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Design and Applications for EMdrive-propelled Spacecraft
by
sanman
on 10 Jan, 2017 06:32
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Okay, sorry to put the cart before the horse, as things are still very much up in the air on the EMdrive.
But just supposing the device works as advertised - then based on what is claimed, what are the applications to best make use of EMdrive and its peculiar features?
Furthermore, how should such spacecraft be designed or engineered? Are there any special considerations here?
Is it as simple as merely mounting a frustrum/device on any old spacecraft, fitting it with appropriate power source (solar panels?) and then you've got a working spacecraft?
Is conventional electric-propulsion the closest analogy? Like DeepSpace-1 or SMART-1?
Would you primarily use EMdrive as your main thruster, and just use a couple of sets of reaction-wheels to change your orientation, to steer you in the desired direction?
In what ways might designs gradually evolve?
As more powerful nuclear reactors become available, would that power be sent to large arrays of frustrums, or to one big frustrum? Could EMdrive propulsion ever be suitable for maneuvering thrusters? (Hey, even cheap cars are switching away from fluid-hydraulics to electro-mechanical steering, because it's less prone to breakdown)
If the device works as claimed, then would interstellar missions be possible?
Would EMdrive face any potential limits in accelerating towards relativistic velocities?
So far, the best applications I see are station-keeping (long duration, low thrust) and long-distance voyages (the longer the distance, the greater the benefits from propellant-mass savings)
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#1
by
Stormbringer
on 11 Jan, 2017 15:22
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Well EW had some nice juicy slides on their drive doing various mission profiles like interplanetary and even interstellar missions -unless i am conflating the EM drive with their other device. For longer range missions would having a secondary propulsion system acting like a JATO to boost the initial acceleration? How much time is wasted getting up to a respectable velocity with an EM drive? Would a rocket based kick in the pants to get it going make sense?
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#2
by
Donosauro
on 11 Jan, 2017 15:35
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... [T]hings are still very much up in the air on the EMdrive.
It is more accurate to say that things are still down on the ground with the EMdrive.
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#3
by
aero
on 11 Jan, 2017 16:15
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There was a very nice analysis in an EW paper of advantages gained using orbital mechanics with constant thrust over the classic boost and coast method required with chemical rockets. The trick was that the acceleration of the EM drive powered spacecraft had to be greater than the acceleration of the sun's gravity at Earth orbital distance, that is, greater than 5.9E-3 meters/sec^2. Of course a = Force/mass so that gives one design parameter of your spacecraft.
The end result was that the 26 month separation between launch windows to Mars went by the wayside resulting in continuously available launch windows with the longest trip time being something like 8 months for the worst case and much better than that over most of the synodic period.
Maybe someone reading this will remember the link to the paper. Paul?
Steve
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#4
by
sanman
on 11 Jan, 2017 19:18
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Well EW had some nice juicy slides on their drive doing various mission profiles like interplanetary and even interstellar missions -unless i am conflating the EM drive with their other device. For longer range missions would having a secondary propulsion system acting like a JATO to boost the initial acceleration? How much time is wasted getting up to a respectable velocity with an EM drive? Would a rocket based kick in the pants to get it going make sense?
Well, EMdrive won't get fragile living cargo through the Van Allen Belts very quickly, it seems. So it would probably be good to have the chemical thrusters to give the higher acceleration in certain situations. So you'd probably have some chemical propellant onboard, but just not as much.
Maybe cryo-propellants could be used to cool any superconductors used by EMdrive.
There was a very nice analysis in an EW paper of advantages gained using orbital mechanics with constant thrust over the classic boost and coast method required with chemical rockets. The trick was that the acceleration of the EM drive powered spacecraft had to be greater than the acceleration of the sun's gravity at Earth orbital distance, that is, greater than 5.9E-3 meters/sec^2. Of course a = Force/mass so that gives one design parameter of your spacecraft.
The end result was that the 26 month separation between launch windows to Mars went by the wayside resulting in continuously available launch windows with the longest trip time being something like 8 months for the worst case and much better than that over most of the synodic period.
Maybe someone reading this will remember the link to the paper. Paul?
Steve
If EMdrive becomes a legitimate form of Solar-Electric Propulsion, then I wonder where the design tradeoffs will be, in the solar array size and mass, so solar flux can generate enough electrical power and thrust to overcome solar gravitational pull.
In missions to the outer solar system and beyond, you'd likely want nuclear-electric.
If space in the gravity wells is called "curved" and space away from them is "flatter", then I wonder how EMdrive would perform farther out in the "flatter" interstellar space as compared to near gravity wells.
