Millisecond Pulsars for Starship Navigation

by Paul Gilster on June 1, 2009

If we can use GPS satellites to find out where we are on Earth, why not turn to the same principle for navigation in space? The idea has a certain currency — I remember running into it in John Mauldin’s mammoth (and hard to find) Prospects for Interstellar Travel (AIAA/Univelt, 1992) some years back. But it was only a note in Mauldin’s ‘astrogation’ chapter, which also discussed ‘marker’ stars like Rigel (Beta Orionis) and Antares (Alpha Scorpii) and detailed the problems deep space navigators would face.

The European Space Agency’s Ariadna initiative studied pulsar navigation relying on millisecond pulsars, rotating neutron stars that spin faster than 40 revolutions per second. The pitch here is that pulsars that fit this description are old and thus quite regular in their rotation. Their pulses, in other words, can be used as exquisitely accurate timing mechanisms. You can have a look at ESA’s “Feasibility study for a spacecraft navigation system relying on pulsar timing information” here (download at bottom of page).

Pulsars have huge advantages. A deep space satellite network to fix position is a costly option — it doesn’t scale well as we expand deeper into the Solar System and beyond it. Autonomous navigation is clearly preferable, tying the navigation system to a natural reference frame like pulsars. The down side: Pulsar signals are quite weak and thus put demands upon spacecraft constrained by mass and power consumption concerns. So there’s no easy solution to this.

But several readers (thanks especially to Frank Smith and Adam Crowl) have pointed out a recent paper by Bartolome Coll (Observatoire de Paris) and Albert Tarantola (Institut de Physique du Globe de Paris) that speculates on a system based on four millisecond pulsars: 0751+1807 (3.5 ms), 2322+2057 (4.8 ms), 0711-6830 (5.5 ms) and 1518+0205B (7.9 ms). The origin of the space-time coordinates the authors use is defined as January 1, 2001 at the focal point of the Cambridge radiotelescope where pulsars were discovered in 1967. Thus, the paper continues:

…any other space-time event, on Earth, on the Moon, anywhere in the Solar system or in the solar systems in this part of the Galaxy, has its own coordinates attributed. With present-day technology, this locates any event with an accuracy of the order of 4 ns, i.e., of the order of one meter. This is not an extremely precise coordinate system, but it is extremely stable and has a great domain of validity.

If these numbers are correct, they represent quite a jump over the ESA study cited above, which worked out the minimal hardware requirements for a pulsar navigation system and arrived at a positioning accuracy of no better than 1000 kilometers. ESA is working within near-term hardware constraints and discusses ways of enhancing accuracy, but the report does point out the huge and perhaps prohibitive weight demands these solutions will make upon designers.

The paper is Coll and Tarantola, “Using pulsars to define space-time coordinates,” available online.

{ 19 comments }

tacitus June 1, 2009 at 12:48

I suspect that by the time we will really need them, the systems will have been miniaturized to the extent that size and weight will not be too much of an issue.

Frank Neuperger June 1, 2009 at 15:02

Perhaps ESA was taking PDOP (Position Dilution of Precision) into consideration on a particularly sensitive axis

Paul Titze June 1, 2009 at 20:47

Studies on Interstellar GPS-like position fixing systems are ongoing, if you look at pulsars in the X-ray regime, these may be compact enough to be practical onboard a small starship, see the XNAV links at:

http://wizlab.com/marine/intstelnav.html

The more position fixing methods are available to the interstellar traveler, the better, a good mariner never relies just on one system to fix his position at sea…

Cheers, Paul.

Adam June 1, 2009 at 23:04

Hey tacitus,

I’m using Firefox and I can’t see any letters when I try to register for your ETI bulletin board and when I listen to the letters, the registration doesn’t accept them. What’s going on?

Ron S June 1, 2009 at 23:13

I read the paper (it’s short, in length and detail). I don’t see much point to it. They talk of determining position within the solar system primarily. We can do this now to exceptional accuracy, and so don’t need this method. Indeed, in space even dead reckoning can be highly accurate.

