The GRACE mission was designed to map the Earth’s gravitational field in exquisite detail (and it has just celebrated a decade in orbit). To achieve this objective, the mission consists of a pair of twin satellites in orbit and the instruments which can measure changes in their separation to incredible accuracy. Over long periods of time the GRACE satellites have built an incredible map of how gravitational field strength varies across the Earth.
Early evening March 17th 2002 I had my telescope set up in the garden just outside the house. It was still twilight but it was dark enough to see the constellations: the brightest stars of Gemini, Taurus and Orion were easily visible. Jupiter and Saturn were also shining and very high in the sky. Then I noticed a bright new star in the sky not far from Jupiter. For a moment I thought it was a satellite but then realised that it didn’t look like it was moving. My next thought was that it might be a new supernova! I got the telescope – a 10 inch Dobsonian – on to the new star very quickly.
The view through the eyepiece was unusual; it was disk shaped – a bit like Jupiter – but bigger and with a brighter core at the centre. Through the eyepiece it did actually appear to be slowly moving. At this point I realised that I was probably watching a rocket from beneath and looking directly into the exhaust.
I watched for a few minutes and then went to get the digital camera. I’d taken a few shots of the moon before, by holding it to the eyepiece. No control over the exposure or flash but I was hopeful I’d get something. Returning to the telescope I watched in amazement as the disk seemed to shatter into hundreds of pieces and disperse. I took this picture:
Two of the pieces seemed more substantial and I watched them for a few more minutes as they slowly drifted apart. I was always curious about what rocket I actually saw there and why it ended up in pieces like that.
So having found the picture again recently I saw that the date and time was stored in the image properties! I googled the date and found that the GRACE mission was launched that day.
GRACE was launched atop a Rokot launch vehicle from Russia earlier that day so I initially thought I’d seen the separation of the individual satellites. I tried to find a way of confirming whether GRACE was visible from the UK on the day of launch. After a bit of digging I found a paper which seemed to confirm that various manoeuvres had to take place in the within visibility of several ground stations. The path of the satellite (shown in the paper) would have made it visible from the UK.
So….a minor mystery solved. I’m not sure I saw the actual separation of the satellites from the rocket – that was supposed to happen 90 minutes or so after launch (I was watching many hours later). It was probably a burn to separate or correct the separation of the satellites. I’m happy to have what may be one of the few pictures of the start of this incredible mission!
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.