Talk:Interstellar travel/Archive for 2013

Beamed Propulsion Cost

In the “Beamed Propulsion” section the statement is made that this method of propulsion “would be considerably cheaper than nuclear pulse propulsion”. No supporting evidence or citation is given. However, at least the electrical cost for beamed propulsion can be estimated with a little calculation..

Under the “Required Energy” section the statement is made “Accelerating one ton to one-tenth of the speed of light requires at least 125 billion kWh,” Obviously, the spaceship will have a mass greater than one ton. The only long term habitable one we have is the International Space Ship which has a mass of 496-tons. Assuming this for lack of any other guide, the required energy would be 496 times the one-ton value or 62-trillion kWh, since required energy varies directly as the mass of the body being accelerated. At a conservative five cents per kWh, the electric bill would be a staggering 3.1-trillion dollars!

It is not really fair to use current Earth-bound prices for energy in costing interstellar travel, beamed or otherwise, as the cost of energy in space could be much lower if solar energy and extra-terrestrial resources were used, as beamed power advocates would likely presume. Of course the cost to develop the infrastructure (transportation, in situ materials-processing, etc) would certainly be large, but impossible to estimate far in the future. I suggest years of current total Earth energy use (~500 x10¹⁸ Joules in 2008) as a more meaningful metric. (By pure chance the energy you quote, of 62-trillion kWh, is essentially the same 500 x10¹⁸ Joules.) Wwheaton (talk) 11:10, 22 September 2012 (UTC)

One has to compare apples with apples. A fusion pulse rocket able to reach 10% of lightspeed would be quite a monster - for example, the interstellar "Orion" proposed by Dyson massed ~100,000 tonnes and required 300,000 tonnes of deuterium fuel to achieve a delta-vee of 0.08c. Using Dyson's 0.05c exhaust velocity - about 25 times better than the 0.01c we can expect with present fusion devices - that means a mass-ratio of ~55 is required for a delta-vee of 0.2c (i.e. cruising at 0.lc then braking to a halt.) Thus 5,400,000 tonnes of deuterium fuel is required. At $3,000/kg for deuterium - which sells at $750/kg as heavy water - that means a fuel bill of $16.2 trillion. A high-efficiency fusion pulse rocket can't be built much smaller due to the limitations of fusion devices, as they can't be made arbitrarily small using the Teller-Ulam design. Large devices, and large rockets, are required for high fusion burn-up fractions, else the fusion debris is slowed and diluted by the heavier elements in the ignition system.Qraal (talk) 08:58, 9 April 2013 (UTC)

A further statement in “Required Energy: “If deceleration on arrival is desired and cannot be achieved by other means than by engines of the ship, then the required energy is considerably higher.” Well, most astronauts would probably very much desire it for the alternative is suicide. As for the required energy to decelerate, based on the conservation of energy law it is precisely equal to the kinetic energy and it makes no difference how it is done, by the ship‘s engines or otherwise. However if it is done by a beam from earth as proposed in “Beamed Propulsion” you can double that bill to 6.2 trillion dollars.Paulkint (talk) 16:37, 21 September 2012 (UTC)

I happen to believe that anything feasible is less expensive than nuclear pulse propulsion because the latter would ablate the hull and leave the remainder emitting hard radiation. I recommend removing unsourced statements which seem unlikely. —Cupco 18:39, 21 September 2012 (UTC)

Pulse designs don't ablate "the hull", but a special pusher-plate, and all the radioactive debris is ejected in the exhaust stream. The prompt radiation causes minimal activation thanks to proper choice of materials. The physics and engineering were well advanced before the "Orion" program was shut-down in the early 1960s.Qraal (talk) 08:58, 9 April 2013 (UTC)

Feasible and Speculative Speeds, At a Glance

It would be valuable if someone expanded the table under non-rocket/light-propulsion tech to include ALL the technologies this articles mentions, currently-feasible or speculative, along with potential speed. --107.203.16.165 (talk) 19:16, 8 May 2013 (UTC)

It is extremely difficult to make meaningful statements about speculative concepts, because one must make almost arbitrary assumptions about various details that would likely prove limiting in practice. About the best we can say is that such & such a concept might address this or that issue, suggesting further thinking. The minute you postulate violations of physics, as currently understood, of course you are in wonderland. I would not dismiss such thinking as useless, as conceptual breakthroughs are always possible and have occurred again and again, but one needs to try to be realistic, or at least cautious, about excited claims made by enthusiasts. Such enthusiasm is likely to drive progress eventually in directions we cannot guess, so we don't really want to discourage it, yet still we mustn't lose sight of the problems, especially when making (or reporting) claims. Wwheaton (talk) 13:00, 25 August 2013 (UTC)