Cluster camera to catch spacecraft separation
13 July 2000One interesting addition to the Cluster spacecraft's payload of 11 state-of-the-art scientific instruments is a digital camera known as the Visual Monitoring Camera (VMC).
The VMC is very similar to the IRIS colour camera that was used on the XMM satellite. It is installed in the umbilical separation connector bracket on the base of the upper spacecraft (CUS) in each Cluster pair, in order to take a series of 27 colour images of the lower spacecraft (CLS) during separation.
The lightweight VMC, which was manufactured by the Belgian company OIP/IMEC, is complemented by an eXternal Memory eXpansion Unit (XMXU) that autonomously stores the images until communications are established with ground control.
The mass of the VMC is 430 grams and of the XMXU is 380 grams, and each of them measures 10 x 6 x 6 cm.
The period of image acquisition, which lasts almost 1½ minutes, will be triggered by the separation of the CLS from the CUS. One colour image will then be taken every 3 seconds, starting when the spacecraft are about 3 metres apart.
The exact field of view depends on the orientation of the spacecraft at the time of separation, but the Cluster team is hoping that at least part of the Earth will be visible in the images. Another uncertainty is the estimated exposure time setting of the VMC, which is derived from simulations in the laboratory.
It is intended to downlink the stored images to the ground once communication with the spacecraft is established about 3 hours after launch. The data will be processed immediately at the European Space Research and Technology Centre (ESTEC) in The Netherlands for distribution to the Cluster Project Team and will subsequently be published on the web.
The two VMCs are the only cameras on board the Cluster quartet. Each spacecraft carries 11 identical scientific instruments to detect and measure charged particles and electromagnetic phenomena. However, since plasma, electric fields and magnetic waves are usually invisible at optical wavelengths, a camera was not included in this impressive instrument package.