On 17 Dec 2017 at 15:26, Robert O'Connor wrote:

> If we look at a wider range of potential accelerations, we get:
>
> (with apologies for potential formatting glitches):
>
> G-hours: acceleration potential in hours (days).
>
> Fuel mass fraction: proportion of vehicle mass in maneuver drive fuel.
>
> Fuel volume fraction: proportion of vehicle volume in maneuver drive
> fuel.
>
> Terminal velocity: if all the acceleration potential was spent in
> building up speed.
>
> G-hours    Fuel mass fraction    Fuel volume fraction Terminal
> velocity, c
>
> 180(7.5)    0.0003    0.004    0.0215
> 360(15)        0.0012    0.017    0.043
> 540(22.5)    0.0028    0.040    0.0645
> 720(30)        0.005    0.071    0.086
> 900(37.5)    0.0078    0.112    0.108
> 1080(45)    0.0112    0.160    0.129
> 1260(52.5)    0.0154    0.220    0.151
> 1440(60)    0.020    0.290    0.173
> 1620(67.5)    0.026    0.365    0.194
> 1800(75)    0.032    0.457    0.216
> 1980(82.5)    0.039    0.557    0.238
> 2160(90)    0.047    0.670    0.259
>
>
> * Conclusions
>
> The values above are consistent with conservation of energy and
> relativity. While they still enable the attainment of relativistic
> speeds, there is no major impact on travel times etc. except for the
> most distant objects in a stellar system.
>
> The power levels required (~hundreds of terawatts) imply that drives
> need to be very efficient radiators; neutrino radiation of waste heat
> works as a handwave that could be applied to the comparatively tiny
> power consumption of other systems.

Slight problem. the ship's kinetic energy depends on which frame of
reference you use.

Extreme examples:

In the ship's frame of reference, it has zero kinetic energy. In that
of a galaxy near the "Hubble limit, it has near infinite kinetic
energy.

It's energy with respect to the star and the various other bodies in
a system will be different for each.

Reaction drives don't have this problem, because the increase in KE
in any frame is matched by an equal and opposite change in KE on the
part of the exhaust.

Reactionless drives don't have that factor. so they will *always*
violate conservation of energy, conservation of momentum, and even
conservation of angular momentum in at least one frame of reference.

Jump drives are even worse.

It is possible to "fix" jump drive by having there be a "prefferred
frame of reference". Though that leads to interesting problems for
anyone trying to use it in other galzies.

For manuever drive, it might fix the conservation problems, but it'd
create a host of others. Including drive performance varying all over
the place with respect to the ship's velocity relative to the
preferred frame.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com