Mars Express Blog

New MEX blog platform

Wed, 18 Jul 2012 05:01:57 +0200

We're renovating!

We're transfering the Mars Express blog to the new Wordpress platform. Effective immediately, all news, updates and information that would have appeared here in the 'old' MEX blog will be published via http://blogs.esa.int/mex.

Mars Express transmits first signal to be received by new ESA station

Fri, 22 Jun 2012 15:25:17 +0200

Great news from the ESA ESTRACK team today!

The first-ever reception of signal took place at ESA's new 35m deep space station at Malargüe, Argentina, on 14 June. There's still a lot of work to be done to have the station fully comissioned, but this is an excellent achievement and an important milestone - and the signal came from our very own Mars Express, orbiting the Red planet some 193 million km away.

Roberto Maddè, the DSA-3 project manager, wrote:

We did a test 'shadow tracking' of Mars Express last week on 14 June, around 22.30 UTC.

The signal in L-band is shown in the picture (at left). We measured a signal/noise ratio of about 56 dBHz, which matches the levels obtained by ESA's existing 35m station at Cebreros during the same pass.

Pointing still needs to be optimised (pointing correction for our test was done manually); these tests are still 'qualitative'. Some quantitative tests (less news-worthy but more useful to understand whether the station is operating within specs) are being done and look promising. Now, the teams on site are recalibrating the beam waveguide mirrors; we'll have more tests in two weeks. But we need to calibrate the pointing first.

DSA-3 is set to enter regular service later this year.

You can see DSA-3 'live' via our webcam (also below) -- Daniel

Tracking tiny slices of time: Phobos blocks Mars Express signal

Fri, 04 May 2012 11:56:29 +0200

On 30 April, in a carefully planned data-gathering exercise, ESA's Mars Express team used the passage of Phobos between Earth and the spacecraft to record precisely when a radio signal was blocked. The data may now lead to the best-ever determination of Phobos's orbit, knowledge that will help scientists better understand our planetary neighbour and its double-moon system.

You'll recall our earlier posting, when we described MEX team plans to take advantage of a rare alignment of Earth - Phobos - Mars Express to measure precisely when the bulk of Phobos would block radio communications between the spacecraft and ESA's 35m Cebreros station in Spain.

The prediction was that the 'occultation' would last around 12 seconds, from 21:21:22.9 to 21:21:34.1 UTC (spacecraft time). The predicted ground receive time was between 21:29:13.0 and 21:29:24.2 UTC (i.e. 7:50 mins later on Earth).

The activity took place as planned on Monday, 30 April.

Based on a reconstruction of the MEX orbit by ESA's Flight Dynamics team at ESOC, results indicate that the expected start time of the occultation by Phobos was 0.5 seconds earlier than that predicted. Similarly, the end time is 0.4 seconds earlier than predicted.

The plot below indicates the actual situation as measured very precisely from Cebreros station.

It shows the view from Earth of the 'expected' occultation of the MEX signal by Phobos. The large, grey-green circle corresponds to the moon's disk; it is shown (at this scale) as a circle having a radius of 13.4 km.

So why was the actual recorded occultation times a few seconds shorter than expected?

ESA's Trevor Morley, lead flight dynamics specialist for Mars Express, says there are two possible reasons:

The best fit ellipsoid for the shape of Phobos has semi-axes of 13.4 x 11.2 x 9.2 km. The dashed circle shown in the plot has a radius of 9.2 km. The occultation duration depended upon the length of the chord across the real face of Phobos between the entry and exit points. The actual profile of Phobos needs to be applied to calculate this length (which is why photos/observations of Phobos are so important - Ed).
A shorter than expected occultation duration would also occur if the present error in our prediction of Phobos's orbit is such that the moon's true position at the time was further towards the south.

