Television signals caused a Russian cargo rocket to miss its rendezvous with the International Space Station (ISS), NASA officials said Saturday.
The engineers indicated they would avoid activating the system during Sunday's second attempt to dock, NASA officials said.
The Progress 38 cargo rocket missed its rendezvous with the ISS by 3km on Friday. A new effort to dock is to be made at 1600 GMT Sunday and be broadcast life on NASA television.
Seeking to pinpoint what went wrong, Russian flight controllers told NASA that the rocket had received a faulty "command to cancel" when a TV transmitter on the ISS was activated.
The TORU TV system was intended to give station commander Alexander Skvorstov a real-time view of the dock, but apparently overrode the automated docking system called Kurs. Engineers initially thought that the Kurs system had malfunctioned.
Russian officials told NASA that they had confirmed the Kurs system is working normally and had not failed.
"Russian officials said the TORU system will not be activated Sunday for the second docking attempt as a precautionary measure," NASA said in a statement.
Russian specialists were conducting tests overnight Saturday to make sure things were working, and would perform another test when Progress is 15 km, or about 50 minutes, from the station.
Space officials were quick to assure that there had been no danger for the six people on board the ISS - three Russian cosmonauts and three US astronauts - as the Progress 38 approached, then veered out of control and glided past the space station.
Russia's Progress 38 is carrying 2.5 tonnes of food, clothing and equipment for the ISS crew. When NASA's space shuttle programme retires early next year, Progress and Soyuz, which transports astronauts, will be the only transport to and from the space station.
