A functional test of the Hubble Space Telescope's Advanced Camera for Surveys, overhauled during a spacewalk Saturday by astronauts John Grunsfeld and Andrew Feustel, indicates success reviving the instrument's heavily used wide-field channel, officials said early Sunday. But testing shows the overhaul failed to resolve power problems with the camera's stricken high-resolution channel and it appears "down for the count."

Illustration of the ACS instrument following the spacewalkers' repairs. Credit: NASA

The ACS, a sophisticated camera installed during a shuttle servicing mission in 2002, was designed to operate in three modes: a high-resolution channel, a wide-field camera and a so-called solar blind channel. Following major power system failures in 2006 and 2007, the heavily used wide-field and high-resolution channels were knocked out of action. The solar-blind channel later was restored to operation.

During Saturday's spacewalk, Grunsfeld replaced four circuit boards in the wide-field channel electronics and attached a replacement low-voltage power supply. Engineers devised a way to "back-power" the high-resolution channel with the new power supply and control electronics, although they were less confident of that plan's success.

The ACS passed an initial aliveness test during the spacewalk and engineers at the Goddard Space Flight Center in Greenbelt, Md., began a more detailed functional test later in the evening. An early step in that procedure turned on the high-resolution channel and almost immediately engineers saw it drawing too much current. The test was halted and commands to the high-resolution channel were taken out. Testing of the wide-field channel later resumed.

"The wide field channel was tested this evening, that was the major focus of the spacewalk yesterday, trying to get that channel back up and running," mission control commentator Josh Byerly said early Sunday. "The payloads officer confirmed that everything looks fine on the wide-field channel. So good news on that front.

"The high-resolution channel, however, ran into some issues, some power fluctuations were seen. ... They did confirm the short in the wiring of the high-resolution channel was actually upstream of where the astronauts were working yesterday. What this means is the repair was not successful on that specific channel."

The wide-field channel is the most heavily used by the science community and as a result, the repair work Saturday is "still considered a success, even with this high-resolution channel being down for the count," Byerly said.

In an interview before launch, Hubble Program Manager Preston Burch described the complexity - and the unknowns - associated with repairing the ACS high-resolution channel.

"It turns out there are shared copper paths between the electronics for both of those channels," he said. "So what we said was, hey, why don't we get to the high-res channel through the electronics paths that are connected to the wide-field channel? We'll just back power the existing printed circuit boards that are in the high-resolution channel CCD.

"We tested that on the ground and sure enough, it turns out to be feasible to do that. The only question mark is the status of the low voltage power supply on the MED 1 and MED 2 sides. In other words, it's possible that if there's damage on the sides of the interpoint converters, the secondary sides that are powering the high-resolution channel, it's possible there are some short circuits there that will prevent this scheme from working. Particularly on the one side that suffered the major damage. That may not work very well."

During the spacewalk Saturday, Grunsfeld installed a new low-voltage power supply "that will try to rejuvenate, or bring back to life, the high-resolution channel by back powering the high-res channel through these shared copper paths that connect to the wide-field channel," Burch said. "I won't say it's a long shot. It IS somewhat of a long shot, but people need to understand that this doesn't have the same degree of rigor as, let's say, building a brand new science instrument or a new black box that we're hooking up to standard interfaces that already exist on the telescope. This is really a bit of an experiment."

Additional coverage for subscribers:
VIDEO: SATURDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: REPAIR OF ADVANCED CAMERA FOR SURVEYS FINISHED PLAY
VIDEO: WATCH AS GRUNSFELD REPAIRS HUBBLE CAMERA PLAY
VIDEO: COSTAR STOWED IN ATLANTIS' PAYLOAD BAY PLAY
VIDEO: UMBILICALS HOOKED UP TO NEW INSTRUMENT PLAY
VIDEO: COSMIC ORIGINS SPECTROGRAPH INSTALLED PLAY
VIDEO: SPECTROGRAPH PREPPED IN LAUNCH CARRIER PLAY
VIDEO: COSTAR OPTICS PACKAGE REMOVED FROM HUBBLE PLAY
VIDEO: SPACEWALKERS OPEN SHROUD DOORS ON TELESCOPE PLAY
VIDEO: NARRATED PREVIEW OF SPACEWALK NO. 3 PLAY
VIDEO: FLIGHT DIRECTOR'S PREVIEW OF MISSION'S DAY 6 PLAY