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#5
by
A_M_Swallow
on 15 Jan, 2017 22:49
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Well, EMdrive won't get fragile living cargo through the Van Allen Belts very quickly, it seems. So it would probably be good to have the chemical thrusters to give the higher acceleration in certain situations. So you'd probably have some chemical propellant onboard, but just not as much.
Maybe cryo-propellants could be used to cool any superconductors used by EMdrive.
{snip}
Alternatively you launch your manned transfer vehicle from GEO or a spacestation at a Lagrange Point. SLS and Orion can fly to Lagrange Points and Dragon V2 will have a good go.
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#6
by
aero
on 16 Jan, 2017 00:57
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Well, EMdrive won't get fragile living cargo through the Van Allen Belts very quickly, it seems. So it would probably be good to have the chemical thrusters to give the higher acceleration in certain situations. So you'd probably have some chemical propellant onboard, but just not as much.
Maybe cryo-propellants could be used to cool any superconductors used by EMdrive.
{snip}
Alternatively you launch your manned transfer vehicle from GEO or a spacestation at a Lagrange Point. SLS and Orion can fly to Lagrange Points and Dragon V2 will have a good go.
It could be done that way but is that the best way to use that chemical propellant considering that the EM drive is propellantless? It is the same mass at the transfer station as it is on Earth so instead of sending the mass of the Orion, just send the EM drive powered spacecraft. Of course that only works if your spacecraft is not much more massive than a fueled Orion or you have a booster more capable than the SLS.
My personal druthers is to boost the EM drive spacecraft up to a meaningful relative velocity on it's outbound trajectory with chemical as that would significantly reduce transit time beyond just the reduction from constant low thrust. That is, work equals force times distance, and with a chemical boost the work per second performed by the EM drive becomes thrust times distance per second, or thrust times velocity.
How does that work out? Check my assumptions but given a low thrust resulting in what 1x10^-8 m/s^2 acceleration, that would be 1x10^-8*86,400^2 per day, or 0.0746 km/sec delta V per day. A modest chemical boost of 1 km/sec then would save 13.4 days of acceleration through the radiation belts and significantly reduce the time length of the voyage.
At least it seems that way to me.
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#7
by
SergioZ82
on 16 Jan, 2017 09:33
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I believe we should re-imagine our concept of spaceship (and probe)
First of all, a spacecraft equipped with an EM engine can thrust as along as the power source is active. This means it can not only visit various celestial bodies in a single mission but also that it can reach speeds that are unattainable with ion/chemical propulsion. It can basically accelerate up to half way from destination, then turn 180° and thrust in opposite direction to slow down.
The best solution to power the engine is a nuclear reactor (and it's even fundamental for deep space missions): I'm talking with PNN in mind, which requires a great amount of current. I think solar panels would be an excellent solution for early EM probes with low thrust values and satellites.
Until we won't have a spacecraft specifically designed around EmDrive (or other EM thrusters like Cannae or PNN) I think our current models will be retrofitted to mount the frustum(s) or tiles (PNN).
I can't help but it comes to my mind an imagine of the Space Shuttle equipped with an array of frustums
I depict this near-future like the hybrid old-new vehicles I've seen in Independence Day Resurgence (but that's daydreaming).
E.M technology would make excellent position thrusters to rotate a spacecraft around all its axes.
If we imagine that tomorrow morning EM propulsion will be used for space application then we can speculate that in 10/20 years the technology will be mature enough to generate massive thrusts, even capable of generating more than 1 g of acceleration. Then a spacecraft will probably levitate and gain orbit in a little time.
We'll also probably laugh at how wrong all sci-fi spaceships have been depicted so far: basically sea ships design transposed in space. With such design if the ships accelerates the crew (and everything is not bolted on the hull) is pushed toward the stern. With 1 g acceleration the best design is.. something similar to a skyscraper
Personally I think that flying saucer design is good too (except for the fact that during space flight it offers a big impact surface to debris like rocks).
Also interstellar travel become instantly far closer than with chemical/ion/antimatter propulsion (basically everything Newtonian).
I invite you to read these two articles from my blog (I link them because as far as I know nothing similar exists on the web)
Sailing across the solar system and beyond/As if one wasn't enough PNN breaks another law/Those are written for PNN but I believe they're also valid for EmDrive
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#8
by
clongton
on 16 Jan, 2017 13:11
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Well, EMdrive won't get fragile living cargo through the Van Allen Belts very quickly, it seems. So it would probably be good to have the chemical thrusters to give the higher acceleration in certain situations. So you'd probably have some chemical propellant onboard, but just not as much.
