Science and Technology
Attitude determination and control system (ADCS)
The ADCS processing will be carried out by a software task running on the On Board Computer. The estimation and control loop will execute at a rate of 1 Hz. It will make use of sensor data from the following sensors:
- 3-axis resistive magnetometer
- Optical sun- and nadir sensors
- 3-axis MEMS gyroscope
- coarse sun sensing using 6 photodiodes
Figure 1. CubeSense attitude determination system.
Figure 2. Torquer rod.
Figure 3. Momentum wheel.
Space sails can be used to increase the area of the spacecraft that interacts with the atmospheric particles. This increases drag and result in a more rapid de-orbiting. The size of the sail required to successfully deorbit a satellite within a given number of years will depend on the mass of the spacecraft and its initial altitude (atmospheric densities).
Figure 4. Lifetime Altitude
The figure above shows de-orbiting times for satellites of up to 500 kg with a 4-by-4-metre deployed sail and optimal pointing control. Satellites that would otherwise remain in orbit for decades beyond the required 25-year lifetime could be brought down quickly with this low-mass, low-power system.
In Earth orbit, drag pressure exceeds solar radiation pressure below approximately 600 km altitude.
Figure 5. Drag vs. SRP
DeorbitSail will use atmospheric drag as its primary method of deorbitation, but the same design can be effective for solar sailing at higher altitudes.
"Solar sailing" is a method of propulsion that uses the very small force exerted by sunlight to propel a spacecraft. This force, solar radiation pressure, is much smaller than the weight of the sail on the earth's surface, even though the sail material is thinner than human hair.
Efficient use of solar radiation pressure requires a very large, very light sail, and also for the sail to be pointed in the correct direction. Because the sail must be very large, it had to be folded for launch and automatically deployed in space. Testing this deployment on Earth can be difficult because the force of gravity is so much larger than the forces the sail has been designed for. One of the challenges is combining computer simulations with experiments to be certain that the sail will deploy in space as it did during laboratory testing. Another challenge is supporting the sail during ground testing of deployment.
Figure 6. Solar Sail