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Getting Curiosity to Mars, One Simulation at a Time
08.02.12
 
By: Denise Lineberry

Though the Curiosity rover is expected to land at approximately 1:31 a.m. EDT, NASA Langley Research Center’s role with the Mars Science Laboratory comes into play at about 1:24 a.m., when a complex sequence of events unfolds during Entry, Descent and Landing (EDL).

Curiosity's Seven Minutes of Terror

Team members share the challenges of Curiosity's final minutes to landing on the surface of Mars. Credit: NASA

"This landing represents 10 years of work by NASA engineers, people in industry, and people in academia who are very excited to see this spacecraft land," said Juan Cruz, an aerospace engineer. "Among those engineers, there is a team here at Langley that specializes in Entry Descent and Landing, or EDL. Basically what we do is try to land payloads on other planets."

Most recently, the EDL team at Langley celebrated a successful Phoenix landing on Mars in 2008. But with Curiosity being the largest rover ever sent to Mars, the team had new challenges to overcome. On Thursday, some of Langley's MSL team members presented their contributions to employees in the Reid Conference Center.

"If you are going to take such a large rover and put it on Mars, you need an equally large Entry Descent and Landing system," Cruz said as he displayed a photo of the aeroshell that is taking Curiosity to Mars. "The mass of the whole entry system, meaning the aeroshell, not counting the crew stage and the rover, is 3,300 kilograms. That’s a lot of mass, which has to go from 5.8 kilometers per second to zero in about seven minutes."

Juan Cruz.
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Juan Cruz, an aerospace engineer, talks to employees about NASA Langley's Entry Descent and Landing (EDL) contributions for the Mars Science Laboratory (MSL). Credit: NASA/Sean Smith

Members of Langley's MSL team.
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After presentations, a panel of NASA Langley Mars Science Laboratory team members answered questions from employees. About 100 researchers and technicians have contributed to MSL. Credit: NASA/Sean Smith

Langley's EDL team has a reversed role, compared to the launch team.

"One of things we like to think about that we do here, is people that do the launch vehicle take the spacecraft from the ground and they put all this energy to get it to Mars," Cruz said. "They have about 30 to 45 minutes ... a rather leisurely pace. Then we get to undo their work in seven minutes at Mars. So, we think we work the hard end of the problem."

But with challenges, also came opportunity.

"One of the things that we are very proud of, as far as the EDL team, is that this is the first landed mission on Mars in which we were able to tell the scientists that there were the four sites, and that we could land safely on all four of them. And the decision of which one of the four sites they chose was completely up to them," Cruz said. "We were confident that we could put it wherever they wanted. That has not always been the case."

Ultimately, scientists chose the Gale crater to search for evidence of a past or present habitable environment for life.

"This sequence of events happens 13.5 light minutes away, which means that there are no questions during this period. The spacecraft is completely on its own," Cruz said as an EDL animation played on the big screen. "You can imagine that if you were to design a spacecraft and do nothing more than design it and send it and expect that it would work on the first time, it wouldn’t. But the thing is that, in fact, we have done it. We have done it about 10 million times or more over the last 10 years."

One of NASA Langley's major roles has been to create a simulation that looks at everything that could happen, end-to-end, from the moment the spacecraft touches the top of the atmosphere to the time it comes to rest on the surface. Millions of analyses look at all uncertainties in all types of combinations.

The EDL team has run flight software, which acts as a physical wind tunnel. They use propulsion models, guidance navigation and control and entry configurations from NASA's Jet Propulsion Laboratory (JPL), which manages the mission.

MSL Entry, Descent and Landing Instrument (MEDLI)

A set of sensors embedded into MSL's heat shield will record the heat and atmospheric pressure experienced during the spacecraft's entry into the Martian atmosphere. Credit: NASA

Moving forward, data about the climate, surface, gravity field and mass properties and other aerodynamic and aerothermodynamic models are Langley’s responsibility.

Karl Edquist, lead for Langley's aerothermodynamics team, managed to boil down a decade of work into one chart on aerothermodynamics.

"Those 5.8 km during entry velocity, represent a lot of energy," Cruz said, speaking to the importance of aerothermodynamics research. "And in fact, if you took the energy and just put it onto the spacecraft in the form of heat, the spacecraft would vaporize."

Because the aeroshell is so large, it will create a significantly greater heat. Endquist has investigated and validated calculations, which he used to size the aeroshell and the heat shield. The PICA (phenolic impregnated carbon ablator) heat shield material, which was developed at NASA Ames Research Center in California, using research compiled by Langley's Orion team, has only been used for one previous mission [Stardust]. Endquist determined how thick the heat shield had to be.

And like Endquist, Mark Schoenenberger, lead for Langley's capsule aerodynamics team also found himself summarizing a decade of work into one slide. Aerodynamic computational analyses and wind tunnel tests provided crucial information for determining capsule aerodynamics.

Cruz spoke to one of his own contributions, creating 13 parachute models, which needed to get three things correct: the parachute opening load, the drag and a prediction of capsule motions. The parachute has about nine percent more area than the parachute used during the Viking missions.

With all of their contributions, outside variables come into play, making EDL simulations the core of Langley's role.

Cruz explained that Phoenix flew through about 50 kilometers of Mars' atmosphere, while MSL is flying about 600 kilometers down through the atmosphere. This exposes MSL to more varied atmospheric conditions and rough terrains, which also affects atmosphere.

Other members from the Langley EDL team are already at JPL continuing to run simulations. Using data from orbiting assets around Mars, simulations are run up to the last minute.

To learn more about Langley's contributions to the Mars Science Laboratory mission, visit:
http://www.nasa.gov/centers/langley/exploration/msl.html

To learn more about the Mars Science Laboratory mission, visit the mission home page at:
http://www.nasa.gov/msl

Using images from Mars Reconnaissance Orbiter (MRO), the team simulates the terrain down to every rock more than 30 centimeters in diameter.

Future missions will have more data for simulations because of MSL Entry, Descent and Landing Instrumentation (MEDLI), which was built at Langley. It consists of seven pressure sensors and seven instrumented plugs and an electronics box that transmits sensor data to Earth.

"MEDLI will provide the first non-Earth entry and aerodynamic data since Mars Pathfinder [1997], and it will provide more data than all previous Mars entry missions," said Alan Little, MEDLI project manager.

According to Little, MEDLI was originally conceived as a late edition to MSL.

"The interesting thing about getting MEDLI started was convincing others to allow us to instrument the heat shield," Little said. "As you could imagine, the thought of drilling holes into a $2.5 billion heat shield can cause a little concern -- especially since the data does not directly benefit MSL; it benefits future missions."

The MEDLI team demonstrated low risks for MSL and great benefits for future missions.

"So, here we are on our way to Mars. Now, we go to Mars for a reason and the reason is not to do this cool landing. The reason is for science," Cruz said. "Mars is the planet that is most similar to Earth. And it seems that in the distant past, it was even more similar than it is now. So, given that, it has the possibility, perhaps in the past, or even perhaps to this day, to harbor life.

"If two planets on the same solar system develop life, then its probably very likely that life is widespread through the universe. And that means we're not alone, which is really an interesting finding."


The Researcher News
NASA Langley Research Center
Editor & Curator: Denise Lineberry
Executive Editor & Responsible NASA Official: Rob Wyman