Chinese sub-probe on Phobos-Grunt

In June 2005, the head of the Russian space agency Anatoly Perminov said that China would join the Phobos-Grunt mission. In November 2006, Russian officials confirmed earlier reports, saying that the Chinese sub-satellite would be released from Phobos-Grunt in the Martian orbit.

On June 27, 2007, Roskosmos announced that the third meeting of the Russian-Chinese group on lunar and deep space exploration took place at the agency's headquarters in Moscow. It considered joint work on Phobos-Grunt, Worldwide Space Observatory/Ultrafiolet and Spektr-R/Radioastron. Two sides signed a contract based on the agreement on the exploration of Phobos and Mars reached on March 26, 2007. The agreement was signed by Chinese President Hu Jintao and Russian President Vladimir Putin during Mr. Hu’s recent visit to Russia.

Chinese specialists were also expected to visit NPO Lavochkin design bureau, which served as a key developer of the Phobos-Grunt project.

Depictions of the Phobos-Grunt released at the time showed Chinese sub-probe, identified as Yinghuo-1 (YH-1), mounted on top of the spacecraft assembly. According to the official Chinese media, the sub-probe had a shape of a 750 x 750 x 600-millimeter box with the mass of 110 kilograms and equipped with a pair of three-section solar panels, which would span 7.85 meters, when deployed.

The Hong Kong Polytechnic University also announced that as a result of the March 26, 2007, agreement, the institution was charged with the responsibility to develop a 230-gramm "Soil Preparation System," capable of grinding and sifting Phobos rock to the size of less than one millimeter in diameter for the in-situ analysis by the Phobos-Grunt lander. The grinding tool would be placed at the end of the remotely controlled manipulator, also carrying a miniature spectrometer and a camera. The system was expected to be used for selecting soil samples, which would be eventually loaded onboard the reentry capsule, for a ride back to Earth.

The decision to add the Chinese spacecraft to the Phobos-Grunt mission, dictated primarily by political rather than economic reasons, proved to be very controversial. Even thought the contract apparently required China to pay a modest amount for the integration of its satellite, the move led to a major redesign of the Russian spacecraft, putting additional pressure on the already tight launch schedule.

The propulsion unit onboard the cruise stage of the Phobos-Grunt probe would no longer be capable of inserting itself and the Chinese satellite into the Martian orbit. Instead, it was now required to give the Fregat upper stage not only its usual role of sending its payload away from Earth, but also a job of slowing down and inserting the vehicle into its orbit around Mars. As a result, Fregat would have to be heavily modified to surive an interplanetary journey.

The task of attitude-control and orientation of such overgrown vehicle was transferred to the cruise stage, while the course correction functions during a cruise flight between Earth and Mars were "moved down" to the Fregat-based propulsion unit, which was renamed MDU.

According to the initial concept, the Chinese satellite would be placed above the main payload, however such configuration would require a major redesign of the spacecraft's structure. After some debate, it was decided to move the Chinese spacecraft below the cruise stage. As a result, the propulsion system of the cruise stage would now be blocked until the separation of its late passenger.