Their method requires keeping track of every pulse of the 4 pulsars (or other beacons) for the duration of the voyage. Unlike GPS, the pulses are not labeled so you have to keep track of them all. This is not achievable, although it would be fairly easy to recover from short duration signal loss and noise.

Because of this limitation, it would not work if, say, you were to drop out of a wormhole at some indeterminate spacetime locus within the galaxy and need to establish position. You wouldn’t even know what to look for. If you did, the direction to the beacons alone would tell you enough to go on for a coarse determination – you could then go on to a finer determination using more local sources.

Pulsars show some excellent short-term stability, but would seem to be unsuitable for the example of a position determination from a random locus since they are directional, vary up and down in rate over longer periods, are largely indistinguishable from other pulsars with similar periods, and may not even exist from a given locus since they have a limited lifetime.

Am I missing something?

george scaglione June 2, 2009 at 9:32

paul,it is always heartening to me to see studies being done they are i feel an important first step.i hope it will not be very long before we are out there with these systems in full swing! lol however what is really meant by “not long” is i fear in this case,say between 75 and 200 years. also, ron, i sure hope dropping out of a wormhole as you refer to it is also in the near future as i have described it but i kind of doubt it .although i myself have gone so far as to see our first starship by perhaps 2075! as i just told paul above – we had better get on with those studies!! thank you as always one and all , your friend george

tacitus June 2, 2009 at 13:14

Hey Adam — just saw your comment. Yeah, things are a bit messed up since I upgraded to a pre-release version of the BBS software. Silly me!! Sorry about that. Check back in the evening or tomorrow and I should have it straightened out!

Administrator June 2, 2009 at 15:19

Ron S wrote:

Pulsars show some excellent short-term stability, but would seem to be unsuitable for the example of a position determination from a random locus since they are directional, vary up and down in rate over longer periods, are largely indistinguishable from other pulsars with similar periods, and may not even exist from a given locus since they have a limited lifetime.

Am I missing something?

Ron, I agree in wondering whether this method could function as advertised. The ESA study seems much more realistic.

tacitus June 2, 2009 at 20:35

Adam, you should be able to register correctly now. Thanks for the heads-up. I’ve out of town at the moment, so I’m not paying as much attention to things as I should.

(I apologize to the CD team for using these messages for communicating with Adam off topic — I promise not to make a habit of it!)

Raziamizan Ramli June 3, 2009 at 3:31

From the comments I’ve read so far, it sems the problem would more likely be trying to differentiate between pulsar signals, as there’s no unique “code” to the pulses, only its regular timing. And you need better hardware and software filtration methods to ensure the pulsars we’re using really are the pulsars we need to use. So I guess this particular method would be backup for more classical (optical star sightings, beamrider navigation, etc) methods that we better understand, and therefore easier to translate into software and hardware we can cram into an interstellar vessel.
Plus, I may be wrong but wouldn’t the signals themselves be subject to red or blue-shifting if used on an interstellar vessel flying at some fraction of the speed of light? I’m thinking about the first quasars detected by radio back in the 1960′s.. as I recall, they were accelerating away from Earth (taken as granted to be a stationary platform) at about 15%-20% lightspeed, and had their spectra redshifted accordingly. So if we were navigating by pulsars, especially if we’re flying in the general direction towards or away from them, wouldn’t we have to compensate for blue or redshifting as well? I’m thinking that while we (humans) can do the compensating without too much trouble, it might not be so easy for an AI unit under relativistic flight with minimal or no guidance from ground control.
But one thing I believe would not be an issue would be signal detection, especially if we consider a case where the pulsars used to track the vessel’s position is off to port or starboard.. a starship flying at 15% lightspeed covers 45,000 kilometers (30,000 miles) a second, so I believe synthetic aperture antenna technology (I guess like synthetic aperture radar, but in passive instead of active mode) could be used so that even a tiny radio signal could be gathered and amplified without too much trouble.

Paul, thanks hosting this blog.. this website rocks!

