December 18, 2018

NASA’s InSight mission lands on Mars to study planet’s hidden interior


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InSight project manager Tom Hoffman motions to an image captured by the spacecraft minutes after landing on Mars. Credit: NASA/Bill Ingalls

NASA’s InSight spacecraft plunged into the rarefied atmosphere of Mars at a speed of more than 12,000 mph Monday and braked to a gentle touchdown, setting the stage for a two-year surface mission to probe the planet’s deep interior.

Cocooned inside a heat shield, the robotic lander weathered extreme temperatures reaching 2,700 degrees Fahrenheit (1,500 degrees Celsius) as it entered the Martian atmosphere, unfurled a supersonic parachute, then pulsed 12 retrorockets up to 10 times every second in the final phase of the descent toward the red planet, finally settling on the surface with three landing legs.

Controllers confirmed InSight’s landing at 2:54 p.m. EST (11:54 a.m. PST; 1954 GMT), roughly eight minutes after the touchdown actually occurred at Elysium Planitia, a broad equatorial plain selected for its relatively flat surface free of large boulders and craters. It took that long for radio signals from InSight to travel from Mars to Earth, a distance of 91 million miles (146 million kilometers).

Tense engineers monitored the $993 million mission’s white-knuckle arrival at Mars from a control center at NASA’s Jet Propulsion Laboratory in Pasadena, California, receiving data from the lander via a pair of briefcase-sized CubeSats sent to the red planet with InSight.

The twin Mars Cube One, or MarCO, microprobes were the first spacecraft of their size to fly to another planet, and the CubeSats were primarily developed as a technology demonstration to pave the way for future interplanetary smallsats.

But the CubeSats carried a radio to relay data from InSight back to Earth. The innovative miniature radio, the size of a softball, converted UHF signals from InSight to an X-band frequency to transmit to the ground.

Engineers were not sure the MarCO CubeSats would work, so InSight’s planners had two other ways to get data from the landing — one in real-time using a weak carrier signal received by huge ground-based dish antennas, and another data relay route through the Mars Reconnaissance Orbiter, a NASA satellite flying around the red planet that recorded telemetry from the lander for later playback to Earth.

The MarCO CubeSat came through Monday, giving officials detailed information about InSight’s status as it maneuvered through the Martian atmosphere.

“Ground stations are observing signals consistent with parachute deploy,” said Christine Szalai, an entry, descent and landing systems engineer at JPL. “Telemetry shows parachute deployment, radar powered on. Heat shield separation commanded.”

Rob Manning, JPL’s chief engineer, provided color commentary on NASA TV’s broadcast of InSight’s landing.

“This is really good news so far,” said Manning, a Mars mission architect who has helped lead entry, descent and landing  teams since the 1990s. “I’m on pins and needles.”

“We have radar activation where radar is beginning to search for the ground,” Szalai said as InSight remained suspended under a 39-foot (11.8-meter) diameter parachute. “Once the radar locks on the ground and InSight is about one kilometer above the surface the lander will separate from the backshell and begin terminal descent using its 12 descent engines.

“Altitude convergence, the radar has locked on the ground!” she continued moments later, prompting applause in the JPL control room. “Standing by for lander separation… lander separation commanded. Altitude 600 meters… gravity turn, altitude 400 meters… 300 meters.. 200 meters… 80 meters… 60 meters… 50 meters, constant velocity, 37 meters… 30 meters… 20 meters… 17 meters, standing by for touchdown…

“Touchdown confirmed! InSight is on the surface of Mars!”

Artist’s illustration of InSight firing its 12 retrorockets. Credit: NASA

Monday’s landing concluded a 301-million-mile (484-million-kilometer) journey for InSight that began May 5 with a predawn fog-enshrouded blastoff aboard a United Launch Alliance Atlas 5 rocket from Vandenberg Air Force Base in California. InSight was the first Mars mission to leave Earth from the West Coast, supplanting Cape Canaveral, the typical departure point for interplanetary probes.

Within a few minutes of landing, InSight radioed its first image from Elysium Planitia, showing a flat, mostly featureless landing site, with sandy soils and a modestly-sized rock near one of the lander’s footpads. Protective lens covers on both of the probe’s cameras will be released late this week, allowing InSight to gain a clearer view of its environment.

“Today, we successfully landed on Mars for the eighth time in human history,” said NASA Administrator Jim Bridenstine. “InSight will study the interior of Mars, and will teach us valuable science as we prepare to send astronauts to the Moon and later to Mars. This accomplishment represents the ingenuity of America and our international partners and it serves as a testament to the dedication and perseverance of our team. The best of NASA is yet to come, and it is coming soon.”

InSight’s arrival on the red planet Monday was the first successful Mars landing in six years. The stationary robot joins NASA’s Curiosity rover already on Mars, exploring Gale Crater roughly 340 miles (550 kilometers) from InSight’s landing zone.

