The thread for space cadets!

[uppi]

Keep in mind that their vaccum was fairly crappy, und even the best vaccum in a laboratory contains many orders of magnitude more atoms than the interplanetary medium. So in principle there was a lot of reaction mass in the chamber.

And even if there was indeed some interesting physics going on, it's at first glance a bit far fetched to ascribe it to virtual particles from quantum vaccum fluctuations.

The vacuum of interplanetary space is not that good and can be reached with serious effort (putting anything in there is likely to spoil that, though).

But yeah, it is going to take a lot more to convince anybody of new physics than some thrust that is unaccounted for. The reason for that "thrust" could be anything, from temperature induced stress to photon recoil.

Here is the more complete paper
http://www.libertariannews.org/wp-c...ustProductionFromanRFTestDevice-BradyEtAl.pdf

Is that supposed to be a serious paper? I would be extremely hesitant to let an undergraduate student pass, if he presented me a paper in such a crappy style.

 

[tokala]

The vacuum of interplanetary space is not that good and can be reached with serious effort (putting anything in there is likely to spoil that, though).

Okay, seems I have exaggerated a bit.

Now how good is it exactly at 1 AU?
I am remembering values in the ballpark of a few atoms/cm³.

A reasonably good UHV at 10^-10 mbar would have what? 10^6 molecules/cm³?

 

[Kaitzilla]

So, ESA's Rosetta probe is finally approaching the -unpronouncablename- Comet, taking first photos of its weird "rubber duck" nucleus.

Spoiler :

In November, a small lander, Philae, will separate from the main probe and land on the comet's nucleus. Here's a cute LEDO education video explaining all the functionalities of the lander:


Link to video.

I hope everything goes according to plan, this was a loooooong mission.

10 years long!

Tomorrow is the big day. They gonna enter orbit.
http://www.csmonitor.com/Science/2014/0804/Comet-chasing-Euro-probe-could-make-history-Wednesday

On Wednesday, Aug. 6, the European Space Agency's (ESA) Rosetta spaceraft is expected to arrive around the nucleus of comet 67p/Churyumov-Gerasimenko, ending a 4-billion-mile (6.4 billion kilometers) journey. For the mission's controllers, the historic rendezvous will mark the end of a careful, years-long game of catch-up.

Rosetta launched on March 2, 2004, and was steered through several "gravity assists" around Earth and Mars. These loops helped Rosetta speed up to get far beyond the orbit of Jupiter, near comet 67P/Churyumov-Gerasimenko. But since May, the spacecraft has been slowing down.

According to ESA, Rosetta needs to get within just 2.2 mph (1 m/s) the pace of the comet, which is currently traveling at about 34,175 mph (55,000 km/h). To match the pace of its icy destination, Rosetta has been commanded to do several tight maneuvers to slow its speed by 1,739 mph (2800 km/h) by Aug. 6.

Hope everything works out ok.

Rosetta is carrying a small lander named Philae designed to touch down on the comet nucleus in November so that it can take samples and conduct experiments.
The spacecraft with stay with the comet as it travels around the sun.

Wonder if the name Philae means anything.

 

[Winner]

We're there, in orbit around a comet for the first time in history!

Next step, identification of landing sites for Philae (it is I think named after the place where an obelisk was found that together with the Rosetta stone helped to decipher hieroglyphs).

 

[uppi]

Okay, seems I have exaggerated a bit.

Now how good is it exactly at 1 AU?
I am remembering values in the ballpark of a few atoms/cm³.

A reasonably good UHV at 10^-10 mbar would have what? 10^6 molecules/cm³?

I couldn't find good values for that, only for the moon and for geosynchronous orbit, which were at 10^-11 mbar. That can be reached with any good UHV system.

If you build a cryogenic XHV system and go to the limit you can reach pressures below 10^-15 mbar, which is probably a lot less than the pressures you have at most places in the solar system.

 

[Kaitzilla]

Hehe, XKCD just came out with a comic poking fun at the anomalous thruster:
http://xkcd.com/1404/

 

[Kaitzilla]

A vacuum chamber that was full of air (or some gas at ambient air pressure)

Why didn't they evacuate the chamber?? I don't know enough to know if that matters, to be honest. But it sounds strange, no?

Gah!
Apparently they did do this experiment while the chamber was full of air.

From the Summary:

...The thrust performance of this next generation tapered test article has been analytically determined to be in the 0.1 newton per kilowatt regime. Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors. The tapered thruster has a mechanical design such that it will be able to hold pressure at 14.7 pounds per square inch (psi) inside of the thruster body while the thruster is tested at vacuum to preclude glow discharge within the thruster body while it is being operated at high power.

I take back all my earlier enthusiasm.

 

[Thorgalaeg]

We're there, in orbit around a comet for the first time in history!

Next step, identification of landing sites for Philae (it is I think named after the place where an obelisk was found that together with the Rosetta stone helped to decipher hieroglyphs).

Having been playing KSP lately, It gives you a pale idea about how insanely difficult must be to rendez vous with a comet and land on it in RL. Not wonder it took ten years.

 

[peter grimes]

Gah!
Apparently they did do this experiment while the chamber was full of air.

From the Summary:


I take back all my earlier enthusiasm.

No, I was wrong. I read a good chunk of the published paper. I don't know why the authors used the term "ambient", but it doesn't mean what I thought it meant.

Here's a wired article that explains a lot of the details.

http://www.wired.co.uk/news/archive/2014-08/07/10-qs-about-nasa-impossible-drive

Basically, it seems this thing is legit! There's a lot of skepticism (rightly!) from the theorists, but this test run was basically validating published results from a Chinese experiment.