Maybe cryo-propellants could be used to cool any superconductors used by EMdrive. {snip}
Alternatively you launch your manned transfer vehicle from GEO or a spacestation at a Lagrange Point. SLS and Orion can fly to Lagrange Points and Dragon V2 will have a good go.
It could be done that way but is that the best way to use that chemical propellant considering that the EM drive is propellantless? It is the same mass at the transfer station as it is on Earth so instead of sending the mass of the Orion, just send the EM drive powered spacecraft. Of course that only works if your spacecraft is not much more massive than a fueled Orion or you have a booster more capable than the SLS.
My personal druthers is to boost the EM drive spacecraft up to a meaningful relative velocity on it's outbound trajectory with chemical as that would significantly reduce transit time beyond just the reduction from constant low thrust. That is, work equals force times distance, and with a chemical boost the work per second performed by the EM drive becomes thrust times distance per second, or thrust times velocity.
How does that work out? Check my assumptions but given a low thrust resulting in what 1x10^-8 m/s^2 acceleration, that would be 1x10^-8*86,400^2 per day, or 0.0746 km/sec delta V per day. A modest chemical boost of 1 km/sec then would save 13.4 days of acceleration through the radiation belts and significantly reduce the time length of the voyage.
At least it seems that way to me.
ISTM that if the EM-Drive spacecraft is to be reusable then we would want to depart from and return to either EML-1 or EML-2. LEO is out of the question. So the trip from earth's surface or LEO with crew aboard to/from the spacecraft would be chemically powered in a separate spacecraft designed as a taxi.
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#9
by
Star-Drive
on 16 Jan, 2017 13:54
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There was a very nice analysis in an EW paper of advantages gained using orbital mechanics with constant thrust over the classic boost and coast method required with chemical rockets. The trick was that the acceleration of the EM drive powered spacecraft had to be greater than the acceleration of the sun's gravity at Earth orbital distance, that is, greater than 5.9E-3 meters/sec^2. Of course a = Force/mass so that gives one design parameter of your spacecraft.
The end result was that the 26 month separation between launch windows to Mars went by the wayside resulting in continuously available launch windows with the longest trip time being something like 8 months for the worst case and much better than that over most of the synodic period.
Maybe someone reading this will remember the link to the paper. Paul?
Steve
Aero/Steve:
The papers you seek are attached.
PS: Adding another EW future Q-Thruster applications presentation.
Best, Paul M.
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#10
by
aero
on 16 Jan, 2017 15:42
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Oh My! That's even better numbers than I remembered. Thanks Paul.
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#11
by
sanman
on 18 Jan, 2017 01:20
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I'd wondered if the EMdrive might possibly produce any roll torque around the thrust axis.
Mwvp replied back, saying that roll torque was likely not going to happen.There would still have to be rigorous long-duration testing to see if even any tiny hint of roll torque shows up.
If you're going for a multi-decadal flight, then can you really get away with short-duration testing?
Given that EMdrive could be used for long-duration/long-acceleration voyages, then if even a slight amount of roll torque occurs which was not planned for, then it could potentially mess things up. Imagine your spacecraft is traveling to some distant star, accelerating using EMdrive thrust for a period of decades. Over a sufficiently long period of time, even a tiny amount of roll torque that wasn't immediately apparent could manifest itself and become very large and problematic if it wasn't a design consideration. Even if your spacecraft has reaction wheels or other types of thrusters to correct its orientation, it's possible that EMdrive could "outlast" them all - ie. your reaction wheels would become saturated, your other corrective thrusters could run out of fuel, long before the EMdrive does.
What about using multiple EMdrives that could mutually offset/cancel any potential roll torques from the others?
I believe we should re-imagine our concept of spaceship (and probe)
First of all, a spacecraft equipped with an EM engine can thrust as along as the power source is active. This means it can not only visit various celestial bodies in a single mission but also that it can reach speeds that are unattainable with ion/chemical propulsion. It can basically accelerate up to half way from destination, then turn 180° and thrust in opposite direction to slow down.
The best solution to power the engine is a nuclear reactor (and it's even fundamental for deep space missions): I'm talking with PNN in mind, which requires a great amount of current. I think solar panels would be an excellent solution for early EM probes with low thrust values and satellites.
Until we won't have a spacecraft specifically designed around EmDrive (or other EM thrusters like Cannae or PNN) I think our current models will be retrofitted to mount the frustum(s) or tiles (PNN).
I can't help but it comes to my mind an imagine of the Space Shuttle equipped with an array of frustums
I depict this near-future like the hybrid old-new vehicles I've seen in Independence Day Resurgence (but that's daydreaming).
E.M technology would make excellent position thrusters to rotate a spacecraft around all its axes.
