New Horizons Sends Signals from the Void

What Green Beacons from the Kuiper Belt Mean

MU69 New Horizons next target
The Kuiper Belt object 2014 MU69 may be a double-lobed object or possibly a more spherical one with a chunk missing. The New Horizons spacecraft will fly by this object in January 2019. Courtesy JHU/APL/SWRI/Alex Parker

Every Monday, the spacecraft team for the New Horizons mission “listens” for a signal from their fast-moving spacecraft. This grand-piano-sized probe is on its way to another object in the Kuiper Belt, called MU69. These beacons are important because they are the only signal the team gets while New Horizons is in hibernation. That means most (if not all) of its systems are powered down or in very limited-use mode. It conserves energy, equipment, and wear and tear on the electronics on the spacecraft while it’s en route to its next target.

Once the beacon is received, the team can get back to work on their planning. Alan Stern, PI of the team, usually tweets a “green beacon” announcement, letting the rest of the world know all is well. He described the beacon process in a “PI’s Perspective” blog entry in 2008.

What New Horizons Beacon Tones Mean

There are several beacon tones that New Horizons could send. Green is the best—it means that everything’s right on the nominal, that nothing is wrong with the sleeping spacecraft. It’s the equivalent of a text message saying, “Doing good, talk next week”. Anything not-green, particularly if it’s a red beacon tone, means there is (or could be) a problem. Luckily, throughout the mission, the green beacons outnumber the reddish ones. Right now the spacecraft is sleeping happily and will do so until mid-year 2018 when flyby operations start up again.

In the meantime, while New Horizons may be slumbering its way across the inner limits of the Kuiper Belt, its scientists and technical support staff members are busy rehearsing the next flyby, which will take place January 1, 2019. At that point, Earth and the spacecraft will be in the neighborhood of 43 astronomical units apart. That’s 6,432,708,440 kilometers, or 3,997,099,712 miles. Signals from the flyby will take six hours to get to Earth, making round-trip communication a 12-hour-long “conversation”.

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