Launching Frequency Requirement 1

[sarclee]

Hi I am reading the article below and found that the launching requirement for satellite frequency is MUST BE LESS THAN ...

I am curious why less than? Isn't it we should design it more than the fundamental frequency?


"The fundamental frequency of the satellite must be less
than 100 Hz in the longitudinal direction and less than
50 Hz in the lateral direction."

Source:

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1754&context=smallsat

 

[IRstuff]

Have you looked at the g-levels in Table 4? Do you want that level to be exciting your fundamental?

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[sarclee]

IRstuff, thanks for the reminder. I would expect the acceptable frequency to be launch freq < resonant freq < freq with higher G in the vibration profile, is it right?

 

[IRstuff]

As a general rule, you do not want your resonant frequency anywhere it can be excited; when systems have a natural rolloff in excitation, you put the resonant frequency higher, but when there's a lot of high frequency, you try to put the resonant frequency lower. Car suspensions have very low resonant frequencies.

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[sarclee]

If I have a list of components in the spacecraft, basically I need to know each component natural freq to make no component within the exciting frequency range, right?

 

[rb1957]

I'd've thought the rocket had it's design spec which would define a "stay out" zone for natural frequency ? Why look at every component ?

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[IRstuff]

If I have a list of components in the spacecraft, basically I need to know each component natural freq to make no component within the exciting frequency range, right?

Not necessarily; our specs for a non-space payload was that component resonances were of concern only if they constituted more than 10% of the total payload weight. That should be pretty intuitive; something tiny with a bad resonant frequency wouldn't necessarily be capable of affecting the entire payload.

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[sarclee]

Hi rb1957, I was thinking some critical components shall be avoided to resonate with the fundamental freq given.

Thanks IRstuff, I would agree that taking 10% of the total payload to pick those critical components...