Using atmosphere as propellant

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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WizWom
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Post by WizWom »

DeltaV wrote:For now, I'd be happy with access to and from LEO. The zero g will help my back.
hey, you can have zero-G for a few seconds any time you like - just jump off a tall building.

Of course, the end of the trip might not be good for your back.
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DeltaV
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Post by DeltaV »

I'd need more than 6 seconds to make it worthwhile.

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IntLibber
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Post by IntLibber »

DeltaV wrote:For now, I'd be happy with access to and from LEO. The zero g will help my back. In case I spot a nice island from orbit, I'd want to be able to visit it without needing an Act of Congress. Refueling needs won't be a concern with Polywell, at least for trips of a week or less. Regarding hyperdrive, I can do without that for now. Who needs the hassle of Klingons, Romulans, Ferengi, Wraith, Replicators, Orai, 14 ft tall silicon-based insects with molecular acid blood, etc. Maybe later, if I get bored.
Dude, you are soooo forgetting the women of Beta... and the Orion slave girls....

rjaypeters
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Add Lightness and Simplicate

Post by rjaypeters »

What a great thread!

I'm pretty sure this thread's posters know the design of SSTO vehicles is a long-time goal of the aerospace industry which has failed for lack of a good power source (and other things, e.g. money and good light-weight materials are also high on the list).

Aside from the over-concentration on the rotary theme, I think the most innovative attempt was the Rotary Rocket Roton. See here:

http://en.wikipedia.org/wiki/Rotary_Rocket

By most innovative, I mean there was no messing with wings (too heavy to be useful for long enough to be worth the weight) or runways.

The helicopter phase solves a last-mile problem. How to land and take off while not building too much speed at low altitude or tearing up the backyard real estate.

Some of us have proposed up to four propulsion systems (did I read that right? turbojet + ramjet + scamjet + reaction drive?) for the Polywell-powered SSTO. Two is the maximum we should permit. So:

1. A helicopter phase powered by the very high voltage DC motors (which are yet to be invented) or stepped-down voltage motor (I know - weight penalty). The advantage here is the motors are kept inside the body of the vehicle and we don't attempt to carry ducts into space. Although I don't much like counter-rotating rotors for this application, they might be the simpler way to counter rotor torque. Else we could use retractable anti-torque fans.

Lift the Polywell SSTO high enough so the reaction drive won't bother the neighbors by making too much noise or tearing up the landing pad.

2. The Polywell-powered reaction drive phase (which could use air as reaction mass but there I go adding complexity). The reaction drive must also provide the bulk of the reentry thermal protection in two ways: reducing the speed of reentry and pushing the stagnation shock boundary away from the bottom of the vehicle (which must have a TPS to protect from the energy of the reaction drive anyway).

When reentry is achieved and speed is slow enough, spin up the rotors for landing.

I really like the concepts of the elliptical arc-pulse engines and REBs, but the point of SSTO is to put mass into orbit and bring it back down again. Extended cruise through the atmosphere? Build a Polywell-powered REB screamer if you must (please - I'd love to ride that puppy!), but don't tack on the requirement to reach orbit.
"Aqaba! By Land!" T. E. Lawrence

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Stoney3K
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Re: Add Lightness and Simplicate

Post by Stoney3K »

rjaypeters wrote:1. A helicopter phase powered by the very high voltage DC motors (which are yet to be invented) or stepped-down voltage motor (I know - weight penalty). The advantage here is the motors are kept inside the body of the vehicle and we don't attempt to carry ducts into space. Although I don't much like counter-rotating rotors for this application, they might be the simpler way to counter rotor torque. Else we could use retractable anti-torque fans.
That almost starts to look like the Avatar-type ships. Small craft have a twin set of counter-rotating (ducted) propellers, where larger craft have four sets, probably for stability reasons.

Either way, we're going to need a way to interact with the atmosphere and create thrust from it. Jets have proven an efficient method to do so, and an engine that transitions from turbofan(or jet) to ramjet, and then to scramjet has already been used on the SR71. The only change would be the mechanism to add energy to the incoming air, which is now provided by the Polywell instead of a combustion source.

A Polywell system is going to produce waste heat anyway, if the product from that is hot enough, it might be able to spin a set of turbines directly and drive a fan. At higher speeds, this waste would be ejected from the spacecraft directly.
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rjaypeters
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Add Lightness and Simplicate

Post by rjaypeters »

Stoney3K: I should have written counter-rotating _coaxial_ rotors at the top of the vehicle. The modified tilt-rotors shown in "Avatar" have their place in a primarily atmospheric vehicle. Note the size of those rotors relative to the size of the remainder of the vehicle.

