Atlas V booster rocket with the research automatic station NASA MSL (Mars Science Laboratory) on board was launched from the Cape Canaveral spaceport (Florida, USA) in November 2011. Nine months later, i.e. in August 2012, it is planned to bring the Curiosity Mars research vehicle to the Red Planet. Its scientific equipment includes Russian device DAN (Dynamic Albedo* of Neutrons) to collect data on the availability of water and hydrogenous compounds, worked out by order of Roskosmos at the RAS Institute of Space Research (IKI). Using this device, scientists are planning to test the hypothesis on the assumed existence of primitive life forms in the course of an early or contemporary development of Mars.

The Curiosity will land near the Gale crater--a huge hollow with a high cone of sedimentary rock in the center that might have been formed by a water stream. The soil at the cone bottom contains sulphur and clay compounds formed in the presence of water. Geographical position of the crater increases chances to find its traces.

DAN consists of two blocks--a pulse neutron generator made at the All-Russia Scientific Research Institute of Automatics named after N. Dukhov, Moscow (Rosatom State Corporation) and a neuron detector designed by the IKI--installed on the Mars research vehicle near its wheels and linked to the space vehicle with a special

Photo of Mars taken by the US space telescope HUBBLE on June 26, 2001.

* Albedo--characteristic of the reflective (dispersing) property of the surface of a material.--Ed.

controlled interface. The mechanism itself is protected from the environment by heat-insulation boxes.

The IKI press-service provided a detailed information on the operation principles of the device designed to actively sound the upper layer of the Martian soil (~1 m thick) and involve our country into the US project arranged by the agreement between Roskosmos and the NASA.

According to the press release, the water ice in the regolith (a material covering surfaces of small and atmosphere-free planets and satellites) of Mars was first discovered by the Russian device HEND* (High Energy Neutron Detector), designed by the IKI for the American space vehicle Mars Odyssey (launched in 2001) that stayed in Martian orbit over 9 years (connection broke in 2010). Obtained measurement results enabled scientists to speak about huge water reserves in the deep layers of the celestial body and assess dynamics of seasonal deposits of atmospheric carbon dioxide on its surface.

Both experiments are based on a single methodology-studies of soil structure and water search from a space vehicle* by means of nuclear planetology. But there are certain differences: while the HEND measured neutrons formed naturally in the sedimentary rock of Mars under the influence of cosmic rays, the DAN is designed

* See: I. Mitrofanov, "Unlocking Martian Enigmas", Science in Russia, No. 6, 2002.--Ed.

* See: E. Galimov, "Prospects of Planetary Studies", Science in Russia, No. 6, 2004.--Ed.

to sound the area where the automatic space vehicle is located. Both gamma - and neutron spectrometry methods (most efficient) will be used to find water.

The physical principle of such measurements is based on the nuances of nuclear physics: the device generates short (~1 µs) but powerful (up to 10 mln particles for one pulse) bursts of neutrons with a power of 14 MeV. Elementary particles without electric charge penetrate into the Martian soil where they interact with primary rock-forming elements. When a neutron collides with a light nucleus of hydrogen atom (H₂), it, like two colliding tennis balls, loses almost half of its energy. When it interacts with heavy nuclei, the energy changes only a little. In other words, if there are hydrogen compounds in the soil, the device will register neutrons with a delay as compared with other particles. Thus, measurement of neutron energy after pulse radiation and during registration, it is possible to assess the content of H₂ in the matter and then make a conclusion on the availability or absence of hydrated minerals or ice in the soil. Sensitivity of the device under consideration enables to register water in the concentration of ~0.1 percent.

According to the IKI press-service, the DAN will make measurements along the whole route of the vehicle. When it finds an area with the increased water content, other equipment will also be attracted for studies of the soil in more detail and search for traces of biological activity.

"Since power resources of the Mars research vehicle do not depend on solar batteries (it is fed by a plutonium source installed on the "stern"), but on the overall design reliability of the apparatus, it can carry out studies of the Martian surface for one Martian or two Earth years," said Igor Mitrofanov, Dr. Sc. (Phys. & Math.), head of the experiment, and of the IKI Laboratory of Space Gamma-Spectroscopy. That is why the neutron generator should have the same reliability.

Specialists of the All-Russia Research Institute of Automatics named after N. Dukhov took this nuance into consideration. They used a serial industrial unit ING-101

as a basis and modified it for MSL tasks. These modifications concerned overall dimensions corresponding to the seats at the laboratory, expansion of thermal range (decrease of minimal working temperature from -- 20 to -- 40 °C) and other parameters to improve reliability of the equipment in extreme conditions.

The vacuum tube acts as a source of neutrons. In fact, it is a miniature linear accelerator with a source of ions on one side and a tritium target on the other side. When bombing the target with accelerated ions, a nuclear reaction resulting in the formation of 14 MeV neutrons required to carry out experiments on Mars takes place.

It is worth saying that American specialists tested the generator within the MSL laboratory in almost real conditions and made the following conclusion: it will stand mechanical and climatic loads during launch of the space vehicle from the Earth, space travel and landing on the planet, and its useful life (10 mln pulses, if generated every 10-20 s) will be enough to cover the whole working period of the Mars research vehicle.

As explained by the press-center, the DAN complex was designed with the participation of the RAS Institute of Mechanical Science named after A. Blagonravov (Moscow) and Joint Institute for Nuclear Research (Dubna, Moscow Region). The experiment on board the Mars research vehicle will be conducted by national and US specialists from the NASA Propulsion Laboratory and the University of Arizona led by Igor Mitrofanov. As he said, "When the Mars research vehicle moves along the surface, it should be controlled by one team. The principle used in orbital space vehicles when one experimenter processes results obtained only by his device, is unacceptable here."

After the materials of the RAS Institute of Space Studies press-service

Illustrations from the web-site of the NASA Mars Science Laboratory and the RAS Institute of Space Studies