Can a Focus Fusion rocket engine take us to the stars?

[belbear42]

Reading about this extraordinary machine that generates fusion energy by emitting a powerful, focused alpha particle beam, (assuming a p-B11 reaction is used), everyone seems to think only “power plant”, which would be fantastic of course. But I was thinking “rocket engine”!

Correct me if I’m wrong, but my idea is that this ion beam shooting out of the reactor must generate quite a recoil on the machine, first carried from the plasmoid through the plasma field lines that connect it with the electrodes, which are held in place by the structure of the machine.
The electron beam that shoots out the other way carries the same amount of charge as the ion beam, but must have much less impulse.
I thought so, if the plasmoid could not take up a recoiling force, wouldnt’ the ion beam shoot out both ways to equalize the impulse?

Now, if instead of decelerating the helium nuclei, you let them escape into empty space (assuming the machine is inside a spacecraft and already in space).
Now a net thrust will be generated with a very high specific impulse, since the already focused ion beam has a tremendous velocity. This exhaust velocity must be a sizeable portion of c, the speed of light, and for rocket engines, exhaust velocity is all what makes the difference between a fuel-economic thruster and a gas guzzler like chemical rockets.
You don’t need to convert anything to a rocket exhaust plume using heat, magnets or whatever, you already have one!
Even if the energy per pulse is always the same, you can throttle up or down by regulating the amount of pulses per second.

And hey: No vacuum pumps needed. Just open an outside valve and you have the best vacuum you can get.

You only would need to:
–generate enough thrust to propel a spacecraft weighing a few hundred tonnes, since the engine and its pulse power source must have a minimum size to generate net energy from fusion. This is not something for small TV satellites to maintain orbital position, this is something for big vessels to cross the solar system and beyond. Current ion-engine designs like Deep-Space-One generate very low thrust in the millinewton range, about the weight of a sheet of paper. We need kilonewtons at least!
–keep unfused fuel atoms from leaking out of the reactor through the exhaust, while posing no barrier for the ion beam.
–emit electrons into the beam to maintain charge neutrality of your spacecraft (that’s the easy part, I guess)
–have enough electric power available to power the fusion thrusters and the rest of the spacecraft, either from a separate electricity-generating fusion power plant or by tapping part of the thruster’s own ion beam energy through a solenoid.
–dampen the vibrations caused by the pulsating thruster beams or you rattle your spacecraft apart, not to mention the crew.

A more earthly alternative could be a fusion-powered jet engine.
Think of an alpha ion beam being fired into a jet engine’s combustion chamber, where the beam’s megawatt energy is converted into heat through collisions with the air molecules. This air is quickly heated to a few 1000’s of degrees and drives the jet just the same like in chemical combustion based jet engines, but without the dirty emissions. No CO2 (global warming), no H2O (contrails), no sooty pollution around airports.

A particular engineering challenge here would be the beam exhaust port, which must let the ion beam pass through unhindered while keeping the hot, dense air out of the near-vacuum reaction chamber.

The air stream can be either subsonic or supersonic, since there is no flame front to blow out, just heating. This turbojet/ramjet would thus be an ideal first-stage engine to get the aforementioned fusion-powered spacecraft off the ground.
And of course you can fly around the globe in a fusion-powered 747 using just a few grams of fuel. Almost-free air tickets, anyone?

Hey, if NASA, or the military would develop the focus fusion device as an aerospace propulsion alternative, we could get a household power plant almost for free. Now that’s what I call a space program spin-off!

Please let me know if you physicists find this idea feasable or hare-brained

Chris

Attached files

[Jolly Roger]

Sorry, but your idea is an old one. NASA’s JPL funded some of Lerner’s research a few years ago.

I found this in the archives:

University of Illinois Space Propulsion
by Admin on Jul 25, 2006 at 09:37 PM
University of Illinois, Air Force Researchers Release Study of Focus Fusion for Space Propulsion.

In a technical paper published last year, researchers from Universe of Illinois and from the Air Force Research Laboratory have described how a dense plasma focus device using hydrogen-boron fuel, (what we call

[Tasmodevil44]

Lerner has indeed already considered this …… I already read about this concept some time ago. And you are indeed correct about how it would have a very high specific impulse for acceleration. Which means so little fuel consumption that only a few grams ( milligrams? ) of decaborane could take you just about anywhere you want to go in the solar system and beyond. In fact, I believe the FF is about the only practical way to make an extended mission to Mars feasible.

Not just for propulsion, but the energy required for an extended stay on Mars once you get there. Because it’s a cold wasteland about as cold as Antarctica, even extremely thick insulation in the walls several feet thick won’t hold all the heat inside so the occupants can stay warm. This will require heat supplied by the FF device …… not to mention electricity to power various instruments and other things. An exploratory roving vehicle could also be powered by fusion …… to make hydrogen or to charge it’s batteries. And water could be extracted from martian soil and used to produce oxygen for breathing.

