It's pretty cool to think about the power of satellite communications (SATCOM), and the advantages it provides for our military customers. What's definitely not cool is the fact that interoperability issues between different generations of UHF equipment can prevent those advantages from reaching the warfighter in the field.

Recently we tried to reduce the likelihood of interoperability issues arising. During the month of November, an industry team led by Intelsat General conducted a UHF legacy terminal compatibility test to verify interoperability between legacy UHF radios and the UHF hosted payload onboard the Intelsat 22 spacecraft (IS-22). IS-22 is scheduled to go into space in a few months.

The IS-22 spacecraft carries three payloads: commercial C and Ku, and UHF for the Australian Defence Force. The UHF payload is an example of a "hosted payload", whereby a dedicated government mission shares the commercial satellite platform. For IS-22, the customers are the Australian Defence Force and the U.S. Department of Defense, both of which need expanded UHF capabilities over the Indian Ocean, Africa, Europe, Asia and, of course, Australia.

Any time new payload designs are developed, questions arise regarding the payload's compatibility with existing equipment being used in the field. Even though the hosted payload on the IS-22 is functionally equivalent to other UHF payloads, the engineering team created a test to verify that the payload would be compatible with legacy equipment.

The plan was to run voice scripts and transfer data from one radioto the satellite and back to another antenna and a separate radio. We conducted the tests in the facility where the satellite has completed its final environmental testing and is undergoing its final flight configuration.

The team used two commonly available UHF radios to transcribe voice tests, checking for clarity, and ran data transfers through bit error rate test equipment. We conducted data tests for all available radio options and compared the bit error results against the standard for all military UHF communications, MIL-STD-188-181C.

Conducting this test presented several risks that required the team to create sub-tests to eliminate any possible damage to the flight-ready spacecraft. Due to the close proximity between the antennas and the satellite, the signal strength coming from the radio and antenna would normally be so strong that it would damage the satellite's sensitive receivers.

In order to mitigate this risk, we used large attenuators and conducted sub-tests, first using a test loop translator and second using the UHF payload from IS-27, currently under construction, as substitutes for the spacecraft in order to properly set attenuation values. Because the IS-27 UHF payload is identical to the one on the IS-22, this sub-test provided additional data points that can be used to show compatibility.

The team established the test set-up outside of the chamber and ran through equipment checks before the green light was given to test on the actual spacecraft. Once the process started, the team set up the equipment in the anechoic chamber, configured the UHF payload and set up the radios. This occurred intermittently over multiple shifts so as to fit in with other tests being run on the satellite, and required the team to be on standby for five days to finish all testing.

Through the hard work of all parties involved, the test was a great success. We found that both sets of radios tested could transfer high-quality voice and data streams at error rates that either met or exceeded the military standard. With these test results, IGC has lowered the risk of interoperability issues between the hosted UHF payload and legacy UHF equipment.