The Hubble Program - Technology

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Optical Assembly

Hubble's optical telescope assembly consists of two mirrors, support trusses, and the focal plane structure. This system is a Ritchey-Chretien design in which two aspheric mirrors serve to form focused images over the largest possible field of view.

Pointing Control System

The Pointing Control System (PCS) aligns Hubble so that the telescope points to and remains locked on a target. The PCS is designed for pointing to within .01 arcsec and is capable of holding a target for up to 24 hours while Hubble continues to orbit the Earth at 17,500 mph. If the telescope were in Los Angeles, it could hold a beam of light on a dime in San Francisco without the beam straying from the coin's diameter.

Sensors

Hubble employs a variety of sensors to detect its own orientation and position. All work in tandem to send the correct information to the actuators to adjust Hubble's position on command.

Fine Guidance Sensors (3)

These sensors are locked onto two guide stars to keep Hubble in the same relative position of these stars.

Coarse Sun Sensors (2)

Measure Hubble's orientation to the sun. Also assist in deciding when to open and close the aperture door.

Magnetic Sensing System

Measures Hubble's position relative to Earth's magnetic field.

Rate Sensor Units (3)

Two rate-sensing gyroscopes measure the attitude rate motion about its sensitive axis.

Fixed Head Star Trackers (3)

An electro-optical detector that locates and tracks a specific star within its field of view.

Actuators

Receiving information from the sensors, the actuators physically adjust Hubble's position and orientation so that Hubble can view the required celestial bodies.

Reaction Wheel Actuators (4)

The reaction wheels work by rotating a large flywheel up to 3000 rpm or braking it to exchange momentum with the spacecraft which will make Hubble turn.

Magnetic Torquers (4)

The torquers are used primarily to manage reaction wheel speed. Reacting against Earth's magnetic field, the torquers reduce the reaction wheel speed, thus managing angular momentum.

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