Huh ?
Quote from: savuporo on 12/28/2014 06:20 amHuh ?The purpose of the ISS experiment is to demonstrate plasma separation.
While theoretically predicted years ago, observation of plasma detachment from the VASIMR® magnetic nozzle has been difficult to measure in the laboratory due to physical constraints in the configuration and parameter range of previous experiments, as well as the vacuum chamber volume and vacuum level in which they were conducted. However, the unique conditions of the VX-200 device and Ad Astra’s large vacuum facility and pumping capacity have made these investigations possible for the first time. These experiments are expected to continue. However the fullrelevance of research on plasma flow in magnetic nozzles will be enabled by Astra’s planned VF-200 experiment on the International Space Station where the absence of chamber walls and virtually infinite vacuum will allow investigators to probe the full parameter space for these systems.
ISS happens to be the only suitable idea with sufficient power generation available for a meaningful TRL 7ish demo.
Read what you just cited. I don't know what you're disagreeing about.
That's the point of the test. To demonstrate exhaust separation. ..
We've been through this. They haven't demonstrated exhaust separation. It doesn't produce thrust. After 37 years, that's pretty impressive!
The purpose of the ISS experiment is to demonstrate plasma separation.
Quote from: savuporo on 12/28/2014 06:20 amISS happens to be the only suitable idea with sufficient power generation available for a meaningful TRL 7ish demo.I am not sure this is true. Getting any experiment on the ISS is a long term project and it is expensive. I think building a standalone experiment might be much cheaper and simpler. Put those batteries on and you can run it with standard COM-Sat solar panels. It may be though that it is easier to get funding for the ISS-project even if it is much more expensive. Otherwise it should not go to the ISS unless it is at least potentially useful for ISS operations.
Sir, i think you are wrong.
Quote from: guckyfan on 12/28/2014 06:33 amQuote from: savuporo on 12/28/2014 06:20 amISS happens to be the only suitable idea with sufficient power generation available for a meaningful TRL 7ish demo.I am not sure this is true. Getting any experiment on the ISS is a long term project and it is expensive. I think building a standalone experiment might be much cheaper and simpler. Put those batteries on and you can run it with standard COM-Sat solar panels. It may be though that it is easier to get funding for the ISS-project even if it is much more expensive. Otherwise it should not go to the ISS unless it is at least potentially useful for ISS operations.ISS is considered suitable for launching cubesats, for crying out loud. I think that kills your argument right there.
I don't think the two are comparable. Throwing a number of cubesats out of the window airlock is not the same as installing some major experiment with demand on ISS power and influence on ISS trajectory are comparable at all.This said. I am not arguing it is so but putting up the idea a separate experiment would be better and cheaper except for the possibility it may be easier to get funding for an ISS project.
VASIMR or this ? http://arc.aiaa.org/doi/abs/10.2514/1.B35250 ( published 2014 )We had a thread on this, there is a previous publication and some previous coverage toohttp://www.nasa.gov/centers/langley/news/researchernews/rn_ColloquiumWinterberg.htmlEDIT: while i was trawling AIAA of 2014 anyway, i came across VASIMR paper ( of course ) too , herehttp://arc.aiaa.org/doi/abs/10.2514/6.2014-4173Full version : http://www.adastrarocket.com/Jared-Space2014.pdfQuoteDetailed mapping of the plasma plume has been accomplished at a power level of 100 kW in a volume extending more than 2 m downstream of the exhaust exit, without significant neutral background interaction. This has led to a compelling demonstration of how the plasma effectively flows away from the magnetic nozzle of a VASIMR® type device.(4)http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6823704QuoteUnderstanding the physics involved in plasma detachment from magnetic nozzles is well theorized, but lacking in large scale experimental support. We have undertaken an experiment using the 150-m³ variable specific impulse magnetoplasma rocket test facility and VX-200 thruster seeking evidence that detachment occurs and an understanding of the physical processes involved. It was found that the plasma jet in this experiment does indeed detach from the applied magnetic nozzle (peak field ~2 T) in a two part processI am not a plasma scientist, but IEEE and AIAA have accepted these publications.My favorite AIAA links this year :http://arc.aiaa.org/doi/book/10.2514/MSPOPS14 ( all free PDF access ) http://arc.aiaa.org/doi/book/10.2514/MSPACE14
Detailed mapping of the plasma plume has been accomplished at a power level of 100 kW in a volume extending more than 2 m downstream of the exhaust exit, without significant neutral background interaction. This has led to a compelling demonstration of how the plasma effectively flows away from the magnetic nozzle of a VASIMR® type device.(4)
Understanding the physics involved in plasma detachment from magnetic nozzles is well theorized, but lacking in large scale experimental support. We have undertaken an experiment using the 150-m³ variable specific impulse magnetoplasma rocket test facility and VX-200 thruster seeking evidence that detachment occurs and an understanding of the physical processes involved. It was found that the plasma jet in this experiment does indeed detach from the applied magnetic nozzle (peak field ~2 T) in a two part process
QuoteYou would be thinking wrong then. Plasma "poop" is made up of charged particles. If you just shoot out positive ions then a massive electric field will form that will be strong enough to pull those ions back to the rocket, thereby cancelling all thrust. That's why ion thrusters also have electron guns, to neutralize the ions, allowing them to leave the rocket system as neutral atoms. Vasimr doesn't use such a neutralizing mechanism. In fact, I've never quite understood how the ions were to be neutralized efficiently. That's what will define how well the ions detach and whether their blue glowy stuff has any kick to it.In an ion drive, the electrons are pulled away from a gas to leave behind ions, which are then accelerated by an electric field. Thus leaves a net charge on the spacecraft unless those stripped-off electrons are then disposed of via the electron gun.
