Bengaluru: It can take up to a decade for a Mars mission to get from the drawing board to operations. And before it can take off, rigorous trials await, or as NASA calls them, “trials by fire, ice, light, and sound”.
Just how rigorous are the trials, you ask? It’s like training for a 10K race in the spring by running 20K in peak Indian summer, during the afternoon, with hurdles to boot.
Because when you are aiming for the stars (and planets), nothing can be left to chance. And you have to be 100 per cent convinced that the parachute meant to carry the spacecraft through the last leg will sail smoothly even with nearly twice the weight.
But it’s all worth it because, when everything falls into place, and the mission finally lands where it is meant to, it’s like watching “science fiction come to life”.
Last month, NASA’s Mars 2020 mission, consisting of the Perseverance lander and the Ingenuity helicopter, touched down on the Red Planet in a crater called ‘Jezero’, which means “lake” in many Slavic languages.
NASA, the US space agency, is a veteran at landing spacecraft on Mars. It has sent 19 missions to the planet so far, including 10 landers and rovers.
However, landing on Mars, with its minimal but non-negligible atmosphere and distance from Earth, comes with many challenges.
Two members of NASA’s Perseverance squad, Soumyo Dutta, an aerospace engineer in the Entry, Descent, and Landing (EDL) team, and Kavita Kaur, a software systems engineer in Ground Data Systems (which provides ground software tools and infrastructure), spoke to ThePrint about how Martian missions are planned and executed, and how the landing was made more precise with the Mars 2020 mission.
Planning for a Mars mission
Talking about the process behind planning a Mars mission, Kaur said, “It can take from eight years to a decade to go from formulation to actual operations.”
She then explained how a whole universe of teams, each with their own set of responsibilities, comes together to make it happen.
The umbrella organisation, Kaur said, is the project system. This consists of multiple sub-segments that cater to specific, core functionalities.
For example, the payload system takes care of instrumentation and payloads; the flight system handles hardware and the building of the spacecraft, as well as its testing and integration; the mission system has two teams — the ground data system, which provides software, support, and infrastructure, and the mission operations system, which actually operates the mission.
Additionally, there is flight software that goes on board the spacecraft, which enables communication and functionality of the mission.
All of the aforementioned systems consist of multiple teams and sub-systems within themselves operating in tandem.
Once these systems are in place, the project proceeds to preliminary design, followed by critical design and implementation, Kaur said. Then come assembly, test, and launch operations. The project then transitions to the operations phase with the launch, which is followed by the cruise, and then EDL, and, ultimately, when the spacecraft is on Mars, the surface operations.
Entry, Descent, and Landing
The EDL system on Perseverance used a heat shield to enter the atmosphere, after which it was jettisoned. A supersonic parachute then opened up, slowing down the spacecraft’s descent. This then released a powered sky crane that manoeuvred a dangling rover and set it on the ground at the desired landing spot, before cutting off its own cables and flying away to fall at a safe distance.
This process is similar to that of Curiosity, another NASA mission that landed on Mars in 2012, but more sophisticated, involving newer operations that made the landing more precise.
“The EDL system itself did a couple of different things that are really going to expand our ability to send missions to Mars,” said Dutta. “We can target different locations on Mars, and we can get to sites that geologists and scientists really want us to get to. As an engineer, when I see the surface of Mars where geologists want to get to, I see hazards. They’re places that I don’t want to land because those are hard for my rover, but we have to come up with the technology to do it.”
Perseverance landed in Jezero Crater, an ancient basin that scientists believe was filled with water in the past, when conditions were more hospitable on the planet. Rocks exposed to water have higher chances of holding biosignatures, if any.
Perseverance had on board a Range Trigger, which changed how the parachute opens. For Curiosity, it was dictated by the velocity at which the craft was moving, but for Perseverance, it was based on the distance from the target landing site.
There was also the Terrain-Relative Navigation, which used onboard cameras that were activated after the heat shield was released, and matched up surface landmarks with existing images. This enabled the rover to manoeuvre with precision within five meters of the planned landing site.
