[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
Melacom

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.

 

Timeline: Mars Express makes closest-ever flyby of Phobos

Find below an outline timeline for the flyby of Phobos around 29 December 2013.

Initial tracking will be provided by DSA 1, ESA's 35m deep-space ground station at New Norcia, Australia. Then NASA will provide support with two of their 70m stations, DSS-63 near Madrid, Spain, and then DSS-14 in Goldstone, California. Finally, Mars Express will be tracked again by New Norcia.


ESA's 35m New Norcia station in action

Phobos flyby timeline

13-362T 17:40:00Z New Norcia (NNO) station starts tracking Mars Express
13-363T 01:30:00Z DSS-63 acquires the signal from MEX
13-363T 03:21:52Z DSS-63 takes over as primary station
13-363T 03:44:05Z NNO stops tracking MEX
13-363T 07:09:00Z Mars Express – closest approach to Phobos (45km from surface)
13-363T 07:20:35Z Signals from closest approach reach Earth (due to the one-way light time)
13-363T 08:55:00Z DSS-14 begins tracking MEX
13-363T 11:02:50Z DSS-14 takes over as primary station
13-363T 11:25:00Z DSS-63 stops tracking MEX
13-363T 17:06:02Z NNO begins tracking MEX
13-363T 18:37:53Z NNO takes over as primary station
13-363T 19:00:00Z DSS-14 stops tracking MEX
13-364T 01:12:30Z The transmitters on MEX start switching off; flyby 'mission' ends

This timeline was taken directly from the operations plan used by the MEX flight team at ESOC; the '13-262' and '13-263' annotation simply refers to the year and day of the year. So, 362 is 28 December, 363 is 29 December and so on. 'Z' time (Zulu-time) refers to GMT time; CET time is +1 hour. All times subject to change.

Tracking stations

The station coverage must be uninterrupted (except during occultation by Mars) for the entire 35-hour period of the flyby mission. Therefore, an overlap in coverage between stations has been intentionally planned so as to be able to detect and eliminate any inaccuracies due to the stations themselves.

"This overlap imposes a very specific handover procedure between the ESA Estrack and NASA DSN networks; this handover has been rehearsed numerous times with the actual ground stations," says Michel Denis, the MEX Operations Manager at ESOC.

The sequence of station hand-over – from ESA to NASA to ESA – makes this a truly international, intercontinental, inter-agency endeavour!

Michel also points out that the use of NASA's 70m stations is critical to the accuracy of the measurements. "We'd like to thank our US colleagues for the provision of some very specific station passes; this is due to the very cooperative efforts of the DSN station scheduling team."

NASA 70m tracking station. Credit: NASA

NASA 70m tracking station. Credit: NASA

Should any of the station listed above become unavailable at the last minute, a backup has been booked in advance using ESA's 35m Estrack stations, which could take over to 'save' the Phobos flyby; this would incur a penalty in reduced measurement accuracy.

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.

 

Melacom – Europe’s voice & ears at Mars

Melacom

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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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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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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