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.

 

Mars Express rocking and rolling with NASA’s Curiosity & Opportunity

On 19 August, Sunday evening (European time), Mars Express will start its first data relay with NASA’s Mars Curiosity rover in style by fitting in not just our first pass with Curiosity but also by ‘rolling away’ afterwards to talk with NASA’s veteran Mars rover, Opportunity.

Still Life with Rover This full-resolution self-portrait shows the deck of NASA's Curiosity rover from the rover's Navigation camera. The back of the rover can be seen at the top left of the image, and two of the rover's right side wheels can be seen on the left. The undulating rim of Gale Crater forms the lighter color strip in the background. Bits of gravel, about 0.4 inches (1 centimeter) in size, are visible on the deck of the rover. Credit: NASA

Still Life with Rover This full-resolution self-portrait shows the deck of NASA’s Curiosity rover from the rover’s Navigation camera. The back of the rover can be seen at the top left of the image, and two of the rover’s right side wheels can be seen on the left. The undulating rim of Gale Crater forms the lighter color strip in the background. Bits of gravel, about 0.4 inches (1 centimeter) in size, are visible on the deck of the rover. Credit: NASA

This will be the first time in the history of the Mars Express mission where this double lander contact has been attempted within a single orbit of the spacecraft (1 orbit around Mars for Mars Express lasts around 7 hours).

As the spacecraft approaches the planet it will turn away from Earth and ‘roll’ over the top of Curiosity’s new home in Gale Crater, keeping the Melacom antennas pointed directly at the new rover.

After this contact, Mars Express will turn back to Earth briefly and then spin away again, performing the same ‘Spot Pointing’ manoeuvre for Opportunity as Mars Express flies over its location in Endeavour Crater. This double relay will be an exciting test of the capabilities of Mars Express, both in relay terms and in pointing, and to not only prove our communication capability with the new (and fantastic!) Curiosity rover but also to continue our commitment to its predecessor – the venerable Opportunity rover.

A Digital Opportunity Rover on Mars Credit: Mars Exploration Rover Mission, Cornell, JPL, NASA Rover Model: D. Maas - Synthetic Image: Z. Gorjian, K. Kuramura, M. Stetson, E. De Jong.

A Digital Opportunity Rover on Mars Credit: Mars Exploration Rover Mission, Cornell, JPL, NASA Rover Model: D. Maas – Synthetic Image: Z. Gorjian, K. Kuramura, M. Stetson, E. De Jong. Via http://apod.nasa.gov/apod/ap051214.html

The past weeks have seen intense cooperation between NASA and ESA to coordinate and plan these activities, which are intended as demonstrations of the relay capabilities of Mars Express. The overflight of Opportunity will be part of a long-standing activity to periodically check the ability of Mars Express to relay data from Opportunity, if ever needed.

Many of these overflights were done leading up to the landing of Curiosity to cement the technical ability of the two agencies to work together on planning routine relay operations. The overflight of Curiosity will be the first time that Mars Express and Curiosity have actually ‘talked’ to each other.

During the landing of Curiosity, Mars Express only listened in and recording the radio signal of Curiosity, but Sunday evening, 19 August, the two spacecraft will actually have a ‘conversation’ and for the first time Mars Express will receive and decode actual data from the lander.

We’re confident in the ability of the two spacecraft to be able to communicate for several reasons – the main one being that both implement an international standard called Proximity-1 [this is mentioned in our earlier Melacom post – Ed].

This standard was designed to make sure that even though the spacecraft come from different manufacturers and different agencies, the way they talk to each other is still the same – it can be thought of like an ‘agreed common language’.

On top of this, is our extensive experience relaying data for Phoenix, Spirit and Opportunity and the fact that a team from QinetiQ (who built our Melacom radio) travelled to JPL to test a copy of it with a copy of the Curiosity radio. However, any new activity in space is challenging and we stand ready at ESOC to investigate, analyse and improve – optimising our ability to support the Curiosity mission for NASA.

All of this will allow Mars Express to make a call to Curiosity in Gale Crater and between the spacecraft agree autonomously to exchange data. Curiosity will send back data that will be decoded by Mars Express and stored ready for forwarding to Earth; then we’ll quickly reset and prepare a very similar activity for Opportunity in Endeavour Crater.

Next, on Monday morning, Mars Express will send the data to ESA’s 35m New Norcia (Australia) ground station and then from there it will make its way to ESOC and on to the control room at JPL.

The data’s journey will be long (Gale Crater/Endeavour Crater -> Mars Express -> New Norcia, Australia -> ESOC, Germany -> JPL, USA) but we’ll make sure it arrives safe and sound – proving the ability of Mars Express to support communications with both Curiosity and Opportunity whenever needed.

