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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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THE HUBBLE SPACE TELESCOPE
OVERVIEW HUBBLE NEWS OPERATIONS TECHNOLOGY SERVICING MISSIONS HUBBLE MULTIMEDIA PRODUCTS

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HUBBLE TECHNOLOGY SUMMARY
SPACECRAFT SYSTEM
HUBBLE OPTICS
Pointing Control System
SCIENCE INSTRUMENTS
Pointing Control System
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 stable 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.

graphic illustrating location of Hubble sensors and actuators

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 (FGS) (3)

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

Coarse Sun Sensors (CSS) (4)

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

Magnetic Sensing System (MSS) (2)

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

Rate Sensor Units (RSU) (3)

Each RSU contains two gyroscopes, used for maintaining stable pointing.

Fixed Head Star Trackers (FHST) (3)

An electro-optical detector that maps areas of the sky to determine Hubble's orientation in space.


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 (RWA) (4)

The reaction wheels work by rotating a large flywheel up to 3000 rpm or braking it. The resulting changes in angular momentum serve to move the telescope from one target to another.

Magnetic Torquers (MT) (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.