From Lab to Launchpad: A Modular Transport Incubator for Controlled Thermal and Power Conditions of Spaceflight Payloads

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is generally well written and understandable, but reads somewhat repetitive. I have a few comments, I belief are worth addressing before publication:

• Line 77: What is meant with “pre-launch diagnostics” in this context?
• Line 125: The authors state that “no internal damping system is required”. Why couldn’t the insulation be combined with damping? For instance a polymer foam?
• I have multiple questions regarding the temperature control:
  • On one hand it is stated that the PTC are self-regulating. On the other hand, later a PID-controller implemented in Arduino is described. I think this should be clarified.
  • What is the steady-state temperature of the PTCs? For my understanding, in the presented setup, the PTC effect avoids dangerous overheating conditions due to a malfunction of the PID-controller, but is not actually part of the control loop. Please clarify.
  • How can the temperature setpoint be changed? Is there an operation element for the user or does the software need modifications?
  • What is the temperature homogeneity within the box? Was this measured?
  • Was the Derivative-part set as well? Or was it actually a PI-controller?
  • From the presented data the statement on line 276, that the temperature is not overshooting and oscillating, is in my view an overstatement. The temperature does overshoot and also oscillate to a certain extend. The reason being that a rather high P-components was chosen.
  • I find the design, to let the temperature overshoot to more than 40°C, rather risky (line 283 and 609), as biological samples are typically very sensitive to heat. How is the user informed hat the samples are overheating and air should be vented?
  • In my view a mean deviation of 0.81°C from the setpoint is rather a lot for biological samples (line 379). I think this needs some justification why the authors think this is acceptable. I am also not fully convinced that choosing such a high P-component was the best option. To reach steady state, it still takes around 1 hour. Likely overshooting and oscillations could be reduced, if a tradeoff to a larger I-component (with anti-windup) would be allowed.
• The schematic of the electronic system is not very intuitive to read.
  • I suggest using official symbols instead of simple boxes, such for the FET or DC/DC-converter.
  • From the schematic, the function of the “DC-DC Step-Down” and the “Lab Power Supply” is not clear. I suggest indicating with two lines, which lead out of the box, that these two devices are used for payloads in the incubators.
  • The term “laboratory power supply” is used with two different meanings. On line 202 likely a power supply is meant that powers the incubator with 24VDC. Later on, on line 235, a internal power supply for experimental hardware is described. I suggest rephrasing to avoid confusion.
  • How can the output voltage of the “DC-DC Step-Down” and the “Lab Power Supply” be set? Are there any measures foreseen to avoid accidental change of the voltage output during operations in the field.
• For the field tests, where the wind conditions simulated in a test chamber or was this the (coincidental) outside condition when testing the hardware?
• Line 428: Is the voltage of the battery monitored and logged by the Arduino?
• Line 440 and following: Why does the voltage signal almost show a digital characteristic? Is this due to the high p-component in the PID?
• Simulation:
  • To me the simulation setup is not fully clear. Maybe a 3D schematic with the boundary conditions and idealizations indicated would help. I would assume that conduction through the insulation layer will dominate the system.
  • What software (and version) was used for the simulation.
  • Why was the bottom layer considered insulated? What if the box stands in soft snow?
• Line 520: How much of the 17.3 W baseline power consumption ends up as a heating baseline in the incubator?
• Paragraph starting at line 512 and paragraph starting at line 534 are identical. One can be removed.
• The number of the figures in is not consistent. Figure 2 appears twice but figure 4 is missing. Also Figure 8 mentioned on line 564 does not exist.

Author Response

Comment 1: The paper is generally well written and understandable, but reads somewhat repetitive. I have a few comments, I belief are worth addressing before publication:

Response 1: We sincerely thank the reviewer for the positive evaluation of the manuscript’s overall clarity.

Comment 2: Line 77: What is meant with “pre-launch diagnostics” in this context?

Response 2: Thank you very much for pointing this out. We realize that the wording “pre-launch diagnostics” may have been too vague and could be misleading. What we intended to express is the possibility to keep experimental hardware powered inside the transport incubator, so that technical and environmental status checks (such as temperature stability, battery charge, power supply to payload electronics, and sensor readouts) can be conducted by the operators shortly before launch. These are not biological diagnostics performed by the incubator itself.

