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

First data via Malargüe station: Mars as seen by VMC

Marking its inauguration, ESA’s Malargüe tracking station receives Mars Webcam image.

First data via Malargüe station: Mars as seen by VMC

An image of the enigmatic Red Planet acquired by ESA’s Mars Express on 15 December 2012 was downloaded via ESA’s new tracking station in Malargüe, Argentina, symbolising ‘first data’ and recognising formal inauguration.

Details on the station's inauguration via ESA web and ESA media.

Mars rover gets instructions daily from NASA via a network of antennae

Nice article today in WaPo:

Brian van der Brug/AP - Activity lead Bobak Ferdowsi

Brian van der Brug/AP - Activity lead Bobak Ferdowsi, who cuts his hair differently for each mission, works inside the Spaceflight Operations Facility for NASA's Mars Science Laboratory Curiosity rover at Jet Propulsion Laboratory (JPL) in Pasadena, Calif. on Sunday, Aug. 5, 2012.

To get its messages to Earth, Curiosity first sends information to a pair of orbiters, Odyssey and Reconnaissance, that were sent in 2001 and 2005, respectively, to analyze Mars from a distance and are constantly circling the planet. (The Mars Express orbiter, operated by the European Space Agency, is also available if necessary.) The antennae on the orbiters are more than 1,300 times as powerful as the antenna on Curiosity. The rover waits for the orbiters to pass overhead to ship its messages, usually around 3 p.m. and again at 3 a.m.

Access full text via Washington Post


Mars Express to relay first science data from Mars Curiosity

This weekend is shaping up to be a big one for ESA/NASA interplanetary cooperation!

Early on Saturday morning, 6 October, central European time, ESA's Mars Express will look down as it orbits above the Red Planet, lining up its Lander Communication System (MELACOM) antenna to point at NASA's Mars Curiosity on the surface.

Mars Express Credit: ESA

Mars Express Credit: ESA

For 15 minutes, the NASA rover will transmit scientific data up to MEX, which will store it on board for a time. Then, two hours later, MEX will line up again, this time pointing its High Gain antenna toward Earth to downlink the precious information to the European Space Operations Centre (similar in role and function to NASA/JPL, but without the glorious California weather - Ed.), Darmstadt, Germany.

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.
Credits: ESA

The signal will be received via ESA's 35m deep space station at New Norcia, Australia, and the data will be immediately made available to NASA/JPL for routine processing.

The inter-Agency communication relay service will send, for the first time, actual scientific data from Curiosity via Mars Express; the previous relay services provided to Curiosity have transmitted either so-called 'open-loop' signals (no data decoded but did include useful radio Doppler information) during Entry, Descent, and Landing, or only housekeeping data and other basic telemetry during early surface operations.

"The command stack to order MEX to slew and point its UHF antennas towards Mars Curiosity during the overflight, to switch the MELACOM radio ON/OFF and to later perform the data download are already programmed on board Mars Express. Our spacecraft is ready to go for this weekend," Mars Express Operations Engineer Olivier Reboud told me this earlier today.

Curiosity - Robot Geologist and Chemist in One! Credit: NASA/JPL-Caltech

This artist's concept features NASA's Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life. Credit: NASA/Caltech-JPL

Now here's the really interesting bit: of all the data that Curiosity might be sending up for relay via MEX (Mars Curiosity carries 10 science instruments plus a drill), it looks as though we'll be handling at least some images!

According to a note sent by NASA's Jennifer Maxwell, at JPL, yesterday, the Mars Express team are expecting to relay:

  • Two images from the Remote Micro-Imager (RMI) of the 'RockNest_3' rock acquired on Sol 57 (57 martian days since Curiosity landed, i.e. 3 October)
  • Three images acquired by the Mars Hand Lens Imager (MAHLI) system of the rock named 'Bathurst Inlet'

(See a previous view of Bathurst Inlet via the Mars Curiosity image page at JPL)

The RMI provides black-and-white images at 1024X1024 resolution in a very narrow 1.1-degree field of view. This provides images equivalent to a 1500mm lens on a 35mm camera. Wow!

'Bathurst Inlet' Rock on Curiosity's Sol 54, Close-Up View Credit: NASA/JPL-Caltech/Malin Space Science Systems

This is the highest-resolution view that the Mars Hand Lens Imager (MAHLI) on NASA's Mars rover Curiosity acquired of the top of a rock called "Bathurst Inlet." The rover's arm held the camera with the lens only about 1.6 inches (4 centimeters) from the rock. Credit: NASA/JPL-Caltech/Malin Space Science Systems

MAHLI comprises a camera mounted on a robotic arm on the Curiosity rover, which is used to acquire microscopic images of rock and soil (a typical MAHLI image resolution is a stunning 21 microns per pixel).

