1,212
edits
Changes
→Heat Pipes
* Damper
Dampers help in dissipation of vibration energy into heat energy. A PVI system can be simplified with the system shown in the figure below:
[[File:PVI1.png|frame|center|Passive Vibration Isolation. Image reproduced from [https://commons.wikimedia.org/wiki/File:Passvib1.svg here]]]
==== Transmissibility Curve <ref name = "ref2">https://en.wikipedia.org/wiki/Vibration_isolation</ref> ====
It gives an indication of how much source vibration will be transmitted through the interface to the satellite. It is a relative measure given as a ratio of vibration at two points: one on the top of the isolator and one on the source. Here is an example of a transmissibility curve of negative stiffness isolation system with natural frequency 0.5Hz.
[[File:Transmissibility.png|frame|center|Image reproduced from [https://commons.wikimedia.org/wiki/File:Passvib2.jpg here]]]
The transmissibility hovers around initially as the frequency of source reaches natural frequency, the amplitude rises catastrophically. We need dampers to damp this kind of vibration to ensures the structural stability and integrity of any payload.
[[File:PVI2.png|frame|center|Image reproduced from [https://commons.wikimedia.org/wiki/File:Passvib3.jpg here]]]
====Types of PVI Systems ====
*[[Pneumatic or air isolators]]
*[[Mechanical springs and spring-dampers]]
*[[Pads or sheets | Pads or sheets of flexible materials such as elastomers, rubber, cork, dense foam and laminate materials.]]
*[[Negative-stiffness isolators]]
*[[Wire rope isolators]]
=== Active Vibration Isolation (AVI) System <ref name = "ref2" /> ===
It can be modeled as spring along with a feedback circuit which consists of a sensor , a controller, and an actuator. The acceleration (vibration) signal is processed by a control circuit and amplifier. Then it feeds the electromagnetic actuator, which amplifies the signal. As a result of such a feedback system, a considerably stronger suppression of vibrations is achieved compared to ordinary damping.
==== Sensors for Active Isolation ====
[[File:Interferometer.png|frame|thumb|Interferometer. Image reproduced from [https://commons.wikimedia.org/wiki/File:Interferometer.svg here]]]
* '''Piezoelectric Accelerometer:'''
**Produces current on mechanical stress
=== Active vs Passive Vibration Isolation ===
{| class="wikitable"
|+ Comparison of Active and Passive Vibration Isolation <ref>https://www.herzan.com/resources/tutorials/active-vs-passive-vibration-control.html</ref>
! style="font-weight: bold;" | FEATURE
! style="font-weight: bold;" | PASSIVE
==== Multi-layer Insulation (MLI) ====
Protects the spacecraft from excessive solar rays. Acts as a radiation barrier.
[[File:MLIPTC1.png|frame|center|Illustration of the working of MLI]]
==== Coatings ====
q(space)= q(loses) + q(electric)
[[File:RadiatorPTC2.png|frame|center|Radiator illustration]]
=== Active Thermal Control (ATC) system ===
*Flat sheet heaters use the Joule effect
[[File:HeaterPTC3.png|frame|center| Patch heater]]
==== Louvers ====
*Shield radiator surfaces to moderate heat flow to space
* '''Principle:''' Bi-metallic spring sense the radiator temperature, open/close the radiator to deep space.
[[File:LoversATC3.png|framethumb|center|600px| Louver mechanism. Image inspired from [http://www.tak2000.com/data/satellite_tc.pdf here]]]
====Heat Pipes====
*Wicking material returns fluid to hot end
*Provide high heat transfer rates even with small temperature differences
[[File:HeatPipe1ATC1.png|frame|left]][center|Heat Pipe Mechanism. Image reproduced from [https://commons.wikimedia.org/wiki/File:HeatPipe2Heat_Pipe_Mechanism.png|frame|centerhere]]]
===Comparison of Passive and Active Thermal Control ===
----
If you are done reading this page, you can go back to [[Mechanical Subsystem]]
== References ==