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

PS: See my original post on the JIVE campaign here: All 'ears' on Mars Express tonight

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

There is one instrument that can be left on during the close flyby of Phobos. ASPERA (Analyzer of Space Plasma and Energetic Atoms) was created to study the interaction between the constant stream of charged particles from the Sun and the Martian atmosphere. 

This stream of particles is called the solar wind and the data ASPERA collects addresses important questions in Martian science.

Graphic illustration of Phobos and Mars Express just prior to closest approach this evening. Credit: ESA/ESOC Flight Dynamics. More in ESA Flickr

For example, how strongly is the Martian atmosphere affected by the solar wind?  Can this interaction explain where the Martian water went? In other words, was the water lost to space? Since liquid water is the fundamental requirement for life, a clear understanding of the fate of the Martian water supply is crucial to resolving the mystery of whether life ever existed on Mars.

During the Phobos flyby, ASPERA will detect and characterise the particle population around Phobos.  The instrument is comprised of four sensors that passively collect any particle that happen to hit it.  So as not to jeopardize the tracking signal accuracy, ASPERA’s detections will be recorded on board and beamed back to Earth later.

At Phobos there is no atmosphere to interact with, and so the solar wind will slam directly into the rocks on the surface of the moon.  This happens to any airless body.  Our own Moon is constantly struck by solar wind particles.  Each impact moves the lunar dust by a tiny amount.  Eventually the process will even destroy the footprints left by the Apollo astronauts – but not for millions of years. At Phobos there are no footprints (yet)! -- Stuart

Those of you who have been following the blog will know that on Monday the estimated flyby distance of 50 km was revised to 67 km.  This will not affect the science investigation and has come about because of what spacecraft engineers call an “over performance”.  This means that during the manoeuvre to place Mars Express on its flyby trajectory, the engine expended just a little bit too much thrust.

The over performance was well within the normal limits of uncertainty but meant that the spacecraft would arrive at Phobos 20 seconds late.  In this time, Phobos would have moved on a little and so the closest distance that Mars Express would find itself to Phobos was going to be 60 km.

If you could stand on the nightside of Phobos tonight, you would see Mars Express zoom past in front of Mars. Credits: Alex Lutkins

The flight team at ESOC then began their calculations to understand exactly what this new scenario would mean and they discovered that the new trajectory would cause Mars Express to pass behind Phobos as seen from the Earth.  So Phobos would block the radio signal to Earth just at the moment when the most precise tracking data was being gathered.  That simply could not happen.

So the spacecraft was manoeuvred once more to delay its closest approach by a little more, meaning that it would remain visible from the Earth at all times.  The drawback is that the altitude would rise more, by 7 km.  However, this is not expected to affect the science – which is what this flyby is all about.

“It will mean the Doppler signal is a little smaller than at 50 km but it will not affect the science.  The main point is that we are significantly closer than 100 km,” says Hannes Griebel of the Mars Express flight control team, and one of our blog contributors. -- Stuart

40m de diámetro del Observatorio Astronómico Nacional en Yebes

I spoke this morning with Mars Express Project Scientist Olivier Witasse, who explained details on an unofficial - but very cool! - radio science tracking activity being conducted by the JIVE (Joint Institute for Very Long Baseline Interferometry in Europe) Institute.

This project is an excellent addition to the 'official' radio science tracking campaign organised by ESA using a number of ESA and NASA ground stations and centred on use of the 70m Deep Space Network station at Robledo, Spain, later this evening during closest approach.

Olivier says that scientists and engineers from JIVE learned about the Phobos flyby campaign and promptly organised a radio tracking campaign of their own, using three stations: Metsahovi (14m, Helsinki, Finland), Wettzell (20m, Munich, Germany) and Yebes (40m, Madrid, Spain).

"JIVE tracking will run for 2 hours around 21:00 UT tonight," says Olivier. "The goal is to record Mars Express signal Doppler with these three stations as an enhancement to ESA's own tracking."

NASA's big dish at Robeledo is the biggest possible 'ear' that we can use to listen to the Mars Express radio signal. But by correlating the data captured by JIVE's smaller stations, it may be possible to extract very precise Doppler data - which is the goal of the Phobos radio science activity.

