Term 3 started off with us reviewing the currently plausible scientific investigations our satellite could perform. The team had narrowed down the possibilities to the three experiments that seemed most feasible to undergo, as well as having the potential to bear useful results to the scientific community. These three experiments are:
- To determine an accurate model of the density of the upper atmosphere, to aid in prediction of the lifespan of LEO satellites
- To measure the effectiveness of different materials as radiation shielding
- To test the capabilities of a revolutionary new hardware in space (specifically, we were suggested by the owners of the company Spacebase to test a form of GPU-accelerated data processing)
With the idea of having one experiment to focus on, we decided to select the most plausible. Our selection was the investigation of the density of the upper atmosphere.
RocketLab’s first 2018 launch carried the ‘Humanity Star’, a geodesic sphere designed to be visible from the surface. The predicted lifetime of the satellite was nine months, after which it would re-enter earth’s atmosphere. However, the Humanity Star reentered far earlier, after only two months and a day.
This shows the lack of information about the upper atmosphere, which could be a potentially costly disadvantage to LEO satellites.
One of the advantages of this experiment is it drastically simplifies the satellite design. The current plan for how the investigation is performed is as follows:
- Launch the satellite
- Obtain satellite tracking from an existing system (eg. the TLE system)
- Determine changes to the orbital parameters over time to infer drag, and therefore density of atmosphere
As you could tell, there is no need for sensors or transmitters aboard the spacecraft, as it only needs to be detectable by the tracking hardware. It can be entirely passive, in other terms. Essentially, what we will be building is a radar reflector, as radar is generally used for tracking.
What makes a good radar reflector? generally speaking, the larger the radar cross-section, the better. Radar cross-section can be improved by employing reflective geometries into the design. For example, rounded objects are good reflectors, and corner reflectors are designed to reflect any ray back towards it’s source.
Using sheets of paper, we began prototyping with designs for deployable radar reflectors.