VIDEO: FLIGHT DAY 5 HIGHLIGHTS MOVIE PLAY
VIDEO: FRIDAY NIGHT UPDATE FROM HST CONTROL CENTER PLAY
VIDEO: FRIDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: SPARE GYRO UNIT INSTALLED INTO THIRD POSITION PLAY
VIDEO: ANOTHER GYROSCOPE UNIT PUT INTO SECOND SLOT PLAY
VIDEO: TROUBLE INSTALLING SECOND GYROSCOPE PACKAGE PLAY
VIDEO: REMOVAL OF SECOND GYROSCOPE PACKAGE FROM HUBBLE PLAY
VIDEO: INSTALLATION OF FIRST GYROSCOPE INTO HUBBLE PLAY
VIDEO: REMOVAL OF FIRST GYROSCOPE PACKAGE FROM HUBBLE PLAY
VIDEO: NARRATED PREVIEW OF SPACEWALK NO. 2 PLAY
VIDEO: FLIGHT DIRECTOR'S PREVIEW OF MISSION'S DAY 5 PLAY

VIDEO: FLIGHT DAY 4 HIGHLIGHTS MOVIE PLAY
VIDEO: THURSDAY NIGHT UPDATE FROM HST CONTROL CENTER PLAY
VIDEO: THURSDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: SOFT CAPTURE MECHANISM PUT ON HUBBLE PLAY
VIDEO: SCIENCE INSTRUMENT COMMAND & DATA HANDLING UNIT PLAY
VIDEO: PARTIALLY FAILED SIC&DH UNIT REMOVED FROM HST PLAY
VIDEO: WFPC2 CAMERA STOWED IN ATLANTIS FOR RETURN PLAY
VIDEO: OVERVIEW OF WIDE FIELD CAMERA 3 INSTRUMENT PLAY
VIDEO: SPACEWALKERS INSTALL THE WIDE FIELD CAMERA 3 PLAY
VIDEO: NEW WIDE FIELD CAMERA 3 PREPPED FOR INSTALLATION PLAY
VIDEO: 16-YEAR-OLD WFPC2 CAMERA REMOVED FROM HUBBLE PLAY
VIDEO: LATCHING BOLT ON WPFC2 FINALLY RELEASED PLAY
VIDEO: FIGHTING WITH TROUBLESOME BOLT ON WPFC2 PLAY
VIDEO: FEUSTEL INSTALLS HANDLE ONTO WPFC2 FOR REMOVAL PLAY
VIDEO: HANDLING FIXTURE DEPLOYED TO HOLD OLD CAMERA PLAY
VIDEO: GRUNSFELD INSTALLS SUPPORT POSTS UNDER HST PLAY
VIDEO: FEUSTEL OPENS LATCHES ON INSTRUMENT CARRIER PLAY
VIDEO: ASTRONAUTS EXIT AIRLOCK TO START EVA NO. 1 PLAY
VIDEO: NARRATED PREVIEW OF SPACEWALK NO. 1 PLAY

VIDEO: FLIGHT DAY 3 HIGHLIGHTS MOVIE PLAY
VIDEO: WEDNESDAY NIGHT UPDATE FROM HST CONTROL CENTER PLAY
VIDEO: WEDNESDAY'S MISSION MANAGEMENT TEAM UPDATE PLAY
VIDEO: WEDNESDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: TIME-LAPSE OF MOVING HUBBLE INTO PAYLOAD BAY PLAY
VIDEO: SHUTTLE ATLANTIS' ROBOT ARM CAPTURES HUBBLE PLAY
VIDEO: FIRST UP CLOSE VIEWS OF HUBBLE IN 7 YEARS PLAY
VIDEO: SHUTTLE ENGINE FIRING TO CIRCULARIZE ORBIT PLAY
VIDEO: INSIGHTFUL OVERVIEW OF ATLANTIS' MISSION PLAY
VIDEO: NARRATED PREVIEW ANIMATION OF HUBBLE RENDEZVOUS PLAY