Trevor says that the recorded timing data will now be shared with the MEX science team as well as with colleagues at NASA JPL; it is expected that they will be able to use these results to improve models of the Phobos orbit:

“The Phobos orbit model that we are presently using was generated by Bob Jacobson of JPL and is almost certainly the most accurate one available. We will provide Bob with all the signal data plus our determined orbit of MEX,” he added.

“Of course we can provide the data to any scientists working on this topic, including those who have been using directional data derived from Phobos images made by the MEX camera for the same purpose.”

Mars Express Spacecraft Operations Manager Michel Denis says:

It's part of the scientific method to make use of every opportunity to investigate our natural world.

Also, it's second nature and ‘pride of craft’ for the mission operators to figure out how to achieve more with the same resources– whether that’s a spacecraft or a ground station. In this case, we could also achieve ‘extra science’ through tight cooperation between several teams here at ESOC – flight dynamics, ground segment, flight controllers – and we were able to fine-tune, second-by-second, an already packed science and communication plan.

The team here have really done a nice job!

Mars Express radio signals to 'track' Phobos orbit

Fri, 27 Apr 2012 15:44:01 +0200

On Monday, 30 April, Mars Express mission controllers at ESOC will take advantage of a rare alignment of the spacecraft with Phobos and Earth to use radio signals to determine the Martian moon's orbit.

A (very) rough sketch of the alignment

If the team's careful planning and preparation pay off, the occultation of Mars Express by Phobos (as seen from Earth) will provide highly accurate data that can be used to determine Phobos's orbit with unprecedented accuracy, possibly improving it by a factor of 2.

Essentially, here's what's going to happen:

On 30 April, Phobos will, for a few seconds, pass between MEX and Earth, blocking the direct line-of-sight path for radio signals transmitted from MEX to ESA's 35m deep-space station at Cebreros, Spain.
In a pointing specially extended for this event, Mars Express will already be turned toward Earth — a mere pale blue dot some 140 mn km away — and will already be transmitting a steady signal to Cebreros.
Special radiometric recording equipment installed at the Cebreros ESTRACK station will record — with sub-second precision — the start/finish time of the break in the transmission.
The occultation is predicted to last just 12 seconds, from 21:21:22.9 to 21:21:34.1 UTC (spacecraft time). The predicted ground receive time is between 21:29:13.0 and 21:29:24.2 UTC (i.e. 7:50 mins later on Earth).
Once the occultation ends, MEX will perform a 'high-speed' slew to re-orient itself so that the HRSC camera and other instruments are pointing toward Mars to conduct a regular observation pass over the Red Planet starting at 21:22 UTC.

Results from Cebreros station will be passed to ESA's flight dynamics team and to our colleagues at NASA's JPL, who will use these times in calculations that, once confirmed, could yield the best-ever determination of the moon's orbit.

"The occultation tracking promises to provide a very nice boost in our understanding of Phobos, an enigmatic body if ever there was one, without affecting routine science," says Mars Express Spacecraft Operations Manager Michel Denis.

We'll keep in touch with the Mars Express mission team at ESOC throughout the weekend and Monday/Tuesday to post any updates; you can also follow news via Twitter (@esaoperations).

The animation below shows what will happen immediately after the occultation tracking, when Mars Express re-orients itself for the Mars observation pass.

-- Daniel

An elegant solution - update in ESA web

Thu, 16 Feb 2012 10:10:13 +0100

A quick link and extract from an update on Wednesday in ESA's Science directorate web pages; it provides a nice overview of the 'return to science' situation. References to our very own VMC camera activities highlighted - and note very nice comments on teamwork! Click link to read the full report.

While full science operations have now been resumed, a number of tasks remain to be completed. Most important among these is the implementation of an OBCP scheduler. This will enable the spacecraft to operate autonomously for up to a week, compared to the few days that are possible with the current FAST system. Work is also in hand to resume operation of the Visual Monitoring Camera (VMC – the 'Mars webcam').

