Faulty switches have been identified as the most likely cause of the Genesis sample-return capsule's crash landing in Utah, US, last month.
The Genesis capsule crash-landed in Utah
The devices were supposed to sense the braking caused by the probe's entry into the Earth's atmosphere and start a sequence that would deploy parachutes.
Nasa says "a design error that involves the orientation" of the switches meant the sequence failed.
The capsule was returning samples of charged atoms blown off the Sun.
These were caught on five collecting plates hung outside the US space agency's Genesis probe for more than 800 days in a region of space about 1.5 million km from Earth.
On the probe's return to its home planet, the plates were despatched to the surface in a capsule that was meant to be caught in mid-air by a helicopter.
But neither the capsule's drogue nor its main parachute opened and the 205kg container slammed into the desert floor at 310km/h, buckling, cracking and, in some places, shattering the collection panels inside.
Nevertheless, painstaking work in a cleanroom has rescued sufficient numbers of the solar atoms that scientists feel confident they can complete the Genesis mission - to understand the original chemical composition of the Solar System.
"This single cause has not yet been fully confirmed, nor has it been determined whether it is the only problem within the Genesis system," Michael Ryschkewitsch, chairman of the Mishap Investigation Board looking into the capsule crash, said of the switch error.
The solar samples have been sent to the Johnson Space Center in Houston for evaluation and cleaning.
The recovered remains of the sample-return capsule are undergoing engineering inspections and tests at the Waterton, Colorado, facility of Lockheed Martin Astronautics, which built the craft.
Its damaged lithium sulphur dioxide battery is being evaluated at the Jet Propulsion Laboratory (JPL) in Pasadena, California.
"Both Lockheed Martin and JPL have been providing every possible support to our investigation," Ryschkewitsch said.
The MIB expected to complete its work by late November, Nasa said.
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