Model and Optimization of the Tether for a Segmented Space Elevator
Round 1
Reviewer 1 Report
This paper considers the problem of optimal staging of a space elevator defined by the use of bundled cables as an alternative to continuous shape optimization. The premise of the paper is intriguing and somewhat convincing. The authors incorporate elongation into the model of the optimization problem, which is also a nice addition. As with other papers by these authors, however, the problem formulation and solution are not well-explained. I could follow a bit of the material on pages 5-6, which defines a number of equations. However, it is not clear how the authors are proposing to solve these equations. As for the formulation of the optimization problem, I was unable to understand even the most basic elements of the problem. What are the: objective function, variables, and constraints? The authors would be well-served by describing their approach in such a way as to be reproducible.
Notes:
\begin{itemize}
\item I think Single crystal graphene has replace CNT as the tether material of choice.
\item Spelling: liberation-libration, spacial-spatial
\item p8 - Complex method? What is this? Reference?
\item p8 - "for example" - example of what?
\item p10 - Table 4-6 -> Tables 4-6
\item I assume stress is being minimized in the optimization problem. Is total mass fixed? The optimization problem is not well-defined.
\item In Table 6, if my previous note is correct, please also include the stress for a continuous optimal shape for uniform stress using the same total mass, or some other equivalent comparison point.
\end{itemize}
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The work is interesting. The following are the suggestions.
- Add the objective of the work in the introduction section.
- There is a need to update the literature with some more recent articles.
- Check all equations and symbols. Some are undefined.
- Put a space between words and citations (for instance; nanotubes[2]).
- Put punctuation marks where necessary, especially at the end of the equation.
- Discussion of the results needs to be added in details.
- Conclusion section should be rewritten by adding the major finding, advantages and future scope of the work.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors,
here are my suggestions:
- Line 69 - It is usually suggested to insert a reference or calculation when precise numbers are presented.
- Line 79-80-81: I think you miss a sentence or a sentence connector: you say that the carbon nanotubes have a shortage even if they are the best choice and used in construction. Instead of the "Therefore" in line 81, I suggest you put a "However" or rephrase. Regardless the shortage, you still use this material in your design because its performances are the best.
- Line 182-183-184: The statement slightly clashes with the one in line93-94-95-96. You said that it is possible to set a specific position for your connection platforms - however, you have an optimization routine to effectively position them in strategic spots that decrease the tensile stress on the tethers. Therefore, can you explain how you would impose specific locations in your optimization algorithm? If it is already there or not?
- Line 209 - it would be nice to have a reference on the "complex method" of optimization or have the full optimization set equation explicit for the reader to easily replicate your results.
- Line 223-224-225: Did you choose these values by iteration or by literature. To ease the reader, you should specify where you get your numbers from.
As general comments:
Your mathematical model (section 3) seems sound. However, it would be nice to have validation with real tethered cases.
The paper is overall well written and the topic is of interest.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
This paper models and optimizes a segmented space elevator. The results are compared with traditional constant section and gradual section space elevators and show the superior performance of the proposed segmented space elevator. The method is mathematically sound. However, there are multiple issues that need to be addressed before accepting for publication:
Major issues:
- Distance units in Tables 3 and 4 are not correct. These values are way larger than the distance from the Earth to the Moon (i.e., 4∗105 km).
- In Table 4, the position of segment points shows a strong pattern. For example, the position of the last segment point, when the number of segments is larger than 2, is always the same. The reason is not explained. In this section, 3 tables and 1 figure are provided, and the result analysis is only 4 lines (one short paragraph). More analysis and interpretations of the results are necessary.
- pp. 13, Figures 12,13,14: legends in these figures (i.e., UAR, GAR, SAR) are not explained anywhere in the paper. It is very hard for readers to interpret the results right away.
Minor issues:
- pp. 1, line 1, constant section/equal section/UAR in Figures 12/13/14. The same type of space elevator design has multiple different names in the paper.
- pp. 12, line 267: "quality" -> "quantity"?
- pp. 12, line 278: typo, "president’s"?
- pp. 12, line 280: "not obvious", it's better to use exact values in a technical paper, especially the results are shown in the figure and values are known.
- pp. 15, line 326-330: too many sentence segments, try to revise to more short sentences.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have made several updates to the paper which seem to have made an improvement. However, several of my previous questions remain unresolved. Specifically, those raised in the summary:
Previous review: "As with other papers by these authors, however, the problem formulation and solution are not well-explained. I could follow a bit of the material on pages 5-6, which defines a number of equations. However, it is not clear how the authors are proposing to solve these equations. As for the formulation of the optimization problem, I was unable to understand even the most basic elements of the problem. What are the: objective function, variables, and constraints? The authors would be well-served by describing their approach in such a way as to be reproducible."
Perhaps the authors missed the summary? In any case, what I'm looking for is a clear MATHEMATICAL formulation of the optimization problem which includes objective function, constraints, and variables.
It would also be helpful if the authors, in their response, could point to particular lines in the text which address the questions raised.
In addition, thanks for the reference to the Complex method. This is the first time I have seen it. Is there a software implementation somewhere?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
I think that this revised version is completely suitable for publication in the journal: Aerospace. The authors have accepted all my requests and prepared this new version. Therefore, I will strongly recommend its publication without any new improvements.
Author Response
We sincerely thank the reviewer for thoroughly examining our manuscript and providing very helpful comments to guide our revision.
Round 3
Reviewer 1 Report
no further comments
