[Laser Debris Removal]
Thrust Measurement Experiment for Space Debris Nudging

RESEARCH OVERVIEW

• The Thrust Measurement Experiment for Space Debris Nudging (ELF-Laser Debris Removal) investigation seeks to clarify the behavior and thrust of simulated orbital debris during laser irradiation under microgravity and the feasibility of removing space debris using the laser orbit conversion method.
• Using the Electrostatic Levitation Furnace aboard the International Space Station (ISS), the target material simulates the thermally and mechanically isolated space debris, and the precise measurement of the propulsive thrust force due to laser beam radiation from one direction.
• This research has great significance to evaluate the feasibility of laser orbit conversion of space debris, which has been proposed for a long time. Moreover, space debris removal using the continuous wave (CW) laser is studied on the ISS for the first time.

DESCRIPTION

A series of studies have been carried out based on a scenario using 1) the Riken-EUSO telescope to detect and track small-size (1-10 cm) space debris and 2) a high-power repetitively-pulsed laser to generate an orbital conversion force on the space debris. Based on that scenario, it has been calculated that the greatest volume of orbital debris is melted and becomes a droplet during laser irradiation, where power is high enough for the orbital conversion of such small-size space debris. Once the space debris is melted, it can be deformed and/or fragmented by a second shot of an intense laser pulse. The possibility of this phenomena occurring is crucial to the feasibility of this scenario: no systematic studies have been conducted yet. The EUSO scenario is based on experimental results of thrust generation via pulse laser ablation in vacuum. While the tested materials have been sufficiently large compared to the heat input, thrust due to laser ablation of a thermally isolated target has yet to be studied.

Furthermore, conducting pulse laser space debris removal would require a huge laser facility to be launched into orbit. As an alternative, a small-power continuous wave (CW) laser is expected to generate the necessary orbit transfer thrust force. However, no existing quantitative experimental data exists because the thrust due to the evaporation of a solid material using a CW laser is sensitive to the temperature of the target material, which can easily be influenced by the heat conduction from the target material to the supporting jig. Moreover, the temperature of the target material exceeds the melting temperature, and such a high temperature target can only be supported using the Electrostatic Levitation Furnace (ELF) without heat conduction to the environment.

In the Thrust Measurement Experiment for Space Debris Nudging (ELF-Laser Debris Removal) study, the propulsive thrust on a thermally- and mechanically-isolated target generated by CW-laser evaporation is measured. The objective is to conclude whether the method of laser orbit conversion of space debris can actually be established based on the obtained observation results and the estimated value of thrust. Further, by comparing results with the numerical simulation model, the basic data for the validation of the tool for the simulation-based design of the system can be obtained.

To simulate isolated debris, the electrostatic levitation furnace is used because it eliminates the effects of heat conduction and convection heat transfer to the surroundings. In addition, the ELF installed in Kibo is equipped with a laser heating device that enables heating from one direction and allows for the observation of phenomena, measurement of temperature time history, and determination of propulsive force based on applied voltage. This simulation requires physical modeling to estimate the charge and ablation thrust applied to the target material from the applied voltage and the dynamic behavior of the target material. This type of experiment can have a significant impact on understanding the feasibility of laser orbit conversion of space debris, which has long been studied.

When debris is melted by laser heating, natural convection occurs inside the molten pool under a gravity environment, which increases the heat transfer from the evaporation interface to the inside the liquid phase, and reduces the evaporation rate and the resultant propulsive thrust force. By comparing the experiment data using the electrostatic levitation furnace on Earth with those obtained in the space experiment, it is expected that the actual thrust in space should be larger than that under gravity conditions.

The experimental data serves as the core data for discussing the design and feasibility of the laser space-debris removal systems. In addition, it can provide a significant impact on the related research development in the future.

SPACE APPLICATIONS

This investigation could help demonstrate the feasibility of using laser orbit conversion to deal with space debris and inform related research in the future.

EARTH APPLICATIONS

Data from this investigation could improve the reliability of computer models for simulating molten materials, which are useful in many materials science and industrial applications.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

The ELF instrument is assembled and installed in the Multi-Purpose Small Payload Rack (MSPR/MSPR2) in Kibo. After setup, the experiment is operated from ground control as required by investigators at Space Station Integration and Promotion Center (SSIPC), Tsukuba Space Center. The experiment procedure is as follows:

A crew member prepares the experiment by inserting the Sample Holder into the Sample Cartridge and inserting the Sample Cartridge into the ELF chamber. The ELF is then activated and configured for operation.

To begin experiment operations, the sample is released into the Experiment Volume by the Sample Release Rod. The sample is charged, its position controlled, and the sample is heated and melted using electrodes and power lasers. During operations, the sample is measured through sensors and cameras.

At the completion of experiment operations, recorded video, pictures, and data are downlinked to Earth.

The experiment is closed out by the deactivation of ELF.

MORI Koichi [Osaka Prefecture University]