"A baseline of ~2500 km between Robledo and Cebreros and Helsinki could provide another vantage point on the Phobos-induced Doppler variation; although Metsahovi is just a 14-metre dish, they expect to obtain good Doppler accuracy," JIVE institute Sergei Pogrebenko says.

Afterwards, the JIVE team will share their results with the Mars Express project team and the MaRS radio science team.

Olivier adds: "This is a very nice contribution, very much appreciated! We know JIVE very well, as they also tracked the descent of ESA's Huygens on to Titan, back in January 2005." Here's an mp3 audio of our discussion earlier today:

(Original mp3 file is here if playback box above doesn't work)

-- Daniel

Daniel and I have just been speaking to Thomas Ormston, Spacecraft Operations Engineer, and contributor to this blog.  We wanted the definitive answer on why the Mars Express camera (HRSC) would not be taking images at closest approach.  It turns out that there are three reasons – each of them alone would be show stoppers for the camera.

 Phobos on 30 August 2007. Credits:  ESA/ DLR/ FU Berlin (G. Neukum)

First is that Mars Express will fly between Phobos and Mars, placing it on the nightside of Phobos.  In fact, for a few seconds at closest approach Phobos will actually totally eclipse the Sun.  So the hemisphere of Phobos that HRSC would see will be in darkness, apart from the tiny amount of light reflected from the surface of Mars back onto the moon.

Second, at 67 km, the surface of Phobos will be moving through the camera’s field of view too quickly.  To track the surface, Mars Express would have to turn or slew as the engineers like to call it.  That is not a problem usually as Mars Express is designed to do this.  But at the speed at which Mars Express will pass Phobos, the spacecraft will have to slew faster than safety allows.  One factor determining the maximum speed is the fragile MARSIS experiment.  This is a 40-metre-wide antenna that could break if the spacecraft turns too quickly.  And MARSIS is still needed to probe beneath the surface of Mars and Phobos.

Thirdly, even if it were daylight and possible to turn the spacecraft fast enough to take the necessary images, this close flyby is specifically designed to probe the gravity field of Mars.  This is a unique experiment and requires the spacecraft to be entirely passive, so that the only deviations to its motion are produced by the gravitational field of Phobos (which for Mars Express is just one billionth the strength of Earth’s gravity at the surface of our planet).  Mars Express will therefore point its high gain antenna fixedly at the Earth for the duration of the flyby.

HRSC will swing into action at the next flyby on 7 March, when Mars Express will pass Phobos at around 107 km. The picture above was taken at a previous Phobos flyby, 30 August 2008, at a distance from the moon's centre of 2366 km. -- Stuart 

Martin Pätzold, MaRS Radio Science Principle Investigator, was here at ESA/ESOC, Darmstadt, a few days ago to prepare for this week's Phobos flyby activities.

I had the chance to ask him how the current Mars Express flyby studies could potentially help Russia's planned Phobos-Grunt ('Phobos soil') sample-return mission, expected in the 2012 timeframe.

His answer was interesting, and the activity will also directly benefit ESA's own Rosetta mission (full info after the jump). -- Daniel

Engineering drawing of Russia's Phobos-Grunt spacecraft

 Full story »

Mars Express is currently working through its series of Phobos flybys, heading for its closest approach on 3 March 2010.  Different instruments are used on different flybys to gain different information about the mysterious moon.

ASPERA is studying the interaction between the sleet of electrically charged particles given out by the Sun, called the solar wind, and the surface of Phobos. HRSC will produce high resolution images of surface, paying particular attention to the Phobos-Grunt landing site.

MaRS will determine the Phobos gravity field allowing the internal distribution of mass to be determined. MARSIS is studying the sub-surface of Phobos, seeking indications of structure and internal composition. SPICAM, PFS, OMEGA are characterising the surface of the moon, with PFS aiming to measure the day and night side temperature. 

