Thermal Simulations of Drilling of Cryogenic Lunar Soils Containing Water Ice

Round 1

Reviewer 1 Report

Dear Authors,

your paper is very interesting and offers useful results in the context of space missions like ExoMars or PROSPECTing the Moon.

The methodology used is very appropriate.

I have only minor points.

- I would like to read further details, for example if the Authors used a commercial software as weel as the number of particles used in these simulations. How much does the number of particles affect the result?

- The initial temperature profile for the soil is costant: a temperature profile as function of depth could be used.

- Did you test other rotational speed?

- Include references in the table of parameters (Tab.2)

- I suggest to reduce the number of figures (for example merging Fig. 5 to 7).

Best regards,

Michelangelo Formisano

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

There are different types of lunar regolith simulant for different purpose. Please specify the composition and morphology, porosity of soil used in the experiment. 

The measured thermal conductivity might not be representative to lunar regolith: The thermal conductivity of Apollo soil sample was in the range of 0.001 - 0.0035 W/mK, which is 3 orders of magnitude lower than the value reported in this paper. 

How do they come up with the particle thermal conductivity is not clearly specified. This makes me worry that the "accurate" results claimed in figure 7 were created by parameter tuning. I would suggest the author provide more detailed information, instead of just provide citation.  

section 5.1: I am interested to learn how did they measure the thermal conductivity of lunar soils with the water-ice contents of 3 - 5% with 3 decimal point accuracy. Again, the calibrated thermal conductivities in vacuum are suspicious. 

No testing data was provide for the drilling in vacuum. 

Section 6 conclusion

It's not very clear to me what is "reasonable" drilling procedure. 

Neglecting phase transition of ice (sublimation) is a bold statement and is questionable. As ice turns into vapor, gas phase might diffuse through the pores between the soil particles, which might heat up other soil particles more effectively. In other word, ETC value can be very high when phase transition happens. 

Missing some important references:

Metzger P. Zacny K. and Morrison P. "Thermal Extraction of Volatiles from Lunar and Asteroid Regolith in Axisymmetric Crank-Nicolson Modeling" DOI:10.1061/(ASCE)AS.1943-5525.0001165.

line 20: ice sublimation to "vapor", not water

line 183 - 186: The sentence is confusing. Please check the grammar. 

line 382: (typo) the temperature of lunar soil in vacuum reached -130

line 383: (typo) reached the temperature of -120

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thanks for the author's response. They addressed my comments very well.