[Spaceships] FWIW: Semi-Hard Science Boost Drive

[DaltonS]

I've had this idea for a more “realistic” boost drive for some time, but had to work out the equations and numbers first.

Mass Conversion Boost Drive (TL10^) [Any!]

This drive is a Reactionless Engine (SS1:p24) that directly converts fuel mass into directional kinetic energy instantaneously applying it to the ship and its contents boosting it to a c-fractional velocity. The kinetic energy of a ship travelling at relativistic velocities is the difference between the total energy of its rest mass (M) and that of its relativistic mass (M/τ) where τ=sqrt(1-(v/c)²) (also known as the tau factor). Thus, with K=Mc²(1/τ-1), the mass converted to kinetic energy would be m=M(1/τ-1), making τ=M/(M+m) and (v/c)=sqrt(1-τ²). The table below assumes that for safety, the fuel tanks contain mass for two boosts; one to accelerate, the other to decelerate. (For this I used M=sqrt(1-0.05*N) and m=r*(1-M) where N is the number of fuel tanks and r is the rate of mass conversion.) The conversion rates are 60% at TL10^, 80% at TL11^ and 100% at TL12^. Use Subwarp drive prices.

_____________________________________________________________________________________
 Fuel  |           Velocities/Tau Factors for Mass-Conversion Boost Drive            |
 Used  |  60% Conversion (TL10^) |  80% Conversion (TL11^) | 100% Conversion (TL12^) |
(Tanks)|  v/c   v(AU/hr) τ-Factor|  v/c   v(AU/hr) τ-Factor|  v/c   v(AU/hr) τ-Factor|
-------+-------------------------+-------------------------+-------------------------|
  1/3  | 10.03%  0.7233  0.99496 | 11.56%  0.8341  0.99329 | 12.91%  0.9314  0.99163 |
  2/3  | 14.21%  1.0254  0.98985 | 16.37%  1.1811  0.98651 | 18.26%  1.3172  0.98319 |
   1   | 17.45%  1.2591  0.98465 | 20.08%  1.4484  0.97964 | 22.36%  1.6132  0.97468 |
   2   | 24.88%  1.7947  0.96856 | 28.50%  2.0563  0.95852 | 31.62%  2.2814  0.94868 |
   3   | 30.71%  2.2158  0.95166 | 35.05%  2.5284  0.93657 | 38.73%  2.7941  0.92195 |
   4   | 35.76%  2.5801  0.93386 | 40.63%  2.9315  0.91372 | 44.72%  3.2264  0.89443 |
   5   | 40.33%  2.9096  0.91506 | 45.62%  3.2913  0.88987 | 50.00%  3.6072  0.86603 |
   6   | 44.58%  3.2160  0.89515 | 50.19%  3.6210  0.86492 | 54.77%  3.9515  0.83666 |
   7   | 48.60%  3.5061  0.87397 | 54.45%  3.9286  0.83873 | 59.16%  4.2681  0.80623 |
   8   | 52.46%  3.7846  0.85136 | 58.48%  4.2191  0.81116 | 63.25%  4.5628  0.77460 |
   9   | 56.21%  4.0548  0.82710 | 62.32%  4.4963  0.78203 | 67.08%  4.8395  0.74162 |
  10   | 59.87%  4.3195  0.80094 | 66.02%  4.7628  0.75111 | 70.71%  5.1013  0.70711 |
  11   | 63.50%  4.5809  0.77254 | 69.59%  5.0208  0.71810 | 74.16%  5.3503  0.67082 |
  12   | 67.10%  4.8408  0.74146 | 73.08%  5.2720  0.68264 | 77.46%  5.5882  0.63246 |
  13   | 70.71%  5.1012  0.70712 | 76.48%  5.5178  0.64423 | 80.62%  5.8164  0.59161 |
  14   | 74.35%  5.3641  0.66870 | 79.83%  5.7596  0.60219 | 83.67%  6.0360  0.54772 |
  15   | 78.06%  5.6317  0.62500 | 83.15%  5.9986  0.55556 | 86.60%  6.2478  0.50000 |
  16   | 81.87%  5.9067  0.57417 | 86.44%  6.2361  0.50280 | 89.44%  6.4527  0.44721 |
  17   | 85.84%  6.1926  0.51303 | 89.73%  6.4736  0.44139 | 92.20%  6.6513  0.38730 |
  18   | 90.03%  6.4950  0.43528 | 93.05%  6.7129  0.36632 | 94.87%  6.8441  0.31623 |
-------------------------------------------------------------------------------------

Dalton “who thinks this makes boost drives relatively realistic” Spence

[johndallman]

Originally Posted by DaltonS

This drive is a Reactionless Engine (SS1:p24) that directly converts fuel mass into directional kinetic energy

Have you read the old Venus Equilateral stories? They had a drive that was a large vacuum tube that converted the mass of its cathode directly into kinetic energy. The setting was limited to the Solar System, but ships cruised around happily at 1G or more.

[DaltonS]

Originally Posted by johndallman

Have you read the old Venus Equilateral stories? They had a drive that was a large vacuum tube that converted the mass of its cathode directly into kinetic energy. The setting was limited to the Solar System, but ships cruised around happily at 1G or more.

I may have (the title seems familiar) but it sounds like that drive actually provides a continuous acceleration. Boost drives by definition instantly change the velocity of the ship without applying G forces. I know this is pseudo-science technology, but at least I'm conserving mass and energy. (You may be able to tell I'm not a great admirer of “pseudo-velocity” drives. ;) )

Dalton “who believes relative realism is better than none at all” Spence

[Anthony]

Conservation of energy doesn't work if you don't have conservation of momentum, because even if the energy works out in one reference frame, it doesn't work in a different one. You could, of course, have a boost cannon that pushes off from a planet, but you might have trouble decelerating unless you're really really accurate.

[Flyndaran]

How would you adjust it to make a "kind of" technically physics obeying reactionless/boost drive?