7 ms·

EmDrive: China claims success with this 'reactionless' engine for space travel

62 points by Osiris30 10y ago

londons_explore 10y ago
Is there a paper or technical source? All the articles I find seem to be copy pasta of one another, none of which have sources...
- aluhut 10y ago
  Pictures come from here: http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
- vanattab 10y ago
  Here is a link to the most recent nasa eagle works paper. http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
  - kobeya 10y ago
    He's asking about the Chinese test. That one appears to be hearsay.
madengr 10y ago
Why after several positive tests, has the physics community not gone full throttle to try and disprove it, like they did with cold fusion? So far the tests have been static torque? Could there be an interaction with the earths magnetic field?
- deleted 10y ago
  [deleted]
- the8472 10y ago
  China is shipping one up to their space station to test it there. That is already a pretty big allocation for research resources considering that there is a large prior against this working: conservation of momentum. So every time a positive result turns up incrementally more effort will be applied to test it, assuming the new result improves on previous ones. Seems like a reasonable approach to me.
  - colordrops 10y ago
    I still haven't heard a good explanation why this must mean that conservation of momentum is being violated. Couldn't there be a new phenomenon at which forces act at a larger or more distant scale on other masses, similar to gravity? That seems more plausible than beating conservation of momentum.
    - the8472 10y ago
      Yes, physicists are more likely to look for new physics than toss out the the conservation. But the new physics would have to be fairly narrow since the standard model is fairly well-tested and consistent with most observations.
    - gus_massa 10y ago
      > Couldn't there be a new phenomenon at which forces act at a larger or more distant scale on other masses, similar to gravity? Gravity doesn't act at large distance. If you have a star like the Sun, it modifies the gravitational field locally. The modifications travel for a while and when the modification hits a planet like the Earth it applies a force to the Earth and modifies it's direction. The modifications are like the gravitational waves that have been recently measured. They travel at the speed of light. If you have a force that can truly act at distance, you can use it to transmit information faster than light and it will break special relativity.
      - colordrops 10y ago
        Well all experiments have been near large large objects so far, so if such a force exists nothing is being said about it being faster than light.
        gus_massa 10y ago
        Near is very near here. Let's analyze a similar case. The weak nuclear force is transmitted by the W+, Z0 and W- particles. They live approximately 1E-25 seconds. Assuming they travel near the speed of light, they can travel 3E-17 meters. That is a very small distance You can think that an electron and a neutrino at 3E-17 meters can somehow interact at distance, because it's very small. But this is not true. The electron has to create one of the W+, Z0 and W- particles, send it to the neutrino, and the neutrino has to absorb it. Even 3E-17 meters is a long distance here, and it's possible to measure indirectly the properties of the intermediate particles. If the Em-Drive device somehow interacts with the floor, walls or the Earth that are a few inches away, this is a extremely very big distance for the current theories. The Em-drive must interact with some kind of field and create some intermediate particles, like photons, gravitons or some new particle. The problem is that if the Em-drive using some field and particles to conserve the energy and momentum locally, then the maximal theoretical output of a device that don't break the currently accepted physics laws is 1/c = 0.0033 mN/KW. I couldn't find in this article the experimental results in China, but it the recent "successful" experiment in NASA measured 4000x this value. [In my opinion, it was an experimental error.] Getting 0.0033 mN/KW is "easy" with a perfect light source, like a perfect laser. Less is easier with a real light source, like a real laser. More is theoretical impossible with the current physics laws.
- arcanus 10y ago
  > Why after several positive tests, has the physics community not gone full throttle to try and disprove it, like they did with cold fusion? No one has any funding to research it. Despite the press, no major research agency is backing efforts to investigate the effect. Cold fusion actually did get serious funding back in the 80s, which made it 'higher profile' to the scientific community. I'll add that cold fusion seemed more plausible. In that it did not violate extremely well understood fundamental principles of physics, e.g. conservation of momentum. While incorrect, cold fusion was at least on the face of it a sensible inquiry at one time. The EM drive has extremely compelling reasons to ellicit extreme skepticism from the scientific community at large.