You would be thinking wrong then. Plasma "poop" is made up of charged particles. If you just shoot out positive ions then a massive electric field will form that will be strong enough to pull those ions back to the rocket, thereby cancelling all thrust. That's why ion thrusters also have electron guns, to neutralize the ions, allowing them to leave the rocket system as neutral atoms. Vasimr doesn't use such a neutralizing mechanism. In fact, I've never quite understood how the ions were to be neutralized efficiently. That's what will define how well the ions detach and whether their blue glowy stuff has any kick to it.
VASIMR heats a neutral gas until some of the electrons separate from their host atoms (form a plasma), but the electrons are left mixed in with the ions, and the plasma overall is electrically neutral. When it is ejected, it carries away equal amounts of positive and negative charge, so no compensation is required.
The electrons do appear to be dragged away from the magnetic field lines through some form of "anomalous transport" as they term it. They don't go easily however, and the initial detachment process forms "turbulence, created by instabilities, where a fluctuating electric field facilitates competing interactions between detached ion and magnetized electrons"
The theory is that electrons and ions detach as a pair, which gives zero parallel electric field. However the more likely scenario is that the electrons will follow the magnetic field lines to a point where it is weaker and then follow the ions from there, not detaching as a pair. Measuring the parallel electrical field would give answer to this question.
The variations in the plasma also can determine how that plasma is able to detach itself from the magnetic field of the nozzle. For instance, in order for dense plasma to escape, the ions and electrons stay together in order to maintain quasineutrality. As listed by Sankaran (2007) [3], there are several ways to address the detachment problem. Firstly, there is resistive detachment, secondly kinetic detachment, thirdly recombination detachment, fourthly non adiabatic detachment, and fifthly electron inertia detachment.
Importantly, this detachment scenario applies while the plasma remains quasineutral, and does not require a net electric current to flow in the magnetic nozzle (as needed for charge conservation of the thruster). In summary, these results prove that plasma detachment is a robust phenomenon based on well-known physical principles, enabling the magnetic nozzle to generate thrust with minimal backflow – a necessary milestone toward demonstrating the applicability of these devices in space plasma propulsion.
VASIMR technology has advantages over Hall when jet power exceeds ~30KW
And one more, setting aside the entire "no thrust" story.Here are the latest mass estimates for flight units:http://spirit.as.utexas.edu/~fiso/telecon/Carter_10-29-14/Carter_10-29-14.pdfhttp://www.adastrarocket.com/IEPC13-149_JPSquire_submit.pdfIt appears the the ISS-bound unit would have to be around half-ton piece at 200kW. But the key takeaway is this :QuoteVASIMR technology has advantages over Hall when jet power exceeds ~30KWThis is based on current flight units under construction and a lot of modeling. The biggest hall effect thruster in service , BPT-4000 is about 10 times smaller ..
Quote from: MP99 on 12/25/2014 08:40 amQuoteYou would be thinking wrong then. Plasma "poop" is made up of charged particles. If you just shoot out positive ions then a massive electric field will form that will be strong enough to pull those ions back to the rocket, thereby cancelling all thrust. That's why ion thrusters also have electron guns, to neutralize the ions, allowing them to leave the rocket system as neutral atoms. Vasimr doesn't use such a neutralizing mechanism. In fact, I've never quite understood how the ions were to be neutralized efficiently. That's what will define how well the ions detach and whether their blue glowy stuff has any kick to it.In an ion drive, the electrons are pulled away from a gas to leave behind ions, which are then accelerated by an electric field. Thus leaves a net charge on the spacecraft unless those stripped-off electrons are then disposed of via the electron gun. Not sure about other electric propulsion drives, but for Hall Effect and gridded ion thrusters the electrons emitted (usually from a hollow cathode gun) are for neutralisation of the ion beam.
QuoteVASIMR heats a neutral gas until some of the electrons separate from their host atoms (form a plasma), but the electrons are left mixed in with the ions, and the plasma overall is electrically neutral. When it is ejected, it carries away equal amounts of positive and negative charge, so no compensation is required. That is true at the engine nozzle exit only. But because ions and electrons have different mass, they are not magnetized to the same extent. The electrons are highly magnetized and will follow the magnetic field lines much more closely than the ions. If the ions detach from the magnetic field lines, then they will need to drag the electrons with them to ensure neutrality. I've just scanned through the recent VASIMR article linked to by savupro*, and this is exactly what they see happening. The electrons do appear to be dragged away from the magnetic field lines through some form of "anomalous transport" as they term it. They don't go easily however, and the initial detachment process forms "turbulence, created by instabilities, where a fluctuating electric field facilitates competing interactions between detached ion and magnetized electrons"A real-world experiment in space is ultimately required to settle the argument of VASIMR thrust.*http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6823704
And one morehttp://iopscience.iop.org/0963-0252/labtalk-article/57987QuoteImportantly, this detachment scenario applies while the plasma remains quasineutral, and does not require a net electric current to flow in the magnetic nozzle (as needed for charge conservation of the thruster). In summary, these results prove that plasma detachment is a robust phenomenon based on well-known physical principles, enabling the magnetic nozzle to generate thrust with minimal backflow – a necessary milestone toward demonstrating the applicability of these devices in space plasma propulsion.Magnetic nozzles may be poorly understood, but i think its beyond the doubt at this point that they actually do work and detachment occurs - hence, thrust.And an illustrative poster of the same workhttp://aero.uc3m.es/ep2/docs/publicaciones/meri12cPO.pdf**ing magnetic nozzles, how do they work??
ISTR Hayabusa (??) had component failures in its thrusters, and was only able to continue by operating the electron gun on a different thruster than was generating thrust.