Q _A Engineering Propulsion Standards TIM 6-13-2025.pdf

Q & A for Propulsion Standards TIM June 13, 2025

1. Q: On Chart 7 regarding the section on tailoring, in the third bullet that is underlined, “except for those requirements specifically called out as Type 2 or in program requirements document”, how is that designation indicated? A search was performed for “Type 2” in the document, and it only appears in the table of standards. This search found “shall” statements elsewhere in the document that were explicitly tagged as Type 2.

A: The word “or” in the 3rd sub-bullet under ‘Tailoring’ on chart 7 was a typo.

It should read “ If [JSC-67723] document is levied by a program as a Type 3, then any “shall” becomes “should in best practice”, except for those requirements specifically called out as Type 2 or in program requirement documents. “

If a program document calls out NASA-STD-6016 as a Type 2, and if JSC 67723 is levied as a Type 3, then that doesn't make NASA-STD-6016 a Type 3 requirement [Note: JSC-67723 calls out NASA-STD-6016 as a Type 2]. So, it's just saying that the program requirements take precedence. If they levy NASA-STD-6016 as a Type 2, that's the precedent.

2. Q: The document itself does not appear to introduce any new requirements that are beyond those already covered in existing standards being referenced.

NASA is not creating any new requirements that are Type 2 that aren't already covered in the existing standards. Correct?

A: No. There are some new requirements called out that are Type 2 that are not already covered by existing standards. These are the gaps that JSC- 67723 addresses.

3. Q: If the [JSC-67723] document is levied as a Type 3, then any “shall” would become “should” right?

A: That's correct.

4. Q: Regarding Chart 11, given that NASA is invoking the total propulsion system, including propellant and pressurization system, is there a potential conflict between requirements with 3.7.3.1 and 3.7.3.4? For example, JSC-08080 F-15 requires full metal separation of the commodities, while 3.7.3.4 allows use of elements like vapor

ISO.

A: In shuttle program, the orbiter OMS/RCS used a short-term system that used vapor isolation, which is a conflict [with JSC-08080 F-15]. JSC-67723 Paragraph 3.7.3.4 [PSR-206G] provides a path or an alternative approach that addresses this conflict for some short duration applications that effectively provides the separation of vapors. NASA’s goal is a test to demonstrate that the design features are actually mitigating the hazard for the required duration.

5. Q: For PSR-36G [reference chart page 15], how is that applied to propellants like hydrogen peroxide that have continuous moderate auto decomposition at normal storage temperatures?

A: There is more detail in PSR-36G, but the requirement is addressing an explosive or decomposition event. So, slow decomposition rates are not an issue with respect to this requirement. The specific hazards that this requirement addresses is a rapid decomposition caused by adiabatically compressing a vapor pocket by a water hammer or transient event that exceed the MDP of the hardware. The requirement is a margin against an explosive hazard.

6. Q: Isn't a throat plug purge a design solution and not a requirement? [Reference PSR-93G on chart 19 and PSR-103G on chart 20].

A: NASA will re-evaluate renaming “a throat plug purge” to “a mitigation”.

The intent is to provide a means to prevent [MMH and NTO reaction]. The purge is intended to prevent the MMH or the NTO from reacting at the fuel [valve] seat. If there's another way to prevent that, then that would be acceptable. If the design meets the intent of NTO fuel vapors from not getting to the MMH fuel seat then that would meet the intent of JSC-67723.

7. Q: Referring to PSR 122 G, does that apply where there is not data, like in MAPTIS, that shows the material is fully compatible with the commodities and duration because it drives long duration testing such as Space station that could be up there for a decade plus? If it drives to require a full duration exposure test in all relevant environments, then that could be definitely cost prohibitive.

