The Mars 2020 rover mission is set to launch in the coming days. We spoke with a NASA engineer to learn more about the challenges of landing a rover on the Red Planet.
In the coming days, NASA will launch the Mars 2020 Mission to the Red Planet with the Perseverance rover in tow. The mission builds on the legacy laid and the lessons learned from its roving Martian predecessors. The rover is scheduled to enter the Martian atmosphere in February of next year. Needless to say, preparing a craft to travel millions of miles through the cold vacuum of space and successfully land a rover on another planetary body is no cosmic cakewalk. We recently spoke with Keith A. Comeaux, deputy chief engineer on the Mars 2020 Mission, about the challenges involved in landing a craft of the Red Planet.
Comeaux joined the Perseverance team in early 2017 as the project’s deputy chief engineer. Prior to his work on the Perseverance, Comeaux joined JPL’s Curiosity Program in 2006 as part of the rover’s entry, descent, and landing team. He also worked on the Assembly, Test, and Launch Operations (ATLO) team testing the rover as well as the systems involved in delivering the craft to Mars.
“I was flight director on console during [Curiosity’s] entry, descent and landing. That guy that’s jumping up and down in the video that you might have seen. That’s me,” Comeaux said.
(In case you have not seen the video, Comeaux can be seen jumping up and down at the 35:33 mark.)
On Perseverance, Comeaux focused on supporting the ATLO program, system engineering, and the mission’s testing program. During this time, he helped design tests and simulations to ensure the successful entry, descent, and landing on Mars. These testing parameters are an integral part of mission planning, however, it’s difficult to completely simulate the environment of another planet from millions of miles away.
“We cannot test the entire system here on Earth because Earth just doesn’t present the same environment, both gravity and atmosphere, that we have on Mars. It really is the first time that we’re ever testing the system when we’re doing it for real at Mars,” Comeaux said.
Entering the Martian atmosphere: Simulations and approximations
If all goes as planned, the craft will enter the Martian atmosphere at about 12,000 miles per hour. While speed is one factor to consider, the atmosphere is another. The Martian atmosphere is 100 times thinner than Earth’s and this makes slowing down all the more challenging.
NASA’s ASPIRE program focused on creating a specially designed parachute capable of slowing down the craft at these high speeds in the Martian atmosphere. To do so, the team used tests at high altitudes here on Earth and high-speed camera footage to understand the parachute inflation in high-speed and high-altitude environments.
Although the ASPIRE program was designed to closely mimic the entry environment on Mars, these tests do not completely simulate these conditions exactly.
“Even the ASPIRE Program tested in Earth’s atmosphere, which is nitrogen and oxygen. Whereas the density was similar to Mars, it was the wrong gases. At Mars, it’s carbon dioxide. Air versus carbon dioxide can behave differently, especially at supersonic speeds,” Comeaux said.
During the Curiosity mission, the parachute was triggered once the craft was within a certain speed range to ensure the structural integrity of the parachute, according to Comeaux. This time around, NASA is taking a different approach to parachute deployment on Perseverance.
“Now we have a lot more confidence about the conditions at which our parachute can be opened and, rather than triggering on the speed, we’re triggering on our location on Mars relative to where we want to actually land and this gives us a much more precise landing capability on this mission compared to all past missions,” Comeaux said.
The Mars 2020 Mission will feature the debut of the Lander Vision System LVS) and Terrain Relative Navigation (TRN) to assist with descent and landing operations. As the parachute slows down the craft, an onboard camera and navigation systems will scan the surface. This system utilizes images stored onboard and compares these maps to the real-time camera information to pinpoint and guide the craft to optimal landing sites.
“We have a camera and a computer onboard, which is taking successive pictures of our landing zones while we’re hanging on the chute, and it’s comparing those pictures to a map that it has stored onboard,” Comeaux said.
