This view of the severely damaged Apollo 13 Service Module (SM) was photographed from the Lunar Module/Command Module (LM/CM) following SM jettisoning. An entire panel on the SM was blown away by the explosion of oxygen tank

Credit: NASA

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MELBOURNE: Forty years ago, on 13 April 1970, NASA's worst nightmare became reality when there was an explosion aboard Apollo 13.

And in Australia, scientists and engineers at the Parkes radiotelescope - celebrated in the 2000 movie The Dish - had to find a way to stay in contact with the stranded astronauts.

"The expertise and skills of Australian scientists proved vital in the tracking of the spacecraft - without which the rescue would not have succeeded," said John Sarkissian, the operations scientist at Parkes.

At the time, U.S. President Richard Nixon said to Prime Minister John Gorton: "On behalf of the people of the United States I wish to express to you and to the people of Australia my deep appreciation for your nation's assistance in the successful recovery of the Apollo XIII astronauts."

Stranded in space

Apollo 13 was launched 40 years ago on 11 April 1970, and was intended to explore the hilly regions on the Moon around the 80-kilometer-wide Fra Mauro crater.

But almost 56 hours into flight, an oxygen tank exploded, which severely damaged the service module and crippled the entire energy system.

NASA's worst nightmare became reality when the Mission Control in Houston received the infamous radio transmission, "Houston, we've had a problem" from command module pilot John Swigert, and repeated by commander James Lovell.

Weakening signal

Lovell, Swigert and lunar module pilot Fred Haise were stranded over 320,000 km from Earth with vital power levels dropping drastically.

The Mission Control centre in Houston allows scientists to simulate the conditions astronauts are experiencing and trial possible solutions, relaying critical instructions to astronauts.

"Communication between the spacecraft and Houston was vital," Sarkissian says.

The diminished power of the spacecraft severely weakened its signal, threatening to hinder communications between Houston and the Apollo 13 astronauts.

Parkes not part of original Apollo 13 mission

The CSIRO Parkes radiotelescope in New South Wales, as one of the biggest and most sensitive telescopes in the world, proved a valuable addition to the series of telescopes tracking the weak signal from Apollo 13.

But Parkes was originally not committed to the Apollo 13 mission. The Moon was too far north for much of the mission to be observed from Parkes, so the equipment required to receive, amplify and relay signals was not set up on the telescope.

When the explosion occurred, Mission Control in Houston was concerned about the low signal levels from the spacecraft and knew they needed Parkes watching the spacecraft. "We wanted to make sure that we got a good telemetry signal, and Parkes was one of the places where we knew we could get it," said Chris Kraft, the director of flight operations in Houston.