To avoid ambiguity, we have revised the sentence accordingly.

The revised text now reads (Abstract, Line 76):

“Its robust design enables technical pre-launch checks of payload hardware and environmental conditions, environmental conditioning, and full mission readiness without depleting onboard resources.”

Comment 3: Line 125: The authors state that “no internal damping system is required”. Why couldn’t the insulation be combined with damping? For instance a polymer foam?

Response 3: We thank the reviewer for this valuable comment. The elastomeric insulation (Armaflex-AF) used in the incubator already provides a degree of passive vibration attenuation in the biologically relevant low-frequency range. Since payload handling during MAPHEUS recovery operations is performed carefully and without significant impact loading, this was sufficient to protect the hardware in our deployment scenarios, and a dedicated damping system was not required. We have clarified this aspect in Section 2 of the manuscript (Line 125). In addition, following the reviewer’s suggestion, we have now included in the Discussion (Line 700) a note that future versions could integrate polymer foam layers to further combine insulation with damping, particularly for long-distance or high-load transport scenarios.

The revised text in Section 2 (Line 125) now reads:

“Since external handling is performed with care and without significant impact loading, no dedicated internal damping system was required, as the closed-cell elastomeric insulation already provides sufficient passive vibration attenuation. Minor mechanical stresses and transport-induced vibrations – such as those encountered during helicopter or ground vehicle transport – are thereby adequately damped.”

The revised text in the Discussion (Line 700) now reads:

“In scenarios involving stronger mechanical loading or pronounced lateral movement – such as during long-distance overland transport – custom-fitted internal mounting frames could be developed to provide experiment-specific mechanical stabilization. In addition, the integration of polymer foam layers could be considered for future versions to combine insulation with enhanced damping properties, thereby tailoring the incubator to more demanding transport profiles without compromising its modularity or biological compatibility.”

I have multiple questions regarding the temperature control:

Comment 4: On one hand it is stated that the PTC are self-regulating. On the other hand, later a PID-controller implemented in Arduino is described. I think this should be clarified.

Response 4: We thank the reviewer for pointing this out. We agree that our wording may have suggested a contradiction. In our design, PTC heaters provide a self-limiting, fail-safe behavior against dangerous overheating in case of control malfunctions; they are not part of the feedback control loop. Temperature regulation of the chamber is performed by the microcontroller using a

PID controller (D = 0). We have revised the text to clearly separate the PTC’s safety function from the active control loop.

The revised text in Line 299 now reads:

„It should be noted that the PTC elements themselves are not part of the feedback loop; their self-limiting characteristic provides an intrinsic safety margin in case of controller mal-function. The PID control algorithm (with the derivative term set to zero) dynamically modulates heating output to maintain the desired internal temperature, ensuring thermal regulation with only minor overshoot and weak oscillations, which result from the deliberately strong proportional action chosen to guarantee fast recovery in cold deployments, while avoiding conditions that could compromise the integrity of biological samples [7, 12, 13].“

Comment 5: What is the steady-state temperature of the PTCs? For my understanding, in the presented setup, the PTC effect avoids dangerous overheating conditions due to a malfunction of the PID-controller, but is not actually part of the control loop. Please clarify.

Response 5: We appreciate the reviewer’s question. In our configuration, the PTC elements are operated under forced convection and below their intrinsic plateau, because chamber temperature is governed by the PID controller. The PTC characteristic (steep resistance increase near the Curie region) is used as a safety boundary only. As the steady-state PTC surface temperature depends on airflow and load, we refrain from quoting a single value here and have clarified this in the manuscript.

The revised text in Section 2 (Line 154) now reads:

„ In our configuration, the PTC elements operate below their characteristic plateau region (typically around 100 °C to 120 °C, depending on airflow and load), as the chamber temperature is actively regulated by the microcontroller. Forced convection and a limited control target (near physiological temperatures) ensure that the PTCs remain well below their intrinsic self-limiting threshold, which acts as a passive safety feature in case of control failure. “

Comment 6: How can the temperature setpoint be changed? Is there an operation element for the user or does the software need modifications?

