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.


Fabulous view of Mars 15 May 2014

Today's post contributed by Michael Khan at ESOC. UPDATED 8.04 – corrected date for Mars & Spica to 17.07, and fixed several minor typos  – Ed.

Once again, it's opposition time. While the Earth requires one year1 to complete a full revolution, a Mars year, due to the planet's wider orbit, lasts 687 days. As Earth and Mars are plying their separate orbits with different speeds, the distance between each varies considerably with time. But once in a period of just over two years, they are aligned in what astronomers call an opposition. On that date, seen from Earth, Mars is located almost exactly in the direction opposite from the Sun, so stargazers can see the Red Planet high in the sky at midnight, and closer and brighter than at any other time.

Earth-Mars distance

The distance from Earth to Mars during the years 2000 to 2019

Because the Mars orbit is eccentric (i.e., it is elongated rather than circular), not all oppositions are equal. Many of you will remember the one in the autumn of 2003, when Mars approached Earth to as close as 56 million kilometres. It appeared like a surprisingly bright red star. In 2014, opposition will take place on 8 April, but again because of the eccentricity of the orbits, closest approach will in fact be a few days later, on 14 April. The distance from the Blue to the Red Planet will then be 92 million kilometres – two-thirds more distant than in 2003, so Mars will appear only a third as bright as it did 11 years ago.

Admittedly, observing Mars in the night sky is a lot less spectacular than it was, and it will again be, as soon as the year 2018. But still, you should have a look. It's impossible to miss, all the more so because right now it is close to the star Spica in Virgo; Spica is special, because it is in fact not one, but two stars – and big ones at that – that are orbiting a common centre of mass at very close quarters. Spica is interesting, it's massive, it's bright... and it's blue! So you currently have the brilliant blue Spica and the brilliant red Mars both in approximately the same direction in the sky.

Surely you don't need any more coaxing than that to get you to do some stargazing  – or do you? All right then... let's see which celestial bodies Mars will encounter in the course of the year. (Of course, we are talking about apparent encounters only, where the bodies involved appear to be separated by only a small angle. In terms of actual spatial distance, the distances will still be 'astronomical', with the exception of comet C/2013 A1 Siding Spring, which will buzz Mars on 19 October 2014. But as avid readers of our blog, you already know that).

Here is a list of star parties to which Mars has been invited this year. You are welcome to join – no need to feel like a gate crasher. All these events will be easily visible to the human eye. Using a pair of binoculars or a telescope is optional, but not mandatory.

On 14 April, the full Moon encounters Mars and Spica

On 14 April, the full Moon encounters Mars and Spica

This is an easy one for starters. And what's more, it happens on the day, 14 April, when Mars is closest to the Earth. Directly in the south around midnight (all times in the star charts below are given in GMT) the full Moon will intrude between Mars and Spica.

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10 years of imaging Mars

Today's post – part of a series of reports marking the MEX 10th anniversary – was submitted by the Mars Express imaging team at Freie Universität Berlin - Ed.

Who would have thought, 10 years ago, that the brave MEX spacecraft would be still alive today?

For 10 years, the High Resolution Stereo Camera (HRSC) onboard Mars Express has provided astonishing images of the surface of Mars in colour and in 3D. From the beginning on, the breathtaking colour images from Mars delighted both the public and the scientists.

For scientists, the Digital Elevation Models (DEMs) derived from the stereo images provided a major step forward in the precise analysis of the martian surface, and the wide and long image swaths give excellent overviews of the terrain and its geological context.

HRSC image of Valles Marineris, the Solar System's grandest canyon!
Credits: ESA/DLR/FU Berlin (G. Neukum)

The public also made use of the HRSC data, not only from our Press Archive where the best images of the returned data are presented, but for example also using HRSC data in the Google Earth-Mars interface. Bit by bit, Mars turns into HRSC colour. Very much appreciated were also the HRSC-movies, created with the Digital Elevation Models and including, for example, a fly-through of the "Grand Canyon" of Mars, Valles Marineris.

Throughout the last decade the HRSC team has recorded 95.5% of the martian surface at a resolution of 60 m/pixel or better and 66.8% with a resolution of 12.5-20 m/pixel.

Due to the elliptical orbit of Mars Express, major challenges had to be mastered concerning the processing of the data and the photogrammetry. Furthermore, much patience was required due to dust-storms and clouds in the atmosphere, which reduced the data quality. Therefore, several regions were targeted multiple times.

Comparing the first images recorded by HRSC with those acquired today, there is no question that with improved image processing techniques the quality of image and DEM products have very much improved over the past 10 years .

The success story of Mars Express continues and we look forward to fully image the Red Planet with HRSC at highest resolution.

Happy Birthday Mars Express!!

Student of Mars

Today's post – part of a series of reports marking the MEX 10th anniversary – was submitted by planetary geologist Damien Loizeau, who is on the hunt for water on Mars - Ed.

Damien Loizeau

I got involved in Mars Express when I started my PhD. Mars Express had been in orbit for a bit more than a year, the first results had just been published, and lots of new and exciting data were transmitted every week. Now I am part of two instrument teams for the mission: OMEGA, the imaging spectrometer, and HRSC, the high resolution stereo camera.

I work on the geology of the surface of Mars and these two instruments are perfect to study it. OMEGA helps us to determine the mineralogy of the surface, that is, the composition of the rocks, and we try to understand the age and the formation of the geological units with HRSC.

It was the first time that we had such a large dataset to understand the geology of Mars, and I was starting my scientific career inside this flow of new discoveries.

