[zapkitty]

Seems that a lot of preliminary work has actually already been done on all-electric propulsion. It’s the obvious next step and keeps showing up in the trade spaces because of the benefits that accrue even if the electric generators are chemically fueled. Funny how that sort thing happens…

Yes, Virginia, you can have a supersonic Prius 🙂

More seriously, the mass savings that are to be had with fully-superconducting engines and all-electric control systems are indeed considerable and several of the larger proposed designs would seem to be large enough to swap FF units in directly. The FFs substitute for the generators and fuel, they would directly power cryocoolers thus reducing the storage volume for needed for cryogens, and they would greatly reduce the frontal drag of intake area as the FF units are not airbreathing.

Going to try and see where all that might take us with FF-powered craft before going to the next step…

An example from the ICAS 2010 conference
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100036222_2010039460.pdf

[zapkitty]

Rezwan wrote:
Thoughts?

Updates that catch us up, provide some eye-candy for those who want it and firmly point out that even with the delays caused by the switches LPP is still on its original schedule.

An aside: It’s a pleasant commentary on the FF public relations front that due to the open (if somewhat randomized) nature of FF information the only thing that was really news to this dilettante was that “pre-shock” is now believed to be “pre-beam” 🙂

[zapkitty]

The projected low cost of an FF unit forces any thermal recovery system to have a very low price if it’s to make sense at all… and such systems are not known for their low pricing.

As you noted classic recovery systems start out costing as much as 1 or 2 complete FF units and only provide a fraction of the power of those new units… and so far “nano” anything has only been cheaper when placed in the context of the current status quo in power plants.

[zapkitty]

Ivy Matt wrote: After reading the article I’m not certain if they meant Li6/Li7+Be9, or if they meant p+Li6/Li7 and p+Be9. I kind of think it’s the latter. I’m not familiar with any fusion reaction involving Be9 as an input, but I am somewhat familiar with the p+Li6 and p+Li7 reactions. The former produces a He4 ion at 1.7 MeV and a He3 ion at 2.3 MeV, for a total of 4 MeV. The latter produces two He4 ions at a total of 17.2 MeV. Lately I’ve been wondering why p+B11 is seen as the “Holy Grail” of aneutronic fusion, and p+Li7 isn’t. There aren’t any downsides to p+Li7 as far as I can tell, and it should be easier for most confinement concepts to achieve.

Well, I’d squirreled that paper away for ideas and references (along with a lot of others) but had not paid attention to their aneutronic fuel list until I began reviewing my spaceplane assumptions. Then the “Be” registered… 🙂

I wonder what lithium compounds might be suitable, if any…

[zapkitty]

mjv1121 wrote: … he stipulates that “fuel must be injected in small quantities in order to prevent uncontrolled magnetic reconnection” – i don’t think this should be much of a problem seeing as there is no such thing as magnetic reconnection!

Is there a magnetic reconnection conspiracy?… 🙂

[zapkitty]

The helium nuclei have no electrons, and thus carry a net charge. That charge is what the field grabs and propels out along the axis.

The electrons have a net charge as well, one that is opposite the He ions, and thus are also grabbed and propelled… but in the opposite direction.

But unlike the ions the electrons don’t get far, instead they are absorbed by the plasmoid that generated the beams, heating it further and causing more fusion events.

Added note: the forces are opposite but due to the setup the resulting effect is unbalanced… and that’s why NASA originally funded DPFs: they wanted a fusion space drive.

[zapkitty]

vansig wrote: I might not want to do mach 24 in the stratosphere, but it is a conversation point.

I understand. But I also have to go back and see if any of my patched-together approximations have any connection to reality…

[zapkitty]

zapkitty wrote: I’m confused… why would you try to do mach 24 in the stratosphere?

…. because that’s what I said in that wishlist I jotted off.

My apologies. I shouldn’t have been juggling metric and imperial. I put 100kft when I was thinking 100km.

[zapkitty]

I’m confused… why would you try to do mach 24 in the stratosphere?

My idea was to start direct alpha augmentation along with the MHDs in the stratosphere in order to accelerate as much as feasible and throw the craft into an arc that would carry it into the thermosphere. By the time the MHDs quit and the FFs ran out of air to augment their thrust… well, by then drag wouldn’t be a problem (until the arc ended in reentry, that is.) I wasn’t figuring on the FF units fighting atmospheric drag by themselves.

