Arthur T Knackerbracket has processed the following story:
A potential hazard for any space mission, including NASA’s Mars Sample Return, is micrometeorites. These tiny rocks can travel up to 50 miles per second (180,000 mph). At these extreme speeds, “even dust could cause damage to a spacecraft,” said Bruno Sarli, NASA engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Sarli leads a team designing shields to protect NASA’s Mars Earth Entry System from micrometeorites and space debris. To test the team’s shields and computer models, he recently traveled to a NASA lab, designed to safely recreate dangerous impacts.
[...] 2-stage light gas guns are used by the lab to accelerate objects to speeds up to 27,500 feet per second (18,750 mph) that simulate micrometeorite and orbital debris impacts on spacecraft shielding. The first stage uses gunpowder as a propellent the way a standard gun does. The second stage uses highly compressed hydrogen gas that pushes gas into a smaller tube, increasing pressure in the gun, like a car piston. The gun's pressure gets so high that it would level the building if it were to explode. "That is why we hung out in the bunker during the test," said Sarli.
[...] While the pellet’s speed is incredibly fast, micrometeorites actually travel six to seven times faster in space. As a result, the team relies on computer models to simulate the actual velocities of micrometeorites. The slower rate will test their computer model’s ability to simulate impacts on their shield designs and allows the research team to study the material reaction to such energy.
Mars Sample Return is a multi-mission campaign designed to retrieve scientifically selected samples of rock and sediment that NASA's Perseverance rover is currently collecting on the surface of the Red Planet. Bringing those samples to Earth would allow scientists to study them using the most advanced laboratory instruments-those that will exist in the coming decade and those in the decades to follow. The campaign is one of the most ambitious endeavors in spaceflight history, involving multiple spacecraft, multiple launches, and multiple government agencies. Goddard is currently designing and developing the Capture, Containment, and Return System that would deliver the Mars sample tubes back to Earth.
Very interesting embedded videos showing high-speed camera frames of the impacts:
Video 1
Video 2
(Score: 2) by Immerman on Tuesday October 25 2022, @02:39PM (1 child)
Seriously they go to the trouble of listing two different units of speed, and *neither* of them are real engineering units?
Fine- I'll do it:
27,500 feet per second = 8,380m/s
So, good enough for testing impacts between with debris when both are in circular(ish) orbits around Earth - but completely inadequate for when either or both are traveling at interplanetary speeds.
I wonder how exactly they use computer simulations to add almost an order of magnitude of velocity? Seems rather like trying to extrapolate the effectiveness of bullet proof armor tests using a baseball pitching machine. You've got some potentially rather severe nonlinearities in material properties between the two.
(Score: 1, Interesting) by Anonymous Coward on Tuesday October 25 2022, @03:06PM
Of course they have to deal with the limitations of their testing apparatus, but I wonder if it might be that the more interesting physics you mention happens at these lower speeds anyway. At very high momenta you might have the situation where for the first few layers you reach a point where it simply punches through with not a lot of dependence upon the momentum (perhaps with something like some scaling with the number of fragments created or energy transferred to them). I can't help but draw comparisons to charged particle interactions where at low energies particles give up a lot of their energy per unit length traversed, but as you increase the particle momentum the amount of energy deposited in matter actually drops until it hits some minimum amount [bnl.gov], then it slowly rises (logarithmically).