Keeping MEX warm

Today's post was contributed by Luke Lucas, a Mars Express spacecraft operations engineer at ESA's ESOC mission control centre. Read to the bottom for more info and registration for the upcoming Open Data Day, 28 October 2016, at ESOC! Link to live webcast also at foot of this post.

The vacuum of space is a challenging thermal environment. The illuminated side of an object may reach more than 250°C while the non-illuminated side may be less than -150°C.

Without careful consideration such temperature differences could cause parts of the spacecraft to break, twist or fail to function.

For example: the temperature difference between the front and back of the arrays may be hundreds of degrees and when the arrays go from the shadow of an eclipse, sudden and dramatic changes in temperature occur, which can lead to expansion, contraction, torsion and twisting. Selection of correct materials and good structural design are essential.

Mars Express eclipse Credit: ESA

Mars Express eclipse Credit: ESA

Maintaining an optimal thermal environment is the task of the craft's thermal subsystem. The thermal subsystem includes electrical heaters where needed to keep the spacecraft warm (e.g. to prevent fuel lines from freezing) and passive radiators to keep other units cool. In this way Mars Express can perform scientific observations.

Cooling of some units to prevent overheating can be achieved by the clever siting of radiators. By placing radiators where they will always be facing deep space, passive cooling occurs.

The use of multi-layer insulating blankets around the spacecraft promotes a stable thermal environment and minimises the loss of heat to space.

Electrical heaters are used to heat Mars Express and maintain units, structures and instruments within their safe, warm operating range, with more than 200 thermistors continually measuring the temperature at various points around the spacecraft. By monitoring the measured temperatures, the heaters are turned on or off as needed.

As well as keeping MEX warm, it is important to know how much power is needed to achieve this. Power is supplied by either the solar arrays (when exposed to sunlight) by the batteries during an eclipse.

Power produced by either the solar arrays or batteries is used for platform operations, thermal operations and whatever remains is available for science. The energy provided by the batteries during an eclipse is finite, so knowing how much power is needed for the thermal subsystems means mission controllers can know how much power is available for science. Knowing accurately how much power is needed by the thermal subsystem means we can really maximise science observations.

So how much power does the thermal subsystem need to keep MEX warm?

Well it depends how cold the spacecraft is. And that, in turn, depends on many factors. The largest factors include:

  • Mars orbit Credit: ESA

    Mars orbit Credit: ESA

    How far away is MEX from the Sun? The Sun emits solar flux, measured in W/m2, (power per square meter received) and the further away from the Sun, the less flux received – and so the cooler is Mars Express

  • What is the solar aspect angle? This is the angle of the spacecraft with respect to the Sun? Where is the Sun is shining on MEX? On the top (+Z face), the bottom (-Z face) or the +X face, and at what angle to that face? This will affect the craft's temperature.
  • How far is MEX from the surface of Mars? The albedo is the amount of energy reflected off the planet. 'Mars shine' refers to the amount of energy being reflected by the planet and can affect MEX’s thermal condition.
  • Mars Express orbit Credit: ESA

    Mars Express orbit Credit: ESA

    How far away is Mars from the Sun? This affects the Mars albedo, which in turn affects MEX.

  • Is there an eclipse happening? As seen above, during eclipse, MEX is in Mars’ shadow, receiving no illumination from the Sun, and this can cause a dramatic cool down.
  • What operations are on going? Certain operations, such as using the transmitter to communicate with Earth, warm up certain sections of the spacecraft.

Here are two thermally representative images of the -Y face, one seen during a communication pass and one when no communications were happening.

In a communication pass with temperatures up to 16°C

Mars Express -Y face, during a communication pass with a ground station Credit: ESA

Mars Express -Y face, during a communication pass with a ground station Credit: ESA

When not communicating with Earth and temperatures as low as -12°C

Mars Express -Y face, not during a communication pass with a ground station Credit: ESA

Mars Express -Y face, not during a communication pass with a ground station Credit: ESA

That is to say, that the thermal power required changes continuously as the craft orbits Mars and as Mars orbits the Sun; no two days are the same. Predicting the thermal power required is a puzzle of many parts. But it is a very important matter, because we want to perform as much science as possible.

