'Out of this world' is how a lot of companies would like their products described. But BP's Castrol lubricants team can make that claim quite literally. Its greases are now keeping the Mars Curiosity rover moving in its quest to learn more about the Red Planet
Castrol’s lubricants are being used in one of the most demanding journeys any vehicle has ever made. The US National Aeronautics and Space Administration (NASA) launched the Mars Science Laboratory spacecraft carrying the Curiosity rover from Cape Canaveral, Florida, on 26 November 2011. It landed more than eight months later, on 6 August 2012, following a 563,000,000-kilometre (350,000,000-mile) voyage. It is the agency’s fourth robotic Mars rover since 1996. Its mission? To explore the enduring question of whether Mars has ever had conditions hospitable to life, and to prepare for potential future human exploration. With its ability to scale obstacles up to 65 centimetres (25 inches) high, cover up to 200 metres (650 feet) a day, take pictures, drill into Martian rock, collect samples and brush away dust, Curiosity is a mobile Martian laboratory. The $2.5 billion mission is expected to last 23 months. As it is impossible to recall something from space for mechanical tinkering should it go wrong, smooth operation is vital to success. That is why a small group of long-standing, high-performance lubricants manufactured by Castrol is playing a crucial part in the success of this mission. The rover has a vast number of moving parts, from wheels and probes to articulated brushes, and no fewer than 17 cameras. It is about the size of a car and its moving parts require lubrication to guard against friction. However, lubricating for operations in space is a world away from putting oil in your engine. The lack of convective heat transfer in the space vacuum means temperatures and temperature gradients are more extreme than those experienced on Earth. Scientific instruments on Earth-orbiting spacecraft that can operate at normal room temperature must be able to survive many years in the vacuum without any maintenance. This means lubricants that can withstand the unearthly temperature variations, cope with the dust and have the required longevity are crucial to avoiding mechanical failure. Braycote 601 EF, made by Castrol at its laboratories in Warminster, Pennsylvania, US, has a long heritage with NASA, having been used frequently since the start of space exploration back in the 1960s. Originally developed for military use and derived from a chemical called perfluorinated polyether, Braycote was acquired by Castrol in the mid-1980s. Sister products include Braycote 600 EF, 602 EF and 815 Z, all of them used to prevent the sort of friction that could mean catastrophic and expensive failure of a mission. “If you have friction, you have wear, and if those moving parts wear down, then they stop operating the way in which they are supposed to and things will grind to a halt,” says Keith Campbell, business development manager for Castrol Industrial Lubricants and Services. “You have got to eliminate friction, or at least reduce it so you don’t have wear, and that is what these lubricants do.”
"If you have friction, you have wear, and if those moving parts wear down, then they stop operating the way in which they are supposed to and things will grind to a halt."- Keith Campbell
What makes a lubricant successful in space is the ability to adapt to dramatic swings in temperature without giving off vapours, a process called outgassing. These vapours can result in the loss of all the oil in the lubricant and lead to reduced performance, as well as condensation on nearby surfaces and possible contamination of the rover’s many sensitive instruments or the surrounding environment. Braycote is formulated to perform in temperatures ranging from -80°C (-112°F) to 204°C (400°F). The products have been used in the Apollo moon missions, the Hubble space telescope, on numerous satellites, the International Space Station (ISS), previous Mars rovers and on the majority of the spacesuits made for NASA and other space agencies. Many of the suits used are made by Massachusetts-headquartered David Clark Company, and its subsidiary Air-Lock Inc, which manufacturers the hard parts of spacesuits, such as clips and connectors, and used a Braycote product to lubricate all the moving parts in the suit worn by record-breaking Austrian space jumper Felix Baumgartner in October 2012. Braycote 601 EF’s ability to drop well below its operating temperature, be brought back up and still work without adverse effects on its ability to lubricate, means it has proven its suitability many times over. Now, the product is enabling Curiosity to remain on Mars for the required period of time to undertake a whole range of scientific experiments. “If the lubricant does not do its job, Curiosity would not be able to last up there as long as it needs to,” says Campbell, who is based in California and works with NASA’s Jet Propulsion Laboratory to meet the needs of the US space programme. “We have been selling this same product line to NASA for years, and we think this product is still the best lubricant out there for being able to operate at very cold temperatures and to retain these low outgassing properties at warmer temperatures.”
