I have just heard some more news about Sunday’s Phobos flyby from Mars Express Project Scientist Olivier Witasse. He says, “We are now entering a new phase for the Phobos flybys. The dayside encounter phase means that remote sensing can proceed at full speed!”
The MARSIS, SPICAM, OMEGA, ASPERA experiments will all be working, as will, of course, the camera (HRSC). The Sunday flyby will take place at an altitude of 107 km, and provide the opportunity for high-resolution imaging. It is a delicate operation.
The camera is fixed in position on the spacecraft and cannot move independently. So, to keep tracking Phobos the whole spacecraft will have to turn. Because of the large MARSIS antenna, which measures 40 metres end-to-end, the spacecraft is usually only turned at a rate of once every 40 minutes. On Sunday, the team will exceed this a little to keep Phobos centred in the camera. But the tracking does means that we will all have to be patient before seeing the images.
The spacecraft cannot point in two directions at once. It cannot track Phobos and keep pointing its high gain antenna to Earth. So the images will be stored onboard and then downlinked at the next available ground station pass. “The images will arrive on the ground on Monday,” says Witasse. The data will then pass straight to the camera team, who will begin the processing.
Witasse suggests that images may be available by Wednesday, once the processing is complete. Watch the blog for updates to this schedule. -- Stuart
Bertrand sent us a recording from his dish of the tone of the Mars Express signal, exactly what we would have heard if our ears were sensitive to the X-Band radio used by Mars Express! Hidden in this tone are tiny variations caused by the presence of Phobos and the MEX scientists are working hard right now to extract these from the recordings from the professional stations (Thanks, NASA!), which have the listening power necessary to detect these very fine variations.
Listen here to the whistle of Mars Express as it hurtles towards Phobos and consider that this signal was generated on Mars Express by a transmitter only slightly more powerful than a light bulb. This tiny signal travelled over 100 million kilometres and was picked up by Bertrand with his 3.5m dish - a truly remarkable achievement! Take a look after the jump for more details on Bertrand's station and the recording he made. -- Thomas
A very effective animation showing Phobos flyby on 3 March created by the team at the Boxx blog (audio in French).
This animation shows the Mars Express orbit very well. The animation uses our original, slightly closer approach (50km instead of the actual 67km) because that's what is in the Celestia files that we posted earlier (unfortunately, we haven't yet had time to upload the 'real' files after measuring the effects of the engine burn earlier in the week - we will do so soon!). The orientation of the spacecraft isn't quite correct because throughout the closest approach MEX stayed pointed at Earth so we could receive the radio signal. Nonetheless, the animation is still excellent, and the illustration of how our orbit crosses Phobos is excellent!
Kester Habermann, one of the flight dynamics team members here at ESOC, kindly sent in the data files for anyone who uses the popular (and free) Celestia real-time, 3D visualisation software. With these files, you can play back the entire flyby sequence (details and links after the jump). Thanks, Kester! -- Daniel
Mars Express Project Scientist Olivier Witasse got an email this morning from Guifre Molera Calves, working at the Metsähovi Radio Observatory in Finland. Metsähovi was one of the three ground stations that took part last night in the 'unofficial' radio tracking campaign conducted by JIVE - the Joint Institute for Very Long Baseline Interferometry in Europe Institute.
Olivier says the report was quite positive. JIVE researchers are still analysing the radio tracking data from the Wettzell station, but at least they detected the Mars Express signal with the Metsähovi and Yebes antennas. Good news, indeed! -- Daniel
According to the bits of telemetry that just came through we have a healthy spacecraft all-around! Despite the heavy use of our batteries with long transmitter times during a season of long eclipses, the spacecraft is in good shape, showing that the flight control team's careful planning of the past weeks paid off.
With a new bag full of high-fidelity radio science data, researchers can now feed their number crunchers for weeks to come. Stay tuned, however, as we have more exciting flybys coming up. The next one as early as Sunday! -- Hannes
Martin Paetzold, Principle Investigator of the Mars Radio Science observation is smiling. This morning, before the flyby, he admits to having been anxious. “There was a very small probability of an occultation at closest approach,” he says. It was a very small possibility but if it happened, Phobos would have blocked the signal with Earth at the critical moment.
There is nothing to be anxious about any more. Closest approach took place at 20:55 CET. It took 6 minutes and 34 seconds for signals to cross the volume of space between Phobos and Earth, and be received on Earth.
If the occultation had taken place, it would have created a gap in the data of five to ten minutes whilst the signal link was re-established with the spacecraft. “We would have had to extrapolate between the two data sets and that would not have been good. Now we have continuous data,” says Paetzold.
The team will receive the data on Friday, and they will begin the full analysis once they receive the precise orbit determination of Mars Express on its way into the flyby. They hope to assess the data and the preliminary results in about two weeks time.
Gerhard is here in the Mars Express Dedicated Control Room at ESA/ESOC this evening and, like everyone, is really pleased with the Phobos flyby:
"I'm very happy that it's working so well. This close encounter by Mars Express has been a great chance to learn more about the inner structure of Phobos. It's also great that we will have a second chance in July 2010 to study Lutetia - another primitive object - with Rosetta from a close distance - both flybys show the benefits of radio science. It's a unique opportunity to do this twice in a short time scale."
Animation developed earlier today based on actual orbital data showing Mars Express makiing its closest approach to Phobos today at 21:55 CET. All instruments OFF, except ASPERA, and Mars Express is transmiting a radio signal to Earth for tracking the influence of Phobos' gravity on the spacecraft.
Mars Express has just locked onto the radio signal from the ground station that it will use to trace the gravity field of Mars. The radio frequency oscillators on the ground are about 100 000 times more stable than those on the spacecraft, so a signal is sent up to the Mars Express and this is returned by the spacecraft to the ground. Variations in the frequency of this signal will then be used to calculate the gravity field of Mars. The more stable the original frequency the better the data.
The light travel time is 6 mins 34 seconds one way (radio waves also travel at the speed of light). So round trip time is 13 mins 8 seconds. -- Stuart
Animation showing Mars, Phobos, Diemos and Mars Express in their relative orbits this evening is now live in ESA Flickr (click on 'HD' at bottom right of Flickr playback window to watch in high resolution):