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


ESAHangout: Mars Express lined up for VMC Schools Campaign

WATCH REPLAY BELOW

22 May – Start 11:00 EDT / 15:00 GMT / 17:00 CEST http://goo.gl/Yw8P5p

Prior to flying the campaign orbits on 25/26 May, this will be the final interactive Q&A session with the Mars Express flight control team for participants in the VMC Schools Campaign. Priority for questions will go to school/club participants. Questions can be posted in the ESA G+ channel or via Twitter using the #VMCSchools hashtag.

We are at Maaaaaaaars!

Today’s post – part of a series of reports marking the MEX 10th anniversary – was submitted by Mars Express Operations Manager Michel Denis, who was in the Main Control Room at ESOC during the night of 24/25 December 2003 when Europe arrived at Mars – Ed.

It was 25 December 2003, in the very early morning hours. As Spacecraft Operations Manager, I was invited from the Main Control Room to the large Conference Centre (where the main event at ESOC was happening – Ed.) to report on the ongoing Mars orbit injection manoeuvre. We know it has started, but we didn’t yet know whether it had completed successfully.

Team in ESOC Main Control Room 24 Dec 2003 (pana, left) Credit: ESA/M. Denis

Team in ESOC Main Control Room 24/25 Dec 2003 (panorama, left) Credit: ESA/M. Denis

Whatever my innermost emotions and questions, I talked to the officials and the journalists in the tone you need for these circumstances. I told them that the 39 commands that perform the ‘now or never’ orbit-injection manoeuvre have been verified innumerable times down to the last bit by the best experts; I repeated that the manoeuvre had been rehearsed exhaustively, using extreme simulations of the software and harsh tests of the spacecraft’s main engine by the manufacturer.

As a rational engineer I know that 100% certainty is impossible to achieve.

I pointed out that, if required, the small thrusters can automatically step in to help reduce our speed by almost 3000 km/h to help us get ‘caught’ by the Red Planet’s gravity.

Team in ESOC Main Control Room 24 Dec 2003 (pana, right) Credit: ESA/M. Denis

Team in ESOC Main Control Room 24 Dec 2003 (panorama, right) Credit: ESA/M. Denis

As a rational engineer, I know that 100% certainty is impossible to achieve, and that much can happen in such a 40-minute-long manoeuvre…

Now I had to return back on console, and went back down to the Main Control Room, where my deputy, Alan Moorhouse, was in charge – mainly of waiting at that particular moment.

If you know ESOC, you certainly know the rotunda – a large spiral staircase leading to the Conference Centre (it’s in the H Building; the MCR is in the E Building – Ed.).

Michel Denis Credit: ESA/J. Mai

Michel Denis Credit: ESA/J. Mai

I start going down the steps, floating between two worlds equally tense; from the glossy world of the public event to the protected world of the Main Control Room – a busy cocoon where we had lived already ten days and nights, where the entry manoeuvre has been prepared based on the computations by Flight Dynamics, where all critical commands have finally been assembled and up loaded to our little spaceship 150 million kilometres away.

Flight Dynamics confirm capture, within 0.5% accuracy.

In the middle of the stairs, between the floor of talks and the floor of acts, the mobile phone wiggles in my pocket. A message from Alan: “Flight Dynamics confirm capture, within 0.5% accuracy.”

In everyone’s private or professional life there are turning points which, however planned and expected, represent ‘a giant leap’, to paraphrase a glorious quote. A point with a Before and an After; ‘after’,  our existence is changed, irreversibly.

In these instants, the present is more intense; more present than ever. Overwhelming.

Rotunda staircase at ESOC. Yelling is normally not permitted. Credit: ESA/J. Mai

Rotunda staircase at ESOC. Yelling is normally not permitted. Credit: ESA/J. Mai

So overwhelming, that when you remember this moment years or decades later, you revive it as it were the first time again.

I am overwhelmed, alone in the huge rotunda, perfectly empty, everyone at ESOC is either sitting in the Conference Centre or standing in the control rooms, waiting for the news. Alone, for a few seconds, in this resonant space that makes sounds impressive, where I often sang Christmas carols with the ESOC Choir. Today is Christmas day; whether child or adult, whether you believe or not, in our lives a special date, very emotional.

“We are at Maaaaaaaars!” I could not refrain from yelling, with my loudest voice, to expel from my chest all the emotions of the night and the years of preparation and the last-minute doubts and angst and the incredible joy that seizes me now, just like Mars has seized Mars Express, just like Europe has seized Mars. We are at Mars: now it is true, and nothing can make this not to have happened.

Merry Christmas Europe!  Welcome to Mars!