Digital terrain model of Phobos derived from HRSC data. Published in M. Wählisch et al., "A new topographic image atlas of Phobos", Earth Planet. Sci. Lett. (2009), doi:10.1016/j.epsl. 2009.11.003 Credits: ESA/ DLR/ FU Berlin (G. Neukum)

The full list of flybys, altitudes and instruments is as follows:

Date Altitude (km) * Instruments used during flyby

16 February 991 PFS, SPICAM, ASPERA

22 February 574 PFS, SPICAM, ASPERA

25 February 398 PFS, MARSIS

28 February 226 PFS, MARSIS

03 March 50 MaRS, ASPERA

07 March 107 HRSC, OMEGA, MARSIS, SPICAM, ASPERA

10 March 286 HRSC, OMEGA, MARSIS, ASPERA

13 March 476 HRSC, SPICAM, PFS, ASPERA

16 March 662 HRSC, SPICAM, PFS, ASPERA

19 March 848 HRSC, SPICAM, PFS, ASPERA

23 March 1341 Not used

26 March 1304 HRSC, SPICAM, PFS, ASPERA

 * Distance from the surface of Phobos

You can read a detailed rundown of the flyby campaign here. -- Stuart

Phobos observed by the HRSC. Credits: ESA/ DLR/ FU Berlin (G. Neukum) 

New webpages went online today allowing anyone to download data from the digital terrain model of Phobos created by the EuroPlanet project, hosted by the German Aerospace Center.  Images and data from the High Resolution Stereo Camera (HRSC) and the Super Resolution Channel (SRC) aboard Mars Express were used to create the three-dimensional representation of the moon. -- Stuart

More information is available here.

Hello once again from the Mars Express flight deck!

OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board Mars Express - Credits: ESA

The first of the two radio-sounding proficiency tests (see my earlier blog entry on the critical radio science experiments) was completed in the night from 22/23 Feb, and went very well. The second test is scheduled for tonight (24.02), and if no problems are encountered, then Mars Express is all set for probing the moon's gravity field with unprecedented accuracy.

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Phobos is doomed. It is gradually spiralling towards Mars and eventually could slam into the planet’s surface, leaving a large crater as its parting gift. Believe it or not, this discovery led to speculation that Phobos could be a space station launched by an advanced Martian civilization.

For the atmosphere to be responsible, Phobos would have to be hollow, like an Easter Egg. If the moon were solid rock, the atmosphere would have little effect. A hollow moon would be susceptible because it contained so much less mass. But if the moon were hollow, it could not be a natural object. 

That's no moon, it's a... no wait, it is a moon.

Credits: ESA/ DLR/ FU Berlin (G. Neukum) 

Writing in the Irish Astronomical Journal in 1964, Estonian astronomer Ernst Öpik noted that there were in fact three possible reasons for Phobos’s orbit. The first was that the observations were in error and Phobos was not spiralling inwards. The second was as Shklovsky suggested – and Öpik agreed that if it were hollow then Phobos was artificial. The third suggestion was that Mars’s gravity acted across the moon producing a so-called tidal force, which could rob the moon of energy.

Dr S. Fred Singer, an American physicist, joined forces with Öpik to investigate. Singer doubted the decay rate was as large as 5 cm per year. He was right. Sadly for the UFO enthusiasts, Phobos was found to be decaying at just 1.8 cm per year and this allowed Singer and Öpik to show that the third case is the correct one. Tidal forces are responsible for the moon slowly spiralling downwards. Star Wars fans will remember the classic line from the first movie, “That’s no moon, it’s a space station.”  For a while in the 1960s, some astronomers actually thought this might be true about Phobos. -- Stuart

"The Mars Express radio science investigators are hoping that the close approach will provide not only much better estimates of Phobos' mass but also how the mass is distributed within the moon. That is, there appear to be pockets of slightly denser material scattered through Phobos; by passing within 50 km, Mars Express may respond to those differences and the Doppler measurements will reveal where the denser material hides. There is a Mars express radio science group working on Phobos: The radio science PI (Principle Investigator) Martin Paetzold, in Cologne, and Tom Andert in Munich and Pascal Rosenblatt in Brussels who work on the data analysis and interpretation."

I thought his note was interesting in that it shows that (a) planetary radar and radio science can provide exquisitely detailed information on the internal structure of bodies in the Solar System, and (b) it shows the international character of such investigations. Yes, it's an ESA mission doing the closest-ever Phobos flyby and it's a European PI team that primarily conducts radio science (the MaRS team under Martin Pätzold at Köln University), but it's an international set of researchers who follow and keenly support this science.

The interesting thing is, understanding more about Phobos composition and theories of formation is not simply an arcane academic exercise. Phobos may, in fact, play a key role in future human exploration of the Solar System (more details after the jump). -- Daniel

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