At least EMdrive maneuvering thrusters would be solid-state, unlike reaction wheels or conventional thrusters- so probably more reliable and less prone to breakdown. Even conventional electrical thrusters may be subject to erosion (eg. grid erosion in ion-drives) in a way that EMdrive would not. Supposing you had to make lots of course adjustments across a long-duration voyage - at least EMdrive wouldn't be in danger of running out of propellant.
If we imagine that tomorrow morning EM propulsion will be used for space application then we can speculate that in 10/20 years the technology will be mature enough to generate massive thrusts, even capable of generating more than 1 g of acceleration. Then a spacecraft will probably levitate and gain orbit in a little time.
We'll also probably laugh at how wrong all sci-fi spaceships have been depicted so far: basically sea ships design transposed in space. With such design if the ships accelerates the crew (and everything is not bolted on the hull) is pushed toward the stern. With 1 g acceleration the best design is.. something similar to a skyscraper
Personally I think that flying saucer design is good too (except for the fact that during space flight it offers a big impact surface to debris like rocks).
Also interstellar travel become instantly far closer than with chemical/ion/antimatter propulsion (basically everything Newtonian).
Imagine living inside a huge skyscraper for a long period of time while accelerating towards another star system - and then suddenly one day the skyscraper has to flip around. Even if that fliparound maneuver is brief, its disruptive potential would probably be the basis for a lot of apprehension.
Heh, it would be their "Y2K" event.
Perhaps a real skyscraper could be used as a training facility for such a spaceship.
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#12
by
SergioZ82
on 18 Jan, 2017 09:51
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I'd wondered if the EMdrive might possibly produce any roll torque around the thrust axis.
...
What about using multiple EMdrives that could mutually offset/cancel any potential roll torques from the others?
This is an interesting uncovered issue. A roll torque might have disruptive effects on the spaceship route and even on the structure itself if the main thruster was powerful enough. Let's hope there won't be the need for reaction wheels.
At least EMdrive maneuvering thrusters would be solid-state, unlike reaction wheels or conventional thrusters- so probably more reliable and less prone to breakdown. Even conventional electrical thrusters may be subject to erosion (eg. grid erosion in ion-drives) in a way that EMdrive would not. Supposing you had to make lots of course adjustments across a long-duration voyage - at least EMdrive wouldn't be in danger of running out of propellant.
Yes I agree. The only reliability problem might be the high working temperatures which might stress the components. PNN thrusters have an overheating issue and maybe this will be a problem for EmDrive too, with an high power supply.
Imagine living inside a huge skyscraper for a long period of time while accelerating towards another star system - and then suddenly one day the skyscraper has to flip around. Even if that fliparound maneuver is brief, its disruptive potential would probably be the basis for a lot of apprehension.
Heh, it would be their "Y2K" event.
Perhaps a real skyscraper could be used as a training facility for such a spaceship.
My example was very simplifying, I guess the first problem of flying a skyscraper is that it'll probably crumble after few moments from take off.
The ship hypothesized in my blog is an hollow cylinder with floors displaced like a common building, hence the analogy. Its structure will must be designed to endure rotational forces that occur during the inversion maneuver.
I don't think it'll be a big problem to flip the ship (within its operational parameters and human body tolerance limits of course), because once the main thrust is switched off there are no other perturbative and potentially dangerous forces.
A different issue would be the route adjustment maneuvers, that is to apply a rotational force when the main thruster is still operative. This would modify the thrust vector, with dangerous consequences for the crew and the ship structure.
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#13
by
sanman
on 19 Jan, 2017 03:11
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EMdrive's promise of propellant-mass savings would be a particular enabler for long voyages involving large spacecraft having higher mass, since these things would otherwise require large amounts of propellant mass.
This is an interesting uncovered issue. A roll torque might have disruptive effects on the spaceship route and even on the structure itself if the main thruster was powerful enough. Let's hope there won't be the need for reaction wheels.
When you say "powerful enough", consider that any roll torque would be accumulating over time -- e̶v̶e̶n̶ ̶a̶ ̶p̶e̶n̶n̶y̶ ̶w̶i̶l̶l̶ ̶e̶v̶e̶n̶t̶u̶a̶l̶l̶y̶ ̶t̶u̶r̶n̶ i̶n̶t̶o̶ ̶a̶ ̶h̶u̶g̶e̶ ̶f̶o̶r̶t̶u̶n̶e̶ ̶w̶i̶t̶h̶ ̶c̶o̶m̶p̶o̶u̶n̶d̶i̶n̶t̶e̶r̶e̶s̶t̶,̶ ̶g̶i̶v̶e̶n̶ ̶e̶n̶o̶u̶g̶h̶ t̶i̶m̶e̶
OOPS: I should have said even your allowance will add up to a lot, given enough time (linear, not geometric)
Yes I agree. The only reliability problem might be the high working temperatures which might stress the components. PNN thrusters have an overheating issue and maybe this will be a problem for EmDrive too, with an high power supply.