Enormous team effort

Completely redesigning the way in which Mars Express is controlled has involved an enormous amount of work for the mission control team at the European Space Operations Centre (ESOC), assisted by their counterparts at the European Space Astronomy Centre (ESAC), PI-teams, other ESA experts and partners in industry. Everyone involved with the mission is extremely grateful for their hard work.

Although the 'Express' in Mars Express highlights that the mission was developed in a short time and with a relatively modest budget, the ability to resume full operations after a very serious failure shows that the resulting design is both robust and flexible.

Mars Express has now been restored to full operational capability and its potential mission lifetime remains unchanged

Full report via ESA Science & Technology

Skill, inspiration and teamwork: deep-space problem solving

Wed, 08 Feb 2012 16:31:28 +0100

"Hang on, lads; I've got a great idea..."

The Italian Job, 1969

Last month, we spoke with several of the Mars Express team here at ESOC about their almost completed activities to restore, reconfigure and return Mars Express to service.

An interview with Mars Express Spacecraft Operations Engineer Daniel Lakey

Spacecraft Operations Engineer Daniel Lakey sitting beside the SSMM

A black box, edge-length 30 cm, is at the centre of the recent trouble with Mars Express.

Daniel Lakey, an engineer working on the mission at ESOC in Darmstadt, looks down at the engineering model of said black box sitting on his desk and recalls the seemingly endless night shifts he has had to pull because of its twin mounted on Mars Express, orbiting the Red Planet many millions of kilometres away.

In mid-August 2011, Mars Express unexpectedly placed itself into safe mode – think blue screen of death and reboot on a PC – because something went wrong either with the Solid-State Mass Memory (SSMM) housed inside this black box or with the on-board channels it uses to pass data to the spacecraft’s data management system (DMS) computer.

To extend the PC analogy, imagine that the memory chips in your computer, the RAM chips, or the memory controllers that tell them what to do, suffered a fault. The memory might continue functioning, apparently normal, but whenever an electronic signal tried to access the faulty unit, the operation would fail and the system would crash. That's what happened with Mars Express.

Holiday phone call at 3 AM

"I was on holidays in England when I got the call at three o'clock in the morning. Since I'm assigned as the mission's software coordinator, the problem fell in my area of responsibility," says Lakey.

Switching into safe mode means that the spacecraft automatically turns its solar panels to the Sun for maximum energy and its antenna to Earth for good communication – ostensibly very helpful in any untoward situation – but this process uses a significant amount of vital fuel. Every unnecessary safe mode reduces the life of this hugely valuable mission, and in safe mode, normal gathering of scientific data stops.

After an initial investigation, it was found that the safe modes were being triggered by the DMS computer whenever a batch of commands transferred from the SSMM was interrupted.

The problem: Big command batches were being interrupted, triggering a fuel-gobbling safe mode

The SSMM is a large-capacity device, and it stores large numbers of commands sent by mission controllers and the instrument scientists, as well as raw data gathered by the instruments (prior to their being radioed back to Earth).

The SSMM then delivers a constant ‘stream’ of commands to the DMS computer one at a time; when the stream was interrupted – either due to a fault in the SSMM or due to some unknown problem with the on-board communication channels – the DMS detects the problem and auto-commands the spacecraft to switch to safe mode.

Taking action - but problems persist

At first, the flight control team executed the standard recovery procedures and restarted observations, hoping that Mars Express would function normally again.

But, frustratingly, safe modes happened two more times in the next few weeks, even though the engineers had tried switching on-board systems to use back-up communication channels (there is only one SSMM), among many other normal fixes. Nothing in the routine procedures, it seemed, could prevent the frustrating safe modes from occurring.

"We had to find a solution," says Lakey, "otherwise the mission would have soon been over."

By late August, the team had already gone through many night shifts trying to coax the recalcitrant spacecraft into some sort of stable configuration, with little luck.

"But then one day, an idea came to mind – while I was standing under the shower," says Lakey, with a laugh. "It occurred to me that, since something was happening to interrupt the flow of commands, triggering the safe mode, the solution might lie in by-passing the checks between the SSSM and the DMS computer, and finding a safe way to ignore problems with the link between the two."

