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Tiny Particle Blows Hole In European Satellite's Solar Panel (go.com)
An anonymous reader quotes a report from ABC News: A tiny piece of debris has punched a gaping hole in the solar panel of one of Europe's Earth observation satellites, causing visible damage but not enough to affect its routine operations, the European Space Agency said Wednesday. The unknown particle just a few millimeters big slammed into the back of a solar panel on Copernicus Sentinel-1A on Aug. 23. Using on-board cameras, engineers have determined that the hole is about 40 centimeters (16 inches) in diameter. The European Space Agency said the loss of power caused by the strike is "relatively small" -- less than 5 percent of the wing's usual output. The likelihood of such a strike is calculated at between 1:35 and 1:130 during the satellite's five-year lifetime, said Holger Krag, who heads the agency's space debris office. While the particle probably had a mass of less than 1 gram (0.04 ounces), scientists calculated that it was traveling at up to 40,000 kilometers an hour (24,856 mph) when it hit Sentinel-1A. Space.com has posted a video about the incident, showing images taken before and after the impact.
Kinetic energy = 1/2 of mass times speed squared.
At 11 km/s, even a mote of dust kicks more than one part of human anatomy.
One half mass of the particle times the square of the velocity applies everywhere. So, given the value of 1 gram, and 40K kph, we get just a bit under 62 kilojoules. While the mass was likely less than a gram, the velocity is the primary issue.
The initial impact area is over maybe a square millimeter at best. Given the kinetic impact of relatively common events, this is roughly 8 rifle bullets. So a 40 cm area is entirely expected. While the actual hole is small (as expected, it punched through) cracks would run through a small group of solar cells, rendering the affected cells useless due to transmitted shock. . .
that is about 60000J of energy, 3 times as much as 50 cal round at 20000J
The answer 61K joules doesn't tell you much unless you are really familiar with energy. .50 Calibre machine gun. That gun is so large, that it is difficult for one person to carry it, and is normally fired from an anchored position (a mount). This is a common ship-board defense weapon against small craft.
So, let's look at another similar energy values to help us understand how much energy the solar panel experienced (for lack of a better word).
This https://en.wikipedia.org/wiki/... bullet (when fired) has a muzzle energy value of about half that amount. This is basically the size of round fired from a
When the density of the particle is high relative to the hardness of the target, there's a very high chance for penetration and low energy transfer.
But when the projectile density is relatively low compared to the target hardness, the projectle is usually deformed and stops inside the target. Or as in this case, is completely atomized, causing nearly perfect energy transfer. (approaching 100%)
So being able to ignore energy loss in the transfer make the math and modeling pretty easy. You just imagine an explosion at the point of contact, with about double the energy of the projectile. (since explosions are omnidirectional, wasting 50% of their energy in the other direction on impact, and in this case, 100% of the energy is transferred into the target)
And at orbital and escape velocities, delta-V is so high that even a very low M yields a lot of joules.
Final thing to consider, these panels aren't terribly sturdy. They're made to be extremely light, store compactly, and self-deploy/assemble in space, making them overall pretty delicate. This isn't built anything like the solar panel on your roof. It's more like the model car in your dad's display cabinet. Shoot that thing with an airsoft gun and see what happens.
I work for the Department of Redundancy Department.
Considering that 3800 joules is the force applied by a 7.62x39 rifle bullet (i.e an AK-47 round), this is the equivalent of about 8 rounds hitting simultaneously in an area likely under a square millimeter. . .
Article and non-flash photos here at ESA web site: http://www.esa.int/Our_Activit...
Aren't particles microscopic, something that can be measured in millimetres doesn't seem like it ought to be described as a particle...
In physics, yes. But they were using the general definition, which does seem somewhat out of place in this case, but is correct. This is similar to talking about a particle of dust getting into a camera lens.