MEX 10-year celebration: We’d like to invite a few of our friends

On 3 June 2013, ESA will host a small in-house event to mark ten years of success at the Red Planet. The event will take place at ESOC, home of the Mars Express mission operations team.

Mars Express over water-ice crater Credit: ESA/DLR/FU-Berlin-G.Neukum

Mars Express over water-ice crater Credit: ESA/DLR/FU-Berlin-G.Neukum

As a way to say ‘thank you’ for following our mission, we’re delighted to invite a small number of Twitter followers to ESA/ESOC on Monday, 3 June. The programme starts at 15:00 CEST and will include expert presentations from the MEX science and operations teams, followed by a small reception:

14:30 – Doors open/arrival
15:00 – Presentations, including

** Olivier Witasse: Host welcome/introduction
** Michael McKay: Mars Express in the international picture
** Alain Clochet: The industrial perspective
** Michel Denis: Mars Express 10 years of operations
Short break
** Jeff Plaut: The US role in Mars Express
** Ernst Hauber: HRSC highlights
** Agustin Chicarro: The Mars Express legacy
Open contributions

17:15 – End of formal programme
17:30 – Reception
~19:00 – Event ends

As much as we’d like to invite all 120k followers of our various Twitter channels, we can’t! 🙁 But we do have a small number of seats available and we’d like to invite you apply for an invitation via the form below. Please apply by 12:00 CEST on 29 May.

NOTE: 29.05: Applications are now closed. Thx to all who submitted!

We’ll contact the selected invitees by email around 16:00 CEST on 29 May, and will look forward to seeing you on the 3rd.

Questions/queries? Contact us via @esaoperations or @esa_de

First Contact! Mars Express’ first ‘conversation’ with Curiosity

As we reported yesterday, Mars Express had a busy Sunday evening, pointing first at NASA’s Curiosity rover on the surface of Mars and then swinging around to do another relay pass with Opportunity. We received the data from both of these passes this morning over ESA’s New Norcia ground station and, on first look, it seems that both relays were very successful.

First Laser-Zapped Rock on Mars

First Laser-Zapped Rock on Mars. This composite image, with magnified insets, depicts the first laser test by the Chemistry and Camera, or ChemCam, instrument aboard NASA’s Curiosity Mars rover. The composite incorporates a Navigation Camera image taken prior to the test, with insets taken by the camera in ChemCam. The circular insert highlights the rock before the laser test. The square inset is further magnified and processed to show the difference between images taken before and after the laser interrogation of the rock. The test took place on Aug. 19, 2012. Credit: NASA/JPL-Caltech/LANL/CNES/IRAP

In ESA’s MEX team, we’re particularly excited to have had our first contact with Curiosity – proof that the amazing new rover from the United States can talk with our veteran European Mars orbiter!

At the start of the contact, Mars Express was over 3600 km from Curiosity’s landing site in Gale Crater and closed in to only 1300 km by the end of the contact – streaking across the sky as seen from Curiosity.

During this overflight by Mars Express, it ‘hailed’ Curiosity in Gale Crater and the rover responded. The two spacecraft then autonomously established a link with each other and Curiosity flowed data back to Mars Express for nearly 15 minutes. This international chat between two spacecraft in deep space is proof of all our preparation, standardisation and cooperation work in action – so it’s something both agencies can be proud of.

ESA's first 35-metre deep-space ground station is situated at New Norcia, 140 kilometres north of Perth in Australia. The 630 tonne antenna will be used to track Rosetta and Mars Express, the latter to be launched in 2003, as well as other missions in deep space. The ground station was officially opened on 5 March 2003 by the Premier of Western Australia, Hon Dr Geoff Gallop. Credits: ESA

ESA’s first 35-metre deep-space ground station is situated at New Norcia, 140 kilometres north of Perth in Australia. The 630 tonne antenna will be used to track Rosetta and Mars Express, the latter to be launched in 2003, as well as other missions in deep space. The ground station was officially opened on 5 March 2003 by the Premier of Western Australia, Hon Dr Geoff Gallop.
Credits: ESA

The actual data that flowed back was made available to NASA earlier today, who will now retrieve and process the data.

Hopefully we’ll have some info from them in the next couple of days about what exactly was contained within. We’ll also receive (within Tuesday) the ‘housekeeping’ telemetry of Melacom – information on how our radio performed. This will allow us to double-check the performance of this first important contact with Curiosity.

The data was sent at a rate of only 8 kbps – 125 times slower than the 1-Mbit/second Internet connection you might have at home!

We wanted to take things easy to start with, though, and test the performance of the link. Nonetheless, we received 955 data packets from Curiosity, totalling 867 kilobytes of data.