  - mordant 10y ago
    >In that it did not violate extremely well understood fundamental principles of physics Cold fusion violated the fundamental principle of 'Where are all the dead grad students caught up in the neutron flux?'.
IgorPartola 10y ago
I thought it was shown that the thrust was due to the power cable's electromagnetic field.
- madengr 10y ago
  No; See page 9 section 3 of paper.
madengr 10y ago
So they used twisted pair DC cabling to minimize torque errors due to DC magnetic field (and the torque follows direction of cavity orientation), but.... I'm wondering if there is DC current circulating in the cavity due to rectification from oxides or impurities on the copper surface; i.e. Passive Intermodulation Distortion (disclaimer I'm an RF EE). They said the torque was strongly non-linear with applied power; which is a hint. DC cavity currents were not listed as a potential error source, but these phenomenon could show up with high power and high Q. Anyway, I just emailed a couple of the NASA guys; see what they say.
- isaiahg 10y ago
  Would be interested to see how they reply.
- londons_explore 10y ago
  I don't understand why they don't just use a battery to power the experiments... Now all power supply related concerns are gone.
  - madengr 10y ago
    No, the RF sources (magnetron) still require DC current.
  - walrus01 10y ago
    on the scale of micronewtons being measured, batteries change significantly thermally as they're discharged. You would have to account for the chemical and thermal activity of the battery which is not a 100% inert thing.
sfifs 10y ago
I kind of expected China would fund a let's try it where measurements are easier amd obvious and see approach. Some experiments just cannot be done properly in of our gravity well. EmDrive claims are tailored made for testing in space.
choxi 10y ago
I'm surprised at how quiet SpaceX has been on this, the tech seems right up their alley.
- espadrine 10y ago
  SpaceX relies on well-understood principles, which the EmDrive is not. The equivalent in programming terms would be a program which nobody understands, and that some say can perform a comparison-based sort in constant time, but only for petabytes of data.
- akvadrako 10y ago
  You shouldn't be - all signs point to this being crackpot science. A couple of the biggest reasons are: 1. The magnitudes recorded in the several badly done experiments are very small and there are plenty of possible experimental errors. 2. The original inventor's own theory of how it works plainly violates very fundamental physics, like how all frames of reference are equivalent. There is really no reason to think this will work, except hope. Still, it's a good idea to do some more research and put the idea to rest.
trelliscoded 10y ago
I just wanted to point out that thrust without expending mass is already possible without an emdrive. Anything that asymmetrically radiates photons will generate a net acceleration. This very mechanism has been experimentally verified as the pioneer acceleration anomaly. If the emdrive is some kind of special case of this mechanism, it's entirely compatible with existing physics. The proposals so far are based on mechanisms which are different, and incompatible with the existing understanding of the universe. It's also worth noting that in 2016 the Chinese research team was unable to replicate their findings after accounting for a power cable that was magnetically inducing a force on the experimental apparatus.
- beevai142 10y ago
  Photon rockets are not actually reactionless, because the emitted photons carry momentum and energy out of the system. This makes conservation laws to hold for such systems, cf. https://arxiv.org/abs/1506.00494 https://arxiv.org/abs/1506.00494 Now, the emdrive people are apparently claiming that it is truly reactionless. If so, you can build a perpetual motion machine of the first kind (produces energy from nothing) out of it --- which should demonstrate the degree of plausibility of such claims. For photon rockets, there's apparently a hard upper bound on the efficiency, which limits the practical usability.
  - trelliscoded 10y ago
    You're right, what I really meant was radiation pressure doesn't require reaction mass.
gabrielblack 10y ago
It smells like bullshit: no source, no paper, no verifiable test available. It seems the classic scientific fraud that , resurrecting like a cockroach again and again in the socials, has only the purpose to feed the conspiracy theories.

