Considerations for space vehicle thermal vacuum retest

The decision to retest a space vehicle (SV) in a system level thermal vacuum will, in most cases, incur significant impact to a program's cost and schedule, and may impact the vehicle's mission life reliability. Despite the consequences of such testing, it is sometimes necessary to re-verify the workmanship associated with removing, reworking/repairing, and replacing flight hardware following an initial vehicle thermal vacuum test. This paper evaluates the technical risks associated with conducting a vehicle thermal vacuum test by: · Assessing the decision process for an SV thermal vacuum retesting used by industry. · Determining the technical rationale used for conducting an SV thermal vacuum retest. · Identifying risks associated with retesting (and not retesting). · Measuring the test effectiveness of the SV thermal vacuum retest. The team that compiled this report developed a list of technical considerations that should be assessed during the retest decision process to address and quantify associated risks. Data collected from 350 space vehicles across 6 major aerospace contractors with thermal vacuum tests between 2000 and 2016 was compared against commercial, civil, and DOD space vehicles. The primary reasons for retesting were anomalies in the initial thermal vacuum test associated with unit workmanship and subsystem interfaces. Retests detected significantly fewer defects than the initial space vehicle thermal vacuum test with less than one failure per retest. It should be noted that the focus of this study was on space vehicles that were retested; the on-orbit success of SVs with post-thermal vacuum test rework/repair that were not retested was not explored.