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The Planetary Society BlogBy Emily LakdawallaA quiet night in DarmstadtFeb. 25, 2007 | 07:38 PST | 15:38 UTC
by Doug Ellison in Darmstadt
 I was shown the door into the main control room itself and the atmosphere was extraordinary. Not much more than a dozen people -- and a duck called Orville -- in a large room with row upon row of flat panel screens showing charts, status pages, and block-diagrams. A lot of green boxes and green text suggesting all was well with Rosetta. But there was a tension, a mild nervousness. If you've not been to a spaceflight operations centre you just can't know what it feels like. The professionalism and intelligence was dripping down the walls with a roll-call of previous missions mounted high up on the wall reaching back to May 1968 with ESRO 2, a spacecraft launched 10 years before I was even born. Every engineer on station looked like they could say. The body language said know what I'm doing, I know I've done everything right, but I still need to a little nervous to make sure I don't miss anything. This wasn't a main engine burn to enter an orbit or a landing, but there was risk. If you cast your mind back, Rosetta was intended to fly to Comet Wirtanen with a launch in January 2003, but a failure of the same type of Ariane 5 rocket that was to be used for Rosetta meant that launch was pushed back to February 2004 and the trajectory had to be redesigned. That old trajectory had a flyby of Mars in August 2005, but not through the shadow of Mars. Rosetta was never designed for a planetary blackout, and putting it through 25 minutes of darkness presented thermal and electrical challenges for the engineers to write sequences so that Rosetta wouldn't panic when it 'lost' the sun. "It's always like that," said Jocelyne. That nervous confident energy inside the control room wasn't reserved for special occasions. These people know they're looking after a spacecraft worth many hundreds of millions of Euros and that responsibility was the source of the ready-to-slice atmosphere behind the huge glass window that separated the small press room and the control room beyond. It was then time for briefings, with one eye on the countdown clock and one eye on the first speaker, David Southwood. He commented on the fact that ESA is people doing things together, but individually. Rosetta has its origins from Italian scientists, one of the oldest members of ESA, and he made mention of one of the newest, Greece, who he hoped would have instrumentation in space with ESA soon.  "Once in a while we do something right in Europe and we chose over 20 years ago to target a flyby of Halley which we called Giotto ... it was Europe first declaring it could do things in the solar system. We lay fallow for quite a few years but in the last few years I think it's fair to say Europe's back in the solar system. We've been to the Moon, to Mars, to Venus and with enormous help from the Americans we went to Titan but happily I think we're going back to a comet. This is back to the beginning again and it's back to the beginning of the solar system ... I don't have any concern or any guilt about spending public money this way, really it's a duty." Tucked away in another room at ESOC was the flight dynamics team, the European equivalent to work of people like Dave Seal who I mentioned yesterday. Head of that time, Dr Uwe Feucht next took the floor to explain the trajectory, the tracking and the manoeuvres involved.  In an image that showed the principle of what we were seeing, Mars is moving left and Rosetta is also moving left, but slower than Rosetta, and so Rosetta runs from left to right in this image which represents the view of Mars from Earth. "Usually we use these flybys to accelerate the spacecraft. Today is different...we are losing a little bit of energy. Today is an important manoeuvre because we do the phasing to the next two important Earth flybys when we then again gain velocity." He gave us the bare stats of the flyby: closest approach at 01:57:59 at a height of 249.1 kilometres with a three-sigma (i.e. how accurate that figure is) of 3 kilometres. The last trajectory correction manoeuvre was on February, the 9th, with a change of just 4.55 centimeters per second, which moved the spacecraft's aim point at Mars by about 60 kilometres. All this aiming was done using the comparatively new European Delta-DOR capacity which previously we Europeans had to borrow from NASA's Deep Space Network and the smallest error ellipse using that is only 4.9 x 3.0 kilometres. I'm sure at JPL they would say this was like hitting a hole in one from LA when the green is in Houston or it's like a dime at 300 miles (I made those up) but these European engineers just give you the cold hard figures. Dr. Feucht explained that while the ellipse was not centred on the actual target point, they were just 11 kilometres from the target point. 