Geological penetrator CHOMIK (Phobos-Ground mission)

Project Name: CHOMIK
Project leader: J. Grygorczuk
Participants in the project: K.Seweryn, M.Morawski, H.Rickman, J.Gurgurewicz, M.Banaszkiewicz, M. Dobrowolski, M.Drogosz, R.Wawrzaszek, L.Wiśniewski, T. Kuciński, K.Skocki, B.Kędziora, A.Cichocki, T.Szewczyk, J.Krasowki, M.Ciesielska
The timeframe of the project:

A unique geological penetrator dedicated for the Phobos Sample Return space mission was constructed at the Space Mechatronics and Robotics Laboratory, Space Research Centre (SRC) of the Polish Academy of Sciences (PAS) in Warsaw. One of the most important goals of the mission is to acquire a soil sample from Phobos, Mars’ moon, and deliver it to Earth. The sample will be collected from the surface of the moon by the Polish penetrator and deposited in a container that is going to land in 2014 in Kazakhstan encased in the Russian re-entry capsule.

Mission’s background

 Planet Mars has two moons and both were discovered by Asaph Hall in 1877. However, it is still uncertain how these two objects have become Mars’ moons.
The first hypothesis maintains that the two asteroids were captured by Mars as might be indicated by the very low albedo of the moons (representative of C-type asteroids) and low density (typical of C and D-type asteroids). These types of objects represent about 75% of the population of asteroids’ main belt located between Mars and Jupiter, from where they could have been captured.


 

The asteroid belt, in the background one can see the inner planets and Jupiter, source: http://upload.wikimedia.org/wikipedia/commons/e/e2/Rodzina_Hildy.PNG
 

However, there is no clear explanation of the mechanism of the capture of these objects. Other hypothesis suggests that moons were formed by combining the particles of matter orbiting around Mars, which in turn was the remnant of a larger amount of matter from which it Mars was formed. Another hypothesis theorizes that at one timeMarswas surrounded by many objects such as Phobos and Deimos, which was the result of a respectively large object crashing onto the surface of Mars. Two of the abovementioned hypotheses were confirmed by the observations of moons in the infrared suggesting that they consist mainly of phyllosilicates, which are also present on the surface of Mars. To find out what is the true history of mysterious moons of Mars, the Russian federal space agency Roskosmos launched the mission Phobos-Grunt, which landing target is one of the two moons of Mars - Phobos.

Phobos, the larger and the innermost of the two Martian moons, is a small, irregular body - 27x22x18 km in dimension, and of low density (1.9 g/cm3). Low gravity makes it a very appealing target for space missions. The escape velocity of 11 m/s is close to that of a sprinter, thanks to which landing and takeoff maneuvers are relatively easy to perform. Furthermore Phobos orbits around Mars at a distance of only 9 400 km, about 40 times closer than the Earth’s Moon. Such a small distance combined with the absence of its own atmosphere makes Phobos a perfect location to examine the Red Planet which covers about one quarter of its moon’s horizon.

Image of Phobos taken by Mars Reconnaissance Orbiter in 2008, Source: http://upload.wikimedia.org/wikipedia/commons/5/5c/Phobos_colour_2008.jpg
 

Phobos-Grunt (Phobos Sample Return) mission
 

Phobos-Grunt Spacecraft , source: http://www.russianspaceweb.com/phobos_grunt.html
 

The history of Phobos-Grunt mission reaches the 1990s. In 1996 the concept of the mission to Phobos, during which the samples of its regolith were to be sent to Earth,  was developed. Over the years,the project remained only on paper and in 2004 funds were granted for its implementation. The Fobos-Grunt mission was to be launched in 2007. However it was launched on November 9, 2011on board the launch vehicle Zenit-2.

During the mission the following three areas will be examined:

 1. Phobos:

     a. The study of physical and chemical properties of regolith and subsurface layers of both on-board the lander as well as in laboratories on Earth.

     b. The study of formation mechanisms of the Mars ‘moons.

     c. The search for life forms or possible signs of life.

     d. The study of orbital and proper motion of Phobos.

 2. Mars’ close environment:

     a. Study of Martian environment (dust, gas, plasma).

 3. Observation of the global dynamics of the atmosphere and surface of Mars:

     a. Observation of the dynamics of the Martian atmosphere and seasonal climate changes.

 

Additionally, the Chinese YingHuo-1 satellite will be located on the Martian orbit for a year. It was launched together with the probe Phobos-Grunt. The task of the Chinese orbiter will be the measurement of the solar wind interaction with Mars.

 

CHOMIK

 

Geological Penetrator CHOMIK

 

One of the key objectives of the mission involves taking asample of regolith from the surface of Phobos. Originally,it was to be carried out using devices that can peel off theouter layer of surface that has the structure of sand. Due to the lack of information on the structure oft he surface of Phobos, the possibility of landing on a hard surface has to be taken into account. Weak gravity force on Phobos limits the pressing force to the surface of a device without the threat of overturning the lander. In this situation, an important goal of the mission would not be realized. A device capable of crushing hard surface was needed – one that would not transfer undesirable forces onto the lander. Additionally, the device had to use little power, be light and ready for integration with the lander before the launch in 2011.