Seriously.

Gah!
Apparently they did do this experiment while the chamber was full of air.

From the Summary:


I take back all my earlier enthusiasm.

 

[LamaGT]

When something is too good to be true, it probably isn't. Let's hope this is an exception to this rule, because such a thing would be a revolution.

 

[Winner]

Haven't followed this debate on Star Trek drives because I was busy following cometary science being done, but is this similar to the:

http://en.wikipedia.org/wiki/Quantum_vacuum_plasma_thruster ?

 

[Winner]

Having been playing KSP lately, It gives you a pale idea about how insanely difficult must be to rendez vous with a comet and land on it in RL. Not wonder it took ten years.

And this is still a relatively low-period (i.e. slow) comet. Now imagine trying to match orbit with the super-long period comets (Though it would be even more interesting, since they're "fresh" from the Oort cloud freezer).

 

[Kaitzilla]

Haven't followed this debate on Star Trek drives because I was busy following cometary science being done, but is this similar to the:

http://en.wikipedia.org/wiki/Quantum_vacuum_plasma_thruster ?

Yes, that is the one being discussed.

Weird that Wired thinks the experiment was done at vacuum and the Wiki claims it was done at atmospheric pressure.
Which one is it?

If the Chinese really scaled it up already, I don't care if it is pushing with QVPT or just more mundane radiation pressure.
Electricity directly into useful amounts of Thrust with no propellant is roughly like Star Trek Impulse Engines if it really works.


One more nice thing from the Wired Article:

4. Why didn't they test Shawyer's EmDrive design as well as the Cannae drive?

It turns out that in January this year they did test the EmDrive design.

The test results for this were also positive, and in fact their tapered-cavity drive, derived from the Chinese drive which is in turn based on Shawyer's EmDrive, produced 91 micronewtons of thrust for 17 watts of power, compared to the 40 micronewtons of thrust from 28 watts for the Cannae drive.

The Cannae was tested in January of last year(2013) and the report just came out which we have been talking about.
The EmDrine was tested this January and presumably its report won't come out for 1 more year.
But just looking at the results, the EmDrive design gives twice the thrust at half the power

 

[peter grimes]

If you read the paper you'll see it was not a complete vacuum but pretty close.

Edited for accuracy

 

[uppi]

Weird that Wired thinks the experiment was done at vacuum and the Wiki claims it was done at atmospheric pressure.
Which one is it?

The confusion comes from the bad writing in the paper. As far as I understand it, the test was done at high vacuum, but nowhere close to the ultra-high vacuum conditions you have in space.

If you read the paper you'll see it was not a complete vacuum but pretty close.

I wouldn't call 10^-6 mbar close. If the effect is in any way reliant on remnant particles, the six orders of magnitude you still have to go can change a lot, because then you would be worse than a simple laser (or even just a lamp) mounted at the back of the spaceship.

There are quite a lot of experiment they could have done to give hints of the origin and/or the scalability of the device. but they didn't do any of those, and I don't know whether this is laziness, incompetence or if they're afraid of the outcome.

 

[Thorgalaeg]

A quantum vacuum drive, wow! A. C. Clarke already predicted it in "The Songs of Distant Earth". Now if the Sun goes to nova the whole story will make sense.

 

[peter grimes]

Thanks for the clarification, uppi!

Edit:
I did some digging, but I'm stuck.
Wiki says that the density of the interplanetary medium is about 5 particles per cm^3 in earth's vicinity. To figure pressure we need temperature, right? Wiki says 160°k

But I can't figure out how to relate that to millibars.

 

[uppi]

Thanks for the clarification, uppi!

Edit:
I did some digging, but I'm stuck.
Wiki says that the density of the interplanetary medium is about 5 particles per cm^3 in earth's vicinity. To figure pressure we need temperature, right? Wiki says 160°k

But I can't figure out how to relate that to millibars.

If you assume that the particles behave like an ideal gas in thermodynamic equilibrium, it is fairly simple. you just use the ideal gas law:

pressure = particle density * Boltzmann constant * temperature.

Using your values (pedantic note: 160 K, no degree symbol!) I get 10^-16 mbar.

However, i would seriously question those assumptions. The particles are more likely to behave like a plasma instead of an ideal gas. (And I don't remember plasma physics well enough to figure out the pressure of a plasma). And with all the sources of particles from different sources around and the low density, it is questionable, whether interplanetary space can really be taken to be in thermodynamic equilibrium.

And I don't really trust those numbers, anyway. So take the calculations with more than one grain of salt.

 

[peter grimes]

Thanks. I knew it must have been more complicated. The degree symbol was required by Wolfram Alpha, otherwise it interpreted it as 160,000.

The wiki did say that it's a plasma, influenced by a electromagnetic fields and such. There was also something about a sheet with a cool graphic. Had to do with space magnets from the sun

 

[hobbsyoyo]

I was at a conference dedicated to small satellites (which has basically come to mean exclusively CubeSats) and there is a ton of RD work going on. I think we're going to see larger satellites phased out for a lot of purposes in the next 20 years or so as the CubeSats become more and more capable. They were talking interplanetary missions! (which is super exciting)

Even the lunar CubeSat mission I'm working on will be a big leap forward for the platform.

Edit:

Oh and I was talking to a guy about a hydrazine based thruster his company made and he tried to tell me hydrazine isn't really as dangerous as people make it out be. I was like lolwtfgtfo