© 2018 Sierra Nevada Corporation Flight-Like Gearbox Testing  Concerns regarding the potential influence of fixture design on the results of the component-level bushing  test and the receipt of the flight-like hardware allowed the team to assemble a three-stage planetary  gearbox which could be used to execute the life test requirements on flight hardware. In the interim  between the component-level bushing tests and this gearbox-level test, JPL changed the life  requirements of the dominating gearbox designs (GB7 and GB8), nearly halving them.  In conjunction with using a flight-like gearbox, this test had the added benefit of testing four bushings  simultaneously (Reference Figure 1) in addition to the other life-limited gearbox components: gears, ball  bearings, and associated lubricant. Concern regarding increased bushing wear seen at cold temperatures  was thought to be due to lubricant starvation related to poor mobility of highly viscous oil in the porous  bushing. This led to a decision to lubricate two of the four bushings with Brayco 814 oil, a discontinued  Castrol product with a pour point and cold temperature viscosity significantly lower than Brayco 815Z oil:   2,121 cSt [7] versus 10,855 cSt [8] at -54ºC. One remaining bottle of Brayco 814 oil was obtained through  distribution. Loads were applied to bushings through the gear mesh inside the planetary gearbox in the  form of resistive torque by a particle brake. Loads on each planet bushing were calculated based on  ANSI/AGMA Standard 6123-B06 [9] Mesh Load factors. This document provides a mesh load factor of  1.25 for four planets with one floating member, meaning the highest loaded planet may carry 31.25% of  the total stage torque.  The first gearbox available for testing was the GB2 design, but the flight-like gearbox bushing wear test  was designed to encompass the load cases from all of the Mars 2020 applications including GB7 and  GB8 as follows:  •Initial run-in at ambient conditions to distribute the lubricant. •Back to back 1X life tests of the “ground test” cycles (total of 2X) with a temperature distribution of 25% ambient (23°C±5°C), 25% hot (+65°C to +70°C), 25% cold (-65°C to -70°C), and 25% ambient (23°C±5°C). •Back-to-back 1X life tests of the “mission life” cycles (total of 2X) were conducted at a sustained -55ºC. It is worth noting that the temperature chamber was held at -55ºC during the entire mission life test, even during periods of non-operation. This was considered important for preventing the lubricant from reflowing better at room temperature, potentially providing a false-positive test result. •All operation, except initial run-in, distributed clockwise and counter clockwise cycles evenly at five-minute intervals. Run-in consisted of 30 minutes operation clockwise followed by 30 minutes operation counter clockwise. In contrast to the component-level bushing test which failed prematurely, the flight-like gearbox test  successfully completed the test protocol. This satisfied the life and loads required for all the Mars 2020  gearbox designs and provided the necessary confidence to proceed with the designed gearbox  configurations. The as-tested loads and durations are summarized in Table 2 and illustrated in Figure 9,  with the component-level bushing wear test loads and durations shown for reference.   NASA/CP—2018-219887 538