Response 6: Thank you for requesting this clarification. In the reported hardware version, the temperature setpoint is a firmware parameter that can be adjusted via a service menu during setup. We have added this information.

The revised text in Section 2 (Line 198) now reads:

„The temperature setpoint is configured via a protected service menu during setup, while chamber temperature is continuously displayed on the front panel.“

Comment 7: What is the temperature homogeneity within the box? Was this measured?

We agree that spatial homogeneity is relevant. In this study, we did not perform a full spatial temperature mapping. The design employs two circulation fans (54 m³/h each) to minimize gradients in the small chamber volume (46 L), and the two sensor paths are placed centrally for control and monitoring. We now explicitly state this and list spatial mapping as a limitation and item for future work.

Response 7: The revised text in Section 2 (Line 164) now reads:

„While a full spatial temperature mapping was not performed in this study, forced convection by two 54 m³/h fans is used to minimize gradients in the small chamber volume. “

The revised text in the Discussion (Line 707) now reads:

„Furthermore, a systematic mapping of spatial temperature homogeneity was beyond the scope of this work and will be addressed in future iterations.

These refinements would further expand the operational temperature range and enhance system stability under less favorable boundary conditions, reinforcing the incubator’s robustness for diverse mission profiles and transport environments.“

Comment 8: Was the Derivative-part set as well? Or was it actually a PI-controller?

Response 8: We thank the reviewer. We used a PI(D) controller (D = 0) to avoid noise amplification from fast sensor signals. This is now clearly stated in the Methods/Hardware section (Line 299).

Comment 9: From the presented data the statement on line 276, that the temperature is not overshooting and oscillating, is in my view an overstatement. The temperature does overshoot and also oscillate to a certain extend. The reason being that a rather high P-components was chosen.

Response 9: We appreciate this observation and agree that our original wording was overstated. We have revised the sentence to explicitly acknowledge the small overshoot and weak oscillation that result from the deliberately strong proportional action.

The revised text in Line 299 now reads:

„It should be noted that the PTC elements themselves are not part of the feedback loop; their self-limiting characteristic provides an intrinsic safety margin in case of controller mal-function. The PID control algorithm (with the derivative term set to zero) dynamically modulates heating output to maintain the desired internal temperature, ensuring thermal regulation with only minor overshoot and weak oscillations, which result from the deliberately strong proportional action chosen to guarantee fast recovery in cold deployments, while avoiding conditions that could compromise the integrity of biological samples [7, 12, 13].“

Comment 10: I find the design, to let the temperature overshoot to more than 40°C, rather risky (line 283 and 609), as biological samples are typically very sensitive to heat. How is the user informed hat the samples are overheating and air should be vented?

Response 10: We thank the reviewer for highlighting user awareness. The incubator provides continuous feedback of chamber temperature and heating activity on the front-panel display, which is monitored by operators during pre-launch handling. Importantly, the rapid warm-up phase that can show a transient overshoot is always conducted before biological payloads or experimental hardware are placed inside the incubator. Once the chamber has reached the target setpoint, payloads are inserted. In case of a transient overshoot during this warm-up, operators are instructed to briefly vent the chamber before loading heat-sensitive samples. In addition, the control unit features a dedicated warning lamp that clearly signals a fault condition if a strong deviation from the target temperature occurs during operation. We have clarified these operational procedures in Section 2 of the manuscript. Furthermore, we now note in the Discussion that a dedicated acoustic over-temperature alarm could be included in future versions to further support field operation with highly sensitive payloads.

The revised text in Section 2 (Line 199) now reads:

“During pre-launch handling, operators continuously monitor the front-panel temperature readout. Importantly, the rapid warm-up phase is conducted before biological payloads or experimental hardware are placed inside the incubator. In case of a transient overshoot during this phase, the chamber is briefly vented prior to loading heat-sensitive samples. In addition, the control unit features a dedicated warning lamp that clearly indicates a fault if a strong deviation from the setpoint occurs during operation.”

