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OEM Report: Aerospace
Friday | 09 January, 2009 | 8:33 am

Blast off

By Lisa Rummler

January 2009 - Any business strives to make products that are out of this world. The Timken Co., Canton, Ohio, certainly does.

The company has produced needle bearings that will be used in a descent brake system from SpaceDev Inc., Poway, Calif., which will be an integral part of the Mars Science Laboratory rover.

"The bearings are the anti-friction component to the gearing in the descent brake," says Tim Schlernitzauer, product designer at Timken. "Our bearings are carrying all the motion that's taking place in the braking system, including the gear forces and rotational speeds."

These needle bearings are more power-dense than ball bearings, which Timken provided for different applications on previous Mars rovers. Scheduled to launch in 2011, this particular rover capsule will separate from the spacecraft, and while entering Mars' atmosphere, an aeroshell and a parachute will slow its descent, according to a press release from Timken.

"In the final stage, a 'sky crane' descent brake system will lower the rover on a 25-foot-long tether to a precise landing on the surface within seconds," it stated.

The short time frame was one of the project's unique aspects that presented challenges to Timken's team, Schlernitzauer says.

"For this particular mechanism, the descent brake, it's a short but extreme duty cycle," he says. "It only operates for a few seconds, but it goes from zero to a high rotational speed quickly."

Additionally, Timken's product designers needed to maximize the bearings' capacity for a specific amount of space, and they needed to meet requirements presented by the environment in which the bearings would operate.

"This requires selecting materials that are suitable for space flight," says Schlernitzauer. "For example, in the vacuum of space, some materials can emit gases that can have a detrimental effect if they were to interact with one another, like lubricants and rocket fuel. There are requirements to make sure that there are no harmful emissions drawn out of the material into the vacuum."

Taking a page from history
Doing this sort of customization work, however, is nothing new for Timken. In addition to providing bearings for applications on past Mars rovers, the company focuses on friction management and creating one-of-a-kind solutions to meet those needs. Timken's history with similar projects helped it meet the extensive requirements for the needle bearings on the upcoming Mars Science Laboratory rover capsule.

"Because we provided other bearings in the past for space missions, we knew a few things about what would work, what types of materials we could use and what kind of conditions they'll operate in," he says. "And we were given specific temperatures and conditions by the customer that we designed for."

The bearings are made of carburizing steel, which is a standard material for the parts, according to Schlernitzauer. They also have a self-lubricating coating to prevent metal-to-metal contact. All components of the bearings underwent extensive testing to ensure they met the Mars rover's specifications.

"In an application like this, we apply special processing requirements to optimize the strength and stability of the material in different ranges of temperatures so that the characteristics of the material don't change in operation," says Schlernitzauer. "We also have special processes and controls that we applied to the coating. Also, the bearings were assembled in a clean room to ensure there was no debris contamination."

All the work that went into the design and post-production process will benefit the Mars Science Laboratory during its mission to analyze soil and rock samples. MM

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