The Hubble Space Telescope (HST) is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter (7.9 ft) aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared. The telescope is named after the astronomer Edwin Hubble.

Hubble's orbit outside the distortion of Earth's atmosphere allows it to take extremely sharp images with almost no background light. Hubble's Ultra-Deep Field image, for instance, is the most detailed visible-light image ever made of the universe's most distant objects. Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.

Although not the first space telescope, Hubble is one of the largest and most versatile, and is well known as both a vital research tool and a public relations boon for astronomy. The HST was built by the United States space agency NASA, with contributions from the European Space Agency, and is operated by the Space Telescope Science Institute. The HST is one of NASA's Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

Space telescopes were proposed as early as 1923. Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When finally launched in 1990, scientists found that the main mirror had been ground incorrectly, significantly compromising the telescope's capabilities. However, after a servicing mission in 1993, the telescope was restored to its intended quality.

Hubble is the only telescope designed to be serviced in space by astronauts. Between 1993 and 2002, four missions repaired, upgraded, and replaced systems on the telescope, but a fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved one final servicing mission, completed in 2009. The telescope is now expected to function until at least 2014. Its scientific successor, the James Webb Space Telescope (JWST), is to be launched in 2018 or possibly later.

A space telescope observing in the far-infrared.

The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest infrared space telescope ever launched, carrying a single mirror of 3.5 metres (11.5 ft) in diameter.

The observatory was carried into orbit in May 2009, reaching the second Lagrangian point (L2) of the Earth-Sun system, 1,500,000 kilometres (930,000 mi) from the Earth, about two months later. Herschel is named after Sir William Herschel, the discoverer of the infrared spectrum and planet Uranus.

The Herschel Observatory is capable of seeing the coldest and dustiest objects in space; for example, cool cocoons where stars form and dusty galaxies just starting to bulk up with new stars. The observatory will sift through star-forming clouds—the "slow cookers" of star ingredients—to trace the path by which potentially life-forming molecules, such as water, form. The United States through NASA is participating in the ESA-built and -operated observatory. It is the fourth 'cornerstone' mission in the ESA science program, along with Rosetta, Planck, and the Gaia mission.

A mission designed to measure the Earth's gravity field, launched on march 2009.

The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) is an ESA satellite that was launched on March 17, 2009. It is a satellite carrying a highly sensitive gravity gradiometer which detects fine density differences in the crust and oceans of the Earth.

GOCE data will have many uses, probing hazardous volcanic regions and bringing new insight into ocean behaviour. The latter, in particular, is a major driver for the mission. By combining the gravity data with information about sea surface height gathered by other satellite altimeters, scientists will be able to track the direction and speed of geostrophic ocean currents. The low orbit and high accuracy of the system will greatly improve the known accuracy and spatial resolution of the geoid (the theoretical surface of equal gravitational potential on the Earth).

The satellite's arrow shape and fins help keep the GOCE stable as it flies through the wisps of air still present at an altitude of 260 km. In addition, an ion propulsion system continuously compensates for the deceleration of air-drag without the vibration of a conventional chemically-powered rocket engine, thus restoring the path of the craft as closely as possible to a purely inertial trajectory. The craft's primary instrument is three pairs of highly sensitive accelerometers which measure gravitational gradients along three different axes.

GIOVE, or Galileo In-Orbit Validation Element, is the name for each satellite in a series being built for the European Space Agency (ESA) to test technology in orbit for the Galileo positioning system.

Giove is the Italian word for "Jupiter". The name was chosen as a tribute to Galileo Galilei, who discovered the first four natural satellites of Jupiter, and later discovered that they could be used as a universal clock to obtain the longitude of a point on the Earth's surface.

The GIOVE satellites are exploited by the GIOVE Mission (GIOVE-M) segment in the frame of the risk mitigation for the In Orbit Validation (IOV) of the Galileo positioning system.

GIOVE-A2

With the delays of GIOVE-B, the European Space Agency again contracted with SSTL for a second satellite, to ensure that the Galileo programme continues without any interruptions that could lead to loss of frequency allocations. Construction of GIOVE-A2 was terminated due to the successful launch and in-orbit operation of GIOVE-B.

GIOVE, or Galileo In-Orbit Validation Element, is the name for each satellite in a series being built for the European Space Agency (ESA) to test technology in orbit for the Galileo positioning system.

