Author Topic: FRC + Imploding Plasma Liner Fusion for the Fusion Rocket (NIAC2)  (Read 89288 times)

Offline Elmar Moelzer

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And just for the conspiracy theorists out there: if a spacecraft like the one they depict were in Earth orbit, it would make a phenomenal anti-satellite cannon. If aimed carefully I imagine a full Li load could take out most of the valuable satellites in a couple of hours. (That is, until it jammed  ;)
That seems like a highly inefficient way to take out satellites.

Offline adrianwyard

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And just for the conspiracy theorists out there: if a spacecraft like the one they depict were in Earth orbit, it would make a phenomenal anti-satellite cannon. If aimed carefully I imagine a full Li load could take out most of the valuable satellites in a couple of hours. (That is, until it jammed  ;)
That seems like a highly inefficient way to take out satellites.
Sorry, I wasn't being serious. It just looks a bit like a gun. I'm sure the plasma will spread too quickly to allow 'aiming' at a satellite. I wouldn't stand behind it though.
« Last Edit: 10/11/2013 06:03 pm by adrianwyard »

Offline adrianwyard

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Don't forget that the loading mechanism is not going to perform at insane repetition rates. We are talking one re -loading every 10 seconds here. So this is not a high performance part in any way. It seems that they have updated the layout of the driver coils to be more cylindrical. This makes the loading even simpler. If we cant make a mechanism like to work reliably, then it might be better to just quit that space business all together.
I agree and disagree. It's a question of life-or-death extreme reliability.

The loading mechanism on automatic weapons is not that complex, and has been refined over decades. I doubt you could improve it much even if you had a billion dollars to spend. Jamming is understood to be a life-or-death failure. But they do jam.

If you told me my life depended on an automatic rifle firing once every ten seconds hundreds of times over a one year period, and never jamming, I'd be worried. And I'm worried about using FDR for human spaceflight for the same reasons.
« Last Edit: 10/11/2013 06:15 pm by adrianwyard »

Offline IRobot

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If you told me my life depended on an automatic rifle firing once every ten seconds hundreds of times over a one year period, and never jamming, I'd be worried. And I'm worried about using FDR for human spaceflight for the same reasons.
I would be more worried in having 300 tonnes of propellant on my back. If you told me that my life depends on a single engine start with no possibility of a repair, I would be more worried.

Offline Elmar Moelzer

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I agree and disagree. It's a question of life-or-death extreme reliability.

The loading mechanism on automatic weapons is not that complex, and has been refined over decades. I doubt you could improve it much even if you had a billion dollars to spend. Jamming is understood to be a life-or-death failure. But they do jam.

If you told me my life depended on an automatic rifle firing once every ten seconds hundreds of times over a one year period, and never jamming, I'd be worried. And I'm worried about using FDR for human spaceflight for the same reasons.
I do not think that the loading mechanism for an automatic weapon is comparable.
The loading mechanism of an automatic weapon is small and the weapon faces a very different environment with dirt, gun powder residue and extreme heat getting into it.
The loading mechanism for the fusion driven rocket would be comparably large. The coils themselves are 1.6 meters in diameter, so the loading mechanism should be about 2 meters. So every part of that would be comparably big and thus rather unlikely to jam. Judging from the driver coils part of it is also separated from the driver coils by a shell of sorts. All that should make it VERY unlikely to jam. I would be much more concerned about complex chemical engines with fast moving parts and the possibility of a hard start.

Offline adrianwyard

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I didn't mean to suggest automatic weapons were mechanically comparable to the liner loading mechanism in any detailed respect. I'm simply saying very reliable simple mechanisms do fail in the long-run. And the FDR loader is so much more complex than a gun - more mechanically complex than anything flown before. Remember, you need to unwind those Lithium spools (switching to a fresh spool when needed, and switching to the next spool-stack when that's needed), cut a length, and form the hoops. I'm guessing you need to weld the hoop closed with some precision. If you detect you've made an out-of-spec hoop do you eject it somehow? And you then need to transport it to the correct compression coil. I gather that's done electromagnetically. Confirming it's correct alignment in the coil seems easy enough.

And it's very true that other propulsion hardware has failure modes (e.g. high-temp/pressure turbopumps) but these can be qualified more easily because they have to operate for minutes not months. And to repeat myself they are mechanically so much simpler.

I'm saddened to be playing devil's advocate here because it sounds like they may have half of the high-speed propulsion problem solved.
« Last Edit: 10/11/2013 07:29 pm by adrianwyard »

Offline Elmar Moelzer

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So, I just talked to David Kirtley from MSNW about this.

