The Hubble Space Telescope


The Hubble Space Telescope was launched on April 24, 1990 by the Space Shuttle Discovery (STS-31), from the Kennedy Space Center in Florida into a ~610 Km low-Earth orbit (~380 miles, nearly the maximum for this class of vehicle), with an inclination of 28.5 degrees and a period of ~96 minutes.

It is a cooperation project of the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA).

The Space Telescope was named after Edwin P. Hubble, the great American astronomer, possibly the most influential after Galileo.

Just as Galileo's first use of a telescope to see the sky [in 1609] gave humanity its first order-of-magnitude increase in resolution for this kind of vision, the HST gave us the second one. The unaided eye can resolve nearly 1' of arc, a ground-based telescope near 1", the HST resolves 0.1" of arc.

The HST is a folded-optical-path design (Ritchey-Chretien, a variation on the Cassegrain design), with a 94.5" (2.4 m) primary mirror and a 12" (30 cm) secondary. Its focal length is 189 feet (almost 58 m), its focal ratio is f/24.
The HST contains more than 400,000 parts and some 26,000 miles of electrical wiring.
The body of the telescope is 13.3 m in length, 4.3 m in diameter, and weights 11,110 Kgr.

HST's current complement of science instruments include two cameras, two spectrographs, and fine guidance sensors (primarily used for astrometric observations). Because of HST's location above the Earth's atmosphere, these science instruments can produce high resolution images of astronomical objects. Ground-based telescopes can seldom provide resolution better than 1.0 arc-seconds, except momentarily under the very best observing conditions. HST's resolution is about 10 times better, or 0.1 arc-seconds.

The HST orients itself in space using a system of three electrically operated flywheels, this way, it does not pollute its environment with exhaust gases that would end up tarnishing its optics.

When originally planned in 1979, the Large Space Telescope program called for return to Earth, refurbishment, and relaunch every 5 years, with on-orbit servicing every 2.5 years. Hardware lifetime and reliability requirements were based on that 2.5-year interval between servicing missions. In 1985, contamination and structural loading concerns associated with return to Earth aboard the shuttle eliminated the concept of ground return from the program. NASA decided that on-orbit servicing might be adequate to maintain HST for its 15-year design life. A three year cycle of on-orbit servicing was adopted. The first HST servicing mission in December 1993 was an enormous success. Servicing missions were planned for March 1997, mid-1999, and mid-2002. Contingency flights could still be added to the shuttle manifest to perform specific tasks that cannot wait for the next regularly scheduled servicing mission (and/or required tasks that were not completed on a given servicing mission).

The five years since the launch of HST in 1990 have been momentous, with the discovery of spherical aberration in the main mirror and the search for a practical solution. The STS-61 (Endeavor) mission of December 1993 fixed some of the effects of the spherical aberration and restored the functionality of HST.

Two months after Hubble was released into its initial orbit, engineers discovered the telescope's main mirror was flawed. The mirror was too flat near the edge by about 2 microns (about 1/50th the width of a human hair). The result: instead of light being focused to a sharp point, light collected by the mirror spread into a fuzzy halo.

Astronomers coped with the problem by using computer processing to sharpen images, and made a string of exciting observations: black hole candidates lurking in the centers of galaxies, expanding rings around a supernova, a rare storm on Saturn.

To realize its full potential, however, the telescope would have to be repaired. The mirror itself couldn't be fixed or changed; so the challenge facing NASA was to develop corrective optics for Hubble's instruments, much like eyeglasses or contact lenses correct human sight.

Although the task proved technically challenging, it was less difficult than it might have been because NASA had always planned to service the telescope. Engineers designed Hubble so astronauts could easily change failed parts or update the telescope with more advanced instruments. Instruments were designed like dresser drawers: they could be pulled out and replaced with others of the same size.

A new camera, called the Wide Field & Planetary Camera-2 (WFPC2), had its corrective optics built right in.
To correct the telescope's other instruments, engineers devised a special instrument, called the COSTAR (Corrective Optics Space Telescope Axial Replacement) that would use mechanical arms to place pairs of small mirrors in front of the openings of the telescope's remaining three instruments. Each pair of mirrors was shaped to properly refocus light from the flawed main mirror.

