How would we navigate to another star accurately so we actually arrive at the destination and not miss the target entirely.
Could we anticipate the stars position thousands of years into the future and make sure our spacecraft is on the correct course. The distance to most stars has a fairly high margin of error how would we correct for this error on route.
You could take the long way and follow the light rather than intercepting it in some future location…
Cymek said:
How would we navigate to another star accurately so we actually arrive at the destination and not miss the target entirely.
Could we anticipate the stars position thousands of years into the future and make sure our spacecraft is on the correct course. The distance to most stars has a fairly high margin of error how would we correct for this error on route.
Orbital mechanics it a pretty well understood phenomena.
we have the proper motion of a lot of close stars, so yes, we can anticipate where it would be in a thousand years.
I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
diddly-squat said:
I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
Running out of toilet roll would present a much more serious challenge.
Bubblecar said:
diddly-squat said:I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
Running out of toilet roll would present a much more serious challenge.
Tamb said:
Isn’t that what happened to Napoleon, too?
Bubblecar said:
diddly-squat said:I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
Running out of toilet roll would present a much more serious challenge.
It happened to us on the island of St Helena. There were no newspapers or phone books to tide us over. Ewwww!
Michael V said:
Tamb said:Isn’t that what happened to Napoleon, too?
Bubblecar said:Running out of toilet roll would present a much more serious challenge.
It happened to us on the island of St Helena. There were no newspapers or phone books to tide us over. Ewwww!
diddly-squat said:
I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
This. It is a trivial problem.
dv said:
diddly-squat said:I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
This. It is a trivial problem.
Even when the determined distances have a fairly high margin of error
Cymek said:
dv said:
diddly-squat said:I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
This. It is a trivial problem.
Even when the determined distances have a fairly high margin of error
But they don’t, we actually have very accurate measurements of distance.
I have wondered how they determine the distances…
Cymek said:
How would we navigate to another star accurately so we actually arrive at the destination and not miss the target entirely.
Could we anticipate the stars position thousands of years into the future and make sure our spacecraft is on the correct course. The distance to most stars has a fairly high margin of error how would we correct for this error on route.
Satellites can navigate in several ways, but one of the easiest is to sight on stars and fix orientation and direction using what is called a star tracker. The simplest star tracker is just four pixels. If the light from star falls to one side or the other, brighter on one pixel or the opposite, adjust the spacecraft track a bit to bring it back on line. This is not much different to, and slightly easier than, the task New Horizons had in steering a precise track past Pluto.
The simplest navigation approach is to head towards the star until you almost hit it, and then veer aside when sensors indicate that it is coming up fast, first by increase in brightness and second by increase in angular diameter.
Star positions are known in an angular sense from Earth extremely precisely. The speed of the star towards us and laterally is known with less precision, but accurate enough. Let’s take Proxima Centauri for example. We know its distance within 0.14%. We know its speed toward us to within 2.3%. We know its lateral speed within 0.27%. That’s accurate enough as there is plenty of time to make adjustments during the trip.
For further stars, distances and motions become less accurate, but that’s what the GAIA spacecraft is for. With a bit of luck it will improve the accuracy of distances and lateral velocities (proper motions) by a factor of ten.
Cymek said:
dv said:
diddly-squat said:I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
This. It is a trivial problem.
Even when the determined distances have a fairly high margin of error
In flight corrections.
dv said:
diddly-squat said:I’d actually go out on a limb and suggest that navigation is probably the least of the problems that would be faced by an interstellar mission.
This. It is a trivial problem.
maybe, but it wasn’t the question.
furious said:
- Even when the determined distances have a fairly high margin of error
I have wondered how they determine the distances…
For nearby stars, parallax. The change in the angle that it appears when viewed from opposite ends of the Earth’s orbit. The earliest success by by Bessel who measured the distance to the star 61 Cygni. The distance to Alpha Centauri followed less than two years later.
Astrometry, the science of the position of stars, progressed slowly over the next hundred years. Leuten and Gliese produced catalogs of nearby stars. Yale produced an excellent catalogue in the middle of the last century. Not that everything was plain sailing, an astronomer called Flint produces a series of execrably bad star distances.
Then came the Hipparcos satellite by ESA, which confirmed and improved on previous distances and proper motions. Now, learning from Hipparcos, the GAIA satellite by ESA has already improved star distances and proper motions enormously with its first data release.
Cymek said:
How would we navigate to another star accurately so we actually arrive at the destination and not miss the target entirely.
Could we anticipate the stars position thousands of years into the future and make sure our spacecraft is on the correct course. The distance to most stars has a fairly high margin of error how would we correct for this error on route.
A light sensor locked into the light spectrum of that peculiar star
and a map of the galaxy or galaxies
maybe star and object maps might be on going works of progress as scanning for objects ( planets, comets, meteorites) would be ongoing, computers would update the maps constantly which eventually get transmitted back to a central database map
mollwollfumble said:
furious said:
- Even when the determined distances have a fairly high margin of error
I have wondered how they determine the distances…
For nearby stars, parallax. The change in the angle that it appears when viewed from opposite ends of the Earth’s orbit. The earliest success by by Bessel who measured the distance to the star 61 Cygni. The distance to Alpha Centauri followed less than two years later.
