Last update: October 8, 2025

Space Telescopes: Humanity's Eye Beyond the Atmosphere

Observing the Universe from Space

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

Advantages of Space Observation

Earth's atmosphere absorbs much of the electromagnetic spectrum. By placing a telescope in space, we gain a complete view of the cosmos, without atmospheric turbulence or absorption. This allows for exceptional angular resolution and increased sensitivity, especially in infrared and ultraviolet.

Onboard Technology

Space telescopes use:

Large segmented mirrors to collect maximum light.
CCD or infrared detectors cooled to very low temperatures to minimize thermal noise.
Gyroscopic stabilization systems for precise pointing.
High-speed data transmission to relay observations to ground-based scientific centers.

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.

Uhuru (1970)

The first X-ray space observatory, Uhuru (Explorer 42) cataloged over 300 X-ray sources, paving the way for high-energy astronomy.

1990: Hubble Space Telescope (HST)

Launched by NASA and ESA, Hubble observed the Universe in visible and ultraviolet light. Its high-resolution images helped estimate the age of the Universe, study distant galaxies, and confirm the acceleration of cosmic expansion.

Compton Gamma Ray Observatory (1991)

This telescope observed gamma-ray bursts, pulsars, and black holes. It enabled the first complete mapping of the gamma-ray sky.

1999: Chandra X-ray Observatory

The Chandra telescope observes the sky in X-rays. It revealed emissions from black holes, supernovae, and galaxy clusters, providing crucial clues about dark matter and high-energy phenomena.

2003: Spitzer Space Telescope

Designed for infrared, Spitzer detected forming stars and protoplanetary disks. Its observations helped study the chemical composition of interstellar clouds and exoplanets.

2009: Herschel Space Observatory

Built by ESA, Herschel explored the far-infrared and submillimeter wavelengths. It revealed the structure of molecular clouds and the thermal evolution of galaxies.

Kepler (2009)

Designed to detect exoplanets via the transit method, Kepler confirmed over 2,600 extrasolar worlds and revolutionized comparative planetology.

Gaia (2013)

The Gaia mission maps over a billion stars in the Milky Way with unprecedented astrometric precision, enabling the study of galactic dynamics in 3D.

TESS (2018)

The Transiting Exoplanet Survey Satellite searches for nearby, bright exoplanets. It complements Kepler's work with near-complete sky coverage.

2021: James Webb Space Telescope (JWST)

The James Webb represents a major advance. With its 6.5 m mirror and infrared instruments, it observes the first galaxies formed after the Big Bang, analyzes exoplanet atmospheres, and explores star formation processes.

Comparison of Space Telescopes

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 rays	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	Mapping of the gamma-ray sky and study of gamma-ray bursts
HALCA (VSOP)	1997	2005	JAXA	Radio	Space interferometry to study active galactic nuclei
SOHO	1995	Active	ESA / NASA	Visible, UV	Continuous observation of solar activity and solar wind
Chandra	1999	Active	NASA	X-rays	Structure of supernovae and black holes
Spektr-R (RadioAstron)	2011	2019	Roscosmos	Radio	Very long baseline interferometry with ground-based radio telescopes
Suzaku (ASTRO-E2)	2005	2015	JAXA / NASA	X-rays	Study of intergalactic hot gas and galaxy clusters
Spitzer	2003	2020	NASA	Infrared	Study of protoplanetary disks and cosmic dust
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 stellar formation
Kepler	2009	2018	NASA	Visible	Discovery of thousands of exoplanets by transit
NEOWISE (ex-WISE)	2009	Active	NASA	Infrared	Search and tracking of near-Earth asteroids
Astrosat	2015	Active	ISRO	UV, visible, X-rays	First Indian multi-wavelength space observatory
Gaia	2013	Active	ESA	Visible	3D mapping of one billion stars in the Milky Way
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
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 the Sun's coronal magnetic field
Einstein Probe	2024	Active	CNSA / ESA	Soft X-rays	Detection of transient events such as supernovae and stellar mergers
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

Source : NASA Missions, ESA Science, CSA.

Lifespan and End of Mission for Space Telescopes

The lifespan of a space telescope depends on many factors: energy availability, thermal stability, sensor aging, 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 maintenance missions by the American space shuttle.

Missions are designed with a nominal operational lifespan, often 3 to 10 years, but many instruments far exceed these predictions due to system robustness. 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.

Several causes lead to the end of a mission:

Fuel depletion necessary for orbital corrections or maintaining the Lagrange point.
Thermal degradation of electronic and optical components due to extreme temperature cycles.
Aging of detectors (CCD, bolometers, photodiodes) affecting spectral sensitivity.
Loss of communication or failure of transmission antennas.
Orbital constraint: for telescopes in low orbit, atmospheric drag causes progressive deorbiting.

At the end of their operational life, telescopes are either deorbited for a controlled re-entry into Earth's atmosphere (like Compton in 2000) or placed in a stable "graveyard" orbit, far away, to avoid contamination of active orbits. Observatories located at the Lagrange point L2, such as James Webb or Euclid, will follow the latter procedure.

Engineers plan a gradual shutdown phase from the design stage to optimize the use of residual energy and ensure safe decommissioning. This step marks the end of a technological cycle but paves the way for a new generation of more powerful observatories.

Future Perspectives

Future space telescopes will further expand our view of the Universe. Projects like LUVOIR or HabEx aim for the direct detection of potentially habitable exoplanets. Others, such as ATHENA and LISA, will explore X-rays and gravitational waves to probe black hole physics and the structure of the primordial cosmos.