OA-6/Atlas V being rolled out to Pad 41 for launch at Cape Canaveral Air Force Station NASA/Ben Smegelsky

Modules aboard three cargo ships returning from the space station will be set fire to in an experiment aimed to test spacecraft safety. The controlled pyrotechnic experiment by Nasa will help understand how fire behaves in zero gravity and thus improve design safety.

The first of them, Cygnus OA-6 will lift off today on March 22 and arrive at the ISS on Saturday night when it will attach the Unity module. Cygnus will deliver almost 7,500 pounds of research gear, spacewalk hardware and crew supplies to the six member Expedition 47 crew. After CRS OA-6 leaves the ISS in May it will not return to Earth, but as always filled with station rubbish and burn up in the Earth's atmosphere. But not before Nasa collects data from an experimental module installed on board for a controlled burn.

The Spacecraft Fire Experiment-I (Saffire-I) will look at how fires grow and spread in weightlessness. As the module automatically carries out the fire experiment the sensors and cameras will transmit data and images of the event to mission control. The three Saffire experiments will be conducted on successive Cygnus missions.

It is designed to simulate the amount of flammable material likely to be present in a spacecraft fire and to examine the flammability limits of materials by using a sample material about 1 m long.
Current experiments conducted in space have been limited to samples no larger than 10 cm (4 in) in length with the station safety in mind.

The other objective is to examine the flammability limits of materials in low gravity to determine if Nasa''s material selection methods are a reasonable predictor of low-gravity flammability. The experiment package is designed to prevent burning debris from interacting with the rest of the cargo.

The sensors will record temperature, oxygen, carbon dioxide, etc while LEDs and cameras will measure the length of the sample as it burns while other equipment will track the spread of the flame.

On Earth, fire rises, but not so in zero gravity, where the fire and its combustion by-products hover about in a sphere rather than flow away. Understanding the way fire spreads can help design spacecraft to minimize mishaps.

High temperatures and how spacecraft material reacts have indirectly been responsible for mishaps like the 2003 Space Shuttle Columbia or the launch pad fire during the Apollo 1 rehearsal in 1967. As Nasa readies for long manned space flights to Mars and beyond, safety of the crew is as important factor as the production of food, water and oxygen which are at various levels of preparation.