Why couldn't the crew of the Phoenix use known pulsars to determine their position?

Question

In C J Cherryh's novel Visitor (17th novel in the Foreigner series), it's revealed that:

All the events in the series so far occurred much closer to our solar system than we thought, and the starship Phoenix certainly never left the Milky Way. (The novels don't mention this possibility, but this question is the reason why I considered it.) The other species with whom the kyo are at war are humans who are unaware of the human colony on the atevi homeworld, and kyo space lies between human space and the atevi homeworld.

In real life, we made a point of engraving the solar system relative vectors of known pulsars on the Pioneer plaque and the Voyager records on the grounds that they have distinctive electromagnetic signatures and could be used to locate the solar system.

So why couldn't the crew of the Phoenix use the known pulsars to determine their position?

Answer 1

They tried. In Foreigner, we have the navigator McDonough:

He started looking for pulsars. When you were out of short yardsticks you looked for the long ones, the ones that wouldn’t lie, and you started thinking about half-baked theories, like cosmic macrostructures, folded interfaces, or any straw of reason that might give a mind something to work on or suggest a direction they’d gone or offer a hint which of a hundred improbables was the truth.

We're led to believe he never found it — that Phoenix is galaxies or universes or millennia away from its starting point — but on close reading, the text is ambiguous. The pilot Taylor, some months later:

Goldberg talked, then, saying how they were clear to hell and gone from Earth and Sol, that they still didn’t know how they’d gotten there…

In Visitor Bren tells us: “Jase claimed the original accident had wiped a lot of the navigation, the maps, the charts.” (Which doesn’t exactly square with what we’re given from McDonough’s or Taylor’s viewpoint in Foreigner.)

It's also suggested both that the location of human space was “lost from Phoenix records hundreds of years ago” and, contradictorily, that it might still be in records available only to the senior captain. I suspect we’ll find out in book eighteen.

Update (spoiler):

Ms. Cherryh quickly tied off the “wait, what? the kyo are fighting humans??” plot thread in a couple of throwaway scenes and has now gone back to Ajuri dynastic shenanigans. We may never know.

Answer 2

I'm not familiar with the series, but perhaps the information was forgotten. Or perhaps the author just doesn't know about pulsars.

Also it's likely that navigation by pulsar is more difficult than was originally assumed. Pulsars emit a narrow beam which sweeps around in a circle as the star rotates; you can only see the pulsar pulse when you are in the path of the beam. It's hard to say without visiting a number of nearby star systems and measuring, but it's quite possible that you wouldn't have to travel very far before you couldn't see enough of these pulsars to get a fix on your position. On the other hand, we know about more than 14 pulsars now, so maybe that wouldn't matter.

Answer 3

If a spaceship travels through a space warp into an unknown region of space or gets lost some other way the navigators should look for familiar objects. Fortunately space is transparent. Very transparent. Very, very, very transparent. The thinnest and most transparent vacuum made on Earth is like a sheet of lead compared to the densest, dustiest part of interstellar space.

From a clear spot you can see forever, so to speak.

So the navigators should look for bright objects in the visible and other parts of the electromagnetic spectrum. They should take the spectra of the 10 or 100 objects that are brightest in each of various bands of visible light, radio, infrared, ultraviolet, X Rays, gamma rays etc., and compare them to the spectra of the 10 or 100 brightest objects in those bands as seen from Earth or their home world wherever it is.

The hope will be that you haven't traveled too far from known space and some at least of the objects observed in the new location will match those on the list as seen from the home world. All you need to do is observe three known objects and then from differences in their apparent magnitudes and the angles between them as seen in your new location and as seen from your home world you can calculate your new position. Modern astronomical instruments that are vital for interstellar navigation can measure such angles to incredible precision.

And the 10 or 100 brightest objects visible in any band of the spectrum from any location will usually be at a great variety of distances. Some just a few light years away, some hundreds, some tens of thousands, some millions of light years away, some hundreds of millions, etc. The ones that are far enough away will still be among the brightest objects in that band no matter where you go within our galaxy.

So you can be Lost in space in the sense of not having a way to get home, but so long as you don't jump millions of light years or something you can't get Lost in space in the sense of not being able to figure out where you are.