Project Review: MMOD Impacts Found on a Returned ISS Cover

August 01, 2016

2-minute read

This article by J. Hyde, J. Read, D. Lear and E. Christiansen originally appeared in Orbital Debris Quarterly News, Volume 20, Issue 3, July 2016

Twenty-six (26) micrometeoroid and orbital debris (MMOD) impact features were found on a returned cover from the International Space Station (ISS). The cover was exposed to MMOD impacts for 1.63 years (from July 2013 to February 2015) before it was returned on the SpaceX CRS-6 mission. It was located at the forward port on ISS pressurized mating adapter 2 (PMA-2), as shown in Figure 1. The cover is a 2-m-diameter multilayer blanket with a beta-cloth exterior surface, which is Teflon coated glass fabric.

The inspection team consisted of JSC Hypervelocity Impact Technology (HVIT) group and Boeing/Houston personnel (shown in Figures 2 and 3). The damages were found on the cover itself as well as straps that were used to hold the cover in place on PMA-2 (Figures 4 and 5).

Table 1 lists the 10 largest damages found in the inspection and Figure 6 shows a histogram of all damages. The largest damage left a 1.2-mm-diameter hole in the external beta-cloth layer of the cover. None of the damages completely penetrated the cover, which has a mass per unit area of 0.46 g/cm2.

The next steps in the inspection will be to determine how deep the damages extend into the cover and to collect samples for examination in the analytical laboratories at JSC to determine, if possible, the composition of the impacting particle. In addition, a comparison will be made between the observed damage and predicted damage using the latest MMOD environment models and damage equations for the cover, based on impact test data.

Figure 1. The cover was exposed to MMOD for 1.63 years at the forward end of PMA-2.

Figure 2. NASA and Boeing personnel inspected the cover for visible damages and located 26 likely MMOD impact sites.

Figure 3: Photographing and measuring the damage

Figure 3. A 3-D digital scanning microscope mounted to an adjustable arm was used to photograph and measure the damage.

Figure 4. An overview of the cover including small labels indicating the location of each impact damage found in the inspection.

Figure 5. An impact damage (no.13) that was found on one of the hold-down straps. This damage is shown in front-light on left, back-light in middle, and through the microscope on right. The hole diameter in the outer beta-cloth layer was 0.75 mm although the dark zone in the back-lighted photo extended well beyond the hole dimensions.

Figure 6. Damage Size Distribution for the PMA cover inspection. The number of damages found in each size bin is given in this graphic (for instance, six damages that were greater than 0.3 mm but less than 0.4 mm were found).