NASA officials were elated with the landing in a press briefing Monday afternoon. More than half of all Mars landing attempts have ended in failure.

“Listening to Christine (Szalai) call out as we got closer and closer to the surface, every time she made a call out, the hairs on the back of my neck would start rising a little bit higher …When we finally got the confirmation of touchdown, it was completely amazing,” said Tom Hoffman, InSight’s project manager at JPL. “The whole room went crazy … My inner four-year-old came out.”

At first glance, InSight’s surroundings appear to match predictions based on imagery from orbiting satellites. Mission managers wanted to send InSight to Elysium Planitia because it was a safe landing site, and offered smooth terrain for the lander’s robotic arm to place a pair of European-built science instruments on the surface.

“There certainly are some small rocks, but those look pretty manageable,” Hoffman told reporters after Monday’s landing.

Bruce Banerdt, InSight principal investigator at JPL, said the lander arrived on flat terrain, with a tilt of just 2 degrees.

A camera on InSight’s robotic arm captured this view after Monday’s landing on Mars. Credit: NASA/JPL-Caltech

Monday’s landing is just the beginning of a months-long process to survey InSight’s landing site and deploy the mission’s two science payloads.

“We were all certain that that first image would help us determine how difficult of a job we would have in placing the instruments, and I’m very happy that it looks like we’ll be able to do it quite easily, we hope,” said Elizabeth Barrett, InSight instrument operations lead at JPL.

A fresh data downlink from InSight through the Mars Odyssey orbiter Monday night confirmed the solar arrays on the lander opened and were collecting sunlight, a crucial step in ensuring the craft’s long-term survival. Post-landing checkouts of InSight’s robotic arm and instruments are planned starting Tuesday.

InSight’s nearly 8-foot-long (2.4-meter) robotic arm will place a French-built seismometer and German-made heat probe on the Martian surface next to the lander in the next few months.

The contributions from CNES — the French space agency — and the German Aerospace Center — or DLR — totaled around $180 million. NASA’s expenditures on the InSight mission come to $813 million, including a $163 million launch contract with United Launch Alliance.

The InSight mission’s robotic arm was originally built for the canceled Mars Surveyor lander that was supposed to launch in 2001. Other leftover parts on InSight include a landing radar originally built as a spare for the Phoenix mission, and surplus structural booms from the Curiosity rover repurposed for a Spanish-built weather station on InSight to collect temperature and wind data.

InSight will first put the seismometer package on the surface near the lander, then the arm will retrieve a wind and thermal shield to cover the instrument. The heat probe will be deployed last for its mechanized mole to start digging into the Martian crust.

“I liken it to … playing that “Claw” game at a carnival, but you’re doing it with a really, really valuable prize, and you’re doing it blindfolded, where you can only take occasional pictures, and then you’re doing it via remote control on another planet,” Barrett said of the carefully-choreographed procedure to deploy InSight’s two science instruments. “It takes a little bit longer. You need take more pauses to make sure you actually have the grapple of the payload before you lift it up, and it’s actually on the ground before you let it go.”

“This entire process, just getting the instruments to the ground, takes approximately two-to-three months, so it’s going to take a little bit of time to get to that point,” Barrett said. “And then another couple of months for the mole to penetrate into the ground and to do the fine-tuning of the seismometer, and at that point, we’ll be sitting back and listening for those marsquakes and measuring the vital signs of Mars, getting all that great science return. We’re really looking forward to that.”

Both instruments will transmit data through electric tethers leading to the lander.

Artist’s illustration of the InSight spacecraft on Mars, with the seismometer and heat probe deployed. Credit: NASA/JPL-Caltech

“Sensitive is really an understatement,” Banerdt said of the seismometer. “It’s an exquisitely sensitive device for measuring the motion of the ground. And when we talk about motion, we’re talking about vibrations that have an amplitude comparable to the size of an atom.

“These are waves that were generated, maybe, by a marsquake on the other side of the planet, have traveled all the way through the planet, getting their waveform modified as they go through the planet and picking up information about the deep interior structure, and then we are able to pick it up when it comes back up to the surface under the seismometer,” Banerdt said.

The seismic sensors aboard InSight evolved from mission concepts in the 1990s and 2000s that would have dispatched multiple small probes to Mars, creating a global geophysical network. InSight will give scientists just one seismic station, but experts have developed techniques to glean information about the interior of Mars, even with a single seismometer.

Researchers have attempted seismic detections on Mars before, but seismometers on NASA’s Viking landers in the 1970s provided inconclusive results. The instruments were mounted the decks of the landers, making them susceptible from interference from spacecraft vibrations and winds.

