Space Telescopes: The Eyes of Humanity

Scientific Summary

This Astronoo article offers a comprehensive review of the major space telescopes, orbital instruments free from atmospheric disturbances. It details their advantages for multi-wavelength observation (from gamma rays to infrared), their technology (mirrors, cooled detectors), and their lifespan. The article provides a historical overview of major missions, from Uhuru (1970) to James Webb (2021), including Hubble, Chandra, and Gaia. It highlights their contributions to cosmology, from exoplanet detection to galactic mapping, and discusses future prospects such as the Habitable Worlds Observatory, NewAthena, and LISA.

What are the main space telescopes, their observation domains, and their scientific contributions?

This Astronoo article answers this question by providing a detailed inventory of space observatories, their technologies, and their discoveries. To overcome the absorption of the electromagnetic spectrum by the atmosphere, these instruments are placed in orbit, offering an intact view of the Universe in wavelengths inaccessible from the ground, such as ultraviolet, X-rays, or infrared. The article structures its response along three axes. First, it explains the technical advantages of space observation (angular resolution, sensitivity) and the associated technological challenges, such as detector cooling or gyroscopic stabilization. Second, it provides a chronological catalog of iconic missions, from the pioneering Uhuru to the revolutionary Gaia, including the essential Hubble, Chandra, and Spitzer. Finally, it synthesizes the major scientific results: confirmation of the accelerated expansion of the Universe, discovery of thousands of exoplanets, three-dimensional mapping of the Milky Way, and observation of the first galaxies. The article concludes by mentioning future missions, which will tackle the detection of habitable exoplanets and the study of gravitational waves, demonstrating that space telescopes are indeed the "eyes of humanity" for unraveling the mysteries of the cosmos.

Observing the Universe from Space

Space telescopes are observatories located beyond Earth's atmosphere, free from optical, thermal, and radio-frequency disturbances that affect ground-based instruments. Their purpose is to observe the cosmos across all wavelengths, from gamma radiation to radio waves, to explore the deep Universe, galaxy formation, and extreme energetic phenomena.

Advantages of Space Observation

Earth's atmosphere absorbs a large portion of the electromagnetic spectrum. By placing a telescope in space, we gain a complete view of the cosmos, free from turbulence or atmospheric absorption. This provides exceptional angular resolution and increased sensitivity, particularly in the infrared and ultraviolet.

