Radio science instrument for ExoMars 2020 mission ready for the Red Planet

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ExoMars prototype rover
ExoMars prototype rover at the Royal Astronomical Society National Annual Meeting 2009 in Hatfield, England. (Credits - Wikimedia Commons)

ESA’s Lander Radioscience experiment (LaRa) for ExoMars Mission 2020 has completed its testing in conditions similar to Mars and will be carried to Russia for its acceptance review, followed by integration onto the Kazachok Surface Platform.

At about 8 x 8 x 20 cm and a trio of antennas, LaRa is a high-operating transponder maintaining an extremely stable direct radio-frequency link between Earth and Mars for a full Martian year. LaRa has been planned by the Royal Observatory of Belgium, developed through ESA’s PRODEX programme and funded by the Belgian Space Policy Office.

The latest testing of LaRa was done in ESA’s Mechanical Systems Laboratory (MSL) at the Agency’s ESTEC technical heart in Noordwijk, the Netherlands. It is able to perform space simulation test, serving spacecrafts, mini-satellites, subsystems.

After vibration testing on an MSL shaker for simulating harsh launch conditions, atmosphere re-entry, landing on Mars, LaRa was placed inside a thermal vacuum chamber for functional testing in hot and cold conditions. At first, it was kept in high vacuum to outgas fumes which could pose problems in space. Then it faced simulated Martian conditions, with 6 millibars of carbon dioxide and varying temperature to test its performance. The electronic box of LaRa will be kept warm by the heater of ExoMars lander.

Developed in collaboration between ESA and Université Catholique de Louvain, the unique antenna will be installed outside the thermally controlled conditions to withstand extreme temperature as cold as -90°C and as hot as 10°C. Engineers advanced to remove sensors and cables fitted for testing after opening the thermal chamber before placing the instrument along with the antennas into sterile bags to avoid microbial infection.

Lieven Thomassen of LaRa prime contractor Antwerp Space said that the interior is made of four layers of circuit board which has been cleaned fully. It is completely sealed, with only 2mm diameter hole to avoid excess pressure in space.

LaRa is one of the two ESA instruments on the ExoMars Surface Platform. The first role of the platform is to make sure that itself and the Rosalind Franklin ExoMars rover, also made by ESA safely lands on the Oxia Planum lowlands in Mars. Then Kazachok will be running 13 experiment packages aboard. LaRa will be receiving X-band radio signal from Earth which will be relayed back again. By measuring the small Doppler shifts in this two-way signal, scientists will identify small periodic shifts in the position of Surface Platform as time passes.

Véronique Dehant of the Royal Observatory Belgium, the instrument’s principal investigator said that this will disclose information of planet’s internal structure, accurate calculation of its rotation and orientation and variation in angular momentum due to mass redistribution such as seasonal transfer of mass in carbon dioxide when a portion of the atmosphere freezes. The main challenge is to maintain the highly stable direct radio link in the planned operating schedule of LaRa, that is two sessions of an hour each per week, especially when Mars is at a maximum distance of 401 million km from Earth.

ESA microwave engineer Václav Valenta, manager of the LaRa project said that they will be using huge 70m antennas of Deep Space Network of NASA for transmitting X-band radio signal towards Mars and to pick up a delayed replica with as low as 5W of radio power generated by LaRa.

On Mars, LaRa will need enough sensitivity to detect very low radio signals. When Earth and Mars approach closer, the Estrack ground stations of Europe will close the link with LaRa. This was successfully tested in the radio frequency compatibility tests in ESOC mission control center in Darmstadt, Germany.

The atmosphere of Mars is a complicating factor. It enables convection for carrying away the waste heat. Though thinner than the atmosphere of Earth, radiofrequency operation leaves a risk of corona effects. Václav said that LaRa was formerly subjected to ESA’s High Power Radio Frequency Laboratory to remove corona risk which is ionization of local gases leading to adverse lightning-like discharge.

It also was tested inside the Maxwell chamber of ESTEC for electromagnetic compatibility to check that all the elements work properly. For verifying the robustness of LaRa against mechanical shocks due to the carrier module separation, a shock model was developed and tested at ESTEC Test Centre. After testing was completed, it was moved to ESA’s Metrology Laboratory for accurate measurements of its surface flatness for perfect fit and thermal contact with its lander interface to maintain a proper operational temperature.

After that, it will be moved to the Space Research Institute of the Russian Academy of Sciences, IKI for final approval testing followed by full assembly-level testing at Cannes in France. Václav said that the LaRa team worked very hard as actual developments for the flight model started a year late. ExoMars 2020 will be launched by the Russian Proton launcher from Baikonur, Kazakhstan on July 2020.

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