TanDEM-X has now begun routine operations, and is working with TerraSAR-X in bistatic mode and recording data for its global digital terrain model. In this post, I look back at an earlier phase of the mission, when this satellite pair orbited the Earth separated by a mere three seconds or 20 kilometres, and each sensor acquired images independently.

Last Thursday, the two German radar satellites of the TanDEM-X formation finally reached their operational orbit configuration, with only a few hundred metres separating them. In this configuration, they act as a unique radar interferometer in space. The next day, on Friday evening, the instruments were switched on, after many careful checks, to acquire the world's first Digital Elevation Model (DEM) data using a free-flying bistatic Synthetic Aperture Radar (SAR) satellite formation. That same night, the jointly acquired data were received and processed by our operational processing chain.

We are off again; the team at the German Space Operation Center (GSOC) and their colleagues from EADS Astrium gathered two days ago in the control room to manage the transition to close formation flight. We began the first manoeuvre on Monday, 11 October 2010; this is referred to as the ‘drift start’ manoeuvre, which gives the TanDEM X satellite (TDX) the necessary momentum to close to a distance of one kilometre behind TerraSAR X (TSX) within a few days.

Even though the 'chit chat' between the satellites has so far consisted of no more than the exchange of synchronisation signals – "Hello, here I am!" – that is been all that was needed for the first simultaneous imagery to be captured by TerraSAR-X and TanDEM-X. Since 22 July 2010, TerraSAR-X has been flying ahead of TanDEM-X at a distance of just 20 kilometres, in a formation defined for test purposes and which also affords scope for a special series of radar experiments. They have now completed the first ever experiment with bistatic radar involving two satellites flying together in formation.

Erhard Diedrich, in charge of the building of the Inuvik satellite station, returned from Canada with his colleagues, a happy man. The inauguration on 10 August was not only moving, but also marked the end of a successful first checkout phase. Over 300 passes of data have been acquired since April this year, among them 60 from the TanDEM-X satellite.

DLR’s new satellite data receiving station in Inuvik, northwestern Canada, was officially inaugurated on 10 August 2010. Representatives of several Canadian space and political organisations travelled to Inuvik for the event, as did we from DLR. The beautiful weather seemed tailor-made for celebrating the cooperation between Canada and Germany, and the event closed with an enjoyable reception.

Satellite data is an indispensable tool for quickly assessment of the situation in cases of natural or environmental disasters and for guiding emergency teams on ground. DLR's 'Center for Satellite Based Crisis Information' (Zentrum für satellitengestützte Kriseninformation; ZKI) and many other international organizations have been using the German radar satellite TerraSAR-X for three years to rapidly obtain reliable data in all weather conditions for such crisis situations. Now, our new satellite, TanDEM-X, has also provided assistance for the first time in a crisis – gathering information on the flood catastrophe in Pakistan. We were able to help not only with radar images but we also used TanDEM-X for interferometry in formation with TerraSAR-X for the first time. This has provided a more reliable technique to map floods instantaneously and more accurately, in one pass and without the need for archived data.

The successful setup of the 'wide' flight formation between the TerraSAR-X and TanDEM-X satellites marked the beginning of the 'TerraSAR-X Add-On for Digital Elevation Measurements' mission in its literal sense: Now, with both satellites flying as a team – three seconds apart – and seeing the same region of the Earth's surface, tricky instrument commanding is no longer needed to acquire interferometric data sets. Ordering, planning and commanding of the synchronous acquisitions, as well as reception and, in particular, processing of the data sets from both satellites are performed completely automatically.

Tirelessly, TanDEM-X is acquiring data while moving ever closer to the TerraSAR-X satellite. As yet, the first flight formation is not set up and thus no interferometric processing is possible. All data received by the TanDEM-X ground station network are transferred to Neustrelitz, where they are processed into SAR images like the operational ones from TerraSAR-X.

