How do you test a helicopter to Mars?

Credit: NASA / JPL-Caltech

The Ingenuity helicopter may be the first vehicle to fly on Mars, but Mars was not the first place to fly so far. Before packing it and blasting it to Red Planet, JPL engineers commissioned a helicopter in a special wind tunnel designed with the help of researchers at the California Institute of Technology.

A custom wind tunnel in a JPL 85-foot high, 25-foot-diameter vacuum chamber managed by the California Institute of Technology for NASA to simulate flight on a planet whose atmosphere is one-hundredth of Earth. Was built. Pressure was reduced in the chamber to get closer to the atmosphere of Mars, and 441 pairs of individually controllable fan arrays blew the helicopter away, simulating forward flight in confined space.

The fan array was designed and built by JPL engineers, incorporating the views of Chris Dougherty and Marcel Veismann of the California Institute of Technology, who currently hold PhDs. Mory Gharib, Professor of Aeronautics and Biology-Inspired Engineering, and Booth-Students working at the Kressa Leadership Chair at the California Institute of Technology Center for Autonomous Systems Technology (CAST). Doherty and Veismann previously oversaw the design and assembly of a similar 1,296-pair fan array for CAST’s Real Weather Wind Tunnel, which opened in 2017. Their designs use off-the-shelf computer cooling fans (although they are currently the most powerful fans). Available).

“This type of wind tunnel is particularly suitable for the intended application because the concept of using a small and inexpensive fan array provides a space-efficient and cost-effective solution compared to a single fan wind tunnel. It was, “said Veismann. Is called. “In addition, these types of fans are relatively robust and safe to operate, and the modularity allows us to test the performance of the walls before building a full-fledged facility.”

Jason Rabinovich, a JPL mechanical engineer working on helicopter testing, contacted the CAST team in 2017. “I got my PhD from GAL CIT. [the Graduate Aerospace Laboratories of the California Institute of Technology]That’s why I knew CAST and its facilities, “says Rabinovic, who is currently an assistant professor of mechanical engineering at Stevens Institute of Technology in New Jersey.

Designing a helicopter that flies on Mars, which has lower gravity and much lower pressure than Earth, presents new challenges for JPL engineers. Just testing the helicopter required new equipment.

Credit: California Institute of Technology

“Even in the large vacuum chambers this was, it wouldn’t be possible to fly forward freely in a meaningful way,” says Doherty. “Therefore, to test forward flight, find a way to build the largest vacuum chamber in history, which is exorbitant in time and cost, or to simulate the forward flight conditions of Mars in an environment confined to an enclosed space. We needed to, and that’s where our fan array comes in. “

Dougherty and Veismann designed a CAST fan array to simulate real-world weather conditions in a partially enclosed environment, with researchers conducting unmanned aerial vehicles under realistic conditions under the supervision of Gharib. I made it possible to test. The 10-foot x 10-foot array is housed in a drone arena on the third floor. Computer programs control the behavior of over 2,000 individual fans, allowing engineers to simulate almost any wind condition a drone may encounter in the real world, from light gusts to strong winds. ..

“If you want to build something that works in the real world, you have to test it in real-world conditions, so CAST has facilities where autonomous systems face real challenges,” said CAST Director. Gharib said. ..

More importantly for Martian helicopters, fan array software provides the flexibility to reproducibly generate realistic turbulence on demand as each fan sends and receives information in seconds.

“I had a lot of questions about aerodynamics,” says Rabinovitch. “I want to understand the performance of the vehicle in the relevant environment. I want to make sure that the vehicle is stable when flying on Mars and that it can perform as expected over a wide range of maneuvers.”

Contrary to intuition, it was important that the Ingenuity test facility was able to generate stable, slow winds. A traditional wind tunnel with one huge fan is designed to generate high-speed wind for testing aircraft flying at hundreds of miles per hour. The team investigated the possibility of using the Transonic Dynamics Tunnel (TDT) at NASA Langley Research Center. This is a wind tunnel that can generate flow conditions for testing aircraft moving faster than the speed of sound at high altitudes. Earth. In contrast, ingenuity helicopters travel at about 10 meters per second, or about 20 miles per hour.

How do you test a helicopter to Mars?

NASA’s Ingenuity Mars Helicopter took this shot, capturing his shadow on April 19, 2021 while hovering over the surface of Mars during the first instance of a powered, controlled flight on another planet. I did. Credit: NASA / JPL-Caltech

“If we went to Langley, they would have had to idle the fans to get the wind speed we were looking for,” said Amiee Quon, JPL’s mechanical integration engineer who helped test the helicopter. Says.

The JPL Mars helicopter team has ensured that one of JPL’s largest vacuum chambers can be used in the project. The chamber is 85 feet high and 25 feet in diameter. It takes about two hours to pump out the air inside to reproduce the state of the atmosphere on Mars.

Building an array of individually controllable fans in a vacuum chamber is not as easy as assembling the unit and turning it on. For one thing, the essence of a vacuum chamber, the fact that it is sealed, means that multiple wires cannot enter or exit.All inputs and outputs needed to be streamlined and downsized

The facility itself was important to JPL’s Mars mission. “This is the chamber that has undergone the main thermal vacuum tests of all Mars probes. It simulates space by pumping out all the air and circulating hot and cold temperatures. It needs to be kept clean. There was, “says Quon. “I was worried about dirt, but I was also worried about outgassing from fan parts.” Due to pollution control requirements, the JPL team rewired the fan and stocked a polyvinyl chloride (PVC) wiring jacket. Had to be replaced with Teflon’s, which releases less chemical gas into the air.

“It was a lot of fun, but there were a lot of details to consider,” says Kuon. “We adopted a facility that was not designed for wind tunnel testing and made it the first wind tunnel,” he said.

Due to the time required to pump down the chamber to mimic the very low atmospheric pressure on Mars, all errors that occurred had to be corrected remotely. To that end, Doherty and Veismann helped Alejandro Stefan-Zavala, a student at the Caltech Summer Undergraduate Research Fellowship (SURF).

How do you test a helicopter to Mars?

A quadcopter drone floats in front of the fan wall at CAST Airfield.Credit: California Institute of Technology

“The type of fan we use here has a built-in sensor that indicates the speed of rotation, so we need to write software to access that sensor,” says Stefan-Zavala. “The 441 pair of fans has a lot of sensors and want to know in real time what’s going on, so we can diagnose if something isn’t working properly.”

If not in a vacuum chamber, it’s a simple process. Simply connect the USB line to the faulty component and connect it to your laptop. To perform this type of error correction in a vacuum chamber required 80 separate USB lines to carry enough data to control the fan.

Instead, Stefan-Zavala developed custom software to monitor the fans remotely and instructed the fans to reprogram automatically if necessary.

The project feasibility study began in 2017 and testing was completed by mid-September 2018. Given the ongoing demand for vacuum chambers that simulate the space environment that JPL researchers are using as space simulators, the team had little time to assemble. Run the fan array, run the tests, and then disassemble everything.

After all, the fan array remained assembled for only a few weeks. “It was tight. We worked a lot at night and on weekends,” says Rabinovic.

Rabinovic said he was not surprised that the students provided the outstanding technical know-how needed to design the first wind tunnel to test the latest technology on Mars. “These were graduate students at the California Institute of Technology,” he says. “I wasn’t surprised at that level of expertise.”

NASA’s Mars helicopter flight can occur as soon as Monday

Courtesy of California Institute of Technology

Quote: How do you test a helicopter to Mars? (April 23, 2021) Obtained April 23, 2021 from

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How do you test a helicopter to Mars?

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