The High Energy Transient Explorer (abbreviated HETE; also known as Explorer 79) was an American astronomical satellite with international participation (mainly Japan and France). The prime objective of HETE was to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft. A unique feature of the HETE mission was its capability to localize GRBs with ~10 arc second accuracy in near real time aboard the spacecraft, and to transmit these positions directly to a network of receivers at existing ground-based observatories enabling rapid, sensitive follow-up studies in the radio, IR, and optical bands. The satellite bus for the first HETE was designed and built by AeroAstro, Inc. of Herndon, VA; the replacement satellite, HETE-2, was built by MIT based on the original HETE design.

Launch attempts

The first HETE was lost during the launch on Nov.4, 1996. The Pegasus rocket achieved a good orbit, but explosive bolts releasing HETE from another satellite (Argentina's SAC-B) and from its DPAF envelope failed to charge, dooming both satellites. A battery on the third stage of the rocket and responsible for these bolts cracked during the ascent.

A second HETE satellite, HETE-2, was launched on October 9, 2000 in a follow-up mission. It was similar to the first HETE, but replaced the UV camera with an additional X-ray camera (Soft X-ray Camera or SXC) capable of higher localization accuracy than the original X-ray instrument (Wide-Field X-ray Monitor or WXM).

The Robotic Optical Transient Search Experiment (ROTSE) is an multi-telescope experiment designed to observe the optical afterglow of gamma-ray bursts. The experiment currently consists of four telescopes located in Australia, Namibia, Turkey, and at the McDonald Observatory near Fort Davis, Texas.

The ROTSE project is a collaboration of astrophysicists from the University of Michigan, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, the University of New South Wales (Australia) and the Max Planck Institute for Nuclear Physics (Germany).

The original ROTSE-I had 4 telephoto lenses of 11 cm aperture, covering a 16x16 degree field of view. This detected the first afterglow of a GRB while the burst was still ongoing, but this was the only burst detected by ROTSE or the very similar Livermore Optical Transient Imaging System. Therefore ROTSE-II was designed, also featuring a large field of view, but it was never built, since new satellites such as HETE-2 and SWIFT could provide smaller error boxes, making a huge field of view unnecessary. This led to the design of ROTSE-III, a more or less conventional telescope designed for fast slewing and operation at multiple locations around the world.

Venus Express (VEX) is the first Venus exploration mission of the European Space Agency. Launched in November 2005, it arrived at Venus in April 2006 and has been continuously sending back science data from its polar orbit around Venus. Equipped with seven science instruments, the main objective of the mission is the long term observation of the Venusian atmosphere. The observation over such long periods of time has never been done in previous missions to Venus, and is key to a better understanding of the atmospheric dynamics. It is hoped that such studies can contribute to an understanding of atmospheric dynamics in general, while also contributing to an understanding of climate change on Earth. The mission is currently funded by ESA through 31 December 2014.

Rosetta is a robotic spacecraft of the European Space Agency on a mission to study the comet 67P/Churyumov–Gerasimenko. Rosetta consists of two main elements:

• the Rosetta space probe;
• the Philae lander.

The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by mid 2014. The space probe is intended to orbit and perform long-term exploration of the comet at close quarters. On 10 November 2014 the Philae lander will attempt to land and perform detailed investigations on the comet's surface. Both the probe and the lander carry a large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted.

The probe is named after the Rosetta Stone, as it is hoped the mission will help form an idea of how the solar system looked before planets formed. The lander is named after the Nile island Philae where an obelisk was found that helped decipher the Rosetta Stone. The spacecraft has already performed two successful asteroid flyby missions on its way to the comet. In 2007 performed a Mars swingby (flyby), and returned images. The craft completed its fly-by of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010, and is presently (2013) in hibernation and on-target for its final destination as of June 2013.

SMOS — the second Earth Explorer mission launched on November 2009 designed to measure Soil Moisture and Ocean Salinity.

The Soil Moisture and Ocean Salinity Satellite (SMOS) is a part of ESA's Living Planet Programme intended to provide new insights into Earth's water cycle and climate. In addition, it will provide better weather forecasting and will also monitor snow and ice accumulation.

Planck —  a  Cosmic Microwave Background explorer, after COBE & WMAP. launched in may 2009.

Planck is a space observatory of the European Space Agency (ESA) and designed to observe the anisotropies of the cosmic microwave background (CMB) over the entire sky, at a high sensitivity and angular resolution. Planck was built in the Cannes Mandelieu Space Center by Thales Alenia Space and created as the third Medium-Sized Mission (M3) of the European Space Agency's Horizon 2000 Scientific Programme. The project, initially called COBRAS/SAMBA, is named in honour of the German physicist Max Planck (1858–1947), who won the Nobel Prize for Physics in 1918.

Planck was launched in May 2009, reaching the Earth/Sun's L₂ Lagrangian point in July, and by February 2010 had successfully started a second all-sky survey. Preliminary data from these surveys have been released, and results are said to indicate that the data quality is excellent. Planck is expected to yield definitive data on a number of astronomical issues by 2012. The mission will complement and improve upon observations made by the NASA Wilkinson Microwave Anisotropy Probe (WMAP), which has measured the anisotropies at larger angular scales and lower sensitivity than Planck. Planck will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early universe and the origin of cosmic structure.

The mission has a wide variety of scientific aims, including:

• High resolution detections of both the total intensity and polarization of the primordial CMB anisotropies
• Creation of a catalogue of galaxy clusters through the Sunyaev-Zel'dovich effect
• Observations of the gravitational lensing of the CMB, as well as the integrated Sachs–Wolfe effect
• Observations of bright extragalactic radio (active galactic nuclei) and infrared (dusty galaxy) sources
• Observations of the Milky Way, including the local interstellar medium, distributed synchrotron emission and measurements of the galactic magnetic field.
• Studies of the local Solar System, including planets, asteroids, comets and the zodiacal light.

INTEGRAL  is the first space observatory that can simultaneously observe objects in gamma rays, X-rays and visible light.

The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.

INTEGRAL is an ESA mission in cooperation with the Russian Space Agency and NASA. It has had some notable successes, for example in detecting a mysterious 'iron quasar'. It has also had great success in investigating gamma-ray bursters and evidence for black holes.

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.