Error-Constrained Fixed-Time Synchronized Trajectory Tracking Control for Unmanned Airships with Disturbances

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Considering what the authors proposed, it is an interesting idea, however, the following points should be clarified:

1. In section 3, the authors must define $CV,BRF,CG$
2. In section 4, the authors address that $p^*$ and $g^*$ are same as $p$ and $g$ these are not shown in lemma 3.
3. I consider that the authors should show more clearly the mathematical developments for a better understanding of the work.
4. In the simulation section, it would be good to present the BS control signal and compare it with the FTSS one, since it is not possible to see a great advantage of what is proposed against the BS.
5. The controller should be checked to see how it works considering that noise is present.
6. The literature review misses one important types of robust controllers that are being recently used in unmanned aircraft, see for instance: Modeling and Passivity-Based Control for a convertible fixed-wing VTOL, Applied Mathematics and Computation, 2024. Robust cascade observer for a disturbance unmanned aerial vehicle carrying a load under multiple time-varying delays and uncertainties, 2024. Real-time robust tracking control for a quadrotor using monocular vision, 2023.
7. The authors should add units to the y-axis in each figure presented.
8. The authors should explain how the values in table 1 were assigned.
9. English language needs polishing. The English grammar and style preferred in the presentation should be enhanced.
10. In the abstract, it should be better to give results.
11. In the introduction section, authors tried to enumerate previous works without having connections between different references.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper proposes a fixed-time synchronized trajectory tracking control scheme for unmanned airships operating under time-varying error constraints and unknown disturbances. To further refine the work and enhance its clarity and impact, consider the following suggestions:

1. Can the authors clearly state in the introduction part what gap in existing literature this work is addressing?
2. Why are only three models considered in the comparison? Have the authors evaluated other recent work in this domain?
3. A few references are quite old. Did the authors consider adding new relevant work references to support relevance?
4. After line 122, the authors should include a flowchart or another graphical representation to clearly illustrate the innovations and their contributions, which would help readers better understand the work.
5. What is the main advantage of using a fixed-time controller over a finite-time controller for airship trajectory tracking?
6. The authors need to explain the results presented in Figures 11-12 in the manuscript.
7. The control inputs in Figures 11–12 show torque magnitudes up to 10⁵ N·m. How is actuator saturation handled in the proposed controller? The current design uses continuous NNS functions, which may generate large control inputs during saturation.
8. The paper contrasts its fixed-time scheme with finite-time methods but does not directly compare it to existing finite-time results. The authors need to explain it.
9. The BS controller serves as a baseline in Figures 7–10. Were other advanced controllers (e.g., sliding mode, MPC) considered for comparison? If not, why?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The submitted manuscript proposes an error-constrained fixed-time synchronized trajectory tracking control approach for unmanned airships with disturbances. The proposed control strategy is analytically verified with simulations. The novel contributions of the manuscript are clear.

 

The introduction properly gives the background of the work and shows the motivation to take the research. I suggest that the authors avoid citing a big group of references (like in line 31 or 73) and instead – add some more information so that each of the reference is commented.  Such groups of references does not bring much to the reader without any in-depth analysis.

 

In order to verify the proposed approach the authors have performed some simulations. Although simulation-based verification is often applied in many domains, it is still a limited “amount” of data to be analyzed. It is recommended to include some other verification methods, e.g. the ones that are more formal. Using the model checking technique could bring some more valuable (reliable) results, especially when adding some verification of safety properties.

 

It should be make sure that all shortcuts are explained when used for the first time in the main body of the paper (not only in the abstract), as e.g. FTSDO (appearing in line 133 without explanation, looking back in the text does not indicate what it is, the description can be found in the abstract).

 

The list of references is sufficient, however it seems that most of them are Chinese-related. I would suggest to add couple of valuable references from other parts of the world in order not to make the choice of papers biased.

Comments on the Quality of English Language

English style should be revised. For example,  the authors should avoid starting a sentence with “The paper []” (line 92) or “reference []” (line 88).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have professionally addressed the Reviewer's comments. The revised manuscript may be accepted in its current form.

Reviewer 3 Report

Comments and Suggestions for Authors

I appreciate the efforts of the authors to improve paper’s quality. I have no other comments.