They did indeed already test a design for the feeding in house. The current design is that they launch the lithium in a strip, about 10cm wide, on continuous spools. It is fed out and cold welded into rings at the feed plate. The 3 rings are the same diameter and are stacked together axially. A single plunger, which is not shown in the animation, moves all three rings into position in a single axial motion. They are secured against the coil with another single actuator at the coil. The plunger is retracted and the liners are launched in sequence. They chose this single, stacked design because they could not internal clearance between the coils for multiple, parallel feed mechanisms (plungers, tracks or in situ welder). Because the liners are so thin, the fact that these are actually 3 liners was not clear in the animation.
You are correct that the positioning of the liners needs to be very precise.

I still think that this is not a show stopper. Lets just think of robotic car factories where a lot more complex processes are executed many times without error.

Offline adrianwyard

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Thanks for the follow-up with MSNW.

Offline alexterrell

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Just been through this thread, and the latest update paper at http://www.iepc2013.org/get?id=372

A couple of highlights:
- The target fire ratio is one shot every 14 seconds*
- Each shot is 0.5kg
- Rocket power is 36MW
- Fusion Gain is 200
- Power comes from 6.2MJ of capacitors (2.5 tons)
- Solar power is 180KW at Mars orbit
- Total space craft mass is 134 tons
- The entire trip needs 120g of tritium and 80g of deuterium

*I think, the text is: will require a rep rate of 1/14 sec-1. This matches the average power of 36MW.

This seems very promising. It might be a little bit uncomfortable with a jolt every 14 seconds. Each impulse gives delta V of only 0.125m/s, which results in daily delta V of 780m/s. Over 14 seconds, this could be absorbed by spring movement of less than 1m.

There was discussion about Tritium supply. (http://en.wikipedia.org/wiki/Tritium). 120g of tritium currently costs $3.6 million. It's made from bombarding Li-6. This process is exothermic given the neutrons. I guess you could modify fission reactors to produce more tritium.

If this engine could be built to the above parameters, it would make Mars colonisation possible.

I think this is the most promising propulsion technology for solar system exploration.

I also don't see why it couldn't be adapted for power generation on Earth.

Offline Elmar Moelzer

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MSNW has a more efficient device for power production in the works as well, via their spin of company Helion. They recently started to work with a new prototype system. http://helionenergy.com/?p=440
There is not much more information about this new prototype available yet. I am planning on doing another thread about that in this forum section.


Offline john smith 19

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Just been through this thread, and the latest update paper at http://www.iepc2013.org/get?id=372

A couple of highlights:
- Total space craft mass is 134 tons
- The entire trip needs 120g of tritium and 80g of deuterium

*I think, the text is: will require a rep rate of 1/14 sec-1. This matches the average power of 36MW.

This seems very promising. It might be a little bit uncomfortable with a jolt every 14 seconds. Each impulse gives delta V of only 0.125m/s, which results in daily delta V of 780m/s. Over 14 seconds, this could be absorbed by spring movement of less than 1m.

There was discussion about Tritium supply. (http://en.wikipedia.org/wiki/Tritium). 120g of tritium currently costs $3.6 million. It's made from bombarding Li-6. This process is exothermic given the neutrons. I guess you could modify fission reactors to produce more tritium.

If this engine could be built to the above parameters, it would make Mars colonisation possible.

I think this is the most promising propulsion technology for solar system exploration.
To put 134 metric tonnes in perspective that's 2 SLS flights, 6 Delta IV Heavy flights or 9 Skylon flights, or 5 Atlas V heavy flights (if it ever gets funded).

If the vehicle can be fully reused (which it seems it can) this is not ridiculously expensive (but it's not cheap).  :(

The loading mechanism on automatic weapons is not that complex, and has been refined over decades. I doubt you could improve it much even if you had a billion dollars to spend. Jamming is understood to be a life-or-death failure. But they do jam.
It's an analogy but I'll go with it.

Your analysis misses several important points.
1) Automatic weapons execute their cycles in fractions of a second. An assault rifle on full auto cycles around 60/second. That imposes huge stresses on the mechanism. A semi automatic pistol cycle is slower but the shock loads will be high.
The biggest causes of mis feeds are due to dirt in the mechanism (caused by the environment it's operated in) and QC issues related to the components (ammunition) being loaded.

