Testing cooperation: ESA’s Mars Express transmits commands to NASA rover

This update sent in earlier today by ESA’s Simon Wood, one of the engineers working on the Mars Express mission operations team at ESOC.

Today, ESA’s Mars Express orbiter will send telecommands to NASA’s Curiosity rover on the surface of Mars.

This self-portrait of NASA's Curiosity Mars rover shows the vehicle at the "Mojave" site, where its drill collected the mission's second taste of Mount Sharp. Credit: NASA/JPL-Caltech/MSSS

This self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the “Mojave” site, where its drill collected the mission’s second taste of Mount Sharp. The scene combines dozens of images taken during January 2015 by the Mars Hand Lens Imager (MAHLI) camera at the end of the rover’s robotic arm. The pale “Pahrump Hills” outcrop surrounds the rover, and the upper portion of Mount Sharp is visible on the horizon. Darker ground at upper right and lower left holds ripples of wind-blown sand and dust. Full image and caption via NASA web. Credit: NASA/JPL-Caltech/MSSS

The transmission is part of a routine quarterly test of the communications link between MEX and Curiosity – NASA’s Mars Science Laboratory (MSL). Aside from its prime science mission, Mars Express is able to provide contingency communications with MSL (or with any NASA rovers) in case of any problems with the normal data relay links.

This particular test consists of MEX hailing MSL – sending a specific signal requesting MSL to listen – then transmitting commands (provided by the MSL team at NASA/JPL) to the rover and then recording data transmitted back.

Background sequence of activities

  • MEX mission planning system schedules pointing of MEX’s UHF (ultra high-frequency) antenna at MSL – end-December 2104
  • MSL team provides command file (i.e. the telecommands to be transmitted) to the MEX flight control team at ESOC – last week of February 2015
  • MEX flight control team uploads the commanding ‘products’ (files to be executed on board MEX) on 27 February; these were generated on 24 February
Mars Express orbiting the Red Planet - artist's impression Credit: ESA/Alex Lutkus

Mars Express orbiting the Red Planet – artist’s impression Credit: ESA/Alex Lutkus

Operations timeline today

All times UTC

14:29 MEX will slew from Earth pointing to pointing its UHF antenna at MSL on the surface
14:41 MEX UHF antenna switches on – takes 15 mins to warm up
14:56 Overflight begins with MEX hailing MSL; overflight lasts 9 mins
15:05 MEX begins to slew back toward Earth pointing

Data received from MSL will be transmitted back to Earth by MEX at around 16:30 UTC via ESA’s deep-space ESTRACK station in Malargüe, Argentina.

Later, NASA’s deep-space network teams will extract the data from the MEX packet archive and pass this on the the MSL team for analysis.

Best regards from the MEX control team at ESOC!

– Simon

Why the S-Band beacon is blocked just now…

You’ll have read in past blog posts that Mars Express will be (has already started) sending a beacon signal to Earth to enable the mission operations team to monitor the craft. It it continues being received, all is (most likely!) well. If it disappears, this could indicate a problem.

Mars Express orbiting the Red Planet - artist's impression Credit: ESA/Alex Lutkus

Mars Express orbiting the Red Planet – artist’s impression Credit: ESA/Alex Lutkus

The beacon was switched ON at 14:48CEST (ground receive time) and is set to run through to the ‘all clear’ at about 21:30CEST tonight. But there was a loss of signal at 15:27CEST – and this was expected. Spacecraft Operations Engineer Andy Johnstone at ESOC explains why:

The blocked signal is caused by the spacecraft itself!

The Large Gain Antenna (LGA) will be hidden by the spacecraft body or the solar arrays at various periods during the transmission of the beacon today [as the craft moves through various pointings], causing a loss of reception on ground.