Compared with lubricant volumes used in the global automotive sphere, volumes of space lubricants are tiny – it is a niche area, after all – but the grease is absolutely crucial. Braycote 600 EF and 601 EF are used in the gearboxes of all Curiosity’s powered mechanisms, including its wheel actuators (a type of motor); its mast deployment, elevation and pivot mechanism; and its robotic arm’s numerous joints. Braycote products are present in the drill mechanisms and dust-removal tool and in the scientific instruments inside Curiosity’s body, and were also vitally important in the success of various mechanisms in the rover’s descent to Mars’s surface. Testing of lubricants is carried out by the space agencies themselves, often in conjunction with the lubricant manufacturers. The tests are run by experts in tribology – the science and engineering behind interacting surfaces in relative motion. The trials subject the greases and oils to a variety of environmental conditions, including vacuum, different temperatures, a range of time periods, cycles and revolutions, in order to assess their suitability for space applications. Dust is a significant consideration, too, and the lubricant’s ability to cope with it is as important as the temperature capabilities. Campbell says: “People who have already decided that they want to use our grease come to us with a lot of technical questions, such as what is the effect on it of atomic oxygen? For example, NASA was at one time looking at putting a manned space station on the moon, and we were asked about the effects of moon dust on 601 EF and whether we had any testing methodology that could be used.
"NASA was, at one time, looking at putting a manned space station on the moon, and we were asked about the effects of moon dust on 601 EF and whether we had any testing methodology that could be used."- Keith Campbell
“I spoke to a chemist colleague in mining and looked at tests we had done for the effects of mining operations on lubricants, and went back to NASA with that information. They incorporated that, together with their findings from tests using ground volcano dust, apparently very similar to moon dust. They let us know the dust did not cause a problem.” High-performance lubricants such as Braycote 601 EF have applications in other environments that preclude the use of an ordinary lubricant. Castrol also sells the product line to companies with manufacturing processes that require a vacuum. Campbell cites the semi-conductor and microchip industry, electronics, flat panel display and hard disk drive manufacturing sectors as examples of such environments. Other uses include commercial aircraft and, as Campbell says, “anyone who might want to put a piece of equipment near the Arctic Circle for 10 years.” But it is in space where Braycote really comes into its own. In 2007, the product was used successfully to prevent a threatened failure of the ISS. The space station is the largest artificial satellite in Earth’s orbit and serves as a long-term cosmic platform. The power needs for the range of research activities carried out by the crew are provided by a number of solar panels that rotate to meet the sun. When a moving part started to show serious anomalies in its operational data in 2007, astronauts investigated and discovered metal shavings where they shouldn’t be and severe degradation. Investigators detected a ‘joint drag’ problem with the bearings, a problem that threatened to lead to what the investigation called an ‘unrecoverable stall of the mechanism’. As the solar power supports the station’s life and all its activities, the problem put the whole ISS at risk, and it was Braycote 602 EF that came to the rescue,vsolving a problem that the astronauts found even pure gold could not fix.
“Volumes might be small, but there are lots of things that make this product very special,” says Hocine Faci, one of Castrol Industrial’s expert technologists based in Mönchengladbach, Germany. “It performs in a vacuum, it is non-toxic and non-reactive with oxygen and other compounds, it has low outgassing and it keeps working for years. “We are not the only company making lubricants that can be used in space, but we have seen what happened on the ISS, for example, and we believe we have the lead in space with this product.” Although mission life requirements were just minutes or hours at the beginning of space exploration, rising to months in the 1960s and to several years now in the case of a space station, the characteristics of the lubricants have barely changed. The Braycote formulation effectively proved itself more than 40 years ago. Approving for space takes years, and doesn’t come cheap. However, as the space industry develops, including the rise of private and space tourism sectors and developments by other space entities, such as the European Space Programme, the customer base for these high performance products is expected to widen. According to NASA, the limiting factor in terms of spacecraft mechanism life and allowable operating temperature range is the lubricant. Lubricant stress limits, such as the 100,000 psi contact pressure limit for Braycote, are important design drivers that determine the physical size and weight of space mechanisms. Exploration of Mars’s higher and colder latitudes would require lubricants that could withstand temperatures even more extreme than those currently experienced, whereas lubricants that could withstand higher temperatures would enable operation on the surface of planets such as Venus. Much of this is as yet unknown territory. But what is known is that space presents environments far more hostile than those currently encountered on Mars by Curiosity and Castrol’s Braycote. Castrol is working closely with NASA and other agencies to develop other lubricants to meet the ever-increasing challenges of space exploration. In theory, the sky is the limit. But as the Braycote line is proving, sometimes you can push those limits just a little farther.
* Images courtesy of NASA/JPL-Caltech/MSSS