We have a model we use to predict the power required, but wondered if anyone could derive something better.

Our engineering approach is to look at the factors involved and create an equation. But it is always good to look at any puzzle from more than one view. So we asked you, the public to look at this, as the Mars Express Power Challenge.

And – Wow! – we were thrilled by the responses we received, the predictive models that were built and the amount of information shared among this wonderful community of data scientists, researchers, and space fans!

The challenge is now over and the winners will present their solution on 28 October 2016, at ESA's ESOC mission control centre, Darmstadt, Germany. On this day, the Centre will host an 'open data day' for the candidates – and anyone interested is welcome to attend!

This will be an exciting, inspiring day, full of great ideas and exchanges!

A few tickets for the open data day are still available here via EventBrite.

Watch live 28 October, 10:00-12:00 and 14:00-16:30 CEST

[UPDATED] Mars Express chats with Curiosity: Practice makes perfect

UPDATE 16 June: MEX Deputy Spacecraft Operations Manager James Godfrey just emailed to report that yesterday's MSL overflight seems to have gone rather well! "We have received good telemetry from the MEX Melacom radio and we are now in the process of analysing the data to extract the signal from MSL."

Today, Mars Express established a communication link with NASA's Curiosity rover (MSL) on the surface of Mars to conduct an important test prior to the arrival of ESA's ExoMars Trace Gas Orbiter (TGO), carrying the the ExoMars Entry, Descent and Landing Demonstrator Module (EDM), Schiaparelli, in October.

Curiosity selfie Credit: NASA/JPL-Caltech/MSSS

Curiosity selfie Credit: NASA/JPL-Caltech/MSSS

The test saw Curiosity serve as a stand-in (rove-in?) for Schiaparelli on the surface, transmitting a signal to MEX similar to how Schiaparelli will transmit during landing on 19 October. From orbit above, MEX had its lander communication system (Melacom) – with recently updated software – configured as it will be in October, and the orbiter tested receiving signals from below.

Here's the timeline of how today's test went, as programmed; all commands were uploaded in advance and the sequence was executed automatically on board (times in UTC).

  1. 2016-06-15 06:22:53.000 - MEX begins to slew to point the radio antenna towards MSL's position on the surface
  2. 2016-06-15 06:40:00.000 - Melacom Switches on
  3. 2016-06-15 06:55:00.000 - MSL starts transmitting its beacon
  4. 2016-06-15 06:55:00.000 - After a 15-minute warm-up, Melacom starts recording the signal from MSL
  5. 2016-06-15 07:05:00.000 - Melacom is powered down and the first part of the recording is complete
  6. 2016-06-15 07:10:00.000 - After a 15-minute wait, Melacom is powered back up
  7. 2016-06-15 07:14:00.000 - No waiting this time; 4 minutes allowed for start up as Melacom starts its second recording
  8. 2016-06-15 07:23:00.000 - MSL stops transmitting
  9. 2016-06-15 07:23:00.000 - Melacom is powered down and the second recording is complete
  10. 2016-06-15 07:23:10.000 - Test complete; MEX now begins to slew back to Earth; data will be dumped in a few hours

A photo of the Melacom UHF communications package carried on Mars Express.

Note: Data were still arriving as we posted this, so no analysis to report yet:

Here's a brief description of the actual Schiaparelli arrival activity that this test was meant to exercise (see also: A little help from friends):

On 19 October, about 80 minutes before landing, expected at 14:48 GMT (16:48 CEST), Schiaparelli will wake up and a few minutes later begin transmitting a beacon signal (Schiaparelli will have se4parated from the ExoMars/TGO orbiter on 16 October).

Mars Express will already have pointed Melacom’s small antenna to the spot above the planet where Schiaparelli will appear, and will begin recording the beacon signal, ‘slewing’ – rotating – continuously so as to keep its antenna pointed to follow the module’s descent trajectory.

ExoMars 2016 Schiaparelli descent sequence Credit: ESA/ATG medialab

ExoMars 2016 Schiaparelli descent sequence Credit: ESA/ATG medialab

“Recording will continue through touch-down and the first approximately fifteen minutes of surface operation, after which Schiaparelli will be programmed to switch off and Mars Express will stop recording,” says Mars Express Spacecraft Operations Engineer Simon Wood.