Giove is the Italian word for "Jupiter". The name was chosen as a tribute to Galileo Galilei, who discovered the first four natural satellites of Jupiter, and later discovered that they could be used as a universal clock to obtain the longitude of a point on the Earth's surface.

The GIOVE satellites are exploited by the GIOVE Mission (GIOVE-M) segment in the frame of the risk mitigation for the In Orbit Validation (IOV) of the Galileo positioning system.

GIOVE-B (previously called GSTB-V2/B), has a similar mission, but has greatly improved signal generation hardware.

It was originally built by satellite consortium European Satellite Navigation Industries, but following re-organization of the project in 2007, the satellite prime contractor responsibility was passed to Astrium.

GIOVE-B also has MEO environment characterization objectives, as well as signal-in-space and receiver experimentation objectives. GIOVE-B carries three atomic clocks: two rubidium standards and the first space-qualified passive hydrogen maser.

Launched on 27 April 2008

GIOVE, or Galileo In-Orbit Validation Element, is the name for each satellite in a series being built for the European Space Agency (ESA) to test technology in orbit for the Galileo positioning system.

Giove is the Italian word for "Jupiter". The name was chosen as a tribute to Galileo Galilei, who discovered the first four natural satellites of Jupiter, and later discovered that they could be used as a universal clock to obtain the longitude of a point on the Earth's surface.

The GIOVE satellites are exploited by the GIOVE Mission (GIOVE-M) segment in the frame of the risk mitigation for the In Orbit Validation (IOV) of the Galileo positioning system.

GIOVE-A

Previously known as GSTB-V2/A, this satellite was constructed by Surrey Satellite Technology Ltd (SSTL).

Its mission has the main goal of claiming the frequencies allocated to Galileo by the ITU. It has two independently-developed Galileo signal generation chains and also tests the design of two on-board rubidium atomic clocks and the orbital characteristics of the intermediate circular orbit for future satellites.

GIOVE-A is the first spacecraft whose design is based upon SSTL's new Geostationary Minisatellite Platform (GMP) satellite bus, intended for geostationary orbit. GIOVE-A is also SSTL's first satellite outside low Earth orbit, operating in medium Earth orbit), and is SSTL's first satellite to use deployable sun-tracking solar arrays. Previous SSTL satellites use body-mounted solar arrays, which generate less power per unit area as they do not face the sun directly.

Launched on 28 December 2005

It was launched at 05:19 UTC on December 28, 2005 on a Soyuz-FG/Fregat from the Baikonur Cosmodrome in Kazakhstan.

It began communicating as planned at 09:01 UTC while circling the Earth at a height of 23,222 km. The satellite successfully transmitted its first navigation signals at 17:25 GMT on 12 January 2006. These signals were received at Chilbolton Observatory in Hampshire, UK and the ESA Station at Redu in Belgium. Teams from SSTL and ESA have measured the signal generated by GIOVE-A to ensure it meets the frequency-filing allocation and reservation requirements for the International Telecommunication Union (ITU), a process that was required to be complete by June 2006.

The GIOVE-A signal in space is fully representative of the Galileo signal from the point of view of frequencies and modulations, chip rates, and data rates. However, GIOVE-A can only transmit at two frequency bands at a time (i.e., L1+E5 or L1+E6).

GIOVE-A codes are different from Galileo codes. The GIOVE-A navigation message is not representative from the structure and contents viewpoint (demonstration only purpose). The generation of pseudorange measurements and detailed analysis of the tracking noise and multipath performance of GIOVE-A ranging signals have been performed with the use of the GETR (Galileo Experimental Test Receiver) designed by Septentrio.

There has been some public controversy about the open source nature of some of the Pseudo-Random Noise (PRN) codes. In the early part of 2006, researchers at Cornell monitored the GIOVE-A signal and extracted the PRN codes. The methods used and the codes which were found were published in the June 2006 issue of GPS World. ESA has now made the codes public.

CryoSat is an ESA programme which will monitor variations in the extent and thickness of polar ice through use of a satellite in low Earth orbit. The information provided about the behaviour of coastal glaciers that drain thinning ice sheets will be key to better predictions of future sea-level rise.

The CryoSat-1 spacecraft was lost in a launch failure in 2005, however the programme was resumed with the successful launch of a replacement, CryoSat-2, launched on 8 April 2010.

