MOSCOW, November 30 (Itar-Tass) - The reasons why the last phase of docking the cargo spacecraft Progress M-21M to the international space station ISS had to be controlled manually will be clear early next week, Monday or Tuesday, the chief of the Russian segment of the ISS, Vladimir Solovyov, told Itar-Tass.

“The docking was normal by and large. At a distance of about 50 meters I asked Oleg Kotov to activate the remote control mode and dock the cargo craft manually,” Solovyov said. “The moment Progress contacted the ISS the Kurs-NA approach control system was turned off.”

Solovyov offered no explanations why he ordered manual docking.

“It is too early to say anything definite about the causes. A special trouble-shooting team will be formed. I believe that the causes will be clear on Monday or Tuesday,” he said.

“This time Progress M-21M docked with the ISS nearly five days after the launch. That was done on purpose to test the new approach control system,” Solovyov said.

Earlier, on November 27-28 Progress closed up with the ISS in a test mode. The manoeuvre was successful. No contact with the ISS was expected then.

The Progress spacecraft docked with the ISS at 02:30 Moscow time on Saturday. At first, the new approach control system Kurs-NA was used, but when the distance between the ISS and cargo spacecraft reduced to 50 meters, ISS commander was told to take over and perform the docking manually, using the remote control joystick, Mission Control said.

A reliable source has speculated that a glitch in the Kurs-NA system was possibly to blame.

For the first time the Kurs-NA system was tested in space in July 2012. The experiment was not impeccable. The Progress M-15M spacecraft equipped with the Kurs-NA was separated from the ISS, but the first attempt at automatic re-docking failed. At a distance of about fifteen kilometres from the ISS the cargo craft’s control system issued an accident risk warning, and the approach control system moved Progress 165 kilometres away from the ISS. Sensor glitches were blamed.

Kurs is the main approach control system installed on the Soyuz and Progress spacecraft. It has been in use since the 1990s. Its new version, Kurs-NA is much smaller, less power consuming and far more accurate.