This will be the first of several contacts with Curiosity in the future, as we better learn how to use and optimise this relay link between the two craft and the two space agencies. Watch this space for more details as we get them on this pass and the future contacts between Mars Express and Curiosity.

 

Getting the data back – Store and Forward

This video shows the view of Mars Express from the Earth before, during and after the Curiosity landing. It demonstrates perfectly why we need to use a method called ‘store and forward’ to get the recording of the descent back to Earth.

At the start and end of the video, you can see Mars Express’ big 1.6-m High Gain Antenna (the grey circle on the front of the spacecraft) pointed right at us. We need that to be pointed at us to be able to talk to Mars Express from Earth.

Unfortunately, to support the landing of Curiosity, we need to point our Melacom antennas at the incoming lander, and they’re fixed perpendicular to the High Gain antenna. That’s why during the middle of the video you see the spacecraft turn the High Gain Antenna away from us – it’s so it can get the best possible view of the incoming lander.

In order to relay the recording of the descent, we store the data in our on-board memory – a bit like saving a picture to the memory card on your digital camera.

We have 12 Gigabits of on-board memory, which might sound small compared to your home computer, but it’s plenty of space for what we need. Once we turn back to Earth, we can tell the spacecraft to forward the recorded data back to Earth, just like plugging in your camera and downloading the results from the memory card. In fact, due to the criticality of the Curiosity recording, we’ll transmit it to Earth three times to make sure it reaches us safely.

So when you’re watching the landing tomorrow, note that’s why it’ll take us a bit of time to swing the spacecraft around and dump the recorded data to ground. The JPL orbiter Mars Reconnaissance Orbiter will do the same thing and so will experience a similar delay.

In contrast, the live relay from Mars to Earth will be provided by JPL’s venerable Mars Odyssey orbiter, the oldest spacecraft currently operating around Mars. It uses a different mode, called ‘bent pipe’, where it takes the incoming data and ‘bends’ it around and blasts it back towards Earth more or less simultaneously.

If all goes according to plan, this direct relay will be NASA’s first confirmation of a successful landing, and the detailed recordings made in ‘store and forward’ by the other two orbiters will follow shortly after to provide us a full picture of this historic landing.

What time is it?

How we solve the problem of multiple time zones

If you saw our descent timeline article, you’ll have noticed that we speak about different time zones (of course with acronyms!). If you’ve also been following the NASA coverage for MSL arrival at Mars, then you’ll see it gets even more confusing. In case you’re wondering what they all are, then we’re here to try and explain!

World time zones

World time zones

First of all, we have to deal with different time zones here on Earth – something you’ve no doubt experienced if you’ve taken a long distance flight.

Here at ESA’s operations centre, ESOC, in Germany, we use CEST – Central European Summer Time – the time zone most of Europe is on during the summer. Over at JPL in California, they are 9 hours behind, on PDT – Pacific Daylight Time – summer time for the west coast of the United States.

This can get really confusing when agencies like ESA and NASA work together on time-critical activities like MSL landing. At NASA, Curiosity will land on 5 August – but here in Europe it’ll land on the 6th! So not only is the time of landing different, but it happens on a different day depending on where you are!

To solve these problems, the space industry (and many other organisations facing similar issues) use a standard time zone called UTC – Coordinated Universal Time.

This time zone was standardised in 1961 to allow our increasingly networked world to work better together. It represents GMT (Greenwich Mean Time), the zero reference for all time zones, but with no daylight savings time shift – so it never changes throughout the year.

At ESOC our short-hand for this time-zone is to put a letter ‘Z’ after the time, which is where UTC gets its nickname of “Zulu Time” (Z = Zulu in the phonetic alphabet).

So when Curiosity lands, Europe (CEST) will be 2 hours ahead of UTC and JPL (PDT) will be 7 hours behind. Thanks to UTC, though, we can coordinate and communicate pretty well together, allowing multiple agencies and nations around the world to work together on this important event.

 

MEX engineers setting up in ESOC’s Main Control Room

Today, the Mars Express team are configuring workstations in ESOC’s Main Control Room to display live MEX data for the media event that will take place on Monday. Mars Express is normally operated from a Dedicated Control Room in a separate building, but with very strong media attendance expected, we’ve moved to the larger MCR.

Mars Express engineers configuring MEX mission data displays in ESOC MCR Credit: ESA

Mars Express engineers configuring MEX mission data displays in ESOC MCR Credit: ESA

Mars Express engineers configuring MEX mission data displays in ESOC MCR Credit: ESA

Mars Express engineers configuring MEX mission data displays in ESOC MCR Credit: ESA