December 03, 2012
Voyager 1 Nears Interstellar Space

The absolutely most amazing thing of all about this story: 35 years after it was launched Voyager 1 is still sending back data and we are able to receive its signal even though it is nearing interstellar space where the sun's heliosphere stops. If we built a space probe to send beyond the solar system today would we use technology that lasts as long?

"Although Voyager 1 still is inside the sun's environment, we now can taste what it's like on the outside because the particles are zipping in and out on this magnetic highway," said Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena. "We believe this is the last leg of our journey to interstellar space. Our best guess is it's likely just a few months to a couple years away. The new region isn't what we expected, but we've come to expect the unexpected from Voyager."

Since December 2004, when Voyager 1 crossed a point in space called the termination shock, the spacecraft has been exploring the heliosphere's outer layer, called the heliosheath. In this region, the stream of charged particles from the sun, known as the solar wind, abruptly slowed down from supersonic speeds and became turbulent. Voyager 1's environment was consistent for about five and a half years. The spacecraft then detected that the outward speed of the solar wind slowed to zero.

The intensity of the magnetic field also began to increase at that time.

Voyager data from two onboard instruments that measure charged particles showed the spacecraft first entered this magnetic highway region on July 28, 2012. The region ebbed away and flowed toward Voyager 1 several times. The spacecraft entered the region again Aug. 25 and the environment has been stable since.

"If we were judging by the charged particle data alone, I would have thought we were outside the heliosphere," said Stamatios Krimigis, principal investigator of the low-energy charged particle instrument, based at the Johns Hopkins Applied Physics Laboratory, Laurel, Md. "But we need to look at what all the instruments are telling us and only time will tell whether our interpretations about this frontier are correct."

So where does Voyager get the electricity to send a signal back to Earth? plutonium-238 nuclear power. The US stopped producing it in 1992. But this has been restarted to use in future space probes.

What I'd like to know: Could we build a probe with today's technology that would use nuclear propulsion to get into interstellar space much more quickly? 35+ years to get a probe to interstellar space is just too long.

Share |      Randall Parker, 2012 December 03 09:51 PM 

Ronald Brak said at December 4, 2012 6:31 AM:

Ion drives have been used on four space probes so far and they could do the job quicker and faster than chemical rockets, given equal engine and propellent mass. So far they have all been solar powered as radioisotope thermal generators are quite heavy. Modern solar cells may have the advantage all the way out to Saturn. But it may be possible that a powered gravity assist at Jupiter using a chemical rocket would be even faster given todays technology, as a powered gravity assist requires a lot of thrust in a short period of time which is exactly the opposite of how an ion drive works.

philw1776 said at December 4, 2012 12:48 PM:

Recently there's been activity on small low weight fission reactors with stirling engines to generate electricity. Couple this with an ion drive and a much faster constant thrust mission to the Kuiper Belt and Oort cloud beyond would be feasible. With just 0.001 G acceleration in 4 months the craft would be traveling at a speedy 100 Km?sec

Engineer-Poet said at December 4, 2012 8:40 PM:

If your only goal is to pass through distant regions without any great specificity, wouldn't a Magsail or the like be the propulsive method of choice?  Just hitch a ride on the stream of the solar wind and let it take you where it goes.

Randall Parker said at December 4, 2012 8:56 PM:


Currently Voyager 1 and 2 are going about a sixth or maybe a seventh of the 100Km/sec speed. But they were going orders of magnitude faster when leaving Earth orbit.

Voyager 1's radioisotopic thermoelectric generators are expected to still be putting out enough power to run some subsystems on Voyager until the year 2025, 48 years after departure.


I think fast probes would make space probes a lot more appealing to taxpayers. They've get faster gratification on their money spent.

philw1776 said at December 5, 2012 3:41 PM:

They were NOT going orders of magnitude faster at launch. Launch velocity was under 15 Km/sec

Ronald Brak said at December 5, 2012 10:29 PM:

Apparently a suitably lightweight solar sail could catch up to voyager in 8 years, but only after first closely approaching the sun. I don't think we're up to building such a solar sail at the moment, but people are working on them. IKAROS is a solar sail probe that's cruising around the inner solar system now. It was designed to test out solar sails and doesn't have much in the way of instrumentation.

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