
'Helical Engine' Concept Could Reach 99% the Speed of Light - SirLJ
https://ntrs.nasa.gov/search.jsp?R=20190029657
======
Tomminn
Okay so here's why this is trivially unsound from the perspective of standard
modern physics.

1) Newton II: F= dp/dt. This particular formulation of Newtons Law is valid in
relativity.

2) Newton III: My own formulation of this is all force arrows are "double-
headed". Again, valid in relativity also.

So any dp/dt on anything inside your engine, requires equal and opposite dp/dt
on something else.

The only new thing that they're doing is trying to make the mass relativistic,
so p /= mv. I have no need of the hypothesis that p=mv in this refutation.
Unless there is something outside that is taking the dp/dt, that this is only
ever going to oscillate.

The reason is this. Lets define the "system" as everything inside the engine
at t=0, and define the "system" as all particles and fields which would not
exist if it weren't for the system at t=0.

The problem is this. The total momentum of the "system" _can never change from
it 's initial momentum_.

It looks like the idea in mind is that magic will happen because of the non-
linearity in the momentum to velocity relation due to relativity. But if we
look at this system as a whole, it's total momentum is fixed _at all times_ at
the initial total momentum, which implies an initial total system drift
velocity, which only depends on account the total _rest_ mass of the system,
_even in relativity_.

The only way to increase the velocity of the _engine_ over is to decrease the
rest mass of the engine over the course of many engine cycles. That is, we
need some of the mass-energy of the system to simply _escapes the engine_ , in
the form of escaping particles or electromagnetic waves.

Sadly, there is nothing that they've shown here that is an explanation of how
we circumvent _that_ part of engine physics.

------
gus_massa
Extensive discussion
[https://news.ycombinator.com/item?id=21250577](https://news.ycombinator.com/item?id=21250577)
(271 points, 7 days ago, 134 comments)

Short version of the comments there:

The article mix classical and relativistic formulas, you must be very careful
when you do that or you can get weird results.

In Classical Mechanic, momentum is conserved.

In Special Relativity, momentum is also conserved, but the definition of
momentum includes the momentum of the electromagnetic radiation.

The device work, but not as the author think. It emits a lot of
electromagnetic radiation. It emits more radiation in one direction, and the
spaceship is pushed in the oposite direction.

The calculation of the energy is slightly of, I'm not sure why, perhaps
because it mix classical and relativistic formulas.

The device is essentially and inefficient Photon Rocket
[https://en.wikipedia.org/wiki/Photon_rocket](https://en.wikipedia.org/wiki/Photon_rocket)
. It's equivalent of using a laser or flashlight in the back of your
spaceship. It emits light in one direction, and the spaceship is pushed in the
oposite direction.

For some reason people that rediscover photon rockets like to call them
massless and claim that they break the laws of physic.

The theoretical maximum thrust/energy ratio of photon rockets is very small,
that's the reason no one use them. In an inefficient photon rocket it's
smaller.

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missosoup
> The engine accelerates ions confined in a loop to moderate relativistic
> speeds, and then varies their velocity to make slight changes to their mass

Wouldn't that change in momentum also have an equal and opposite reaction on
the accelerator?

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dvdkhlng
Description reads like a reaction-less drive [1] so at least quite speculative
if not even violating the law of conservation of energy (because kinetic
energy goes up with the square of velocity, but a reaction-less drive converts
stored on-board energy into kinetic energy linearly).

[1]
[https://en.wikipedia.org/wiki/Reactionless_drive](https://en.wikipedia.org/wiki/Reactionless_drive)

------
campfireveteran
_Thunderf00t and EEVblog (Dave) entered the chat_

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c0nducktr
What exactly is this? Comments so far are all dunking on it, but it's on
nasa.gov, so .. ¯\\_(ツ)_/¯

~~~
campfireveteran
Ever heard of perpetual motion or snake oil? That's what the title alludes to,
and here's the summary from the page

 _A new concept for in-space propulsion is proposed in which propellant is not
ejected from the engine, but instead is captured to create a nearly infinite
specific impulse._

Yeah, it doesn't look good at all. Maybe some solar freakin roadways: space
edition.

EDIT: the end of the slides is telling that this abortion hasn't been
validated in the slightest:

 _Basic concept is unproven_ _•Has not been reviewed by subject matter
experts_ _•Math errors may exist!_

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nradov
This is just one person's slide deck. It hasn't undergone peer review and
doesn't address conservation of momentum.

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egdod
It could if momentum isn’t conserved.