CryoSat-2 is a European Space Agency environmental research satellite which was launched in April 2010. It provides scientists with data about the polar ice caps and tracks changes in the thickness of the ice with a resolution of about ¹⁄₂ inches (1.3 cm). This information is useful for monitoring climate change. Cryosat 2 was built as a replacement for CryoSat-1, whose Rokot carrier rocket was unable to achieve orbit. ESA built a replacement, with software upgrades and greater battery capacity, which carries an interferometric radar range-finder with twin antennas which measures the height difference between floating ice and open water. CryoSat-2 is operated as part of the CryoSat programme to study the Earth's polar ice caps, which is itself part of the Living Planet programme. The CryoSat-2 spacecraft was constructed by EADS Astrium, and was launched by ISC Kosmotras, using a Dnepr-1 carrier rocket, on 8 April 2010. On 22 October 2010, CryoSat-2 was declared operational following six months of on-orbit testing.

CryoSat-2 is operated from the European Space Operations Centre (ESOC) in Darmstadt, Germany.

CryoSat-1, also known as just CryoSat, was a European Space Agency satellite which was lost in a launch failure in 2005. It was to have been operated as part of the CryoSat programme to study the Earth's polar ice caps.

The CryoSat spacecraft was intended to operate in low Earth orbit for three years. It had a mass of 750 kilograms (1,700 lb) Its primary instrument, SIRAL, was to have used radar to determine and monitor the spacecraft's altitude in order to measure the elevation of the ice, and for radar imaging of the ice caps. A second instrument, DORIS, was to have been used to calculate precisely the spacecraft's orbit. It also carried an array of retroreflectors which would have allowed measurements to be made from the ground to verify the orbital data provided by DORIS.

CryoSat was launched from Site 133/3 at the Plesetsk Cosmodrome at 15:02:00 UTC on 8 October 2005. The launch was conducted by Eurockot, using a Rokot carrier rocket with a Briz-KM upper stage. The command to shut down the rocket's second stage engine was missing from the flight control system, and consequently the stage burned to depletion. This prevented the second stage from separating from the Briz-KM, and as a result the rocket was unable to achieve orbit. It reentered over the Arctic Ocean, north of Greenland. A replacement satellite, CryoSat-2, was successfully launched in 2010.

Envisat  ("Environmental Satellite") is an Earth observation satellite. Its objective is to service the continuity of European Remote-Sensing Satellite missions, providing additional observational parameters to improve environmental studies.

In working towards the global and regional objectives of the mission, numerous scientific disciplines use the data acquired from the different sensors on the satellite, to study such things as atmospheric chemistry, ozone depletion, biological oceanography, ocean temperature and colour, wind waves, hydrology (humidity, floods), agriculture and arboriculture, natural hazards, digital elevation modelling (using interferometry), monitoring of maritime traffic, atmospheric dispersion modelling (pollution), cartographyand study of snow and ice.

It was launched on 1 March 2002 aboard an Ariane 5 from the Guyana Space Centre in Kourou, French Guyana into a Sun synchronous polar orbit at an altitude of 790 km (490 mi) (± 10 km (6.2 mi)). It orbits the Earth in about 101 minutes with a repeat cycle of 35 days.

Envisat is the largest earth observation satellite put into space (as of late 2006), being 26 m (85 ft) × 10 m (33 ft) × 5 m (16 ft) and having a mass of 8.5 t (8.4 long tons; 9.4 short tons).

The Envisat mission ended on 08 April 2012, following the unexpected loss of contact with the satellite.

Envisat data collectively provide a wealth of information on the workings of the Earth system, including insights into factors contributing to climate change.

COROT (French: COnvection ROtation et Transits planétaires; English: COnvection ROtation and planetary Transits) is a space mission led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA) and other international partners.

The mission's two objectives are to search for extrasolar planets with short orbital periods, particularly those of large terrestrial size, and to perform asteroseismology by measuringsolar-like oscillations in stars. It was launched at 14:28:00 UTC on 27 December 2006, atop a Soyuz 2.1b carrier rocket, reporting first light on 18 January 2007. Subsequently, the probe started to collect science data on 2 February 2007. COROT is the first spacecraft dedicated to the detection of transiting extrasolar planets, opening the way for more advanced probes such as Kepler and possibly TESS and PLATO. It detected its first extrasolar planet, COROT-1b, in May 2007, just 3 months after the start of the observations. Mission flight operations were originally scheduled to end 2.5 years from launch but operations were extended to 2013.