America's latest bid to send astronauts into space has researchers at NASA Ames hard at work, trying to figure out how to safely get a hulking 320-foot tower of metal stuffed with 733,000 gallons of fuel out of the atmosphere.
Standing inside a wind tunnel complex on the Mountain View campus, aerospace engineer Nettie Roozeboom described how rockets carrying precious cargo — including crew members — have to withstand powerful forces while making the ascent into space. Low-frequency forces with a whole lot of energy are going to pound on the rocket, she said, and the design has to be able to weather the blows.
That's where wind tunnels come in. In designing a new rocket intended for missions bound for the moon, Mars and even one of Jupiter's moons, Ames researchers have spent recent years making true-to-life models of the new Space Launch System (SLS) and blasting them in a wind tunnel. By replicating the rocket's ascent off of earth and seeing where turbulence and shaking are most likely to cause problems, researchers can refine the design to ensure nothing is damaged.
Scientists can theorize what will happen once the rocket is hit with high-velocity winds, but it's critical to replicate those forces in a real-life environment to know for sure.
"If you have these low frequencies just banging on your vehicle at some unsteady frequency, that's where you don't know how to design your vehicle," Roozeboom said. "That's where you need to go and test. You can't do that in theory, you can't do that computationally, you need to go do that experimentally. And so that's what we do."
NASA Ames gave a public debut of its wind tunnel testing on Monday, Jan. 10, highlighting just one small piece of a sprawling multi-part space exploration endeavor called the Artemis program. It includes an orbiting "Lunar Gateway" around the moon, a rover designed to drill for resources and a plan to put astronauts on the moon by 2024. The latest budget proposal by the Trump administration, released this week, bumps NASA's budget to $25.2 billion for 2021, a 12% increase over the last year.
It's a tight timeline, but the bigger budget proposal would certainly help keep the agency on track, said Ames director Eugene Tu. He said the Mountain View research center receives about $750 million in federal funding each year, which goes to pay for a 3,000-employee workforce and operate one-of-a-kind facilities, including some of the most powerful supercomputers in the world.
Those supercomputers came in handy for wind tunnel experiments, in which researchers collected a staggering 150 terabytes of data over the course of five days and needed to make sense of it. In past years, that meant transferring data onto a dozen hard drives, shuttling it across campus and loading it into the supercomputer over the course of three to six months. Now with a direct link to the supercomputer, it only took weeks to analyze the trove of data.
At the heart of any wind tunnel test, the question is always finding where significant or erratic pressure is being applied to any aerospace vehicle. In order to track precisely how the SLS will fare during lift-off and re-entry, a model is coated with specialized, pressure-sensitive paint. The paint, typically a bright bubble-gum pink, can be used to visualize pressure fluctuations up to 20,000 times per second, with the color changing based on how much pressure is applied to the surface.
The latest analytical tools means that a normally unwieldy haul of data, monitoring changes in the paint's appearance at 10,000 frames per second, can be quickly transformed into a detailed visualization for researchers. A slowed-down video of the of recent SLS model design, intended to send an orbiter to Jupiter's moon Europa, shows how the tip of the rocket and its accompanying boosters would take the brunt of the high-velocity wind pressure during ascent.
"That's where you get those really big highlights at high and low pressure, at the top where the air interacts with the nose cone and here on these attachments," Roozeboom said.
The bulk of the research is based on neither low-speed or high-speed aerospace travel, but transonic speeds slightly above or below the speed of sound. That's where any model is going to be exposed to the most danger.
The strength and frequency of these pressure changes are a big deal in order to avoid unsafe situations where the rocket becomes unstable. Roozeboom said there are also scenarios where frequencies are so high they can deafen and even kill astronauts — something researchers like herself need to be mindful of when conducting these wind experiments.
Life and limb of the occupants aside, there's also a worry that cargo being transported aboard the rocket could get damaged or destroyed during launch.
"If you have this significant fancy avionic system and this fancy satellite, but you just bang it apart, that's not great either," Roozeboom said.