A large part of testing these processes involve simulations on computers followed by end-to-end actual testing of equipment. The rover went through intensive testing, described by NASA as “trials by fire, ice, light, and sound”, for conditions that are much more severe than on Mars, to ensure safety and survival.
The rover was tested with random waves of sound up to 143 decibels (louder than a jet engine up close) as a part of acoustical tests. For light and heat tests, the rover was placed in a vacuum chamber for entire days, exposed to powerful xenon lamps that simulated conditions of extreme sunlight. The same chamber was cooled down to -129 degrees Celsius to test for the intense cold it has to endure during long Martian nights. The average surface temperature of Mars is -63 degrees Celsius.
The prototypes of the parachute that opened up after the heat shield was discarded — each of them held a binary coded message that read “Dare Mighty Things” — were tested in wind tunnels. The actual parachute itself that flew to Mars was tested thrice using sounding (sub-orbital) rockets and carried a 37,000kg weight — about 85 per cent more than the parachute was expected to encounter during deployment.
“Basically we tested it to higher conditions than would be ever expected on Mars, just to make sure that we have what we call ‘margin’ in our system design,” said Dutta. “That’s really key, that we have a large margin of safety built into our engineering design so that we can feel confident when we send it to its planetary destination.”
Communications and data stream
About six to eight months prior to launch, the mission operation system develops processes and identifies roles for operations. They then start simulations of operations through different levels of testing. These tests recreate scenarios of critical events and how data is obtained through them. The operations team also provides tools and infrastructural support.
Communications during an operation are monitored by the Deep Space Network, a series of three antennae placed around the globe at 120 degrees — in California (USA), Madrid (Spain), Canberra (Australia) — such that, at any time during the Earth’s rotation, one antenna always faces the spacecraft.
The direct-to-Earth (DTE) signals are ones where the antennae relay signals and data directly to ground station for processing, while the reverse occurs in Direct-from-Earth (DFE) signals.
The EDL process itself is autonomous since operations occur much faster than the time taken to relay signals to Earth and back. Additionally, the landing process is choreographed meticulously by scheduling overhead passes of orbiters currently around Mars. These orbiters sent back landing confirmations through signals and images before Perseverance itself could.
The images and other media from the rover arrive as raw data that are downloaded through a data pipeline and automatically processed by software. They are then reviewed and uploaded to the outreach website before they are processed, either in-house or by external experts.
“The pipeline is all fully automated, there is a little bit of human intervention required every now and then, during operations when we have to upgrade the software, but it’s primarily automated,” said Kaur.
Objectives and future missions
Kaur said the “big objective” that NASA is trying to accomplish “with this mission is to seek signs of ancient microbial life on Mars”.
“I think it’s a very fundamental question that has been intriguing humanity as a whole, whether there’s life anywhere else beyond the Earth, and we’re going there to find the answer to that question,” she added.
The Jezero crater shows evidence of a delta and outflow of water, and such structures hold clays and rocks that have the potential to harbour biosignatures. Perseverance is expected to sample some of these rocks and soil, and even store them in secure containers on the surface of the planet for future sample-return missions to bring them back to Earth for further analysis.
While previous rovers such as the advanced Curiosity, described by Dutta as “the most sophisticated geologist ever sent to Mars”, did perform in-situ analysis of soil, Perseverance hopes to find more with its complex payloads.
There are two main systems on Perseverance that are newer and more complex than Curiosity’s payloads — the sample caching system and MOXIE.
The sample caching system is a robotic arm within the rover, different from its primary robotic arm, that will take materials and store them in clean sample tubes, said Dutta. The MOXIE system, which stands for Mars Oxygen In-Situ Resource Utilization Experiment, is an experimental payload that uses the Martian atmosphere to create oxygen on the planet. It is expected to aid future missions, including crewed landings on the planet.
The mission is expected to fly the Ingenuity helicopter in the first week of April, pulling off the first powered flight on another planet.
“After the year 2020 that all of us have gone through, it’s a really bittersweet moment but also really exhilarating that we could have done that,” said Dutta. “I still can’t believe it happened, it’s science fiction come to life.”
(Edited by Sunanda Ranjan)