Spaceships 2-8 new drives

[Joseph Paul]

Do any of the Spaceships books 2-6 + book 8 have any rules on drives that don't use propellant such as the theorized Mach Effect thrusters and EM Drive? I know there are paranormal drives in 7 - would any of those work as rules for theorized EMdrive or Mach Effect thrusters?

[malloyd]

Originally Posted by Joseph Paul

Do any of the Spaceships books 2-6 + book 8 have any rules on drives that don't use propellant such as the theorized Mach Effect thrusters and EM Drive? I know there are paranormal drives in 7 - would any of those work as rules for theorized EMdrive or Mach Effect thrusters?

These are Reactionless Engines. See Spaceships 1 p.24. As super-science (or at best something that works on undemonstrated principles) there isn't a lot you can say about a specific "theorized" version - they can have any statistics whatsoever.

[Joseph Paul]

Good - making sure I am not missing a relevant update. Thanks.

[PTTG]

I'd adjust the numbers given in Spaceships if you're representing EMdrives or some other part of that crowd. A (supposedly working) TL 8 Microwave Cavity drive probably has something like 0.01G per system; they cost as much as a Rotary reactionless drive. A TL 8 superconductiong one requires extra radiators and provides .1G per system, and costs as much as a Standard drive. TL 9 and up superconducting drives do not require significant additional radiators and provide .2G per system.

Presuming the hype is correct, of course.

[Fred Brackin]

Originally Posted by PTTG

I'd adjust the numbers given in Spaceships if you're representing EMdrives or some other part of that crowd. A (supposedly working) TL 8 Microwave Cavity drive probably has something like 0.01G per system; they cost as much as a Rotary reactionless drive. A TL 8 superconductiong one requires extra radiators and provides .1G per system, and costs as much as a Standard drive. TL 9 and up superconducting drives do not require significant additional radiators and provide .2G per system.

Presuming the hype is correct, of course.

Note that for the hype to be true the drive not only has to diss Newton (equal but opposite reaction) but Einstein as well (E=MC2).

An EM Drive that didn't cause a ship to gain more KE from acceleration than electricity put into it could explain would have very low performance.

[malloyd]

Originally Posted by Fred Brackin

Note that for the hype to be true the drive not only has to diss Newton (equal but opposite reaction) but Einstein as well (E=MC2).

I believe all reactionless drives with (thrust > power/c) - that is more than 3.3 newtons (0.75 lbs) per gigawatt do that in some reference frame.

[Joseph Paul]

Thanks to PTTG for the number crunch. I will take a look at what that can do.

malloyd - interesting reduction of the standard model to a useful limit.

Fred - How do you feel about the defenses written by Shawyer and Woodward concerning the EMDrive and Mach Effect Thrusters respectively?

[Fred Brackin]

Originally Posted by Joseph Paul

Thanks to PTTG for the number crunch. I will take a look at what that can do.

malloyd - interesting reduction of the standard model to a useful limit.

Fred - How do you feel about the defenses written by Shawyer and Woodward concerning the EMDrive and Mach Effect Thrusters respectively?

Never heard of them. I haven't gone into these things extensively but I've never seen anything to indicate that I should. It all sounds like a re-skin of the Dean Drive stuff.

The big thing would be my point about E=MC2. Even if some heretofore unexpected quirk of physics allows for a novel way of generating thrust I will be stunned and amazed if it revolutionizes things. The limits of energy->thrust are severe.

Consider it this way. Say you have some sort of EM Drive that turns electricity into thrust. Where does you electricity come from? If it's some hypothetical highly efficient fusion reactor you're turning a small percent of the reactor mass into energy with the most usable forms of that energy being in the form of the KE of charged particles. Gamma rays being produced are much more difficult to turn into usable energy in an efficient manner.

So you feed the charged particles into an MHD and get electricity which you feed into an EM drive to make thrust. How can this possibly be more efficient than using the charged particles directly as reaction mass? You're inserting a middle man into the process rather than cutting out some inefficient step.

So even if there is something there how can it work better than some simpler competitor? I just don't see it.

[Varyon]

Originally Posted by Fred Brackin

Consider it this way. Say you have some sort of EM Drive that turns electricity into thrust. Where does you electricity come from? If it's some hypothetical highly efficient fusion reactor you're turning a small percent of the reactor mass into energy with the most usable forms of that energy being in the form of the KE of charged particles. Gamma rays being produced are much more difficult to turn into usable energy in an efficient manner.

Going off my Vehicles conversion, at TL9 (when they become available), a fusion reactor system (1/20th vessel mass) produce 100 kW of usable energy per ton of vessel weight. With a near-100% efficient reactionless drive, 100 kW/ton is going to increase KE by 100 kJ/ton every second, which is going to be around 0.45 m/s/s, or just shy of 0.05G. If we drop down to 20% efficiency, that's 0.01G.

Now, that's not so great compared to many superscience drives. Compared to real drives? That's pretty solid, and that drive needs refueled only every 200 years. Earth to Mars (0.5 AU) takes about 3 weeks with 0.01G, and you can repeat that trip over 3,000 times before needing refueled. You aren't going to get that kind of performance out of a reaction drive. Granted, that's a whole heaping helping of energy - an entire fusion system for your drive - but still pretty darn useful. Even at high thrust, VASIMR has 1/5th the performance (but probably lower energy requirements), and at low thrust (1/50th performance) it uses up 1.5 fuel tanks to go between Earth and Mars once and takes nearly half a year (probably less if we have enough drives to use up all of a fusion plant's output, like our reactionless drive, but never anything close to a week).

[Joseph Paul]

Fred - The American Institute of Aeronautics and Astronautics will publish "Measurement of Impulsive Thrust from a Closed Radio Frequency Cavity in Vacuum" and is authored by "Harold White, Paul March, Lawrence, Vera, Sylvester, Brady and Bailey" in December 2016.

Now getting into a peer-reviewed journal doesn't prove that it works but it might be worth it to look at what Shawyer wrote about why he thinks it doesn't violate conservation of momentum. The Mach Effect Thrusters are in much the same boat but Woodward's defense seems to rest on the effect being part of the universe's gravinertial field.


http://www.ibtimes.co.uk/emdrive-aia...-paper-1579443