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It will take six and a half minutes for InSight to go from 5.5 kilometers per second to less than 2.5 meters per second just before touchdown. (credit: NASA / JPL-Caltech) |
by Jeff Foust
Monday, November 26, 2018
The seven minutes of terror are back. Or, more precisely, the six and a half minutes of terror.
Later in the day, NASA's InSight probe will encounter the Martian atmosphere. The official start of this phase of entry, descent and landing (EDL) will take place at approximately 2:47 pm EST (7:07 pm GMT) at an altitude of approximately 125 km, when Spacecraft will encounter the upper fringe of the planet's atmosphere at 5.5 km. per second. (The hours here are hours received by the Earth, as InSight signals arrive, given the short duration of the journey, InSight will have already landed – or crashed – by the time transmissions from the beginning of the EDL will arrive on Earth.)
| "Going to Mars is really very difficult," Zurbuchen said. |
Most of this velocity will be destroyed, literally, by the spacecraft's heat shield, with a maximum deceleration of 7.5 g. Three and a half minutes after entering the fleet, the probe, deployed about 11 km from the ground and moving at a speed of 385 meters per second, deploy his parachute. Less than half a minute later, he will drop his heat shield and roll out his landing legs, while a speed camera prepares to collect data on speed and speed. altitude.
Forty-five seconds before the landing, InSight jettisoned the backshell that covered the top of the landing gear and his parachute. Twelve downhill engines will start shooting at the undercarriage. They now descend to 60 meters per second and one kilometer above the landing site at Elysium Planitia. The thrusters further slow down the undercarriage and rotate it so that its two solar panels are aligned east-west.
At 14:54, Eastern Time, the landing gear, which had decelerated from 5,500 to less than 2.5 meters per second over the previous six and a half minutes, would land on the Martian surface. If all goes well.
On Mars, of course, things do not always go well. "Going on Mars is really very difficult," said Thomas Zurbuchen, NASA's assistant administrator for science, during a briefing at the Jet Propulsion Laboratory on November 21. "As human, explorers from around the world, we are fighting about 50%, or less, of successful missions."
Mission officials, however, seemed confident about their chances. At this JPL briefing, officials said the Space Shuttle was working well and was following the planned trajectory so closely that it had already skipped a course correction maneuver ( TCM) earlier in the mission and was considering giving up a last MCT on November 25th, the day before the landing. .
However, at the final briefing before the landing on November 25, officials announced that they had decided to run the latter MCT in order to adjust the center of the ellipse. Landing less than 20 kilometers, enough so that the edges of the landing ellipse are not rougher. land at Elysium Planitia.
"We listened to all the contributions and the final decision was to go ahead and proceed to the TCM and get back to that red X," said Tom Hoffman, InSight Project Manager at JPL. , evoking how the desired target was marked on the cards. of the region. Thanks to this maneuver, InSight "will be exactly where we really want to land, from a security point of view, and make sure we have the right location for our scientific instruments."
| "We are expecting a very simple day on the landing on Mars, and we are very happy about it," said Grover. |
The InSight design is also tested on Mars. The spacecraft, built by Lockheed Martin, is based on the design used for the Phoenix mission that landed in the northern polar regions of Mars a decade ago. "The spacecraft itself is almost identical," said Rob Grover, EDL Manager for InSight at JPL. The main difference in the landing, he said, is that the Phoenix landing site was at an altitude of about 1.5 km, providing more time and atmosphere to slow it down.
InSight was also equipped with a thicker heat shield to prepare for any dust storm. The weather, however, will not be a problem for the landing. In June, when a huge dust storm had invaded the planet and interrupted communications with the rover Opportunity that had not yet been restored, this storm has since faded. "It's been about a month since things were really good," said Grover. "We are expecting a very simple day on the landing on Mars, and we are very happy."
If all goes well, the controllers will be informed of the landing in a few moments thanks to a pair of 6U cubesats, called Mars Cube One (MarCO) launched with InSight in May. The cubesats will fly on Mars and serve as relays, rebroadcasting the telemetry of the lander on Earth. (Mars Reconnaissance Orbiter and Mars Odyssey satellites from NASA will also be able to restore data, but with some delay, while InSight will broadcast an X-band "beep" seven minutes after landing.)
"When entering, descending and landing, InSight will send UHF data," said Anne Marinan, MarCO-B Mission Manager. "MarCO satellites will listen to these data and take them to Earth almost in real time."