The Schiaparelli signal data will be saved on board Mars Express in two segments; the first, larger, segment will record signals from wake up of the module until about 20 minutes before it reaches the Martian atmosphere, while the second, smaller, segment will record the descent through the atmosphere, touch down and the first 15 minutes of surface operations.

“Then, Mars Express will re-orient its main antenna toward Earth and download the second, smaller segment of recorded data, which should contain the first in-situ confirmation from Mars of Schiaparelli’s arrival and landing,” says Simon.

The data will be received via ESA’s Cebreros deep-space ground station, in Spain, by the Mars Express flight control team at ESOC, ESA’s mission control centre in Darmstadt, Germany, and then passed on to the ExoMars mission controllers.

Even more friends

Mars Express won’t be the only ‘set of ears’ listening in to Schiaparelli’s descent that day.

At Mars, NASA’s Mars Reconnaissance Orbiter (MRO) will monitor signals from Schiaparelli, but only after its landing, due to MRO’s orbital geometry.

MRO - Mars Reconnaissance Orbiter

Credit: NASA/JPL-Caltech

The TGO orbiter, while conducting its own critical orbit entry manoeuvre, will also record Schiaparelli’s descent and landing, but this data can only be downloaded some hours after it has completed orbit entry.

In the following days, Mars Express and MRO – as well as the other NASA Mars orbiters, Odyssey and MAVEN – will each serve as data-relay platforms, overflying Schiaparelli’s landing site in Meridiani Planum once or twice per day, picking up data transmitted from the lander during its nominal two- to four-day surface science mission, and relaying these to Earth.

Mars Express will also support the Schiaparelli mission through remote sensing measurements over the landing site during several weeks prior to the event.


Best wishes from Mars Express

A super-nice note and team photo sent in by the Mars Express flight control team at ESOC! This was written by Luke Lucas, on behalf of the team who fly ESA's venerable Mars mission – now looking forward to a new buddy in orbit!

Mars Express has been orbiting Mars for just over 12 years, and soon will be joined by another ESA explorer. The excitement is building here at ESOC as the final preparations for the ExoMars launch are made.

MEX Flight Control Team at ESOC Credit: ESA

MEX Flight Control Team at ESOC Credit: ESA

Recently, teams from industry, the science community and ESTEC have been arriving; and here at ESOC, the simulation campaign is drawing to a close. The simulation campaign involves the flight control team (FCT), practising and practising the launch and other mission phases using a spacecraft simulator (computer program). The ExoMars team will have practised nominal and contingency operations, ensuring that procedures are ready and – most critically – that the FCT are as prepared as possible to successfully operate the spacecraft.

The ExoMars dress rehearsal is set for tomorrow; then, the next time the team are in the Main Control Room it will be for actual launch and real telemetry from the very real spacecraft, not a simulator...

Any launch is a mixture of high pressure and great excitement. An unforgettable occasion!

We wish the ExoMars team all the best and look forward to greeting a fellow explorer at Mars.

Kind regards

– Luke & Mars Express

Skimming Phobos

Inputs from today's blog post were provided by Thomas Duxbury, an interdisciplinary scientist on MEX for the Mars moons and Mars geodesy/cartography (and also a co-investigator on the HRSC scene team), Dmitri Titov, ESA's Mars Express project scientist, and Simon Wood, from the MEX mission operations team at ESOC, ESA's European Space Operations Centre, Darmstadt, Germany.

On Thursday, 14 January, ESA’s Mars Express spacecraft will make an unusually close flyby of the largest Martian moon, Phobos, passing the surface at just 53 km at closet approach at 16:00:21 UTC (17:00 CET) on orbit 15260.

The event will mark the spacecraft’s closest flyby of the moon in 2016, and, as a point of comparison, most of the other almost-60 Phobos flybys this year will occur between several hundred up to almost 2000 km. So it’s a real skimmer!

Phobos flyby 14012016

Predicted view from MEX for the 14 Jan 2016 Phobos flyby. The centre image is the predicted perspective view of Phobos at closest approach. This shows the view along Phobos’ shorter axes and it appears smaller than the other two images, which show the view along Phobos’ longest axis. Credit: T. Duxbury

The flyby will enable Mars Express instruments, especially the HRSC – the High Resolution Stereo Camera – to see points of the moon’s surface that have not previously been observed from such a close range.

