anyway, a nuclear-powered pusher-plate craft would, by assumption, have a pusher-plate capable of absorbing high energy particle radiation. So, a pusher-plate craft could accelerate, then coast in an "end over" (stern first) orientation, using its pusher plate to "snow plow" the ISM. However, even to drive an aircraft-carrier-sized ship (100Ktons) to Mars and back ([math]\Delta v \approx 10 km/s[/math]) would require circa 100Gtons of nuclear warheads for fuel. i think that's about the entire global stockpile of nukes. So, all earth could spend trillions of dollars, to load a huge stockpile of fuel pellets aboard a craft, for one trip. (Moreover, 100Gtons probably masses 100Ktons or more? So, at least on the outbound leg, there'd be no room for cargo.)

 

Edited May 20, 201312 yr by Widdekind

National Geographic made a documentary that includes a nuclear bomb propelled interstellar ship.

 

See: "Nat Geo Evacuate Earth"

Edited May 20, 201312 yr by EdEarl

Please ponder a fusion-powered rocket, of initial mass M, which converts 0.007M into (kinetic) energy. Energies are low w.r.t. rest-mass energy, and (so) velocities are low w.r.t. light-speed. So, classical approximations are accurate (if not precise):

 

[math]M c^2 = M' c^2 + \frac{1}{2} M' v^2[/math]

[math]\frac{\Delta M}{M'} = \frac{1}{2} \beta^2[/math]

[math]\epsilon \approx \frac{1}{2} \beta^2[/math]

[math]\beta \approx \sqrt{2 \epsilon} \approx 0.12 [/math]

 

i.e. [math]\approx \frac{c}{8}[/math]. So, an ideal fusion rocket can only accelerate to an eighth of light-speed. And, if you wanted to be able to decelerate at destination, then you would have to save half the energy, and halving the energy of acceleration from departure would reduce speed by [math]\sqrt{2}[/math] to about 0.08c.

 

So, self-nuclear-fusion-propelled space-craft can only accelerate to about 8% of light-speed; externally accelerated "space slingshotted" space-craft could coast at 12% of light-speed, and still carry enough on-board fusionable energy to decelerate at destination.

 

Anything out there traveling faster than 12% of light-speed was externally accelerated, i.e. a "space bullet" fired from some "space gun". Hypothetically, an externally accelerated "space-bullet-craft" loaded with anti-matter could be accelerated to ... and still have enough on-board energy to decelerate at destination:

 

[math]E_0 = \gamma \left( M_{ship} + m_{fuel} \right) c^2[/math]

[math]c P_0 = \gamma \beta \left( M_{ship} + m_{fuel} \right) c^2[/math]

[math]\Delta E = \gamma m_{fuel} c^2 = c \Delta P = c P_0[/math]

[math]\gamma m_{fuel} c^2 = \gamma \beta \left( M_{ship} + m_{fuel} \right) c^2[/math]

[math]m_{fuel} = \beta \left( M_{ship} + m_{fuel} \right)[/math]

[math]\frac{m_{fuel}}{M_{ship} + m_{fuel}} = \beta \le 1[/math]

 

So, a hypothetical externally accelerated space-craft, loaded with externally-supplied anti-matter (& matter) fuel, could cruise at near-light-speed, and still decelerate at destination, depending upon the ratio of fuel-mass to total-ship-mass. The ship would decelerate, by projecting a high-powered laser-like blast, in the forward direction ("focused pair-instability SNe GRB blast"), which could be aimed at the target world, to annihilate any indigenous lifeforms.