residency at the KSC pads.

After the stand-down of the LON requirement was given during STS-125, Endeavour would then be transported from Pad B to Pad A and prepared for her primary mission, STS-126.

As Atlantis launched on STS-125, the Rotating Service Structure (RSS) on 39B was closed to protect Endeavour.

Atlantis STS-125 launches as Endeavour STS-400 sits on 39B – via NASA

Had Atlantis suffered major damage during ascent, the first option would have been to attempt spacewalks to repair the areas of concern via onboard items such as the Tile Repair Ablator Dispenser (T-RAD).

If the orbiter were in such a state that she was deemed unable to return the crew safely, Endeavour would have launched within a week.

The STS-400 crew would have been a subset of her STS-126 crew, four crew members, led by Commander Christopher Ferguson and pilot Eric Boe.

Endeavour would have arrived at the stricken Atlantis before Atlantis grappled onto Endeavour via her robotic arm. Endeavour’s robotic arm would be used to help transfer the crew via the two orbiters.

The two orbiters during the grapple and crew transfer – via NASA

A full day’s worth of EVAs would take place, transporting the seven crew members of the STS-125 to Endeavour.

The transfer was more complicated than “just” transferring the crew, as EMU space suits and the crew’s entry suits also had to move during the transfer.

The complex transfer between Atlantis and Endeavour – via L2

Following capture, a 90‐degree yaw of the arm would put the two vehicles payload bay‐to‐payload bay, providing the most stable attitude and position relative to the Earth’s location, ahead of the three spacewalks by Atlantis’ crew to relocate
to Endeavour.

The third day of the mission would have been dedicated to setting up the translation path from Atlantis to Endeavour and starting crew transfer. The crew would have strung a cable along the length of the robot arm to serve as the translation path, and the first crewmember would have been moved to Endeavour.

The first spacewalk would have been scheduled to last four hours and 50 minutes, followed by three more. The final spacewalk was budgeted for about two hours and 30 minutes. Prior to leaving Atlantis, the orbiter would reconfigure the vehicle so that she could be ground commanded through a deorbit disposal burn.

Once all the crew and equipment were transferred, the command would be given to ungrapple Atlantis ahead of the return home. The additional crew members on Endeavour would have been accommodated via additional seats installed on the middeck.

Returning the Atlantis crew – via L2 and NASA

Thankfully, none of these procedures were required, as STS-125 was carried out successfully, and Atlantis returned home safely.

This removed what would have been one of the riskiest missions undertaken during the 30-year career of the Space Shuttle Fleet, where a crew of four would have launched on an orbiter just days after an event had crippled the orbiter on the previous launch.

The STS-400 crew would have launched on a rescue mission where they would have placed themselves in danger with no backup plan, resulting in both the STS-125 and STS-400 crews being left to their ultimate fate in space.

Ultimately, the Hubble Servicing Mission gamble paid off.

For Endeavour, the original plan was to move to 39A for STS-126 after the STS-400 standdown. However, with the delay to 125 from October 2008 to May 2009, Endeavour’s primary mission was STS-127 instead, but it still used the four-person STS-126 subset crew.

Launching STS-125

As NASA approached launch in September 2008, a malfunction occurred in one of the systems that commands the science instruments and directs the flow of data within the telescope. With an uncertain future for Hubble, NASA wasn’t going to leave it without a backup, delaying the launch to May 2009.

Atlantis launches on the STS-125 mission. (Credit: NASA)

Space Shuttle Endeavour sat by on 39B as Atlantis took to the skies on the final shuttle repair mission to Hubble, lifting off on May 11, 2009.

Following a day of checking Atlantis’ tiles for damage using a special tool called the Orbiter Boom Sensor System (OBSS) and orbital maneuvering system (OMS) engine burns, the crew of seven had rendezvoused with Hubble.

Astronaut Megan McArthur got the honor of grappling Hubble with the shuttle’s Canadarm and attaching it to a special platform inside the payload bay, where it would stay until repairs were completed.


With the tight schedule and demanding workload, the crews working during each spacewalk would rotate, allowing them some breaks in-between extravehicular activities (EVA). Through all of this, McArthur, along with Commander Scott Altman and Pilot Gregory Johnson, would assist from inside the shuttle. They would be known as the intravehicular activity (IVA) support team.