A: If it can be shown that the component exposure to propellant is only while it is at vacuum on-orbit, and that the propellant and component are isolated while on the ground such that it is not exposed to atmosphere and other fluids, and all it does is see the vacuum when the component is exposed to for decade plus, then MAPTIS data should apply. However, databases such as MAPTIS do not necessarily address the relevant fluids that might have been in the component from processing or the exposure to humidity and air. NASA conducted fleet leader testing in the shuttle program to address component level testing for duration and cycles. Test data at the component level in the relevant environments and duration is required to address issues such as corrosion, seat swell, etc.

8. Q: Why was N204 listed under monopropellant requirements with N204 being an oxidizer? [Reference charts 19 and 20]

A: No, N204 was not listed, only hydrazine, hydrogen peroxide, nitrous oxide are under monopropellants, in PSR-92G. Any propellant that's a monopropellant has potential for rapid compression or detonation of it.

With nitrous oxide, there is not a full understanding of what happened with the scaled composites failures as well as there's a couple other ruptures of nitrous oxide systems.

9. Q: Is PSR-136 intended to be inspection along the entire length of a tube?

Or just critical areas like weld joints or potential contamination traps? [Reference chart 22]

A: It may not be possible to do full length borescope inspections of a particular tube. The traps are more likely to be where you find contamination.

PSR 137-G addresses where it may not be fully possible to inspect that whole length of a welded assembly. This surveillance of larger diameter tubing is intended to demonstrate that the process is meeting cleanliness requirements.

10. Comment. There were three potential root causes for Scaled Composite N2O explosion:

1. There were no controls for static charge dissipation in their N2O fuel flow system.

2. The oxidizer flow plumbing was not cleaned prior to use, so may have been hydrocarbon contaminants.

3. N2O can go super critical and explode if above 97.7°F.

A: The reference reports provided in JSC-67723 PSR-87G is intended to address those hazards. If not, then this requirement will be updated.

11. Q: PSR-220G [reference chart 29]. For systems that are only using propellant vapor pressure for pressurization. E.g. self-pressurized nitrous oxide. How would this requirement be evaluated? Does this requirement preclude the use of cavitating venturis for flow control?

A: PSR-220G is definitely not intended to preclude self-pressurized nitrous oxide or cavitating venturis. A specific note to 220-G will be added as necessary to clarify that it is not meant to preclude a cavitating venturis or to preclude a self-pressurized system. The intent of PSR-220G is to address damaging vapor bubble collapse, where it is not intended to be happening.

12. Q: There was a procedural improvement to the fill and drain valves on Shuttle to not cycle the valves with a pressure differential. The DP caused an extensive load on the gears when lifting the visor of the seat. [reference chart 28]

A: Agree. There is additional data in the provided references.

13. Q: For the Pyro valve section, should some of these requirements be generalized to include single-use non pyro valves that are drop in replacements to traditional pyro and have some similar features like frangible elements for instance, shape memory alloy valves and stored mechanical energy valve.

A: This will be considered.

14. Q: For PSR-293-B in SMC-S-025 as written, those four engine samples are allowed to be two times verification samples and two times qualification samples. Is the intent for the two additional samples to be verification or qualification standard?

A: Relative to PSR-283, which states four engineering EDUs and two qual units, the increase from 4 to 6 test engines could be broken down into 4 engineering units (structurally equivalent to flight engines) and two qual units.

The point here in PSR-293 is mainly to emphasize the exceptions that are being taken related to SMC-S-025, because there are some conflicts between standards, such as with NASA-STD-5012. This section is trying to deconflict those two.

15. Q: This goes back to some of the engine thruster items. For the engine thruster margin factors. Why is there no margin for cold/hot starts, especially for hydrazine thrusters? Cold starts may be more demanding.

A: Yes. This will be clarified. In 286G, see reference chart 36, there is a requirement to qualify by test the number of cold and hard restarts. This is not like a separate test but built into the qualification testing that addresses the 2x service life and the 4x pulse count to include the number of cold and hot restarts. It should be to a 4x. This should also apply equally to all monopropellant engines. There are going to be range of start conditions with respect to engine hardware and propellant temps. The setting of the minimum catalyst bed and propellant temperatures is a key parameter to get the required life.