“Not only do you have to have a very sensitive device for measuring those motions but you have to protect it from everything else that might affect it,” he said. “We have several different layers of protection, it’s sort of like a Russian doll.”

Philippe Lognonné, head of the InSight seismic investigation team at the Institut de Physique du Globe de Paris in France, said scientists do not have a confirmed detection of marsquake, but evidence suggests weak tremors occur on the red planet.

“We have no clear data on seismic activity on the planet,” Lognonné in an interview with Spaceflight Now before InSight’s launch. “We imagine it because we see faults on the surface. In some places, we have seen where a boulder may have fallen down from a scarp. But again, we have no data.”

Lognonné said, based on existing theoretical models, the seismometer could register around 20 or 30 quakes per year, sensing ripples from all types of seismic waves moving through the planet.

“We cover all the seismic waves, and we even have sensitivity to tides, the Phobos (Mars’s biggest moon) tide especially,” Lognonné said. “We cover all the signals to be generated by a quake.”

Artist’s rendition of the interior structure of Mars. Credit: NASA/JPL-Caltech

Once placed on the surface of Mars, the Heat Flow and Physical Properties Package, know as HP3, will hammer to a depth of 16 feet, or 5 meters, a process expected to take around six weeks with roughly 10,000 individual hammer blows, accounting for several planned pauses to allow the instrument to record thermal conductivity measurements.

“If you have an astronaut on the planet, you can do this in maybe 20 minutes or half an hour,” Banerdt said of the heat flow experiment. “But if you want to do it robotically, you have to get a little bit more clever.”

The metallic mole will probe deeper into the Martian crust than any past lander.

“We think this remote probe can actually go down about 15 feet, which gives us a better baseline to measure the temperature increase with depth and be able to estimate the amount of heat coming out of Mars,” Banerdt said.

“And that amount of heat is tied to the geological activity of the planet. It’s the heat engine of the planet that drives volcanism, it drives tectonic activity, it drives mountain-building. So all the geological processes that happen on a planet are driven by its heat engine, and we want to measure sort of the vigor of that heat engine.”

“We switch on the temp sensors and record the temperature over depth and time for up to two years,” said Tilman Spohn, HP3 investigation lead from DLR, the German Aerospace Center, in Berlin. “Taking the temperature gradient, or the rate at which the temperature increases (with depth), gives us the heat flow. Very simple and straightforward, but as planetary science often is, very difficult. The devil is in the details.”

Scientists will also measure Mars’ polar wobble by analyzing radio signals transmitted between InSight and Earth-based antennas.

“By the timing of that signal, we can track the location of the spacecraft at Mars … with an accuracy of something around a foot or so, maybe a little bit less,” Banerdt said. “To me, that’s the closest we can get to magic with science.”

With that information, scientists can determine which way the Martian north pole is pointing as the planet rotates.

“Over the course of a year, we can watch the north pole wobble just a little bit because of the core sloshing around inside of the planet, and that will give us a very, very tight constraint on the size of that core and its density, and so its composition,” Banerdt said. “That tells us the structure of Mars. The structure of Mars tells us something about the processes that put that structure together. We can put this into our mdoels, extrapolate it to Earth, and understand how the Earth formed four-and-half billion years ago.”

Much of the ancient geologic record on Earth has eroded away, but Mars may still hold clues about how it was born, accreted rock and dust, and formed a hot, high-pressure mantle and core as heavier elements sunk deep beneath its surface.

“How we get from a ball of featureless rock into a planet that may or may not support life is a key question in planetary science,” Banerdt said. “And these processes that do this all happen in the first tens of millions of years.”

Discoveries made by InSight at Mars could inform scientists how the Earth formed and evolved.

“Mars is a smaller planet,” Banerdt said. “It’s less active than the Earth, so it has retained the fingerprints of those early processes in its basic structure — the thickness of the crust, the compositon of the mantle, the size and composition of its core,” he said. “By mapping out these boundaries, these various different sections of the inside of the planet, we can then understand better how the planet formed, and how our planet got to be the way it is.”

InSight was originally supposed to launch in March 2016, and reach Mars later that year, but problems sealing a vacuum enclosure containing the French seismic sensors forced officials to postpone the mission. Mars launch opportunities come once every 26 months, when the planets are in the proper positions in the solar system, so the next chance to send InSight came this year.

Engineers redesigned the vacuum enclosure to eliminate an air leak in a feed-through, or wiring interface, used to route data between the seismic sensors inside the instrument and electronics and communications equipment aboard the InSight spacecraft. The fix passed testing, and officials cleared the probe for launch.

NASA’s next Mars mission, the Mars 2020 rover, is scheduled for liftoff from Cape Canaveral atop an Atlas 5 rocket in July 2020, and should reach the red planet Feb. 18, 2021.

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Follow Stephen Clark on Twitter: @StephenClark1.


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