Scientific CubeSat Concept Study
This project consisted in the conceptual design of a 2U CubeSat mission aimed at measuring the concentration of CO2 in the thermosphere. The development was carried out following a concurrent design approach.
The proposed spacecraft is also a technology demonstrator for the use of deployable solar arrays for passive attitude bias, SLS 3D printing for the primary structure and shape memory alloys in deployment mechanisms.
My work was centred on the Attitude Determination and Control System (ADCS), for which I took full responsibility. The ADCS's task is to satisfy the pointing requirements imposed by other subsystems, such as the payload and power raising. The first step in the development of the ADCS consisted in precisely defining the mission's pointing requirements. This was a joint task between all the spacecraft subsystems.
To satisfy the defined tolerances, the CubeSat was provided with an Earth sensor, a fine Sun sensor, a GPS receiver and an artificial coarse Sun vector created by combining the power output measurements from each array.
The required control authority depends on the magnitude of the expected environmental disturbances. In LEO, notable disturbances can arise from aerodynamic drag, gravity gradients, and to a lesser extent, magnetic moments and solar radiation pressure. The impact of each of them was individualy assesed and quantified at both beggining and end-of-life altitudes.
The main source of disturbances came in the form collisions with the rarefied gases present in the high atmosphere (≈400km), which were in the other of µNm. The main pointing requirement demands the spacecraft to point in the "wind" direction. To achieve this, the use of slightly angled deployables to create a passive restoring moment was studied.
The drawback of this solution is that it speeds up orbital decay. The impact of this solution was assesed using STK's built-in propagator tools for different panel deployment angles.
