This is an excellent paper which illustrates development and testing of a melt probe that can be recovered. 

If the space allows, it might be good to provide more technical details such as structure of the cable (eg number of wires, redundant wires?, shield), what voltage was used to sent power down to the probe (some kind of an electrical block diagram would be useful), how the tensioning mechanism worked, which parts of the probe were flooded, which were dry, was the water sample analyzed in a lab to reveal something interesting?

General assessment:

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The manuscript provides an interesting and well-done summary about a the novel melting probe concept (RECAS) developed by the authors and its field test results in 2022 in Antarctica.

General Comments:

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The devices of others are "probes" but your device is a "sonde". What is the difference that justifies another name?

On page 5, in the discussion of later extraterrestrial deployments, the authors should state that the current dimensions, mass, and power consumption may be problematic and miniaturisation may be an issue … and, well, the diesel generator will not work :)

The English is understandable but could be improved.

Technical Comments:

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Page 2: "Russian team" => "a Russian team", "UK team" => "a UK team". (Dozens of "a"s and "the"s are missing in the manuscript, but they will hopefully be inserted during the generation of the proof.)

Page 3: The Philberth-type probe was proposed in "(1976)"? It reached 1005 m in 1968? So it was proposed before 1968 and maybe the original paper, in which it was proposed, should be cited instead.

Page 3, "move in the borehole using inner cable recoiling mechanism on the same way as a spider climbs on the silk line": Well, I'm not an arachnologist, but I'm quite sure that spiders do not have such a device :) So it may be better to write "move in the borehole using an inner cable recoiling mechanism similar to a spider climbing on the silk line"

Page 3: The changes between "the team", "we", "research personnel", "ourselves" is a bit confusing. Are they different people? Could be harmonised.

Page 3, line 85: "send" => "sent"

Page 4, "Even the site demonstrates cold-based condition …": I don't understand this sentence.

Page 4: When the test hole was started on January 18, why was the field test 2021–2022?

Page 5, "… can be back in safely and reliable manner": Better: "can be returned to the surface in a safe and reliable manner."

Review Aspects:

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Does the paper address relevant scientific questions within the scope of TC? yes

Does the paper present novel concepts, ideas, tools, or data?

Are substantial conclusions reached? yes

Are the scientific methods and assumptions valid and clearly outlined? yes

Are the results sufficient to support the interpretations and conclusions? yes

Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? not with this paper alone, but probably with given references

Do the authors give proper credit to related work and clearly indicate their own new/original contribution? yes

Does the title clearly reflect the contents of the paper? yes

Does the abstract provide a concise and complete summary? yes

Is the overall presentation well structured and clear? yes

Is the language fluent and precise? yes, enough, but could be improved 

Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? N/A

Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? no

Are the number and quality of references appropriate? yes

Is the amount and quality of supplementary material appropriate? N/A

Summary

This paper is a good general summary of the progress made of a novel sonde instrument, its current capabilities and recent successes in field testing. It is great to see progress being made in this direction with due consideration of the unique aspects of subglacial lake access.

Page 2

The methods section is a little confusing as it is largely written in the past tense following an idealised deployment.

Maybe a more detailed and more heavily annotated diagram of the deployment and recovery process could replace much of the more prosaic descriptions of the deployment? Personally I would like to see a diagram of the instrument itself, similar to that found in the associated paper on electrical

Page 3

Line 69: Paragraph above this point should be in the introduction

Line 72: What mechanism is actually used, is it anything like a spider climbing?

Line 76: How closely to deployment was sterilisation carried out? Was there any sampling of sonde surfaces before and after deployment to verify cleanliness? Any background measurements of the camp/snow to help identify potential sources of contamination?

Line 82: Was the system left entirely unsupervised? What was the reasoning behind this? Was there remote real time monitoring available? Is there redundancy in the system to manage problems if they occur i.e. power downs?

Line 85: Where is 'mainland'? Jilin or still in Antarctica?

Line 86: What sort of control does this allow? Real time access or a subset of data transmitted periodically?

Line 87: Be more explicit that a subglacial lake wasn’t actually entered during this test. Or am I wrong and you did actually enter a lake at 200m?!

Line 88:Was this data internally logged and/or returned to the surface? What proportion of data collected was returned to the surface?

Line 91: Some detail of how the spooling works might be nice here, if not covered earlier in the paper

Page 4

Line 106: Some examples of the preparations that are specific to this instrument would be interesting here

Line 110: How was the base of the ice stream recognised by the sonde?

Line 111: Was the sampling system triggered automatically or manually?

Line 113: How does the lay up of the cable on the spool work? How is it monitored? Is the top of the sonde identical to the bottom? Does the cable penetration through the heated tip have any effect on melting on recovery to the surface?

Line 116: Any knowledge of the temperature profile through the ice column? Can a temperature profile be recovered from the probes’ measurements?

Page 5

Line 134: I know this is for future work, but I would be interested to know if there are plans to protect the hose and instrument cable from tangling together whilst hot water reaming 2400m+ borehole.