On 2 Jan 2018 at 14:42, Rob O'Connor wrote:

> Leonard Erickson wrote:
>  > I think you blew your calculations *badly* somewhere.
>
> Yes. I was wrong. I posted the wrong equation initially and then
> corrected. The energy-momentum relation is:
>
> (energy)^2 = (momentum x c)^2 + (rest mass x c^2)^2
>
> So the quantity
> (energy)^2 - (momentum x c)^2 = (rest mass x c^2)^2
> must be the same in all inertial frames if the rest mass doesn't
> change.
>
> Your examples can be generalised to *any* space vehicle or cosmic
> body. This doesn't make their motion impossible ;-)

Well, I was pointing out that the KE and momentm differ significantly
in different frames.

We'd already noted that with reaction drives, the KE and momentum of
the exhaust balances things out.

> Traveller reactionless drives don't make sense because they violate
> conservation of momentum and energy as written.

Yup.

> To enable momentum conservation, momentum needs to be generated
> locally (by 'pushing' against space-time itself?) or harvested from
> the general vicinity.

Pushing against space time has it's own set of problems.

> My initial post proposed a range of fuel values and drive efficiencies
> that would allow conservation of energy. The momentum generated by
> making photons or neutrinos from the fuel is far less than the
> performance level required by canon.

Yep.

Many years back on the list we had some fun with working the specs
for an M-drive that worked by "pushing"(via gravity or some such) on
planets or other bodies.

Some day I'll find those posts again and have the formula we worked
out.

It'd be a great thing to throw into a story, because the performance
*looks* great near the planet, but the faster you are going relative
to the planet the less of a velocity increase you get for every
joules you put into the drive.

Your acceleration curve drops like a rock. :-)
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com