GMRT

The second phase of the GMRT upgrade draws popular response from the global user community

From 15th October 2016 onwards, the 2nd phase of the upgraded GMRT (uGMRT) started real observations, following proposals that were submitted in July. We are happy to announce that this time allocation cycle was oversubscribed by a factor of more than 3, indicating the widespread interest of the user community in the capabilities of the uGMRT. In addition to the 2 of the 4 new wideband systems that are now equipped on all the 30 antennas of the GMRT (as reported in the last eNews edition), the exciting new band that is beginning to get populated on all the antennas is the Band-4 (550 to 900 MHz) system. Sample spectral line results from this new band of the uGMRT, obtained with just a few antennas, are shown in the figure — clearly, this promises exciting new science in the future when it is completed on all 30 antennas! Full use of the uGMRT is expected to provide a significant stepping stone towards science with the SKA-1.

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Figure 1: Expected sensitivity performance of the upgraded GMRT compared to other major facilities in the world, present and projected (courtesy: Nissim Kanekar, NCRA)

Tracking ESA’s Schiaparelli Mars lander module with the GMRT

About 2 years ago (September 2014), members from JPL/NASA contacted GMRT/NCRA to explore if GMRT could provide ground support for NASA’s Mars lander (Insight mission) then scheduled around September 2016 (& also a similar European Space Agency, ESA’s, ExoMars mission to Mars scheduled thereafter in which also the JPL team were collaborators). The primary need for GMRT was to detect the feeble radio frequency signal (sine wave carrier frequency at ~ 400 MHz) transmitted by the ‘lander’ module that will be injected by the Mars ‘orbiter’. The lander’s trajectory from the ‘orbit’ around Mars to the surface of Mars lasts for about 8 minutes. During this phase of the ‘lander’, the only method of monitoring its health / satisfactory movement / trajectory is through detection of the beacon radio signal (at around 400 MHz) and its motion inferred from comparing the observed radio frequency with that expected due to the Doppler shift.

The JPL team had explored 3 possible options for ground based support from radio astronomy facilities which would have visibility for the event: Effelsberg (Germany), Jodrell Bank (UK) and GMRT, and concluded that the GMRT is the best option given its high sensitivity and significantly reduced risk of radio frequency interference (RFI) affecting the radio detection. Although the 400 MHz frequency was not covered by the legacy GMRT receiver system available then, the new upgraded GMRT system (under mass production) covers this frequency. At that point of time when this discussion initiated, very few GMRT antennas had this new receiver system installed – but this was expected to grow with time.

Then on the evening of 19th October 2016, the GMRT added a unique feather to its cap of achievements by successfully detecting the weak UHF radio signals emitted by the Schiaparelli space probe of the ExoMars project, as it made its descent through the atmosphere of Mars. Before that, it also confirmed the successful separation of the Schiaparelli from its parent orbiter (the TGO) on 16th October.

The Schiaparelli Entry and Descent Module (EDM) of the ExoMars project separated from the parent spacecraft – the Trace Gas Orbiter (TGO) – on Sunday, 16th October after a 7 months’ journey from Earth to Mars, and followed a trajectory that brought it to the point of entering the Martian atmosphere for a landing, on the evening of 19th October. The 6 minutes’ journey through the atmosphere is the most hazardous part of the project, and many previous Mars lander missions have failed at this critical juncture. In order to monitor the health of the EDM during this crucial phase, NASA (on behalf of the ExoMars project collaboration) requested the GMRT to act as a receiver station for this mission. The signal, at the frequency of 401 MHz, is very weak – emitted by a 5 W transmitter on the EDM; and it required the high sensitivity and interference free environment of the GMRT to be able to detect it. The receivers covering this frequency have been developed by NCRA as part of the upgrade of the GMRT, are were ready well in time for this mission. The detection was made possible by adding the signals from the GMRT antennas and analysing it with special signal processing software that was developed jointly by GMRT team members and JPL team members from NASA. The system was tested during August – September, with similar test signals generated by the Mars Rover of NASA that is already exploring the surface of the planet and GMRT was successful in detecting these test signals.

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On 19th October evening, the GMRT was able to clearly detect and track the weak signal from the Schiaparelli EDM from 7:04 pm IST onwards, all the way into the last phases of the descent of the module through the Martian atmosphere, till about 8:27pm. The display from GMRT was streamed live to the ExoMars mission control centre in Germany, which provided valuable real-time monitoring facility to the project team. The ground based support that GMRT provided to track the space probe in the final minutes of the journey was very important. This has been a historic achievement for us at GMRT. We have demonstrated our capability to participate in such international space missions as a ground support observatory and expect to play a significant role in future missions of this kind.


Report provided by GMRT