Page 69 - All About Space 68 - 2017 UK

Mach propulsion

Constant mass
The thruster features
a lump of brass that
acts as an unvarying
foundation mass,
like the bulk of the
potential spacecraft.

Ernst Mach's critism of Newton's theories about space
and time foreshadowed Einstein's theory of relativity.
Varying mass
Currently, the only way we have to propel vehicles Test thruster A stack of piezoelectric
in space is by shooting something out the back discs acts as both the
A crucial part of the new source of mechanical
(reactive mass); whether that is combustion project is laboratory tests movement and the
products, ionised gas molecules accelerated by to try to discover ways of varying reactive mass.
electromagnetic fields, or inert gas heated by nuclear scaling up the tiny thrust,
reactions — this profoundly limits our ability to using scale models.
explore our galaxy and beyond. Piezoelectric discs
We must carry everything with us that we will Piezoelectric material
expands slightly when
expel for thrust over an entire journey; to go further electrified, making the
or faster needs more reactive mass, and even that Capacitor whole stack vibrate
mass we are carrying for later in the journey itself Fearn and Woodward's theory suggests that if against the brass lump.
needs to be propelled as payload by more reactive a capacitor (also here formed by the stacked
mass, leading to impossibly large spaceships. What discs) absorbs energy whilst accelerating it will
we need is a new way to propel craft that doesn't fluctuate in mass around its stationary value.
relay on leaving stuff behind, that can react against
the universe itself, and that is what a new NASA
study might enable.
Dr Heidi Fearn of California State University is “ What we need is a new way to propel craft
working with NASA to investigate a concept called
Mach propulsion, named for German physicist that doesn't relay on leaving stuff behind,
Ernst Mach, who is also the namesake for Mach
numbers. As well as studying fluids, Mach proposed that can react against the universe itself"
a concept of inertia, which is the way objects take
exertion to speed up and to slow down again. The notice in daily life. Dr Fearn’s colleague Professor piezoelectric capacitor section will be slightly
leading theory of inertia is that it is the result of the James Woodward first proposed Mach propulsion, heavier when it pushes away from the brass, and
cumulative gravitational effect of the entire universe and they hope to employ this effect to enable a slightly lighter when it retracts. In this way it may
acting on every piece of matter. The inertia of our spacecraft to recover its reactive mass and use it produce thrust without emitting anything, but in
reactive mass is what gives our rockets something again. Their experimental set-up consists of a lump effect pushing against the rest of the universe.
to push against, but imagine if we could change of brass supported on a stack of alternating metal The current project is to find ways to increase
the inertia of our reactive mass. If we could push and piezoelectric discs. Piezoelectric materials the minuscule effect claimed so far, but Fearn and
a mass backwards and then reduce it's inertia, we stretch when they are electrified, so by feeding in Woodward believe it should scale up with size and
could recover that mass and not move as far back an electric current pulsing at a high frequency it’s power. If they are right, then a spacecraft with a
as we have travelled. If we could then increase its possible to make the mass of brass vibrate, whilst small nuclear reactor and a Mach thruster might be
inertia we could push on it again, travelling forward at the same time the stack of materials forms capable of interplanetary trips at 1G acceleration, the
by repeating this cycle, and this what Fearn believes a capacitor. Capacitors are devices that absorb fastest we could comfortably go. The craft would
might be possible. electrical energy by accumulating electrons, and accelerate for the first half of the journey, then turn
Serious theory suggests that the inertia of an so may possibly lose inertia when they are both around and slow down for the last half, giving free
object may fluctuate as it absorbs energy, but so charging and physically accelerating, which would gravity in the process; reaching the Moon in four © Adrian Mann
quickly and on such a small scale that we don't happen as it vibrates. If the theory is correct, the hours, Mars in five days and Jupiter in a week!

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