6 ms·

I hope we'll find out in practice: http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-cubesat-reactionless/ http://www.popularmechanics.com/s

I hope we'll find out in practice: http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-cubesat-reactionless/ http://www.popularmechanics.com/science/energy/a22678/em-dri... (via lobster_johnson) "Proud to say that we have a partnership now - so the launch is already funded, and we hope to get a launch slot in 2017."

cperciva 10y ago
Being in space doesn't solve the problem of errant forces completely. You can push against the earth's magnetic field, for example.
- JumpCrisscross 10y ago
  Satellite orbits degrade overtime due to drag, among other things [1]. Operators counter this decay with periodic boosts. (The International Space Station is boosted, on average, once a month [2].) Boosting, even electric propulsion boosting, consumes propellant. If this works by impelling against the Earth's magnetic field, provided it is more efficient than a simple magnet, it could still have a market with satellite manufacturers. [1] https://en.wikipedia.org/wiki/Orbital_decay https://en.wikipedia.org/wiki/Orbital_decay [2] http://space.stackexchange.com/questions/9087/how-often-does-iss-require-re-boosting-to-higher-orbit#9088 http://space.stackexchange.com/questions/9087/how-often-does...
  - sandworm101 10y ago
    For the power required to generate minimal thrust, this will not be useful in low orbit. The solar panels required to power the drive would result in more drag than the truster might overcome. So no market. And this test flight will not result in a clearcut "it stays up" rather "it fell slower than expected". There will be much calculation and debate re drag, magnetics and gravitational anomolies, so small are the expected forces. To get a clear result we need something out closer to geostationary, flying for months well away from the earth's irregularities.
    - JumpCrisscross 10y ago
      > For the power required to generate minimal thrust, this will not be useful in low orbit A recent paper [1] quotes this system's predicted efficiency at 1.2 mN/kW. Hall thrusters, a propellant-throwing electric engine, perform at 60 mN/kW. Non-propellant systems like light sails, laser propulsion and photon rockets perform around 0.0033 to 0.0067 mN/kW. If this works, and that's a big if, a 50x performance improvement over the prototype is not unrealistic. [1] https://regmedia.co.uk/2016/11/09/q_thruster.pdf https://regmedia.co.uk/2016/11/09/q_thruster.pdf
      - sandworm101 10y ago
        But how big will the panels need be? And how much extra aerodynamic drag will they create in a low orbit?
  - dom0 10y ago
    > If this works by impelling against the Earth's magnetic field That's a completely different premise than the em-drive has, though. It's supposed to not depend on an external field; developing a force between two magnets wouldn't exactly qualify as (non-)rocket science today.
    - matheweis 10y ago
      But it would represent an improvement on what we have today, which is a finite amount of fuel use to keep the satellite in orbit that eventually runs out.
    - stale2002 10y ago
      The way science works is by doing experiments. The people have been doing experiments on the EM drive and have been getting unexpected results. Nobody really knows why yet, but that's kinda the point. Is thermodynamics flawed? Is it pushing off of "dark matter"? Is it a completely new and novel scientific effect? Any of these circumstances would be interesting.
      - DanielBMarkham 10y ago
        Yes. Even if it's the most likely thing, experimenter error, for a half-dozen teams to all have errors and not spot them? That's quite interesting! It's the same situation we had with the FTL neutrinos a while back.
        euyyn 10y ago
        Except the neutrino paper then was a big lot of physicists asking colleagues to help them review, so as to find where the problem was. What I see here is just hype. The former, as opposed to the latter, is what gives confidence that the people involved are doing their darnest not to fool themselves. That what they're doing is actually science.
        DanielBMarkham 10y ago
  - roywiggins 10y ago
    Electrodynamic tethers push off the Earth's magnetic field directly and don't need fuel.
- evo_9 10y ago
  So no proof will ever be enough for some? Are EM-Deniers going to be a 'thing' now?
  - hwillis 10y ago
    If it can accelerate forever, thats proof enough for everyone. However violating the conservation of momentum is a Big Deal. Mathematically that shouldn't be possible due to Noether's. The bar to proof is therefore very high.
    - naasking 10y ago
      General relativity doesn't conserve energy in some spacetimes, so it's not unheard of.
      - andrewflnr 10y ago
        I'm fairly certain GR conserves momentum, even if it doesn't conserve energy.
        naasking 10y ago
        I thought so too until recently, but in GR energy and momentum are unified in an energy-momentum metric which is only locally conserved [1]. [1] https://en.wikipedia.org/wiki/Physical_theories_modified_by_general_relativity#Conservation_of_energy.E2.80.93momentum https://en.wikipedia.org/wiki/Physical_theories_modified_by_...
  - gus_massa 10y ago
    I'm also a yeti-denier! With enough proof you can convince the physics community, even if the result is initially weird. My favorite examples are https://en.wikipedia.org/wiki/Wu_experiment https://en.wikipedia.org/wiki/Wu_experiment and https://en.wikipedia.org/wiki/High-temperature_superconductivity https://en.wikipedia.org/wiki/High-temperature_superconducti... . I think you can push a little against the magnetic field to rotate and change your orientation, but to gain height the magnetic field is not useful. [Edit: Mmmm I'd change "but to gain height the magnetic field is not useful." to "but to gain height pushing against the magnetic field is not efficient."]
- hwillis 10y ago
  If it does, I think that would be detectable. As the device gets into higher orbits, the magnetic field will get weaker and the force will drop. I'm not sure how much the orbit would have to change to make that apparent though. It might take a very long time. Another way it might work is by freeing atoms from the backplate of the resonant cavity, like an ion thruster. I hope they include a method of measuring the degradation of the backplate. I suspect it just won't work, though.
- zamalek 10y ago
  According to the inventor, The Mach thruster (also discussed, and potential underlying physics for the EmDrive) supposedly "pushes against" the Earth's gravity.

cperciva 10y ago

Being in space doesn't solve the problem of errant forces completely. You can push against the earth's magnetic field, for example.

