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The Voyager 1 spacecraft rocketed off our planet in 1977. It's now about 15 billion miles away. That's farther out than any other object made by humans. And the spacecraft still talks to Earth. But as NPR's Nell Greenfieldboyce reports, lately its messages don't make any sense.
NELL GREENFIELDBOYCE, BYLINE: Voyager 1's problem started a few months ago, back in mid-November. Suzanne Dodd is the Voyager project manager.
SUZANNE DODD: It basically stopped talking to us in a coherent manner.
GREENFIELDBOYCE: The spacecraft is just sending back alternating ones and zeros. Her team has tried the usual tricks to try to reset things with no luck. It looks like there's a problem with the onboard computer that takes information and packages it up to send home. Dodd says this technology is primitive compared to, say, a car key fob.
DODD: The button you press to open the door of your car - that has more compute power than the Voyager spacecrafts do. You know, it's remarkable that they keep flying and they and that they've flown for 46-plus years.
GREENFIELDBOYCE: Voyager 1 and its twin, Voyager 2, have outlived many of those who designed and built them. To try to fix Voyager 1's current woes, the dozen or so people on Dodd's team have had to pore over yellowed documents and old mimeographs.
DODD: They're doing a lot of work to try and get into the heads of the original developers and figure out why they designed something the way they did and what we could possibly try that might give us some answers to what's going wrong with the spacecraft.
GREENFIELDBOYCE: She says they have a list of things to try. Since their go-to approaches haven't worked, they'll have to take measures that are more bold and risky. This could take weeks, months of sending commands to the spacecraft. Voyager 1 is so distant, it takes almost a whole day for a signal to travel out there, then a whole day for its response to return.
DODD: So we'll keep trying, and it won't be quick.
GREENFIELDBOYCE: In the meantime, Voyager 1's discombobulation is a bummer for researchers like Stella Ocker. She's with Caltech and the Carnegie Observatories.
STELLA OCKER: We haven't been getting science data since this anomaly started, and what that means is that we don't know what the environment that the spacecraft is traveling through looks like.
GREENFIELDBOYCE: That environment isn't just empty darkness. There's gases, dust, cosmic rays. Only the twin Voyager probes are far away enough to sample this cosmic stew, and only Voyager 1 is still able to take the particular measurements she needs.
OCKER: So the science that I'm really interested in doing is actually only possible with Voyager 1.
GREENFIELDBOYCE: Now, she wasn't even born when the Voyagers launched. For other scientists who've been with the Voyager program from the start, Voyager 1 is like an old, dear friend who suddenly has been hit with a terrible illness.
TOM KRIMIGIS: Well, frankly, I'm very worried.
GREENFIELDBOYCE: Tom Krimigis is with the Johns Hopkins University's Applied Physics Lab.
KRIMIGIS: My motto for a long time was 50 years or bust (laughter), but we're sort of approaching that.
GREENFIELDBOYCE: So even if this current crisis gets solved in a couple of years, the ebbing power supply will force managers to start turning off science instruments one by one. The very last instrument might keep going until 2030. After that, Krimigis says both of these legendary space probes will basically become space junk.
KRIMIGIS: Pains me to say that.
GREENFIELDBOYCE: And while the spacecraft will keep moving outward, each carrying a set of golden records that have recorded greetings in many languages, Krimigis doubts that any alien will ever stumble across Voyager and have a listen. Nell Greenfieldboyce, NPR News.
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