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It Gets Chilly Up There: Time for a Whole New Type of “Space Heater”

01/27/2017

Orbiting the earth at thousands of miles per hour can make for some pretty intense temperature swings.  The Iridium NEXT satellites, and their AireonSM hosted-payloads move in and out of direct sunlight on each orbit, which occurs approximately 14 times per day.  To account for the extreme shifts in temperature, the engineers behind Aireon’s system installed electric heaters inside the payload housing to keep the electronics from freezing over.  These new “space heaters” are needed when the Aireon payload is powered off for extended periods of time. This can occur for the following reasons:

  • After launch and before the satellite reaches mission orbit. Which is technically before the payload was turned on after manufacturing tests.
  • When the satellite enters a “safe hold” mode due to an anomaly, and preserves power to help address the issue.
  • If the Iridium NEXT satellite is an on-orbit “spare” and not being currently used in the active constellation.

Without the heaters, the payloads would be subject to -50 degrees Celsius (-58 degrees F) temperatures when out of sunlight, but to ensure they don’t overheat when in the sunlight, the team had to create a temperature-agile system.  To offer some perspective on just how cold things could get without their heaters, here are a few Earthly examples of freezing temperatures:

  • When temperatures dip to about -11 degrees Celsius, bubbles will freeze. Yes, bubbles.[i]
  • Your tongue will stick to a flagpole at 0 degrees Celsius – Yes, really. So, there’s no need to try it.[ii]
  • Despite the name, “anti-freeze” will freeze. The temperature can vary based on how “strong” it’s made, but the temperatures will range from -37 degrees Celsius to -64 degrees Celsius.[iii] 

So how do we ensure the heaters know when to help prevent the payloads from going the way of the frozen bubble?

The Aireon heaters are controlled by the satellite bus, which is essentially the infrastructure of the spacecraft.  Similar to how a motherboard works for a computer, the bus has been programmed with a set of temperatures which tell it when to turn the heaters “on” and when to turn them “off”. This is an extremely important point, as the Aireon payload is part of the greater Iridium NEXT network. By relying on the larger satellite network, it’s made Aireon a cost-effective, technologically advanced solution for surveillance of aircraft. We rely on the greater Iridium® network as the backbone of the constellation and do it while being a hosted payload.

Now that first launch is behind us, Iridium is currently receiving real telemetry from the ten satellites in orbit.  Part of that telemetry is the temperature of each Aireon payload and whether or not the heaters have been energized by the satellite.  In the near future, this information will be provided to the Aireon payload manufacturing team at Harris Corporation, so they can validate their thermal modeling of the Aireon payload using real data.  This data is invaluable to ensure accurate thermal modeling of each payload is accomplished so the satellite  can accurately predict when to expect temperature fluctuations.

Stay tuned for more about the launch of the world’s first and only 100 percent global aircraft surveillance system, from Aireon.

[i] http://www.livescience.com/42437-crazy-cold-weather-phenomena.html
[ii] http://www.livescience.com/32237-will-your-tongue-really-stick-to-a-frozen-flagpole.html
[iii] https://en.wikipedia.org/wiki/Antifreeze#Measuring_the_freeze_point

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