Onboard Technology

Table of major space telescopes
Mission	Launch year	End date	Space agency	Wavelengths	Scientific results
Uhuru	1970	1973	NASA	X-rays	First complete catalog of galactic X-ray sources
Granat	1989	1998	USSR / CNES	X-rays and gamma	Observation of black holes and pulsars, study of galactic gamma radiation
Hubble	1990	Active	NASA / ESA	Visible, UV, near IR	Measurement of the Universe's expansion rate, observation of distant galaxies
Compton	1991	2000	NASA	Gamma rays	Gamma-ray sky mapping and gamma-ray burst study
SOHO	1995	Active	ESA / NASA	Visible, UV	Continuous observation of solar activity and solar wind
HALCA (VSOP)	1997	2005	JAXA	Radio	Space interferometry to study active galactic nuclei
Chandra	1999	Active	NASA	X-rays	Structure of supernovas and black holes
XMM-Newton	1999	Active (extended in 2026)	ESA	X-rays	Study of black holes, galaxy clusters and neutron stars
Spitzer	2003	2020	NASA	Infrared	Study of protoplanetary disks and cosmic dust
Swift	2004	Active	NASA	Gamma, X, UV, visible	Multi-wavelength detection and follow-up of gamma-ray bursts
Suzaku (ASTRO-E2)	2005	2015	JAXA / NASA	X-rays	Study of hot intergalactic gas and galaxy clusters
Fermi-LAT	2008	Active	NASA	Gamma rays	Study of gamma-ray bursts, blazars and pulsars
Herschel	2009	2013	ESA	Far infrared	Observation of the cold Universe and star formation
Kepler	2009	2018	NASA	Visible	Discovery of thousands of exoplanets by transit
NEOWISE (ex-WISE)	2009	2024	NASA	Infrared	Search and tracking of near-Earth asteroids; deorbited and disintegrated in the atmosphere on November 1, 2024
Spektr-R (RadioAstron)	2011	2019	Roscosmos	Radio	Very long baseline space interferometry with ground radio telescopes
Gaia	2013	2025	ESA	Visible	3D mapping of over 1.8 billion stars in the Milky Way; observations completed on January 15, 2025, satellite switched off on March 27, 2025
IRIS	2013	Active (extended in 2026)	NASA	Ultraviolet	Study of the Sun-atmosphere interface and the solar corona
Astrosat	2015	Active	ISRO	UV, visible, X-rays	India's first multi-wavelength space observatory
HXMT (Insight)	2017	Active	CNSA	X-rays	Observation of pulsars, black holes and gamma-ray bursts
TESS	2018	Active	NASA	Visible	Detection of nearby and bright exoplanets
CHEOPS	2019	Extended until 2029	ESA / Switzerland	Visible, near IR	Precise characterization of already known exoplanets
Spektr-RG (eROSITA / ART-XC)	2019	Active	Roscosmos / DLR	X-rays	Complete X-ray sky mapping, study of dark matter
Solar Orbiter	2020	Active	ESA / NASA	Visible, UV, X	Study of solar wind and magnetic field of the solar corona
IXPE	2021	Active	NASA / ASI	X-rays	Measurement of X-ray polarization to study extreme magnetic fields
James Webb	2021	Active	NASA / ESA / CSA	Mid and near infrared	Observation of the first galaxies and exoplanetary atmospheres
XRISM	2023	Active	JAXA / NASA / ESA	X-rays	High-resolution spectroscopy of hot cosmic plasma
Euclid	2023	Active	ESA	Visible and near infrared	Cosmological mapping of dark matter and dark energy
Einstein Probe	2024	Active	CNSA / ESA	Soft X-rays	Detection of transient events such as supernovas and stellar mergers
Nancy Grace Roman	2026 (scheduled Aug 30)	Planned ~2036+	NASA	Infrared	Cosmology (dark energy), exoplanets, coronagraphy; field of view 100 times wider than Hubble
PLATO	2026 (scheduled late 2026)	~2031+	ESA	Visible	Search for terrestrial exoplanets in the habitable zone of Sun-like stars; asteroseismology
SVOM	2026 (scheduled Jun 24)	~2030+	CNES / CNSA	Gamma rays, X	Rapid detection and localization of gamma-ray bursts
Xuntian	2026 (scheduled)	~2036+	CNSA	Near UV, visible, near IR	Precision cosmology, coronagraphic exoplanet imaging, terahertz
ARIEL	2029 (scheduled)	~2033+	ESA	Infrared	Study of the atmospheres of ~1000 exoplanets
NewAthena	late 2030s (scheduled)	~2045+	ESA	X-rays	Next-generation X-ray observatory; study of the hot and energetic Universe
LISA	2035 (scheduled)	~2041+	ESA / NASA	Gravitational waves	First space-based gravitational wave observatory; supermassive black hole mergers

Note:
The mentions "Active" and the end dates reflect the status of missions as of the update date of this article (August 13, 2026) and are subject to change. Missions marked "scheduled" are under development and launch dates are indicative.
Missions added in 2026: Nancy Grace Roman, PLATO, SVOM, Xuntian. Future missions: ARIEL, NewAthena, LISA.

Major Historical Space Telescopes

Since the launch of Hubble in 1990, several space observatories have revolutionized our understanding of the cosmos, each exploring a different part of the electromagnetic spectrum. Beyond dates and raw numbers, each mission has its own story: a unique launch context, an unprecedented technical feat for its time, and often an unexpected discovery that surpassed initial objectives.

1970: Uhuru

The first space observatory dedicated exclusively to X-rays, Uhuru (Explorer 42, or SAS-1), was launched on December 12, 1970, from the Italian San Marco floating platform off the coast of Kenya; this date coincides with the seventh anniversary of Kenyan independence, in honor of which the satellite takes its name, meaning "freedom" in Swahili. With an instrument weighing only 65 kg, the satellite scanned about 95% of the sky and cataloged more than 300 X-ray sources, but its most remarkable discovery remains the rapid variability of Cygnus X-1, the first source considered a serious candidate for a stellar black hole — a major conceptual breakthrough for high-energy physics.

1990: Hubble Space Telescope (HST)

Launched by NASA and ESA, Hubble has observed the Universe in visible and ultraviolet light. Shortly after its commissioning, astronomers discovered a manufacturing defect in its primary mirror (spherical aberration) that blurred its images; the problem was corrected in 1993 with the installation of a corrective optical system (COSTAR) during the first servicing mission by the Space Shuttle Endeavour. Since then, its high-resolution images — including the famous Hubble Deep Field — have helped estimate the age of the Universe, study distant galaxies, and confirm the acceleration of cosmic expansion.

