Transcript Launch Loads and Flight Events

Spacecraft Structure Development
- Vibration Test -
(60 minutes)
2007/04/24
1
Outline
•Basic Concept
•Sinusoidal Vibration Test
•Random Vibration Test
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Basic Concept
3
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
10
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)
10-2000
Level
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 below
Frequency (Hz)
5-23
23-100
100-200
Level
0.4" DA
11.3g
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 -
1.LVBA060x
4.LVBA150x
65.LVBA240x
68.LVBA330x
Contract Requirement
10000
• Satellite sustains the
launch separation shock?
• Component shock
specifications adequate?
Shock Response, G's
1000
100
10
1
0.1
1
10
100
1000
10000
100000
Frequency, Hz
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Pyro-Shock Test
- FORMOSAT-1 Test Results Analysis -
Payload Platform
Ram Platform
contains components
Center Platform
Closure Panel
contains inverse cone,
propellant tank
Wake Platform
Solar Panel
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)
Booster Adapter
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Pyro-Shock Test
- FORMOSAT-2 example -
Before
After
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