In a pre-proof article posted in the Journal of Space Safety Engineering, researchers discussed and demonstrated the accomplishments of a conceptual study on the potential advancement made in the application of satellite laser ranging (SLR) in the field of space debris.
Satellite laser ranging is an exact and cheaper substitute for radars to track orbiting targets. It has become a novel and fundamental technique in the space debris field due to its successful attempts to track resident space objects without retroreflectors.
The high-power continuous wave lasers consisting of ground stations arranged in an elaborate network can be used to effectively contribute to the low earth orbit (LEO) collision avoidance maneuvers of space debris. Therefore, it can utilize satellite laser ranging to achieve on-orbit collision avoidance.
The researchers discussed the findings that helped them explore the purposes of a laser tracking and momentum transfer (LTMT) station, the minimum size for LEO collision avoidance activity of an LTMT network, the present technological hindrances, and the gaps that need to be filled before its execution to achieve the successful application of satellite laser ranging for collision avoidance.
Satellite Laser Ranging (SLR) and Space Debris Mitigation
A noticeable paradigm shift in space traffic over the past five years has led to an increase in the number of objects placed in orbit each year, particularly in the LEO area.
This tendency is most likely brought on by the launch of massive constellations and the miniaturization of spacecraft. The failure of around 20% to 40% of payloads in LEO to adhere to space debris mitigation methods during the last 10 years must also be taken into account. Better solutions are needed for on-orbit collision avoidance in which satellite laser ranging can play a vital part.
Various laser momentum transfer (LMT) proposals have been put forward for space- and ground-based system topologies.
Atmospheric factors, such as turbulence, absorption, and scattering, impact a ground-based laser momentum transfer architecture, limiting the debris velocity change that can be achieved.
A ground-based laser momentum transfer system is limited by weather influences on station accessibility. However, the key benefits of a laser momentum transfer ground station are the accessibility of high-power lasers, the lack of electrical power restrictions, the ability to maintain or repair the system, the continuity of operation, and upgradeability and integration with laser tracking systems.
The researchers discussed the significant findings from the "Laser ranging and momentum transfer systems evolution study" (LARAMOTIONS) activity emphasizing ground-based implementation.
The primary goal of the LARAMOTIONS project was to conduct a conceptual examination and a viability study on the potential effects of using laser photon pressure technology for space debris collision avoidance.
Laser Ranging and Momentum Transfer Systems Evolution Study and Its Technical Feasibility
The LEO orbital regime has been the primary focus of the study. All the investigations have been based on a subset of LEO space debris consisting of 9101 resident space objects (RSOs) that were all inactive and larger than 10 cm in size, taking into account both unimpaired objects and fragments.
Decisions about maneuvering depend on the probability of collision (PoC) during close approach situations.
The PoC mostly depends on the separation between RSOs and their orbit uncertainty. As a result, the PoC can be decreased by improving the precision and accuracy of the RSOs' orbits or by changing the trajectories of the objects. Both these methods have been addressed in the current study to make satellite laser ranging feasible.
Based on two mechanisms - photon pressure and ablation - two distinct ground-based laser momentum transfer models have been presented, depending on the laser beam parameters.
In the photon pressure technique, the resultant thrust is slight and the laser intensity is lower than what would be needed for surface vaporization. Regarding collision avoidance, this laser momentum transfer strategy works better than for removal. In contrast, at higher laser fluence values over the ablation threshold, the laser beam vaporizes some of the debris, causing a jet of debris to move away from the target. According to a NASA concept validation study, the increased recoil that results might be used to remove debris.
The two primary tasks of the LTMT network's ground stations are laser momentum transfer and laser tracking. There are various options for an LTMT station's design.
The space debris tracking laser and the laser momentum transfer uses the same telescope mount and beam path in a so-called hybrid station. It is a suitable alternative to bistatic installations that separate the laser momentum transfer and the laser tracking telescope sites.
The Promising Potential of Ground-Based Tracking Stations in Space Debris Collision Avoidance
The significant findings of the LARAMOTIONS study, presented in the current work, show that using an LTMT network to achieve collision avoidance is feasible. This idea has been researched while considering a specific population of LEO space debris and various factors, such as astrodynamics restrictions, atmospheric laser propagation, and associated station needs.
When a 40-kW continuous wave laser is utilized and a tracking accuracy of 0.1 arcsec is guaranteed using adaptive optics, comprehensive calculations on the laser-matter interaction have shown that successful collision avoidance maneuvers may be performed on several operational orbital regime (OOR) objects. Therefore, the data proves the feasibility of satellite laser ranging in debris management.
The network performance analysis in the laser catalog scheme has shown that even 24 globally dispersed stations operational around the clock are insufficient to maintain accurate orbit data for the OOR population. In contrast, a system of nine stations will be able to maintain a catalog of 1500 LEO objects under pragmatic weather conditions.
The collision rate (CR) may be reduced by 95% due to a network for on-demand tracking made up of five European stations. Even though a global network would not be required, it is undoubtedly recommended in light of the enhanced performance of networking the current and future satellite laser ranging stations.
E. Cordelli, A.D. Mira, T. Flohrer et al. Ground-based laser momentum transfer concept for debris collision avoidance. 2022. Journal of Space Safety Engineering. https://www.sciencedirect.com/science/article/pii/S2468896722000738