The Investigation of Plume-Regolith Interaction and Dust Dispersal during Chang’E-5 Descent Stage

Round 1

Reviewer 1 Report

The paper contains some new interesting material concerning lunar dust. The authors study the plume-surface interaction that occurs as a result of a variable-thrust engine exhaust plume impinging on lunar soil during landings. They build a simulation model with constraints from landing photos to characterize the erosion properties induced by low-thrust engine plume. The authors consider the low-thrust plume-surface erosion process and the erosion properties during Chang’E-5 mission. They find the erosion depth, total ejected mass, and maximum particle inclined angle during Chang’E-5 landing period. The results of the paper will be of interest for scientists studying dust and dusty plasmas at the Moon, for researchers and engineers developing the future lunar mission design, etc.

The authors give rather extensive introduction, mention lunar dust detected within  Apollo 11, Apollo 12, Apollo 15, and Chang’E-3 missions. However, they do not include material characterizing contribution of lunar dusty plasma (see, e.g., S. I. Popel, L. M. Zelenyi, A. P. Golub', and A. Yu. Dubinskii, Lunar Dust and Dusty Plasmas: Recent Developments, Advances, and Unsolved Problems, Planetary and Space Science 156 (2018), 71-84). Furthermore, the mechanism of an appearance of lunar dust detected by the Chang'e 3 Lander has been discussed in A. P. Golub' and S. I. Popel, On the Fluxes of Dust Particles Detected near the Lunar Surface by the Chang'e 3 Lander, Solar System Research 55, No. 5 (2021), 389-397. It differes from the mechanism considered in the author's paper. The authors have to discuss the importance of dusty plasma effects and the effects described in the above paper published in Solar System Research from the viewpoint of their results.

I would like to review a revised version of the paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors, Thank you for this very interesting paper. I have a few questions/comments/suggestions to improve my understanding (and the readers' one): 

1/ r1 radius determination is interesting, r1 definition is clear into Fig.1 but page12 it is mentioned that r1 is derived from table2 whereas only r0 is included in table2. Could you explain how you've determined r1? by computation only or also with using images? What is the relative uncertainty?

2/Could you better described mu and sigma factors used in images analysis?

3/ To avoid any misunderstanding it would be worth to mention that the inclination angle is measured from the horizontal plane (and not normal plane)

4/ What did you consider as the grain size distribution? Does the value selected has a significant impact on the results (r0 and r1 computations)

5/ It would be highly valuable to add 2 more figures:

- one similar to Fig.5 showing the particles density (regarding the volume) around the lander at different times during landing operations OR the particles flux distribution for a given particle size (small) vs distance from the lander

- one describing the solid particles velocities distribution around the lander for example for the smallest ones

6/ Do you consider any impact of dust on the lander? or any particles rebounds toward the lander? If not, it could be useful to mention it as an assumption/limitation for the model? If I understand correctly your model doesn't predict any dust impact on the lander...do you have any confirmation of this through images from the previous missions?

7/  I am not sure to understand correctly what is said on page 13: Roberts model is taking into account erosion with ejecting dust particles towards lunar space...Could you detail a little bit more? Does it mean that some particles have an inclination angle larger than 4deg and probably impact the lower face of the lander??

8/ Your model is very interesting because it estimates the zone (radius) impacted by the landing. Do you per chance have an idea of the maximum zone (radius) where the dust ejected by the landing might relocate and by this process could impact the optical properties of the surface?

Thank you very much in advance for your explanations. I would like to thank you for this interesting article.

Author Response

Please see the attachment

Author Response File: Author Response.pdf