Over the past decades, astronomical research has evolved, with scientists working hard to develop better ways to facilitate space missions. However, experts are still unsure how massive the universe is, so astronauts need a reliable reference to estimate their actual position in space.
Within the Solar System, interplanetary spacecraft depend on Earth-based systems for navigation. This technique uses a network of radar systems on Earth which are in constant communication with the spacecraft. However, interstellar missions need a different approach.
Navigating With Pulsars
In principle, a spacecraft can use onboard systems such as clocks and gyroscopes as it navigates autonomously. However, interstellar missions can only last for decades at a minimum, and even minor errors and uncertainties in these onboard systems can cause the spacecraft to stray off course.
Space travelers can depend on pulsars or rotating objects that appear to flicker or rotate at regular intervals. Since every pulsar has a unique rotation period, they can serve as reliable beacons for deep-space travel.
Relying on pulsars, however, only works within a relatively small region near the Solar System. This is because measuring the rotation period can be contaminated by interstellar dust, and the traveler can get lost once they lose track of a particular pulsar.
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Estimating Position With Stellar Parallax
An interstellar spacecraft will need a simple, reliable approach to estimating its position within our galaxy. According to Coryn A.L. Bailer-Jones from the Max Planck Institute for Astronomy, the solution could be the stars themselves.
This proposed technique is based on the principle of parallax, or the apparent displacement of an object due to the change in the observer's point of view. It was through parallax that astronomers were first able to measure the distance to stars.
Before launch, a spacecraft will be loaded with an accurate map of all the known stars in our galactic vicinity. As it speeds away from the Solar System, the spacecraft will measure the relative distances between multiple pairs of stars. As the spacecraft moves, the stars closer to it will appear to shift significantly, while the more distant stars will remain relatively fixed.
The navigator can measure multiple pairs of stars and compare the measurements with the original Earth-based map. Doing so will enable them to figure out which stars are which and how far away the spacecraft is from those stars. This way, the navigator can get an accurate 3D position of its spacecraft in the galaxy.
Getting the velocity of the spacecraft, however, is a little trickier since it relies on special relativity. If the spacecraft is not moving quickly enough, objects can appear to be in different locations than they are. The position of an object will appear to be shifted in the direction of the navigator's motion.
This effect is called aberration, and fortunately, it is measurable from Earth. If the spacecraft moves quickly enough, onboard systems can measure this aberration. The navigator will only need to identify which star shifts away from its expected position and by how much so they work out its 3D velocity.
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