... [T]hings are still very much up in the air on the EMdrive.
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?
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
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}
Quote from: sanman on 01/11/2017 07:18 pmWell, 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.
Quote from: A_M_Swallow on 01/15/2017 10:49 pmQuote from: sanman on 01/11/2017 07:18 pmWell, 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.
Quote from: sanman on 01/11/2017 07:18 pmWell, 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.
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}
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'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?
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.
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.
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.
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.
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.
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.
Just curious, why a new thread?
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.
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.
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?
.. Solar panels to jettison near Jupiter, RTG takes over from there at reduced power level.