COSTAR is not a science instrument; it is a corrective optics package that displaced the High Speed Photometer during the first servicing mission to HST. COSTAR is designed to optically correct the effects of the primary mirror's aberration on the three remaining scientific instruments: Faint Object Camera (FOC), Faint Object Spectrograph (FOS), and the Goddard High Resolution Spectrograph (GHRS).

In the early morning darkness of December 2, 1993, seven astronauts strapped themselves on board Space Shuttle Endeavor and rocketed into space to undertake the most difficult and challenging satellite repair mission ever attempted. When they returned to Earth eleven days later, the astronauts had accomplished everything they had planned to do and in the process, racked up a record five space walks in a single mission.
During this mission, Endeavor also rose the HST from some 350 miles to an orbit at about 360 miles.

The first servicing mission restored Hubble's vision and led to a string of remarkable discoveries in a very short time. During the second servicing mission, in February 1997, astronauts installed two new instruments. This servicing mission, like the first, has taken more than three years of planning and preparation and incorporates lessons learned from the first servicing mission.

Some Pre and Post-Servicing comparison images:

 [HST comp star]  [HST comp NGC 1068]  [HST comp M100]

This are (from left to right): A star, NGC 1068, and M100)

After the 1997 and 1999 missions, one more mission, in 2002, was planned for keeping Hubble Space Telescope functioning efficiently and improving its vision even further.

Responsibility for conducting and coordinating the science operations of the Hubble Space Telescope rests with the Space Telescope Science Institute (STScI) on the Johns Hopkins University Homewood Campus in Baltimore, Maryland. STScI is operated for NASA by the Association of University for Research in Astronomy, Incorporated (AURA).


HST's initial orbit, is low enough to be somewhat affected by atmospheric drag, lowering it around half a mile per month, depending on Solar activity (which affects our atmosphere's extension) and the space craft's in-orbit attitude.
Whenever the HST drops some 325 miles, it would have to be re-deployed to a higher orbit.

The prior Hubble Space Telescope service mission (3A), was in December '99, on the Space Shuttle Discovery (STS-103). It was a eight-day flight that included two European Space Agency (ESA) astronauts.
NASA officials decided to move up part of the servicing mission that had been scheduled for June 2000 after four of the telescope's six gyroscopes failed. Three gyroscopes must be working to meet the telescope's very precise pointing requirements.
The failure forced the telescope into a protective safe mode in mid-November '99 that ended scientific use of the telescope.
In addition to replacing all six gyroscopes, the crew replaced a guidance sensor, the spacecraft's computer, the data recorder, and a radio transmitter.

The most recent service mission (3B) began in February 28 '02, with the Space Shuttle Columbia (STS-109). It installed a new science instrument, the Advanced Camera for Surveys (ACS), with a bigger field of view and more sensitivity. This replaced the WFPC2.
The current 8-year-old solar panels were replaced by smaller rigid ones that produce 30% more power. The original Power Control Unit was replaced too.
The mission also installed a new cooling system for the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which became inactive three years ago when it depleted the 230-pound block of nitrogen ice that had cooled it since 1997. The new system is a closed circuit, much like a household refrigerator.
The astronauts also replaced one of the four reaction wheel assemblies that make up Hubble's pointing control system.

See Hubble's Advanced Camera Unveils a Panoramic New View of the Universe (STScI - PR02-11) April 30, 2002

The next service mission (SM4) would have been in February 2004; The final servicing mission to the Hubble Space Telescope. It is to include new batteries, new gyroscopes and a new Aft Shroud Cooling System. The new cooling system will carry heat away from scientific instruments and allow the instruments to operate better at lower temperatures. It also will allow multiple instruments to operate simultaneously. Hubble's remaining original Fine Guidance Sensor (FGS) will also be changed out during this service mission.
Two new science Instruments are to be installed on the SM4 flight: the Cosmic Origins Spectrograph and the new Wide Field Camera-3.

Servicing Mission 4, the last scheduled flight of the space shuttle to the Hubble Space Telescope, was cancelled.
On January 16 '04, NASA Administrator Sean O'Keefe announced his decision to call off the mission, which would have performed Hubble maintenance work and installed new instruments. O'Keefe cited the new safety guidelines set out following the Columbia tragedy as the primary basis for his decision, still under review. Since June 1 '04 a robotic Servicing Mission was being considered.

