Space Telescopes
Why put telescopes in space at all? Because Earth's air blurs starlight, blocks whole kinds of light, and glows faintly itself. Above the air, a telescope sees clearly, in every kind of light, day and night. This page is the fleet: what each telescope was built for, what its work has proved or helped with, and where to find its public home.
Hubble Space Telescope — launched 1990, still working
Built for: sharp pictures of the universe in visible, ultraviolet, and near-infrared light, from low orbit around Earth. It launched with a flawed mirror in 1990 and was fixed by astronauts in 1993 — one of the great repair jobs in history.
What it proved and helped with: Hubble pinned down the age of the universe, took the deepest pictures of the sky ever made, and helped show that the universe's expansion is speeding up, not slowing down — the discovery of dark energy. Its star measurements are the foundation of the nearby side of the expansion argument.
Public home: NASA's Hubble Space Telescope.
James Webb Space Telescope — launched 2021, working
Built for: the first stars and galaxies, and the air of planets around other stars, seen in infrared light from a million miles away.
What it proved and helped with: Webb re-checked Hubble's star measurements and found them solid, ruling out the crowding worry in the expansion argument. It has photographed the earliest galaxies ever seen and is studying planet atmospheres in detail no telescope could before.
Public home: NASA's James Webb Space Telescope. Its own tensor page is here.
Nancy Grace Roman Space Telescope — launched 2026, getting ready
Built for: giant surveys of the sky in infrared light — dark energy, dark matter, and a census of planets in our galaxy, including planets no star holds onto.
What it has proved and helped with so far: Roman is still on its way to its observing spot and in its getting-ready phase, with first science pictures expected in early 2027. Its surveys are the ones our Roman tensor leg will use.
Public home: NASA's Roman Space Telescope. Its data lives on the Roman Research Nexus. Its own tensor page is here.
TESS — launched 2018, still working, and it deserves more credit than it gets
Built for: finding planets around the brightest, nearest stars, by watching for the tiny dips in starlight when a planet crosses in front of its star. TESS watches the whole sky, sector by sector, and it also photographs everything else that changes in brightness: asteroids, pulsing stars, exploding stars in faraway galaxies.
What it proved and helped with: TESS has passed 1,000 confirmed planets, and re-checking its first year of data alone turned up more than 10,000 new planet candidates. Here is the part that gets skipped: the planets Webb now studies in detail — the ones in all the famous atmosphere results — are mostly TESS's finds. TESS does the finding; Webb gets the fame. TESS is the middle link between the earlier Kepler planet hunt and Roman's coming planet census, and its bright-star planets are exactly the ones we can follow up and learn the most from.
Public home: NASA's TESS mission.
Euclid — launched 2023, working
Built for: mapping the dark universe. Euclid, from the European Space Agency, is photographing more than a third of the sky and measuring billions of galaxies out to 10 billion light-years, building the largest three-dimensional map of the universe ever made.
What it proved and helped with: Euclid's map shows how the universe has expanded over time and how its large-scale structure is arranged — the two clues that bear most directly on dark matter and dark energy. It works hand in hand with Roman: the two telescopes' maps check each other.
Public home: ESA's Euclid mission.
Chandra X-ray Observatory — launched 1999, still working
Built for: seeing the universe in X-rays — the light given off by the hottest, most violent things: gas falling into black holes, the wreckage of exploded stars, and the thin, million-degree gas between galaxies.
What it proved and helped with: Chandra has mapped black hole jets, supernova leftovers, and the hot gas in galaxy clusters in unmatched detail. It even took its own independent shot at the expansion number, using galaxy clusters — a completely different method from either side of the main argument.
Public home: Chandra X-ray Center.
Gaia — launched 2013, retired March 2025, still giving
Built for: measuring the positions, distances, and motions of about a billion stars with unmatched precision — the most exact three-dimensional map of our own galaxy ever made.
What it proved and helped with: Gaia's star map underlies nearly all modern work on the Milky Way: how our galaxy is shaped, how it moves, how it grew by swallowing smaller galaxies. Its data is still being processed into the final catalog, and scientists will be mining it for years.
Public home: ESA's Gaia mission.
And more, still up there
The fleet is bigger than one page: Fermi and Swift watch the sky for gamma-ray bursts and other sudden violence, XMM-Newton studies X-ray sources from Europe, SPHEREx is mapping the whole sky in infrared, and more observatories keep joining. They will get their own entries here as this page grows.