The double spaceship, formerly called MarCO-A and B, but named Wall-E and Eve after the main characters of the animated film Wall-E, are mainly technology demonstration missions. The spacecraft has already tested a propulsion system incorporating a thruster also used in fire extinguishers (hence the Wall-E connection), an X-band deployable antenna and a small camera.
The flyby will mark the end of MarCO's main mission, but project engineers suggested that it might be possible to extend the mission for some time after the flyby, until the spacecraft, in their orbits heliocentric, too far away to maintain communications.
No prolonged future mission however is in their minds at the moment. "The team is focused on the EDL," Marinan said.
"That's the answer I asked for," Zurbuchen added. "I am a strong believer in success, it is the attention to priority. It is the nature of the extended mission that could be possible, he said, but we will have these discussions at the end of this exciting weekend. "
InSight with its two main instruments, a seismometer (left) and a heat flux probe, deployed on the surface. (credit: NASA / JPL-Caltech) |
Inner Insights of Mars
However, the mission of InSight will only begin. Sixteen minutes after the landing – a gap to allow the dust from the spacecraft's thrusters to settle – the spacecraft will begin deploying its two circular solar panels, which will take another 16 minutes. Confirmation of a successful deployment is only five and a half hours after landing, when Odyssey will fly over the site and be able to relay telemetry to Earth.
The scientific mission of InSight will begin then, although slowly. "InSight is a kind of idle and casual mission," said Bruce Banerdt, JPL's senior in-house investigator. Engineers and scientists will first examine the area around the landing site, looking for the best location to place the two main instruments of the spacecraft, a seismometer and a heat flow sensor. Then, the robotic arm of the lander will deploy the seismometer, followed by the thermal probe.
"It will probably take us at least two to three months, at least, to get our instruments," said Banerdt, saying it would be "early next spring" before these major instruments begin to return data.
The seismometer, formerly known as seismic experiment for interior structures (SEIS) and provided by the French space agency CNES, will measure seismic waves from earthquakes inside the planet, as well as impacts meteors and even traction on the crust of the planet. Phobos, the tallest of his two moons, passes over his head.
| "The first question we want to answer is: what is the structure and energy of the interior of Mars," Banerdt said. |
SEIS is also the reason why InSight is not already on Mars. The launch of the space shuttle was scheduled for March 2016, the old window of Mars missions, but by the end of 2015, NASA decided to postpone it, due to the persistence of vacuum maintenance issues in SEIS necessary for the instrument to reach the desired sensitivity. CNES had to rethink the instrument and finally solved the problem.
"At first, it was simply impossible to build," said Philippe Lognonné, project manager for the CNES instrument. "But we did it with the help of our partners."
The other major instrument is the heat flux and physical properties probe, or HP3. It features a mole that will penetrate three to five meters into the surface, using a striking mechanism that will perform up to 20,000 shots to reach that depth.
The instrument will collect temperature data from 15 sensors over the entire length of the probe. "By combining the increase in temperature with thermal conductivity, we can actually calculate the heat flow," said Tilman Spohn, lead investigator for the probe at the German space agency DLR.
While SEIS and HP3 are the main instruments of InSight, the satellite has further investigations. The Rotation and Interior Structure Experiment, or RISE, will use InSight's X-band radio to detect disturbances in the planet's rotation, which can help scientists understand the inside of the planet. A set referred to as an auxiliary payload sensor subsystem includes a magnetometer and instruments for measuring Martian weather conditions.
"This is going to be a unique data set of continuous measurements of temperature, barometric pressure, wind speed and direction, all day, all night, for a whole season on Mars," Banerdt said. . "That goes obviously, I think, to have a huge wealth of scientific information for us."
Together, scientists hope to learn more about the Martian interior. "The first question we want to answer is: what is the structure and energy of the interior of Mars," Banerdt said. This includes the size and density of the planet's core, the thickness of the Earth's crust, and the structure of the mantle.
"I've been waiting for this information personally for decades," said Sue Smrekar, JPL's Assistant Principal Investigator at InSight, "and I'm really excited to be able to send this LG to the field and start using that data."
An image of the Jezero Crater, the landing site of the Mars 2020 mission, which presents the remains of a river delta that can preserve signs of life. (Credit: NASA / JPL-Caltech / MSSS / JHU-APL) |
Back to the search for life
InSight is a detour to NASA's exploration strategy for the planet Mars, focusing on the study of past and present water and its consequences for the livability of the planet. (InSight, in fact, is not formally part of Mars' global exploration program on directed science missions, but rather the Discovery program of inexpensive, competitively-chosen missions.) InSight studies in-depth the planet and the formation processes of Mars compared with other terrestrial planets, rather than the mantra "follow the water" that guided NASA's missions on Mars for nearly two decades.
| "The delta is a good place to deposit evidence of life and preserve it for billions of years since the lake was first established," Farley said. |
The next mission, however, will come back to this goal. The March 2020 rover, which is scheduled to launch on February 18, 2021 in July 2020, will resume studies on Mars' past habitability. More importantly, he will collect samples for later return to Earth for further study.