In April '05 NASA's new chief, Michael D. Griffin, told the Hubble servicing team at the Goddard Space Flight Center in Maryland to resume preparations for a possible shuttle flight to upgrade the orbiting observatory. Although a decision on returning astronauts to Hubble would not be made until after at least two successful shuttle missions to the International Space Station, the telescope's prospects looked better then than they had at any time since Griffin's predecessor, Sean O'Keefe, abruptly canceled Hubble servicing in January 2004 — a decision that outraged astronomers, key members of Congress, and the public.

Hubble servicing mission preparations would have had to begin then to keep the possibility of a mission alive. A mission, were it approved, could take place around mid-2007 or early 2008.

In October 31 '06 NASA announced that it will go ahead with one final space shuttle mission to repair and upgrade Hubble after months of debate over the risks of such an endeavor.
The decision was taken by NASA's chief Michael Griffin, who had said for 18 months that he would support a proposed Hubble servicing mission provided its risk did not exceed that already accepted for other shuttle flights. The Service Mission 4 will add 5 years onto the Hubble’s lifetime and could help NASA prepare the space telescope for its ultimate, but controlled, plunge through the Earth’s atmosphere.
Griffin said the upcoming servicing mission will launch in May 2008 between construction flights to complete the International Space Station (ISS), and is expected to feature at least five spacewalks to upgrade Hubble’s optics and make other repairs.
For safety, NASA would have a second shuttle nearly ready to fly before staging the servicing flight.

In May 22 '08 NASA announced that the HST 4th Service mission would be Shuttle Atlantis' STS-125 mission, then targeted for October 10, 2008.
See NASA Updates Space Shuttle Target Launch Dates (NASA News Release, May 22 '08)

Astronomers hope this decision means Hubble could still be in operation by 2014, when NASA's next great observatory - the James Webb Space Telescope - is planned for launch.
Hubble's visible and ultraviolet spectrum observations will not be possible from the JWST, which will scan primarily in the infrared wavelengths.

Hubble-bound shuttle astronauts had a formidable task ahead of them. Their work would include:

See Shuttle Astronauts to Upgrade Hubble Again (NASA Servicing Missions, October 31, '06)

See Servicing Mission 4 (HubbleSite)

See NASA Resumes Work on Shuttle Flight to Hubble (Sky and Telescope, May 9 '05)

Hubble Anomaly Delays Servicing Mission:
NASA hosted a media teleconference on Sept. 20, 2008, to discuss a significant Hubble Space Telescope anomaly that occurred the previous weekend. The anomaly affected the storage and transmittal of science data to Earth. Preparing to fix the problem delayed space shuttle Atlantis's Hubble servicing mission for May 2009.

The SM4 mission departed on May 11 and returned successful on May 24 '09, after completing all of the installations and almost all of the repairs - STIS is not fully operational.

The Hubble Space Telescope began delivering images to the public in September 2009.

See Hubble Opens New Eyes on the Universe (HubbleSite - NewsCenter, Sep. 9, 2009)
See Images from Refurbished Hubble (NASA, Sep. 9, 2009)

See NASA to Discuss Hubble Anomaly and Servicing Mission Launch Delay (NASA)

See NASA Managers Delay Hubble Servicing Mission (NASA, Oct. 30, 2008)

See Hubble Scores a Perfect Ten (Galaxies Arp 147, HubbleSite - NewsCenter, Oct. 30, 2008)

See Servicing Mission 4 (NASA)

See What's Next for Hubble? (HubbleSite)

The above picture is part of a frame from the IMAX film Destiny in Space.
With Earth's sky and sea reflected in its door, the Hubble Space Telescope is being deployed from the cargo bay of the Space Shuttle Discovery (STS-31).
HST will remain in space for many years, observing a large variety of astronomical objects, from neighboring planets to the most distant galaxies and quasars.

© MCMXCIV Smithsonian Institution/Lockheed Corporation

Further Information from the Space Telescope Science Institute (STScI):

Other source of information:
"The Hubble Wars", by Eric J. Chaisson, HarperCollinsPublishers, 1994.

Updated: September 9 '09

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