Earlier this year (May 2020) space enthusiasts were granted some temporary relief from their day to day terrestrial concerns as NASA astronauts Robert Behnken and Douglas Hurley blasted off to the International Space Station (ISS) aboard a rocket and spacecraft developed by Elon Musk’s SpaceX corporation.
The launch marked a symbolic moment. Not only was it the first time in almost a decade that US astronauts had launched from American soil but it was also the first NASA mission of its kind to use a privately developed spacecraft, and therefore represented a significant landmark moment in the rise of commercial space technology.
But whilst Bob and Doug’s trip to the ISS will no doubt grab the biggest share of column inches, this month (July 2020) sees the launch of a mission that is arguably far more technically significant, as the latest chapter of NASA’s robotic exploration of Mars begins.
Scheduled to launch from the Kennedy space complex between July 17 and August 5th, NASA’s Mars 2020 mission will see Perseverance - an advanced rover bristling with an array of newly developed scientific instruments - set off on a seven month long trip to the red planet, where it will probe the surface for signs of ancient life; collect and cache rock samples; and trial technologies that will pave the way for a manned mission to the planet.
The mission will follow in the footsteps (or more accurately tyre tracks) of the Curiosity rover which is still operational after landing on Mars in August 2012 and will replicate many of the aspects of that earlier mission.
This includes elements of Curiosity’s audaciously inventive landing sequence which used thrusters, then a parachute, to slow the descent of the rover-carrying spacecraft before deploying an elegant “sky crane” manoeuvre in which the rover was lowered gently to the surface on nylon tethers suspended from the hovering spacecraft.
Described as “seven minutes of terror” by the engineers involved this landing was famously seat-of-the pants first time round, but valuable lessons were learned from the mission, and thanks to a number of innovations, NASA scientists hope that Perseverance’s landing will be a slightly less nerve-jangling affair.
A key development here is an innovation known as range trigger technology that will choose precisely the right moment to deploy the parachute in order to help the rover land as close as possible to its prime scientific target: Jezero Crater, an area which scientists believe was once home to an ancient river delta.
According to NASA this system, which makes a calculation based on the spacecraft’s position relative to the landing target, enables scientists to reduce the size of the landing elipse (the oval shaped landing target) by as much as 50 per cent and could save as much as a year’s worth of “commuting” time by placing the rover close to the areas of most scientific interest.
With the parachute deployed, a further system known as terrain relative navigation will help to further optimise the rover’s descent. This technology will compare images taken by orbiters with images of the fast-approaching surface gathered by the rover, and adjust the direction of the descent vehicle accordingly. NASA says that this will be critical to helping land the rover in the challenging terrain that is considered most interesting from a scientific point of view.
As the rover descends, a new suite of advanced sensors, cameras and microphones will help engineers understand more clearly what is happening, as well as potentially give viewers back on Earth a ringside seat at one of space science’s most exciting spectacles.
The rover itself also owes an engineering debt to its predecessor whilst boasting several improvements.
Largely based on the engineering design for the Curiosity rover, Perseverance is around 3 metres long, 2.7 metres wide, 2.2 metres tall and weighs 1025kg. Like Curiosity, it is powered by a multi-mission radioisotope thermoelectric generator that converts heat from the natural radioactive decay of plutonium into electricity. It also boasts three communications antennas for sending data directly back to Earth.
Key improvements over the earlier system include larger diameter, and more robust aluminium wheels, and an advanced new software system developed to help the rover manage its daily activities more effectively, and to operate with greater independence than Curiosity.
But perhaps the biggest difference is the system that will be used to gather and cache samples that will be collected and returned to Earth by subsequent missions.
Described by the mission’s chief engineer Adam Steltzner as “the most complicated, most sophisticated mechanism that we have ever built, tested and readied for space flight,” this system consists of what are effectively three separate robots designed to work in tandem.
The most visually striking element is the rover’s two-metre-long robotic arm, a five jointed structure bolted to the front of the chassis. This carries a large hand (or turret) which features a percussive drill that will be used for collecting and saving rock samples.
A robotic carousel provides drill bits and empty sample tubes to the drill and moves tubes containing samples into the rover chassis, whilst a third robotic system, a half metre long sample handling arm - will move these samples between the carousel and storage stations within the rover.
In addition to the sample caching system the rover is equipped with a payload of various scientific instruments for measuring the atmospheric characteristics of the planet, assessing the mineralogy of the Martian surface, and probing the subsurface.
A further instrument, the Mars Oxygen ISRU Experiment (MOXIE) will even attempt to produce oxygen from Martian atmospheric carbon dioxide, an effort that could pave the way for technology able to produce oxygen for propellants for future Mars Ascent Vehicle (MAV).
But Perseverance will save what is arguably its most eye-catching party trick until around two months after it lands, when a small helicopter will emerge from the rover’s belly to perform what is hoped to be the first powered flight on Mars, or indeed any planet other than the Earth.
Dubbed Ingenuity, this solar powered autonomous vehicle will perform a series of test flights and help inform decisions relating to the use of helicopters on future Mars missions, where it’s thought they could be used as robotic scouts to survey terrain from above and to carry out further scientific experiments.
Powered flight on Mars presents some significant challenges: whilst the gravity is around a third of that on Earth, the atmosphere is around 1 per cent the density of Earth’s, making it much harder to generate lift.
Developing an aircraft capable of flying these conditions required miniaturisation of many of the key components so that it is light enough to take off. Powered by solar energy, the aircraft weighs just 1.8kg and is propelled by two 1.2-metre-long rotors that spin at upto 2400 rpm.
The aircraft will operate autonomously and is equipped with inertial sensors, a laser altimeter and two cameras to help it make sense of its environment. Its first flight will be short hover lasting around 30 seconds, and it will then attempt incrementally more challenging missions, culminating in flights of around 300 metres at altitudes of 10 – 15 feet above the ground.