The Hubble Space Telescope’s main camera, the Advanced Camera for Surveys (ACS), stopped working over the weekend, forcing the aging observatory to rely on backup instruments, NASA said on Monday. At 7:34 a.m. EST on Saturday, Jan. 27, the telescope entered into a protective "safemode" condition, most likely triggered by a short circuit in the ACS, NASA said in a statement, and the backup electrical power supply failed. The camera had been running since June on its secondary backup electrical system after the primary system malfunctioned. The electrical system had also shut down in September as operators were switching between two of its three instruments. Investigators said they think debris stuck in a switch caused that shutdown.Hubble's main camera, the Advanced Camera for Surveys (ACS), before launch. ACS took over from the Wide Field and Planetary Camera 2 as Hubble's "workhorse" camera in 2002. (Photo: Ball Aerospace & Technologies Corp.) While a review board will look into the situation, "it is expected that the main part of ACS will most likely not be restored," NASA said. Hubble was recovered from safemode around 2 a.m. EST on Sunday, and science observations will resume this week using the remaining Hubble instruments: Wide Field Planetary Camera 2 (WFPC2), Near Infrared Camera Multi-Object Spectrograph, and the Fine Guidance Sensors, NASA said. Engineers currently are assessing the option to return ACS science operations to the primary electronics so that observations could resume in a reduced mode. In November 2006, the Space Telescope Science Institute in Baltimore selected a set of backup non-ACS science programs for use in case of a future ACS malfunction. These programs now will be used to maintain the observing program, NASA said. The ACS is a third-generation instrument consisting of three electronic cameras, filters and dispersers that detect light from the ultraviolet to the near-infrared. The instrument was installed during a March 2002 servicing mission to increase Hubble's vision and has provided the clearest pictures yet of galaxy formation in the early universe. It was developed jointly by NASA's Goddard Space Flight Center, Greenbelt; Johns Hopkins University, Baltimore; Ball Aerospace, Boulder, Colo.; and the Space Telescope Science Institute, which conducts Hubble's science operations. "ACS took over from WFPC2 as Hubble's 'workhorse' at the last servicing mission in 2002. Although we are taking a step back, it is far from 'game over' for Hubble," said European Space Agency (ESA) Hubble scientist Bob Fosbury. The telescope is a project of international cooperation between NASA and the ESA. The space agency is urging astronomers that use Hubble to change their upcoming observing programs to take the camera failure into account. The deadline for submitting changed proposals for the present observing cycle, Cycle 16, is Feb. 9, NASA said. Out of a total of 750 proposals submitted, 500 requested use of the ACS camera.Located about 6500 light-years from Earth, the Crab Nebula is the remnant of a star that began its life with about 10 times the mass of our sun. Its life ended on July 4, 1054, when it exploded as a supernova. Here, the Hubble Space Telescope has zoomed in on the center of the Crab to reveal its structure with unprecedented detail. (Image: NASA and The Hubble Heritage Team) An Anomaly Review Board was appointed yesterday to investigate the ACS shutdown and decide the best course of action. The board will decide whether ACS can be returned by using the primary electrical system to enable one of its parts, the Solar Blind Channel, to return to operation. The board is scheduled to present its recommendations by March 2. "It is too early to know what influences the ACS anomaly may have on Hubble Space Telescope Servicing Mission-4 planning," said Preston Burch, associate director/program manager for the Hubble Space Telescope. "It is important that the review board conduct a thorough investigation that will allow us to determine if there are any changes needed in the new instruments that will be installed on the upcoming servicing mission so that we can be sure of maximizing the telescope's scientific output. We are continuing to make excellent progress in our preparations for the servicing mission, which is presently targeted to fly in September 2008." In Oct. 2006, NASA approved a plan for astronauts will make one final house call to Hubble as part of a mission to extend and improve the observatory's capabilities through 2013. Now NASA said it will investigate options for repairing the ACS during this mission.In one of the most detailed astronomical images ever produced, NASA's Hubble Space Telescope captured an unprecedented look at the Orion Nebula. This turbulent star formation region is one of astronomy's most dramatic and photogenic celestial objects. More than 3,000 stars of various sizes appear in this image. Some of them have never been seen in visible light. These stars reside in a dramatic dust-and-gas landscape of plateaus, mountains, and valleys that are reminiscent of the Grand Canyon. The Orion Nebula is a picture book of star formation, from the massive, young stars that are shaping the nebula to the pillars of dense gas that may be the homes of budding stars. (Image: NASA,ESA, M. Robberto Space Telescope Science Institute/ESA and the Hubble Space Telescope Orion Treasury Project Team) The two new instruments to be installed are the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). The COS is the most sensitive ultraviolet spectrograph ever flown on Hubble. The instrument will probe the cosmic web, the large-scale structure of the universe whose form is determined by the gravity of dark matter and is traced by the spatial distribution of galaxies and intergalactic gas. WFC3 is a new camera sensitive across a wide range of wavelengths (colors), including infrared, visible and ultraviolet light. It will help Hubble provide images of early and distant galaxies currently beyond its reach. Other planned work includes installing a refurbished Fine Guidance Sensor that replaces one degrading unit of the three already onboard. The sensors control the telescope's pointing system. An attempt will also be made to repair the Space Telescope Imaging Spectrograph. Installed in 1997, it stopped working in 2004. The instrument is used for high resolution studies in visible and ultraviolet light of both nearby star systems and distant galaxies, providing information about the motions and chemical makeup of stars, planetary atmospheres, and other galaxies. For more information, visit: www.nasa.gov/hubble