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Spacecraft Structure DevelopmentSpacecraft Structure Development- Vibration Test -- Vibration Test -

(60 minutes)(60 minutes)

2007/04/24

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OutlineOutline

•Basic Concept

•Sinusoidal Vibration Test

•Random Vibration Test

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Basic Concept

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Basic Concept in Vibration Test(1/7)

Acceptance Test:An acceptance test is applied to all items of flight hardware, whose design integrity has previously been verified by a qualification test on a prototype item. The goal is to detect workmanship errors and/or material defects in the manufacture and assembly of the hardware, and to demonstrate that the hardware is representative of the qualified design.

Qualification Test:The purpose of a qualification test is to demonstrate with margin that a hardware design is adequate to perform as are required throughout the mission environmental exposures. 6dB above acceptance for two minutes

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Basic Concept in Vibration Test(2/7)

Alternative Methods: – Protoflight Test:

A protoflight test is applied to one-of-a-kind flight hardware to meet the goals of both qualification and acceptance testing. 3dB above acceptance for one minutes

– Protoqualification Test:With a protoquallfication strategy, a modified qualification (protoqualification) is conducted on a single item and that test item is considered to be available for flight. The normal acceptance test is then conducted on all other flight items. 3dB above acceptance for two minutes

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Basic Concept in Vibration Test(3/7)

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Definition and Equations for Use in Vibration Test(4/7)

Decibel: the ratio between two like quantities expressed logarithmically by 10.

– Acceleration, velocity, displacement

• db = 20 log 10 (A2/A1)

– Power Spectrum Density

• db = 10 log 10 (A2/A1)

Octave: the ratio between two frequencies expressed logarithmically by 2

– Let N = octave number (2, 4 ….)

• N = log 2 (FH/FL) , FH = upper frequency, FL = lower frequency

• or N = 3.33 log 10 (FH/FL)

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Definition and Equations for Use in Vibration Test(5/7)

Logarithmic Sinusoidal Sweep

– Let R = N/T (octaves/minute)

– the time duration of the sweep

• T = N/R = (1/R) log 2 (FH/FL)

• example: 5 ~ 2000 Hz @ 4 oct/min, the duration = 2.17 min

Mean Squared Acceleration in a Frequency Band for Random Vibration Test

A). arbitrary shape spectrum:

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Definition and Equations for Use in Vibration Test(6/7)

B). Flat portion of spectrum:

C). Constant slope portion of spectrum

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Definition and Equations for Use in Vibration Test(7/7)

Overall Mean Squared Acceleration :

– The overall RMS acceleration is:

Sound Pressure Level

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Sinusoidal Vibration Test- Sine Survey Test -

Sinusoidal vibration is periodically varying motion which is described by amplitude (displacement, velocity or acceleration) , frequency and phase angle.

Types of sinusoidal vibration tests include the sine survey (or low level survey) test, the swept sine test, the sine pulse test and the sine dwell test.

The sine survey is a low amplitude test conducted through a specified frequency range at a prescribed rate. The main purpose of this test is to identify the primary structural resonances of the test item.

A typical specification for sine survey testing is presented below

Frequency (Hz) Level

10-2000 0.5g

All axes Rate ： 2 oct/min

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Sinusoidal Vibration Test- Swept Sine Test -

The swept sine test is normally conducted over a smaller frequency region than the sine survey test.

During this test, the test item is usually subjected to significant input levels in spectral regions of primary structural concern. This amplified level may be the result of a vehicle anomaly, a primary structural resonance or a locally-induced perturbation.

Thus the primary function of this test is to demonstrate that the hardware will endure the loading which may develop as a result of these events.

A typical specification for swept sine testing is presented belowFrequency (Hz) Level

5-23 0.4" DA

23-100 11.3g

100-200 6.4g

Rate ： 4 oct/min for All axes

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Sinusoidal Vibration Test- Sine Burst Test -

The sine burst test is a test performed at a level which simulates a static load, or steady state, condition on the test item.

This test is short in duration and is conducted at a particular frequency for a specified number of cycles.

The frequency at which the test is performed is chosen to be well below the fundamental frequency of the test item so as to avoid any dynamic amplification during the test.

The test article is not exposed to the larger number of vibratory cycles thus minimizing any concerns for fatigue.

A specification for a sine pulse test must include the test level, frequency and duration. For a system with a natural frequency greater than 60 Hz, the following sine pulse test may be specified:

Test level - 14.0 g

Test frequency - 15.0 Hz

Test duration - 13 half-cycles (i.e., 6H full cycles) at

maximum level

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Random Vibration Test (1/2)

Random vibration is vibration containing all frequencies at once whose instantaneous magnitude cannot be explicitly defined.

Random vibration contains nonperiodic or quasi-periodic components and thus an exact value at a future time cannot be predicted.

The instantaneous magnitude is specified by probability distribution functions giving the mean square value that lies within a specified frequency range.

Random vibration tests are examined as energy inputs to the system and usually provide greater power inputs in the higher frequency ranges.

As a result of this, electronic configurations, which generally have higher resonant frequencies, are usually exercised to a greater extent than primary structure.

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Random Vibration Test (2/2)

FORMOSAT-3 test input for a random vibration test is shown in below. The rms (root mean square) value of a random vibration input is obtained by integrating the power spectral density over the frequency range and taking the square root.

Freq (Hz) Test Level (g2/Hz)

20 0.01

25 0.022

35 0.022

45 0.01

1000 0.01

2000 0.0025

Grms 3.87 (g)

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Vibration Test - FORMOSAT-2 Example -

RSI Vibration Test FS2 Vibration Test

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Vibration Test - FORMOSAT-3 Example -

Single FS3 Vibration Test

Stacked Vibration Test

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Shock Test (1/3)

Shock testing involves exposing the hardware to a non-periodic excitation that is characterized by its suddenness and severity.

Spacecraft hardware is subjected to shock environments due to the firing of pyrotechnic bolts during separation from the launch vehicle and deployment of spacecraft appendages such as antennae, solar arrays and instrument covers.

The acceleration generated from a shock event can be represented in terms of a shock response spectrum (SRS). The SRS will depend on the assumed damping. This is usually expressed in terms of the amplification Q. For most applications, an amplification of 5 or 10 for the system is used.

Although the shock level appears to be significant, the energy quickly dissipates through each joint and with increasing distance from the shock source. As a result, in many cases, shock levels are not the controlling design parameters.

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Shock Test (2/3)- SRS -

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Shock Test (3/3)- SRS Specification -

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Pyro-Shock Test - FORMOSAT-1 example -

0.1

1

10

100

1000

10000

1 10 100 1000 10000 100000

Frequency, Hz

Sho

ck R

espo

nse,

G's

1.LVBA060x 4.LVBA150x 65.LVBA240x 68.LVBA330x Contract Requirement

• Satellite sustains the launch separation shock?

• Component shock specifications adequate?

• Satellite sustains the launch separation shock?

• Component shock specifications adequate?

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Pyro-Shock TestPyro-Shock Test- FORMOSAT-1 Test Results Analysis -- FORMOSAT-1 Test Results Analysis -

Payload Platform

Ram Platform

Center Platform

Wake Platform

Closure Panel

Solar Panel Booster Adapter

contains components

contains inverse cone, propellant tank

Payload Platform (0.02, 0.02, 0.04)

Antenna (0.07, 0.07, 0.14)

Solar Array(0.15)

Center Platform (0.17, 0.17, 0.23)

Wake Platform (0.30, 0.19, 0.23)

Sep Plane (1.0, 1.0, 1.0)

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Pyro-Shock Test - FORMOSAT-2 example -

Before After