Voyager in the Doldrums

by Paul Gilster on December 15, 2011

One of the pleasures of writing Centauri Dreams is digging into a paper to look at it from various directions, as I did recently with Jim Benford’s work on cost-optimized beamed sails. Jim has been working on these concepts for a long time, and although I had originally intended to devote two days to his latest, the depth of his analysis led me to extend the discussion to a third day. That kind of focus invariably means I get behind in other stories, though, so I want to be sure to catch up with matters like the recent news about the Voyagers as they continue to exit our system.

I always point to the still functioning instruments of the Voyagers as an outstanding example of how we can build spacecraft for the long haul — these tough platforms show what can be done with careful design, and future craft fully optimized for even longer flights certainly seem practical. In this case, three instrument packages — the Cosmic Ray Subsystem, the Magnetometer and the Low Energy Charged Particle instrument — have told us that Voyager 1 is now in the doldrums of the Solar System, a place at the outer edge of the heliosphere where the solar wind has dropped to zero and the magnetic field is being compacted and intensified.

Image: Image: NASA’s Voyager 1 spacecraft has entered a new region between our solar system and interstellar space, which scientists are calling the stagnation region. In the stagnation region, the wind of charged particles streaming out from our sun has slowed and turned inward for the first time, our solar system’s magnetic field has piled up and higher-energy particles from inside our solar system appear to be leaking out into interstellar space. This image shows that the inner edge of the stagnation region is located about 113 astronomical units (10.5 billion miles or 16.9 billion kilometers) from the sun. Voyager 1 is currently about 119 astronomical units (11 billion miles or 17.8 billion kilometers) from the sun. The distance to the outer edge is unknown. Credit: NASA/JPL.

At the same time, Voyager has seen the energetic particles from within our system declining, now about half as abundant as they had been during the past five years, while the intensity of high-energy electrons from elsewhere in the galaxy is up 100-fold. All of this adds up to the approach of true interstellar space. Here’s Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator (JHU/APL):

“We’ve been using the flow of energetic charged particles at Voyager 1 as a kind of wind sock to estimate the solar wind velocity. We’ve found that the wind speeds are low in this region and gust erratically. For the first time, the wind even blows back at us. We are evidently traveling in completely new territory. Scientists had suggested previously that there might be a stagnation layer, but we weren’t sure it existed until now.”

Out of the doldrums and into interstellar space, where the winds are galactic — what an outcome for the twin craft launched in 1977. The new findings were announced at the at the American Geophysical Union’s fall meeting in San Francisco, and we can count on the Voyagers staying in the news for a while longer, as the boundary they’re crossing may take no more than a few months — or several years — to transit. Where next after Voyager? Ralph McNutt’s Innovative Interstellar Explorer is a robust take on an interstellar precursor mission that would be the logical follow-up, a mission study that could put instruments out to 200 AU and test numerous technologies. Let’s hope IIE finds the support it will need to turn it into actual hardware.

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{ 10 comments }

Tom W December 15, 2011 at 20:21

I’m all for a 200AU follow up mission but I think it really needs a big USP to get it funded. Voyager had the first fly-byes of the outer solar system, New Horizons has Pluto, this doesn’t really have that tbh. I also think that they should be taking into account the Falcon Heavy when looking at launch vehicles, which they don’t seem to be, as by the time this project lifts off it will have flown a good few times. It offers the capability to radically reduce transit time compared to the Delta 4 Heavy.

ljk December 16, 2011 at 10:28

The selling point for the IIE is that it is a major stepping stone/milestone on our way to the stars. Plus it will flyby Jupiter for a gravity assist and as we saw with New Horizons, new imagery and information will be obtained.

Has IIE been funded lately? I see on the NASA Web site for it that the first launch window is 2014. How far have they gotten with that probe?

Paul Gilster December 16, 2011 at 11:29

Larry, the 2014 launch window is now out of the question for IIE and a possible launch has been pushed well back, probably decades. But what I hope to do is get an update from Ralph McNutt, who is still actively working on the precursor concept. I’ll post what I learn here in the near future. You may have heard, too, that Ralph is an active player in the Project Icarus design.

ljk December 16, 2011 at 15:04

Thank you, Paul. I had the feeling that was the case but wanted to check just the same. I do not want IIE falling off the radar either with NASA or the public. Look at what we are getting with the Voyager probes, and they were not meant to last much after Saturn! So imagine what a probe deliberately designed to go much farther and longer can do!

