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Spacecraft Tracking Systems

Equipment for Positioning the Spacecraft

To communicate with a spacecraft up to 400 million kilometers (249 million miles) away, engineers must know not just where it is, but in which direction it is pointing. There are three on-board systems to help:

  • two star trackers, one on each side of the spacecraft, identify the direction in which the spacecraft is pointing by analyzing the patterns of stars through small telescopes

  • three laser gyros measure the spacecraft's rotation

  • two sun sensors that allow the spacecraft to orient itself with respect to the sun

Small corrections to the spacecraft's orientation can be achieved by altering the rotation of spinning reaction wheels attached to the underside of the spacecraft. They correct any jitter that could disturb observations when the thrusters are fired and also rotate the spacecraft slowly as it moves round its orbit so that the instruments or antenna are kept pointing in the right direction.

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