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Raumfahrt - NASA Mars Rover 2020 Mission-Update-6

4.05.2019

NASA's Mars 2020 Mission Passes Critical Heat Shield Test

This is how engineers recreate the hellish conditions of Martian reentry to test components that will go up against the real thing.

When your one-of-a-kind rover is 38 million miles from home, falling toward an alien planet at supersonic speed, it would be nice to know the spacecraft can handle the trip.

Today Lockheed Martin announced that its engineers have completed a slate of critical torture tests on the connection between the spacecraft carrying the Mars 2020 rover and its protective aeroshell, making sure it can handle the stress of the interplanetary journey.

Hammering Out Weaknesses

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The final assembly of the Mars Science Laboratory with the Curiosity rover housed inside, November 10, 2011. The top section is the cruise stage, the middle is the aeroshell, and it’s all protected by the heat shield on the bottom, also built by Lockheed Martin.

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There is an inherent weakness in any vehicle or structure wherever two different materials are joined together. Each side reacts to stress differently, deforming under pressure or reacting to temperature changes. In spacecraft these small flaws can become fatal, so the engineers have to simulate these insane pressure loads and temperature swings.

For the Mars 2020 mission, the spacecraft (made by CalTech and NASA) must deliver an automobile-sized rover to the surface of Mars. The aeroshell—shaped like a shallow-bowl on the “bottom” of the spacecraft—is made of material designed to burn away, protecting the craft and its cargo from the intense heat caused by the entering the Martian atmosphere.

But first, the craft has to get off of Earth safely. “The first environment is surviving launch, because of the high accelerations, and the vibration from the acoustic environment,” says Neil Tice, Lockheed Martin Mars 2020 heat shield program manager. “And then you’re going into space. You start out at room temperature. And shortly after you can get into orbit, the temperatures start dropping rapidly. As it turns out, the heat shield is looking towards deep space. It continues to cool for several days after getting into space and heading off to Mars.”

The Hell That Is EDL

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Animation of NASA's planned descent of the Mars 2020 rover.
NASA/JPL-CALTECH

Escaping Earth's gravitational grasp is tough enough, but the engineers don’t even test the spacecraft for this part of the mission. Reentry is so violent that passing those simulations is enough to ensure launch won’t be a problem.

“Typically, a space craft's worst environment is launch. But in this case EDL (entry, descent and landing) is so severe an environment, both mechanical and thermal, that it becomes the driving case,” Lockheed lead engineer for the test, Derek Shannon, told Popular Mechanicsafter the final verification test. “For example, launch G loading is on the order of 5 to 6 Gs. And the entry pressure is on the order of 12 Gs.”

The shield will be at about -250 Fahrenheit when the craft reaches Mars. That soon changes as the spacecraft starts EDL with the compression of the atmosphere forming a superhot plasma that reaches 3,800 Fahrenheit.

“THE TEST LAST WEEK WAS REALLY TO VERIFY THAT THE STRUCTURE CAN SURVIVE THAT ENTRY PRESSURE LOAD."

“The test last week was really to verify that the structure can survive that entry pressure load,” Shannon says, after his team set the shield on a test stand made to operate in a vacuum. “There's an air cavity in between the heat shield and test fixture, and there's a rubber bumper that goes between the rim of the heat shield and test fixture.”

When his team sucked the air out to create differential pressure on the surface of the heat shield, Shannon says it “bent the entire heat shield down, pushed it towards the plate, and splayed out the outer rim of the heat shield. That put a lot of bending stress and depression stress into the structure.”

This created a 6.1 psi differential pressure, which produced the 140,000-pound pressure load on the heat shield needed to simulate EDL.

A Needed Win

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The successful test is good news for NASA and Lockheed, who discovered a crack in the aersoshell during tests in late April last year. NASA officials say that creating a new heat shield won't delay the launch. Which is a good thing, considering the next launch window after 2020 would be sometime in the second half of 2022.

“While the fracture was unexpected, it represents why spaceflight hardware is tested in advance so that design changes or fixes can be implemented prior to launch,” NASA said in a statement.

Lockheed also has more tests on the aeroshell beyond verifying that the new heat shield won’t also crack. Engineers say there are also tests of the shield’s ablative material planned later this year. One of the hallmarks of the Mars 2020 mission is how much it relies on previously-used designs, but the reality is that everything needs to be tested.

On a trip like this one, it pays to be thorough.

Quelle: PM

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Take It Beyond The Limit: Lockheed Martin Completes Critical Testing Milestone For NASA JPL's Mars 2020 Rover Heat Shield

Protecting against the extremes of space travel is critical to the success of any mission. Lockheed Martin (NYSE: LMT) has successfully completed the flight hardware structure of the heat shield, validating the physical integrity with a final static test after exposing it to flight-like thermal conditions. The heat shield is half of the large and sophisticated two-part aeroshell that Lockheed Martin is designing and building to encapsulate NASA Jet Propulsion Laboratory's Mars 2020 rover from the punishing heat and friction of entry through the Martian atmosphere.