Joy December 16, 2011 at 15:17

I don’t see how IIE would take imagery of Jupiter on flyby, the justification for putting an imaging system on the craft is pretty weak. Besides, Juno will image Jupiter ad infinitum.

200 AU is a pretty uninspiring target, Voyager is already 60% of that distance. Aiming a little higher, at the gravitational lens focus, has more appeal. Note that a craft which can travel 200 AU in 15 years can go 600 AU in 45 years, so greater spacecraft speed is not needed, just the kind of durability we are getting out of the Voyagers.

Tom W December 17, 2011 at 17:41

I don’t see how it is a major stepping stone to the stars (or more accurately the Alpha Centauri system, 200AU is > 0.01% of the distance). If you are designing an interstellar mission you would probably want to look at new propulsion systems which have to possibility to scale up down the road, thinking beamed propulsion, Vasmir (if you can get the power density sorted) etc. Also communication alternatives, thinking gravitational microlensing and possibly quantum entanglement could be trailed out to see if they could work in practice.

ljk December 18, 2011 at 1:27

There are other aspects and methods about Jupiter to be measured besides taking images. In addition, since there is no guarantee that a dedicated mission to that gas giant planet or its moons will exist by the time IIE flies by, any chance to examime the Jupiter system up close even for a brief time is better than none at all.

NS December 19, 2011 at 0:12

Even if the IIE had made the 2014 launch window, I would have been 88 years old when it achieved 200 a.u. I think the best chance of an interstellar precursor mission in our lifetimes is a sun-diving solar sail. Although it would take years to develop, once launched its flight time would be on the order of 5 years instead of the ~30 required for the IIE.

Brian December 20, 2011 at 12:54

Why not 1% of a light year? I think that has a ring to it that might resonate with people. That would only be about 3 times further than the 200 AU figure. It’s pretty encouraging and exciting to think we can actually do that; realistically get something out to a distance where it is in the percents of a light year and not just AUs or fractions of a percent.

ljk January 18, 2012 at 9:39

Voyager Instrument Cooling After Heater Turned off

http://www.jpl.nasa.gov/news/news.cfm?release=2012-017

January 17, 2012

Voyager Mission Status Report

PASADENA, Calif. — In order to reduce power consumption, mission managers have turned off a heater on part of NASA’s Voyager 1 spacecraft, dropping the temperature of its ultraviolet spectrometer instrument more than 23 degrees Celsius (41 degrees Fahrenheit). It is now operating at a temperature below minus 79 degrees Celsius (minus 110 degrees Fahrenheit), the coldest temperature that the instrument has ever endured.

This heater shut-off is a step in the careful management of the diminishing electrical power so that the Voyager spacecraft can continue to collect and transmit data through 2025.

At the moment, the spectrometer continues to collect and return data. It was originally designed to operate at temperatures as low as minus 35 degrees Celsius (minus 31 degrees Fahrenheit), but it has continued to operate in ever chillier temperatures as heaters around it have been turned off over the last 17 years.

It was not known if the spectrometer would continue working, but since 2005, it has been operating at minus 56 degrees Celsius (69 degrees Fahrenheit.) So engineers are encouraged that the instrument has continued to operate, even after the nearby heater was turned off in December. (The spectrometer is likely operating at a temperature somewhat lower than minus 79 degrees Celsius, or minus 110 degrees Fahrenheit, but the temperature detector does not go any lower.)

Scientists and mission managers will continue to monitor the spectrometer’s performance. It was very active during Voyager 1′s encounters with Jupiter and Saturn, and since then an international team led by scientists in France has been analyzing the spectrometer’s data.

This latest heater shut-off was actually part of the nearby infrared spectrometer, which itself has not been operational on Voyager 1 since 1998.

The Voyager spacecraft were built by NASA’s Jet Propulsion Laboratory in Pasadena, Calif., which continues to operate both. JPL is a division of the California Institute of Technology in Pasadena. The Voyager missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate in Washington.

For more information about the Voyager spacecraft, visit:

http://www.nasa.gov/voyager and http://voyager.jpl.nasa.gov

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

2011-017

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