Assessment of satellite equipment vulnerability to hypervelocity impacts by using the SRL ballistic limit equation

Risk for spacecraft to hypervelocity impacts is typically assessed using risk analysis software such as ESA's ESABASE/DEBRIS or NASA's BUMPER code. The number that characterizes the risk is the Probability of No Penetration (PNP). The PNP is a measure for the statistical time interval between two penetrating impacts on a spacecraft. The software tools calculate the PNP using (a) flux models that provide the number of meteoroid and debris particles that impinge on the spacecraft and (b) empirical equations that describe the penetration resistance of the spacecraft structure wall, so called ballistic limit equations (BLE). This approach is justified for manned modules. For an unmanned spacecraft, the perforation of the external wall is not necessarily critical for the spacecraft mission. The current methodology for assessing the risk to spacecraft can be improved by modeling the limit of damage sustainable by equipment inside the spacecraft. The SRL equation has been developed for calculating the ballistic limit impact parameters of typical satellite equipment placed behind typical satellite structure walls. The considered equipment is fuel pipes, heat pipes, high pressure vessels, liquid filled pressurized tanks, harness, electronics boxes and batteries. The considered structure walls are typical sandwich panel- or Whipple shield structure wall configurations. By using the SRL equation, the intrinsic penetration resistance of the equipment such as equipment casing walls, insulations, coatings, etc, is considered, thus enabling a more comprehensive look at satellite impact risks than what is possible with the current risk assessment methodology. In this paper, the SRL equation is presented and its application explained. To demonstrate the capability of the equation, it is applied in a simplified risk-analysis to a box-shaped satellite orbiting in a sun-synchronous orbit. The simplified satellite has a typical structure wall and contains pressure equipment. The PNP calculated with the SRL equation is then compared to the PNP as calculated from the approach currently followed.