New approach features aggressive load reduction to reduce risk.
This innovation presents a spacecraft aerobraking approach that reduces heating and optimizes corridors, which reduces overall risk. This is accomplished by combining solar panel aspect ratio and edge features with simple spacecraft packaging optimization and integrated thermal-analysis techniques that also allow specifying a more benign temperature corridor.
There has been a perceived general aerobraking risk in early-stage mission designs. The aero-heating of the solar panels during aerobraking in the warmer Venus thermal environment is considered riskier than Mars aerobraking.
Most missions were not optimized for aerobraking, particularly the solar-panel and spacecraft-shape aspect ratio and thermal features. Mars aerobraking had more uncertainty, but lower solar heating rates and more actual mission data. Venus has more solar heating, higher initial temperature conditions, and fewer real-life examples, but less atmospheric change. Lingering aerobraking risks applied to such missions in the early stage required more aggressive early-phase reduction of risks. Older designs did not pursue aggressive solar panel thermal load reduction features, or optimization of temperature, and instead focused on heat rate corridors.
This approach combines multiple new features into one combined solution. The first feature is lower heating from past designs by applying the lowest aspect ratio solar-panel layout, resulting in lowest heating for the solar-panel area required for the mission. A new “picture frame” edge is added to solar panels. The outside 3 to 6 in. (≈7.6 to 15.2 cm) of the panels are directed 45 to 30° into the flow. This reduces heating by an additional 15%. The projected drag surface is increased, which reduces the ballistic coefficient that can be used to either decrease aerobraking duration or increase thermal margin. These edges, which receive higher heat flux, are protected with high-temperature multi-layer insulation.
The new high-temperature solar panel features high-temperature graphite epoxy facesheet and solar array design. The solar arrays are pre-cooled by turning away from the Sun a mission-specific number of minutes before the drag pass. The developed thermal analysis integrated with the trajectory simulation approach is used to fly a temperature corridor instead of a heat-rate corridor, which results in better control of temperatures. This yielded an overall aerobraking approach with shorter aerobraking durations and substantial temperature margins.
This work was done by Charles Baker, Michael Amato, David Steinfeld, and Jeff Stewart of Goddard Space Flight Center; and Jill Prince, Derek Liechty, and John Dec of Langley Research Center. GSC-16407-1