We do have a second LGA on top of the spacecraft that could have also been used (between them they are visible from any angle) but we elected not to move the antenna selection switches during the flyby. It is something we only do rarely and decided that, as we are conducting (important!) nominal science during the flyby, we would accept the three blackout periods. It also gives us an opportunity to map the true limits transmit of the LGA – we are always keen to sneak in additional tests and learn more about our spacecraft wherever possible!

Editor’s note: Beacon blackouts will run

  • 15:27-16:15 CEST
  • 17:33-18:32 CEST
  • 21:53-23:09 CEST

Space is really, really big – except sometimes it isn’t

Editor’s note: Here’s the next installment in the continuing story of how the Mars Express team is preparing for Comet Siding Spring flyby, 19 October 2014. This week: introducing the spacecraft’s subsystems and structure – and wondering how we can absorb impacts.

Now that we have looked at some of the external factors affecting Mars Express, let’s take a look inside and see how the spacecraft was built and what it’s made from.

This diagram shows the major components in the spacecraft body. Credit: ESA

This diagram shows the major components in the spacecraft body. Credit: ESA

This diagram shows the major components in the spacecraft body. There are a lot of acronyms, which we will explain in more detail in future postings. For now, briefly:

  • AOCS (blue): Attitude and Orbit Control System – this controls where Mars Express is pointing (the attitude) and can change the speed of the spacecraft to modify its orbit.
  • DMS (pink): Data Management System (sometimes also called OBDH – On-Board Data Handling) – The computers and storage that interpret commands from Earth, collect data from sensors and transmit telemetry back to Earth.
  • Instruments (purple): The payload. The sole purpose of Mars Express is to carry provide support to these by pointing them at their targets, collecting their data, keeping them at the correct temperature and feeding them with power.
  • Power/Thermal (green): Generating, storing and distributing electricity throughout the spacecraft and maintaining the temperature within acceptable limits.
  • TT&C (yellow): Tracking, Telemetry and Control – the radio communications system of Mars Express.

There is one other subsystem that we will look at in a little more depth today – Structure.

This ‘system’ is the only subsystem that we cannot change in flight – but with the upcoming comet encounter, and the possibility of any sort of comet dust impact, we have been looking at the structural design in much detail!

Each wall of the square, box-like Mars Express is made from aluminium sandwich panel. This comprises two sheets of thin aluminium separated by a honeycomb of aluminium.

These panels are very popular in many aerospace and motorsport applications as they have fantastic strength-to-weight ratios and are incredibly stiff, which is extremely important when factors like the alignment of instruments is concerned. The trade-off in this case is that we are using thin materials with thicknesses similar to that of a carbonated drink can, which – while very strong – does not provide much protection from hypervelocity impact penetration.

Inside the right wall of Mars Express, looking in from the front of the spacecraft. Credit: ESA

Inside the right wall of Mars Express, looking in from the front of the spacecraft. Credit: ESA

This picture is of the right wall, looking in from the front. The aluminium sandwich panel is visible on the left of the photo and is 20mm thick.

The three black boxes are the CDMU2 (bottom), RTU (top) and the RFDU (right). A reaction wheel is also visible, at bottom right.

The other thing you probably noticed is the harness – the huge mass of cables that connect the different parts of the subsystems together.

The solar arrays are of the same construction and the high-gain antenna is based on an aluminium core but is has an additional skin on either side with six layers of carbon-fibre composite.

Now, we’re sure that some of you are thinking that this is mad – how could we possibly send such a valuable spacecraft out with so little protection? Well, the first answer comes from the Hitchhiker’s Guide to the Galaxy:

“Space is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space…”

In normal circumstances, the chances of our spacecraft being hit by anything significant is quite small. For a spacecraft, the worst place to be (with the exception of a comet coma) is in low-Earth orbit, and even in this relatively cluttered environment, only a few spacecraft have ever suffered enough damage due to impacts to have their missions affected.

Unfortunately, while the chances of an impact are normally very, very low, should an impact happen, it can be quite devastating. Why? Here’s the other thing to remember: in space, collisions tend to be fast – very fast – and the energy of a collision increases with the square of the speed.