The rover is set to land in the Jezero Crater, an area with a “high potential” for detecting evidence of ancient microbial life. Over the years, orbiters have provided detailed images of this region. This area is filled with boulders, cliffs, depressions, and another rugged terrain that could pose a hazard to the descent vehicle system and the rover. This visual system is engineered to avoid these surface structures en route to predetermined landing sites.
“When the time comes to actually release the backshell and the parachute, we fire up the thrusters on the powered descent vehicle, we basically do a maneuver to go target one of those safe areas that it has determined based on pictures that it took,” Comeaux said.
After the descent vehicle has nimbly navigated any barriers in its path, the craft will then be positioned directly above the final landing spot. The vehicle will begin its vertical descent and then slowly lower the rover to the surface using a series of tethers. Once the rover’s wheels come into contact with the Martian surface the craft signals to the overhead vehicle, explained Comeaux.
“Then we cut bridles, we cut the electrical umbilical, and then the descent stage flies away about several hundred meters away to safely crash on the surface and then the rover is ready to go to work,” Comeaux said.
Margins for error and learning from past miscalculations
During the entry, descent, and landing there’s tremendous potential for disaster and virtually no margin for error. The craft will perform numerous reconfigurations, onboard guillotines cut cables to enable progress to the next stage, and any recontact between surfaces during separations could damage the rover.
Let’s not forget about the launch itself and the millions of miles of spacefaring between Earth and Martian entry.
Interestingly enough, NASA has made miscalculations with past rover missions without compromising the mission. Comeaux discussed one mathematical error on Curiosity in particular.
“The problem that I like to recall is the fact that we got gravity wrong on Mars, which is stunning,” Comeaux said.
It all comes back to the idea of simulation and modeling from afar. Engineers can simulate these Martian atmospheres in Earth laboratories, but sometimes teams don’t know what they don’t know.
“We run Newton’s Laws to simulate the entire entry, descent and landing sequence. One of the things that you’ve got to tell the simulation is, ‘What is the gravity of Mars?’ So we assumed we knew what it was and we stuck a number in there, but it turns out that gravity is not constant everywhere on a planet,” Comeaux said.
The surface terrain such as cliffs as well as subsurface elements affect the overall gravity of a given area, explained Comeaux.
“It varies from place to place, depending on whether you’re nearby mountains, or craters, or large mass concentrations that are underground, that you can’t even see. So our knowledge of Mars’ gravity was not super great,” Comeaux said.
At the time, the team did not factor in the exact gravity of Curiosity’s exact landing area.
“We put the best number that we knew for our landing site, but it turns out we’re landing in a 96 mile crater next to a 15,000-foot mountain, and so the local gravity in that spot was a little bit different,” he continued.
In the time since Curiosity, the team has utilized this knowledge of Martian gravity to enhance entry, descent, and landing operations on the latest Mars rover.
“Now in our simulations for Perseverance, we actually vary the gravity. We do these large Monte Carlo simulations where we run that simulation hundreds of thousands of times and we perturb each one of the inputs, just a little bit, every time to see if there’s any major effect. We didn’t used to do that for gravity at Mars and now we do, because of what we learned on Curiosity,” Comeaux said.
The Mars 2020 Mission features other instrumentation firsts to provide the space agency with a better understanding of entry, descent, and landing operations and build on these insights. The mission will include a series of cameras on the rover and other decent vehicles to monitor the parachute as it deploys, a first-hand glimpse of the surface as the vehicle approaches, as well as a camera on top of the rover to watch as the skycrane flies away after the successful touchdown on Mars.
“That whole landing sequence, we’ve never really seen it with human eyes. We had telemetry, but that data is limited,” Comeaux said.
NASA has taken a surprisingly low-tech approach to these aforementioned onboard optics.
“It’s a commercial, off the shelf package that we added to our systems. There’s a chance that it may not work simply because it’s commercial components,” Comeaux said.
Other sensors, such as (MEDLI2) located in the craft heat shield, will gather data related to pressure and temperature to help NASA gain a better understanding of flight dynamics as the craft enters the Martian atmosphere, explained to Comeaux.
