Why The Equinox Can Make Your Credit Card Fail
Twice a year, people listening to signals from satellites in geostationary orbit face a problem known as a solar outage, a solar transit, or sun fade. Around the spring equinox, the Sun approaches the equator from the south, as the north gets ready for spring. In the fall, near the autumnal equinox, the Sun appears to move back below the equator. During these times, it comes into the view of Earthbound satellite dishes directed at geostationary satellites positioned some 22,000 miles above the equator.
When a ground receiver, the satellite it’s looking at, and the Sun all line up, the radiation from the Sun can temporarily overwhelm the satellite receiver. Think of it like when you’re driving on a westbound road close to sunset, and you’re staring straight into the setting sun—it gets hard to read the road signs.
The effect is temporary: a maximum of 12 minutes at any given location for several days in a row. But it can affect everything from a satellite TV dish to credit card processing at your local gas station—even public radio stations receiving live programming over the satellite network.
SciFri’s Charles Bergquist talks with Chris DeBoy, who teaches a course in satellite communications at the Johns Hopkins University (and is also the RF communications lead for the New Horizons Mission to Pluto, and the Space Engineering Branch Manager at the Johns Hopkins Applied Physics Laboratory), about the advantages and disadvantages of geostationary satellites, and what can be done to minimize the impact of solar outages. They are joined by MaryJane Peters, technical operations chief at KAZU in Monterey, California, who describes the effect the seasonal outages have on station operations.
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Chris DeBoy teaches a course in satellite communications at the Johns Hopkins University, and is also RF communications lead for the New Horizons Mission to Pluto and Space Engineering Branch Manager at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
MaryJane Peters is the technical operations chief at KAZU in Monterey, California.
IRA FLATOW: This is Science Friday. I’m Ira Flatow. This week marked the start of meteorological spring. But if you ask an astronomer, the true start of spring is that until the equinox on the 20th. And we, baseball fans mark spring training hopefully this year, as our spring marker. Here’s SciFri’s Charles Bergquist with another Rite of Spring.
CHARLES BERGQUIST: Ah, spring, flowers poking up, trees starting to bud, and satellite receivers having problems.
MARY JANE PETERS: You’re getting interference. So it’ll be some noise like that. And then eventually, it’ll completely be silent. And then it’ll slowly come back.
CHARLES BERGQUIST: That’s Mary Jane Peters, technical operations chief at KAZU in Monterey, California.
MARY JANE PETERS: It would vary anywhere from a minute to three minutes. We could figure it out. And it was pretty close to right on time. I would be running the board in the midday. So I was always ready for it.
SPEAKER 4: Attention KAZU listeners, we are experiencing a solar outage.
CHARLES BERGQUIST: It’s a phenomenon that affects people listening to signals from satellites in geostationary orbit. It’s called a solar outage, a solar transit, or sun fade. And it happens without fail, twice a year, right around now, in fact.
CHRIS DE BOER: During what we call the spring and fall equinoxes, the sun approaches the equator from the south as the north gets ready for spring. And then in the fall as well, the sun is dropping down from the north into the equator and below as we head to winter in the northern hemisphere.
CHARLES BERGQUIST: Chris De Boer teaches a course in satellite communications at the Johns Hopkins University. He’s also the RF communications lead for the New Horizons mission to Pluto and the space engineering branch manager at the Johns Hopkins Applied Physics Laboratory.
CHRIS DE BOER: But at this time viewed from the Earth, the satellite out in geostationary orbit right behind it is the sun. And the sun is not just emitting energy in the visible range. It also emits energy in microwave frequencies. And microwave frequencies are used by communication satellites.
CHARLES BERGQUIST: He explained why these geostationary satellites are so attractive.
CHRIS DE BOER: If you go out about 22,000 miles around the Earth and you put the satellite’s orbit in the equator, it turns out that the satellite is orbiting the Earth at the same rotation rate that the Earth is spinning. And so the satellite, in this special orbit we call the geostationary orbit, stays fixed in the sky from wherever you are on the Earth’s surface, which makes it great for lots of things.
CHARLES BERGQUIST: For one, from that distance, a satellite can see one entire half of the Earth at a time. For another, it means that a listener on the ground won’t have to constantly re-aim their satellite dish to follow the satellite.
CHRIS DE BOER: The geostationary belt is some of the most valuable real estate in space. Because each satellite is assigned a longitude basically, in that belt. And every longitude is occupied with companies wanting to provide communication services to people here on Earth.
CHARLES BERGQUIST: If you’re listening to a live national broadcast on your public radio station, there’s a good chance it’s been delivered to the station from a geostationary satellite called Galaxy 16, positioned at 99 degrees west longitude. But during these twice a year outages if you draw a line directly from the station satellite dish to Galaxy 16, the sun shows up right behind it. Think of it like when you’re turning onto a west bound road close to sunset and you’re staring straight into the setting sun. It gets hard to read the road signs.
CHRIS DE BOER: The ground station are the eyes of the satellite operators looking up at the satellites with very powerful binoculars, so to speak. And you can imagine, if the sun gets in your eyes, well, you don’t like it. The sun’s noise power can be hundreds of times more than the background noise power in a typical satellite link. While the sun is behind or near that satellite, it’s going to swamp the signal. And you basically lose contact for that time.
Mercifully, the sun although, is relatively small in space. It’s about half a degree in diameter. And it moves one diameter about the 1/2 degree every two minutes or so. So the maximum amount of time for these outages is limited to about 12 minutes and sometimes less.
CHARLES BERGQUIST: Any given location on Earth will have to deal with these momentary outages for a stretch of a few days at a time. And it’s not just public radio stations. These outages affect any kind of satellite receiver looking at a geostationary satellite, from satellite TV to phone communications with distant areas.
SPEAKER 4: There was a surprising number of industries that use satellite on a regular basis, government services, military services, and industry commercial service. If you go to the gas station, and a lot of the transactions are beamed up through very small aperture terminals to geostationary satellites, things you may not think about. But satcom, satellite communications touches us multiple times in every day.
CHARLES BERGQUIST: So how do you deal with the problem?
CHRIS DE BOER: Well, we can’t turn off the sun. That would be a bad thing for everybody. A couple of things that one can do if there are additional satellites in the neighboring region that your satellite operator has access to, you can shift your signals to that satellite in a neighboring slot in a geostationary belt. And while your prime satellite is in a sun outage, you can get your service from that other satellite and then flip it back. In today’s world, terrestrial return, so getting data off of the internet or through some specialized feed, during these times is a good backup.
CHARLES BERGQUIST: Mary Jane Peters says at her station, she sees a couple of workarounds. If a station is playing local programming or something that’s prerecorded, you’d never hear a problem. New receivers at stations can start playing an internet stream in the event of an outage. So you might hear a little glitch, your clocks might seem off, or you might not even notice.
Stations can also download episodes of a show in advance or have some music standing by to cover any uncomfortable silence. And in the public radio world, there’s always another workaround.
MARY JANE PETERS: We experienced these outages. It seems to happen around our pledge drive. So it gives us an opportunity to break away from programming anyway, whether we like it or not and ask for help from our listeners.
CHARLES BERGQUIST: Another rite of spring– for Science Friday, I’m Charles Bergquist.