Presumably, highly-optimized EMdrives would have frustrums made of materials offering highest Q - which would normally be superconductors. Hopefully, some combination of thermoelectric and radiative cooling would guarantee the superconductors can be reliably kept cold for a decades-long voyage, to ensure continuous EMdrive operation for the duration of the trip.
If your EMdrive broke down part-way during the trip, then you could be headed for your destination without any means to slow down. You'd either hit it, or overshoot it.
If EMdrive is to be reliable for a long-distance/interstellar journey, then all of its components have to be reliable, and all of its supporting systems (power supply) have to be reliable.
What kind of reactor design would be most reliable for long duration voyages?
My example was very simplifying, I guess the first problem of flying a skyscraper is that it'll probably crumble after few moments from take off.
The ship hypothesized in my blog is an hollow cylinder with floors displaced like a common building, hence the analogy. Its structure will must be designed to endure rotational forces that occur during the inversion maneuver.
I don't think it'll be a big problem to flip the ship (within its operational parameters and human body tolerance limits of course), because once the main thrust is switched off there are no other perturbative and potentially dangerous forces.
The ship would be experiencing what are essentially static load forces for nearly all of the journey, except for during that brief fliparound maneuver.
As with other more conventional types of electric propulsion, at least EMdrive won't likely create any vibrational loads/stresses. I read that NASA people said DeepSpace-1 flew like a dream, trouble-free.
A different issue would be the route adjustment maneuvers, that is to apply a rotational force when the main thruster is still operative. This would modify the thrust vector, with dangerous consequences for the crew and the ship structure.
The bigger the spacecraft, the bigger the loads we can expect, I guess. Imagine if your interstellar spacecraft is a mile long, carrying many people on a decades-long voyage. Hey, why not - there are skyscrapers and supertankers approaching that height/length - and those skyscrapers and supertankers are even able to tolerate lateral loads from winds and currents (although they're not constructed to save as much mass as when building a spacecraft, even a large one.) EMdrive's propellantlessness offers more advantages for big space vessels.
Regarding forces arising from course correction - just as you said with the fliparound, if the magnitude of that rotational torque/force is not too large, and if the main thruster could be shut off in the meantime (or at least throttled back), it could help in keeping loads tolerable. In space, there's lots of room to maneuver.
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#14
by
aero
on 19 Jan, 2017 16:47
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Addressing this paragraph above:
Regarding forces arising from course correction - just as you said with the fliparound, if the magnitude of that rotational torque/force is not too large, and if the main thruster could be shut off in the meantime (or at least throttled back), it could help in keeping loads tolerable. In space, there's lots of room to maneuver.
We don't yet know enough about the EM drive know how that would work. These engines may even have a "reverse!" But admittedly using reverse in a huge spacecraft for long duration would seriously complicate arrangement of the living quarters and structure. Still, turn-over (flip around) not need to be done quickly, What does a few weeks taken for turn-over amount to on a generation long voyage? Well, there is the problem of shielding from space dust if the velocity at turn over is to high.
As for undesirable torque caused by the engine - The navigation system will use guide stars as is current practice for voyages to Jupiter and beyond. Rotation of the spacecraft will be very quickly detected and corrected by the attitude control system. It is reasonable to assume, even knowing so little as we do now about EM drive capabilities, that the attitude control system would find the correct power level for the EM drive attitude thrusters to operate continuously balancing the drive engine torque.
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#15
by
rfmwguy
on 19 Jan, 2017 23:41
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Just curious, why a new thread?
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#16
by
sanman
on 20 Jan, 2017 00:39
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Just curious, why a new thread?
Sorry about that - just wanted to mainly talk about the types of spacecraft that would be possible if the EMdrive idea works, along with their uses, and how such spacecraft would be designed.
So not really focusing much on the particular internal workings/principles of the EMdrive itself. Just treat it like a "macguffin" or "black box" or appliance, that has certain specs.
We don't yet know enough about the EM drive know how that would work. These engines may even have a "reverse!" But admittedly using reverse in a huge spacecraft for long duration would seriously complicate arrangement of the living quarters and structure. Still, turn-over (flip around) not need to be done quickly, What does a few weeks taken for turn-over amount to on a generation long voyage? Well, there is the problem of shielding from space dust if the velocity at turn over is to high.