62 points by Osiris30 10y ago

Is there a paper or technical source? All the articles I find seem to be copy pasta of one another, none of which have sources...

aluhut 10y ago
Pictures come from here: http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
vanattab 10y ago
Here is a link to the most recent nasa eagle works paper. http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
- kobeya 10y ago
  He's asking about the Chinese test. That one appears to be hearsay.

madengr 10y ago

Why after several positive tests, has the physics community not gone full throttle to try and disprove it, like they did with cold fusion? So far the tests have been static torque? Could there be an interaction with the earths magnetic field?

deleted 10y ago
[deleted]
the8472 10y ago
China is shipping one up to their space station to test it there. That is already a pretty big allocation for research resources considering that there is a large prior against this working: conservation of momentum. So every time a positive result turns up incrementally more effort will be applied to test it, assuming the new result improves on previous ones. Seems like a reasonable approach to me.
- colordrops 10y ago
  I still haven't heard a good explanation why this must mean that conservation of momentum is being violated. Couldn't there be a new phenomenon at which forces act at a larger or more distant scale on other masses, similar to gravity? That seems more plausible than beating conservation of momentum.
  - the8472 10y ago
    Yes, physicists are more likely to look for new physics than toss out the the conservation. But the new physics would have to be fairly narrow since the standard model is fairly well-tested and consistent with most observations.
  - gus_massa 10y ago
    > Couldn't there be a new phenomenon at which forces act at a larger or more distant scale on other masses, similar to gravity? Gravity doesn't act at large distance. If you have a star like the Sun, it modifies the gravitational field locally. The modifications travel for a while and when the modification hits a planet like the Earth it applies a force to the Earth and modifies it's direction. The modifications are like the gravitational waves that have been recently measured. They travel at the speed of light. If you have a force that can truly act at distance, you can use it to transmit information faster than light and it will break special relativity.
    - colordrops 10y ago
      Well all experiments have been near large large objects so far, so if such a force exists nothing is being said about it being faster than light.
      - gus_massa 10y ago
        Near is very near here. Let's analyze a similar case. The weak nuclear force is transmitted by the W+, Z0 and W- particles. They live approximately 1E-25 seconds. Assuming they travel near the speed of light, they can travel 3E-17 meters. That is a very small distance You can think that an electron and a neutrino at 3E-17 meters can somehow interact at distance, because it's very small. But this is not true. The electron has to create one of the W+, Z0 and W- particles, send it to the neutrino, and the neutrino has to absorb it. Even 3E-17 meters is a long distance here, and it's possible to measure indirectly the properties of the intermediate particles. If the Em-Drive device somehow interacts with the floor, walls or the Earth that are a few inches away, this is a extremely very big distance for the current theories. The Em-drive must interact with some kind of field and create some intermediate particles, like photons, gravitons or some new particle. The problem is that if the Em-drive using some field and particles to conserve the energy and momentum locally, then the maximal theoretical output of a device that don't break the currently accepted physics laws is 1/c = 0.0033 mN/KW. I couldn't find in this article the experimental results in China, but it the recent "successful" experiment in NASA measured 4000x this value. [In my opinion, it was an experimental error.] Getting 0.0033 mN/KW is "easy" with a perfect light source, like a perfect laser. Less is easier with a real light source, like a real laser. More is theoretical impossible with the current physics laws.
arcanus 10y ago
> Why after several positive tests, has the physics community not gone full throttle to try and disprove it, like they did with cold fusion? No one has any funding to research it. Despite the press, no major research agency is backing efforts to investigate the effect. Cold fusion actually did get serious funding back in the 80s, which made it 'higher profile' to the scientific community. I'll add that cold fusion seemed more plausible. In that it did not violate extremely well understood fundamental principles of physics, e.g. conservation of momentum. While incorrect, cold fusion was at least on the face of it a sensible inquiry at one time. The EM drive has extremely compelling reasons to ellicit extreme skepticism from the scientific community at large.
- mordant 10y ago
  >In that it did not violate extremely well understood fundamental principles of physics Cold fusion violated the fundamental principle of 'Where are all the dead grad students caught up in the neutron flux?'.