“This flyby will provide very good viewing, within 1,000 km, of an area previously not seen well,” Dmitri Titov, ESA's Mars Express project scientist. “HRSC will be taking images; the MARSIS radar and the ASPERA-3 particle instrument will operate as well to sound the subsurface and plasma environment of the moon.”

+ marks the spot

The “+” in the predicted images (see above) indicates a possible landing site for the future Russian Phobos Grunt sample return mission.

“This flyby is important as it will allow us to finally view this area on Phobos that has yet to be seen at high resolution and excellent lighting,” says Thomas Duxbury, professor in planetary science at George Mason University, USA.

In the past, Mars Express has made closer flybys, but not by much. On 29 December 2013, Mars Express flew by at just 45 km, close enough that the moon’s gravity pulled the spacecraft slightly off its course, enabling new estimates of the Phobos mass and density.

Phobos 2010

Phobos as seen by the HRSC nadir channel during Mars Express Orbit 7926 in 2010. Credit: ESA/DLR/FU Berlin (G. Neukum)

The flyby is an operational challenge as well as a scientific opportunity, as the positions of the moon and Mars Express must be known very, very precisely in order to safely make the ‘skim-by’.

Commands on board

Commands to trigger the instruments’ observations were uploaded  Thursday, 7 January, following last-minute optimisation of the expected position of Phobos relative to the spacecraft provided by the flight dynamics team at ESOC , Darmstadt.

“This is needed due to the high level of precision required to target Phobos with the instruments at such a close distance,” says Mars Express Spacecraft Operations Engineer Simon Wood.

“The activity will then take place fully automated and without intervention by the operations team at ESOC, who will be closely monitoring the flyby.”

Deciphering Phobos

Flybys such as this help generate evidence to understand how the moon was formed.

The mass of Phobos is estimated as 1.0603 x 10^16 kg (uncertainty less than 0.5 %) and the density is 1862 kg/m3 (uncertainty less than 2%). For comparison, the density of Mars is about 3930 kg/m3, and Earth has a density of around 5520 kg/m3.

The low density of Phobos is consistent with the moon having a high porosity with an uneven mass distribution; in other words, it is essentially a rubble pile with large empty spaces between the rocky blocks that make up the moon’s interior.

This favours the formation scenario in which Phobos was born in orbit around Mars from a disc of debris and is not a captured asteroid – one of the other leading theories for how Phobos and its sibling Deimos came into existence.

Mars Express in orbit around Mars. Credit: ESA/AOES Medialab

Mars Express in orbit around Mars. Credit: ESA/AOES Medialab

The debris disc could have resulted from a large impact on the surface of Mars, or perhaps Phobos (and maybe Deimos) formed from left-over debris from the formation of Mars itself.

Data from such flybys will also prove valuable in planning future robotic or even human missions to land on the moon, and ideal location from which to observe Mars.

It is expected that the initial results from this flyby will be available in the coming weeks.


Editor's comment: It is interesting to note that, because the polar orbit of Mars Express intersects the equatorial orbit of Phobos, at some point in the future – long after Mars Express has depleted its fuel and has been shut down – the spacecraft is likely to impact the moon.

Update 28 May

Today's update from the MEX team at ESOC on progress of the VMC Schools Campaign, via Spacecraft Operations Engineer Simon Wood.

All VMC observations are complete and ran as planned; all images are now on ground. Initial processing has begun!

With approximately 2000 of them, Simon mentions that it is going to take a bit of time to prepare, process and sort the images for distribution to the VMC Schools participants. We'll keep you updated.

Update 27 May

Today's update from the MEX team at ESOC on progress of the VMC Schools Campaign, via Spacecraft Operations Engineer Simon Wood. More VMC images are expected to arrive today and tomorrow.

DSA 3 Malargüe

This image, taken in 2012, shows DSA 3 Malargüe station, one the world’s most sophisticated tracking stations used for deep space communications, as it neared inauguration in Malargüe, Argentina. Credit: ESA - CC BY-SA IGO 3.0

We had small glitch in the connection to the Malargüe DSA 3 ground station (DSA 3) during yesterday's data downlink. This happens from time to time, however it is not a problem for us, as Estrack ground stations store all the data received at the station for at least 8 days.

