Feasibility Study of Low Mass and Low Energy Consumption Drilling Devices for Future Space (Mining Surveying) Missions

Round 1

Reviewer 1 Report

This article deals with the possibilities of extrapolating mining processes to the special conditions of space conquest missions.  In this sense, among the first operations performed are the drilling of some extraterrestrial geological formations. For this, drilling methods require drilling equipment with low mass and low energy consumption. Also, these techniques are recommended on Earth in the conditions in which we face serious ecological imbalances, generated mainly due to the very high energy consumption. The article presents a well-documented synthesis of the main disadvantages of current energy sources used around the globe, compared to new feasible solutions for the energy future of mankind and, in particular, for the exploration of outer space. These space drilling systems are very important in the evaluation of space deposits, which is why these systems and autonomous means of operating drilling devices are documented and detailed, which must be adapted to very difficult extraterrestrial operating conditions. Taking into account all these aspects, the authors propose a drilliability test stand, for analyzing the feasibility of low-energy drilling with the use of small values of rotational speed and weigth on bit tool. On this stand, a series of drilling tests were performed on eleven samples made of various materials / rocks. The results obtained from the tests were analyzed from a scientific point of view, of the technical performances and of the energetic consumption. These tests showed that hard rocks can be drilled with a power consumption at less than 100 W, feasibly for extraterrestrial space. Following the analysis of the article, we found that it is well documented and written, the research presented is future, and the results are interesting, and deserve to be disseminated through publication.

Note: For the whole article, it is recommended that instead of 6 [MPA] or 24 [V], etc., be written 6 MPA or 24 V, etc.

Comments for author File: Comments.pdf

Author Response

Thank you for your comments and positive review. I have made the changes as suggested. I attached corrected manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

1) Minor English change examples: 

(Line) (problem) = (correction)

18  construing = constructing
22 on economically = at an economically
37 phenomenon = complex system 
59 than it was = than they were
43 paragraph is an observation - please provide references
256 gramma - thanks to, ??? missing end of phrase
267 he does not = they do not
310 remove but
316 this = these
354-55 Mars, 100 = Mars with up to 100
446 better = more

2) Introduction has too much irrelevant content. I would suggest removing lines 43-152. Energy/climate change overview is not appropriate for justification for this experiment

3) Poor experimental design. A new bit should have been used for each sample. A worn bit caused failure during one sample (line 450) - this is probably not representative of the hardness of the rock, but of wear. This puts doubt on all results due to the unknown and unmeasurable amount of wear on the bit for each sample.

Author Response

Manuscript with changes attached.

Ad. 1 Minor English change examples: 

Answer: Thank you for your comments and proofreading. I entered all the remarks.

 

Ad. 2 Introduction has too much irrelevant content. I would suggest removing lines 43-152. Energy/climate change overview is not appropriate for justification for this experiment

Answer:

I agree with the reviewer that the primary motivation behind the test is to see if it is possible to drill into the rocks with low power and torque drill modules. However, research always serves a purpose. Usually it is an increase in knowledge or a solution to a specific problem important for people or industry.

When we became interested in the subject of space drilling, scientific demand was dominant, and economic issues were an additional justification and a topic of a more future. Advances in the space industry changed that. Today, more and more governments, companies and institutions are interested in exploring space for resources.

The advancing climate crisis forces the search for new energy resources in space, which will require verification of deposits (detected by reconnaissance satellites) with the use of drilling methods. The themes of climate protection, space mining and space drilling are starting to become closely related.

I myself recently experienced the effects of extreme weather events, when last Thursday I could not go home for about 3 hours because there were no free taxis. Extreme rainfall lasting only one day flooded the viaducts, interrupted communication routes in my city, and the inhabitants of one of the districts in my city experienced flood.

The problem becomes serious and affects millions of ordinary people. Big investments in renewable energy sources are to be expected. Renewable energy is brilliant, it is a fantastic business and without a doubt the future of energy. However, it also has its limitations. Governments will be forced to look for alternative ecological energy resources (also in space) that will complement renewable energy and stabilize the entire energy system. The future is the diversification of green energy sources. It cannot be done without mastering the methods of drilling and mining in space.

That is why I think that the presentation of the climate context and energy problems makes this article more attractive. I would ask the reviewer to agree to my request and leave this fragment of the text.

