The Hubble Space Telescope is one of the most important spacecraft ever placed in low Earth orbit because it carries a large observatory above most of Earth’s atmosphere. From that orbit, Hubble can measure faint light without atmospheric blur, clouds, or much ultraviolet absorption. It is also a major astronautics achievement because it was designed to be serviced by astronauts, not just launched and abandoned.
Its history shows how spacecraft design, orbital mechanics, human spaceflight, and science instruments can work together.
Key Facts
- Hubble orbits Earth at about 540 km altitude in low Earth orbit.
- Orbital speed near Hubble’s altitude is about 7.6 km/s.
- Orbital period can be estimated by T = 2πr/v, giving about 95 minutes for Hubble.
- Hubble’s primary mirror diameter is 2.4 m, which helps collect faint light and resolve fine detail.
- Angular resolution improves as θ = 1.22λ/D, where D is mirror diameter and λ is wavelength.
- Hubble was launched in 1990 and was repaired or upgraded during five Space Shuttle servicing missions.
Vocabulary
- Low Earth orbit
- Low Earth orbit is a region of space close to Earth, usually below about 2000 km altitude, where spacecraft move fast enough to keep falling around the planet.
- Servicing mission
- A servicing mission is a crewed or robotic mission that repairs, replaces, or upgrades parts of a spacecraft after launch.
- Primary mirror
- The primary mirror is the main light-collecting mirror in a telescope that gathers and focuses incoming light.
- Reaction wheel
- A reaction wheel is a spinning device inside a spacecraft that changes the spacecraft’s pointing direction without using fuel.
- Angular resolution
- Angular resolution is the smallest angle between two objects that a telescope can distinguish as separate.
Common Mistakes to Avoid
- Treating Hubble as if it is outside Earth’s gravity is wrong because it remains strongly affected by gravity and stays in orbit by continuously falling around Earth.
- Assuming Hubble sees well only because it is closer to stars is wrong because stars and galaxies are still extremely far away, and the main advantage is being above the atmosphere.
- Using altitude as the orbital radius is wrong because orbital radius is measured from Earth’s center, so Earth’s radius must be added to the altitude.
- Thinking repairs were simple plug-in fixes is wrong because astronauts had to work in spacesuits with limited time, special tools, and careful procedures in microgravity.
Practice Questions
- 1 Hubble orbits at an altitude of 540 km. If Earth’s radius is 6370 km, what is Hubble’s orbital radius measured from Earth’s center?
- 2 Use T = 2πr/v to estimate Hubble’s orbital period in minutes if r = 6.91 x 10^6 m and v = 7.6 x 10^3 m/s.
- 3 Explain why Hubble’s ability to be serviced by astronauts was important for both engineering reliability and scientific discovery.