Multiply Design factor with Qualification Factor for spacecraft?

sarclee · Nov 1, 2022

Hi, I wonder if we need to multiply the limit load with all the factors at qualification test level.

Static load = Limit Load x Design Factor X Yield Design Factor X Qualification Test Factor?

If I am extracting the bolt forces from the FEM model, should I also consider fitting factor as well?

Thank you!

rb1957 · Nov 1, 2022

This should be spelt out in the NASA STD, but I would not think so. I think the design factors are applied to your analysis, and the test factors are applied to your test.

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SWComposites · Nov 2, 2022

The Ult and Yield factors apply to separate Ult and Limit load analyses, respectively. You have to do both analyses, with different allowables. The fitting factor applies to both of those analyses, as appropriate.

The test factors are just that, they apply to test loads, not to analyses.

IRstuff · Nov 2, 2022

I've never quite gotten these sorts of tables. If they want you to design to spec*1.5, then the spec is 1.5 * spec. not spec; ditto the test load.

Seems like laziness; the customer copied/pasted some older spec and "updated" it with the actual requirement, but want you to do the math to get the right values. Hopefully, you'll catch it during the proposal phase and upcost your bit accordingly.

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rb1957 · Nov 2, 2022

is this saying that your ultimate FoS is 1.4 ... your design spec is limit load, if you do "protoflight" then you need a minimum FoS of 1.25

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

SWComposites · Nov 2, 2022

yes, the FoS on Yield/Limit analysis for protoflight approach is 1.25. the two approaches are defined elsewhere in the doc.

sarclee · Nov 3, 2022

Thank you so much to all of you.

According to the launcher's specification, we need to apply 1.25 times to limit load for qualification level.

Limit load is provided by launcher.

For Acceptance Level : 1.10 x Limit Load
For Qualification Level : 1.25 x Limit Load

I am not sure if I need to multiply design factor on top of the factor above for qualification (for example): design factor x 1.25 x Limit Load...

rb1957 · Nov 3, 2022

that's not what the launcher spec says (as you've written it).

design factors apply to analysis, test factors apply to tests.

who is asking the question ? if you, is there someone there you can ask ? someone with the launcher team ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

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Multiply Design factor with Qualification Factor for spacecraft?

sarclee

Mechanical

rb1957

Aerospace

SWComposites

Aerospace

IRstuff

Aerospace

rb1957

Aerospace

SWComposites

Aerospace

sarclee

Mechanical

rb1957

Aerospace

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