Taking the first step towards a Martian moon: Polish-built soil sample instrument completes first stage

Tests of the flight module of the CHOMIK instrument were concluded at the Space Research Centre of the Polish Academy of Sciences (SRC PAS) at the beginning of April. The device, intended for geological studies and investigations in microgravity conditions, has just been handed over to the Space Research Institute of the Russian Academy of Sciences. In Moscow, the instrument will be first connected to an automated manipulator and then integrated with the Phobos Sample Return probe. Next year, the mission lander will reach the surface of the Martian moon Phobos. CHOMIK will then collect a soil sample, which will reach Earth in three years.

The Space Research Centre of the PAS signed the agreement concerning the construction of the CHOMIK instrument with the Space Research Institute of the Russian Academy of Sciences and the Lavochkin Research and Production Association last year in March. "Such complex projects usually take five years to implement. We have managed to do it in less than a year. It was possible because CHOMIK is a second-generation instrument and we were able to draw on earlier experiences," explains dr Jerzy Grygorczuk, engineer at SRC PAS, main constructor of the CHOMIK instrument and MUPUS penetrator for the Rosetta cometary mission.

The insertion of a geological penetrator under low gravity conditions requires caution. There are concerns that reaction forces could even knock the lander over. "Our design prevents this from happening," says Marcin Dobrowolski, one of the constructors. "CHOMIK transmits very weak reaction forces to the lander. During digging, it relies on the friction between the ground and the walls of the inserted container."

CHOMIK is a small instrument weighing only 1.4 kg, designed and built entirely at SRC PAS. It consists of three main components: a penetrator, an electronic control unit and a lock & release mechanism. The latter protects the instrument against vibration and overload during the take-off and the landing on Phobos.

The penetrator itself consists of an electromagnetic hammer and a long rod with a discardable casing at the end. The casing can take a few cubic centimeters of ground sample. The motion of the hammer will drive the casing into the regolith of Phobos. The appropriate shape of the container and special algorithms controlling the process of the insertion make it possible to collect material from rocky, porous and loose ground. Once the container with the sample is discarded, it will expose a pivot at the end of the penetrator and two sensors. The pivot will allow crushing rocks and preparing samples for other instruments of the lander and the sensors will measure the thermal properties of the soil of the Martian moon. Mechanical properties of the ground will be measured by analysis of the immersion growth after each stroke of the hammer.

Four models of CHOMIK were created at SRC PAS in the course of the project. The first one was a simplified structural and thermal model, which since September has been used by engineers in Moscow in works related to the integration of the device with the manipulator and the lander of the Phobos Sample Return probe. "Two subsequent qualification models were fully operational and we and our Russian colleagues used them for intensive electronic, vibration and thermal tests," says Tomasz Kuciński, master's degree student, member of the project team. It is the forth model that will fly towards Mars.

The Russian Phobos Sample Return probe will be launched in November 2011 and will reach the Red Planet after several months. A week after the landing on Mars, the probe will launch a re-entry module containing a capsule with, among others, the soil sample encased in the Polish container. The capsule will land in Kazakhstan in mid-2014. After extracting the sample and following a period of quarantine, the container will return to the Space Research Centre of the PAS.

The Martian moon Phobos is an irregular body, 27×22×18 km in dimension, with a relatively small density. It is believed to be either highly porous or made up of ice and rocks. The escape velocity on the moon is close to that of a sprinter, which makes landing and take-off manoeuvres relatively easy. "Phobos is an immensely interesting object. It might be similar to bodies from the fringes of the Solar System forming the Kuiper belt beyond the orbit of Neptune," explains dr Joanna Gurgurewicz, and adds that a rival hypothesis holds that the moon was not captured by Mars but formed on its orbit. The measurements carried out by the CHOMIK instrument will help solve this mystery.

The CHOMIK project was financed by the Ministry of Science and Higher Education within the framework of a non co-financed international project "'CHOMIK' instrument for the Phobos Sample Return Mission -- scientific and exploratory research," which includes the construction of a next, more powerful geological instrument.

Devices designed at the Space Research Centre PAS take part in high-level space missions. Sensors built at SRC PAS were, among others, part of the Huygens lander, which landed on the surface of Titan, a moon of Saturn, in 2005 -- it was the farthest landing in the history of humankind. The MUPUS penetrator installed on the Rosetta mission lander will soon insert itself into the nucleus of the 67P/Churyumov-Gerasimenko comet. A cutting-edge instrument KRET (Polish word for mole) has also been built at SRC PAS, with future geological investigations of the Moon in mind.