“This gives us a profile of the pressure through the vertical direction in the atmosphere and helps us better understand the flight dynamics. After landing, we can reconstruct what actually happened and know a little bit more about how to fly through the Martian atmosphere,” Comeaux said.
Whether it’s fine-tuning the gravity modeling or a better understanding of flight dynamics, each mission builds on the lessons learned in previous programs. In fact, as Comeaux pointed out, the Perseverance mission actually utilizes the same guidance algorithm that was originally designed for the Apollo program. This suite of advanced instrumentation will help NASA plan for missions to Mars in the years ahead.
For now, the spacecraft is stowed away in its payload fairing. The Mars 2020 Mission launch window opens on July 30. There’s certainly no shortage of challenges standing between the launchpad at Cape Canaveral and the surface of our distance celestial neighbor.
If all goes as planned, in about seven month’s time, the craft is set to land in the Jezero Crater and provide never before seen views of this strange, alien landscape.
“There’s a fair chance that we could land right next to that river delta, and be looking at it when we open our eyes and start taking pictures. Can you imagine the sight? It would be like landing in some national park when we take those first pictures,” Comeaux said.
Be in the know about smart cities, AI, Internet of Things, VR, AR, robotics, drones, autonomous driving, and more of the coolest tech innovations. Delivered Wednesdays and Fridays
Thales Alenia Space will provide the IRIS altimeter for the Copernicus CRISTAL mission
(21 September 2020 – Thales) Thales Alenia Space has today signed a close to €88 million contract with Airbus Defence and Space, prime contractor of the satellite, to develop the two IRIS flight models (Interferometric Radar Altimeter for Ice and Snow) of the Copernicus polaR Ice and Snow Topography ALtimeter (CRISTAL) mission.
The CRISTAL mission is part of the expansion of the Copernicus Space Component programme of the European Space Agency, ESA, in partnership with the European Commission. The European Copernicus flagship programme provides Earth observation and in situ data and a broad range of services for environmental monitoring and protection, climate monitoring, natural disaster assessment to improve the quality of life of European citizens.
The CRISTAL satellite will carry, for the first-time, a dual-frequency Ku/Ka bands radar altimeter to measure and monitor sea-ice thickness and overlying snow depth. Measurements of sea-ice thickness will support maritime operations and they will help in the planning of activities in the polar regions. IRIS will also measure and monitor changes in the height of ice sheets and glaciers around the world, thanks to its interferometric radar mode. IRIS will significantly improve the measurement accuracy of its predecessor SIRAL-2 (a Ku band only altimeter on board ESA’s CryoSat-2 Earth Explorer mission) thanks to the dual frequency operation and by adding the measurement of sea surface height as part of the mission objectives. The CRISTAL global mission is essential to better understand and monitor Earth climate in a context of the rapid climate change.
CRISTAL (courtesy: Airbus Defence and Space)
Hervé Derrey, CEO of Thales Alenia Space declared: “By providing the IRIS altimeter onboard CRISTAL, Thales Alenia Space is pleased to contribute to improve the data already provided by SIRAL-2 on board Cryosat and ensure the continuity of ice monitoring. Polar regions have a real influence on patterns of global climate, thermohaline circulation, and the planetary energy balance. A long-term program to monitor Earth polar ice, ocean and snow topography is therefore of the utmost interest to both operational and scientific users of Arctic and Antarctic measurements.”
Marc-Henri Serre, VP Observation and Science domain, at Thales Alenia Space in France added: “Thales Alenia Space will bring all its expertise and long-standing heritage on space altimetry, and its flight proven heritage acquired with SIRAL-2 to serve this crucial mission to understand and monitor the climate”.
The IRIS altimeter is designed and it will be built from the legacy of several altimeter programs of the Thales Alenia Space product line, including SIRAL-2, Poseidon 4 on board Sentinel-6/Jason-CS, Alti-Ka on the CNES/ISRO satellite, and KaRIn on board the CNES/JPL SWOT satellite. Thales Alenia Space is also the first to have flown an interferometric SAR altimeter (SIRAL) offering a unique expertise in interferometric radar electronics and interferometric antennas.