This meant that we were able to recall the missing few minutes of yesterday's communication pass from the ground station and feed it into the mission control system here at ESOC this morning, so no data were lost.

The last image received in yesterday's downlink was a nice image of Phillips crater!

First VMC School Campaign images are down!

This is a collage of Visual Monitoring Camera (VMC) images acquired on 25 May and downloaded to Earth early on 26 May 2015. They are among the first in a series of over 2000 images that are being acquired by Mars Express in support of the VMC Schools Campaign!

Collage of Mars Express VMC images acquired 25 May 2015 Credit: ESA/Mars Express/VMC – CC BY-SA IGO 3.0

Collage of Mars Express VMC images acquired 25 May 2015 Credit: ESA/Mars Express/VMC – CC BY-SA IGO 3.0

We wanted to share a low-resolution mash-up with you, just so you knew 'your' images are being delivered! The complete image sets, at full VMC 640X480 resolution will be delivered to campaign participants starting as early as Friday this week.

Update 26 May

A very brief update from MEX Spacecraft Operations Engineer Simon Wood at ESOC, who, together with the Mars Express team, are now just checking telemetry – on-board status information – and some **initial** VMC data that were downloaded last night. Simon writes:

First images downloaded last night; everything going OK so far. Good shots of Mars South Pole – Northern hemisphere looks quite cloudy/dusty.

More details later.


VMC Schools Campaign: Uploading commands

Update from MEX Spacecraft operations Engineer Simon Wood at ESOC

The commands to run next week's observations are now all confirmed on board Mars Express!

To give an idea of what these commands are and what they look like, here is a screen shot from the mission control system showing the commands on board for the first observation orbit on Monday, 25 May.

Uploading command stack to Mars Express

Uploading command stack to Mars Express

In essence, they are broken down into three groups: turning the spacecraft away from Earth (we call this a 'slew'), the observation itself and then the slew back to pointing at Earth.

For the first group, the slew away, we first have a command to set what we call the 'out of Earth timeout'; this starts a timer by the end of which the spacecraft must be back to Earth pointing. If it is not Earth pointing when the timer expires, then the spacecraft will put itself in safe mode.

This is a precaution that is taken for every pointing we do; in the event of a problem, the spacecraft won't get stuck pointing the wrong way.

There are then the commands to update the mode in which the attitude and orbit control system (AOCS) is in and to tell the craft to start to slew. Finally, there are commands to update the position of the solar arrays to ensure that when the spacecraft has turned to its new attitude, that sufficient power is being generated.

Once in position, we can then start the observation.

Here we have the command to start the on-board control procedure (OBCP), which is a small computer program that runs on board the spacecraft and that controls the VMC camera. This program switches on and initialises the camera (this takes around two minutes) and then it enters into the programmed observations.

For the VMC Schools Campaign, this is means taking approximately 1 image per minute, cycling through 3 exposure settings. As this is a long-duration observation, there are also a group of commands that will keep updating the AOCS such that it keeps turning the spacecraft to keep Mars in the view of VMC.

The final group is the end of observation activities. Here we start another OBCP, which switches VMC off. Then the solar arrays are commanded to rotate again to optimise the power output and AOCS is then commanded to turn the spacecraft so the antenna is pointing at Earth.

After that, the transmitter will then switch on and the on-board computer will begin sending the VMC images back to Earth.

– Simon Wood

Orbit visualisations – 25/26 May 2015

These three animations give you an accurate visualisation of the three orbits that will be dedicated to the VMC Schools campaign next week. We'll Ask the MEX team to explain these in detail during Friday's ESAHangout. They are posted below in the order in which they'll be flown.

What you see in them is VMC's view of Mars during the observations.

Video 1 - DOY 145 (25 May) Orbits 14456,14457 14458 Starting at 05:25 to 21:00

Video 2 DOY 146 (26 May) Orbit 14459 Stating 03:00 - 08:00.

Video 3 Doy 146 (26 May) Orbit 14461 -14462 Starting 21:30 - 06:45