We’ll post more details when we know the results of the test and can hopefully announce on Monday that Mars Express has been ‘qualified’ as a really-long-distance relay for Curiosity – expanding the network of spacecraft and cooperation at Mars in spectacular style!

Time delay between Mars and Earth

Spacecraft event time vs. Earth receive time

Mars Express Light Time Delay Display

A photo of the Mars Express delay display on the control system, showing us the critical numbers of one-way light time, two-way light time and the distance from Earth.

One of the most difficult things about operating a spacecraft around Mars (not to mention the different time zones), compared with the Earth, is that it’s so far away!

Mars is so far away in fact that it takes radio signals quite a long time to get from the spacecraft back to Earth. During Curiosity EDL, this delay will be 13 minutes, 48 seconds, about mid-way between the minimum delay of around 4 minutes and the maximum of around 24 minutes.

This makes it a challenge to operate Mars Express because it’s hard to have a conversation with the spacecraft, or react if anything happens on board. If there is a problem and the spacecraft tells us, we won’t know for 13 minutes, and then even if we react straight away it’ll be another 13 minutes before our instructions get back to Mars – there’s a lot that can happen in half an hour at Mars (for example a whole Curiosity landing)!

To keep Mars Express flying safely, we load all the commands for the mission in advance and built in lots of autonomy to let the spacecraft take care of itself – you could say that for the Curiosity landing we’re running completely on autopilot!

The delay is nothing to do with the spacecraft or the hardware on the ground – it can’t be improved by a faster computer or a more powerful radio. In fact it is obeying the fundamental speed limit of the universe – the speed of light.

At 1,079,000,000 km/hour, light is pretty quick; you could get from here to the Moon in a little over a second! But that just underlines how far away Mars is.

All light (or electromagnetic radiation, which includes radio signals) travels up to this speed, and radio waves from Earth to Mars Express and back are no exception. Take a look at the Wikipedia article on the speed of light and you’ll see how, in 1905, Einstein came upon the concept of this cosmic speed limit.

Above all, for tomorrow’s coverage of the Curiosity landing it makes it challenging for us to work out when to tell you what’s happening (as you’ve seen in our three column timeline)!

At ESOC, we talk about two different times – Spacecraft Event Time (SCET) and Earth Received Time (ERT). The former is what’s actually happening at Mars right now, although we won’t hear about it until over 13 minutes later, a time we call ERT.

The delay between the two is usually called the One-Way Light Time (OWLT) and the time for a message to go to Mars and come back is the Two-Way Light Time (TWLT), or round-trip time.

During all our coverage we’ll follow NASA’s lead and generally communicate events here and on Twitter to you in ERT because that’s when we’ll actually know what’s happened. If we do communicate something in SCET we’ll let you know so you (and us too) don’t get confused – it’s all part of the fun of exploring the Solar System!

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

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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What time is it?

How we solve the problem of multiple time zones

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

World time zones

World time zones

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

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

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

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

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

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

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

 

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

Link

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” (http://eyes.jpl.nasa.gov/).

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!

Animations: Mars Express supports Curiosity

As spacecraft operations engineers we’re used to operating without being able to see what we’re doing – we rely on the telemetry data from the spacecraft: numbers, statuses, bits and bytes to find out what’s happening. However, with something as big and complex as supporting an incoming lander it helps to see what’s going on, like this great Celestia simulation of Mars Express as it turns and tracks Curiosity down to the surface of Mars:

To learn more about this video, and what it shows, click ‘Continue’ to read on…

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Commands away!

Mars Express has now been almost fully prepared for the upcoming arrival of MSL! This week’s Spacecraft Operations Coordinator, James Godfrey, has confirmed that all the commands to Mars Express for the MSL tracking activities have been transmitted to Mars.

Two clicks (and a lot of background work!) was all it took to start the command file transmission to Mars Express. At 11:04 CEST our Spacecraft Controller at ESOC hit the ARM button then the GO button and the commands began their journey to Mars. Take a look at the video above to see the commands flying off our control system.

From the control system at ESOC they were sent around the world to our deep space antenna at New Norcia, Australia, and from there they were modulated onto a radio signal and blasted with 10 kilowatts (that’s like 10,000 mobile phones all calling at once!) from the antenna toward Mars.

Their journey of 245,750,000 km took 13 minutes and 39 seconds. Once they arrived, Mars Express turned the radio signal back into bits and bytes and stored it on the spacecraft.

The whole command file contained all the instructions for Mars Express to follow over the next week of operations, including the critical instructions to the spacecraft to perform ESA’s support of the MSL landing with Mars Express. These commands will wait on the spacecraft’s on-board memory (its ‘hard drive’) and then execute automatically according to the schedule we created here on Earth.