I could meet many of the leading European and American Mars scientists during the Mars Express instrument team meetings, where the most recent discoveries were presented and discussed. I also had the chance to work directly with the principal investigators of OMEGA and HRSC, in Orsay (France) and Berlin (Germany), respectively.

My first focus was on identifying minerals formed with liquid water. Liquid water is crucial for life on Earth, and it’s of utmost importance to evaluate if Mars was habitable, and if life had a chance to develop there. We mapped clays in different regions of Mars with OMEGA. On Earth, clay minerals mainly form over long periods by the interaction of rocks with liquid water. With the help of the orbiting high resolution cameras like HRSC, we observed that almost all the clay detections corresponded to rocks formed in the very early Martian history. This is a major sign of the drastic climate change that the Red Planet suffered more than 3 billion years ago.

I had the opportunity to make the map below for one of the Mars Express press conferences to illustrate our work, and I have been very happy to see it circulating on the web and in conferences for many years since.

Perspective view of clay-rich rocks (blue) on the old plateaus around the valley of Mawrth Vallis (left) and the crater Oyama (centre), made from a compilation of OMEGA, HRSC and MOLA (NASA Mars Global Surveyor) data. Credits : ESA/OMEGA/HRSC

Lately I had the opportunity to work for two years in one of ESA’s centres – ESTEC – in the Netherlands. I could follow more closely the missions with the scientists in charge of them, and the future projects like ExoMars. It was quite different from the academic world, with lots of new acronyms to remember!

Today, with the help of the instruments of the NASA Mars Reconnaissance Orbiter, we are discovering the diversity of environments were liquid water has been present in the past on Mars, not only at the surface, but also at kilometre depths. But there is still a lot to discover both within the datasets from the spacecraft still in orbit around Mars, and from future missions. Exciting times lie ahead!

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.

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!

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.


Experience MSL Landing with ‘Eyes on the Solar System’ from JPL


If you liked our animations of Mars Express tracking the landing of MSL then you can watch it live or preview it yourself with a great website from JPL called "Eyes on the Solar System" (

You can see all the different stages of the entry, descent and landing of Curiosity and control the camera and speed yourself to experience the landing in every way possible!

ESA, NASA, Parkes: Big ears on Earth will listen to MSL descend

Editor's note: We're delighted to post this update on the international, behind-the-scenes cooperation to implement the MSL 'ground listening' campaign. It highlights the hard work, months of preparation and terrific cooperation between ESA, NASA and international partners on a technical, operational and interpersonal level. Thanks to NASA's Susan Kurtik and ESA's Wolfgang Hell for kindly providing information for this report.

On 6 August, ground stations and a radio telescope operated by multiple nations will be listening to signals from NASA's MSL mission as it descends through the Martian atmosphere to deliver the Curiosity rover safely onto the Red Planet's surface.

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 stations involved are all in the Land Down Under, since that's the bit of Earth that will be facing Mars at around 01:00 CEST next Monday morning, as MSL approaches its nail-biting plunge into the Mars atmosphere to touch down in Gale Crater.

During this crucial phase of the mission, MSL will transmit two radio links – one direct to Earth in X-band, which is also being used  for routine telecommanding during the cruise to Mars, and a ‘proximity link’ in the UHF band for direct communication with spacecraft orbiting Mars.

To get a good idea of the importance of the ground campaign, let's first look at the in-flight tracking efforts for the proximity link.

International fleet tracks MSL from Mars orbit

"The primary monitoring of MSL's Entry, Descent and Landing – EDL – phase will be provided by two NASA spacecraft in orbit around Mars: Mars Reconnaissance Orbiter [MRO] and Mars Odyssey. These two 'platforms' will be backed up by ESA's Mars Express [MEX]," says Michel Denis, MEX Spacecraft Operations Manager and responsible for MEX tracking support to MSL at ESOC.

(See our earlier post, 'Mars Express to track 7 minutes of terror' for details – Ed.)

Odyssey is the only one of the three that can provide the so-called 'bent-pipe' (or real-time) relaying of signals and is expected to give the first indication to NASA that Curiosity has arrived; confirmation of safe landing is expected by NASA at around 07:31 CEST.

Odyssey over Mars' South Pole: NASA's Mars Odyssey spacecraft passes above Mars' south pole in this artist's concept illustration. The spacecraft has been orbiting Mars since October 24, 2001. Credit: NASA

Odyssey over Mars' South Pole: NASA's Mars Odyssey spacecraft passes above Mars' south pole in this artist's concept illustration. The spacecraft has been orbiting Mars since October 24, 2001. Credit: NASA

In contrast, MRO and MEX can only track, store and then forward recorded signals later.

Artist's concept of the Mars Reconnaissance Orbiter. Image credit: NASA/JPL

Artist's concept of the Mars Reconnaissance Orbiter. Image credit: NASA/JPL

"Only Odyssey can receive, decode and then relay to Earth the actual telemetry data coded into the those signals. Conversely, MRO and MEX will save on board 'open-loop' recordings," says Denis.

This means they will record only the spectra of the radio signals and the related Doppler variations in signal intensity, and not the encoded telemetry.

(NASA's Susan Kurtik, MSL Mission Interface Manager at JPL, adds: In fact, we will be able to extract telemetry from the MRO open-loop recording, although it will take ~8 hours to process - Ed.)

(The variations in signal strength due to the Doppler effect are explained by the rather famous ambulance siren analogy.)

Ground tracking campaign provides crucial support

Now, let's look at the ground tracking campaign, the crucial, 'behind-the-scenes' activity in support of Curiosity's arrival at Mars provided by stations on Earth.

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