3 ms·

> What if this thing works and momentum is still being conserved? What if it's pushing against something That's what they are claiming: gravitational waves tra

by jules 12y ago

> What if this thing works and momentum is still being conserved? What if it's pushing against something That's what they are claiming: gravitational waves travel back in time, and move all the other matter in the universe a little bit so that momentum is conserved. Or something.

gus_massa 12y ago
If they use gravitational waves, it's a gravitons thruster. It's essentially like a photon thruster (aka backlight). One of the problems is that the ratio of momentum to energy is fixed at 1/c, which is 3.3E-6 N/kW. It's very low and I guess they are getting more than this (and I guess that it's a measurement error).
- api 12y ago
  If this were the case it would be no better than laser propulsion. You could theoretically propel a spacecraft with a beam of photons, but you'd need to borrow God's laser pointer and a power plant that pumps out a couple exawatts to get any meaningful thrust. But only a massless drive could beat the specific impulse... with an iSP of infinity. :) My reading is that this thing, assuming it worked, would have the same problem as ion drives in that it would require a massive power plant. It solves about 1/3 the technical problem of a star drive: where to get the mass. But about 2/3 of the problem of star travel is where to get the energy. High-power-density fusion and antimatter-matter annihilation are the only sources I know of that make star travel thinkable on anything like a human time scale.
  - TeMPOraL 12y ago
    > High-power-density fusion and antimatter-matter annihilation are the only sources I know of that make star travel thinkable on anything like a human time scale. Which, funnily, leads back to a point others and I were making in a different subthread[0] - that any device that allows interplanetary travel in timespans reasonable for humans is at the same time a weapon of mass destruction. Humanity needs to get its act together if we're ever to get out of this rock :). [0] - https://news.ycombinator.com/item?id=8654683 https://news.ycombinator.com/item?id=8654683
    - dragonwriter 12y ago
      > Which, funnily, leads back to a point others and I were making in a different subthread[0] - that any device that allows interplanetary travel in timespans reasonable for humans is at the same time a weapon of mass destruction. We already have plenty of weapons of mass destruction -- sufficient to eradicate modern civilization if not human life entirely -- so its hardly as if not developing technologies necessary for interplanetary travel protects us from such weapons.
  - gus_massa 12y ago
    The energy from the power plan comes from the transformation of a little of the mass of the fuel into energy. (This is usually explained for nuclear power plant, where the mass of the nuclei decrease in the fission (or fusion). But this is also applicable to electric batteries, gasoline+oxygen, ... where the mass comes from the breakup of the chemical bounds. In this cases the differences is completely negligible, but that means that you need a bigger fuel depot.) The mass of the photons is exactly the mass that the power plant loss, so this doesn't solve the mass problem.

by jules 12y ago

gus_massa 12y ago

If they use gravitational waves, it's a gravitons thruster. It's essentially like a photon thruster (aka backlight). One of the problems is that the ratio of momentum to energy is fixed at 1/c, which is 3.3E-6 N/kW. It's very low and I guess they are getting more than this (and I guess that it's a measurement error).

api 12y ago
If this were the case it would be no better than laser propulsion. You could theoretically propel a spacecraft with a beam of photons, but you'd need to borrow God's laser pointer and a power plant that pumps out a couple exawatts to get any meaningful thrust. But only a massless drive could beat the specific impulse... with an iSP of infinity. :) My reading is that this thing, assuming it worked, would have the same problem as ion drives in that it would require a massive power plant. It solves about 1/3 the technical problem of a star drive: where to get the mass. But about 2/3 of the problem of star travel is where to get the energy. High-power-density fusion and antimatter-matter annihilation are the only sources I know of that make star travel thinkable on anything like a human time scale.
- TeMPOraL 12y ago
  > High-power-density fusion and antimatter-matter annihilation are the only sources I know of that make star travel thinkable on anything like a human time scale. Which, funnily, leads back to a point others and I were making in a different subthread[0] - that any device that allows interplanetary travel in timespans reasonable for humans is at the same time a weapon of mass destruction. Humanity needs to get its act together if we're ever to get out of this rock :). [0] - https://news.ycombinator.com/item?id=8654683 https://news.ycombinator.com/item?id=8654683
  - dragonwriter 12y ago
    > Which, funnily, leads back to a point others and I were making in a different subthread[0] - that any device that allows interplanetary travel in timespans reasonable for humans is at the same time a weapon of mass destruction. We already have plenty of weapons of mass destruction -- sufficient to eradicate modern civilization if not human life entirely -- so its hardly as if not developing technologies necessary for interplanetary travel protects us from such weapons.
- gus_massa 12y ago
  The energy from the power plan comes from the transformation of a little of the mass of the fuel into energy. (This is usually explained for nuclear power plant, where the mass of the nuclei decrease in the fission (or fusion). But this is also applicable to electric batteries, gasoline+oxygen, ... where the mass comes from the breakup of the chemical bounds. In this cases the differences is completely negligible, but that means that you need a bigger fuel depot.) The mass of the photons is exactly the mass that the power plant loss, so this doesn't solve the mass problem.