Astrometry, the science of the position of stars, progressed slowly over the next hundred years. Leuten and Gliese produced catalogs of nearby stars. Yale produced an excellent catalogue in the middle of the last century. Not that everything was plain sailing, an astronomer called Flint produces a series of execrably bad star distances.
Then came the Hipparcos satellite by ESA, which confirmed and improved on previous distances and proper motions. Now, learning from Hipparcos, the GAIA satellite by ESA has already improved star distances and proper motions enormously with its first data release.
If you want to read more about the nearby stars we could visit, their properties and how the distances to them were measured, or if you just some exceedingly boring reading, then read the book I wrote.
A text only version is here.
http://freepages.misc.rootsweb.ancestry.com/~hallsofjamaica/neareststarsbookdraft2.txt
The full version of my book on the nearest stars: NearestStarsBookDraft2.zip is on Dropbox. Not quite sure how to give you access.
mollwollfumble said:
Star positions are known in an angular sense from Earth extremely precisely. The speed of the star towards us and laterally is known with less precision, but accurate enough. Let’s take Proxima Centauri for example. We know its distance within 0.14%. We know its speed toward us to within 2.3%. We know its lateral speed within 0.27%. That’s accurate enough as there is plenty of time to make adjustments during the trip.
What’s its Lyapunov time?
btm said:
mollwollfumble said:
Star positions are known in an angular sense from Earth extremely precisely. The speed of the star towards us and laterally is known with less precision, but accurate enough. Let’s take Proxima Centauri for example. We know its distance within 0.14%. We know its speed toward us to within 2.3%. We know its lateral speed within 0.27%. That’s accurate enough as there is plenty of time to make adjustments during the trip.
What’s its Lyapunov time?
It’s what? (Checks web) “Lyapunov time is the characteristic timescale on which a dynamical system is chaotic.”
This applies to n-body systems bound by gravity, for sufficiently large n.
I assume you’re talking about the Lyapunov time for stars rather than for the spacecraft.
For the disruption of galaxy tidal streams, https://arxiv.org/pdf/1507.08662.pdf we have the assumption “On
a weakly chaotic orbit with a chaotic timescale predicted to be >1000 Gyr.” But remember that this is an assumption.
Another paper, https://arxiv.org/pdf/1601.06790.pdf referring to the much denser concentrations of stars in the bar of a barred spiral galaxy, gives a Lyapunov time of 400–1100 Myr.
Not a problem for spacecraft navigation.
mollwollfumble said:
btm said:
mollwollfumble said:
Star positions are known in an angular sense from Earth extremely precisely. The speed of the star towards us and laterally is known with less precision, but accurate enough. Let’s take Proxima Centauri for example. We know its distance within 0.14%. We know its speed toward us to within 2.3%. We know its lateral speed within 0.27%. That’s accurate enough as there is plenty of time to make adjustments during the trip.
What’s its Lyapunov time?
It’s what? (Checks web) “Lyapunov time is the characteristic timescale on which a dynamical system is chaotic.”
This applies to n-body systems bound by gravity, for sufficiently large n.
I assume you’re talking about the Lyapunov time for stars rather than for the spacecraft.For the disruption of galaxy tidal streams, https://arxiv.org/pdf/1507.08662.pdf we have the assumption “On
a weakly chaotic orbit with a chaotic timescale predicted to be >1000 Gyr.” But remember that this is an assumption.Another paper, https://arxiv.org/pdf/1601.06790.pdf referring to the much denser concentrations of stars in the bar of a barred spiral galaxy, gives a Lyapunov time of 400–1100 Myr.
Not a problem for spacecraft navigation.
I actually meant Proxima Centauri specifically, but if it’s on that scale, it wouldn’t be a problem, as you say.
btm said:
mollwollfumble said:
Another paper, https://arxiv.org/pdf/1601.06790.pdf referring to the much denser concentrations of stars in the bar of a barred spiral galaxy, gives a Lyapunov time of 400–1100 Myr.Not a problem for spacecraft navigation.
I actually meant Proxima Centauri specifically, but if it’s on that scale, it wouldn’t be a problem, as you say.
One small concern over Proxima Centauri that I carefully glossed over above is that its orbital period about Alpha Centauri remains poorly known. Currently it is at a wide angle to Alpha Centauri and is moving further away from Alpha Centauri as seen from both Earth and Alpha Centauri. In about 25,000 years, Proxima and Alpha Centauri will be the same distance away from the Earth.
Proxima Centauri is not in a circular orbit around Alpha Centauri. One paper gives its eccentricity as 0.78 (like a long period comet, eccentricity 1 is parabolic), another paper gives its orbit as hyperbolic. Wikipedia says only that the orbital period is probably greater than 500,000 years.
Whatever the orbit of Proxima Centauri, the gravity from Alpha Centauri is so weak can be almost totally ignored in calculating the spacecraft track.