It’s 2021, and finally we don’t have to worry about our spaceship getting lost in an intergalactic space.
Using the position and moving light of stars, both near and far, astronaut Coryn AL Bailer-Jones has demonstrated the possibility of independent, on-the-fly navigation for traveling spacecraft far beyond the Solar System.
Intercontinental location address may not seem to be an immediate problem. However, already in the last decade, human instruments have entered an intersex space, as the first Voyager 1 (in 2012) and Voyager 2 (in 2018) went over at the end of the Solar System called the heliopause.
It’s only a matter of time before New Horizons joins them, and then more probes in the future. As these spaceships travel farther and farther from their home planet, communication with Earth takes longer and farther.
New Horizons is currently nearly 14 hours of light from Earth, meaning it will take 28 hours to send a signal and receive a response; it is not an impossible tracking and navigation system, but a unanimous system.
At greater and greater distances, however, this will no longer be reliable.
“When traveling to the nearest stars, signals will be far too weak and there will be light travel times of order years,” Bailer-Jones wrote in his paper, which is currently available on the arXiv preprint server , where he awaits peer review from the astronomy community.
“So an interstellar spacecraft must sail independently, and use this information to decide when a course correction or instrumentation should be made. Such a spacecraft must- space to be able to position and determine its speed using just on – board measurements. “
Bailer-Jones, who works at the Max Planck Institute for Astronomy in Germany, was not the first to think of this. NASA has been working on pulsars navigation, using the regular hits of dead stars as the basis for galactic GPS. This method feels good, but may be subject to errors at longer distances, due to the signal being turned by the intersex medium.
With a catalog of stars, Bailer-Jones was able to show that spacecraft coordinates can be calculated in six dimensions – three in space and three in distance – with great accuracy, based on position. of these stars change from the view of the spaceship.
“As a spacecraft moves away from the Sun, the position and speed of the stars will change compared to those in an Earth-based catalog due to parallax, aberration, and Doppler influence,” he wrote.
“By simply measuring the square distances between pairs of stars, and comparing them to the catalog, we can find the coordinates of the spacecraft through a iterative remodeling process.”
Both parallax and aberration refer to the apparent change in position of stars as a result of the Earth’s motion. The Doppler effect is the change in wavelength of light from a fixed star that appears to be moving closer to or away from the observer.
Since all of these influences involve the relative position of the two bodies, a third group (the spacecraft) in a different position will see a different arrangement of the stars.
Of course, the distances to stars are very difficult to determine, but we are getting a lot better. The Gaia satellite is on an ongoing mission to map the Milky Way in three dimensions, and has provided us with the most accurate map of the galaxy to date.
Bailer-Jones tested its system using a catalog of symbolic stars, and then on nearby stars from the Hipparcos catalog compiled in 1997, at relevant spacecraft distances. While this may not be as accurate as Gaia, that is not very important – the goal was to test that the navigation system can work.
With just 20 stars, the system can determine the position and speed of a spacecraft within 3 celestial units and 2 kilometers per second (1.24 miles per second). This accuracy can be developed within the square root of the number of stars; with 100 stars, the accuracy dropped to 1.3 celestial units and 0.7 kilometers per second.
There are some connections that need to be worked out. The system did not pay attention to large binaries, nor did it consider the instrument. The goal was to show that it could be done, as a first step towards achieving it.
It is even possible that it could be used in conjunction with pulsar navigation so that the two systems can reduce each other’s defects. And then the sky is, literally, the highest.
The paper is available on arXiv.