Impact Feature Types

• Hypervelocity impact craters on ductile metals, A0187-1 and S1003
• Impact induced discharges, A0201
• Hypervelocity impacts craters with spall and fracture zones, A0201

Impact craters on metal surfaces

Central craters were usually near-circular shaped, although some features on the S1003 Aluminum surfaces are clearly elongated Diameter measurements were taken as described in the M & D preliminary report, page 8:
"(...)In practice, the microscope was focused on the top of the feature's rim, and the center of the ridge which was in focus was used to make the estimated diameter measurements(...)."
Be aware that diameter measurements reported in hypervelocity impact related literature might have been taken as diameter of the central crater at the level of the undisturbed surface.

Diameter measurement for an impact feature into Al.

Impact induced discharges on MOS detectors

Measurements for these sensors were taken as follows:

• Central crater of the discharge zone, center of edge of the discharge zone either as seen under the optical microscope or on an SEM image
• Discharge or vaporization zone, the approximately 50-60 micrometer diameter area surrounding the crater, from center of rim to center of rim.
• For larger features that caused an impact with asciated spall zone, almost resembling a "normal" impact into a brittle surface, the central crater had melting from the discharge effect associated with it. Measurements were taken from the apparent place of transition between the melt zone and the spall zone.
• Impacts with associated spall zones also have spall zone extensions giving apparent maximum and minimum spall zone diameters as measured from the edges of the spall zone through the apparent center of the central crater.

Diameter measurements for a larger impact feature with discharge (fused central crater) and spall zone

Hypervelocity impacts craters with spall and fracture zones

Measurements for these fetures were taken as follows:

• Center of central crater rim to center of crater rim for impacts with an obvious central crater
• Center of line of apparent transition from former central crater to spall zone to center of line of apparent transition from former central crater to spall zone for larger impacts with no circular shaped central crater but showing a central shatter zone.
• Minumum and maximum spall zone diameters measured from spall zone edges through the apparent center of the central crater.

Notes:

• For elliptical features minimum and maximum diameter values are given. This affects:
  • Central crater diameters
  • Discharge zone diameters
• For some of the features no diameter value is available. This might either be due to the fact that no records were kept, or no photograph could be found for this particular feature during the time period available for the archiving process. In this case, the feature diameter may be deducted from SIMS images showing substrate material giving:
  • The maxmimum extent of the crater lips for impacts on Al and Ag surfaces,
  • The diameter of the discharge zone (Al and Ca images), and of the central crater (Si and Si2 images) for MOS sensors,
  • The size of the spall zones (e.g. Ge images) for impacts into brittle materials (e.g. Ge witness plates)
  This being assumptions more than measurements this archive does not contain size values deducted from SIMS images.