The Mars 2020 mission will be one of the most challenging entry, descent and landings ever attempted on the Red Planet. The heat shield aerodynamics serve as a "brake" to slow the spacecraft from about 12,000 mph (19,300 kph) so the structure needs to be flawless. As the tenth aeroshell system that Lockheed Martin has produced for NASA, this is one of the largest at 15 feet (4.5 meters) in diameter.

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Lockheed Martin Mars Heat Shield

The Lockheed Martin-built heat shield, shown here in the testing phase, is just one component in the final aeroshell that will protect the Mars 2020 rover on its long journey to Mars.

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Lockheed Martin Heatshield Test

As seen in the control room, the photogrammetry visuals provide insight in to the real-time displacements and strains on the heat shield while pressure is being applied.

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Lockheed Martin Mars Aeroshell

The Lockheed Martin-built heat shield, shown here in the testing phase, is just one component in the final aeroshell that will protect the Mars 2020 rover on its long journey to Mars.

"Our experience building aeroshells for NASA Mars missions does not mean that it is 'easy'," said Neil Tice, Lockheed Martin Mars 2020 Aeroshell program manager. "Tests like this structural test are absolutely essential to ensuring mission success in the long-run."

The static test was conducted on April 25 and was designed to mimic the load that the heat shield will experience during the most extreme part of its journey; the entry phase. To do that, engineers used vacuum pumps to simulate the pressure of approximately 140,000 pounds on the structure. The structure was tested to 120% of the expected flight load to push it to the limit.

For this particular test, the team also integrated a new form of instrumentation. Historically, this test utilizes conventional strain gauges and extensometers to monitor structural response at distinct points during loading. Partnering with NASA Langley Research Center, the team also applied a new tool called Photogrammetry or Digital Image Correlation. This allowed the team to monitor full-field strains and displacements over the entire visible area of the structure in real time. To use this technique, a vinyl wrap, similar to a decal, that has different visual cues (dark random speckles over a white background) was applied to the heat shield. During the test, a set of digital cameras optically monitor any changes in the pattern and generate a three-dimensional map of displacements and surface strains as the applied load increases.

"While we have used this full-field photogrammetry technique on test articles in the past, this is the first successful implementation on official flight hardware," said Dr. Sotiris Kellas, NASA Langley aerospace engineer and lead for the technical demonstration. "This technology will allow us to safeguard hardware during testing but more importantly provide data for test analysis correlation and improvement of our design and analysis tools."

Following this test, the Lockheed Martin team will apply Phenolic Impregnated Carbon Ablator (PICA) thermal protection system tiles to the structure. Once complete and through all environmental testing, the full heat shield will be mated to the backshell in early fall.

The Mars 2020 Project at NASA JPL manages rover development for the Science Mission Directorate at NASA Headquarters in Washington. The NASA Engineering and Safety Center at NASA Langley Research Center provided the photogrammetry support for this test.

Quelle: Lockheed Martin

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Update: 18.05.2019

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Mars 2020 Is Coming Together

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Credit: NASA/JPL-Caltech

An engineer inspects the completed spacecraft that will carry NASA's next Mars rover to the Red Planet, prior to a test in the Space Simulator Facility at NASA's Jet Propulsion Laboratory in Pasadena, California.

From the top down, and suspended by cables, is the complete cruise stage, which will power and guide the Mars 2020 spacecraft on its seven-month voyage to the Red Planet. Directly below that is the aeroshell (white back shell and barely visible black heat shield), which will protect the vehicle during cruise as well as during its fiery descent into the Martian atmosphere. Not visible (because it's cocooned inside the aeroshell) is the completed rocket-powered descent stage and the surrogate rover (a stand-in for the real rover, which is undergoing final assembly in JPL's High Bay 1 cleanroom).

The Mars 2020 spacecraft was tested in the 25-foot-wide, 85-foot-tall (8-meter-by-26-meter) chamber in the same configuration it will be in while flying through interplanetary space. The 2020 rover carries an entirely new suite of instruments, including a sample-caching system that will collect samples of Mars for return to Earth on subsequent missions. The mission will launch from Cape Canaveral Air Force Station in Florida in July of 2020 and land at Jezero Crater on Feb. 18, 2021.

The image was taken on May 9, 2019.

JPL is building and will manage operations of the Mars 2020 rover for the NASA Science Mission Directorate at the agency's headquarters in Washington.

Quelle: NASA

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