At such energies, impacting particles/objects and any part of a satellite they hit behave more like liquids than solids, and break up violently. Spacecraft that have been designed to operate in environments where they need to be protected from impacts use a system called a Whipple shield for protection – serving basically as armour plating (see “Hypervelocity impacts and protecting spacecraft” for much more detail – Ed.).

In Whipple shielding, a thin plate is mounted some distance offset from one or more additional shield plates. The first one will cause any impacting object to break up into fragments, and then the multiple layers behind this absorb the remaining energy of the fragments.

One of the best examples of this was ESA’s Giotto probe that flew just 596km from Halley’s comet in 1986.

Mars Express was not built with a Whipple shield and as it was not expected to face such a fierce environment as Giotto, but we’re sure you can work out from the image at the top of this post (and from last week’s post on pointing restrictions) which side is the least vulnerable (we think it’s the front of MEX – with the big radio antenna acting as a Whipple shield! Ed.).

Of course every decision we make is a trade-off, and we will see why in later weeks.

Andy, Michel, Kees, Simon and Luke

Why orienting our spacecraft is the heart of the challenge

Today’s post continues where we started last week with an update from the Mars Express Flight Control Team at ESOC on their preparations for the 19 October Comet Siding Springs flyby. Today: defining the challenge!

Comet C/2013 A1 Siding Spring

NASA’s NEOWISE mission captured images of comet C/2013 A1 Siding Spring, which is slated to make a close pass by Mars on Oct. 19, 2014. The infrared pictures reveal a comet that is active and very dusty even though it was about 355 million miles (571 million kilometers) away from the sun on Jan. 16, 2014, when this picture was taken. Credit: NASA/JPL

Before we look at Mars Express in more detail and decide what we can do to try and protect it from the speeding particles in the comet’s coma (the cloud of dust and gas surrounding the nucleus), we should take a moment to briefly describe the spacecraft and the encounter period.

The shape and structure of spacecraft are normally described using a coordinate reference frame. For Mars Express, we on the team often use a more informal description where the high-gain antenna is referred to as the ‘front’, the thrusters are on the ‘bottom’ and the instruments face out from the ‘top’.

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

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

Nice view of MEX – Click image for a 3D model

As these directions are given from the Mars Express point of view, the MARSIS (Subsurface Sounding Radar / Altimeter) booms are therefore mounted on the right of the spacecraft.

Further, the left and right side each have a solar array extending away from the main spacecraft body that can rotate through 360°.

Hacked-up version of the nice view showing spacecraft directions (some of you may prefer to assemble your own MEX paper model – Ed.)

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

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

Constraints, constraints…

The spacecraft is, in principle, able to turn in any direction, however the left, right and rear sides have radiators for shedding heat from the platform and payload systems and should not be illuminated by the Sun.

The top should also not be pointed toward the Sun as some of the instruments require cooling to operate effectively and optics may be damaged by direct sunlight.

During scientific observations, the instruments are pointed toward a target to collect data, and – for communication – the antenna must point toward Earth.

These two tasks, as you may have guessed, do not happen at the same time and science data is recorded and downlinked to Earth later.

Also, for the majority of observations, the attitude of a science observation is in no way compatible with communications pointing.

Finally, the solar arrays should be pointed towards the Sun whenever possible to generate electricity (although power can be stored in batteries for short periods).

The orientation of things

Siding Spring flyby of Mars - Mars orbit plane. Credit: ESA/M. Khan

Siding Spring flyby of Mars – Mars orbit plane. Credit: ESA/M. Khan

This image illustrates the relative orientations of Mars, the comet, Earth and the Sun on 19 October.

The particles in the coma are ejected away from the comet with a speed of a few metres per second (m/second) but as the overall speed is so high we are treating them as arriving along a line parallel to the path of the comet.

In other words, we are treating them as a stream of hyper-velocity particles washing past, over and around MEX.

