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Above: The final architecture of the Phobos-Grunt spacecraft and its major components as of 2011. Credit: IKI
Traditionally for the Russian planetary exploration program, NPO Lavochkin serves as the prime developer of the spacecraft platform, while the Institute of Space Research, IKI, of the Russian Academy of Sciences, leads the development of the science program, involving numerous institutions inside and outside Russia. A total of five billion rubles were reportedly spent for the Phobos-Grunt program. Of this amount 1.5 billion was required to build the spacecraft itself and 3.5 billions were spent on various upgrades of the Russian deep-space segment of the nation's ground control network and test facilities at NPO Lavochkin.
The main platform of the Phobos-Grunt spacecraft (often referred to as spacecraft bus) was developed from scratch, however its architects hoped it could serve as a base for future missions to the Moon and planets, following Phobos-Grunt. The design went through several incarnations before starting to appear in metal.
All systems of the spacecraft were placed in unpressurized compartments and were designed to function in the vacuum of space. The main cruise stage of the Phobos-Grunt spacecraft combines the functions of the spacecraft itself and of a space tug, which reportedly enabled weight savings of around 300 kilograms. (286)
The largest planetary probe built in the former USSR, Phobos-Grunt consisted of three major components:
The Cruise Stage, PM - (from Pereletny Modul) is sometimes referred to as Flagman. It was newly developed for the Phobos-Grunt mission, but its basic architecture was promised to be the base for a whole generation of future planetary missions, including Luna-Glob, Luna-Resurs and Luna-Grunt to the Moon; Venera-D to Venus; Mars-NET and Mars-Grunt to Mars and, possibly, Sokol-Laplas to Jupiter. The platform's developer - NPO Lavochkin - stressed that in different configuration, the same bus could be adapted as an orbiter or as a lander.
The cruise stage would sport its own propulsion system and a newly developed flight control system or BKU (Bortovoy Kompleks Upravleniya). As one of the most technically challenging and controversial aspects of the project, BKU was developed internally at NPO Lavochkin, with major components of the TsVM22 main computer supplied by Tekhkom, itself a spinoff of NPO Argon design bureau. Although, the new-generation BKU introduced progressive and mass-saving technologies (apparently reducing the mass of such system from 30 to 1.5 kilograms (554), problems in its development were primarily responsible for pushing the launch date of the Phobos-Grunt mission from 2009 to 2011.
The cruise stage would also be equipped with the following systems, which would be integrated with the BKU flight conrol system:
For the Phobos-Grunt mission, the cruise stage would be equipped with a 13-kilogram radar, known as DISD - Doppler Measurer of Velocity and Range developed by OAO Vega. Its data would be used for the final approach and landing on Phobos. Particularly, DISD would be used to determine the exact timing of final maneuvers during descent.
For purposes of science and flight navigation, the cruise stage would be equipped with a Television System of Navigation and Observation, TSNN. Data from the TSNN would be complemented by measurements from the star tracker unit, BOKZ-MF.
A pair of solar panels for the cruise stage was developed at Kaluga branch of NPO Lavochkin.
Known specifications of the Phobos-Grunt cruise stage, PM as of 2010:
The Return Vehicle (VA) would carry the landing capsule (SA) with soil samples from the surface of Phobos back to Earth. A smaller version of the flight control computer from the cruise stage would be installed on the return vehicle. Unlike the cruise stage, the return vehicle would lack a fly wheel system for attitude control and would be spinning in flight to achieve stabilization in empty space.
Systems onboard the return vehicle, which were borrowed unchanged from the cruise stage:
The propulsion unit onboard the return stage developed by NIIMash would use a pressure-fed propellant supply system. The main engine would have a thrust of 130.5 Newtons (13 kilograms) and burn UDMH and AT. Attitude control would be maintained with the help of 16 small thrusters using nitrogen gas and delivering 0.08 kilograms of thrust.
A cluster of four tanks would contain individual propellant components - UDMH and AT, and two side tanks would contain nitrogen gas to feed the attitude control thrusters.
The propulsion system of Phobos-Grunt was based on the versatile Fregat upper stage, which underwent a number of changes. In all previous missions, Fregat would carry its own flight control computer, developed by Moscow-based NPTs AP center. However during the Phobos-Grunt mission, the MDU would be controlled by a newly developed computer system, BKU, installed onboard the spacecraft itself.
Since the MDU would have to fly all the way to Mars along with the rest of the probe, the space tug's thermal-control system, SOTR - Sistema Obespecheniya Teplovogo Rezhima, had to be significantly reworked.
MDU's propulsion system was certified for a total of seven firings during the mission with its main engine capable of low- and high-thrust propulsion modes. It was potentially capable of as many as 50 firings, according to some sources. The main engine firing would be preceded by the operation of the low-thrust Ignition Provision Systems, SOZ, which was designed to create some acceleration in order to press the propellant toward engine supply lines in weightlessness. The procedure would last around a minute. Low-thrust attitude-control thrusters onboard MDU had a combined thrust of 20-25 kilograms.
The MDU propulsion unit was to carry 7,050 kilograms of propellant in its main tanks and 3,050 kilograms in its jettisonable external tank designed to be dropped after the first engine firing in the Earth orbit.
Mass breakdown for the Phobos-Grunt spacecraft in kilograms and its evolution:
*Estimate based on the sum of the main propulsion system and the fueled external tank;
Known characteristics of the Phobos-Grunt spacecraft (432):
Propulsion systems employed onboard the Phobos-Grunt spacecraft (as of June 2009):
Page author: Anatoly Zak; last update: February 16, 2012
Page editor: Alain Chabot; Last edit: May 20, 2011
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A payload section of the Phobos-Grunt mission on the Zenit rocket, as of 2011. Credit: Roskosmos
A configuration of the Phobos-Grunt spacecraft on the surface of Phobos, after the departure of the return rocket with soil samples, as of 2008. Click to enlarge Copyright © 2008 RussianSpaceWeb.com via NPO Lavochkin
Major elements of the Phobos-Grunt spacecraft as of 2008. Click to enlarge Copyright © 2008 RussianSpaceWeb.com via NPO Lavochkin
The ascent stage of the Phobos-Grunt as of 2011. Credit: IKI
The reentry capsule of the Phobos-Grunt spacecraft as of 2011. Credit: IKI
A full-scale prototype of the reentry capsule for the Phobos-Grunt mission undergoes aerodynamic testing in the T-105 wind tunnel at the TsAGI research institute in Zhukovsky. Credit: TsAGI
A scale model of the T-105 wind tunnel facility in Zhukovsky, which was originally designed for testing of helicopters but also helped to validate the critical design of the reentry capsule carrying samples of Phobos back to Earth. Copyright © 2005 Anatoly Zak
The propulsion system for the return stage of the Phobos-Grunt spacecraft. The propellant for the main engine is contained in the four center tanks and nitrogen gas for the small thrusters in the two side tanks. Credit: NIIMash
A Multi-functional Propulsion Unit of the Crusie Stage, MDU PM. Credit: Roskosmos
Engines used onboard the Phobos-Grunt spacecraft. Copyright © 2009 Anatoly Zak
Electric batteries for the Phobos-Grunt spacecraft developed by AO Saturn of Krasnodar, Russia. Credit: AO Saturn
A 0.42-kilogram hardened laser altimeter for the Phobos-Grunt spacecraft developed at Vavilov State Optics Institute, GOI, in St. Petersburg. Credit: Vavilov GOI