About industrial contributions for CRISTAL
Thales Alenia Space in France is prime of the IRIS altimeter, with contribution from Thales Alenia Space in Belgium for the Ku and Ka band Solid State Power Amplifiers power supply, Thales Alenia Space in Italy for the Ultra stable Oscillator. Thales Alenia Space in Spain will provide the S-Band transponder (SBT) of the CRISTAL satellite.
Thales Alenia Space: world leader in space altimetry
Thales Alenia Space is a world leader in space altimetry, a technique that lets us study sea surface height, sea ice thickness and river and lake levels, as well as land, ice sheet and seabed topography. The company has provided a whole host of instruments for oceanography, like the Poseidon altimeters on the Topex-Poseidon and Jason 1, 2 and 3 missions for the CNES. Thales Alenia Space also built the AltiKa Ka-band altimeter for the French-Indian SARAL oceanography satellite, and the SIRAL 2 very-high-resolution SAR (synthetic aperture radar) altimeter on ESA’s Cryosat-2 satellite, capable of measuring variations in sea ice thickness and continental ice mass balance with unprecedented accuracy. In addition, Thales Alenia Space supply the SRAL SAR altimeters for Sentinel-3, the SWIM altimeter on the CFOSat satellite for CNES, which measures wave spectra, and the SADKO altimeters on Russia’s GEO-IK satellites.
About Thales Alenia Space
Drawing on over 40 years of experience and a unique combination of skills, expertise and cultures, Thales Alenia Space delivers cost-effective solutions for telecommunications, navigation, Earth observation, environmental management, exploration, science and orbital infrastructures. Governments and private industry alike count on Thales Alenia Space to design satellite-based systems that provide anytime, anywhere connections and positioning, monitor our planet, enhance management of its resources, and explore our Solar System and beyond. Thales Alenia Space sees space as a new horizon, helping to build a better, more sustainable life on Earth. A joint venture between Thales (67%) and Leonardo (33%), Thales Alenia Space also teams up with Telespazio to form the parent companies’ Space Alliance, which offers a complete range of services. Thales Alenia Space posted consolidated revenues of approximately 2.15 billion euros in 2019 and has around 7,700 employees in nine countries.
Plans underway for new polar ice and snow topography mission
(21 September 2020 – ESA) Monitoring the cryosphere is essential to fully assess, predict and adapt to climate variability and change. Given the importance of this fragile component of the Earth system, today ESA, along with Airbus Defence and Space and Thales Alenia Space, have signed a contract to develop the Copernicus Polar Ice and Snow Topography Altimeter mission, known as CRISTAL.
With a launch planned in 2027, the CRISTAL mission will carry, for the first time on a polar mission, a dual-frequency radar altimeter, and microwave radiometer, that will measure and monitor sea-ice thickness, overlying snow depth and ice-sheet elevations.
These data will support maritime operations in the polar oceans and contribute to a better understanding of climate processes. CRISTAL will also support applications related to coastal and inland waters, as well as providing observations of ocean topography.
The mission will ensure the long-term continuation of radar altimetry ice elevation and topographic change records, following on from previous missions such as ESA’s Earth Explorer CryoSat mission and other heritage missions.
With a contract secured worth € 300 million, Airbus Defence and Space has been selected to develop and build the new CRISTAL mission, while Thales Alenia Space has been chosen as the prime contractor to develop its Interferometric Radar Altimeter for Ice and Snow (IRIS).
ESA’s Director of Earth Observation Programmes, Josef Aschbacher, says, “I am extremely pleased to have the contract signed so we can continue the development of this crucial mission. It will be critical in monitoring climate indicators, including the variability of Arctic sea ice, and ice sheet and ice cap melting.”
The contract for CRISTAL is the second out of the six new high-priority candidate missions to be signed – after the Copernicus Carbon Dioxide Monitoring mission (CO2M) in late-July. The CRISTAL mission is part of the expansion of the Copernicus Space Component programme of ESA, in partnership with the European Commission.