Raziamizan Ramli
Kuala Lumpur @ Malaysia.

devicerandom June 3, 2009 at 11:14

Does such a system account for the relative motion of the pulsars?

george scaglione June 3, 2009 at 12:34

ok everybody and correct me if i am wrong…something i thought of since yesterday.wouldn’t you pretty much want/need to know where you were going to be before you dropped out of a wormhole!? heck what if that spot was at the center of a star! i know that this probably adds alot of technical nightmares but it seems the logical direction from which to proceed.thanks as always george

James M. Essig June 3, 2009 at 13:51

Hi Folks;

The simmilarity of using pulsars as navigational aids reminds me of the days when light houses were the main source of coastal waterways navigation route checks.

I have become really enamoured as of late with the concept of beam sails, stellar sails, and CMBR sails. One idea that especially intreagues me is the notion of a Casimar Force type of zero point energy sail wherein unbalanced casimar forces would preferentially push the craft in one direction.

There is something romantic about using the pulsars as natural light-houses in conjunction with interstellar sailing.

George;

I definately see the possibility of the first star ship by 2075. With enhanced medical science, I might be 113 years old and be able to see it launched. Better yet, would be the prevelidge of going into LEO and cracking a bottle of champaign on its bow on the day of its commissioning.

As I like to say, we neen a road map before attempting long journeys and that applies especially to the interstellar domain. I can see the future existence of emergency hard copy pulsar interstellar maps for redundancy and emergency navigation purposes.

Thanks;

Your Friend Jim

george scaglione June 3, 2009 at 15:26

jim thank you i agree this is a very important subject and lol,funny thing i would be 126!!! in 2075 – see that “first star ship”,i wonder?i envision that that ship will be slightly less than the enterprise however,but you have to begin someplace.good to hear from you george

Ron S June 3, 2009 at 17:02

Raziamizan,

Seems I was mostly wrong when I said that pulsars with similar periods are largely indistinguishable. The ESA paper Paul referenced addresses this. Seems that the pulse shape is unique to each pulsar, which they then fingerprint using a Fourier analysis and stochastic analysis. It’s an imperfect method and I can think of a variety of challenges to be overcome.

As to doppler, this isn’t too big an issue since the pulse is broadband.

The ESA paper goes into quite a lot of detail (92 pages!) and I only had time to lightly skim it. There are many, many challenges identified, and some solutions proposed. For example, the pulsar signal is well below the noise — under typical parameters they calculate S/N at -50 db — so you not only have to know its direction to have a chance of hearing it, the integration times could stretch into hours and the stochastic fingerprinting becomes unreliable.

If this interests you, go have a look at the article (see Paul’s link).

One general concern I have is that the pulsar method is not compared with alternatives. This gives the impression of a solution in search of a problem.

ljk August 18, 2009 at 11:35

Pulsar science with the Five hundred metre Aperture Spherical Telescope

Authors: R. Smits, D.R. Lorimer, M. Kramer, R. Manchester, B. Stappers, C.J. Jin, R.D. Nan, D. Li

(Submitted on 12 Aug 2009 (v1), last revised 17 Aug 2009 (this version, v2))

Abstract: With a collecting area of 70 000 m^2, the Five hundred metre Aperture Spherical Telescope (FAST) will allow for great advances in pulsar astronomy. We have performed simulations to estimate the number of previously unknown pulsars FAST will find with its 19-beam or possibly 100-beam receivers for different survey strategies.

With the 19-beam receiver, a total of 5200 previously unknown pulsars could be discovered in the Galactic plane, including about 460 millisecond pulsars (MSPs). Such a survey would take just over 200 days with eight hours survey time per day.

We also estimate that, with about 80 six-hour days, a survey of M31 and M33 could yield 50–100 extra-Galactic pulsars. A 19-beam receiver would produce just under 500 MB of data per second and requires about 9 tera-ops to perform the major part of a real time analysis.

We also simulate the logistics of high-precision timing of MSPs with FAST. Timing of the 50 brightest MSPs to a signal-to-noise of 500 would take about 24 hours per epoch.

