Pulsar Navigation: Beacons in the Darkness

by Paul Gilster on January 17, 2013

In a world of search engines, GPS and always-on connectivity, I sometimes wonder what’s happening to serendipity. Over the years, I’ve made some of my best library finds by browsing the stacks, just taking some time off and walking around scanning the book titles. Odd ideas show up, mental connections get forged, and new insights emerge. Targeted searching is generally what we do (think Google), but never forget the value of the odd juxtaposition that comes from random wanderings. Too much targeting can produce tunnel vision.

For that matter, have you noticed how hard it is to get lost these days? I’m just back from Oakland, where Marc Millis and I went for interviews with the History Channel in the gorgeous setting of Chabot Space & Science Center in the hills above the city. The view on the drive up was spectacular, and my guide used an iPad to continually update our position on the map, so getting lost was impossible. My son Miles drove up from his home south of San Francisco and after the interview he drove me back to the hotel, where we met Marc for dinner at a nearby restaurant. All the way down from Chabot, he was keeping one eye on the smartphone he was using for navigation, flawlessly threading his way through streets that were new to him.

Maybe someday the whole idea of getting lost and running into the unexpected will seem quaint — we’ll know where we are at every moment. I can see the value in that even though I enjoy occasionally taking random streets just to see where they lead and surprising myself. Watching city lights under flawless night skies from my window on a Southwest flight last night, I was musing about navigation and stars and remembering being taught the now antiquated art of celestial navigation by a gruff flight instructor who used to do it for real back in the 1930s, when he was flying biplanes and knew how to read the stars like most of us read a roadmap.

Of course, navigating among the stars is going to demand much more precision than this when we’re talking about actual interstellar missions. This morning, pre-coffee and still jet lagged, I was looking through some saved links and ran across a BBC story called Dead Stars to Guide Spacecraft, recounting the work of Werner Becker (Max-Planck Institute for Extraterrestrial Physics). Becker’s team has been studying positioning methods for spacecraft using the X-ray signals sent by pulsars, rapidly rotating and extremely precise sources of emissions.

PSR-Nav_2

Pulsar beams are tightly focused and sweep around the sky as the pulsar spins. What we’re looking for is a way to place a spacecraft in a three-dimensional frame, taking advantage of the sheer regularity of pulsars by measuring the time of arrival of their pulses, which offer a stability akin to that of atomic clocks. Carrying the right equipment, our space voyagers should be able, in Becker’s view, to position themselves within five kilometers anywhere in the galaxy. As Becker tells the BBC’s Jonathan Amos, “These pulsars are everywhere in the Universe and their flashing is so predictable that it makes such an approach really straightforward.”

Image: Artist’s impression of ESA’s Rosetta spacecraft, imagined as if it navigated in deep space using pulsar signals. Credit: ESA/MPE.

The accuracy of pulsars and their characteristic time signatures amount to a method of navigation that some are likening to GPS satellites and their signals here on Earth. The needed miniaturization for making X-ray detection practical as a navigation tool is on the way, and Becker believes that within fifteen to twenty years, lightweight X-ray mirrors for navigation devices based on pulsar methods will be available for testing. Their advantages may become quickly apparent if the technology is sound. Right now the positioning errors for the Voyager probes amount to several hundred kilometers, using Earth-based antennae and communications travel times to make the call.

I see that the UK’s National Physical Laboratory and the University of Leicester are working with the European Space Agency to investigate pulsar methods, noting that traditional ground-based space navigation is over-taxed, only able to support a limited number of spacecraft at a time. A future pulsar technology would allow spacecraft to handle navigation chores onboard.

So the benefits are near-term but could reach deep into the future. I like Werner Becker’s enthusiasm, as found in this Royal Astronomical Society news release: “Looking forward, it’s incredibly exciting to think that we have now the technology to chart our route to other stars and may even be able to help our descendants take their first steps into interstellar space.” Indeed. While I will always extoll the pleasures of serendipity, I wouldn’t want to be traveling at random on an interstellar journey, just as I was glad last night that Southwest’s crew was keeping an eye on their gauges while I mused on dark landscapes and distant lights as I crossed the continent.

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Anthony Mugan January 17, 2013 at 11:52

What a fascinating idea. On reading this I began to wonder how such EM signals might look if (and that ‘if’ should probably be in italics, bold and underlined!) something along the lines of an Alcubierre warp metric, or something along those lines such as being discussed over the years by Dr Harold White, should ever come to pass.

Presumably a huge amount of blue shifting from perspectives facing forward (compressed space time) and red shifting from the rear facing perspective?..but is that too simple. Any thoughts on how a beam of radiation would change (and our perception of it shift) as it moved through the modified region of space time, including the ‘flat’ centre part.

Anthony Mugan January 17, 2013 at 11:54

Actually – my rather dim initial thought on which way the red and blue shifting would work may well be wrong…but now my head hurts!

Winchell Chung January 17, 2013 at 14:33

In The Star Trek Maps (1980) they use this concept.

In Star Trek, they have access to FTL ships. So all the pulsars can be visited and each “current” frequency can be determined. The pulsar frequency decays at a fixed rate. We have no FTL ships so we cannot use this method.

A star ship can observe a navigation pulsar’s visible frequency, and subtract the “current” frequency to determine the amount of decay. The decay rate yields the distance to the pulsar.

This means the starship is located on the surface of a sphere of that radius centered on that pulsar. Repeat with two more pulsars and the intersection of the three spheres yields the starship’s position.

Tarmen January 17, 2013 at 15:37

Navigation between the stars. It’s good that we’ll soon have this one problem solved. But it will do us no good knowing exactly where we are if we run into uncharted rocks and pebbles, like reefs in the ocean. We’ll need Google Galaxy. We must travel at high speeds with confidence that we’ll reach our destination.

