Discovery
| Parameter | Value |
|---|---|
| Launch date | April 24, 1990 (STS-31, Space Shuttle Discovery) |
| Orbital altitude | 547 km (low Earth orbit) |
| Orbital period | 96 minutes |
| Mass | 11,110 kg |
| Primary mirror | 2.4 m diameter, ULE (Ultra-Low Expansion) glass |
| Optical configuration | Ritchey-Chrétien (Cassegrain variant) |
| Angular resolution | 0.05 arcsec |
| Spectral range | 115 nm (UV) to 2,500 nm (near-IR) |
Technical Explanation
1. Optics above the turbulence — Earth's atmosphere causes typical seeing of 0.5–2 arcsec (convective agitation, refractive index gradients). In orbit, Hubble reaches the theoretical diffraction limit of its mirror: θ = 1.22 λ/D ≈ 0.05 arcsec at 500 nm. This is the telescope's entire raison d'être.
2. Spherical aberration and the COSTAR correction — The primary mirror was ground with a 2.2 μm error at the edge (conic constant of –1.0139 instead of the correct –1.00230). Images were blurred (80% of light spread beyond 0.7 arcsec). In December 1993, the STS-61 mission installed COSTAR: pre-deformed corrective mirrors that compensated for the aberration, restoring full optical performance.
3. Detection instruments — Hubble has carried a succession of instruments: WF/PC2 (wide-field imaging), STIS (UV-visible spectrograph), NICMOS (near-IR), ACS (deep imaging), WFC3 (wide-field camera, 2009). Each servicing mission upgraded the detectors: from CCD 800×800 (1990) to CCD 4096×4096 (2009).
4. Precision pointing — The Fine Guidance Sensors (FGS) use interferometers to achieve pointing stability of 0.007 arcsec. The equivalent: aiming a laser at a coin from 320 km away and holding it steady.
Why It Worked
Despite the initial aberration (caused by a miscalibrated null corrector at Perkin-Elmer), Hubble was designed to be serviceable in orbit — a visionary architectural decision. The five servicing missions (1993–2009) transformed it into an instrument 100× more powerful than the original version. Access to UV and near-IR wavelengths (inaccessible from the ground due to atmospheric absorption) multiplied the discovery potential.
The Hubble Deep Field observation (1995) epitomizes the telescope's power: ten days of exposure on a seemingly empty patch of sky in Ursa Major revealed ~3,000 galaxies in an area of just 5.3 arcmin² — equivalent to a grain of sand held at arm's length. Every "empty" region of the sky contains billions of galaxies.
Causal Chain
Space telescope concept (Lyman Spitzer, 1946) → NASA funding (1977) → Mirror fabrication at Perkin-Elmer → STS-31 launch (1990) → Spherical aberration detected → COSTAR on STS-61 (1993) → Hubble Deep Field (1995) → Accelerating expansion (Type Ia supernovae, 1998) → Nobel Prize for Perlmutter/Riess/Schmidt (2011) → JWST successor (2021)
Anecdote
The Hubble Deep Field images (1995) were obtained by pointing the telescope at an apparently empty patch of sky (in Ursa Major) for 10 consecutive days. The result: ~3,000 galaxies in a field of 5.3 arcmin² — the equivalent of a grain of sand held at arm's length. Every seemingly "empty" spot in the sky contains billions of galaxies.
Sources
References verified during the August 2026 fact-checking audit: these are the pages
against which this bulletin's claims were checked.