The main camera on the Hubble Space Telescope (HST) has shut down after an electrical failure, Nasa has said.
Astronomers are calling the malfunction of the Advanced Camera for Surveys a "great loss" as it has taken the clearest pictures yet of the Universe.
US space agency engineers said only one-third of the camera's functions were likely to be restored.
Hubble is due to receive a new camera during a planned servicing mission by space shuttle in 2008.
This should recover all of the capability lost in the latest failure.
"The successful completion of [the shuttle mission] and insertion of Wide Field Camera-3 (WFC3) will take us fully back to not only where we are now, but where we want [the telescope] to be in the future," said David Leckrone, Nasa's senior project scientist on Hubble.
The Advanced Camera for Surveys has been the most in-demand instrument on the observatory since its installation in 2002.
The ACS actually consists of three sub-cameras that detect and filter light from the ultraviolet to the near infrared.
HUBBLE SPACE TELESCOPE
Named after the great US astronomer Edwin Hubble
Launched in 1990 into a 600km-high circular orbit
Equipped with a 2.4m primary mirror and five instruments
Length: 15.9m; diameter: 4.2m; Mass: 11,110kg
Observations have probed about 24,000 celestial objects
Made more than 93,000 trips around our planet
Generates about 10 gigabytes of data each day
Astronomers can continue to use Hubble's other instruments - which include the Field Planetary Camera-2 and the Near Infrared Camera Multi-Object Spectrograph - but the loss of its primary camera is being mourned by the scientific community.
"Science will continue, but it's a great loss, no doubt," said Mario Livio at the Space Telescope Science Institute which manages Hubble.
"It's a great loss because this was a fantastic camera that just produced incredible science."
This is the third time electrical problems have taken the ACS out of action since June last year.
The latest upset pushed the space telescope into a protective "safe mode" on Saturday.
Officials managed to bring the observatory back online by Sunday, minus its ACS capabilities.
Two of the instrument's three channels - its wide field and high-resolution channels - were unlikely to be restored, engineers said.
These channels have been used to obtain ultra-deep views of the cosmos and detailed data on individual stars.
Nasa engineers hope the third channel - known as the Solar Blind channel and frequently used to study objects in our Solar System - can be recovered in time to make support observations of Jupiter as it is passed by the New Horizon's spacecraft next month.
Nasa has set up an Anomaly Review Board to investigate the latest incident.
"It is too early to know what influences the ACS anomaly may have on Hubble Space Telescope Servicing Mission-4 planning," said Preston Burch, the programme manager for Hubble.
"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 maximising the telescope's scientific output."
The servicing mission to be conducted by astronauts on the Discovery shuttle should launch in September of 2008.
In addition to the Wide Field Camera-3, the crew will fit the Cosmic Origins Spectrograph (COS). Together, the new instruments will improve significantly Hubble's ability to probe distant, faint objects in the early Universe.
New batteries and gyroscopes will maintain the telescope's power and pointing systems.
The servicing mission should extend Hubble's orbital lifetime to at least 2013, by which time Nasa will be getting close to launching a successor: the James Webb Space Telescope.
Hubble is the result of a joint venture between the US and European space agencies.
SERVICING THE HUBBLE SPACE TELESCOPE
Shuttle Discovery will grab Hubble with a robotic arm and pull it on to a work platform to allow astronauts easy access to its interior
Hubble has six gyroscopes that are critical to its control and pointing systems. These have started to fail and all will have to be replaced
Six new batteries will rejuvenate the electrical system; astronauts will attach new thermal blankets to insulate sensitive components
The telescope has two instrument bays; the COS and WFC3 will be slid into racks made vacant by the removal of older instruments
An attempt will also be made to repair the Space Telescope Imaging Spectrograph (STIS) which stopped working in 2004