The revised text in Section 4 (Line 708) now reads:

„A dedicated acoustic over-temperature alarm could further support field operation with heat-sensitive payloads.“

Comment 11: In my view a mean deviation of 0.81°C from the setpoint is rather a lot for biological samples (line 379). I think this needs some justification why the authors think this is acceptable. I am also not fully convinced that choosing such a high P-component was the best option. To reach steady state, it still takes around 1 hour. Likely overshooting and oscillations could be reduced, if a tradeoff to a larger I-component (with anti-windup) would be allowed.

Response 11: We thank the reviewer for this important point. The reported mean deviation (~0.8 °C) lies within the operational requirement of ±1 °C stability around the setpoint and is biologically acceptable for short handling periods. This deviation reflects a deliberate tuning choice to guarantee rapid thermal recovery under −5 °C ambient conditions. Nevertheless, we agree that heat-sensitive samples may benefit from a more conservative controller configuration. We have therefore added clarifications in the Results and Methods sections to state the ±1 °C requirement and to describe an alternative tuning option (reduced P, increased I with anti-windup) for minimizing overshoot and oscillation at the cost of slower warm-up.

The revised text now reads:

Section 3, Line 451:

“The observed mean deviation lies within the defined requirement of maintaining ±1 °C accuracy around the setpoint and is considered biologically acceptable for short handling periods. The thermal control loop is deliberately tuned for robustness under cold deployment conditions, prioritizing rapid recovery. Importantly, during the initial warm-up phase, no biological samples or experimental hardware are present inside the incubator, so the brief overshoot during startup poses no risk to payload integrity. For highly heat-sensitive payloads, however, a conservative alternative (reduced P, increased I with anti-windup) can be selected to minimize overshoot and oscillation at the expense of a slower warm-up.”

Section 2, Line 314:

“The tuning thereby meets the operational requirement of maintaining ±1 °C stability around the setpoint during steady-state operation.”

Comment 12: The schematic of the electronic system is not very intuitive to read. I suggest using official symbols instead of simple boxes, such for the FET or DC/DC-converter.

Response 12: We thank the reviewer for this remark and have improved Figure 3 accordingly. To balance readability for non-engineering readers and technical clarity, we redrew the schematic using standard IEC symbols for the key components, while retaining a simplified block-diagram style for higher-level system elements. We believe this provides the best compromise between accessibility and technical accuracy.

Comment 13: From the schematic, the function of the “DC-DC Step-Down” and the “Lab Power Supply” is not clear. I suggest indicating with two lines, which lead out of the box, that these two devices are used for payloads in the incubators.

Response 13: We thank the reviewer for this helpful remark. We agree that the role of the “Lab Power Supply” and the “DC-DC Step-Down (CV)” was not sufficiently clear from the schematic. The “Lab Power Supply” represents the integrated programmable power unit, which provides precisely defined voltage and current from either external input (12–24 VDC or 230 VAC) or the onboard batteries to the payload. The “DC-DC Step-Down (CV)” is used to generate a stable auxiliary voltage for potential payload control signals.

Comment 14: The term “laboratory power supply” is used with two different meanings. On line 202 likely a power supply is meant that powers the incubator with 24VDC. Later on, on line 235, a internal power supply for experimental hardware is described. I suggest rephrasing to avoid confusion.

Response 14: We thank the reviewer for this helpful remark. The wording in one instance was indeed misleading. The incubator is powered by onboard batteries or external 24 VDC input, not by an external laboratory power supply. The term “laboratory power supply” was intended to describe the integrated programmable DC power supply that delivers regulated voltage and current to the experimental payload. We have corrected this wording in the manuscript and updated the caption of Figure 3 accordingly to avoid confusion.

Comment 15: How can the output voltage of the “DC-DC Step-Down” and the “Lab Power Supply” be set? Are there any measures foreseen to avoid accidental change of the voltage output during operations in the field.

Response 15: We thank the reviewer for this important question. The integrated programmable DC power supply is configured via a protected service menu, as stated in the manuscript, and remains locked during field operation to prevent accidental changes (now line 193). The DC-DC Step-Down (CV) converter provides a fixed auxiliary control voltage for payload signals. This value is identical for all our payloads and therefore configured once before a campaign using a trimmer potentiometer. As this setting is mechanically fixed and not accessible during operation, accidental changes in the field are excluded. We have clarified this aspect in Section 2 of the manuscript.

