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.
Lubricants must keep the rover moving for its entire life on Mars
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.
“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.”
Temperature on the Red Planet is critical consideration
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.
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. Castrol lubricants are used in the gearboxes of all of Curiosity’s powered mechanisms, including its motors; its mast deployment, elevation and pivot mechanism; and its robotic arm’s numerous joints. They are also present in the drill mechanisms and dust-removal tool and in the scientific instruments inside Curiosity’s body, and were vitally important 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 greases and oils are subjected 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.
Braycote lubricants continue to reach for the stars
Mission life requirements were just minutes or hours at the beginning of space exploration. This rose to months in the 1960s and to several years now in the case of a space station, but the characteristics of the lubricants have barely changed.
Exploration of Mars’s higher and colder latitudes would require lubricants that could withstand temperatures even more extreme than those currently experienced. Conversely, 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.
Two years on, Curiosity is still active, and on 11 May 2016, it completed its second Martian year since landing inside Gale Crater nearly four Earth years ago. For updates on the rover, follow @MarsCuriosity.
This article was first produced by BP Magazine in April 2014, and has been reproduced by the QEPrize with the permission of BP. The article has been edited for length and clarity.
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