But by far the most exciting concepts is how it could revolutionize the entire transportation sector …… both here on planet Earth and off of it.

[Jolly Roger]

From “DREAD Weapon System” thread:

Brian H wrote:

I never thought of that. But yes, an incredibly powerful focus fusion laser could theoretically be used to accelerate a solar sailing craft to Mars. Or beyond Neptune, Pluto, even beyond the solar system.

I don’t see why you’d bother. Take along a tonne of decaborane and an FF generator or ten, harvest a bit of hydrogen along the way from the interstellar medium, and you could get far more power and acceleration and control and options. With a solar sail, you can’t wander out of the beam or you’re helpless until a signal can be aimed back to the source and the laser re-directed. Braking is tricky, too. You have to pop a counter-mirror out front and turn the sail around to get the bounce-back, or SLT.

You may find this site of interest:

http://www.ess.washington.edu/Space/propulsion.html (Advanced Electric Propulsion)

(minor edit for clarity)

Advanced Electric Propulsion

Chemical rockets have limited application for space applications due to the fact that the fuel is relatively slow (low specific impulse) relative to the speeds needed to move efficiently about the solar system. As a result, chemical systems are massive, and the trip times for missions are very long. Research at UW (University of Washington) in this area is for the development of faster propellants that can provide substantial reductions in cost and trip time. To achieve these efficiencies plasma systems (i..e. charged particles) are required where electric and magnetic fields can be used to accelerate the plasma propellants to speeds more than an order of magnitude faster than can be achieved by chemical rockets. The systems below detail devices under active development:

High Power Helicon (HPH) is an electrodeless plasma thruster that is able run at kW to 100’s kW to produce thruster levels as high as several Newtons (N) of force, at high power and gas efficiency.

Mini-Magnetospheric Plasma Propulsion (M2P2) is a system that can leverage energy from the solar wind to augment the onboard propulsion for spacecraft while minimizing the spacecraft power requires. Potential for radiation shielding is still under investigation.

PlasmaMagnet has the ability to create large magnetic systems without the need for any pre-existing magnets. These systems provide new capabilities for plasma sails and radiation shielding.

MagBeam combines the key features of M2P2 /PlasmaMagnet with high power beam plasma sources such as HPH to produce a system where large orbiting spacecraft can be used to push payloads between the planets with very little cost and thereby facilitate a permanent human presence in space.

(edited)
The MagBeam System is a plasma-magnetic equivalent to the Laser/Solar Sail system above, but has the advantage of being self-aiming, adjustable at the payload, and reversible (push or pull). All the components of the system need power, which Focus Fusion (FF) could provide.

An FF could also serve directly as a plasma source. However, it is probably more useful as the power source of the HPH. Even though FF has a high specific impulse (high velocity), it does not have the high mass throughput, hence Thrust, of an HPH.

BTW, 1 N thrust = ~ 0.1 g acceleration per kilogram of payload. A 100-(metric)ton craft would need about 1,000,000 Newtons (1MN) thrust for 1 g.

NB: M2P2 /PlasmaMagnet can brake at the destination by interacting with a planet’s magnetosphere or a star’s solar wind.

[annodomini2]

Given current information and extrapolations, what sort of volume and mass would a 2000TW focus fusion reactor need to be?

Just an idea i’m playing with.

[Jolly Roger]

According to information in the patent application, the maximum net output of each reactor vessel is 5 MW Alpha beam and 2 MW X-rays. With conversion losses, that would be about 5 – 6 MW electricity. However, the capacitor bank, which is the most massive component, can power up to 500 reactor vessels, so total installation output could be as high as 2.5 – 3 GW.

A 2,000 TW application would require 666,667 – 800,000 FF installations.

I will leave it to others with more information to correct mine and/or calculate the mass and volume.

[annodomini2]

Jolly Roger wrote: According to information in the patent application, the maximum net output of each reactor vessel is 5 MW Alpha beam and 2 MW X-rays. With conversion losses, that would be about 5 – 6 MW electricity. However, the capacitor bank, which is the most massive component, can power up to 500 reactor vessels, so total installation output could be as high as 2.5 – 3 GW.

A 2,000 TW application would require 666,667 – 800,000 FF installations.

I will leave it to others with more information to correct mine and/or calculate the mass and volume.

Big then, could be interesting

Is there any scalable possibility for the technology?

[Aeronaut]

Jolly Roger wrote: From “DREAD Weapon System” thread:

The MagBeam System is a plasma-magnetic equivalent to the Laser/Solar Sail system above, but has the advantage of being self-aiming adjustable at the payload, and reversible (push or pull). All the components of the system need power, which Focus Fusion (FF) could provide.

