Hubble Space Telescope

A joint venture between the European Space Agency and the National Aeronautics and Space Administration. The Hubble Space Telescope was first proposed in the 1940s, designed and constructed in the 1970s and 1980s, and was launched in 1990 by the crew of the space shuttle Discovery.

The Hubble Space Telescope is in a low earth orbit at an altitude of 595 km (370 mi) and circles the earth every 97 minutes. Since it is above the earth's atmosphere, HST has an optical resolution that is ten times better than ground-based telescopes.

The Hubble Space Telescope is also equipped with cameras and spectrographs that provide information on the chemical composition, temperature and density of objects that are many light years away.

If you wish to operate a telescope from the surface of the earth you are faced with several problems. Light from nearby towns may spoil your observations. The turbulent atmosphere introduces all kinds of interferences (that is why stars appear to twinkle) and even totally absorbs some wavelengths. And if all that wasn't bad enough if it's a cloudy night you won't see anything at all.

Some of these problem can be solved by installing telescopes in remote areas, high in the mountains, or where the weather is known to be good. Clever correction systems have been designed to compensate for the effect of atmosphere, but at the end of the day, the one way to solve all these problems is just to put the telescope into space. Hermann Oberth speculated about this as early as 1923 but it wasn't until the 70's that a joint project from NASA and the European Space Agency began to take form, and it was not until 1990 that the Hubble Space Telescope was launched.

Unfortunately although placing a telescope in space solves many problems it also creates new ones. You have to actually get it there in the first place. If it ever breaks down, fixing it is going to be difficult. Satellites are regularly submitted to rapidly alternating extremes of heat and cold. Precision optics do not like that. It's also a pretty bumpy ride on the Space Shuttle which delicate instrumentation tends to shun.

A brief timeline

• 1969: The American National Academy for Sciences approves a Large Space Telescope Project.
• 1975: The European Space Agency (ESA) joins the project, providing 15% of the funding in the form of the Faint Object Camera and the solar panels, in exchange for at least 15% of the telescope's time.
• 1977: Funding is approved by Congress.
• 1981: Space Telescope Science Institute (STScI) begins operations in Baltimore, Maryland.
• 1984: Space Telescope-European Co-ordinating Facility (ST-ECF) begins operations in Garching, Munich.
• 1985: 2 years later than planned, the telescope is complete and due for launch in 1986.
• 1986: The Challenger disaster. NASA grounds its fleet for 2 years. The engineering team take advantage of this delay to further improve Hubble.
• 1990: Hubble finally takes off aboard Space Shuttle Discovery on April 24th. Hubble is deployed on April 25th. On the 25th of June, a spherical aberration is discovered on Hubble's main mirror. Hubble still produces incredible images. Shortly after, COSTAR an optical correction system designed to compensate for the fault in Hubble's main mirror is approved.
• 1993: Endeavour meets up with Hubble for the first servicing mission. COSTAR is installed, taking the place of the High Speed Photometer. The Wide Field and Planetary Camera is upgraded.
• 1997: The second servicing mission takes place, this time by astronauts on board Discovery. The Faint Object Spectrograph was replaced by the Space Telescope Imaging Spectrograph and the NICMOS (Near Infrared Camera and Multi-Object Spectrograph) replaced the GHRS (Goddard High Resolution Spectrograph).
• 1998: HST Orbital Systems Test
• 1999: Servicing Mission 3A, flown by Discovery. Hubble's gyroscopes were replaced, to avoid the telescope spinning out of control, which could have happened had another gyroscope failed.
• 2002: Servicing Mission 3B, flown by Columbia. The solar panels were replaced, a new cooling system for NICMOS was installed and the Advanced Camera for surveys (ACS) was installed.

There is a further servicing mission planned for 2005 and a final one in 2010 when Hubble is expected to be retired.
Update: 17/01/2004: Grzcyrgba informs me the servicing mission planned for 2005 (SM4) has been cancelled. The mission would have added 2 important instruments, the Wide Field Camera 3 and the Cosmic Origins Spectrometer. In the mean time if anything goes wrong (for example if 2 of Hubble's 4 remaining gyroscopes fail) then NASA will have lost Hubble, making it unlikely that it will survive until the James Webb Space Telescope replaces it in 2012. Apparently this decision is because with the loss of Columbia, all space shuttle flights are for the ISS. Since it is not easily feasible to get in between Hubble's orbit and the ISS's orbit the mission had to be cancelled.