The European Copernicus flagship programme provides Earth observation and in situ data, as well as a broad range of services for environmental monitoring and protection, climate monitoring and natural disaster assessment to improve the quality of life of European citizens.
Astronomers solve mystery of how planetary nebulae are shaped
(17 September 2020 – Center for Astrophysics | Harvard & Smithsonian) Following extensive observations of stellar winds around cool evolved stars scientists have figured out how planetary nebulae get their mesmerizing shapes.
The findings, published in Science, contradict common consensus, and show that not only are stellar winds aspherical, but they also share similarities with planetary nebulae.
Gallery of stellar winds around cool aging stars, showing a variety of morphologies, including disks, cones, and spirals. The blue color represents material that is coming towards you, red is material that is moving away from you. Image 8, in particular, shows the stellar wind of R Aquilae, which resembles the structure of rose petals. (courtesy: L. Decin, ESO/ALMA)
An international team of astronomers focused their observations on stellar winds—particle flows—around cool red giant stars, also known as asymptotic giant branch (AGB) stars. “AGB stars are cool luminous evolved stars that are in the last stages of evolution just before turning into a planetary nebula,” said Carl Gottlieb, an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and a co-author on the paper. “Through their winds, AGB stars contribute about 85% of the gas and 35% of the dust from stellar sources to the Galactic Interstellar Medium and are the dominant suppliers of pristine building blocks of interstellar material from which planets are ultimately formed.”
Despite being of major interest to astronomers, a large, detailed collection of observational data for the stellar winds surrounding AGB stars—each made using the exact same method—was lacking prior to the study, which resulted in a long-standing scientific misconception: that stellar winds have an overall spherical symmetry. “The lack of such detailed observational data caused us to initially assume that the stellar winds have an overall spherical geometry, much like the stars they surround,” said Gottlieb. “Our new observational data shapes a much different story of individual stars, how they live, and how they die. We now have an unprecedented view of how stars like our Sun will evolve during the last stages of their evolution.”
Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed something strange: the shape of the stellar winds didn’t conform with scientific consensus. “We noticed these winds are anything but round,” said Professor Leen Decin of KU Leuven University in Belgium, and the lead author on the paper. “Some of them are actually quite similar to planetary nebulae.” The new findings may have a significant impact on calculations of galactic and stellar evolution, most pointedly for the evolution of Sun-like stars. “Our findings change a lot,” said Decin. “Since the complexity of stellar winds was not accounted for in the past, any previous estimate of the mass-loss rate of old stars could be wrong by up to a factor of 10.”
The observations revealed many different shapes, further connecting stellar wind formation to that of planetary nebulae. “The winds we observed exhibit various shapes that are similar to planetary nebulae,” said Gottlieb. “Some are disk-like, while others are shaped like eyes, spiral structures, and even arcs.”
Astronomers quickly realized that the shapes weren’t formed randomly, and that companions—low-mass stars and heavy planets—in the vicinity of the AGB stars were influencing the shapes and patterns. “Just like a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind,” said Decin. “All of our observations can be explained by the fact that the stars have a companion.”
In addition, the study provides a strong foundation for understanding Sun-like stars and the future of the Sun itself. “In about five billion years, the Sun will become more luminous,” said Gottlieb. “Its radius will expand to a length that is comparable to the current distance between the Sun and Earth, and it will enter the AGB phase.” Decin added, “Jupiter or even Saturn—because they have such a big mass—are going to influence whether the Sun spends its last millennia at the heart of a spiral, a butterfly or any of the other entrancing shapes we see in planetary nebulae today. Our current simulations predict that Jupiter and Saturn will create a weak spiral structure in the wind of the Sun once it is an AGB star.”
About Center for Astrophysics | Harvard & Smithsonian
Headquartered in Cambridge, Mass., the Center for Astrophysics | Harvard & Smithsonian (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.