Section 2, Line 268:

“For our payloads, this auxiliary control voltage is identical across campaigns and is therefore configured once before deployment using a trimmer potentiometer. As this adjustment is mechanically fixed and not accessible during field operation, accidental changes are excluded.”

Comment 16: For the field tests, where the wind conditions simulated in a test chamber or was this the (coincidental) outside condition when testing the hardware?

Response 16: We thank the reviewer for this question. The field validation was performed outdoors, and the wind conditions reflected coincidental ambient conditions, not generated in a wind chamber. Wind speed was monitored with a handheld anemometer during each test, and the outdoor experiments were repeated multiple times to ensure sufficient statistical robustness. The measured wind conditions were subsequently used as boundary inputs for the thermal simulation. We have clarified this in Section 3 of the manuscript.

The revised text in Section 3 (Line 565) now reads:

“Wind speed was monitored with a handheld anemometer during each test, and the experiments were repeated multiple times to ensure sufficient statistical reliability. The measured wind conditions were subsequently used as boundary input for the thermal simulation.”

Comment 17: Line 428: Is the voltage of the battery monitored and logged by the Arduino?

Response 17: We thank the reviewer for this question. The Arduino continuously measures the battery voltage, which was calibrated against a laboratory bench multimeter. The measurement is internally processed to indicate over- or undervoltage conditions and is permanently displayed on the front panel. In the case of an external vehicle power source, the input voltage is also monitored and displayed. Continuous logging of voltage values is not implemented in the current version but could be added in future iterations. We have clarified this in Section 2 of the manuscript.

The revised text in Section 2 (Line 193) now reads:

“Battery voltage is continuously measured by the Arduino, calibrated against a laboratory bench multimeter. The values are internally processed to trigger under- and over-voltage warnings and are permanently displayed on the front panel. In case of external vehicle power supply, the input voltage is monitored in the same way."

Comment 18: Line 440 and following: Why does the voltage signal almost show a digital characteristic? Is this due to the high p-component in the PID?

Response 18: We thank the reviewer. The near-digital voltage shape reflects the time-proportioning actuation of the heaters. The PI controller (D = 0) computes a continuous control signal which is applied as a duty cycle; the resulting discrete load steps appear as voltage plateaus. It is therefore not caused by the strong proportional action per se.

The revised text in Section 3 (Line 471) now reads:

“The near-digital appearance of the voltage trace results from this time-proportioning actuation: the PI controller (D = 0) computes a continuous control signal that is translated into a duty cycle, producing discrete load steps visible as voltage plateaus.”

The revised text in Section 4 (Line 688) now reads:

„The discrete step-like appearance of the battery voltage observed in the field tests is characteristic of the time-proportioning actuation of the heaters and does not impair thermal regulation.“

Comment 19: To me the simulation setup is not fully clear. Maybe a 3D schematic with the boundary conditions and idealizations indicated would help. I would assume that conduction through the insulation layer will dominate the system.

Response 19: We thank the reviewer for this suggestion. We have clarified the description of the simulation setup in the text. As correctly noted, conduction through the insulation layer represents the main thermal pathway. However, the magnitude of this heat flow is sustained by external convection at the incubator’s outer shell, which continuously enforces a large temperature difference between inside and outside. Radiative exchange was neglected in this model. We believe that this clarification addresses the reviewer’s concern without the need for an additional schematic.

The revised text in Section 3 (Line 552) now reads:

“Conduction through the insulation layer forms the dominant thermal pathway between the interior and exterior. The magnitude of this heat flow is sustained by convective cooling at the incubator’s outer shell, which continuously enforces an energy loss, resulting in a temperature difference between inside and outside. This, in turn, increases the power loss via conduction, which is dependent on this difference. Radiative exchange was neglected”

Comment 20: What software (and version) was used for the simulation.

Response 20: We thank the reviewer for this question. The simulation was performed in MATLAB R2022a using the built-in ODE solver suit (ODEbox Version 1.1, Solver ode45) . This information has been added to Section 3 of the manuscript.

The revised text in Section 3 (Line 562) now reads:

“All simulations were implemented in MATLAB R2022a using the standard ODE solver (ODEbox Version 1.1, Solver ode45)”

Comment 21: Why was the bottom layer considered insulated? What if the box stands in soft snow?