Comments: 9 pages, 10 figures; accepted for publication in A&A

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Cite as: arXiv:0908.1689v2 [astro-ph.IM]

Submission history

From: Roy Smits [view email]

[v1] Wed, 12 Aug 2009 12:20:16 GMT (235kb)

[v2] Mon, 17 Aug 2009 09:08:40 GMT (235kb)

http://arxiv.org/abs/0908.1689

ljk August 20, 2009 at 12:39

Radio detection of LAT PSRs J1741-2054 and J2032+4127: no longer just gamma-ray pulsars

Authors: F. Camilo, P. S. Ray, S. M. Ransom, M. Burgay, T. J. Johnson, M. Kerr, E. V. Gotthelf, J. P. Halpern, J. Reynolds, R. W. Romani, P. Demorest, S. Johnston, W. van Straten, P. M. Saz Parkinson, M. Ziegler, M. Dormody, D. J. Thompson, D. A. Smith, A. K. Harding, A. A. Abdo, F. Crawford, P. C. C. Freire, M. Keith, M. Kramer, M. S. E. Roberts, P. Weltevrede, K. S. Wood

(Submitted on 18 Aug 2009)

Abstract: Sixteen pulsars have been discovered so far in blind searches of photons collected with the Large Area Telescope on the Fermi Gamma-ray Space Telescope.

We here report the discovery of radio pulsations from two of them. PSR J1741-2054, with period P=413ms, was detected in archival Parkes telescope data and subsequently has been detected at the Green Bank Telescope (GBT). Its received flux varies greatly due to interstellar scintillation and it has a very small dispersion measure of DM=4.7pc/cc, implying a distance of ~0.4kpc and possibly the smallest luminosity of any known radio pulsar. At this distance, for isotropic emission, its gamma-ray luminosity above 0.1GeV corresponds to 25% of the spin-down luminosity of dE/dt=9.4e33erg/s. The gamma-ray profile occupies 1/3 of pulse phase and has three closely-spaced peaks with the first peak lagging the radio pulse by delta=0.29P.

We have also identified a soft Swift source that is the likely X-ray counterpart. In many respects PSR J1741-2054 resembles the Geminga pulsar. The second source, PSR J2032+4127, was detected at the GBT. It has P=143ms, and its DM=115pc/cc suggests a distance of ~3.6kpc, but we consider it likely that it is located within the Cyg OB2 stellar association at half that distance. The radio emission is nearly 100% linearly polarized, and the main radio peak precedes by delta=0.15P the first of two narrow gamma-ray peaks that are separated by Delta=0.50P. Faint, diffuse X-ray emission in a Chandra image is possibly its pulsar wind nebula.

PSR J2032+4127 likely accounts for the EGRET source 3EG J2033+4118, while its pulsar wind is responsible for the formerly unidentified HEGRA source TeV J2032+4130.

Comments: accepted for publication in ApJ

Subjects: Galaxy Astrophysics (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

Cite as: arXiv:0908.2626v1 [astro-ph.GA]

Submission history

From: Fernando Camilo [view email]

[v1] Tue, 18 Aug 2009 20:12:14 GMT (1338kb)

http://arxiv.org/abs/0908.2626

ljk September 23, 2009 at 10:46

September 22, 2009

High School Student Discovers Strange Pulsar-Like Object

Written by Nancy Atkinson

A high-school student from West Virginia has discovered a new astronomical object, a strange type of neutron star called a rotating radio transient.

Lucas Bolyard, a sophomore at South Harrison High School in Clarksburg, WV, made the discovery while participating in a project in which students are trained to search through data from the Robert C. Byrd Green Bank Telescope (GBT).

Bolyard made the discovery in March, after he already had studied more than 2,000 data plots from the GBT and found nothing.

The project is the Pulsar Search Collaboratory (PSC), which allows students to do real scientific research by looking at data from the GBT, the largest radio telescope in the US.

Full article here:

http://www.universetoday.com/2009/09/22/high-school-student-discovers-strange-pulsar-like-object/

DW September 30, 2009 at 11:02

Using pulsars for navigation has already been patent by researchers at the Naval Research Lab (developers of GPS).

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