Flexible Circuits and Man-made Satellites

thermal_management_imgThe first satellite was launched by the USSR in 1957.  The US successfully launched its first satellite, Explorer 1, in 1958 while announcing the intention to “win” the race to outer space Source. Today satellites serve a number of vital purposes.  They are used for telecommunications, weather observation, global navigation, climate analysis, space observation, land stewardship and military uses.  There are currently over 1300 satellites in active orbit Source.   About 80 satellites are launched into space every year and the technology “race” continues with new satellite suppliers aggressively competing for additional applications.

Flexible circuits have been used in satellites for several decades.  They have been used in antennas, power bus bars, electronic interconnects, solar arrays, battery connections, and for thermal management. As space applications continue to proliferate, the utility offered by a lightweight, flexible and highly reliable electronic interconnection will also naturally grow.  Oversized flexible circuits (>22” in length) are often adopted as the interconnection circuitry among a variety of satellite subsystems, replacing heavier and bulkier wire harnesses. Flexcircuits in excess of 15 feet have been used in some satellites.

Satellites are generally classified in terms orbital altitude:

  • Low Earth Orbit (LEO) ranges from 100 miles to 1200 miles above the earth’s surface. Manned satellites such as the International Space Station (ISS), earth observation and spy satellites tend to be LEO because they allow a better view of the earth’s surface.  Manned satellites stay at low altitudes because the radiation exposure at high altitudes would limit the time a human can remain at the station.  Also satellites requiring occasional servicing would be LEO so they are more accessible.  LEO satellites will have a relatively short orbit life without occasional propulsion due to the drag caused by the relatively denser atmosphere.  Most LEO satellites have some self-propulsion capabilities.
  • Medium Earth Orbits (MEO) range from 1200 miles to around 22,000 miles. Satellites used for wireless communication tend to be MEO.  Their altitude is high enough to maximize communication coverage, yet low enough to allow relatively low powered transmitters.
  • High Earth orbit (HEO) is 22,000 miles or greater. The speed needed to maintain stable orbit depends on the altitude of the satellite. The higher the altitude the lower the velocity required.   At 22,236 miles, a satellite will achieve geosynchronous orbit where the velocity matches the rotation of the earth.  A satellite achieving geosynchronous orbit will appear to be stationary from the earth’s surface view point, as it maintains a static position relative to the earth.  Satellites in Geosynchronous orbit are frequently used for weather observation as a satellite can view the same area of the earth over long periods of time.

Many satellites are launched with the intention of lasting only a few years.  A satellite in high earth orbit can theoretically stay in orbit forever as there is very little atmospheric drag to cause the orbit to decay.  Satellites in medium and Low earth orbit can stay in orbit for years without propulsion, but will eventually decay to the point of losing orbit. Many satellites break up in space due to wear and tear of equipment malfunction or collision with space debris.  NASA is tracking over 17000 artificial objects in orbit, which is just a fraction of the amount of debris that is estimated.   Source. The life of a satellite depends on the orbit altitude, the robustness of the materials and electronics and its purpose.

Physical demands on a satellite’s electronic systems vary through its journey as component parts must initially withstand an incredible launch stress. Intense shock and vibration place unusual reliability demands on interconnections. Highly reliable wiring systems are designed with flexcircuits eliminating connectors by integrating hard wired bundles and rigid circuit boards into a single flexcircuit product design. Minimizing power consumption is another key product characteristic of an electronic interconnection in space. The ability to carry tremendous amounts of data with controlled impedance circuitry is an additional reason flexcircuits are utilized in these high performance applications.

The high vacuum environment required for space applications can cause outgassing to become an issue. Gasses released in this vacuum may create problems as condensation occurs on sensitive components, most specifically camera lenses, and clouds the equipment’s visioning capability. ASTM International has developed a test standard ASTM E 595 as a method to evaluate outgassing. A variety of flexcircuit material constructions are available in the marketplace with adhesiveless substrates being a favored material in space application environments. Source

Flexible circuits are ideal for many satellite applications because they allow lighter packages using less space.  Flex circuits are also a very reliable and have a long life expectancy.  They can be designed with tight impedance control which is often a requirement for high frequency signals.  Similar in construction and also being a low weight advantage vs. competitive alternatives, flexible heater circuits are used to assist in the thermal controls needed to maintain the operation of system electronics.

Sources:

https://www.space.com/17825-explorer-1.html

http://www.astronomy.com/news/2017/01/interactive-satellite-chart

https://www.nasa.gov/mission_pages/station/news/orbital_debris.html

http://mwexpert.typepad.com/rog_blog/2010/11/what-is-outgassing-and-when-does-it-matter.html

 

Other Resources:

http://spacenews.com/newer-satellites-meet-threats/

http://spacenews.com/construction-of-onewebs-new-satellite-factory-is-moving-quickly/

http://www.bbc.com/news/science-environment-34324443

https://defensesystems.com/articles/2014/03/21/satellite-communications-future-options.aspx