With a little checking, Lakey was able to determine that the problem was, in fact, an issue of 'transient communication problems' between the SSMM and the computer. "When the main computer sees this interruption, it interprets it as a serious problem and stops executing its 'To-Do' list of commands – because it doesn't know whether the list is complete," says Lakey.

Fortunately, there's another, back-up, memory inside the DMS computer that could store the command stack, but it's much, much smaller than the SSMM, holding only 117 commands vs. over 3000.

So the engineers set about reconfiguring the spacecraft's systems to transfer commands from the SSMM to the onboard computer's memory in a different way. Rather than a constant stream of commands, one at a time, the commands would be transferred as a discrete block of commands relating to one complete spacecraft activity, just before that activity started.

"I thought we could use a trick, by packing the commands into smaller stacks and telling the on-board software to act only when it received a complete package. This 'all-or-nothing' scheme means we're no longer affected by the SSMM problems, but now we have more limits on what we can schedule in one go – but that's been proven to be acceptable."

But would they buy it?

As soon as he could, Lakey presented the idea to his colleagues.

"Perhaps predictably, they reacted with an operations engineer's traditional caution and scepticism. The first answers were, 'No, no, that won't work, No way...' But, after a lot of discussion, they slowly came around to 'Oh wait... maybe we should look at this... it could work'," Lakey tells.

The solution: make command batches small

With a clear consensus and the approval of Mars Express Spacecraft Operations Manager Michel Denis, the team set to work designing operations procedures that could be implemented using reduced command stacks, working first on just a certain set of basic on-board activities. This was a huge challenge.

As designed, Mars Express normally makes use of thousands of commands; for example, it takes up to 50 separate commands to simply take a single photo of Mars using the HRSC camera. Using the new, reduced command stacks would prove worthless if engineers couldn't actually do anything with the reduced command stacks.

Thus, making the solution work entails a massive amount of reprogramming to drastically reduce the number of commands needed to do anything on board. This work is what has kept the mission operations team on extended hours since November 2011.

Smiles all around

But, to everyone's delight, the solution is working and the team is substantially finished the work of converting thousands of commands to on-board procedures to be used much more efficiently than its designers had ever envisaged.

"We are confident that all the Mars Express instruments and systems can be commanded using the reduced command stacks," says Lakey.

"Now, we only need a few commands to capture an image and we can switch on and operate all the instruments at one time," he explains.

"We can proudly say that Mars Express is working properly again – and, with luck – the fuel left could last for another ten years."

All Mars Express instruments return to routine operations

Thu, 26 Jan 2012 15:13:52 +0100

The team examining the Engineering Model SSMM (solid state mass memory) during a Flight Control Team weekly 'FAST concept review' meeting. Left to Right are: Dan Lakey (DMS engineer), Erhard Rabenau (Mission Planning), Michel Denis (SOM), James Godfrey (Deputy-SOM), Olivier Reboud (AOCS/TTC Engineer)

A complete 'phase 1' set of instrument OBCPs (on-board control procedures) was uplinked successfully to Mars Express on 15 January, and following extensive ground validation - both on the software simulator and in the OBCP test & development environment, these have been flight tested on the spacecraft one-by-one over the last two weeks.

As of this week, all instruments can now be returned to routine operations. In addition, the radio science experiment (which has no dedicated instrument on board, and requires no OBCPs) will restart in two weeks' time. The OBCPs replace longer sequences of telecommands with macro 'on-board control procedures' - started with a single command - and allow several instruments to be operated simultaneously within the limited capacity (117 telecommands) of the 'Short-MTL' we now use for the on-board timeline execution.

Orcus Patera on Mars: What's in the crater?

