With Radiations Shield Technologies Demron it may be possible to remove a lot of the other shielding, maybe all of it for a blanket of the stuff, which claims to be able to stop alpha particles, beta particles, neutrons, x-rays, low energy gamma which is the harmful stuff; so it seems to cover everything you need, take up less space and less mass

http://www.radshield.com/

QuantumDot - 08 February 2011 05:22 PM

With Radiations Shield Technologies Demron it may be possible to remove a lot of the other shielding, maybe all of it for a blanket of the stuff, which claims to be able to stop alpha particles, beta particles, neutrons, x-rays, low energy gamma which is the harmful stuff; so it seems to cover everything you need, take up less space and less mass

http://www.radshield.com/

... but it’s as dense as lead and in the amounts needed for FF applications it would be as heavy as lead.

http://www.radshield.com/pdf/RST_Livermore_Summary.pdf

http://www.radshield.com/pdf/Lead_Equivalency.pdf

Demron’s advantages are its flexibility and the claimed non-toxicity and, in thicknesses under .5 mm, it outperforms lead of similar thickness by a rather surprising margin.

But at .5 mm thickness lead shields about as well… and an FF array will need somewhat more than a half millimeter of shielding

zapkitty - 08 February 2011 06:00 PM

QuantumDot - 08 February 2011 05:22 PM

With Radiations Shield Technologies Demron…

... but it’s as dense as lead.

Oooooooops… my apologies. I had looked at the wrong figure for the density..

Demron density is actually only 3.14 g/cm^3.

If the shielding scales well for greater thicknesses this would be interesting…

The halving thickness of lead is 1 cm and that of water is 18 cm so with Demron you’d get ~18x the shielding of water for only 3.14x the mass.

If 5.5 cm of Demron equals 100 cm of water then it’d be 17.27 grams per sq cm shielded vs 100 grams/sq cm for water and ~4.2 tons minimum per module becomes ~724 kilograms.

If so then arranging the cores becomes much easier as well.

zapkitty - 08 February 2011 04:49 PM

... but energy density is still the problem. Even with the most optimistic shielding estimates you still have to have over 4.2 metric tons of water with each power module in addition to the FF cores, caps, onion etc… and both safety and cooling mean that you will not be able to squeeze all the cores into one module.

not quite. the power modules don’t need to be shielded from each other; so really there is just enough shielding to protect the payload and crew. i haven’t worked the numbers through, for EHD, as i’m not yet optimistic about it, for different reasons. but regardless, it seems the biggest problem to manage is heat, after all.

for 10 GWt of heat rejection,
keeping airfoil surfaces below glowing red hot, or around 800 kelvin, requires either a radiative surface area of 43 hectares,
or expulsion of coolant mass. ( 800 K radiates at most 23.226 kW/m²; and 10 GW / 23.226 kW/m² = 4.30e5 m² )
the situation is improved if very high temperatures can be tolerated. for 1600 K, 2 hectares would do; and for 3200 K, 1681 m² would do.
Ta4HfC5 melts at 4488 K, but is not exceptionally resistant to oxidation; layered hafnium carbide/silicon carbide seems the most resistant to ablation in air, (ablation rate of 5 µm/s measured at 595 kW/m², which corresponds to T=1800K).

it would be nice if all of the heat could somehow be carried away by air flowing over the wings and through the engine, but to accomplish that, i am told, we’d have to avoid stagnant air anywhere in the system.

you might want to look at the Skylon cryogenic system and LACE systems. Skylon uses liquid hydrogen to cool the system and the air that it uses to just a little before it turns liquid, while the lace system will cool it until it does become liquid.

http://www.reactionengines.co.uk/
http://www.sworld.com.au/steven/space/lace.txt

and cpu’s can get very hot so you might want to look at the cooling systems designed for them
various liquid cooling
air cooling passive or active( fan, or ionic wind aka plasma)
pelter or other heat pumps to move the heat to cool the important systems
heat sinks
cryogenic systems
thermoelectric, pyroelectric, and other similar systems

vansig - 09 February 2011 10:43 AM

zapkitty - 08 February 2011 04:49 PM

... Even with the most optimistic shielding estimates you still have to have over 4.2 metric tons of water with each power module in addition to the FF cores, caps, onion etc…

not quite. the power modules don’t need to be shielded from each other; so really there is just enough shielding to protect the payload and crew.

