Design of a Mars Ascent Vehicle Using HyImpulse’s Hybrid Propulsion

Round 1

Reviewer 1 Report

The paper constructs the basic structure of a hybrid electric vehicle and evaluates the structural integrity of the hybrid electric vehicle in a variety of complex environments. This work is interesting. However, the paper as a whole is more like a simulation report rather than an academic paper, and the relevant research lacks sufficient academic innovation. In addition, the article has the following flaws:

1)       The necessity of this work is not explained in detail in the introduction, especially the challenge to the mechanical integrity of the aircraft in the complex environment. It is suggested to merge the literature review with the introduction, which is meaningless from the reader's point of view.

2)       In "2 sizing", the specific MAV structure design method is not given, especially how the results of Table 3 are obtained, it is recommended to add.

3)       The description of the model-building process in "Structural Analysis" is not necessary, especially the discussion of its basic concepts, such as: “A "hard contact" behavior prevented penetration, while a rough tangential behavior prevented sliding.”

4)       For the analysis of grid independence, it was obvious that Von Mises Stress did not converge completely when the number of grids exceeded 60,000, and the displacement showed a linear decline when the number of grids exceeded 60,000, so it could be considered that the 60,000 grid had sufficient precision.

Then there are the details:

1)       Are Table 1 and Table 2 also obtained from the past literature, it is suggested to supplement the literature reference.

2)       In “4.2 materials”, "Commonly considered materials include aluminum alloys, titanium, and sometimes composites." is unnecessary and confusing and is recommended to be deleted.

Author Response

The innovation is to propose a low cost/low risk MAV design based on innovative hybrid propulsion which offers performance similar to a bipropellant MAV solution at a fraction of the complexity and cost.

For the flaws outlined:

1) The Literature review and the Introduction have been merged, and a requirement table has been added to help the reader understand the challenges associated with the design.

2) A more more detailled description of how Table 3 (now Table 4 in the revised document) have been added to document.

3) The editor asked for a more detailed description of the model to ensure reproductability of the analysis. The sentence: "A "hard contact" behavior prevented penetration, while a rough tangential behavior prevented sliding." has been removed.

4) The paragraph has been corrected to: "Given this, a mesh consisting of 60,000 elements has been selected to ensure an adequate level of precision".

5) Table 1 (Table 2 in the revised document) is obtained from the literature (reference [10] added in the text). Table 2 (now Table 3 in the revised document) contains values set by the authors for the design.

6) The sentence has been removed to avoid confusion.

Reviewer 2 Report

1.  Literature Review should be included in introduction.

2. N2O4 is toxic, why the author choose this as oxidizer?

3. NASA’s solid MAV concept was mature, improved propellant storability is not true since solid propellant is most convinient.

4. This paper is more like a technical report than an academic paper. There is not much academic innovation.

Author Response

1. The Introduction and Literature Review sections have now been merged into a single section.

2. The choice to use Mixed Oxides of Nitrogen (MON), which contains N2O4, is justified in section 1.3 (in the revised document) due to its low freezing point.

3. The storability of the solid propellant used by NASA is challenged by the temperature conditions on Mars. As stated in the paper, a nominal temperature of -40°C is expected at the launch site, and a heavy and complex heating system is required to maintain the solid propellant at a temperature that won't compromise its integrity. MON has a lower freezing point and does not require such a heating system to be operational.

4. The innovation is to propose a low cost/low risk MAV design based on innovative hybrid propulsion which offers performance similar to a bipropellant MAV solution at a fraction of the complexity and cost.

Reviewer 3 Report

See attached pdf file

Comments for author File: Comments.pdf

See attached pdf file

Author Response

English Edits:

The english edits you mentioned were all corrected, except the use of reference 6 and 7. These two references must be kept because they contaign specific data on each of NASA's Mars Ascent Vehicle early proposition. Some of the values helped redact the comparison between the three propulsion types.

Technical Issues

1. Sentence has been modified to: "Key challenges include the MAV's ability to endure the 15 G loads during the SRL's EDL [4] and avoid a resonance of the structure below 24 Hz."
2. The authors have made a deliberate design choice by selecting a value of 2.5 for the L/D ratio of the combustion chambers.  To avoid confusion the sentence has been modified to: "To fulfill height restrictions, the choice was made to design the combustion chamber to achieve an L/D ratio of 2.5."

Content Issue:

A "conclusion" section was added where a deeper focus is made on future work needed to continue the project.

Reviewer 4 Report

This paper focuses on the preliminary design and structural analysis of a two-stage Hybrid Mars Ascent Vehicle (MAV) for the Mars Sample Return Mission. The scientific significance of the study is somewhat reduced by the authors' use of commercial software. However, considering that the design optimization problem was solved, this is acceptable. There is no doubt that the topic is appropriate for the Aerospace journal.  The paper can be accepted after minor revisions.

My suggestions:

1. Line 50 "...MAV must withstand drastic temperature drops and launch at an operational temperature of -40°C." The authors refer to low operating temperatures, but do not specify the temperature at which the structural analysis was performed. To what temperature do the properties in Tables 4 and 5 correspond?

2. Line 223. There is no need for reference [16], since its authors just give the well-known Barlow's formula (see P. Barlow "A treatise on the strength of materials", 1867);

3. CFRP have directional strength properties. Successful design optimization depends, among other things, on the orientation of the fibers. Has this been taken into account? Please comment.

4. Please add units (mm?) to the "Thickness" column of Table A1.

Author Response

1. Table 4 and 5 (which are respectively Table 5 and 6 in the revised document), gather mechanical values at nominal atmospheric temperature of +20°C. The simulation does not take into account the influence of the temperature. This a relevant concern wich has been included in the conclusion has a future work.
2. Reference removed
3. Only one orientation of the fibers has been tested; they were oriented to provide the best rigidity to the static landing load of 15G. The influence of fiber orientations was overlooked and must be addressed in a more detailed structural analysis. This concern is included in the future work section.
4. Corrected

Round 2

Reviewer 1 Report

It is worth acknowledging that the application of hybrid rocket engines on ascending spacecraft on Mars is a good idea. However, the specific research conducted in this article is deemed meaningless. Its main issues can be summarized as follows:

1）Lack of innovation in research content. The article's review mainly focuses on the challenges faced by Mars spacecraft but does not present an innovative approach to addressing these issues. Simply stating the use of innovative hybrid propulsion methods is insufficient and does not reflect the author's contribution.

2）Model accuracy needs improvement. As seen in Figure 8, Von Mises stress does not fully converge when the number of grids exceeds 60,000. The simulation accuracy with 60,000 grids is far from sufficient for this model.

3）Insufficient innovation in design methods. In the description in Section 3, it is not clear how this article innovates compared to previous work in design methods.

4）Lack of consistency between analysis and conclusions. The primary analysis in this article focuses on stress, displacement, and resonance frequency research, but the conclusions fail to reflect the role and value of the relevant analysis. Additionally, the main conclusion of the article, "Compared to NASA's Two-stage Solid rocket, this European MAV shows great engine performance and low Gross Lift-off Mass," is not elaborated upon in the analysis.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Accept

Author Response

No further comments