Space Sunday: Curiosity’s 10th, and motors for rockets

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.

This series of images shows the Martian moon Phobos as it crossed in front of the Sun, as seen by NASA’s Curiosity Mars rover on Tuesday, March 26th, 2019 (mission Sol 2359). Credit: NASA/JPL / MSS

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.

A view across the slopes of “Mount Sharp” captured on September 9th, 2015 using Curiosity’s MastCam. The circle denotes a boulder roughly the size of the rover, to the left of which is “Paraitepuy Pass,” which Curiosity started traversing in 2022. Credits: NASA/JPL

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.

Centred in this 360-degree collage of 27 images is the boulder circled in the above image, and which Curiosity drove by on July 15th, 2022 (mission day Sol 3533). Credit: NASA/JPL
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”.

Captured earlier in 2022, this image shows the damage suffered by Curiosity’s left centre wheel after almost 10 years of operations on Mars. Credit: NASA/JPL

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.

SpaceX Starship Update

SpaceX is moving closer to getting back on-track with its Starship flight test programme following the Booster 7 spin-start mishap on July 11th, 2022 (see: Webb’s Views, Booster Bang + Rogozin’s Roulette),  although unsurprisingly, the company is well behind Elon’s Musk’s predications that things would be on track “within a week” in the days after the mishap.

Over the course of the weekend of August 6th/7th, Booster 7 made a returned to the orbital launch facilities at Boca Chica, Texas, in the expectation it would be undertaking one or more static fire tests of the 20 Raptor engines which had been refitted following the July incident, a necessary step in clearing the Booster in readiness for the orbital launch attempt it is due to make with Starship 24.

The first tests came on Monday, August 8th, when the booster was partially fuelled – as was Ship 24; however, these tests weren’t static fire operations, but spin start tests similar in nature to the one that caused the July 11th incident. After fuelling, two spin-start were performed an hour apart on one of Booster 7’s 20 Raptors, with two tests similarly performed later in the day with 2 of the motors on Ship 24 – marking the 6th and 7th such tests the Starship has carried out.

Tuesday August 9th: a single Raptor 2 (of the 20 fitted) ignites on Booster 7, marking the firs static first test for the launcher, and the first such test to be completed from the Starship / Super Heavy orbital launch platform at Starbase, Boca Chica, Texas. Credit: SpaceX

Then, on Tuesday, August 9th both vehicles were again partially fuelled, and the news came of an imminent static fire test, causing some excitement among SpaceX fans that all 20 Raptors on to booster would be fired. This was not to be as, some four minutes after the schedules time of the test, a single Raptor on Booster 7 fired for 3 seconds. Whilst not the spectacle some had hoped for, the test nevertheless marked the first successful test for both Booster 7 and the orbital launch pad. Several hours later, Ship 24, completed its first static fire test with two of its engines.

Finally, on Thursday, August 11th, Booster 7 underwent a “long duration” static fire test, lasting 20 seconds. This was again using a single Raptor motor, and allowed a test of the autogenous repressurisation system. In short, this is feeding gaseous methane and oxygen back from the motors to their respective propellant tanks, thus helping them to remain correctly pressurised as they are drained of liquid propellants, rather than a dangerous vacuum forming which could cause a tank to collapse and avoiding the need for a separate gas – such as helium – having to be carried by the booster in order to achieve the same result.

Tuesday August 9th, 2022: Starship 24 completes a 2-enger static fire test while mounted on a sub-orbital launch stand, several hours after Booster 7 had completed its initial firing. Credit: StarshipGazer.

Following these tests, Booster 7 was rolled back to the production area, presumably for final inspections, installation of the remaining 13 Raptor motors and the engine shielding, some of which was clearly absent from the booster during the tests. It’s not clear why the static fire test was only with one engine, or whether that means there will yet be further tests once the booster again has its full complement of 33 engines.

Russia (and Ukraine) Out for Antares

Northrop Grumman and Firefly Aerospace have announced they are to work together with a new version of Northrop’s Antares launch vehicle in a move that will put an end to any reliance on Russian and Ukrainian supplied vehicle elements.

Antares is the purpose-built booster vehicle used to lift Cygnus automated re-supply vehicles on their way to the International Space Station (ISS). It was originally designed by Orbital Science Corporation (later Orbital ATK, and purchased by Northrop in 2018), a company with little experience with large liquid-fuelled rocket stages.

A Ukrainian-built, Russian motor powered Antares 230 on the pad at MARS in September 2020. Credit: Northrop Grumman Corporation

Because of this, the company outsourced the development, construction delivery of the Antares first stage to two Ukrainian aerospace companies, the stage initially using Ukrainian AJ26 motors before switching to the functionally similar, but more powerful Russian RD-181 motors. With Russia’s invasion of Ukraine, the future of Antares first stage deliveries were thrown into doubt, forcing Northrop Grumman to seek a means of ending – or at least bypassing – any issue of vehicle first stage deliveries.

Cygnus generally visits the ISS two times a year, the Northrop has enough available Antares first stages to meet two further launches: NG-18 (October 2022) and NG-19 (February 2023); after this, things looked a little dicey.

A view of the base of an Antares 230 launch vehicle, showing the two Russian RD-181 motors. The 330 vehicle will replace these with seven Firefly Miranda motors. Credit: Northrop Grumman Corporation

However, under the new partnership with Firefly, Antares will be extensively redesigned. The first stage will be updated to use seven of Firefly’s Miranda motors, with the stage being jointly built by both companies. A revised upper stage for the vehicle (already built by Northrop) will also be developed, with the entire vehicle being designated the Antares 330.

Overall, the work will remove all non-US reliance for constructing Antares and see an increase the vehicle’s payload-to-orbit capability, enabling future Cygnus vehicles to deliver 5 tonnes of cargo to the space station, with launch operations continuing from MARS (the Mid-Atlantic Regional Spaceport), Virginia.

The development work is to be fast-tracked by both companies, with a target of 2025 for the launch of the first Antares 330 / Cygnus combination – which is an exceptionally aggressive time frame. However, it still leaves a shortfall of three planned missions: Cygnus NG-20 through NG-22; to overcome this, Northrop has contracted SpaceX to supply a Falcon 9 vehicle for each of these (yet to be formally scheduled) launches out of Kennedy Space Centre.