Day: August 15, 2022

Ten years ago, on August 6th, 2012, the world held its breath as a capsule the size of a small truck slammed into the Martian atmosphere at the start of 7-minute descent referred to as the “seven minutes from hell”.

It would either end with the extraordinary sight (had we been able to see it) with a rocket-propelled platform hovering just metres above the surface of the planet as it gently winched a rover the size of an SUV to the floor of Gale Crater – or in a fresh new crater within the crater.

Fortunately, the former was the case, marking the true start of the Mars Science Laboratory (MSL) mission on Mars, an attempt to seek evidence that, billions of years ago, Mars had the conditions needed to support microscopic life. Coincidentally, it marked the start of the column that would morph into Space Sunday.

Since that heady day, the rover – called Curiosity – has clocked up some impressive statistics, including:

• Achieving its primary mission objective – to discover whether Mars had the conditions under which life may have arisen – within its initial 90-day mission period.
• Driving almost 29 kilometres around Gale Crater.
• Ascending 625 metres above the floor of the crater.
• Analysing 41 rock and soil samples using its onboard suite of science instruments, furthering our understanding about Mars.
• Providing huge insights into the Martian climate and weather.
• Being so successful, it has seen its mission initially extended to its full 2-year “post landing” period, and then in multi-year increments, including a recent 3-year further extension.

While Curiosity’s work has been more recently overshadowed by its sibling, Perseverance, it is still ongoing. In the last ten years, the rover has studied the Red Planet’s skies, capturing images of shining clouds and witnessing the transit of the Martian moons Phobos and Deimos across the face of the Sun, causing very localised eclipse phenomena.

In addition, the rover’s radiation sensors have helped scientists measure the amount of high-energy radiation future astronauts would be exposed to on the Martian surface, increasing our understanding of what will be needed to keep them as safe as possible – both in terms of practical protections and the types of procedures required to minimise their overall exposure whilst working on the surface of Mars.

However, Curiosity’s most important work is that of determining that liquid water as well as the chemical building blocks and nutrients needed for supporting life were present for at least tens of millions of years in Gale Crater – and that similar conditions could exist elsewhere on Mars. These discoveries directly confirmed the need for the Mars 2020 mission with Perseverance – which is designed to look for the direct evidence that microbial life did take hold in the conditions Curiosity found to be true.

After exploring the bedrock floor of the crater, Curiosity started on a major phase of its mission – scaling the flank of “Mount Sharp”, a 5-km high mound of materials deposited against and around the crater’s central impact peak during the many warm, wet periods that marked the very early history of Mars, and which meant Gale Crater was once the site of a huge lake of liquid water.

The climb has taken up the majority of the rover’s time on Mars, and is still continuing, with Curiosity recently move into an entirely new phase of operations. For the last few months the rover has been making its way along a canyon marking the transition between the more submerged parts of “Mount Sharp” – officially called Aeolis Mons – a region believed to have formed as water was drying out, leaving behind salty minerals called sulphates.

We’re seeing evidence of dramatic changes in the ancient Martian climate. The question now is whether the habitable conditions that Curiosity has found up to now persisted through these changes. Did they disappear, never to return, or did they come and go over millions of years?

– Ashwin Vasavada, Curiosity’s project scientist

The team plans to spend the next few years exploring the sulphate-rich area. Within it, they have targets in mind like the Gediz Vallis channel, which may have formed during a flood late in Mount Sharp’s history, and large cemented fractures that show the effects of groundwater higher up the mountain.

All this progress has come at a cost, however. Along the way, Curiosity had suffered several issues – all of which have been overcome as a result of a team of literally hundreds of engineers and scientists based at the Jet Propulsion laboratory (JPL) and other NASA centres as well as research centres and universities across the United States.

This has allowed major issues that might otherwise have crippled the rover’s abilities. How Curiosity drills for samples has been reinvented a number of times to overcome problems that as the very least might have ended the rover’s ability to drill at all and at worse, crippled its ability to use its robot arm.

Another area of concern has been the rover’s aluminium wheels. These bear the brunt of the sheer force of Curiosity’s progress as it makes its way over the unforgiving Martian landscape; and even while the rover’s daily progress can only be measured in metres-per-day, the fact is that it is constantly traversing terrain which could rip any one of the large aluminium wheels apart given sufficient time. As such, damage was to be expected – but the speed with which it occurred early in the mission still came as a shock, with engineers going so far as to have the rover reverse course and find a new way around some particularly rough terrain at the foot of “Mount Sharp”.

To counter the risk of wheel breakage, Curiosity’s driving has been extensively revised, and new algorithms written to help the rover better maintain traction whilst manoeuvring over rocks and to better analyse feedback from wheel motors to prevent them overworking or forcing the rover into an manoeuvre that might result in the loss of a wheel. In addition, the rover routinely examines the state of its wheels using both the MastCam system and the MAHLI imager on the robot arm.

Another threat to the rover’s future is that of electrical output. Curiosity utilises the radioactive decay of plutonium pellets within its radioisotope thermoelectric generator (RTG) to create heat which can be converted into electrical power. On the plus side, this means the rover is not dependent on the vagaries of solar power and can (initially) produce much higher levels of electrical power – some 2,000 2atts on its arrival on Mars.

The downside, however, is that the 4.8 Kg of plutonium within Curiosity’s RTG have a half-live of 14 years – and the rover is now 10 years into that period. As such, it is generating a lot less heat that can be turned into electrical power,, and as a result engineers and scientists are now looking at ways to operate the rover more efficiently and reduce the daily power requirements. This includes switching some operations to run in parallel, effectively sharing power.

Despite this latter points, Curiosity is still performing at near-optimal levels for this period in its life, and with caution and forethought, in is not inconceivable to believe the rover will not still be investigating “Mount Sharp” – even on a reduced basis – in another 10 years.

Continue reading “Space Sunday: Curiosity’s 10th, and motors for rockets” →