Red planet poses challenges for bearings
18 December 2012
The Curiosity rover that landed on Mars in early August features the largest, most advanced scientific payload of any Mars mission yet and most of its robotic functions depend on the faultless operation of mechanical bearings designed for operation in this inhospitable environment. Les Hunt reports.
As far as bearing suppliers to the NASA-JPL-Caltech Mars missions are concerned, Kaydon is something of an old hand. The Curiosity rover is the third Mars exploration mission for which the company has supplied bearings and, as in previous missions, its Reali-Slim thin section bearings were the components of choice.
These bearings, which are available exclusively in the UK from R A Rodriguez, have a proven track record for saving space and weight without compromising performance, and are widely used by the aerospace and defence sectors for a variety of mission critical applications.
The five pairs of duplexed bearings specified for Curiosity operate in two important areas: a mechanism for preparing rock material samples for analysis and supporting the steering actuators for the rover’s wheels.
One pair of Reali-Slim bearings is in the Collection and Handling for In-Situ Rock Analysis (CHIMRA) system, one of a number of devices mounted on a turret at the end of the robotic arm. These angular contact bearings with a 3in outside diameter are a key part of a mechanism that prevents clogging of the primary sieve, ensuring that rock samples can reach the analytical instruments.
Jet Propulsion Laboratory (JPL) engineers decided early on in the project that thin section bearings were the best way to handle the load in the small space available and effectively built the remaining design around them.
The other four sets of Reali-Slim bearings, with a 7in outside diameter and a 6in bore, support the steering actuators on Curiosity’s four corners and relieve some of the load at these points - a critical factor during the spectacularly ambitious landing sequence. They too are angular contact in type and fitted in duplex pairs with races and balls of 440C stainless steel and a built-in pre-load.
JPL requested that the bearings should all be shipped dry, including the phenolic separators, so they could apply a space-rated lubricant that would not become viscous in the extreme cold or evaporate in the thin atmosphere.
Plain bearings, too, have an important role to play in the continuing success of the Curiosity rover mission. GGB Bearing Technology’s DU metal- polymer bearings are critical components in the drill that Curiosity will use over the coming months to sample the Martian geology.
As GGB president, Ken Walker says, his company’s products are used in tens of thousands of critical applications every day on our own planet, but it was an honour to be included as a supplier to this Mars mission. “ It’s always our goal to provide superior, high-quality solutions to our customers’ needs, no matter where those needs take our products,” he says.
The self-lubricating DU bearings feature high resistance to wear and an ability to function in the harsh conditions and low temperatures so characteristic of the Martian atmosphere. GGB says they are capable of operating at temperatures in a range from -200oC to +280oC, which more than adequately prepares them for this environment.
Curiosity’s key mission is to investigate conditions on Mars to see if they may have been conducive to microbial life, an investigation that requires the collection and analysis of dozens of samples scooped from the ground or drilled from rocks. The rover’s robotic arm collects samples by drilling into the Martian soil to a depth of approximately 2.5cm, the drill action being a combination of rotation and percussion, with a force being constantly applied to the bit.
Three DU metal-polymer bearing segments serve as the primary suspension components for the drill spindle, one of four robust components that support the drill’s movements. In addition to the spindle, which rotates the bit, the drill includes a chuck that engages and releases the bit, a percussion mechanism that provides the hammering action and a linear translation mechanism.
At the time of writing, Curiosity had just taken its first soil sample from the Martian surface, with preliminary analysis indicating that its composition was not unlike that of soil found on Hawaii's Mauna Kea volcano.