11 kilometres, 249.1 kilometres... well the 11 kilometres is the total distance the actual flight path is away from the target. That remaining 0.9 kilometres is how much of that 11 kilometres is the element of that error in line to the centre of Mars at closest approach. Next up: Dr Gerhard Schwehm, mission manager. He summarised the flyby remind us that the important thing was the navigation we had just seen: job number one is to get that flyby right so it's lined up for the next Earth flyby (the similarities to the New Horizons flyby of Jupiter are very strong in this regard). The science is a good opportunity to get some calibration and a unique opportunity with some of the instruments. The main instruments for the flyby are the imaging system OSIRIS, the UV spectrometer ALICE and the IR mapping spectrometer VIRTIS and some in situ science with the plasma package RPC. The latter is a useful for a tie-in with observations with Mars Express. "Sitting in the first row tonight" is Philae, the Rosetta lander, as it can live on its own batteries when Rosetta has to turn most things off. Philae's CIVA imaging instruments, and ROMAP, the magnetometer and plasma instrument, would work through closest approach.  As he was talking...the clock clicked down and through zero...and for a while I forgot that the countdown was on spacecraft time; Earth received time was another 17 minutes later. Bang on time however, the voice of Elsa Montagnon came over the network "All stations on the loop we have lost the S-band signal indicating start of occultation." Andrea Accomazzo, Rosetta Spacecraft Operations Manager told us that we should get that S-band signal back in 15 minutes and while in eclipse the spacecraft was working on batteries that it hadn't had to really use for 3 years. Manfred Lugert briefed us on the ground facilities involved in this event, the signal being received by the 500-tonne New Norcia station in Western Australia, 150 kilometres north of Perth. The signal strength being monitored is like a 50-watt light bulb at 315 million kilometres and so received signal is 1/100th of a picowatt. He also described the rest of the European network which currently includes a similar dish in Madrid that spends much of its time tracking Venus Express. ESA currently is looking for a third ground station site possibly somewhere in South America to be built in the next 6 years. Accomazzo returned to explain that we wouldn't see the reacquisition of the signal on the big screen spectrum analyser as it is so weak but the demodulators at the ground station would lock on and give us confirmation that the spacecraft survived the first part of the flyby, the occultation, with a further 10 minutes of eclipse to follow. "A bit less than one minute to get the signal back" Why was I so nervous? "10, 15 seconds away" Wow...15 seconds can take what seems like hours, my mini disk recorder says it was exactly 15 seconds...but bang on time, Montagnon again "we have S-band secure indication end of occultation." Accomazzo told us that by having the signal bang on time we now knew the spacecraft was healthy and had survived the first 15 minutes of eclipse perfectly well, because otherwise, it would have turned the transmitter off. Another 10 minutes of eclipse to go though...not totally out of the woods. Uwe Keller spoke next, showing the image that you have already seen, which has now been augmented by two more on the ESA website which you can see here With the S-band signal they had telemetry back at 250bps, and so when the spacecraft moved back into sunlight, they would see it as housekeeping data. "I'm cold, I'm cold...said the spacecraft" said Keller to no one in particular. I laughed...no one else did. But Accomazzo ended the nervous quiet telling us that the spacecraft came out of eclipse, and by telling us on time, we knew that it was healthy and the flyby was a perfect success. "Now we can all sleep" he said. And so we did...handing back my pass to the security guards as I walked out of a cold dark park of office buildings into Darmstadt to get a taxi back to the hotel...to sleep and wait for the pictures. And as I write these words -- literally -- a refresh of the ESA website shows me the first colour image from the Philae lander...  Just four minutes before closest approach at a distance of 1000km with the back of a solar array visible, hanging like an airless wing over the planet below -- that astronaut's eye view of the red planet I dreamed of at 30,000 feet over Europe yesterday morning. It's time to wrap things up here in Darmstadt. I head home very early tomorrow morning and when I get home hopefully they will have released more images and I can tie it all together as we wish Rosetta well on its way back home...for another flyby on its way to a rendezvous with Comet Churyumov-Gerasimenko in 2014.
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