1991: Compton Gamma Ray Observatory

At 17 tons, Compton was the heaviest scientific satellite ever placed in orbit at the time of its launch. Its BATSE instrument recorded over 2,700 gamma-ray bursts and demonstrated, through their uniform distribution across the sky, that they originate from distant galaxies and not from our own Milky Way — a discovery that ended years of debate about their origin. In December 1999, the failure of one of its three gyroscopes led NASA, as a precaution, to voluntarily deorbit the observatory; its controlled re-entry into the atmosphere on June 4, 2000, remains the first maneuver of its kind ever performed on such a large satellite.

1999: Chandra X-ray Observatory

Named in honor of astrophysicist Subrahmanyan Chandrasekhar, Chandra observes the sky in the X-ray domain with an angular resolution of 0.5 arcseconds, unmatched to this day for this type of instrument. Its highly elliptical orbit, which takes it up to one-third of the Earth-Moon distance, keeps it far from the Van Allen radiation belts and allows for continuous observations lasting several tens of hours. It has revealed emissions from black holes, supernovas, and galaxy clusters — notably those of the Bullet Cluster, providing one of the most convincing observational proofs of the existence of dark matter.

2003: Spitzer Space Telescope

Designed for infrared observations, Spitzer detected forming stars and protoplanetary disks. After the expected depletion of its liquid coolant in 2009, it continued a "warm mission" for over a decade with two of its detectors remaining operational. It was during this phase that it made one of its most sensational discoveries: in 2016-2017, nearly 500 hours of nearly continuous observation of the dwarf star TRAPPIST-1 confirmed a system of seven Earth-sized planets, three of which are in the habitable zone — a record still standing for a single star.

2009: Herschel Space Observatory

Built by ESA, Herschel explored the far-infrared and submillimeter range using a 3.5-meter diameter mirror, the largest ever sent into space at the time — nearly one and a half times that of Hubble. Positioned at the L2 Lagrange point, it operated until its liquid helium coolant was exhausted in April 2013, revealing the filamentary structure of star-forming regions and the thermal evolution of galaxies throughout the Universe's history.

2009: Kepler

Designed to detect exoplanets using the transit method, Kepler fixed a single field of about 105 square degrees in the constellations Cygnus and Lyra for four years, continuously monitoring the brightness of over 150,000 stars. The loss of two of its four reaction wheels in 2012 and 2013 ended this fixed observation, but the team devised the extended K2 mission, using solar light pressure to stabilize pointing and explore new fields until 2018. In total, Kepler confirmed over 2,600 extrasolar worlds and revolutionized comparative planetology.

2013-2025: Gaia

The Gaia mission mapped over 1.8 billion stars in the Milky Way with unprecedented astrometric precision, allowing the study of galactic dynamics in 3D. Due to a lack of cold gas to stabilize its pointing, the satellite completed its scientific observations on January 15, 2025, before being placed on a retirement heliocentric orbit and permanently deactivated on March 27, 2025. However, data exploitation will continue for many years: the Data Release 4 is expected in 2026, and the final publication, Data Release 5, toward the end of the decade.

2018: TESS

The Transiting Exoplanet Survey Satellite searches for nearby and bright exoplanets. Unlike Kepler, which scrutinized a fixed and distant field, TESS scans nearly the entire sky in successive sectors, targeting nearby bright stars more suitable for follow-up observations. This complementary strategy has identified thousands of planetary candidates accessible to detailed characterization by other instruments, notably James Webb.

2021: James Webb Space Telescope (JWST)

The James Webb represents a major breakthrough. With its 6.5-meter segmented mirror, folded at launch and deployed in orbit like origami, and its infrared instruments passively cooled to about -233°C by a sunshield the size of a tennis court, it observes the first galaxies formed after the Big Bang, analyzes exoplanet atmospheres, and explores star formation processes.

Lifespan and End of Mission for Space Telescopes

Multiple Factors and a Notable Exception

The lifespan of a space telescope depends on many factors: availability of power, thermal stability, aging of sensors, etc. Unlike ground-based observatories, they generally cannot be repaired or resupplied once in orbit, with the notable exception of Hubble, which benefited from five servicing missions by the US Space Shuttle.