It is worth noting the relative direction of Earth and Sun; if we want to stay in touch with the spacecraft during the flyby, the antenna must point toward Earth.

So, in summary, the direction in which we orientate the spacecraft and the solar arrays has a big impact on how Mars Express communicates with Earth, generates power, controls its temperature and conducts science observations.

Siding Spring - trajectory in 2014 Credit: ESA/M. Khan

Siding Spring – trajectory in 2014 Credit: ESA/M. Khan

Now we have additional factors, as we have an interesting target passing by that our science teams really wish to observe as directly as possible – but with it comes a stream of potentially damaging particles!

The threat…

These particles might not only physically abrade the outer surface of the spacecraft (which can damage insulation, radiators and instrument optics), but also – if large enough – can penetrate parts of the spacecraft structure.

Additionally, at the impact speed expected here, even minute specks of dust will be converted into an electrically charged plasma, which can lead to a current and might short out and damage some of the electronics.

The challenge…

So the challenge we face is simple: how do we orient the spacecraft to maximise the science possibilities, best protect the most vulnerable and critical areas of the spacecraft body, respect the always-present pointing restrictions, maintain communication and minimise the possibility of any damage from hyper-velocity impacts?

The answer, which we are developing now, will undoubtedly lie in trade-offs: to reduce risks and maximise science and survivability.

We do know one thing for certain: there is no perfect answer!

More news next week!

Andy, Michel, Kees, Simon and Luke

 

Why no radar science?

During Phobos flyby on 29 December, @AsteroidEnergy asked a question via Twitter:

It took some time (due to holidays – Happy New Year!!!), but we now have a reply from ESA’s Olivier Witasse, MEX Project Scientist at ESTEC.

Mars Express in orbit around Mars with the MARSIS antenna unfurled. Credit: ESA

Mars Express in orbit around Mars with the MARSIS antenna unfurled. Credit: ESA

The radar was originally designed solely for the observation of Mars. For safety reasons, the radar software blocks operations when the target is closer than 240 km. In the case of past Phobos flybys, because the distance is sometimes lower than that, the radar was therefore re-configured to operate at close distance by bypassing protections preventing the opening of the receiver before a certain time from transmission had elapsed.

Although not without risk, this procedure was thoroughly tested and successfully used throughout several Phobos flybys. The operational distance is now *** 175 km ***. Therefore, we usually switch on MARSIS when the minimum flyby distance is around 175-200 km.

See you in 2014!

– Olivier

Spacecraft in good shape

Update from James Godfrey in the Mars Express control room at ESOC about 1 hour ago.

The signal from the spacecraft is now being modulated with telemetry – meaning that housekeeping information on the status and health of Mars Express is being downloaded.

During the flyby this morning, this modulation was turned off so as to concentrate all of the energy transmitted by the spacecraft into the main carrier radio signal and maximise the possibility of detecting the (very small!) changes in frequency as the spacecraft was accelerated by Phobos’ gravity.

Now that the most critical radio science measurements have been completed, we have been able to turn the modulation back on so that we can receive the telemetry data.

As expected: everything looks OK!

Mars Full Orbit Video 2.0: Kepler rocks the Red Planet

Just in time to celebrate the 10th anniversary of Mars Express: a new and enhanced Full Orbit Video delivered by the VMC camera – the Mars Webcam!

The version below is a special ‘MEX birthday preview’ – we’ll post a somewhat extended version late next week (along with a more detailed explanation on how this video was produced), to coincide with the next expected VMC image set arriving from Mars.

What’s the ‘Full Orbit video’, you ask? Access the original FO video produced in 2010 for the full description.

Thanks to the Mars Express Science & Operations teams for generating a fabulous, unique-in-our-Solar-System view of the Red Planet.

Happy Birthday, Mars Express!

Ten years of the Planetary Fourier Spectrometer (PFS)

Today’s post – part of a series of reports marking the MEX 10th anniversary – was submitted by Marco Giuranna, the Principle Investigator for the PFS instrument. Marco works at the IAPS Istituto di Astrofisica e Planetologia Spaziali (INAF), Rome – Ed.