An FF could also serve directly as a plasma source. However, it is probably more useful as the power source of the HPH. Even though FF has a high specific impulse (high velocity), it does not have the high mass throughput, hence Thrust, of an HPH.

BTW, 1 N thrust = ~ 0.1 g acceleration per kilogram of payload. A 100-ton craft would need about 1 million Newtons thrust for 1 g.

NB: M2P2 /PlasmaMagnet can brake at the destination by interacting with a planet’s magnetosphere or a star’s solar wind.

The MagBeam is new to me today, Jolly Roger. I’ve always been assuming that a ship would spend half the flight accelerating, then turn around and decelerate for about the same amount of time (distance). Now the question is how fast we can decelerate a “relativistic” ship without the paying passengers griping (too much) and without needing more mass in the ship’s frame.

Mass is the reason for not lugging a ton of decarbane around with us if we only need an ounce for redundant backup storage. Excess mass is penalized by the theory of relativity as well as lowering the delta-vee, hence our speed and manueverability maximums.

Therefore, if 10 N= 1G of acceleration, a 100-ton ship would require only 1kN for 1G. For clarity, that would be tons of mass, not earth weight. 100 metric tons of mass would still be a sizable (and hefty) 1,000 metric tons or 3,200 tons (US) weight.

I’m looking forward to learning more about this runway to orbit FF Jet engine, also.

Cheers

Matt

[Jolly Roger]

Here is a site for scifi writers that has some interesting information.

http://www.projectrho.com/rocket/rocket3c2.html#table

It states that we may expect a Hydrogen-Boron rocket engine to have an exhaust velocity of 980 km/sec, thrust of 61 kN and engine mass of 300 metric tons.

We expect an FF engine to have a mass closer to 3 tons, but perhaps the other numbers are in the ballpark. If so, our spacecraft will have a top speed of 980 km/sec or 0.33% of the speed of light. I think that relativistic effects will be minimal.

With a top speed such a small fraction of the speed of light, extra-solar missions will be limited to robots, sleepers or generation ships. However, it should do fine for getting around the solar system, even out to the brown dwarf, Barbarossa, thought by some amateur astronomers to be orbiting the Sun, currently at about 218 AU.

http://www.metaresearch.org/msgboard/topic.asp?TOPIC_ID=770&whichpage=33

The critical factor then is the thrust. At 61 kN, our 100-metric ton ship will have an acceleration of 61 cm/sec^2. It would hit top speed in a few weeks, but it would still take 13 months to accelerate, coast/cruise, and decelerate to Barbarossa. A larger ship, with the 2,000 ton mass of the Space Shuttle, would take 25 months for the same journey.

The brown dwarf Barbarossa is not to be confused with the asteroid of the same name. Barbarossa may be the Dark Star Marduk/Nibiru that author Andy Lloyd is looking for.

http://www.darkstar1.co.uk/solution.html

[Jolly Roger]

Aeronaut wrote:
… Therefore, if 10 N= 1G of acceleration, a 100-ton ship would require only 1kN for 1G. For clarity, that would be tons of mass, not earth weight. 100 metric tons of mass would still be a sizable (and hefty) 1,000 metric tons or 3,200 tons (US) weight.

I don’t understand your math. I will explain mine.

1 Newton (N) of thrust will accelerate 1 kilogram (kg) of mass by 1 meter per second per second (m/sec^2).

10 N will accelerate 1 kg by 10 m/sec^2. 1 Gravity (G) = 9.8 m/sec^2, so 10 N/kg = 1.02 G = ~1 G.

1 metric ton mass is 1,000 kg, therefore it would take ~10,000 N (10 kN) to accelerate it to 1 G.

100 metric tons mass is 100,000 kg, therefore it would take ~1,000,000 N (1 MN) to accelerate it to 1 G.

The Space Shuttle has a mass of ~20,000 metric tons. It needs ~200 MN thrust for 1 G.

[annodomini2]

Jolly Roger wrote: Here is a site for scifi writers that has some interesting information.

http://www.projectrho.com/rocket/rocket3c2.html#table

It states that we may expect a Hydrogen-Boron rocket engine to have an exhaust velocity of 980 km/sec, thrust of 61 kN and engine mass of 300 metric tons.

We expect an FF engine to have a mass closer to 3 tons, but perhaps the other numbers are in the ballpark. If so, our spacecraft will have a top speed of 980 km/sec or 0.33% of the speed of light. I think that relativistic effects will be minimal.