The system runs a very slow cycle in comparison (low stress until the ring is launched) and the environment is likely to be either vacuum (which imposes it's own problems, but they are known) or inert gas.

For a fusion drive system redundant actuators are an option and the fact the rings are made "on site" means (in principal) they can be checked and discarded if they fail QC, not really an option for ammunition. Obviously if the percentage that failed got too high you'd be in trouble if you couldn't recycle them, but that's a design problem.  :)

A lot of these problems can be worked out in sounding rocket or zero g plane flights long before a full vehicle is designed.
« Last Edit: 10/28/2013 01:44 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Elmar Moelzer

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To put 134 metric tonnes in perspective that's 2 SLS flights, 6 Delta IV Heavy flights or 9 Skylon flights, or 5 Atlas V heavy flights (if it ever gets funded).
If the vehicle can be fully reused (which it seems it can) this is not ridiculously expensive (but it's not cheap).  :(
Or 3 Falcon Heavy flights, which would even leave some extra margin. For a reusable mars mission architecture that allows for 90 day transfers and if all goes well, even 30 day transfers, that is cheap, at least in my book.

Offline IRobot

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For me the most interesting thing is that it includes fuel for an orbit insertion back on Earth, meaning the spacecraft would be fully reusable right from LEO. Meaning a sustainable space exploration program.

Offline Elmar Moelzer

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For me the most interesting thing is that it includes fuel for an orbit insertion back on Earth, meaning the spacecraft would be fully reusable right from LEO. Meaning a sustainable space exploration program.
Exactly!

Offline adrianwyard

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A lot of these problems can be worked out in sounding rocket or zero g plane flights long before a full vehicle is designed.
Hmmm, I see the problem being the opposite: you cannot do representative testing of the reload mechanism on a small scale (sounding rocket), and/or small time-scale (aircraft). This is a large complex mechanism that includes multi-meter transport of components, cold-welding them with very fine-alignment, in vacuum zero g. Just two full cycles will take ~28 seconds.

Not to say it can't be done, but it was Elmar who suggested upthread we think of this mechanism as akin to placing a robot assembly line (i.e. well understood and highly-reliable) in orbit. I think that analogy is a good one.

To get confidence in (man-rate) a mechanism that is required to run for thousands of cycles to keep your crew safe, I think you need to launch a full-scale test article and run it for a representative period. While the mechanism is hoped to be just a few tonnes, a long-run test will require a lot of liner components, and that's going to be heavy.

As for reliability and recovering from a jam, given the number of failure points and the likelihood of in-flight repair being minimal, I think you just include two or three FDRs on the spacecraft to get full redundancy.
« Last Edit: 10/28/2013 04:28 pm by adrianwyard »

Offline Elmar Moelzer

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Even if the thing was able to jam somewhere, I think it should be possible to do a simple in flight repair with something like the Robonaut, which should only take a few minutes with a few prepared spare parts. Considering that the overall flight time is still months, a few hours of delay, should be acceptable (and should be factored into safety margins).

Offline IRobot

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One question: if we wanted to double the average thrust, what would be the path?

Scale up the engine? Shorten time between pulses?

Putting two engines in tandem does not seem to be viable.

Offline Elmar Moelzer

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One question: if we wanted to double the average thrust, what would be the path?

Scale up the engine? Shorten time between pulses?

Putting two engines in tandem does not seem to be viable.
I believe (!) that there are two approaches. Judging from their papers, I assume that MSNW is hoping to increase the fusion gain over time, as the design matures (from 200 to 500). This would mean more "bang per shot". I also think that there is a lot to be gained from increasing the pulse frequency. I think that this has a physical limit though, as one has to wait for all the products of a shot to completely clear the engine and the vehicle over all and improved designs might only be able to improve this by so much.
A higher pulse frequency might make for a more comfortable ride though. So, I would personally hope for that.
« Last Edit: 10/28/2013 05:26 pm by Elmar Moelzer »

Offline alexterrell

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One question: if we wanted to double the average thrust, what would be the path?

Scale up the engine? Shorten time between pulses?

Putting two engines in tandem does not seem to be viable.

I don't see why you couldn't put 2 engines in tandem. Four would be better, then fire them 2 at a time to prevent bending moments.

Other than that, the lithium ring is the smallest they could make it, so it could be expanded. But I think increasing the firing rate would be easiest, and it doesn't need any increase in capacitor banks.

Offline Elmar Moelzer

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I once had an idea for a sort of revolver like design to increase frequency. I think you might need two side by side engines for that to work though to counter the momentum of the revolver(s)

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