It’s been ten years since Mars Express was launched on 2 June 2003. Ten years full of exciting moments, challenges, and beautiful memories. I could never forget that moment.

It was 10 January 2004. We were all insidem a small room at the European Space Operations Centre (ESOC), Darmstadt, Germany, in the very early morning hours. It was very cold outside, something like -10°C, or even colder. All the PIs for the various instruments were in that room, together with a couple members of each science team. I was among them, as a member of the Planetary Fourier Spectrometer (PFS) team. We were all waiting for the very first observation of Mars!

At that time, Vittorio Formisano was the PI for PFS. I was only a young student. I was responsible for the calibration of PFS; in other words, I had to transform the raw data sent by the instrument into quantitative measurements of Mars.

The room was silent, with only some whispering here and there. “Will the instrument switch on? Will it work properly?” I bet everyone was wondering the same questions.

All of a sudden: sounds of keyboards everywhere, people running around talking loudly… It took me a few seconds to realize what was going on: the first data were arriving!

We checked our data… everything was OK and PFS was working well. Everyone was so happy!

Everyone, except me.

Well, it’s not that I wasn’t happy. Of course I was, but an additional challenge was awaiting me: calibration.

Will the algorithms developed in the laboratory work also for Mars? I couldn’t answer that question – I was so nervous. But the moment has come. I got the data and loaded them into the software. All I had to do was to press the ‘run’ button… and hope for the best. Click.

“Mars is warmer than the Earth!” I shouted.

Single PFS measurement of Mars acquired during the very first set of observations around the equator, January 2004

Single PFS measurement of Mars acquired during the very first set of observations around the equator, January 2004. The signal around 1300 cm-1 gives a first estimation of the surface temperature: 285K.

 

Yes! The calibration was successful!

The first PFS observations of the Red Planet passed over the equator, and allowed a first estimation of the temperature of the surface there: around 285 K (~12 °C), much warmer than in Darmstadt!

I was so happy, I took a screenshot of the first calibrated measurements of PFS and sent it by email to all the Co-investigators around the world. I will never forget the expression of Vittorio. After all those years of hard work, his instrument was finally observing Mars!

Since then, PFS has collected almost two million measurements of Mars, allowing analyses of its atmospheric composition, circulation and climatology: ten years of top-quality science and exciting results. Who could imagine that a little feature observed in the PFS measurements would have led to one of the ten most important discoveries of the last years, and of Mars Express: methane on Mars!

First detection of Methane with PFS. Credit: ESA/IANF/IAPS

First detection of methane (CH4) with PFS (adapted from Formisano et al., 2004. Science 306, p1758).

PFS is still operating and will continue to monitor the Martian atmosphere for new, exciting results.

Happy Birthday, Mars Express!

Mars in a Minute: What happens when the Sun blocks our signal?

Well, not ‘our’ signal  – this is in fact a NASA video referring to what happens when their Curiosity rover’s signal gets blocked. But precisely the same thing happens with ESA’s Mars Express, which happens regularly (see previous reports in ESA web here).

But we love this nifty JPL video that illustrates the situation in a fun and humours way – and wanted to make sure you saw it, too!

Malargüe station mosaic

A mosaic depicting ESA’s new 35m deep-space tracking station at Malargüe, Argentina, composed of several hundred low-resolution Visual Monitoring Camera (VMC) images acquired by Mars Express.

Malargüe station mosaic

On 18 December 2012, the station downloaded a VMC image from Mars Express orbiting some 328 million kilometres from Earth to mark the station’s formal inauguration and the symbolic transmission of ‘first data’. The image was received at ESA’s European Space Operations Centre, Darmstadt, Germany, and processed by the Mars Express mission operations team.

Photo mosaic generated using AndreaMosaic, an excellent piece of software!