You know what it’s much closer to? Navigating with the Omega system. This was a radio based system until 1997. There were 8 stations all broadcasting at frequencies around 10 kHz, low enough that the signal was audible if you connected a big antenna to some headphones without a radio receiver. They took turns broadcasting steady tones something like a second long, and there was no other navigation information encoded in them (as there is with GPS). Taking turns allowed for the fact that it’s hard to point a portable antenna at just one source when the wavelength is many miles. The phase relationship between all the signals was entirely what the navigation was based on, as it would be with pulsars (which run constantly but could be precisely aimed at to select just one).
I do want to point out that Ephemerides have added in portions of General Relativity, and that even the Voyager missions couldn’t have carried enough fuel to go on their “Grand Tour” without it. The parameterized post-Newtonian formalism or PPN formalism is one method that this has been accomplished.
In fact JPL created version DE432 to account the librations that were required for New Horizons.
https://ssd.jpl.nasa.gov/?ephemerides
While the pure Newtonian model is useful in many cases, and you can use brute force for correcting for the errors it is often impossible to meet mission goals and provide enough fuel to use that simpler model.
Remember that under a Newtonian model of gravity when you walk across your living-room Alpha Centauri needs to instantaneously feel that change in force. This superluminal instantaneous universe wide change in forces is essential to the Newtonian model and the man himself had serious problems with that fact.
Because most of that complexity is hidden in the JPL produced Ephemeris, or sometimes that complexity is handled through the Deep Space networks tracking and errors correction but every interplanetary mission post Mariner 6 and 7 have used data that moved well past the simple corrections method. Spacetime tells matter how to move; matter tells spacetime how to curve. And fuel for getting up to speed, and to accurately slow down to orbit another star will be a highly constrained resource.
While I hesitate to mention it, the reason that orbits seem to be some type of perpetual motion machine, providing acceleration in a circle for “free” is incorrect. The Earth is following the shortest path through space-time, and is following the geodesic which is the shortest (straightest) path through space-time and is not experiencing a gravitational force or acceleration. That is purely what is called a fictional force or a perceived force cased by a chosen frame of reference. But the straightest point in space is a segment of the hyperbole and not a straight line (just as it is on a globe)
One would need to most closely follow the geodesic on a long distance tip, and while one may use star location to detect that one couldn’t probably use a simple model to follow this path.
Note that any trip that was traveling at a speed that would be practical for human travel would also have the effects of Gamma increase greater than 1 in very significant ways.
Since Star Wars was invoked, let me state how celestial navigation is handled in Star Trek:
A Heading is a coordinate system for interstellar travel based on the center of the galaxy as the origin.
A Bearing is a coordinate system for in-system travel based on a more arbitrary origin…the ship itself (though possibly a planet or star).
Has anyone played with Celestia? It violates SR and GR in some genuinely dreadful ways, but it is still pretty cool. You get about 30-some ly away from here and our system is completely lost to view – in the visible spectrum, at least.
Simple question: How many stars are mapped, to any level of “accuracy?” (The proviso to notionally separate the question from OP per se.)
I can’t comment on the mythical hyper space model but there are estimates of ~10,000,000,000,000 icy objects in the Oort cloud that would give you trouble leaving our own solar system for the first light year or 100,000 AU.
They aren’t mapped and haven’t been observed outside of a rare comet visiting us from time to time.
The Wikipedia entry for star catalogs has numerous entries, here’s an example:
So two million stars, two thousand extragalactic objects for frames of reference.
Should also point out, if you are not familiar with it, the spectral sequence. based on size (generally) and age, stars give off characteristic spectra. Properly cataloged, these can help with identification; also help us distinguish between a red giant or O star (very bright) vs. a lesser star that happens to be very close.
So generally, unless your slower-than-light ship has been going for a million years or more, odds are you will be able to roughly position yourself - Andromeda and the Milky Way will look the same. If necessary, the globular clusters orbiting the galaxy can serve as rough timeclocks on that scale, with orbits measured in millions of years.
I’m assuming the time scale of a ship voyage, while erratic, typically would be known within an order of magnitude, say… So that gives a basis to start from… Where is the center, where is the Orion arm, let’s find the brightest stars in the earth neighbourhood (alternatively, the network of pulsars), let’s infer from their current position the approximate drift since we began our voyage.
If the timescale is too long, then things may not be recognizable. But then, we don’t have the complete data to create a navigation database today. Shorter voyages will give us better parallax and more accurate measurements of the nearby stars, and their motion. We’ve had what, maybe 100 years of good accurate star photos to catalog proper motion. Give it another hundred years, we’ll know more. We know rough distances based on a parallax of 16 light-minutes. Imagine what 4 light years could tell us. If you went back to Manhattan 400 years after it was bought from the Indians, or London 400 years after the great fire, how much would be familiar? For now, navigating beyond our solar neighbourhood a few hundred light years is like setting out on an ocean voyage with a large world map; you know roughly what you’re looking for, but the precise detail is lacking.