VIDEO: FLIGHT DAY 2 HIGHLIGHTS MOVIE PLAY
VIDEO: TUESDAY NIGHT UPDATE FROM HST CONTROL CENTER PLAY
VIDEO: TUESDAY'S MISSION MANAGEMENT TEAM UPDATE PLAY
VIDEO: SLOW-MOTION OF DEBRIS THAT APPARENTLY HIT TILES PLAY
VIDEO: TILE DAMAGE FOUND DURING INSPECTIONS PLAY
VIDEO: CAPCOM CALLS CREW ABOUT MINOR DAMAGE PLAY
VIDEO: TUESDAY'S MISSION STATUS BRIEFING PLAY
VIDEO: PREVIEW ANIMATION OF HEAT SHIELD INSPECTIONS PLAY

VIDEO: FLIGHT DAY 1 HIGHLIGHTS MOVIE PLAY
VIDEO: THE FULL STS-125 LAUNCH EXPERIENCE PLAY
VIDEO: LAUNCH REPLAY: EXTERNAL TANK CAMERA PLAY
VIDEO: FOOTAGE OF FUEL TANK AFTER JETTISON PLAY

VIDEO: LAUNCH REPLAY: FRONT CAMERA PLAY
VIDEO: LAUNCH REPLAY: BEACH TRACKER PLAY
VIDEO: LAUNCH REPLAY: PAD PERIMETER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: UCS-23 TRACKER PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-1 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-2 PLAY
VIDEO: LAUNCH REPLAY: CAMERA CS-6 PLAY
VIDEO: LAUNCH REPLAY: VAB ROOF PLAY
VIDEO: LAUNCH REPLAY: PRESS SITE PLAY
VIDEO: LAUNCH REPLAY: WEST TOWER PLAY
VIDEO: LAUNCH REPLAY: CAMERA 009 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 041 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 049 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 050 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 051 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 060 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 061 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 063 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 070 PLAY
VIDEO: LAUNCH REPLAY: CAMERA 071 PLAY

VIDEO: SPACE SHUTTLE ATLANTIS BLASTS OFF! PLAY | HI-DEF
VIDEO: STS-125 POST-LAUNCH NEWS CONFERENCE PLAY
VIDEO: INSIDE MISSION CONTROL DURING LAUNCH PLAY
VIDEO: NARRATED ANIMATION OF DAY 1 INSPECTIONS PLAY

VIDEO: FINAL PRE-LAUNCH READINESS POLLS CONDUCTED PLAY
VIDEO: SHUTTLE'S CREW MODULE HATCH CLOSED FOR FLIGHT PLAY
VIDEO: MISSION SPECIALIST MEGAN MCARTHUR BOARDS PLAY
VIDEO: PILOT GREG JOHNSON BOARDS ATLANTIS PLAY
VIDEO: MISSION SPECIALIST JOHN GRUNSFELD BOARDS PLAY
VIDEO: SHUTTLE COMMANDER SCOTT ALTMAN BOARDS PLAY
VIDEO: CREW DEPARTS QUARTERS FOR LAUNCH PAD PART 1 | PART 2
VIDEO: ASTRONAUTS DON SPACESUITS FOR LAUNCH PLAY
VIDEO: TIME-LAPSE OF LAUNCH PAD GANTRY ROLLBACK PLAY

VIDEO: HUBBLE'S FUTURE AFTER ATLANTIS SERVICING PLAY
VIDEO: TOP DISCOVERIES MADE BY HUBBLE TELESCOPE PLAY
VIDEO: THE ROLLERCOASTER LIFE OF HUBBLE PLAY
VIDEO: WHAT IS HUBBLE'S PLACE IN HISTORY? PLAY
VIDEO: ENTERTAINING LOOK AT ATLANTIS' CREW PLAY
VIDEO: HUBBLE SPACE TELESCOPE HISTORY MOVIE PLAY
VIDEO: A TRIBUTE TO THE CAMERA THAT SAVED HUBBLE PLAY
VIDEO: HUBBLE TELESCOPE PROGRAM BRIEFING FROM SUNDAY PLAY

VIDEO: SUNDAY'S COUNTDOWN STATUS AND WEATHER UPDATE PLAY
VIDEO: THE STS-125 PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: SATURDAY'S COUNTDOWN STATUS AND WEATHER UPDATE PLAY
VIDEO: ASTRONAUTS ARRIVE AT THE CAPE FOR LAUNCH PLAY
VIDEO: FRIDAY'S COUNTDOWN STATUS AND WEATHER UPDATE PLAY