Response 21: We thank the reviewer for this question. In the model, the bottom surface was treated as insulated because the incubator is operated slightly elevated above ground with negligible airflow and contact, so convective coupling at the bottom is minimal. A direct conductive exchange would only occur if the unit were placed in soft snow. In such a scenario, initial melting of the snow by the warm bottom surface would rapidly reduce conductive contact, leaving only radiative coupling, which was neglected in our simplified model. Since the simulation was primarily designed to provide an order-of-magnitude estimate of heating demand and was verified against outdoor measurements, neglecting this bottom exchange has only minor influence on the results. We have clarified this assumption in Section 3 of the manuscript.

The revised text in Section 3 (Line 557) now reads:

“The bottom surface was modeled as insulated, reflecting the slightly elevated installation of the incubator and negligible convective coupling at the bottom. Direct conductive exchange would only occur if the unit were placed in soft snow; in that case, initial melting would limit sustained contact. This boundary condition was therefore neglected as a minor influence compared to convective losses at the outer shell."

Comment 22: Line 520: How much of the 17.3 W baseline power consumption ends up as a heating baseline in the incubator?

Response 22: We thank the reviewer for this important clarification request. The measured baseline power consumption of 17.3 W originates primarily from the conversion electronics and auxiliary systems located outside the conditioned chamber volume. Only a negligible fraction of this power is dissipated as heat inside the incubator; therefore, in the thermal model, the baseline is treated as an external load and not as an internal heating contribution. We have clarified this in Section 3 of the manuscript.

The revised text in Section 3 (Line 594) now reads:

“This baseline arises predominantly from conversion electronics located outside the incubator’s conditioned volume; only a negligible fraction couples thermally back into the interior. Accordingly, it was treated as an external load rather than as an internal heating contribution.”

Comment 23: Paragraph starting at line 512 and paragraph starting at line 534 are identical. One can be removed.

Response 23: We thank the reviewer for noticing this duplication. The redundant paragraph has been removed in the revised manuscript.

Comment 24: The number of the figures in is not consistent. Figure 2 appears twice but figure 4 is missing. Also Figure 8 mentioned on line 564 does not exist.

Response 24: We thank the reviewer for pointing out these inconsistencies. The figure numbering has been corrected throughout the revised manuscript.

 

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript is on the development of a transport incubator for biological spaceflight payloads. The authors describe the construction of the incubator, the main hardware components, including power supplies, microcontroller, temperature sensors, heaters, PID control system, and elastomeric lining. Authors perform thermal and power characterization of the incubator during typical working conditions in extreme cold environments. They developed and benchmarked a thermal model to virtually stress-test the system under conditions difficult to realize, and predict worst-case power requirements. Main contributions include a depiction of the type of equipment used to carry biological payloads in cold environments and the development and benchmarking of a model to validate the system and predict worst-case scenarios. It was nice to see a discussion of the PID control tuning used. A major strength is that the incubator was tested in real world conditions.

This reviewer did not find major weaknesses in the manuscript. The manuscript was limited to thermal and power control and authors define some limitations. For example, experimental conditions were limited to cold ambient temperatures. The authors mention that the heat created by the power supplies may limit the system's ability to maintain physiological conditions in ambient temperatures of +30C, such as those commonly found in tropic and desert regions. The authors acknowledge that mechanical vibrations can influence biological cells and mention in the discussion and outlook section the addition of data loggers for acceleration sensing and environmental telemetry, which in my opinion are necessary to fully evaluate a transport system for biological payloads.

I found three errors: (1) an incorrectly captioned figure in Page 10, (2) a repeated term in the Abbreviations section, and (3) a reference in line 564 to a Figure 8.

(1) The temperature versus time figure in section 3.1 is mislabeled as Figure 2 where it should correctly be labeled Figure 4.  

(2) The "1U / 2U Standardized unit sizes for payload modules (1U = 10×10×10 cm)" abbreviation is repeated in the Abbreviations section. 

(3) Line 564 references a Figure 8, but there are 7 Figures in the manuscript. I understand it should be referencing Figure 7. 