The weekend relay will provide further operational confirmation that Mars Express can serve as a back-up relay platform for NASA's new rover; it has already done so for NASA's other surface missions (Phoenix and the Mars Rovers, Spirit and Opportunity) in the past couple of years.

This cross-support underscores the strong cooperation between the two Agencies, who have worked diligently for a number of years to set technical and engineering standards to enable sharing data, information and telecommand links between spacecraft, networks, ground systems and ground stations, which helps reduce risk and boost back-up capabilities in both directions.

In ESA's MEX team, everyone's really looking forward to the first 'science contact' with Curiosity – which, as mentioned in a previous post by Thomas Ormston, should provide more "proof that the amazing new rover from the United States can talk with our veteran European Mars orbiter!"

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.

Melacom – Europe’s voice & ears at Mars


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

When Curiosity lands on Mars, the radio receiver on Mars Express which will be listening in is Melacom. This radio was developed for Mars Express by the UK company, QinetiQ in order to support the Beagle-2 lander which was carried on Mars Express.

Sadly the Beagle-2 lander failed to land successfully, but the Melacom lander communications package was not wasted and has been used to contact every single Mars lander to successfully land since the Mars Express launch in 2003.

Mars Express has a large X-Band and S-Band radio system that lets it talk to Earth, but Melacom was specially designed as a separate UHF radio system to let it talk to landers on the surface of Mars. The radio supports a number of different modes, including the ability to hold a two-way data communication with a lander and the open loop mode we described earlier. It implements a standard known as Proximity-1, developed by CCSDS - an international committee that works on standards such as this to ensure that any spacecraft can talk to any other, such as the European Mars Express and the American Curiosity [more details on the excellent work done at CCSDS by ESA, NASA and other agencies here - Ed.].

Melacom Communications System Installed On- board Mars Express

Another shot of Melacom after installation on Mars Express, taken while the spacecraft was being built.

The radio has been used successfully many times, including open loop recording of JPL's Phoenix lander as it landed on Mars in 2008.

In preparation for the arrival of Curiosity, our in-flight testing intensified and we've conducted a number of demonstration passes with NASA's Opportunity Mars Exploration Rover, operated by JPL. During these passes we demonstrated the ability of spacecraft from two agencies to coordinate and work together at Mars, exchanging telemetry data and commands and conducting recordings.

In anticipation of the arrival, a team from QinetiQ also took a test model of the Melacom radio to JPL to perform ground compatibility testing with a similar model of the Curiosity radio. Through all of these activities, we're confident that we'll all be speaking the same language at Mars when Curiosity arrives tomorrow.

To learn a lot more in depth information about the Melacom radio and our support of the Curiosity mission using it, take a look at this conference paper by our Melacom engineer, Olivier Reboud.

What is Open Loop Recording?

How Mars Express will listen to Curiosity

3-D waterfall diagram showing the open loop recording made by Mars Express of MER-B (Opportunity) during the rehearsal overflight for Curiosity EDL.

You'll see a lot on our coverage of the Curiosity landing about Open Loop Recording,' something which was hinted at in a previous post about the difference between 'signal' and 'data'.

OLR refers to the type of recording that will be made by Mars Express as Curiosity descends towards Mars, and in parallel by ESA's New Norcia station here on Earth.

In open loop recording, we don't try to decode the bits and bytes being sent by the descending lander but instead try and listen to as much of the radio spectrum as we can, hopefully detecting the tone of the lander's transmissions within this spectrum. Think of it like listening to a crowd of people – you can either focus on the words one person is saying, or listen to the whole crowd to get a full picture of what's going on; that's what we'll do with open loop recording.

On Mars Express we'll use our UHF Melacom radio to listen in on the UHF part of the spectrum – usually used on Earth for radio and television transmissions; it's also used at Mars as the frequency that different orbiters and landers use to talk to each other.

From New Norcia we'll be listening to the X-Band part of the spectrum – used on Earth mainly for radar systems but also as a way of communicating with spacecraft across the solar system (Mars Express uses X-Band for its main link back to Earth).

Each of these parts of the spectrum is actually a wide range of frequencies and in open loop we listen to as many as possible, creating a diagram like the one in the picture above.

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Difference between ‘signal’ and ‘data’

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

If you read the web article last week announcing the planned support by Mars Express for NASA's MSL landing on Mars  (see ESA's Mars Express supports dramatic landing on Mars), you may have come away with the impression that Mars Express will receive actual data transmitted by MSL during entry descent and landing.

As pointed out by Michael Khan, a mission analyst at ESOC, the way the article is worded is not actually wrong. However, anyone who doesn't know the technical details might get the wrong impression.

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