VIDEO: NEWS BRIEFING FOLLOWING FLIGHT READINESS REVIEW PLAY

VIDEO: REFRESHER BRIEFING: THE STS-125 MISSION PLAY
VIDEO: REFRESHER BRIEFING: HUBBLE SPACE TELESCOPE PLAY
VIDEO: REFRESHER BRIEFING: THE SEVEN ASTRONAUTS PLAY

VIDEO: BIOGRAPHY MOVIE OF ATLANTIS' CREW PLAY
VIDEO: INTERVIEW WITH COMMANDER SCOTT ALTMAN PLAY | '09 UPDATE
VIDEO: INTERVIEW WITH PILOT GREG JOHNSON PLAY
VIDEO: INTERVIEW WITH MS1 MIKE GOOD PLAY
VIDEO: INTERVIEW WITH MS2 MEGAN MCARTHUR PLAY
VIDEO: INTERVIEW WITH MS3 JOHN GRUNSFELD PLAY | '09 UPDATE
VIDEO: INTERVIEW WITH MS4 MIKE MASSIMINO PLAY | '09 UPDATE
VIDEO: INTERVIEW WITH MS5 DREW FEUSTEL PLAY | '09 UPDATE

VIDEO: SHUTTLE ATLANTIS ARRIVES AT LAUNCH PAD 39A PLAY | HI-DEF
VIDEO: THE SUN RISES ON ATLANTIS DURING ROLLOUT PLAY | HI-DEF
VIDEO: ATLANTIS EMERGES FROM ASSEMBLY BUILDING PLAY | HI-DEF
VIDEO: ORBITER VERTICAL FOR MATING TO FUEL TANK PLAY | HI-DEF
VIDEO: ATLANTIS MOVES BACK TO ASSEMBLY BUILDING PLAY | HI-DEF

VIDEO: ATLANTIS LEAVES LAUNCH PAD 39A IN OCT. PLAY
VIDEO: TIMELAPSE OF THE ROLLBACK GETTING UNDERWAY PLAY

VIDEO: ASTRONAUTS REHEARSE QUICK SHUTTLE EXIT PLAY
VIDEO: CREW BOARDS ATLANTIS FOR MOCK COUNTDOWN PLAY
VIDEO: ASTRONAUTS DON SUITS FOR PRACTICE COUNTDOWN PLAY
VIDEO: CREW'S TRAINING ON ESCAPE BASKETS AND BUNKER PLAY
VIDEO: ASTRONAUTS CHAT WITH PRESS AT LAUNCH PAD PLAY
VIDEO: CREW TEST DRIVES EMERGENCY PAD ESCAPE VEHICLE PLAY
VIDEO: COMMANDER AND PILOT PRACTICE LANDING APPROACHES PLAY
VIDEO: CREW ARRIVES AT CAPE FOR PRACTICE COUNTDOWN PLAY
VIDEO: COMMENTS FROM COMMANDER AFTER ARRIVING PLAY

VIDEO: AERIAL VIEWS OF ATLANTIS AND ENDEAVOUR PLAY | HI-DEF

VIDEO: PRE-FLIGHT BRIEFING: THE STS-125 MISSION PLAY
VIDEO: PRE-FLIGHT BRIEFING: THE FIVE SPACEWALKS PLAY
VIDEO: PRE-FLIGHT BRIEFING: THE SEVEN ASTRONAUTS PLAY
VIDEO: PRE-FLIGHT BRIEFING: NASA LEADERSHIP PLAY
VIDEO: PRE-FLIGHT BRIEFING: SHUTTLE PROGRAM BOSS PLAY
VIDEO: PRE-FLIGHT BRIEFING: HUBBLE OVERVIEW PLAY
VIDEO: PRE-FLIGHT BRIEFING: HUBBLE SCIENCE PLAY

VIDEO: SHUTTLE ARRIVES ATOP PAD 39A PLAY
VIDEO: ATLANTIS EMERGES FROM VEHICLE ASSEMBLY BUILDING PLAY
VIDEO: TIME-LAPSE MOVIE OF ATLANTIS' ROLLOUT TO LAUNCH PAD PLAY

VIDEO: ATLANTIS ROLLS FROM HANGAR TO VAB PLAY
VIDEO: ATLANTIS LIFTED INTO PLACE FOR ATTACHMENT PLAY
MORE: STS-125 VIDEO COVERAGE
NEW! HIGH DEFINITION VIDEO
SUBSCRIBE NOW