With a top speed such a small fraction of the speed of light, extra-solar missions will be limited to robots, sleepers or generation ships. However, it should do fine for getting around the solar system, even out to the brown dwarf, Barbarossa, thought by some amateur astronomers to be orbiting the Sun, currently at about 218 AU.

http://www.metaresearch.org/msgboard/topic.asp?TOPIC_ID=770&whichpage=33

The critical factor then is the thrust. At 61 kN, our 100-metric ton ship will have an acceleration of 61 cm/sec^2. It would hit top speed in a few weeks, but it would still take 13 months to accelerate, coast/cruise, and decelerate to Barbarossa. A larger ship, with the 2,000 ton mass of the Space Shuttle, would take 25 months for the same journey.

The brown dwarf Barbarossa is not to be confused with the asteroid of the same name. Barbarossa may be the Dark Star Marduk/Nibiru that author Andy Lloyd is looking for.

http://www.darkstar1.co.uk/solution.html

The maximum speed of the ship is not limited by the exhaust velocity as the action is relative

Due to newtons 1st law:”Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed”

There is very little friction in the approximate vacuum of space so relatively no force to slow the ship

Due to Newtons 2nd law: “The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed”

As the action is relative the force remains constant

And Newtons 3rd law: “For a force there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions.”

Just because the ejected mass is stationary or moving away from relative to the earth it is still travelling at 980km/sec relative to the ship

If your statement was the case we would never achieve orbit with current technology

The speed limitation is mainly one of fuel, the ship will keep accelerating forever with infinite fuel and time, however as you approach the speed of light the net acceleration drops significantly as the relative mass increases.

[Jolly Roger]

annodomini2 wrote:
The maximum speed of the ship is not limited by the exhaust velocity as the action is relative… The speed limitation is mainly one of fuel, the ship will keep accelerating forever with infinite fuel and time, however as you approach the speed of light the net acceleration drops significantly as the relative mass increases.

My Bad! Thank you. I stand corrected. I was assuming that the equation for final velocity was:

Vf = Ve,

where Vf is the final velocity and Ve is the exhaust velocity.

The correct equation is:

Vf = Ve * ln(Mi/Mf)

where ln is the natural log, Mi is the initial mass of the ship, and Mf is the final mass.

I will do some calculations with various mass ratios and post my results later.

[Tasmodevil44]

Or for greater versatility of propulsion, you could use a combination of focus fusion techniques, instead of just one. I still don’t know exactly what advantages such a system might have right off – hand, but what if you employed both a focus fusion laser for solar sailing, as well as an additional onboard focus fusion rocket or ion engine?

Every time your solar sailing craft wandered out of the path of the fusion – powered laser beam, onboard fusion thrusters could also propel it back into the laser beam for additional thrust.

Also, in sailboat sailing, there’s such a thing called tacking, where you can actually propel a craft upwind and against the wind. To do this, the sailboat has to travel in a zig – zag fashion back and forth. In a similar way, onboard fusion engine thrusters might be able to propel a craft back and forth in such a way as to catch the solar wind easier for travelling upwind against it. This way, you would have two methods of propulsion working together and assisting each other.

[annodomini2]

Tasmodevil44 wrote: Or for greater versatility of propulsion, you could use a combination of focus fusion techniques, instead of just one. I still don’t know exactly what advantages such a system might have right off – hand, but what if you employed both a focus fusion laser for solar sailing, as well as an additional onboard focus fusion rocket or ion engine?

Every time your solar sailing craft wandered out of the path of the fusion – powered laser beam, onboard fusion thrusters could also propel it back into the laser beam for additional thrust.

Also, in sailboat sailing, there’s such a thing called tacking, where you can actually propel a craft upwind and against the wind. To do this, the sailboat has to travel in a zig – zag fashion back and forth. In a similar way, onboard fusion engine thrusters might be able to propel a craft back and forth in such a way as to catch the solar wind easier for travelling upwind against it. This way, you would have two methods of propulsion working together and assisting each other.

Why not just move the laser?

[Jolly Roger]

Jolly Roger wrote:

The maximum speed of the ship is not limited by the exhaust velocity as the action is relative… The speed limitation is mainly one of fuel, the ship will keep accelerating forever with infinite fuel and time, however as you approach the speed of light the net acceleration drops significantly as the relative mass increases.

My Bad! Thank you. I stand corrected. I was assuming that the equation for final velocity was:

Vf = Ve,

where Vf is the final velocity and Ve is the exhaust velocity.

The correct equation is:

Vf = Ve * ln(Mi/Mf)

where ln is the natural log, Mi is the initial mass of the ship, and Mf is the final mass.

I will do some calculations with various mass ratios and post my results later.

I kicked around a few numbers. With multiple stages, the ratio can get quite high. Then it turns out that the low acceleration becomes the limiting factor. Even at an almost respectable 0.6 m/sec^2, it would take almost 6 months to get out to my brown dwarf.

[Author]

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