On this, I agree with Casagiannoni,
we need to find better ways of propulsion
for our spacecraft. Here is one.

from
https://phys.org/news/2023-02-spacecraft-solar-autonomously-pulsars.html

FEBRUARY 2, 2023

Soon every spacecraft could navigate the solar system autonomously using
pulsars
by Scott Alan Johnston, Universe Today

A pulsar with its magnetic field lines illustrated. Credit: NASA
If you want to know where you are in space, you'd better bring along a
map. But it's a little more complicated than riding shotgun on a family
road trip.

Spacecraft navigation beyond Earth orbit is usually carried out by
mission control. A series of radio communication arrays across the
planet, known as the Deep Space Network, allows operators to check in
with space probes and update their navigational status. The system
works, but it could be better. What if a spacecraft could autonomously
determine its position, without needing to phone home? That's been a
dream of aerospace engineers for a long time, and it's getting close to
fruition.

Pulsars are the key.

Pulsars are rotating neutron stars—the ultra-dense cores of exploded
supergiant stars—which emit jets of electromagnetic radiation from their
poles. They act like interstellar lighthouses that repeatedly wash radio
signals over Earth in a dependable rhythm. The first pulsar was
discovered by Jocelyn Bell in 1967 and was nicknamed LGM-1 (Little Green
Men 1), because until a second one was discovered, extraterrestrial
intelligence couldn't be ruled out as the pulsar's cause. Now, we know
of thousands, and are confident they are natural phenomena.

Because pulsar beams are so predictable, they can be used for a sort of
triangulation, in which a spacecraft receiving overlapping pulsar
signals ought to be able to work out its position in space to within
about 5 to 10 kilometers.

NICER, a prototype pulsar navigation system installed on the exterior of
the International Space Station. Credit: NASA
The theoretical foundation of this method is solid. So much so that the
golden records (time capsules of Earth and human culture) which were
attached to the side of the Voyager and Pioneer spacecraft in the 1970s
graphically indicated the position of our sun relative to 14 pulsars,
just in case any LGMs stumble across the spacecraft and want to visit us
here on Earth. We've given them directions.

But if pulsars are such an effective form of navigation, why aren't they
already in use? After all, studies into the subject have been ongoing
since the 1970s, when the Jet Propulsion Lab first began looking into
the prospect.

With all space missions, one of the primary considerations is weight.
It's expensive to launch things into space, so every kilogram on every
vehicle has to count. Any workable pulsar navigation system would have
to be very small, and very lightweight, otherwise important scientific
instruments or fuel for propulsion might have to be downsized to make up
for it. This is a significant barrier to designing a viable pulsar
navigation system. Pulsars are usually incredibly faint point sources,
making them difficult to detect without powerful (heavy) equipment,
especially in radio frequencies.

Luckily, there is a solution that might make it feasible, and that is to
use an X-ray telescope instead. These can be smaller and more
lightweight, and can still pick up pulsar signals just as well as a
radio antenna.

In recent years, astronomers have been working on improving the methods
by which a spacecraft processes pulsar signals, increasing the system's
efficiency and narrowing the error margins. Hardware has even been
tested on the International Space Station, where the
washing-machine-sized NICER/SEXTANT experiment has been successfully
tracking the station's location using pulsars since 2018.

Now, teams are working on developing hardware that's even more compact
for deep space missions. A preprint released on arXiv last month
describes a prototype navigation unit called PODIUM, which will weigh
just 6kg, use 20W of power, and fit in a box 15 cm by 24 cm by 60 cm.
The initial results are promising. PODIUM should be able to determine a
spacecraft's position within about 10km, using X-ray signals from a
catalog of pulsars.

Soon, these prototypes might become the real thing, guiding the next
generation of space probes to their destinations. They are likely to
guide human-rated spacecraft too, with NASA's upcoming Lunar Gateway
space station expected to be outfitted with a pulsar navigation system.
We are on the cusp of autonomous deep-space navigation: like GPS, but
for the galaxy.

More information: Francesco Cacciatore et al, PODIUM:A Pulsar Navigation
Unit for Science Missions, arXiv (2023). DOI: 10.48550/arxiv.2301.08744

Provided by Universe Today

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