XMM-Newton seen high over Europe
17 April 2000
Teamwork by an amateur astronomer and a retired member of the European Space Agency has resulted in the first picture of XMM-Newton seen from the Northern Hemisphere. ESA's new X-ray observatory - launched on 10 December 1999 and now going through the calibration phase of its science instruments - had already been snapped on 11 January by Australian amateur Gordon Garradd.This latest picture of the satellite was taken by a secondary school physics teacher in Bellinzona, Switzerland. Working from his home-based observatory in Gnosca, a small town in the south of the country, Stefano Sposetti was able to locate XMM-Newton in the sky on 8 April with the help of an emphemeris provided by German Bruno Tilgner who retired from ESA in 1998. Amongst his responsibilities, Tilgner was deputy project manager at ESTEC for the TD-1A astronomical satellite.
It was Tilgner's idea to attempt to snap XMM-Newton. He and Sposetti - who have never met each other - had successfully collaborated two years ago on a project to track the cluster of then seven ASTRA geostationary satellites all night long for nearly three weeks. It was only natural that they would team up once again for XMM-Newton, another very challenging object to observe.
Stefano Sposetti's picture of XMM-Newton was taken at 04:00 UTC using a front-illuminated CCD camera through a 40cm f/4 telescope. The exposure time was 30 seconds and the field of view 20' x 20'. The satellite was then near its perigee at a distance of 8440km. On the image it leaves a long trail, travelling from the right to the left side at an angular speed of 2.4 degrees/minute. On the picture taken from Australia, XMM-Newton was then near its apogee point of 114 000km from Earth, leaving only a short trail visible.
"Bruno's calculations were excellent and enabled me to locate the satellite on my first attempt" says Sposetti. "There was a 2 arc minute difference, which is perfectly acceptable. However XMM-Newton passed 13 seconds later than expected".Tilgner offers a possible explanation for this slight discrepancy. "I relied on orbital parameters available from USSPACECOM (NORAD) and their orbit propagation models were perhaps not designed for high-eccentricity orbits".
Sposetti's amateur astronomy activities focus on all moving objects in the solar system - a passion that stems, he recalls, from his childhood when, woken by his mother in the middle of the night, he saw his first comet. Today his photograph album contains an impressive collection of comets, minor planets, meteors and artificial satellites - to which he today is now adding XMM-Newton.
Bruno Tilgner remembers his six years at ESTEC working on the TD-1A project. The satellite, launched in 1972 and Europe's very first three-axis stabilised spacecraft, can be considered as one of XMM-Newton's ancestors. It was primarily a stellar ultraviolet mission but also carried a gamma-ray detector and a cosmic X-ray detector. One of the two ultraviolet experiments on board TD-1A was provided by the University of Utrecht, which has also contributed with the X-ray Spectrometer (RGS) to the XMM-Newton mission.
