Simulators prepare star trackers for spaceflight
SSTL’s Optical Payload Group is currently building two Dynamic Multi Star-field Simulators (DMSS) at its Sevenoaks facility that will be used to test star trackers that will be flown in space under simulated operating conditions here on Earth.
Star trackers are an essential subsystem in any satellite, providing information that allows the spacecraft's on board computer to determine its orientation or “pointing” at any point in time.
DMSS assembly
This information is then sent to an attitude control system that corrects for the drift by using on-board thrusters or other motion-generating devices to maintain the correct satellite pointing.
Any time a satellite is manoeuvred in orbit, the pointing information from star trackers is vital to the spacecraft’s control systems. For example, solar panels must be aligned to capture the maximum available light from the Sun, and communications antennae pointed towards the Earth.
Star trackers are now available that operate in autonomous modes. These units are able to dynamically monitor the star fields in orbit and provide correction information back to the satellite to counteract adverse platform manoeuvres, such as slews and spins, which is particularly useful in the early stage of mission operations or following a major system failure.
To test these units on the ground prior to launch, it is essential to present the star trackers with a dynamically varying star field. This is where the DMSS comes in.
Optical Collimator
An optical collimator is a device that generates a parallel beam of light by using a curved mirror or lens with some type of light source at its focus. This makes it possible to replicate a target at infinity without parallax.
The DMSS consist of a large optical collimator that presents the output of a very high resolution Liquid Crystal Display (LCD) to the star tracker under test, simulating stars at infinity. Specially engineered software drives the LCD, presenting a range of moving star field configurations to the star tracker. Customers can use these simulators to test star trackers linked to the satellites, enabling end-to-end tests of the satellite control system - an exceedingly valuable capability.An optical collimator is a device that generates a parallel beam of light by using a curved mirror or lens with some type of light source at its focus. This makes it possible to replicate a target at infinity without parallax.
The basic principle behind any pre-launch review is to validate systems as best as possible to reduce the risk of something going wrong once the satellite “goes it alone” in space. Once a satellite is launched, the first minutes are critical to gain control of the spacecraft, initiate power systems and establish communications. Innovations like the DMSS play a valuable role in validating and assessing system performance and functionality before they are flown in space.
This entry was posted by Robin Wolstenholme on Thursday, April 22. 2010 at 11:33.
and is filed under Innovation.
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