Advanced optics to benefit Earth Observation Satellite

Optical Surfaces Ltd. (Kenley, UK) has supplied three high precision aspheric mirrors that form key elements at the heart of the advanced optical system to be used by the novel low-cost TopSat Earth Observation satellite.

Jointly funded by the UK Ministry of Defence (MoD) and British National Space Centre (BNSC) the TopSat project has drawn upon the expertise of a consortium of companies with world class capabilities in small satellites and high performance space missions.

Due for launch in 2004, TopSat consists of a low mass optical telescope able to form 15 x 15 km images of the Earth’s surface with a panchromatic resolution of 2.5m integrated with a micro-satellite platform to enable image data to be downloaded to a mobile ground station.

The long effective focal length and large optical aperture required for 2.5m imagery in the TopSat satellite design necessitated that Optical Surfaces produce three ultra smooth off-axis aspheric mirrors. Using proprietary manufacturing techniques Optical Surfaces was able to produce in Zerodur the three thin off-axis mirrors, the largest of which was 240 x 280 mm and only 25mm thick.

All mirrors were finished to achieve a uniform lambda/15 peak-to-valley over the whole working area. Alignment and focus of the TopSat optical system are maintained by the high thermal stability of the monocoque construction, fabricated in low mass carbon fibre reinforced plastic composite materials. To maximise coverage and sensitivity whilst minimising size and mass, push-broom imaging with a linear CCD has been used.

Optical Surfaces were selected for their proven record in manufacturing and
testing demanding high precision astronomical and space optics.

Thin edge optics would be impossible without our skill in localising surfaces after machining.