You don't even need a reverse - you could just have another set of frustrums pointing the other way and switch to them for deceleration. That other set could even be used to take over if the first set failed (if you were to flip around just to make them useable).
But then, as you say, it complicates living arrangements - because without a fliparound, your switch from accelerative to decelerative mode means what used to be your ceiling is now your floor, etc.
As for undesirable torque caused by the engine - The navigation system will use guide stars as is current practice for voyages to Jupiter and beyond. Rotation of the spacecraft will be very quickly detected and corrected by the attitude control system. It is reasonable to assume, even knowing so little as we do now about EM drive capabilities, that the attitude control system would find the correct power level for the EM drive attitude thrusters to operate continuously balancing the drive engine torque.
Makes sense - lots of little touch-up corrections smoothing out the journey, rather than accumulating big errors requiring big accelerative corrections.
I do still wonder though, about how EMdrive would operate in "flatter" interplanetary/interstellar space, as compared to the more "curved" space of a gravity well. Yeah, I realize that challenges the Equivalency Principle, but hey, if EMdrive works, then it'll be challenging a lot of previous assumptions.
My only point is that "flatter" space is most likely where EMdrive would be operating. So it might be best to validate it out on the "high seas" rather than in the "lagoon", so to speak.
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#17
by
rfmwguy
on 20 Jan, 2017 03:02
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If I was asked to lay out an initial spacecraft, I'd make it a linear unmanned probe with a single emdrive as a proof of concept. About 4 meters in length, lightweight truss with drive at one end, solar panels, comm and control section at midway point and finally the RTG at nose opposite drive. Solar panels to jettison near Jupiter, RTG takes over from there at reduced power level. We can generate more electricity with panels but near Jupiter they are diminished. RTG is lower power but does not need sun to provide electricity. Centaur could place in earth escape trajectory towards alpha cen. Key to first interstellar probe will be lightweight and higher initial thrust levels taking advantage of solar radiation for electricity. Simple transponder and inertia sensors only to save weight and cost. Basic commands and programming. Small conventional thrusters to fine tune trajectory. Gravity assist a plus. First probe should be simple and low cost. Think of small scale version of Discovery ship from 2001.
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#18
by
aero
on 20 Jan, 2017 03:43
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Gravity assist does not work well with low thrust engines to gain velocity. It is a matter of the work done by the engines while the spacecraft is traveling at high speed. Work is force times distance. High speed allows the chemical rockets to travel a great distance during the short, high thrust engine burn interval. The EM drive would travel the same distance but the force is much reduced so the work done is much reduced. Hence the question becomes, is that much smaller work done to speed the spacecraft by gravity assist worth the time and energy cost of aligning the encounter? Maybe, but maybe not. Someone better versed in orbital mechanics than I could answer that question. And of course gravity assist will still work well to change directions.
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#19
by
SergioZ82
on 20 Jan, 2017 13:01
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When you say "powerful enough", consider that any roll torque would be accumulating over time -- even a penny will eventually turn into a huge fortune with compound interest, given enough time.
Yes, I didn't think about it.
Presumably, highly-optimized EMdrives would have frustrums made of materials offering highest Q - which would normally be superconductors. Hopefully, some combination of thermoelectric and radiative cooling would guarantee the superconductors can be reliably kept cold for a decades-long voyage, to ensure continuous EMdrive operation for the duration of the trip.
If your EMdrive broke down part-way during the trip, then you could be headed for your destination without any means to slow down. You'd either hit it, or overshoot it.
If EMdrive is to be reliable for a long-distance/interstellar journey, then all of its components have to be reliable, and all of its supporting systems (power supply) have to be reliable.
What kind of reactor design would be most reliable for long duration voyages?
I agree with you, reliability of EmDrive components is paramount. In an early phase, with first generation e.m engines, it would be a wise choice to add a fair amount of spare parts to the payload.
I think, as rfmguy already said, that RTG is a good choice but, I add, for slow but steady thrust values comparable with actual EmDrive. If we talk about future manned interplanetary/interstellar starships instead there'll be the need of something capable of generating hundreds of thousands (millions?) of amperes to power the main thruster (I'm thinking to a steady 1g acceleration). This amount could be probably reduced, I suppose, with technological advancements of the engine: better materials, better configurations, a deeper understanding of the principles etc..
Regarding forces arising from course correction - just as you said with the fliparound, if the magnitude of that rotational torque/force is not too large, and if the main thruster could be shut off in the meantime (or at least throttled back), it could help in keeping loads tolerable. In space, there's lots of room to maneuver.