JumpCrisscross 10y ago
Satellite orbits degrade overtime due to drag, among other things [1]. Operators counter this decay with periodic boosts. (The International Space Station is boosted, on average, once a month [2].) Boosting, even electric propulsion boosting, consumes propellant. If this works by impelling against the Earth's magnetic field, provided it is more efficient than a simple magnet, it could still have a market with satellite manufacturers. [1] https://en.wikipedia.org/wiki/Orbital_decay https://en.wikipedia.org/wiki/Orbital_decay [2] http://space.stackexchange.com/questions/9087/how-often-does-iss-require-re-boosting-to-higher-orbit#9088 http://space.stackexchange.com/questions/9087/how-often-does...
- sandworm101 10y ago
  For the power required to generate minimal thrust, this will not be useful in low orbit. The solar panels required to power the drive would result in more drag than the truster might overcome. So no market. And this test flight will not result in a clearcut "it stays up" rather "it fell slower than expected". There will be much calculation and debate re drag, magnetics and gravitational anomolies, so small are the expected forces. To get a clear result we need something out closer to geostationary, flying for months well away from the earth's irregularities.
  - JumpCrisscross 10y ago
    > For the power required to generate minimal thrust, this will not be useful in low orbit A recent paper [1] quotes this system's predicted efficiency at 1.2 mN/kW. Hall thrusters, a propellant-throwing electric engine, perform at 60 mN/kW. Non-propellant systems like light sails, laser propulsion and photon rockets perform around 0.0033 to 0.0067 mN/kW. If this works, and that's a big if, a 50x performance improvement over the prototype is not unrealistic. [1] https://regmedia.co.uk/2016/11/09/q_thruster.pdf https://regmedia.co.uk/2016/11/09/q_thruster.pdf
    - sandworm101 10y ago
      But how big will the panels need be? And how much extra aerodynamic drag will they create in a low orbit?
- dom0 10y ago
  > If this works by impelling against the Earth's magnetic field That's a completely different premise than the em-drive has, though. It's supposed to not depend on an external field; developing a force between two magnets wouldn't exactly qualify as (non-)rocket science today.
  - matheweis 10y ago
    But it would represent an improvement on what we have today, which is a finite amount of fuel use to keep the satellite in orbit that eventually runs out.
  - stale2002 10y ago
    The way science works is by doing experiments. The people have been doing experiments on the EM drive and have been getting unexpected results. Nobody really knows why yet, but that's kinda the point. Is thermodynamics flawed? Is it pushing off of "dark matter"? Is it a completely new and novel scientific effect? Any of these circumstances would be interesting.
    - DanielBMarkham 10y ago
      Yes. Even if it's the most likely thing, experimenter error, for a half-dozen teams to all have errors and not spot them? That's quite interesting! It's the same situation we had with the FTL neutrinos a while back.
      - euyyn 10y ago
        Except the neutrino paper then was a big lot of physicists asking colleagues to help them review, so as to find where the problem was. What I see here is just hype. The former, as opposed to the latter, is what gives confidence that the people involved are doing their darnest not to fool themselves. That what they're doing is actually science.
        DanielBMarkham 10y ago
- roywiggins 10y ago
  Electrodynamic tethers push off the Earth's magnetic field directly and don't need fuel.
evo_9 10y ago
So no proof will ever be enough for some? Are EM-Deniers going to be a 'thing' now?
- hwillis 10y ago
  If it can accelerate forever, thats proof enough for everyone. However violating the conservation of momentum is a Big Deal. Mathematically that shouldn't be possible due to Noether's. The bar to proof is therefore very high.
  - naasking 10y ago
    General relativity doesn't conserve energy in some spacetimes, so it's not unheard of.
    - andrewflnr 10y ago
      I'm fairly certain GR conserves momentum, even if it doesn't conserve energy.
      - naasking 10y ago
        I thought so too until recently, but in GR energy and momentum are unified in an energy-momentum metric which is only locally conserved [1]. [1] https://en.wikipedia.org/wiki/Physical_theories_modified_by_general_relativity#Conservation_of_energy.E2.80.93momentum https://en.wikipedia.org/wiki/Physical_theories_modified_by_...
- gus_massa 10y ago
  I'm also a yeti-denier! With enough proof you can convince the physics community, even if the result is initially weird. My favorite examples are https://en.wikipedia.org/wiki/Wu_experiment https://en.wikipedia.org/wiki/Wu_experiment and https://en.wikipedia.org/wiki/High-temperature_superconductivity https://en.wikipedia.org/wiki/High-temperature_superconducti... . I think you can push a little against the magnetic field to rotate and change your orientation, but to gain height the magnetic field is not useful. [Edit: Mmmm I'd change "but to gain height the magnetic field is not useful." to "but to gain height pushing against the magnetic field is not efficient."]
hwillis 10y ago
If it does, I think that would be detectable. As the device gets into higher orbits, the magnetic field will get weaker and the force will drop. I'm not sure how much the orbit would have to change to make that apparent though. It might take a very long time. Another way it might work is by freeing atoms from the backplate of the resonant cavity, like an ion thruster. I hope they include a method of measuring the degradation of the backplate. I suspect it just won't work, though.
zamalek 10y ago
According to the inventor, The Mach thruster (also discussed, and potential underlying physics for the EmDrive) supposedly "pushes against" the Earth's gravity.