The manuscript is very clear and relevant in the field of instruments for thermal regulation and power requirements for biological payloads.

The manuscript is more a engineering characterization than a hypothesis-driven work. It is scientifically sound, and the experimental designs are appropriate.

I understand that the methods section is clear enough so methods would be reproducible by a group with the relevant expertise.

The images and figures are appropriate, and they properly show the data, are easy to interpret, and results are appropriately and consistently interpreted throughout the manuscript.

This reviewer suggests accepting this manuscript after the minor edits in the text described above.

Author Response

Comment 1: This manuscript is on the development of a transport incubator for biological spaceflight payloads. The authors describe the construction of the incubator, the main hardware components, including power supplies, microcontroller, temperature sensors, heaters, PID control system, and elastomeric lining. Authors perform thermal and power characterization of the incubator during typical working conditions in extreme cold environments. They developed and benchmarked a thermal model to virtually stress-test the system under conditions difficult to realize, and predict worst-case power requirements. Main contributions include a depiction of the type of equipment used to carry biological payloads in cold environments and the development and benchmarking of a model to validate the system and predict worst-case scenarios. It was nice to see a discussion of the PID control tuning used. A major strength is that the incubator was tested in real world conditions.

This reviewer did not find major weaknesses in the manuscript. The manuscript was limited to thermal and power control and authors define some limitations. For example, experimental conditions were limited to cold ambient temperatures. The authors mention that the heat created by the power supplies may limit the system's ability to maintain physiological conditions in ambient temperatures of +30C, such as those commonly found in tropic and desert regions. The authors acknowledge that mechanical vibrations can influence biological cells and mention in the discussion and outlook section the addition of data loggers for acceleration sensing and environmental telemetry, which in my opinion are necessary to fully evaluate a transport system for biological payloads.

Response 1: We sincerely thank the reviewer for the positive evaluation and for highlighting the strengths of our study. We are pleased that the discussion of the PID tuning and the validation of the thermal model were found useful. We also appreciate the reviewer’s emphasis on additional sensing and telemetry; these aspects are indeed mentioned in the Outlook as promising extensions for future versions of the incubator.

Comment 2: I found three errors: (1) an incorrectly captioned figure in Page 10, (2) a repeated term in the Abbreviations section, and (3) a reference in line 564 to a Figure 8.

Response 2: We thank the reviewer for carefully checking the manuscript. All three errors have been corrected in the revised version: the figure caption on page 10 was adjusted, the repeated term in the Abbreviations section was removed, and the incorrect reference to Figure 8 was deleted.

Comment 3: (1) The temperature versus time figure in section 3.1 is mislabeled as Figure 2 where it should correctly be labeled Figure 4.  

Response 3: We thank the reviewer for pointing out this labeling error. The figure in Section 3.1 has been corrected to Figure 4 in the revised manuscript.

Comment 4: (2) The "1U / 2U Standardized unit sizes for payload modules (1U = 10×10×10 cm)" abbreviation is repeated in the Abbreviations section. 

Response 4: We thank the reviewer for noticing this duplication. The repeated entry has been removed from the Abbreviations section in the revised manuscript.

Comment 5: (3) Line 564 references a Figure 8, but there are 7 Figures in the manuscript. I understand it should be referencing Figure 7. 

Response 5: We thank the reviewer for catching this error. The incorrect reference to Figure 8 has been corrected to Figure 7 in the revised manuscript.

Comment 6: The manuscript is very clear and relevant in the field of instruments for thermal regulation and power requirements for biological payloads.

The manuscript is more a engineering characterization than a hypothesis-driven work. It is scientifically sound, and the experimental designs are appropriate.

I understand that the methods section is clear enough so methods would be reproducible by a group with the relevant expertise.

The images and figures are appropriate, and they properly show the data, are easy to interpret, and results are appropriately and consistently interpreted throughout the manuscript.

This reviewer suggests accepting this manuscript after the minor edits in the text described above.

Response 6: We sincerely thank the reviewer for this very positive assessment. We are pleased that the clarity, reproducibility of the methods, and appropriateness of the figures were highlighted. We are also grateful for the recommendation to accept the manuscript after minor edits, which have all been implemented.