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Lightweight Carbon Fiber Antenna Boosts Payload Data Downlink Speed

In the near future, satellites will be able to acquire almost limitless amounts of data.
The use of carbon fiber allows a much bigger horn size for comparable mass.
However, the amount of data made available to the end user will always be determined by a number of factors, including how quickly that data can be downlinked from the satellite to Earth.

A typical pass of a low Earth orbit satellite over a ground station lasts just 10 to 11 minutes, and all data required must be downlinked in this time. Small satellites are able to image in higher and higher spatial resolution; in the last decade Surrey small satellites have gone from a default resolution of 32 meters (with DMC satellites like NigeriaSat-1) to being capable of sub-meter-resolution imaging (with Surrey’s high-resolution 300-S1 platform). This, along with other platform improvements, has resulted in a huge increase in the data throughput capability and amount of imagery generated. Subsequently, the speed of data transfer between the satellite and ground station must increase.

The gain (amplification) of a satellite’s antenna has a significant effect on the quality and strength of the signals that can be transmitted, and therefore the bandwidth and data rate. Lengthening the antenna increases its gain, and enlarging the horn size on the antenna concentrates the signal, both allowing a higher bandwidth link to the ground station for faster data transfer.

But this required increase in size must be balanced with the need to keep mass down and keep small satellites, small. Faced with this challenge, Surrey’s composites facility developed a new high gain antenna. The use of the advanced lightweight composite material carbon fiber allowed a significant jump in performance without changing the mass. The redesigned carbon fiber antenna provides an increased gain of 18 dBi (from 15 dBi) and a narrower beam-width (3 dB) of 18° (from 26°) which effectively doubles the data rate capability compared to Surrey’s existing antenna system.
 
Carbon fiber antenna on TechDemoSat-1


Using composite materials meant that Surrey could create a higher capability subsystem that is still compatible with existing satellite platforms and systems. The detailed horn antenna is typically used on board an Antenna Pointing Mechanism, which is used to maintain the line of sight with the ground station during a pass even allowing for a satellite that changes its orientation during the pass. By restricting the mass of the horn antenna assembly via carbon fiber materials, the core backbone components of the Antenna Pointing Mechanism did not need to be changed to incorporate the larger sized antenna, such as the motor, transmission, and bearings.

This approach keeps costs down and allows Surrey to incrementally improve the capability of its satellites, instead of having to redesign entire platforms every time.

In 2000, Surrey satellites downlinked at 38.4 Kbps—roughly the same as an old dial-up modem. Dial-up is a thing of the past now. NigeriaSat-2, which was Surrey’s highest performance Earth observation satellite when launched in 2011, had two antennas, each offering 105 Mbps data rate. The new carbon fiber antennas can support data rates up to 500 Mbps and represent a significant step change in downlink speed just since 2011.

Used in conjunction with other newly developed subsystems, like the high-data-rate X-Band Transmitter, High Speed Data Recorder, and Flash Mass Memory Unit, the carbon fiber antenna will help increase the capacity of Surrey’s small satellites to acquire, store, and downlink high-resolution images. These subsystems will all be tested in orbit on the Surrey technology demonstration mission, TechDemoSat-1, later this year.

 

04 February 20140 Comments1 Comment

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