... and the people under your craft, above your craft, beside your craft, behind your craft…

Shadow shielding requires adding the operational costs of building dedicated special facilities unrelated and unattached to current cargo and passenger handling infrastructure and the need for exclusive routing in air and space will make it much more expensive than integrating a fully-shielded craft into the traffic control system.

vansig - 09 February 2011 10:43 AM

... but regardless, it seems the biggest problem to manage is heat, after all.

I think the problem is requiring ~1400 5MWe cores to do something that a Skylon or a Falcon 9 can do… and do much cheaper. 

I’m still rebuilding my basic flight proposals so I’m figuratively down in the soup at the moment but I think you might be spending too much time in the upper atmosphere… how many G’s do you pull at the max?

ground crews can retreat to safe distance when the craft is in operation. otherwise we’d have to space anodes as close as 3 or 4 cm apart, tesselating a sphere, to get shielding mass under 100t.

when it comes to space, propellant cost is king. it isn’t a fair comparison to say Falcon, etc. is cheaper, as those represent single-use vehicles and a mature technology, whereas the purpose of envisioning this is to have routine, possibly daily (hourly?), surface-to-orbit and return missions. the facilities cost is amortized over many launches and vehicles. final cost is more to do with day-to-day operation.

let’s see.. 600 kN nominal but probably 1800 kN max thrust at lift-off;
1800 kN / (100t x 9.8) = 1.84 gee.

vansig - 10 February 2011 11:55 PM

ground crews can retreat to safe distance when the craft is in operation. otherwise we’d have to space anodes as close as 3cm apart, tesselating a sphere, to get shielding mass under 100t.

Caps, cooling and aux gear to drive 1400 cores… er… wouldn’t you save time, volume, and lots of money by having a few dozen cores drive the fans until ~mach 6, let straight chemical take you out of the atmosphere and then let the cores take it from there? 

vansig - 10 February 2011 11:55 PM

when it comes to space, propellant cost is king.

...me being didactic again ... constraints on the mass and volume of propellant drive launch vehicle costs… the actual cost of propellant is a negligible factor in current launches.

vansig - 10 February 2011 11:55 PM

it isn’t a fair comparison to say Falcon, etc. is cheaper, as those represent single-use vehicles and a mature technology, whereas the purpose of envisioning this is to have routine, possibly daily, surface-to-orbit and return missions. the facilities cost is amortized over many launches.

Er… The Falcon line is intended to be reusable, or in this context “refurbishable” might be better. And they intend to be able to launch as often as people can pay. A reusable fusion spaceplane only gets you so far if the ballistic launchers are cheaper from the get-go.

But kudos on referring to rockets only as a mature technology. All too many space fans think of it as a perfected technology and it is far from that… there’s still lots of room for improvement.

vansig - 10 February 2011 11:55 PM

let’s see.. 600 kN nominal but maybe 1200 kN max thrust at lift-off;
1200 kN / (100t x 9.8) = 1.2 gee. it’s like an elevator ride

Uh… your bird is carrying propellant, right? If so then gravity and drag losses would eat your lunch, your dinner, your midnight snack, your breakfast and will probably take out options on the Thanksgiving turkey. Spaceplanes actually tend to pull a bit more g’s than ballistic launch vehicles.

i edited the numbers, to bring it up a bit. but, no, this is based on no use of on-board propellant in atmosphere.

the 600 kN is based on 80 kg/s air inflow at 36 km altitude and mach-2.4; inflow can be a lot higher at full atmosphere, and the 5 MW anodes could maybe run at 20 MW each for the first minute.

Ive tried to keep things as simple as possible; hybrid propulsion gets really complicated; the only thing to manage here is the amount to choke the input flow in the engine. even so, it is quite challenging to find an operating niche.

Perhaps I should revise that to say propellant cost, in terms of mass, is king.
for launches beyond LEO, you could spend 99.9% of your lift mass using conventional rockets. I’m seeking an end to that as a fundamental barrier

Something to keep in mind is that this bird operates along several gradients: 1G to virtually no G; atmosphere to vacuum; mass of propellant remaining onboard are the obvious ones. Skin and frame temperatures may be another. There may be a specific flight profile which minimizes required mass (mainly of propellant and its storage).

help… I’ve invented a fusion-powered wing de-icer…