The idea of keeping the main thruster always active is to have a constant illusion of gravity due to the 1g acceleration. However for probes and less sci-fi future spaceships with far less power, that is astronauts still experiencing microgravity under constant acceleration, your solution is effective and easily applicable.
.. Solar panels to jettison near Jupiter, RTG takes over from there at reduced power level.
Why to jettison the solar panels? The e.m drive (provided it's powerful enough) wouldn't have problems to carry extra weight, as it has no fuel constraints.
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#20
by
rfmwguy
on 20 Jan, 2017 14:11
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When you say "powerful enough", consider that any roll torque would be accumulating over time -- even a penny will eventually turn into a huge fortune with compound interest, given enough time.
Yes, I didn't think about it.
Presumably, highly-optimized EMdrives would have frustrums made of materials offering highest Q - which would normally be superconductors. Hopefully, some combination of thermoelectric and radiative cooling would guarantee the superconductors can be reliably kept cold for a decades-long voyage, to ensure continuous EMdrive operation for the duration of the trip.
If your EMdrive broke down part-way during the trip, then you could be headed for your destination without any means to slow down. You'd either hit it, or overshoot it.
If EMdrive is to be reliable for a long-distance/interstellar journey, then all of its components have to be reliable, and all of its supporting systems (power supply) have to be reliable.
What kind of reactor design would be most reliable for long duration voyages?
I agree with you, reliability of EmDrive components is paramount. In an early phase, with first generation e.m engines, it would be a wise choice to add a fair amount of spare parts to the payload.
I think, as rfmguy already said, that RTG is a good choice but, I add, for slow but steady thrust values comparable with actual EmDrive. If we talk about future manned interplanetary/interstellar starships instead there'll be the need of something capable of generating hundreds of thousands (millions?) of amperes to power the main thruster (I'm thinking to a steady 1g acceleration). This amount could be probably reduced, I suppose, with technological advancements of the engine: better materials, better configurations, a deeper understanding of the principles etc..
Regarding forces arising from course correction - just as you said with the fliparound, if the magnitude of that rotational torque/force is not too large, and if the main thruster could be shut off in the meantime (or at least throttled back), it could help in keeping loads tolerable. In space, there's lots of room to maneuver.
The idea of keeping the main thruster always active is to have a constant illusion of gravity due to the 1g acceleration. However for probes and less sci-fi future spaceships with far less power, that is astronauts still experiencing microgravity under constant acceleration, your solution is effective and easily applicable.
.. Solar panels to jettison near Jupiter, RTG takes over from there at reduced power level.
Why to jettison the solar panels? The e.m drive (provided it's powerful enough) wouldn't have problems to carry extra weight, as it has no fuel constraints.
F=MA
A=F/M
Lower mass = faster acceleration
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#21
by
SergioZ82
on 20 Jan, 2017 14:35
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@rfmwguy
got it.
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#22
by
sanman
on 04 Feb, 2017 06:23
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Does EMdrive have to be placed on the back end of a spacecraft? Can it be placed on the front end of a spacecraft, like "front-wheel drive"?
Whether or not it's a "Q-thruster", does EMdrive produce any appreciable "exhaust" that people in the vicinity of its resonant cavity would have to worry about?
What are the main safety precautions/considerations required for people in relation to EMdrive?
Does higher Q-value (eg. superconducting cavity/frustrum) minimize any radiation leakage hazard?
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#23
by
Asteroza
on 23 Feb, 2017 03:01
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Does EMdrive have to be placed on the back end of a spacecraft? Can it be placed on the front end of a spacecraft, like "front-wheel drive"?
Whether or not it's a "Q-thruster", does EMdrive produce any appreciable "exhaust" that people in the vicinity of its resonant cavity would have to worry about?
What are the main safety precautions/considerations required for people in relation to EMdrive?
Does higher Q-value (eg. superconducting cavity/frustrum) minimize any radiation leakage hazard?
So a Valkyrie style tractor spacecraft, with a tensegrity spine? (a recent example of a tractor configuration being the ship in the movie Avatar).
If there is an "exhaust" issue, using a slight thruster cant from the primary axis shouldn't hurt too much if the spine is long enough.
But if there is no exhaust issue, then there would be the tradeoff between larger individual thrusters, and distributing the engines along a tractor configuration spine to cut spine weight (if the cargo can be modularized to be spread out on the spine).
So a stack of T's versus a tall T shape then, assuming you didn't centralized the thruster on the spine itself (differential thrust from thruster pairs on arms at the top of the T seems attractive).
Extreme T example is a thruster bar with a very long rollout solar array trailing (perhaps with inflatable/rigidizable tubes to stiffen the solar panel after deployment). Make the thruster bar cylindrical and you could ostensibly wrap the solar array around it like a roll tube, then inflate deploy out like a party favor.