Michael January 17, 2013 at 17:04

An issue with Pulsar navigation is that the beams are fairly narrow, maybe one or two light years wide depending on the distance. As we venture further away some beacons will be lost, still a great method of finding our orientation in space for free.

Paul Titze January 17, 2013 at 19:16

Hi Paul,

Interesting article, any method of fixing one’s interstellar position that does not rely on Earth is a must. There’s another method that I looked into that relies on more straightforward sextant angles between stars measured from the starship (not as accurate as pulsar navigation) but is an alternative:

http://vixra.org/abs/1106.0053

A good mariner never relies solely on one position fixing method (even GPS).

Cheers, Paul Titze.

A. A. Jackson January 17, 2013 at 21:18

The International Celestial Reference Frame (ICRF), used by all astronomers… even JPL’s Planetary Ephemeris which trumps all such, uses the ICRF.
(Some people know the ICRF from of the J2000 system.)
(It is a reference coordinated between the International Astronomical Union, the US Naval Observatory and International Earth Rotation Service.)
The ICRF is based on the position of extra galactic sources, especially quasars. The origin of right ascensions is defined by fixing
the right ascension of 3C 273B.
Quasars are extremely distant, bright, and small in apparent size.
Because they are so distant, they are apparently stationary to our current technology. They are the most useful reference points in the sky.

Nik January 18, 2013 at 11:18

“I was alone in the confidence of the stars.”

Ron S January 18, 2013 at 12:08

I’m still a little unclear on how one goes about getting so lost in the first place that one needs these techniques of establishing one’s spacetime position. If nothing else we can still only dream of having to deal with such a vexing problem.

And if you do get really, really lost you can always measure the CMB temperature. ;-)

Mike January 18, 2013 at 15:42

To Nik.
Are you quoting Amelia Earhart?

Mike January 18, 2013 at 16:07

I think interstellar navigation should be a breeze. But as Tarmen mentions the danger lies with the uncharted, unseen objects. At anything close to a large fraction of c even a grain of dust is big trouble. Try to detect and avoid the larger objects and have enormous front facing shields to deal with the smaller objects. Like using an entire asteroid as a shield. Energy, energy.
Would something like an Alcubierre drive warp obstacles out of the way of our starship? That would be a lucky physics break if true.
I wonder if the difficulty of interstellar travel, perhaps proving even more difficult as we learn more about space and physics, could prove to be the answer to Fermi’s paradox.

ljk February 12, 2013 at 10:30

http://www.technologyreview.com/view/510886/einsteinhome-project-discovers-24-new-pulsars-in-old-data/

Einstein@Home Project Discovers 24 New Pulsars in Old Data

The Physics arXiv Blog

February 11, 2013

Einstein@Home Project Discovers 24 New Pulsars in Old Data

Astrophysicists apply 17,000 CPU core years of number crunching to a 15-year old data set and find 24 new pulsars

Einstein@Home is a citizen science project that allows anybody to donate computer processing time to the search for gravitational waves in experimental data. In recent years, the project has also begun to analyse the data from radio telescopes hunting for the signals from rapidly spinning neutron stars or pulsars.

Today Einstein@Home announces the discovery of 24 new pulsars, six of them members of binary systems. That’s a significant feat but what’s even more impressive is that the new pulsars have come from an old data set gathered by the Parkes Radio Telescope in Australia back in the 1990s.

This data set has already been cut and diced by astrophysicists in several different ways. In the process, they’ve found some 800 new pulsars. And yet there is still gold in them thar hills, say Benjamin Knispel at the Max Planck Institute for Gravitational Physics in Germany and a number of pals.

These guys point out that previous number-crunching techniques have all suffered important limitations. One problem in particular is related to the Doppler effect which changes the frequency of a pulsar signal moving towards or away from us.

This effect changes very rapidly for pulsars in short binary orbits and tends to confuse standard analyses. In fact, no previous approach has been able to identify binary pulsars with an orbital period of less than 3 hours.

The Einstein@Home team have got around this thanks to the sheer brute force of the computing power at their disposal. This allows them to compare each potential signal against a number of circular orbit templates to see whether it fits, a process that is powerful but computationally intensive.

The task has indeed been huge. In the late 1990s, astronomers used the Parkes 64-metre radio telescope to make 3000 35-minute recordings of radio signals from the Milky Way, a project that produced some 4 terabytes of data.

Having found many pulsars already in this data, computational astrophysicists noticed that the number of binary and short period pulsars was disportionately low. This suggested that the analyses must be missing some interesting objects out there.

Now Knisel and co say they’ve found at least some of them using the Einstein@Home computational resources. “The method…is only possible with the computing resources provided by Einstein@Home,” they say. In total, it provided 17,000 CPU core years to do the number crunching.

The newly discovered pulsars are important. Binary pulsar systems, in particular, create and experience huge distortions in space time and so are important laboratories for testing general relativity and alternative theories of gravity.

Binary pulsar systems that spiral together and merge should also generate gravitational waves that can be detected on Earth. So these sightings should help astronomers estimate the total number in the galaxy and therefore the likelihood of seeing their gravitational wave signals on Earth.

Despite the success of the new approach, Knispel and co say that it is still computationally limited and cannot detect pulsars with frequencies higher than 160Hz. “More than a decade after the completion of the [Parkes Survey], the data still cannot be analyzed with the highest possible sensitivity to relativistic pulsars,” they admit.

So watch this space–there’s still more to be mined from the Parkes data. But don’t hold your breath!

Ref: http://arxiv.org/abs/1302.0467: Einstein@Home Discovery of 24 Pulsars in the Parkes Multi-Beam Pulsar Survey

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