XNAV — or
X-ray Navigation — could be the GPS of the solar system (or even the
galaxy). X-ray astronomers have mapped a substantial number of x-ray pulsars
whose pulsed emissions are as regular as atomic clocks. Several papers will be
presented at the IEE/ION PLANS 2008 conference describing how this idea could
be applied for spacecraft navigation.
An X-ray
pulsar is a magnetized neutron star in a binary star system with a normal
companion star. The strength of the magnetic field of a neutron star is a
trillion times as large as the Earth's magnetic field strength measured on the
Earth's surface.
Material from the companion
star is taken in by the neutron companion, directed into the magnetic poles.
This gas falls into the neutron star at speeds of up to half the speed of
light; the resulting hotspots generate temperatures of more than a million
degrees. As the neutron star rotates, these polar hotspots produce regular
pulses of x-ray radiation like lighthouses.
These sources are highly
reliable, and are fixed in position. Phase measurements of these sources can be
used to establish the location of a spacecraft.
Several different improvements
to the use of X-ray Navigation have been proposed. In Noise Analysis for
X-ray Navigation Systems, it is suggested that the performance of an XNAV
system beyond the orbit of Jupiter could be accurately predicted.
In Online Time Delay
Estimation of Pulsar Signals for Relative Navigation using Adaptive Filters
it is suggested that the positions of two spacecraft could be determined if
both are locked to a known pulsar which emits a waveform that reaches them with
a differential time delay that is proportional to the distance between the
spacecrafts. The spacecrafts' relative inertial position could be determined by
observing appropriately distributed pulsar sources.
Astronomers have thought
long thought about pulsars, which were discovered in 1967, as some kind of
interstellar beacon. The incredible regularity - and rapidity - of the signal
pulsation seemed (at that time) to have no natural explanation.
However, science fiction
writers thought about it at least fifteen years earlier. And what's more, suggested
that it might be possible to create beacons. In his 1952 story Troubled
Star, writer and engineer George
O. Smith wrote about space beacons which were created to ease galactic
space travel:
"We
use the three-day variable to denote the galactic travel lanes. Very effective.
We use the longer variable types for other things - dangerous places like
cloud-drifts, or a dead sun that might be as deadly to a spacecraft as a shoal
is to a seagoing vessel. It's all very logical."
"...you're going to
make a variable star out of Sol, just for this?"
Scyth Radnor shook his
head. "Please do not think us hard... You're not going to insist that your
animal comforts are more important than the functioning of a galaxy-wide
civilization?"
(Read more about space
beacons)
From IEE/ION PLANS 2008 via io9.
(This Science Fiction in
the News story used with permission of Technovelgy.com)
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