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#24
by
oben
on 15 Apr, 2017 08:52
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Space drive has actually 2 models
1-EM drive is nonrelativist and beam "photons" are quasi particles with accelaration of order a~10ēģ m/sē
It uses Newton's third law for its thrust !!
2-Alcubierre warp drive using Emergent gravity techology not the Quantum vacuum plasma technology of Harold "Sonny" White
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#25
by
qraal
on 12 May, 2017 23:13
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From Mike McCulloch's blog, where I made this point...
One thing we should discuss is the power supply needs for the 1 gee space-craft and the EM-Drive parameters needed for that performance. Say we have a 1,000 ton spaceship and we accelerate at 1 gee. Thus 10 MN thrust is required. At Eagleworks' observed performance of 1.2 millinewtons per kilowatt, the power to get 10 MN thrust is 8.3 TW, which is probably unrealistic for a 1,000 ton ship to supply. We might be able to do it with a laser bank beaming at a high-efficiency collector, but it's still herculean by modern standards (we're just starting to make sustained 100 kW lasers.) It's still much better than the laser power needed for a purely photonic drive, some 3 petawatts, but it's a long way from our state of the art.
Of course the performance increases with the Q-factor. Tune the cavity and make it superconducting. If we take the NASA EM-Drives and pump the Q factor to ~30 million, then about 2 GW power is needed for the sustained 1 gee thrust. A fast-spectrum reactor with a thermal output of ~ 6 GW and ~35 % thermal conversion efficiency would be a first pass design to supply the power. Assuming ~100% burn-up the fuel used over 20 years masses 4.2 tons. If the reactor mass was limited to ~200 tons, then it'd need to supply power at 10 kWe/kg of reactor mass, which is very high performance. A gas-core or magnetic collimator fission-fragment reactor might be up to the job, but both are somewhat futuristic.
Fusion reactors are presently *hoped* by propulsion engineers to be able to supply power in the 100 kWe to 1 MWe range, though no working fusion power-reactor has yet been demonstrated. As the joke goes, fusion has been "just 20 years away" for the past 60 years and always will be...
I wonder just how high a superconducting EM-Drive's Q-value can go?
Addendum: I've read of Q factors in the billions. Thus 20 MW would then be sufficient for a 1,000 ton 1-gee spacecraft. Much easier to supply with a mobile fission reactor.
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#26
by
Bob012345
on 14 Jun, 2017 19:13
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I believe we should re-imagine our concept of spaceship (and probe)
First of all, a spacecraft equipped with an EM engine can thrust as along as the power source is active. This means it can not only visit various celestial bodies in a single mission but also that it can reach speeds that are unattainable with ion/chemical propulsion. It can basically accelerate up to half way from destination, then turn 180° and thrust in opposite direction to slow down.
The best solution to power the engine is a nuclear reactor (and it's even fundamental for deep space missions): I'm talking with PNN in mind, which requires a great amount of current. I think solar panels would be an excellent solution for early EM probes with low thrust values and satellites.
Until we won't have a spacecraft specifically designed around EmDrive (or other EM thrusters like Cannae or PNN) I think our current models will be retrofitted to mount the frustum(s) or tiles (PNN).
I can't help but it comes to my mind an imagine of the Space Shuttle equipped with an array of frustums
I depict this near-future like the hybrid old-new vehicles I've seen in Independence Day Resurgence (but that's daydreaming).
E.M technology would make excellent position thrusters to rotate a spacecraft around all its axes.
If we imagine that tomorrow morning EM propulsion will be used for space application then we can speculate that in 10/20 years the technology will be mature enough to generate massive thrusts, even capable of generating more than 1 g of acceleration. Then a spacecraft will probably levitate and gain orbit in a little time.
We'll also probably laugh at how wrong all sci-fi spaceships have been depicted so far: basically sea ships design transposed in space. With such design if the ships accelerates the crew (and everything is not bolted on the hull) is pushed toward the stern. With 1 g acceleration the best design is.. something similar to a skyscraper
Personally I think that flying saucer design is good too (except for the fact that during space flight it offers a big impact surface to debris like rocks).
Also interstellar travel become instantly far closer than with chemical/ion/antimatter propulsion (basically everything Newtonian).
I invite you to read these two articles from my blog (I link them because as far as I know nothing similar exists on the web)
Sailing across the solar system and beyond/
As if one wasn't enough PNN breaks another law/
Those are written for PNN but I believe they're also valid for EmDrive
The PNN stuff seems like utter nonsense. Their video showed absolutely nothing.