 

The task that had to be fulfilled and the difficulties associated with it are broadly in line with the ones in Rosetta mission. It is the European Space Agency mission to comet 67P/Churyumov-Gerasimenko. Rosetta’s task is not to get samples; however, one of the objectives of the mission is to study the mechanical properties of the material from which the comet is made. The instrument to study the mechanical properties of the comet, which allows  driving sensors under the surface, was designed and constructed at the Space Research Centre, PAS by PhD Eng. Jerzy Grygorczuk. The device commonly known as space hammer, formally occurred as MUPUS(Multi-Purpose Sensor for Surface and Subsurface Science).

Information about MUPUS reached the persons responsible for the Phobos-Grunt mission. After seeing how the MUPUS’ show model works, no one had any doubt that this type of device should be a part of the Phobos-Grunt mission. The contract for the development of the instrument was signed on April 2nd,  2010. Hammering device and other components have been redesigned and/or added to adjust the instrument to the new mission.

 

Hammering device

 

Hammering device

Hammering device is based on the three masses concept. The first mass is the housing and the rod, the second mass is a hammer, the third mass – a counter-mass. The hammer is resiliently connected with the counter-mass, and the counter-mass is resiliently connected with the rod. At the beginning, all the elements are in start positions. The hammer is accelerated towards the rod. In the second phase the hammer strikes the rod causing the rod tip to drive into the surface, to crush the surface or to fill the container that is installed at the end of the rod with a sample. In the third phase the hammer bounced from the rod moves in the opposite direction. In the fourth phase, the hammer moves up causing displacement of the counter-mass. Due to the ratio of the masses, the counter-mass, while  moving slightly, acquires the post-impact energy from the hammer. Owing to this, the reaction forces of the device are damped. In the fifth phase, the resilient elements force the counter-mass to return to its start position, which in turn causes another strike on the rod, this time by the counter-mass. This is the second time in the entire cycle that results in the energy transfer to the other end of the rod. Afterwards everything goes back to the staring position and the device stores electrical energy for the next cycle. Below is a schematic illustration which shows the locations of the masses in every phase of the process.

 

Functional diagram of the hammer mechanism


Lock and release mechanism


 

Lock and release mechanism

The lock and release mechanism keeps a part of the penetrator in a fixed position during storage of the instrument on the Earth, during the take-off, and the entire flight to Phobos. Only after arrival at the final destination of Phobos-Grunt mission, and after using a manipulator placing CHOMIK over a desired location where the sample is to be taken, the mechanism will release the mentioned part of the penetrator. The main task of this mechanism is to protect parts of the hammer against mechanical damages, and to temporary removes all degrees of freedom, so that the hammer does not slide with respect to the manipulator. This ensures the security of the instrument and its fixed position in all phases of the mission prior to sampling. Accumulated energy in the spring mechanism aims to open it; however, it encounters resistance fromtwo elements which prevent movement  resulting from the mechanism’s construction. The parts that block the mechanism are also comprised of resilient elements that tend to move the blockade. They are also being hampered by Dyneema string, which is verystress-resistant. In fact, this string stops the mechanism from opening. However, the string is guided in such a way that it not only keeps the blocking elements in fixed positions,but it also rests itself against the resistors. It means that just an activation of a proper electrical circuit causes resistors to heat up, which in turncauses the Dyneema string to burn. Once they burn, the mechanism frees the hammering device.

 

Container separation mechanism

 

Container separation mechanism

Container in which the sample will be collected is a hollowed inside titanium cylinder. The edge of the containerhas asharpend, and regularincision, forming a teeth. To transport the sample to Earth, the container with the content has to be separated from the rest of the device. This is one of the key moments of the mission; therefore, the separation mechanism should be reliable. Additionally, during the filling of the sample into the container, the mechanism must carry loads associated with the impacts of the hammering device. Just as in the lock and release mechanism, there is also a spring which is capable of executing motion of the mechanism and Dyneema spring that prevents this movement. The moving part of the separating mechanism moves on the thread and it has a lever at the end. Burnout of Dyneema string causes spring expansion and thus, rotation of the moving mechanism and linear movement resulting from the thread pitch. This in turn separates the container from the device.

 

Electronic components and sensors on board theCHOMIK

Box with electronic components

Inside the enclosure,also serving as a mechanical interface betweenCHOMIK and a manipulator, the electronic components are placed. It is thanks to this that the Polish instrument will communicate with the on-board computer and power supply of the lander. The impulse for the penetrator to commence operation will be through these components converted into a sequence of work of different mechanisms. Moreover, two sensors to study the surface of Phobos after the sample is collected were placed on the CHOMIK device. The first sensor is the temperature sensor of the Phobos’surface, the second is a thermal conductivity detector of the regolith. Both are placed on the same level as the separation mechanism and their operation and pre-processing of data also comes within the responsibility of CHOMIKs electronic components.

 

Basic properties of CHOMIK

Power consumption 2W
Weight 480g- hammering device

Stroke energy 0.8 J

CHOMIK weight 1400g
Dimensions 418x109x109 mm
Dimensions inside the sample container Ø14mm, l39mm

CHOMIK instrument
Geological penetrator CHOMIK (Phobos-Ground mission)