The Station passes the radar

The German satellite TerraSAR-X has observed the International Space Station in a rather unusual way...

 

The TerraSAR-X satellite (artistic impression). Credit: DLR

Launched on 15 June 2007, TerraSAR-X is an Earth observation satellite born from a partnership between the German Aerospace centre (DLR - Deutschen zentrums für Luft und Raumfahrt) and EADS Astrium. Remarkably, on 13 March 2008, it scanned the International Space station with its radar. The image acquired was published on 4 March 2010.

The International Space Station "viewed" by the radar of satellite TerraSAR-X on 13 March 2008. Credit: DLR

X-ray image of the ISS?
In order to understand this amazing image, the name of TerraSAR-X itself can guide us.  Terra is of course there to indicate that this orbital sentinel observes the Earth. SAR means Synthetic Aperture Radar. More simply, the principle is based on that of the radar: a device emits radio waves then "listens" to the echo returned by the encountered objects. The time taken for the wave to return and the changes in the reflection provides valuable information which enables a radar image to be produced.  Operating with Synthetic Aperture, the SAR of the TerraSAR-X carries out a real scan as the German satellite moves through its orbit. Indeed, on 13 March 2008, it passed above the Station at a distance of 195km and "scanned" it...

Explanation of the TerraSAR-X radar image with a photo of the Station taken from the shuttle Endeavour at the end of mission STS-123 in March 2008. The shuttle was docked to the ISS when the german satellite made this image. Thanks to Daniel Schulze of the DLR who confirmed this diagram. Credit: DLR/NASA/Enjoy Space

However, the ISS, and the astronauts on board (at the time 7 from the shuttle Endeavour flight STS-123 and three from Expedition 16 were on the ISS) were not X-rayed! Indeed, the letter X in TerraSAR-X does not refer to the radiation used in medical imagery, but indicates that the radar works on the X-band, which is a radio frequency range from 8 - 10 GHz (microwaves).

A Station which has changed significantly!
This image from TerraSAR-X shows us how much the ISS has changed in two years.  In March 2008, it was noted that the last set of solar panels were missing and that Kibo, the Japanese laboratory was still to be set up. Flight STS-123 brought its first component: a pressurised storage module. Today, and since last February's STS-130 mission, the Station is almost complete thanks to the addition of the Tranquillity module and the Cupola observation post. The four remaining shuttle flights will bring a small Russian module, the AMS scientific experiment (detection of antimatter) as well as equipment and supplies (see this Enjoy Space article for the schedule).

The ISS in March 2008 (left) and March 2010 (right). It has changed significantly! Credit: NASA/Enjoy Space

Published 5 March 2010