[From April 2001 issue of ORBITAL DEBRIS QUARTERLY NEWS, NASA JSC http://www.orbitaldebris.jsc.nasa.gov/newsletter/v6i2/v6i2.html#news4] ISS Space Shuttles Examined for Debris Impacts Two Space Shuttles, Discovery (OV-103) and Endeavour (OV-105), have recently been examined for orbital debris and meteoroid impacts following missions to the International Space Station (ISS) late last year. Both exhibited numerous impacts on a variety of inspected orbiter surfaces, covering more than 200 m2. Discovery visited ISS last year on the STS-92 mission for seven days of its 13-day flight in October 2000. A total of 38 impacts were identified on the orbiter window thermal panes from orbital debris (9), meteoroid (7), and unknown (22) particles. The largest impact feature with a diameter of nearly 1 cm was apparently caused by collision with a small paint particle. Three of Discovery's thermal panes were subsequently replaced. Six impacts (3 orbital debris, 1 meteoroid, and 2 unknown) were found on the radiators with three of these achieving penetration. The largest radiator impact site was approximately three-quarters of a millimeter in extent and was caused by a meteoroid strike. Four other impacts were also discovered: three on the flexible reusable surface insulation (FRSI) covering the external payload bay doors and one on the vertical stabilizer. Of these, two were meteoroids, one was orbital debris, and one was of unknown material. In December Endeavour conducted the 11-day STS-97 mission, which again included seven days docked to ISS. Although the number of identified window impacts decreased to 30, the number of impacts to the radiators and the FRSI (12 and 6, respectively) actually increased compared to the longer duration STS-92. A total of two windows were replaced. Of the 12 radiator impacts, only one penetrated the thin aluminum sheet, but two struck the silver-teflon-aluminum doubler installed recently to protect the radiator coolant loops. Four additional impact sites were found on the leading edges of the orbiter wings, two from orbital debris particles and two from unknown sources. Overall, the number of identified impactors of all sizes is roughly evenly divided between orbital debris and meteoroids. However, a significant number of impactors cannot be identified by type, particularly for the smaller window strikes. Complete inspection details are provided in STS-92 Orbiter Meteoroid/Orbital Debris Impact Damage Analysis, JSC-29318, January 2001, and STS-97 Orbiter Meteoroid/Orbital Debris Impact Damage Analysis, JSC-29373, March 2001. ***** A related technical article "International Space Station Debris Avoidance Operations" is available in the same issue of the newsletter at http://www.orbitaldebris.jsc.nasa.gov/newsletter/v6i2/v6i2-3.html#project_re views .