Facts and Figures

Now that you have the history, some facts and figures

• Orbiting time: 97 minutes
• Average speed: 27,200 km/h
• Dimensions: 13.2m long, 4.2m wide at its widest point.
• Weight: 24000 lbs
• Main mirror diameter: 2.4 m (by comparison the largest earth based telescopes have mirrors with diameters of the order of 8 m)
• Cost: $1.5 billion to build and launch, yearly budget since deployment around $230-250 million.
• Distance travelled since launch: over 1.5 billion miles
• Initial altitude: 600 km
• Data acquired: Over 8 terabytes, delivering between 10 and 15 gigabytes per day.
• Observations made: over 330 thousand
• Power Supply: 2 2.4 x 12.1 m solar panels, providing around 3000W of power each. Hubble is equipped with NiMH batteries for when it is in the earth's shadow.

Hubble was not just revolutionary in terms of the incredible quality of its observations. Many new techniques were pioneered during its conception. The 4 servicing missions have seen the use of many new tools and have a number of firsts to the their name, for example the Pistol Grip Tool, which was the fist cordless power tool used in space or the first use of a computer-controlled space tool, the Power Ratchet Tool. The solar panels are the largest structure ever replaced in space. Its design is modular, allowing components to be easily changed by astronauts. This modularity has allowed Hubble to remain at the cutting edge of observing technology.

Instruments

Hubble has 5 instruments on board:

• The Wide Field and Planetary Camera: Hubble's main camera, used to observe a variety of objects.
• The Faint Object Camera: Hubble's most precise camera, used for very detailed observations over a small field of view. Replaced by the Advanced Camera for Surveys in March 2002.
• Advanced Camera for Surveys: A versatile instrument, combining 3 cameras: a wide field camera (twice the width of the WFPC), a high-resolution camera and the solar-blind camera used for observing UV radiation from hot stars
• Near Infrared Camera and Multi-Object Spectograph: An infrared camera, suitable for observing objects obscured by interstellar gas and dust.
• Space Telescope Imaging Spectrograph: A spectrograph capable of sampling up to 500 points simultaneously, thus greatly improving Hubble's efficiency
• Fine Guidance Sensors: Not used for taking pictures, these are used to keep Hubble pointing in the right direction. Hubble tracking systems perform feats are equivalent to focussing on a dime from 200 miles away.

A telescope that needs glasses?

Almost everyone knows that when Hubble was launched its mirror had a defect that made Hubble "short-sighted". Hubble's main mirror actually had what is known as a spherical aberration, caused by a malfunction of the device used to measure the surface of the mirror while it was being polished. Hubble still bettered ground-based telescopes in many ways. In 1993 the Corrective Optics Space Telescope Axial Replacement (COSTAR) was installed, restoring the telescope's imaging capabilities. After 2005's servicing mission, each instrument will include an internal correction device derived from COSTAR, allowing COSTAR to be removed.

The Future of Hubble

Over the past 12 years Hubble has provided astronomers with invaluable data and produced a myriad of stunning pictures with never before seen clarity and sharpness. 2010 is the end of Hubble's planned life. At that date it could be brought back down to earth, end its life as a fireball or possibly be moved back to a higher orbit. What will take its place in the skies? The James Webb Space Telescope is expected to be launched around 2010 to take Hubble's place (although its focus is not on the visible part of the spectrum). With a primary mirror diameter 2.5 times greater than Hubble's, and operating further away from earth it will be ideally placed to continue observing the skies, with a cost just one third of Hubble's.

Sources: http://www.jwst.nasa.gov/FAQ/FAQans.htm
http://hubble.nasa.gov/
http://hubble.esa.int/
http://hubblesite.org
http://news.bbc.co.uk/1/hi/sci/tech/3406079.stm