The first spacewalk saw John Grunsfeld and Drew Feustel replacing one of the most famous cameras, Wide Field Camera 2 (WFC2), responsible for taking well known photos like the pillars of creation. This was replaced by Wide Field Camera 3 (WFC3), which mainly observed in UV and infrared light. It produced a much wider view with higher sensitivity than its predecessor.

WFC2 is currently located at the Smithsonian Air and Space Museum after being returned to Earth on this mission.

This first spacewalk also installed a low impact docking system meant to allow an uncrewed spacecraft to dock that would help deorbit Hubble near the end of its life.

Astronauts John Grunsfeld and Andrew Feustel work to replace Hubble’s Wide Field and Planetary Camera 2 with Wide Field Camera 3 during EVA 1. (Credit: NASA)

EVA 2 saw Michael Good and Mike Massimino primarily focus on installing new gyroscopes as well as fresh batteries inside Hubble.

The next new instrument came on the third spacewalk, when Grunsfeld and Feustel installed the Cosmic Origins Spectrograph (COS). Taking the place of COSTAR inside the telescope, it was known as the most sensitive ultraviolet spectrograph ever planned to fly. COSTAR had been deemed obsolete following the installation of a newer version of the optical fix during HSM 3B in 2002.

The duo also attempted to repair an instrument never designed to be worked on in orbit. The Advanced Camera for Surveys (ACS), one of the main visible light cameras, needed its power supply fixed. In fact this camera took the world-famous Hubble ultra deep field picture which gave us a true scale of the universe.

The crew used custom made tools to remove an access panel and replace the camera’s four circuit boards, plus install a new power supply. All but one instrument aboard ACS came back to life.

The fourth spacewalk saw Good and Massimino attempting to remove a second instrument that required special attention due to its Earth-only repair design.

Astronauts Michael Good and Mike Massimino work to remove a handle with a stripped screw inside of Hubble during EVA 4. (Credit: NASA)

The Space Telescope Imaging Spectrograph had failed five years earlier due to a blown power supply. The instrument, though, was located behind a panel which required four handles to be removed. That would be followed by the removal of 111 small screws and washers.

The first issue came as they removed the handles. The first three came off without a problem, however the last one had a stripped bolt on the bottom. Crews worked on the ground in real-time to try and come up with a solution. In the end, brute force was needed.

“This was just done, just now, at Goddard on a flight equipment unit and it took 60 pounds linear at the top of the handhold to fail the single bolt in the lower right position at the bottom,” said the CAPCOM in Mission Control in Houston.

“OK. Mass, you copy that? Sixty pounds linear at the top of the handrail to pop off that bottom bolt,” noted Good. “I think you’ve got that in you.”

“I can try,” replied Massimino.

Despite concerns over debris, the handle was forcefully removed by Massimino and safely disposed. This now allowed for the attachment of a device known as the fastener capture plate (FCP). All 111 small screws and washers were removed and held between the box cover and the capture plate so none floated away, allowing for the repair of the spectrograph.

The Fastener Capture Plate following its return to Earth. (Credit: Sawyer Rosenstein for NSF)

Then came the last-ever spacewalk to fix Hubble, where Grunsfeld and Feustel installed a second battery module, a refurbished fine guidance sensor, new thermal blankets where the current ones had degraded, and additional small final quality of life improvements.

Hubble’s Future

On May 19, 2009, Hubble was released from the shuttle’s payload bay for the final time. Atlantis safely landed back at Edwards Air Force Base in California following a successful 14 day mission.

Despite the addition of the docking adapter, it is unknown if there is a plan to use it once Hubble reaches its end of life.

Jared Isaacman, who has flown on Inspiration 4 and will fly aboard Polaris Dawn, has proposed using a SpaceX Dragon capsule to rendezvous with and dock to Hubble using the equipment installed on STS-125. He believes they could raise the spacecraft’s orbit, extending its life, and even possibly conducting more repairs.

“No matter what…you want this amazing asset to just be healthier and when we put it into a higher orbit… you can kick that that bad boy up and give it another 10 or 15 more years of of life,” Isaacman told NSF during a recent NSF Live.

(Lead image: The Hubble Space Telescope inside the payload bay of the Space Shuttle Atlantis during the STS-125 mission. Credit: NASA)

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