IgorPartola 10y ago

I thought it was shown that the thrust was due to the power cable's electromagnetic field.

madengr 10y ago
No; See page 9 section 3 of paper.

madengr 10y ago

So they used twisted pair DC cabling to minimize torque errors due to DC magnetic field (and the torque follows direction of cavity orientation), but.... I'm wondering if there is DC current circulating in the cavity due to rectification from oxides or impurities on the copper surface; i.e. Passive Intermodulation Distortion (disclaimer I'm an RF EE). They said the torque was strongly non-linear with applied power; which is a hint. DC cavity currents were not listed as a potential error source, but these phenomenon could show up with high power and high Q. Anyway, I just emailed a couple of the NASA guys; see what they say.

isaiahg 10y ago
Would be interested to see how they reply.
londons_explore 10y ago
I don't understand why they don't just use a battery to power the experiments... Now all power supply related concerns are gone.
- madengr 10y ago
  No, the RF sources (magnetron) still require DC current.
- walrus01 10y ago
  on the scale of micronewtons being measured, batteries change significantly thermally as they're discharged. You would have to account for the chemical and thermal activity of the battery which is not a 100% inert thing.

sfifs 10y ago

I kind of expected China would fund a let's try it where measurements are easier amd obvious and see approach. Some experiments just cannot be done properly in of our gravity well. EmDrive claims are tailored made for testing in space.

choxi 10y ago

I'm surprised at how quiet SpaceX has been on this, the tech seems right up their alley.

espadrine 10y ago
SpaceX relies on well-understood principles, which the EmDrive is not. The equivalent in programming terms would be a program which nobody understands, and that some say can perform a comparison-based sort in constant time, but only for petabytes of data.
akvadrako 10y ago
You shouldn't be - all signs point to this being crackpot science. A couple of the biggest reasons are: 1. The magnitudes recorded in the several badly done experiments are very small and there are plenty of possible experimental errors. 2. The original inventor's own theory of how it works plainly violates very fundamental physics, like how all frames of reference are equivalent. There is really no reason to think this will work, except hope. Still, it's a good idea to do some more research and put the idea to rest.

trelliscoded 10y ago

I just wanted to point out that thrust without expending mass is already possible without an emdrive. Anything that asymmetrically radiates photons will generate a net acceleration. This very mechanism has been experimentally verified as the pioneer acceleration anomaly. If the emdrive is some kind of special case of this mechanism, it's entirely compatible with existing physics. The proposals so far are based on mechanisms which are different, and incompatible with the existing understanding of the universe. It's also worth noting that in 2016 the Chinese research team was unable to replicate their findings after accounting for a power cable that was magnetically inducing a force on the experimental apparatus.

beevai142 10y ago
Photon rockets are not actually reactionless, because the emitted photons carry momentum and energy out of the system. This makes conservation laws to hold for such systems, cf. https://arxiv.org/abs/1506.00494 https://arxiv.org/abs/1506.00494 Now, the emdrive people are apparently claiming that it is truly reactionless. If so, you can build a perpetual motion machine of the first kind (produces energy from nothing) out of it --- which should demonstrate the degree of plausibility of such claims. For photon rockets, there's apparently a hard upper bound on the efficiency, which limits the practical usability.
- trelliscoded 10y ago
  You're right, what I really meant was radiation pressure doesn't require reaction mass.

gabrielblack 10y ago

It smells like bullshit: no source, no paper, no verifiable test available. It seems the classic scientific fraud that , resurrecting like a cockroach again and again in the socials, has only the purpose to feed the conspiracy theories.