ESA’s X-ray Observatory Satellite, which studied the X-ray emission from most classes of astronomical objects, including active galactic nuclei, white dwarfs, stars, supernova remnants, clusters of galaxies, cataclysmic variables and X-ray binaries. It was the first ESRO/ESA science satellite entirely funded by the Agency, launched in May 1983, with mission end on reentry in May 1986.

Geos was designed for geostationary (GEO) orbit to study the particles, fields and plasmas of the Earth’s magnetosphere. Unfortunately, Geos-1 was left in a low transfer orbit because of a stage-2/3 separation problem on its launch in April 1977. As a result, the Qualification Model was launched with an identical payload in July 1978 and successfully reached GEO, becoming Geos-2. In spite of its orbit, Geos-1 made a significant contribution to international magnetospheric research until its mission end in 1980. Geos-2, whose mission ended in 1985, created a huge database for magnetospheric studies and plasma research in general.

Giotto was ESA’s first cometary close flyby, and additionally ESA’s first deep space mission and first reactivation of a spacecraft. Launched from Kourou in July 1985, its flyby of Comet Halley in 1986 provided unprecedented information on this famous comet, returning over 2000 images. The closest approach of 596 km occurred on 14 March, and the mission end for the Halley flyby was on 2 April 1986. Giotto was subsequently reactivated in 1990 for the Giotto Extended Mission, for a flyby of Comet Grigg-Skjellerup, with closest approach at about 100km in July 1992.

ESRO’s HEOS programme (Highly Eccentric Orbit Satellite), achieved three ‘firsts’ for European space activities: first probe into cislunar space, first magnetically clean satellite and first highly-eccentric polar orbit. HEOS-1 (launched 1968) studied magnetic fields, radiation and solar wind outside Earth’s magnetosphere. HEOS-2 (launched 1972) investigated northern polar regions.

Hermes was to have been part of a manned spaceflight programme providing independent European manned access to space. The Hermes spaceplane would have been launched using the Ariane-5 rocket.

In the early 1980s, the French space agency CNES started investigating a small spaceplane design to be launched on an Ariane rocket. The Hermes vehicle would have consisted of two parts: a cone-shaped Resource Module attached to the rear of the vehicle, serving as an adaptor to the Ariane 5 launcher and jettisoned before re-entry. Only the 19m long spaceplane would re-enter Earth's atmosphere and land.

In 1985, CNES proposed to proceed with Hermes development under the auspices of the ESA. The project was approved in November 1987, but subject to numerous delays and funding issues, before it was cancelled in 1992.

The High Precision Parallax Collecting Satellite was the first space-based astrometric survey. It had the single goal of producing the most accurate positional survey of more than 100 000 stars, determining their distances, motions and other characteristics.

It was launched in August 1989 from Kourou and its science operations ended in March 1993 (communications ended in August 1993). The Hipparcos Catalogue (118 218 entries) and Tycho Catalogue (a less accurate ‘Tycho’ survey with 1 058 332 entries) were declared final in August 1996 and published by ESA in 1997, fundamentally affected every branch of astronomy, especially on theories of stars and their evolution.

Horizon 2000 was the first long-term plan for the disciplines of space science under the ESA Directorate of Science, covering the period 1984 to 2006. The study, which led to the 20-year plan, was initiated in September 1983 and was coordinated by a Survey Committee composed of scientists from different areas of fundamental science. Horizon 2000 facilitated the development of eight missions between 1985 and 1995 including four cornerstone missions– SOHO and Cluster II, XMM-Newton, Rosetta, and Herschel.

The Hubble Space Telescope mission was a NASA-ESA partnership to operate a 2 m-class astronomical telescope in orbit for at least 15 years as an international observatory. Hubble was launched in April 1990 on Space Shuttle mission STS-31 from Kennedy Space Center and, after five servicing missions, is still operational today.

ESA’s 15% contribution consisted of the Faint Object Camera (FOC, a prime focal plane instrument), the first two solar wings that powered the spacecraft and a team of space scientists and engineers at the Space Telescope Science Institute in Baltimore, USA. Almost 7000 images were recorded with the FOC giving close-up views of almost every type of astronomical object and revolutionising modern astronomy.

The International Sun-Earth Explorers (ISEE) programme consisted of three spacecraft: a mother/daughter pair (ISEE-1 and ISEE-2) and the ISEE-3 spacecraft (later renamed International Cometary Explorer). The programme was a cooperative mission between NASA and ESRO (later ESA) designed to study the interaction between the Earth's magnetic field and the solar wind. ISEE-1 (Explorer 56) and ISEE-3 were built by NASA, while ISEE-2 (ISEE-B) was built by ESA. It was launched in tandem with NASA’s ISEE-1 on 22 October 1977 and its mission ended with reentry in 1987.

The International Space Station (ISS) programme evolved from the Space Station Freedom, a 1984 American proposal to construct a permanently crewed Earth-orbiting station, which was cancelled in 1992 over technical problems and costs. In 1993, NASA and Roscosmos negotiated an agreement to merge their space station plans into the renamed the International Space Station, with planned modules from ESA and the Japanese space programme.