[zapkitty]

Unfortunately all that happens then is that the sharks who make money off of sharks raising money thank you for eliminating the middleman and take you darker than black with clever, clever fundraising instruments… while eating you alive and telling you that things are going swimmingly.

And they won’t be lying in that regard… things will indeed be going swimmingly… for them.

[zapkitty]

Aeronaut wrote:
A central core flanked by the remaining cores would only need about a 1 foot spacer in the front to get all the beams to converge where you want to heat the propellant. In that case, existing “Beware Jet Blast” signage should suffice, unless you want to add an image of Donald Duck getting blown *ss over tea kettle.

The problem here is the radiation flux from the cores. Channels that would let the alphas out would perforce let other things out that aren’t nearly so benign.

Aeronaut wrote: What might happen if we approached this from ionizing atmospheric nitrogen for the MHD? That’s the bulk of a turbojet engine’s reaction mass. All the oxygen does is make the fuel combustible.

Not really an issue, I think. The MHDs can handle the atmospheric portion of the flight pretty much as they are described in the literature.

The issue is the transition from .1 atm at 65kft to .001 atm and beyond. My brilliant idea had the cores augment the MHD thrust by direct alpha heating the atmosphere as long as there was atmosphere to get in the way. I figured that’d be sufficient to get a suborbital trajectory at mach 18+… enough that the FF thrusters could take over alone and complete the ascent to orbit as my initial estimate had the craft at 34 tons… it was a tiny thing… but onboard propellant and the structure to hold it will change that…

… of course if you go old-school and just have a shadow shield the problem is easily solved but the operational costs will go up accordingly…

[zapkitty]

Aeronaut wrote: I thought ‘less than friendly neighbor’ meant drastically limiting shielding mass…

For the concept that I wandered off exploring the FF cores are the thrusters. But that involves passing the alpha beams through the shielding

The only hazard in that concept would be if you were directly behind the ship… but that would get very unhealthy very fast. Thus the cost of doing business with that design goes up equally fast.

And with the power available with FF we’re no longer at the stage of trying to reach orbit by any means possible.

The MHD research means that FF-powered supersonic jets can be done for far less MWe than I had thought… but there’s a ways to go from Mach 3 to orbit.

[zapkitty]

Tulse wrote:

mach 8-10, which seems to be an optimal velocity to launch to orbit from…

Perhaps I’m not following, but can you clarify what you mean here? Isn’t orbital velocity ~ Mach 25?

“… optimal velocity to launch to orbit from…”

Spacecraft of all types want to get above the sensible atmosphere first before seriously putting on speed. Chemically-powered spaceplanes scoop air to supplement their fuel while in atmosphere but they have to carry all of the fuel and oxidizer for that final sprint to orbit when the air runs out… as well as the fuel for the air-breathing portion of the flight.

So spaceplanes want to get as high and as fast as is feasible before heading for orbit… but pushing that too far ends up hurting more than it helps as they have to carry and burn up fuel that could be better used on the climb to orbit. Different concepts take off for orbit between mach 8 and mach 12 depending on the design.

I just got carried away with the fuel-free aspect of DPF flight without realizing I was literally poking holes in my “friendly neighbor” paradigm. Shiny objects, y’know 🙂

(for something often compared to an ion drive the FF version of a DPF can actually pack quite a kick for something that can be treated in the short term as an essentially fuelless thruster)

[zapkitty]

Oooh… even with a 1cm channel through a meter of shielding the radiation is kinda fierce… x20 channels is not as friendly a neighbor as I’d hoped for. To maintain the safety margin either closable ports w/ the added weight and complexity or use beam heating all the way and onboard propellant for the last stage… ouch… needs more MWe…

… but as the MHD units have to have beams anyhow for their work…

[zapkitty]

Edit jan 30: I screwed this up royally the first time around mixing feet and km. Shouldn’t have started doing stream-of-consciousness jotting until I was sure I was actually conscious…

spaceplane sanity check: wishlist

4 tons payload in a
3 meter x 4 meter payload module
(most space payloads are light for their bulk)
2 crew
2 mission specialists/passengers
and/or
4 more ms/p in a passenger module

2 power modules with 10 FF cores each for 100 MWe

2 compressor/MHD engine nacelles providing 250 kn each

air breathing to mach 3 @ 10km
air breathing w/DPF augment from 10km to 100km
straight DPF from 100km to orbit.

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