Asteroid Ryugu Sample Collection: Feasibility Analysis and Innovation

Asteroid Ryugu Sample Collection: Feasibility Analysis and Innovation

This paper evaluates the feasibility of an in-orbit asteroid sample collection mission using a hydrogel capture device at the L2 point Liapunov orbit. The study focuses on asteroid Ryugu and analyzes the capture of ejected particles using a hydrogel-based system. This document addresses several key questions and provides suggestions for enhancing the capture process:

1. Please introduce the reason for choosing asteroid Ryugu.

The selection of asteroid Ryugu was based on its characteristics, including its composition, size, and orbital trajectory. Ryugu is a C-type asteroid, known for its carbonaceous composition, offering valuable insights into the early solar system. Its relatively small size and slow rotation make it easier to study and collect samples from.

2. The legend of Figure 1 on page six is wrong. β = 8.02315 · 10−4 should be changed to β=0.037297.

This error has been corrected. The legend of Figure 1 on page six now correctly reflects β=0.037297.

3. What is the difference between the TDM1 and TDM2 positions on page ten?

TDM1 and TDM2 represent two distinct locations within the capture region. TDM1 is situated closer to the asteroid, while TDM2 is positioned further away. These locations are chosen to optimize the capture process, accounting for the trajectory of ejected particles and the spacecraft's movement.

4. In Figure 5 on page twelve, why is the range of impact angles for Point mass restitution coefficients larger than that for Rigid body restitution coefficients?

The larger range of impact angles for point mass restitution coefficients compared to rigid body coefficients is attributed to the simplified nature of the point mass model. In the point mass model, the impact angle is not constrained by the physical dimensions of the object. Therefore, it can accommodate a wider range of angles, resulting in a larger range of impact angles.

5. On page eighteen, why did the study only use the Liapunov orbit among the nine types of orbits?

The Liapunov orbit was chosen because it offered the most favorable conditions for capturing ejected particles. This orbit provides a stable and predictable trajectory, enabling the spacecraft to maintain a close proximity to the asteroid, increasing the probability of capturing ejected particles.

6. On page twenty, in the last line, 'However, since the orbit is much bigger, it can not be ensured that, when an ejecta is escaping, the spacecraft will be there and not in another tract of its path.' Suggestion: On page twenty, in Figure 12, two capture spacecraft can be placed at the two ends of the orbit to increase the capture probability and prevent the required particles from escaping.

This suggestion is a valid approach to enhance the capture probability. Placing two capture spacecraft at the two ends of the Liapunov orbit would significantly increase the chance of capturing ejected particles. This strategy ensures that even if a particle escapes from one spacecraft, there is a higher probability of it being captured by the other.

7. In addition to this, from Figure 3.1 it is known that bigger particles feature a higher vej: change to In addition to this, from Figure 3 it is known that bigger particles feature a higher vej:

This correction has been implemented. Figure 3.1 has been updated to Figure 3, accurately reflecting the source of information.

8. The abstract of this paper states that the work evaluates the feasibility of in-orbit asteroid sample collection missions, but the size of the asteroid ejecta particles in the article is small (1.1809-10mm), and the size of the capture device is much smaller than the Liapunov orbit size at L2. Please provide a detailed introduction on how to use hydrogel for large-scale asteroid ejecta collection at the Liapunov orbit at L2, and emphasize the innovation of this paper, such as using the zero velocity surface for capturing asteroid ejecta.

This paper proposes a novel approach to capture large-scale asteroid ejecta using hydrogel at the L2 point Liapunov orbit. The use of hydrogel is particularly advantageous because of its ability to absorb and retain a large volume of material. This allows for the capture of a wide range of ejecta sizes, including smaller particles that might otherwise escape traditional capture methods.

The innovation lies in utilizing the zero velocity surface (ZVS) for capturing ejecta. The ZVS is a region where the gravitational potential energy of the ejecta is equal to its kinetic energy. By positioning the hydrogel capture device within the ZVS, the study exploits the natural gravitational forces to efficiently trap ejecta particles. This method allows for capturing a greater volume of ejected particles compared to relying solely on the spacecraft's movement.

The study's findings suggest that the proposed method of using hydrogel at the L2 point Liapunov orbit, combined with the strategic use of the ZVS, provides a feasible approach for in-orbit asteroid sample collection missions. This innovative technique can significantly contribute to our understanding of asteroid composition and the early solar system.