There is also one additional problem. I already have one review. I do not know if the change in the introduction will not cause this reviewer's protest. Therefore, the more I will be grateful to the reviewer for agreeing to my request.

 

Ad.3 Poor experimental design. A new bit should have been used for each sample. A worn bit caused failure during one sample (line 450) - this is probably not representative of the hardness of the rock, but of wear. This puts doubt on all results due to the unknown and unmeasurable amount of wear on the bit for each sample.

Answer:

We agree that it is possible to build an even more precise measuring station and obtain more accurate measurement results. We have these results, and we will present them in future articles in Energies. However, they relate to testing the drill module we designed and the measurements had a different purpose than the one presented in the peer-reviewed article.

Our main goal of the tests presented in this peer-reviewed article was to find out if low power, WOB, torque drilling is possible and to analyze this process in terms of the design of future improved versions of drilling modules for space missions.

If we observed that the rock is being mined, it was a proof for us that with such parameters (WOB, torque) we can start drilling the rock and we recorded how the process is proceeding, what is the power consumed, what are the problems, after what time we will observe the impact of the shortage cleaning the hole.

We do not claim that the obtained numerical results are optimal, but we believe that they can be an excellent reference for other research teams. We would be very disappointed if the other teams (testing their designed drill bits) obtained worse or similar results. This would mean that they did not make any optimization of drilling parameters, construction of drilling tools and rock cutting elements.

I agree with the reviewer that using separate drill bits for each rock would be better and produce more reliable results. However, despite the progressive wear of the cutting elements, we obtained the effect of drilling even hard rocks, which further confirms that it is possible to build effective drilling modules for space missions. During a space mission, there will be no comfortable working conditions for these type of devices and there will be many unknown factors accelerating the wear of the tools, which will have to work sequentially in different formations. We believe that not changing the drill bit for subsequent rock samples may be an advantage in our testing and results, although this was not the intended action.

It is also not always possible to use new core bits for subsequent rock samples. During the tests presented in the article, this was possible because the test laces were relatively cheap. We could no longer afford it in later tests, when we tested the drill module we designed, which cost between 15,000 and 30,000 euros. The budget we had at that time was around 200,000 euros. The cutting elements were permanently soldered. Due to the minimization of energy consumption, we had to strive to minimize the thickness of the drilled ring (kerf) and the wall thickness of the tool was small. Creating a reliable design with an easily replaceable tip containing blades was an engineering challenge and we abandoned it. In practice, a colleague conducting the tests watched under a stereoscopic microscope how the cutting elements of our tool were wearing and, if necessary, he sharpened the cutting elements ensuring the appropriate angles of the blade attack. However, we did not perform such a precise procedure in the tests presented in the article, because the purpose of the measurements was completely different and we wanted the tool to gradually blunt and see how it affects the mining of subsequent rocks.

When it comes to testing tool wear (blade height, diamond grain height), their accurate performance is always troublesome, even if you have precise measuring equipment, but it is possible. During the conducted tests, we conducted a more qualitative assessment of tool wear using visual methods, and this was dictated by the main purpose of the tests: whether the drilling process is happening, how it is going. I agree with the reviewer that such measurements would further improve the quality of work.

In poor literature on this subject (space drilling), I have not found a similar article in which similar rock drilling tests would be performed and discussed. There are articles that test prototypes of drilling modules for future space missions, but I haven't seen similar tests that are fundamental. There are many articles presenting the results of drilling tests for various rock samples, but these are mainly articles for the drilling industry and do not take into account the specific needs of space missions. This is the reason why we believe our results will be of interest to other teams developing drilling devices for future space missions, despite the test imperfections mentioned by the reviewer. It should be noted that still most of the teams working on the subject of space drilling focus mainly on the issues of control engineering and robotics, not taking into account that the process of drilling even a shallow several-meter borehole can be a big challenge and the issues of drilling technology should be well recognized. These teams still assume (just like our partners in the past) that reducing weight, torque, WOB, power consumption is only an extension of the drilling process time, and the drilling process is as simple as drilling in a room wall.

The reviewer's remarks are important and, in my opinion, it is worth mentioning them in the text. I would like to ask if the additional text below at the end of the conclusion would satisfy the reviewer ?

“In future tests, tool wear should be analyzed in more detail during subsequent tests. If possible, separate drilling tools should be used for each successive test rock sample to eliminate the influence of tool wear in previous tests on the measurement result. "

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I accept author's changes and recommendations