Operational Lifespan: Forecasts Often Exceeded

Missions are designed with a nominal operational lifespan, often 3 to 10 years, but many instruments far exceed these projections thanks to the robustness of their systems. For example, Spitzer operated for nearly 17 years instead of the planned 5, while Chandra and Hubble are still active more than two decades after their launch.

Main Causes of Mission End

Fate of Telescopes: Deorbitation or Graveyard Orbit

At the end of their operational life, telescopes are either deorbited for controlled re-entry into Earth's atmosphere (like Compton in 2000 and, more recently, NEOWISE in 2024), or left on a stable, distant "graveyard orbit" to avoid contamination of active orbits. Observatories located at the L2 Lagrange point, such as James Webb or Euclid, will follow the latter procedure. Gaia, also positioned at L2, was moved in 2025 to a retirement heliocentric orbit before its final deactivation.

The Decommissioning Phase: A Programmed End of Cycle

Engineers plan a progressive decommissioning phase from the design stage to optimize the use of residual energy and secure the shutdown. This step marks the end of a technological cycle but prepares the advent of a new generation of more powerful observatories.

Future Prospects: From Design to Adoption

Several major space telescope projects, long relegated to the conceptual stage, have recently crossed decisive milestones toward their concrete realization.

Habitable Worlds Observatory (HWO)

The competing concepts LUVOIR and HabEx, once separately considered by NASA, were merged following the recommendation of the decadal survey (Astro2020 Decadal Survey) published in late 2021. The agency is now developing a single project, the Habitable Worlds Observatory, a telescope with a segmented mirror at least 6 meters in diameter observing in ultraviolet, visible, and near-infrared. Designed as a "super-Hubble" repairable in orbit, it will aim for direct detection and characterization of Earth-sized planets in the habitable zone around nearby stars, with a launch envisioned in the 2040s.

NewAthena

The European project ATHENA, selected by ESA in 2014, was resized in 2023 to account for budget constraints and renamed NewAthena. This X-ray observatory, intended to study the growth of supermassive black holes and the structure of the hot and energetic Universe, is to be formally adopted by ESA in 2027, with a launch planned for the late 2030s.

LISA, the First Space Ear for Gravitational Waves

After several decades of study, the LISA mission (Laser Interferometer Space Antenna) was officially adopted by ESA on January 25, 2024, in partnership with NASA. Composed of three satellites forming an equilateral triangle with 2.5 million kilometers on each side, it will detect low-frequency gravitational waves emitted notably by the merger of supermassive black holes. Its launch is planned for around 2035.

FAQ: Everything You Need to Know About Space Telescopes

What is a space telescope and what is its main advantage over ground-based telescopes?

A space telescope is an observatory placed beyond Earth's atmosphere. Its main advantage is that it eliminates optical disturbances (turbulence), thermal issues, and atmospheric absorption, which block a large part of the electromagnetic spectrum. It can thus observe the Universe across all wavelengths, from gamma rays to radio waves, with unparalleled resolution and sensitivity, particularly in the infrared and ultraviolet.

What is the typical lifespan of a space telescope and what happens to it at the end of its mission?

The nominal lifespan is generally 3 to 10 years, but many instruments far exceed these projections (e.g., Spitzer operated for 17 years). At the end of the mission, due to fuel depletion, component aging, or a failure, the telescope is either deorbited for a controlled re-entry into the atmosphere (like NEOWISE in 2024), or placed on a "graveyard orbit" or a retirement heliocentric orbit, stable and distant, to avoid collisions. This is the case for observatories located at the L2 Lagrange point, such as James Webb or, more recently, Gaia, deactivated in March 2025.

What are the most iconic space telescopes mentioned in the article and what did they discover?

The article mentions several flagship missions: Hubble (visible/UV) measured the Universe's expansion rate; Chandra (X-rays) revealed emissions from black holes; Spitzer (infrared) detected protoplanetary disks; Kepler (visible) discovered thousands of exoplanets; Gaia (visible), active from 2013 to 2025, mapped over 1.8 billion stars in 3D; and James Webb (infrared), the latest breakthrough, observes the first galaxies and exoplanetary atmospheres.

What future space telescope projects are mentioned?

The article mentions the Habitable Worlds Observatory, which succeeds the LUVOIR and HabEx concepts and will aim for direct detection of potentially habitable exoplanets, with a launch envisioned in the 2040s. It also mentions NewAthena, a resized version of the ATHENA project, which will explore X-rays, and LISA, a gravitational wave space observatory officially adopted by ESA in 2024 with a launch planned for around 2035, intended to probe black hole physics and the structure of the primordial cosmos.