# Why do they believe that the Bigelow Expandable Activity Module has “taken a hit”?

In NPR's news item After A Year In Space, The Air Hasn't Gone Out Of NASA's Inflated Module there is a quote that's interesting:

"We do believe we've taken at least one hit," says Crusan. "Very small in nature, and actually we can't even visually see where it's at."

Crusan says there was no loss of pressure from the hit.

Without a leak, or a visible site, what is it that makes them think they've "taken a hit"? I assume it's a meteorite or particle impact they are referring to, right?

above: Photo credit: NASA, from here.

above: "Astronauts Peggy Whitson and Thomas Pesquet are photographed inside BEAM, which has an interior roughly the size of a medium school bus." Photo credit: NASA, from here.

above: "Flight engineer Kate Rubins checks out the Bigelow Expandable Activity Module, which is attached to the International Space Station." Photo credit: NASA, from here.

• If I had to guess, they probably detected an impact at some point through vibration. I don't know how to verify, however. – Arthur Dent Jul 26 '17 at 19:57
• Part of Bigelow's design is it's a self-healing structure, much like many modern automobile tires, so that being pierced by micrometeors doesn't destroy the integrity of the module. – FKEinternet Jul 26 '17 at 19:58
• @ArthurDent ya I'm thinking microphonics of some kind. – uhoh Jul 26 '17 at 19:58
• :face palm: yeah, I guess it helps to read the question, not just the body of the post ... – FKEinternet Jul 26 '17 at 20:02
• If a wayward cubesat had hit it there very well might not be an ISS anymore. Impacts in space are usually at high speed and thus very destructive. – Loren Pechtel Jul 28 '17 at 3:35

Since the module is a prototype the main purpose is to test and verify the concept. Primarily goal is to test the module's ability to withstand space debris. For this purpose the module is equipped with sensors to detect impacts. There are a few articles you can find some information about this at

NASA

Researchers at NASA’s Langley Research Center in Hampton, Virginia, continually analyze data from internal sensors designed to monitor and locate external impacts by orbital debris, and, as expected, have recorded a few probable micrometeoroid debris impacts so far. BEAM has performed as designed in preventing debris penetration with multiple outer protective layers exceeding space station shielding requirements.

or 3ders

The first year of the expandable module’s life on the ISS has been mostly about resisting space debris. Sensors in the module, which are monitored by staff at NASA’s Langley Research Center in Hampton, Virginia, indicate that the blow-up structure has taken a few hits. Fortunately, the kevlar-like weave of the module has done its bit, preventing any penetration from outside forces.

After some research and this article I found out that they are using a system called Distributed Impact Detection System (short DIDS) to detect these impacts. NASA describes the system like:

DIDS units are high-speed, four-channel digitizers that record ultrasonic noises. Instead of listening for the hiss of air, these units detect the high-frequency sounds moving through the metal itself

There are a few of these systems installed in different modules at the ISS

Detailed information about the system can be found in this technical report of NASA.

• +n! This is an excellent, model SE answer! Thanks for the research, quotes, and even the backup NASA technical report with full documentation! I see there the sample rate is nearly a MHz (850kHz), which can indeed potentially provide directional information with the quad sensors shown spaced by oder 10's of centimeters and ~600,000 cm/s sound velocity. Beautiful. – uhoh Jul 27 '17 at 11:43