Impact Time Control Cooperative Guidance Law Design Based on Modified Proportional Navigation

Round 1

Reviewer 1 Report

The authors proposed a minor modification to the existing body of literature. While the proposed developments are interesting, I doubt the extent of novelty proposed in this manuscript. Therefore, I suggest to add more quantitative and qualitative analysis, more explanations and better framing of the problem, including stating all the underlaying assumptions, providing all the necessary mathematical proofs and citations to original works.

- There has been a wide pool of research papers written on the topic of (cooperative) impact time control guidance and time-to-go estimation (many specifically devoted for PN guidance law). Therefore, the authors should unambiguously explain their relevant contributions relative to the existing literature as well as include all relevant sources. Several pioneering and impactful works are missing.
- The authors should briefly discuss how their proposed method compares to other cooperative strategies such as cooperative impact angle guidance
- In the introduction section, the following claim is made: "During the flight, there is no communication between the aircraft." This sentence appears without any context. Is this an assumption utilised in the paper? In general, this is obviously not true.
- Assumption 1, "range are short during the terminal phase" is very ambiguous. The authors should quantify.
- Assumption 2: "The missile is considered as an ideal point-mass model, which means the acceleration of the missile is the same with the acceleration command." This is conceptually wrong. I don't see why "the acceleration of the missile is the same with the acceleration command" due to the assumption that "The missile is considered as an ideal point-mass model"? 
- Assumption 3: "The target is stationary. If the target moves with a low speed and its speed can be ignorable compared with the missile velocity, the target is assumed to be 138 stationary." There are contraindicatory claims in this assumption. The first part claims that the target is "stationary", while the second part relaxes it. I would reformulate the whole assumption, focusing on targets with zero or very small speed when compared to the missile speed.
- Some derivations presented in section 3.1 are known derivations present in earlier publications. The authors should acknowledge the original source/authors.
- Not all the underlaying assumptions are listed for the steps performed in section 3.1 and 3.2
- Section 4.1, the authors should compare their time-to-go estimation method with other, state-of-the art estimation methods. Also, a plot depicting the actual estimation error would be more appropriate.
- Section 4.2 and 4.3, why are the initial flight-path angles different for the salvo and cooperative attacks? How do different initial conditions constitute a fair comparison?
- The acceleration histories are fairly aggressive, one would wonder what are the practical implications/potential of the proposed method.
- Conclusions are vague, for instance: "A more accurate method of time-to-go estimation of proportional navigation guidance law is first proposed..." a more accurate method than what? Point 2) is more like a listing of what has been done, rather than a "conclusion" point of what has been discovered, what is the striking novelty, etc.
- Finally, i believe that the naming choice "two-layer cooperative guidance architecture" is not the most appropriate. Normally, in the missile guidance community, the word cooperative is reserved for designating a cooperating among several entities (e.g., among missiles, among missile(s) and aircraft, etc.). A "cooperation" which occurs in a single missile at an algorithmic level, the word "integrated" is often used, e.g., an integrated design of the guidance law and the missile autopilot.

Minor comments:
- some acronyms in the abstract are not defined
- some lines in Fig.5 and 7,8  have the same line coding (two dashed lines), while having very similar color coding (black vs. blue). This might turn out ambiguous when printed in b/w 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The proposed manuscript deals with a topic of interest to the Aerospace journal. Writing is clear, as well as included graphics. With respect to content, Authors report their solution to the proportional navigation intercept problems, correctly offering [likewise eqs.17-18, nd later in section 4] a comparison with existing literature. Above all, it i appreciated their motivated interest to multiple agents' guidance. Significant simulations, with relevant plots, confirm the validity of the proposed ideas. Overall, the paper is deemed as correctly built, and this reviewer fully shares the three items in the conclusions, deemed all of them as duly proofed in the body of the paper. Some minimal corrections to be applied in the final draft:

line 87: there is no communication between the aircarft AND ?

line 103: this reviewer does not understand the meaning of the words "As for the flowers...", please clarify [I think is "followers", to be also corrected in line 105.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have improved their manuscript compared to the original submission.