On Wednesday, 5th September, a group of students from the club attended a tour of the Fluid Dynamics laboratory at the nearby University of Canterbury.
The reason for this trip was primarily to investigate the Wind Tunnels, part of the equipment held in this laboratory. UC owns two wind tunnels, a closed circuit tunnel that pushes the air around a loop, and an open circuit tunnel that sucks air in from outside.
If we are to use our satellite for testing the atmospheric properties of the upper atmosphere, we are going to need to know the aerodynamic properties of our satellite.
We questioned the Project Manager of the laboratory our idea, and received some useful feedback:
- We can measure the aerodynamic force exerted onto the satellite by mounting it to the 6-axis force balance situated in the closed-circuit wind tunnel. A specialized ‘stinger’ will have to be designed to hold the satellite’s structure in place.
- The aerodynamic properties of the upper atmosphere are not as simple as they seem. Because the density of the gas at that altitude is so much drastically smaller than what it is at close to sea level, it stops acting conventionally, like a fluid. Instead, exerted atmospheric forces have to be thought about in terms of the individual collisions between molecules in the gas and our satellite (a field of study known as Rarefied Gas Dynamics). Our experiment won’t be as simple as determining the drag coefficient, but a wind tunnel test is still required.
Knowing this, we got to work. We need to create a to-scale model of the satellite that as closely as possible replicates the structure of it in it’s deployed state. This model will be used for running wind tunnel tests.
We had begun prototyping a couple of weeks ago, and the design that seemed most popular among the students was a 8 cornered-cube reflector (essentially 8 corner reflectors placed in a cube shape). Not only does this design have a relatively large radar cross-section, it also retains high reflectivity at all orientations, as the satellite will most likely be tumbling in orbit.
We decided sheet aluminium would be adequate for this model. A finalized design was made using card, and we cut the appropriate metal pieces using a guillotine and a band saw.
Deciding it looked a bit bland as just white aluminium, we coated it with a carbon fiber-looking vinyl and added some racy gold decals. The end result looked quite sleek!
To test the reflective properties of the design, we shone a laser diode at it from multiple angles. The air was sprayed with an aerosol to make the beam visible.
One can see the green light illuminating the spot where the laser beam originated. A closer shot reveals how the beam is reflected within the reflector’s geometry:
Before we can run wind tunnel tests, we need to create a specialized stinger to hold the reflector in position, which will be covered in the next post.