Session: 01-12-03: Spacecraft Structures 3

Paper Number: 162316

162316 - Deployment and Attitude Control Device for Large Flexible Spacecraft 

Solar power satellite systems that collect power in orbit and wirelessly transmit it to earth will have large size and minimal mass. The Caltech's Space Solar Power Project (CSSPP) envisions a 60 m x 60 m spacecraft covered with flexible photovoltaics, DC-to-RF power converters forming a large phased array.  A lightweight composite deployable structure was recently demonstrated in orbit. It is quite challenging to perform station keeping operations of such a large complex system. Moreover, it has been shown in earlier research that to achieve optimal power transfer, the spacecraft needs to undergo attitude changes according to its position relative to the sun and ground station. How does one design a lightweight attitude control actuator for this kind of system? We look towards an approach which is multifunctional. It can help in reducing overall mass and also fit within the spacing of another essential subsystem. This presentation presents a control momentum device that also serves as a deployment mechanism.

The packaging scheme for the CSSPP structure involves folding it into a star-fold pattern and then coiling the star-folded structure onto a central solid cylindrical hub and four cylindrical supports. Deployment is achieved by rotating out the four cylindrical supports. In the current design, once the deployment is over, these cylinders remain functionally inactive and become a dead mass. We propose to use these cylinders as momentum storage devices and show that they can be transformed into an actuator throughout the mission life of the system.

Time duration and the angle of the attitude change for the maneuver play an important role in sizing the momentum device. We use Euler's equation of motion for rotations along with the change in angular momentum stored in the cylinders to execute a maneuver.  Given the change of spacecraft angle with time, we compute required change of orientation of the cylinders. The momentum exchange is limited by saturation of the system.  The existence of solutions of the above system of equations provides a set of constraints from which we estimate the physical dimensions of the cylinders and their angular velocities to carry out the required maneuver. 

Once the sizing of the system is carried out, the next step is to focus on the physical performance. The equations of motion can help generate multiple solutions based on position of the cylinders at the beginning. However, some of them can lead to internal singularities which can render the system torque-less about the maneuver axis. While others may lead to interference between cylinders during the maneuver.  These complexities are addressed by exploring the four-dimensional space of initial cylinder orientations. Another caveat is the non-periodic nature of some solutions. Meaning that once the maneuver is completed, the cylinders do not return to their original positions. After each maneuver is done, it is more efficient if the cylinders return to their initial positions for the next maneuver. Thus, a periodic solution guarantees optimal positioning.  After thoroughly studying all the possible initial orientations of the cylinders, a set of solutions that result in periodic-constrained movements of the cylinders has been obtained. All these studies are not only relevant in the design of weight optimal momentum devices but could also be beneficial to develop an efficient way of operations throughout mission life.  

Presenting Author: Divesh Soni California Institute of Technology

Presenting Author Biography: Divesh Soni joined Space Structures Laboratory (SSL) in 2022 after receiving his Master’s degree in Space Engineering at Caltech. He earned his Bachelor’s degree in Aerospace Engineering from Indian Institue of Space Science and Technology (IIST) in Trivandrum, India in 2016. Before joining SSL, Divesh worked as a Scientist in Spacecraft Mechanisms Group at Indian Space Research Organization (ISRO), Bangalore, India. At ISRO, he worked on deployable appendages and docking of spacecrafts. At SSL, he is working on attitude control and dynamics of flexible structures.