Delayed ISS Separations Because so much effort was put forth into meeting velocity and safety  mission requirements no one fully considered the possible adverse effects  of a near simultaneous separation. Care was taken to adjust the two  Lightbands such that they separated as closely as possible. Repeatable separations within 0.01 second were achieved in ambient testing and the  consensus off all involved parties was that this was “good enough”. The  concept of re-collision was never considered. Table 1 shows data from the  ambient testing to fine-tune the ISS separation times. It can be seen from  the testing that a difference of 0.02 second was a distinct possibility as the post flight analysis presumes happened.  Temperature was also a significant contributor to the flight anomaly. Based  on initial on-orbit data taken from the satellites, it is believed the ICU was - 25 °C or colder at separation. Although not out the theoretical flight limits  this was significantly colder than realistically expected. ISS motion was first  noticed from the Shuttle video 42 to 43 seconds after ICU ejection from CAPE. This means the ISS Lightbands took approximately 2x to 3x times  longer to separate than at room-temperature. The av ionics timer was verified throug h ground testing.  None of its components are believed to be temperature sensitive. Assuming the avionics timer worked  properly, the suspect component is the Lightband itself. The mechanism that initiates separation in the  Lightband consists of worm gears, brush motors, ball bearings, and a ball screw all lubricated with NYETORR 5200 vacuum gre ase. At this low temperature the viscosity of the grease increases  substantially and thus increases the torque load on the motor. Testing performed on several Lightbands  at similarly cold temperatures has shown that an increase in separation time from 0.9 sec to 3 seconds is  entirely possible. This rise in torque and separation time further increases the standard deviation and  probability of a delay between the ISS separations relative to ambient delays.  Table 1. ISS Separation  Timing Preloading the Satellites  The use of Viton o-rings to preload the satellites resulted in several unknown affects to the separation  event. Viton was chosen because it has low outgassing properties and is readily available. However, the  limiting factor of standard Viton is that its rated minimum temperature is typically only -23°C. The o-rings  may have been below this temperature when the ICU actually separated. No testing was performed on  the o-rings at this temperature so it is unknown what their stiffness or condition was at separation and  how that may have impacted the separation event. At the time no data was available on the percentage of  stored energy in a compressed o-ring that imparts kinetic ene rgy upon inst antaneous compression  release. It was believed low, but  at the time unknown. As mentioned earlier, the 2D separation test fixture  did not accommodate o-rings.  Since the flight, testing has been performed to determine the energy ratio of Viton as a function of  temperature. A 380-mm diameter Lightband separation system was separated on a 5 degree-of-freedom  air bearing fixture to obtain a baseline velocity. A 7-mm thick, 180-mm OD o-ring was then placed inside  the Lightband and compressed to a known preload and distance. The Lightband was again separated  and velocity measured. The change in kinetic energy due to the o-ring could then be calculated. The  results can be seen in Figure 10.  152