Hubble Space Telescope launch

From blurry-mirror embarrassment to the Deep Fields and the age of the universe — still working 35 years on.

The story

On 24 April 1990 the Space Shuttle Discovery carried the Hubble Space Telescope to a 540 km orbit — a 2.4 m mirror and 11 tonnes, fulfilling Lyman Spitzer's 1946 proposal to observe from above the turbulence of the atmosphere 44 years after he made it. The launch had been delayed four years by the Challenger disaster.

Two months later the first images came back blurred. The edge of the primary mirror had been ground 2.2 micrometres wrong — a fiftieth of a hair's width — a spherical aberration that made Hubble a "billion-dollar blunder" for a while. In December 1993 the servicing mission aboard Endeavour fitted the corrective optics package COSTAR like a pair of glasses, and everything changed.

The 1995 Hubble Deep Field stared at an empty patch of Ursa Major for ten days and pulled out 3,000 galaxies; Cepheid observations narrowed the age of the universe to 13.8 billion years; and supernova observations in 1998 supplied decisive data for the discovery that cosmic expansion is accelerating — dark energy.

Hubble is the only space telescope designed to be repaired. Five shuttle servicing missions between 1993 and 2009 replaced cameras, gyroscopes and batteries, effectively renewing it generation by generation. Thirty-five years on, observing proposals are still oversubscribed more than five to one, and operations are expected to continue into the mid-2030s.

Why it matters

How humanity sees the universe divides into before and after Hubble. When ground-based resolution was pinned near one arcsecond by atmospheric turbulence, Hubble opened a view of 0.05 arcseconds — twenty times sharper. Galactic-centre black holes, spectra of exoplanet atmospheres and the moons of outer-solar-system bodies all came out of that resolution.

Hubble proved that a space telescope can be fixed. The success of the 1993 repair rescued the credibility of the shuttle programme, and orbital part-swapping became the rehearsal for assembling the International Space Station. James Webb was later designed with no servicing at all — Hubble's lesson applied in reverse.

Its pictures became visual culture beyond science. The "Pillars of Creation" in the Eagle Nebula (1995), the Deep Field and the portraits of spiral galaxies became textbook plates and wallpaper, and Hubble's policy of releasing all data after one year became the standard for every large facility since.

How to watch

Hubble is a bright satellite circling every 95 minutes at 540 km. When it passes over it reaches magnitude 2–3 to the naked eye; switch on satellites in the sky view for the pass times and track from your location (satellite display is for supporters and above).

Find the Hubble Deep Field in the sky view — near the handle of the Big Dipper, RA 12h 36m, Dec +62° — and zoom in to see how empty that patch looks. Three thousand galaxies came out of it.

The subjects of Hubble's famous pictures can be found at their real distances in the 3-D interstellar view and the sky view's deep-sky list — the Eagle Nebula (7,000 light-years), the Whirlpool Galaxy M51 (23 million light-years), the Andromeda Galaxy and others.

Background

The aberration traced to a lens in the mirror maker's test instrument being 1.3 mm out of place. Two other test devices had flagged the error during fabrication but were dismissed as less precise. The episode became a textbook cautionary tale for NASA quality control.

The last of the five servicing missions (2009, Atlantis) had been cancelled after the 2003 Columbia disaster and was revived under public and congressional pressure. The Wide Field Camera 3 and Cosmic Origins Spectrograph installed then are the workhorses of Hubble observing today.

When James Webb arrived in 2021 Hubble did not retire but became its partner — Hubble in visible and ultraviolet light, Webb in infrared. Gyroscope failures forced a one-gyro mode in 2024, yet observing continues, and orbital decay is expected to bring re-entry in the mid-to-late 2030s.

FAQ

Why were the first images blurred?

A spherical aberration — the mirror's edge was ground 2.2 micrometres wrong. Corrective optics installed in 1993 fixed it.

Can Hubble be seen with the naked eye?

Yes — it reaches magnitude 2–3 on a pass; the sky view's satellite display shows pass times.

How much longer will it work?

Observing is expected into the mid-2030s, after which orbital decay brings re-entry.

Does James Webb replace Hubble?

No. Webb covers infrared and Hubble visible and ultraviolet light; they complement each other.

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Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.