Science

How a Telescope in Maharashtra Helped Track the Fate of ExoMars Lander

“GMRT is a world-class instrument, recently upgraded with new receivers, and was able to detect the very faint signal” coming from the ultimately doomed Schiaparelli EDM lander on Mars.

The GMRT (Giant Metre-wave Radio Telescope), NCRA. Credit: National Centre for Radio Astrophysics/Tata Institute of Fundamental Research

The GMRT (Giant Metre-wave Radio Telescope), NCRA. Credit: National Centre for Radio Astrophysics/Tata Institute of Fundamental Research

In December 2003, a British mission to Mars called Mars Express was nearing the red planet for the final part of its journey. It consisted of two parts: the Mars Express Orbiter, which would get into orbit and study the planet’s surface and subsurface composition and atmosphere; and the Beagle 2 lander, a set of instruments that would drop to the surface, remain stationary and make measurements of their own. The deployment was supposed to happen on December 19 – and it did. By December 25, the Mars Express Orbiter was in an elliptical orbit around the planet and began its observations. However, even by February 2004, mission scientists didn’t know what had happened to Beagle 2.

In fact, they wouldn’t know until 12 years later, when NASA’s Mars Reconnaissance Orbiter spotted the lander sitting intact on Mars’s surface. Scientists hadn’t been able to contact Beagle 2 because two of its solar panels hadn’t fully unfurled, blocking the antenna.

Since the 1960s, scientists have had bad luck with Mars landers, especially in the late 1990s. However, in all this time, they haven’t equipped landers with radio antennae that transmit data as the craft descends to the surface, instead choosing to rely on the communications antenna that comes online only after the lander has landed healthily. Before the Beagle 2 failure in 2003, there was NASA’s Mars Polar Lander failure in 1999, whose fate hasn’t been confirmed still. And after Beagle 2, there was the Schiaparelli lander of the Euro-Russian ExoMars mission on October 19 this year. Though the ExoMars Trace Gas Orbiter got into Mars orbit comfortably, the lander appears to have crashed on the martian surface.

This time, however, there was confirmation – as well as live transmission as the lander descended, thanks to the world’s largest telescope of its kind located in Maharashtra, India.

A world-class telescope

The National Centre for Radio Astrophysics (NCRA) to the city’s north is home to the aptly named Giant Metre-wave Radio Telescope (GMRT). Built at $20 million and going operational in 1995, the GMRT is actually an array of 30 telescopes each observing radiation coming in from space with a wavelength in the order of metres – or radio-frequency. The telescopes rely on a technique called aperture synthesis to make their studies. The larger a telescope’s antenna is, the higher the resolution with which it can observe its targets. Aperture synthesis allows multiple telescopes to act as a single giant antenna, where the size of the antenna is the distance between the most separated telescopes in the network. In the case of GMRT, this is 25 km.

There is no telescope bigger than the GMRT when it comes to observing in the metre wavelength, which corresponds to radio waves. It is often used to study distant galaxies, blackholes, quasars and other high-energy cosmic objects billions of lightyears away. And because of its sensitivity, the GMRT can also be used to detect faint radio signals coming from objects closer to Earth – for example, a lander descending on Mars.

“It wasn’t that the technology didn’t exist,” Jonathan McDowell, an astrophysicist at the Centre for Astrophysics at Harvard University, told The Wire. “In the earlier landing failures, there was no live radio link with Earth. I think this was mostly to save money. They didn’t put a transmitter on the probes that was strong enough to reach Earth.” However, after the failures in 1999 and 2003, it became imperative to be able to understand how landers failed so frequently. “After those losses, people realised it was a very bad idea not to have a radio link, you just don’t know what went wrong if it failed.”

In the case of the Schiaparelli lander of the ExoMars mission, scientists found that a software glitch could have forced the lander’s parachute to separate sooner than necessary, causing the lander to crash at 300 km/hr. This information wouldn’t have been available now if not for the GMRT.

In fact, scientists have also noted a difference between data received at the GMRT and that collected by probes orbiting Mars when Schiaparelli stopped working, and are currently following this up.

The GMRT experiment

The Schiaparelli lander had been equipped with an ultra-high frequency (UHF) radio onboard to allow it to communicate with orbiters currently around Mars; the orbiters would’ve then relayed the signal to receiving stations on Earth. But with the ExoMars mission, scientists wanted to experiment with the GMRT – even though Schiaparelli’s UHF radio wasn’t powerful enough to transmit all the way to Earth, a distance of 54 million km, the telescope seemed sensitive enough to be able to pick that up.

According to Thomas Ormston, a spacecraft operations engineer at the European Space Operations Centre in Darmstadt, Germany, “In practice testing during Schiaparelli separation from the [ExoMars orbiter], we did see the weak trace of the signal from the lander at GMRT” with only 18 telescopes in the array available at the time. Ormston also wrote that there had been some concerns during the descent phase that GMRT might not receive the signal if Schiaparelli’s radio was facing away.

McDowell clarified that “the amount of radio interference in [the radio] waveband is lower in Maharashtra than in some other parts of the world where there are radio telescopes”. According to the NCRA, which operates the GMRT, “Manmade radio interference is considerably lower in this part of the spectrum in India.”

Separation of EDM from TGO as detected at GMRT, Pune, on 16 October 2016. Caption: Thomas Ormston/ESA. Credit: GMRT/NASA/JPL

Separation of EDM from TGO as detected at GMRT, Pune, on 16 October 2016. Caption: Thomas Ormston/ESA. Credit: GMRT/NASA/JPL

Good for Russia and India

Moreover, the ExoMars mission is being conducted in two phases. The first just finished while the second begins in 2020, when the European Space Agency (ESA) and its Russian counterpart Roscosmos will jointly deploy a rover on the martian surface. Knowing now as to what killed the lander, as opposed to 12 years down the line, will be of great help in lowering the rover properly. “GMRT is a world-class instrument, recently upgraded with new receivers, and was able to detect the very faint signal,” McDowell explained. “That signal will help engineers study the ExoMars EDM lander’s descent, both seeing how well the bits that work did work and seeing what went wrong with the bits that didn’t.”

According to people familiar with the upgrades, NASA’s Jet Propulsion Laboratory in Pasadena, California, helped equip GMRT with the special receivers.

That the GMRT experiment was a success is also good news for Russia as well as India. Between 1960 and 1988, the USSR participated in 17 missions to Mars; and between 1996 and 2016, in three (including Schiaparelli). And in these 20 missions, the Russians have found success only in two missions – the last time in 1973. Even then, the Mars 5 mission lasted just nine days against its planned lifetime of at least one year. In fact, the USSR/Russia’s last successful interplanetary expedition was the Vega program to Venus, followed by a flyby of Halley’s comet, that concluded in 1985.

Though ESA has declared the Schiaparelli part of the mission a success (because it did demonstrate that its way of landing almost worked), its landing gear was built by Russian engineers, the same people who will be responsible for landing the rover in 2021. With GMRT data – as McDowell said – they will know now what bits worked and what didn’t.

As for India: the Indian Space Research Organisation (ISRO) plans to launch a rover as well as a lander on Mars between 2020 and 2022, in a mission it has called Mangalyaan 2. As with the previous mission, which succeeded in September 2014 when the Mars Orbiter got into orbit around Mars, the rover and lander may also be successful on ISRO’s first try. And the GMRT could play an important role in ensuring that.