And now, NASA knows where Mars 2020 will land. The agency announced on November 19 that the rover would land in a 45 km wide crater called Jezero. Scientists have said that this crater housed a lake of a depth of up to 250 meters 3.5 to 3.9 billion years ago. The crater images also show the remains of a delta of a river that has flowed into the crater at that time.
Sedimentary deposits left by the lake and delta attracted scientists. "This is a major attraction from our point of view," said Ken Farley, scientific lead for the March 2020 project, at a briefing to announce the site. "The delta is a good place to lay evidence of life and preserve it for billions of years since the lake's presence."
The selection of Jezero was the culmination of a process extending over several years. Michael Meyer, scientific leader of NASA's exploration program on the planet, said: "During the first workshop on landing sites in 2014, 64 sites were identified as potential sites."
By the time the scientists met in October for the fourth and final landing site assessment workshop, they had reduced this number to four. Besides Jezero, there was a neighboring area called Northeast Syrtis that seemed to have some interesting old rocks. Midway takes its name from its location between Jezero and the north-east of Syrtis, allowing scientists to sample ancient rocks like those in northeastern Syrtis while staying away from Jezero. A fourth site, the Columbia Hills area visited by the rover Spirit, fell to the sidelines in this workshop, with scientists split between the other three.
Just as InSight is based on the last Phoenix lander, Mars 2020 uses the same design as the Curiosity rover being explored by the Gale Crater, including its "Skycrane" landing system. March 2020 will be added to the use of a new technology called relative terrain navigation, in which the spacecraft will take images during its descent, compare them to the maps on the spacecraft itself and will use this information to navigate to a more accurate landing.
This will allow Mars 2020 to avoid obstacles at Jezero that range from boulder fields and sand pits to cliffs on the edge of the delta. "Scientists always want to see outcrops, which are rocks and cliffs, and the people responsible for safely laying the rover really try to avoid these situations," Farley said.
Mr Zurbuchen said that a final decision regarding the use of ground-based navigation for March 2020 would be made next fall, he said, after "further analysis and in-depth "of what he called an" exciting technology ".
March 2020 will be equipped with dozens of metal tubes specially designed to store rock and soil samples for their return to Earth. However, when and how these samples will be returned must still be determined.
| "I will control myself as well as possible until we get a first successful landing notification," Hoffman said. After that, "I'm going to let go of my four-year-old child." |
More than a year ago, NASA unveiled what it called a "lite" architecture for returning samples. According to this approach, March 2020 will be followed by two missions. One of them will land in the same area as March 2020, with a rover designed to collect the sample tubes and place them in an aircraft carrier, which the new undercarriage will then launch onto the aircraft. orbit of Mars. The second follow-up mission will consist in collecting this sample in the orbit of Mars and bringing it back to Earth, either directly or at an intermediate location, such as the International Space Station or the new lunar bridge.
None of these follow-up missions have been implemented: March 2020 remains the only mission on Mars listed in NASA's books after InSight. NASA signed an agreement with the European Space Agency earlier this year to explore potential cooperation on returning samples, but the details of any cooperation still need to be clarified.
"We will clarify what exactly this means in the next budget cycle," Zurbuchen said in June. "The first time we will really start taking action, making decisions, because we are also conducting parallel joint investigations in Europe, it's the end of 19. It's not a decision this week, next week or next month. "
This is still the case five months later. "I have no update today" on the status of sample return planning, said Zurbuchen at the announcement of the landing site of March 2020.
He made it clear that NASA was planning to launch the final elements of this architectural example back in the late 2020s. "Depending on how the details are revealed, it would be in the early 30s that the samples would come back to Earth, "he said.
For now, the excitation and voltage are focused on InSight. At the last briefing before the landing on November 25, Hoffman said he had family visiting for Thanksgiving, including three young grandsons. "When they are excited, they run like madmen, raising their hands, screaming and screaming, continuing. I have to tell you that inside me, I'm pretty much the same, "he said.
He's holding it back for the moment. "I will control myself as well as possible until we receive a first successful landing notification," he said. After that, "I'm going to let go of my four-year-old child."
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