As for the odds of hitting something - good question. How close does a piece of debris have to be to appreciably eclipse a distant star? The fact that such events seem to be rare suggests there is not a huge amount o f moderate dark obstructions out there… Meteor strikes were a common event in early interplanetary travel stories, but generally there does not seem to have been one of significance in 50 years. Perhaps the number of objects is trumped by the sheer volume of empty space.
When it starts to be important, the necessary data will be accumulated to provide navigation tools.
That’s the important point. The OP scenario was advanced sub-light interstellar travel using existing physics. Even given propulsion for free, there would be various technical and developmental challenges, and navigation is not the hardest. The navigation aspect is easily attainable using current and attainable knowledge.
We already have a form of interstellar navigation – Voyager 1 is currently in interstellar space 13 billion miles from earth. Its distance and position can be accurately measured by ground-based radio. According to this article the velocity and position of deep space probes can be measured to 0.05 millimeters per second and three meters: How do space probes navigate large distances with such accuracy and how do the mission controllers know when they've reached their target? | Scientific American
The Voyager antenna is only 3.7 meters (12 feet) in diameter. The manned spacecraft in the OP scenario would be vastly larger with similarly upgraded antennas, optics, computing and on-board power. How large? There are already radar reconnaissance satellites in earth orbit with umbrella-like antennas the size of a US football field: Magnum (satellite) - Wikipedia
Such an antenna on a sub-light deep space vehicle would enable precise radio-based navigation, limited only by time lag due to earth’s distance. Eventually that would become impractical but in the OP scenario things aren’t happening that fast. At 50% the speed of light it would take about 10 years to reach Alpha Centauri. An earth-based navigation fix which supplemented on-board methods might be usable out to a light year or so.
When approaching another star system the same on-board system could provide highly accurate radar navigation and distance ranging. Today, using smaller antennas we can already bounce radar signals off the sun, planets and asteroids to determine exact distance and velocity:
Goldstone Solar System Radar - Wikipedia
If the Apollo project is a guide, there would be multiple redundant navigation methods. Obvious possibilities are some form of inertial navigation updated by stellar or pulsar sightings – which have already been demonstrated.
Currently the best inertial platforms have a drift rate of about 0.00005 degrees per hour. In practice some type of “sensor fusion” system updates the platform periodically.
People on a sub-light interstellar spacecraft which traveled to Alpha Centauri could easily see the earth’s sun – without a telescope. Using navigation telescopes, it seems likely earth’s sun would be visible from any practical distance a sub-light spacecraft could travel. Using the sun and other navigation stars, the 3D position in space can be accurately determined: iPage
If greater survey accuracy of stellar positions and motions was needed for a navigation database, that is straightforward to obtain using existing and attainable technology. However since the experiment on ISS already demonstrated 5 km accuracy using pulsar navigation, purely stellar methods might supplement this. A blend of several navigation methods including but not limited to the above would probably be used : https://www.nasa.gov/sites/default/files/atoms/files/session_3_-_2_x-ray_pulsar_navigation_for_deep-space_autonomous_applications_jason_mitchell_0.pdf
Not to nitpick, but from your own links, Star Trek heading and bearing are the same as in the Terrestrial maritime definitions (with a 3rd dimendion).
Heading is the direction your ship is traveling (head North or 000 mark 000)
Bearing is where another object is relative to you (there is an aircraft bearing Northeast or 045 mark something)
Presumably Star Trek (and Star Wars for that matter) has some sort of coordiante system to describe where systems are relative to each other in the galaxy. Angular distance from some arbitrary “north” (Earth maybe) x distance from the galactic center x distance +/- from the galactic plane. Or maybe use Earth as your center if you only have the capability to go a few dozen light years. Like Earth is the oddball planet still using feet and miles from Earth’s sun while everyone else is “metric” distance from the galactic center.
Of course, the most important star for navigation purposes is going to be the one that’s your destination. And that can certainly be detected from on board the ship, at least using a telescope, because it was detectable through a telescope from Earth. It must have been detectable from Earth, because you had to observe it and learn something interesting about it before you would have chosen it as your destination.
And the second-most-important star for navigation purposes is going to be Sol. Assuming that your destination is an Earth-like planet, then its star is probably Sol-like. Which means that, if that star is detectable from here, then Sol will also be detectable from there.
So we’re already guaranteed that of the two most important reference points, at least one is sure to be visible for the entire voyage, and the other probably will be.
It should be noted that the galaxy does have its own magnetic field. Galactic magnetic compasses would probably be a thing for celestial navigation.
If you’re bringing a magnetometer along, it’s because you’re interested in learning about the magnetic field of the Galaxy itself, not in using the magnetic field to determine anything about where you are or where you’re going. The field isn’t uniform, or at least, we have no reason to expect that it would be.