April 19th saw aviation and space flight history made 288 million kilometres from Earth, when a tiny drone-like craft weighing just 1.8 kg spun-up two contra-rotating rotor blades, each 1.2 metres in diameter, to 2,500 rpm and then rose into the tenuous atmosphere of Mars to a height of 3 metres, hovered rotated about its vertical axis, then descended to land on the Martian surface once more.
Ingenuity, a proof-of-concept system to test the feasibility of controlled, powered flight on Mars, is a remarkable little vehicle that holds great promise for the future of the exploration of that world. While this initial flight was short – under a minute in total length from spinning-up its rotors to touch-down, it opens the door to more extensive flights over the coming days that will see the vehicle complete more complex manoeuvres. In doing so, it will provide vital information on the behaviour of rotary vehicles on Mars, vehicles that could in the future provide enormous additional potential and capabilities to future robotic missions on Mars and eventually support human missions.
The flight occurred at 07:31 UTC on Monday, April 19th, with telemetry being recorded by the helicopter’s own systems and relayed to the Mars 2020 Perseverance rover, which also recorded the event using its Mastcam-Z camera system and its navigation cameras. The initial data from the flight was then transmitted to Earth some three hours later, with additional images and video being transmitted throughout the day.
The first indication of the success of the flight came not through any pictures but via a simple graphic track of altimeter readings made by Ingenuity. Mostly flat to show the vehicle was sitting on the ground, the track was marked by a sudden “bump” recording the vehicle rise to just over 3 metres, its hover, and then its descent. It was enough to get the helicopter’s flight team – a handful at JPL practising social distancing in a large room, the rest working from home – rejoicing. But the chart was just the opening treat.
Following the initial receipt of data, still images in low-resolution captured by Perseverance’s navigation cameras clearly showed the helicopter “jumping” between to close-together points, indicating that during the period between the images, it had flown and landed. However the biggest treat came later in the day with a stream of frames captured by the Mastcam-Z system on the rover. When strung together, these produced a video of the flight.
Ingenuity is a project more than six years in the making, and has uniquely involved not only multiple NASA space and science centres, but also their aviation research and development centres as well. It was actually a late addition to the Mars 2020 mission, requiring some extensive changes to the rover that had to be made in order to mount the helicopter beneath the rover’s belly, and include a mechanism for deploying Ingenuity onto the surface of Mars.
Ahead of the Mars 2020 launch, Ingenuity want through extensive testing to simulate flight conditions on Mars. This involved placing the vehicle a large vacuum chamber filled with carbon dioxide to a pressure to match the surface atmospheric pressure on Mars – which is the equivalent of Earth’s at an altitude of 30 km. To simulate the low Martian gravity (38% that of Earth’s), a special rig was attached to the demonstrator to counter 62% of its mass. Finally, a wall of 900 computer fans was used to simulate typical surface wind speeds on the surface of Mars, as recorded by the Mars Science Laboratory rover Curiosity.
All of this allowed engineers to define the optimal size of the helicopter’s rotors, balancing them against Ingenuity’s mass and size and to determine things like their required rate of spin to achieve flight – between 2,400 and 2,500 rpm – five times the speed of Earth-based helicopter rotors.
Even so, flying an engineering test model in a controlled environment is very different to doing the same on Mars – hence a lot was riding on this first flight.
Ahead of it, the area selected for the test flight sequence and previously dubbed “the airfield” was unofficially renamed “Wright Brothers Field”. Having safely dropped off the helicopter there in early April, Perseverance had driven some 70 metres from Ingenuity at a rise overlooking the area that NASA has dubbed “Van Zyl Overlook” in honour of key Ingenuity team member Jakob van Zyl, who passed away unexpectedly in August 2020. From this vantage point it is hoped that the rover will be able to record all of Ingenuity’s flights.
Prior to the flight, and as noted in my previous Space Sunday update, the flight team had to make some changes to the software overseeing Ingenuity’s first flight. Not only have these adjustments worked well, it is hoped that they will remove any need for running a complete software re-installation on the vehicle – a process that could take several days to complete and severely impact the ability to complete all of the remaining four planned test flights. However, the option of a full re-installation is being kept open should further issues arise with the timing and control processes.
Inn the meantime, it’s going to be a few days before all of the data from the first flight has been analysed. As such, the next flight for Ingenuity has yet to be scheduled.
When it does goes ahead, it should see the helicopter rise to an altitude of around 5 metres, then translate into horizontal flight for a distance of some 50 metres before coming to a stop, then returning once more to land.
As it is, the initial telemetry from Ingenuity shows it is a good health – better, in fact than before it lifted off. This is because the flight removed dust that had been accumulating on the solar cells located above the vehicle’s rotors, interfering with their efficiency.
In all the Mars Helicopter project has three goals:
- Show via Earth-based testing that it should be possible for a heavier-than-air vehicle to take flight on Mars – achieve via the vacuum tests described above.
- Achieve stable flight on Mars – now achieved through this first flight.
- Obtain data that can inform engineers as to the design and capabilities required by future aerial vehicles that could be deployed to Mars – and also elsewhere in the solar system, such as Saturn’s moon Titan.
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