SPACE DEBRIS
Spaceflight has had profound effects on our way of life and on society by enabling technologies that are now often taken for granted. One of the most easily recognizable technologies enabled by spacecraft is the Global Positioning System and navigation. Weather prediction, monitoring, and crisis response activities are aided by Earth-observing spacecraft. In some locations, internet, television, and phone services are provided through communication satellites. Many of today's capabilities would either decrease in effectiveness, or cease to exist altogether should these spacecraft be destroyed.
Source: ESA
The operation of spacecraft is currently jeopardized by space debris, as collisions with debris may render a spacecraft inoperable. In fact, operational spacecraft are frequently required to perform collision avoidance maneuvers to avoid collision in the current space environment. Space debris, which consists of all non-functional objects in orbit (including spacecraft that have reached their end of life), is generated from every rocket launch and through collisions. Every piece of debris increases risk of collision between operable spacecraft and debris, or debris with other debris. In the event of a collision, additional debris is generated and the risk of additional collisions rises. This cascade of collisions is termed "Kessler Syndrome" and was predicted by Donald J. Kessler in 1978. In fact, collisions with debris have already happened and the number of debris in orbit has been steadily rising since the 1960s.​
ACTIVE DEBRIS REMOVAL
Prior to 2022, multiple organizations globally implemented a guideline to ensure that any low-Earth orbit (LEO) satellite de-orbits within twenty-five years after mission completion to reduce the growth of space debris. However, these efforts were inadequate and the Federal Communications Commission (FCC) implemented a rule to ensure all LEO spacecraft de-orbit, whether naturally or via de-orbit thrusting, within five years of their mission completion. However, although this rule addresses mitigation of space debris, methods are still required to remove current space debris.
The removal of space debris is suggested to be performed through active debris removal (ADR) missions. Some promising methods of ADR are robotic arm capture and tethered methods such as tethered robotic manipulators, nets, or harpoons. Although still low on the technology readiness level, multiple organizations are working on these technologies and some demonstration missions are under development.​
Our lab (the Space Systems Dynamics and Control Lab) is researching tethered methods of ADR. When compared to robotic arms, tethered methods allow for a larger range of objects to be captured, and are regarded as safer as they allow for greater distances to be maintained during capture of debris. Tethered methods are also more ideal for capturing larger targets, which are some of the most dangerous debris on orbit, as collisions with them would generate large amounts of additional debris. ​
Photo: ESA-David Ducros
Although promising, tethered methods present difficulties once the targeted debris is captured. As debris is often tumbling, yanking of the tether by either the debris or the chaser spacecraft (the spacecraft that captures the debris) may cause collision. To avoid collision and maintain safe post-capture operations, our research focuses on cable-based de-tumbling of debris.​
Safe post-capture operations are obtained through maintaining a desired distance between the chaser spacecraft and debris, and by de-tumbling and maintaining a desired orientation of the debris in space. This requires control algorithms to be applied through the tether, but it also requires knowledge of different debris parameters that are often unknown. To obtain these unknown parameters, we need to implement estimation algorithms using various sensors that would be available on the chaser spacecraft. In order to develop and test our algorithms, we must first model and simulate the system on computers. Once our algorithms are developed, we aim to test them on physical test beds.
To read more on our research, click below!
