Friction Modifier Aids Mars Mission


After losing the Mars Polar Lander four years ago, Americas space agency was thrilled this month when the first of two Mars Exploration Rovers landed safely and began sending back information about the Red Planet. One specialty lubricant company was proud to say that it played a part – even if doing so meant providing more, not less friction.

Landing is the toughest part of the 35-million-mile journey. The spaceship must slow from a speed of 17,000 miles per hour before it entered Mars atmosphere to just over a few miles per hour by the time it touches down. The atmosphere helps a lot, cutting the speed to 1,500 miles per hour. A parachute is then deployed to slow the landing modules fall to 200 miles per hour.

Then the lander breaks out retro-rockets designed to exert upward force to further slow the descent. The hitch is that the rockets and landing module need some distance between them to protect the latter from damage. NASA provides that distance by attaching the rockets – and parachute – to a frame mounted on landers back. When the ships heat shield is ejected, after entering the atmosphere, the module is lowered on a standard airline industry descent rate limiter, which uses a steel strap that unwinds from a spool.

Actually, a steel strap was used until the Rovers. The strap and spool worked fine on explorers, which weighed less than 300 pounds in the low-gravity Martian environment. But NASAs Jet Propulsion Lab discovered in late 2002 that the strap was not strong enough to handle the increased momentum created by the Rover lander, which is heavier.

A troubleshooting team decided to replace the strap with a synthetic rope. But then they hit another snag: The rope, if subjected to large loads while still wound on the spool, would bury itself under the inner layers of the rope. The troubleshooting team needed a second spool that could store the rope at low tension and then pass the rope around a separate shaft to engage the brakes that would ease the modules descent from the frame. Easy enough. But the system needed that shaft to have a very high-friction surface to keep the rope from slipping across it.

That is where General Magnaplate Corp. came in. That NASA would turn to the Linden, N.J., company is somewhat ironic, since Magnaplate is in the business of providing dry coatings that lubricate. But the companys Ventura, Calif., facility had already developed a high-friction coating that was put on support pads to keep the module from moving during testing. The new coating is a version of Magnaplates Plasmadize, an enhanced thermal spray composite that resists temperatures of up to 1,300 degrees F.

The trouble-shooting team learned of the coating that Magnaplate had developed for the support pads and the next day took the brake-shaft from the modified descent rate limiter to the companys Ventura facility to be coated. The following day the team tested a prototype of the new system at the China Lake naval testing facility and found that it worked perfectly.

The team spent the next six weeks refining the system and shrinking it from the size of a computer monitor to the size of a tissue box. It tested a dozen devices during that time, applying a new coating for each test.

Because the new device worked so well and could be integrated without any actual changes to the Lander, the troubleshooting team was given the go ahead to incorporate the new design into the spacecraft. The final design had twice as much load carrying capacity as standard descent rate limiters and was delivered to NASA in Florida in December 2002.

The Rovers were launched in June and July 2003. The lead one landed Jan. 3, much to Magnaplates excitement.

This was a highly unusual problem for us because normally Magnaplate is asked to provide dry-lubricant coatings that actually reduce levels of friction, said Mike Prager, head of Magnaplate’s California facility. We developed a new product especially for this project, and the results were very successful.

Related Topics

Market Topics