Mon, 02 Jan 2012 14:30:46 +0100

A nice New Year's post starting the year with a question (and answer!) on the fabulous high resolution stereo camera (HRSC) image of Orcus Patera, first published by ESA (here) in 2010, and reposted as the Image of the Day on 31 December 2011 at the Mars Travel blog. Best wishes to everyone for a healthy and successful 2012. Details below! -- Daniel

First, here's the image (click image to access the original post in ESA web):

Click for hi-res version

Orcus Patera is an enigmatic elliptical depression near Mars’s equator, in the eastern hemisphere of the planet. Located between the volcanoes of Elysium Mons and Olympus Mons, its formation remains a mystery. Often overlooked, this well-defined depression extends approximately 380 km by 140 km in a NNE–SSW direction. It has a rim that rises up to 1800 m above the surrounding plains, while the floor of the depression lies 400–600 m below the surroundings.

Earlier today, Mars Travel blogger David Geaney sent in a question:

If you look at one of the central craters in Orcus Patera using the HRSC image, you will see there is something blue in the crater. What is the blue material? Thank you for your time and patience.

We passed the query to Mars Express project scientist Olivier Witasse, who wrote:

Hi David,

The blue is not a lake....

It's dust, which emits in the blue part of the spectrum. In the data processing, the blue part is somewhat enhanced, which sometimes creates a wrong impression.

Cheers,

--Olivier

MARSIS completes measurement campaign over Martian North Pole

Fri, 16 Dec 2011 15:19:24 +0100

A comment today from Mars Express Spacecraft Operations Manager Michel Denis on this week's report: "MARSIS completes measurement campaign over Martian North Pole." The report gives good news!

"The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on board Mars Express has recently completed a subsurface sounding campaign over the planet's North Pole. The campaign was interrupted by the suspension of science observations several times between August and October due to safe modes and to anomalies in the operation of the spacecraft's Solid-State Mass Memory (SSMM) system. As MARSIS best observes in the dark, which for the North Pole only occurs every few years, it was among the first instruments to resume observations once a partial work-around for the problems had been implemented."

In his comment below, the 'FAST Method' that Michel refers to is the operations team's newly developed way of uploading commands to Mars Express, which avoids using the problematic Solid State Mass Memory (SSMM) for critical commanding.

The 'File-based Activities on Short Timeline' method essentially means that commands are grouped in very short self-contained files that can be loaded safely, in advance of execution, from the SSMM into an alternative memory unit (that is reliable but not as capacious as the SSMM).

Michel writes:

The FAST method - loading short command files upon need into the short onboard mission timeline - was put into use at the end of October 2011 with the (excellent) result that we could save what was remaining of the North Pole observation campaign by the MARSIS radar.

The net loss in data collection was mitigated by using the existing MARSIS command sequences as soon as possible. Meanwhile, as for the other instruments, new MARSIS on-board control procedures (OBCPs) are under development and will allow operation with fewer commands, therefore enabling the operation of several science instruments in parallel.

My main point? We did our job: contrary to widespread received wisdom, the spacecraft operators' role is not to simply watch over (supposedly) boring routine operations during the many long years of a mission - nor simply saving a spacecraft that experiences problems. In fact, we are relied upon to deliver safely as much of the expected (precious) scientific data as possible within the resources available - despite adversity. And that's what we're doing!

ASPERA switch-on success :-)

Tue, 13 Dec 2011 14:11:04 +0100

This in this morning from Jonathan Schulster on the Mars Express operations team:

The ASPERA (Energetic Neutral Atoms Analyser) instrument high voltage (kV) lines and equipment were successfully switched on today, a few minutes ago at Mars (~09:57 CET), using the new on-board control procedures (OBCP).

These will run for one hour until 10:40CET today and the ASPERA science team will examine the recorded science data before giving the 'go-ahead' for full operations of ASPERA using only OBCP's starting 9 Jan uary 2012.

Cheers!

- Jonathan Schulster
Mars Express Mission Planning & Flight Control Team

Looks like another instrument is set to return to action! -- Daniel