On its launch date, 21 June 2010, roughly 16,000 kilometres separated TanDEM-X from its twin satellite, TerraSAR-X. Now, that distance has shrunk to just 2000 kilometres. The time has come for the relative movement between the two satellites to be slowed down, and for them to be set up for formation flying. To accomplish this, the Flight Dynamics Group at the German Space Operations Center (GSOC) will carry out a total of 10 orbital manoeuvres over the next eight days.

As Mission Operations Director at the Space Operations Center in Oberpfaffenhofen, I am responsible for operation of TanDEM-X satellite. The first few days after the launch are always the most tense, because you obviously cannot know whether the satellite has weathered the launch well. To cover this phase as effectively as possible, we work the first week in shifts around the clock – to be ready, just in case. In this and the next few blog posts, I will report on the atmosphere and duties in the control room.

There were recently two successful launches (our congratulations!) – the payloads of the Prisma and Picard missions were launched together from Yasny. We followed these events via their live streams online. As will be the case with TanDEM-X, a Dnepr launcher was used. Problems with the launcher would likely have affected our launch date. So obviously, we were relieved about the smooth launch. And TanDEM-X is next in line!

As our loyal readers already know, the TanDEM-X satellite is installed in the launcher’s upper stage and ready for transport. The Dnepr rocket is fuelled and waiting in the launch silo a few miles away. But how does the upper stage get to the launcher? Using a special vehicle, naturally.

We did it! The new German radar satellite TanDEM-X is packed and prepared for dispatch – the upper stage of the launcher with its precious contents stands ready. This is the result of impressive team performance. A group picture of all those who have worked towards this goal in recent days will not go amiss here.

Yesterday was all about fitting the 'square' (the TanDEM-X satellite) into the round (the upper stage of the launcher). With these cross sections, TanDEM-X proves that the old German football saying about the round having to go into the square is not invariably true. Well, at least in space...

A short, but very up-to-date report, prepared during our lunch break. The TanDEM-X satellite was lifted out of its mechanical handling system and placed temporarily on a tripod.

I have now settled myself in Baikonur and become acquainted with everyday issues. As of last Tuesday, I have replaced my colleague Michael Bartusch as the project management representative of the space agency here at the launch site. I will be reporting about the TanDEM-X satellite (TDX) on this blog up until the launch.

With finalisation of the functional tests for the satellite bus and instrument, we have reached another important milestone. Evaluation of the test data confirmed that everything was nominal. In one of the last tests, the satellite was powered up solely by its internal supply and the external power was switched off. This too was successful, so the satellite was turned off and the wiring to the electrical test equipment was removed – a slightly melancholic moment. The next time we receive a signal from the spacecraft it will be in orbit, having separated from the launcher.

TanDEM-X has left the integration facility for its reaction control system tank to be filled with hydrazine over the next few days. To do this, the satellite has been moved to the fuelling station as was reported earlier. Fuelling is a dangerous job, because the propellant used is quite toxic. When you enter the fuelling hall, the sign over the entrance reminds everyone to not forget the dangers. Translated, it reads, "Regardless of how urgent your work is, safety comes first." This is a reference to the devastating Nedelin fuelling catastrophe here in Baikonur in 1960, which took 126 lives.

We are now in the second week of our TanDEM-X launch campaign here in Baikonur. The satellite has been installed on its test rig and a quick check shows that the instrument and spacecraft are in good health. Meanwhile, the propulsion and cold gas systems have been pressurised to check that they are leak tight.

It was a long, long way to Baikonur. Already, at the beginning of the trip, the cargo plane – loaded with 37 tons of TanDEM-X and its support equipment in six containers – was delayed for several hours. It was not until 22:45 that we were able to leave Munich. One might have hoped that the stop in Ulyanovsk would be short – but on the contrary, the customs checks were extensive and time consuming.

Right on time for 'shipment' of the German radar satellite TanDEM-X this coming Thursday, 29 April 2010, we are launching the TanDEM-X blog – and looking forward to our first mission weblog on the new platform. The plan at this time is for Mission Manager Stefan Buckreuss and the DLR Communications team to be joined on the blog by colleagues working in the areas of project management, science, mission operations, the ground station network, flight dynamics, radar, calibration and data processing.