For interacting with the surrounding medium, the greatest efficiencies are found by accelerating the greatest amount of mass by the least change in velocity, consistent with the other constraints on your technology. External rotors are the best at low speeds near liftoff and landing.

Also note, these external rotors would fold against the body of the vehicle for high speed flight. Another reason not to like counter-rotating is one must arrange for stowage of two sets of rotors...

"...scramjet has already been used on the SR71..." No, sir. The SR-71 used a very heavily augmented turbojet. We haven't built operational scramjets, yet. That I know about...

Certainly the Polywell will reject heat to the environment. The problems come in when attempting to use the waste heat.
"Aqaba! By Land!" T. E. Lawrence

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Post by kunkmiester »

Although I don't much like counter-rotating rotors for this application, they might be the simpler way to counter rotor torque. Else we could use retractable anti-torque fans.
Mass is the important part in countering torque. A proper set of counterweights can be held inside the vehicle, and will do just as much, though with a higher mass penalty.
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DeltaV
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Post by DeltaV »

I'm thinking embedded, ducted, electric lift fans for VTOL. Better for redundancy. Say, 8 fans embedded in a large-planform vehicle. The lift fans can be mounted in semi-spherical gimbals for thrust vectoring. Mechanically simpler than external rotors that must be stowed. Separate, embedded, electric turbines for higher speeds up to REB start (~M2.5), the turbines sharing inlets/exhausts with the REB (used for orbit boost). Sliding doors to seal where necessary for boost/reentry. Metallic TPS, doable with a "fluffy", large-planform vehicle. That's my baseline. Modify as appropriate for elliptical arc pulse engines or whatever...

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Post by rjaypeters »

kunkmiester wrote: "Mass is the important part in countering torque. A proper set of counterweights can be held inside the vehicle, and will do just as much, though with a higher mass penalty."

Yes, since we must counter torque, I'd like to get some lift out of in the bargain and avoid higher mass.

DeltaV: Although you certainly want to build a sexy vehicle, I don't think we are going to agree, but here goes...

Please tell me how eight fans closing inlet doors distributed around the vehicle are simpler and lighter than one or two helicopter hubs at the top of a conical or pyramidal shell.

Large platform = mass. IMO, the better SSTO efforts (including the Clipper demonstrator) showed the way with smaller platforms and planforms to minimize structure.

I can't tell from my fuzzy memory this morning, are you proposing to lift this large planform straight up through the atmosphere? If so, please include the drag penalty in your trajectory calculations.
"Aqaba! By Land!" T. E. Lawrence

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Stoney3K
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Post by Stoney3K »

rjaypeters wrote:Yes, since we must counter torque, I'd like to get some lift out of in the bargain and avoid higher mass.

DeltaV: Although you certainly want to build a sexy vehicle, I don't think we are going to agree, but here goes...

Please tell me how eight fans closing inlet doors distributed around the vehicle are simpler and lighter than one or two helicopter hubs at the top of a conical or pyramidal shell.
First of all, DeltaV has a point when he claims that a hovering pyramid is just going to look plain hideous. Not very beneficial when you want the craft to be commercially viable, and customers will want to park it in their back yard. :mrgreen:

Secondly, a craft with a form factor like that is not going to be very efficient in *horizontal* flight. It may be very effective in vertical take-off and landing, but not reallly useful when you want to make short hops in the atmosphere.

My idea is more like a craft that can take off from a regular airfield (or meadow) and travel through the atmosphere or ascend to orbit at will.
Large platform = mass. IMO, the better SSTO efforts (including the Clipper demonstrator) showed the way with smaller platforms and planforms to minimize structure.

I can't tell from my fuzzy memory this morning, are you proposing to lift this large planform straight up through the atmosphere? If so, please include the drag penalty in your trajectory calculations.
Isn't the magic number here just 'power to weight ratio'? I mean, if you have enough grunt to get 1kg off the floor, you will also have enough if you scale it up 1000-fold and lift a ton. The equation is a bit iffier with chemical rockets, as they will lose weight over the course of the trajectory, but with a craft powered by a Polywell, the power output is (in theory) constant.

So if you want to lift this large planform (say, the sky carrier Valiant), just add more grunt. You could haul an asteroid or a moon if you wanted to, space tugs anyone?
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Post by rjaypeters »

First of all, DeltaV has a point when he claims that a hovering pyramid is just going to look plain hideous. Not very beneficial when you want the craft to be commercially viable, and customers will want to park it in their back yard.
I take your point, but please look at the Rotary Rocket wiki entry (see my earlier post). I thought the Roton was appropriately svelte for a SSTO. The pyramidal shape would be also tall and slender for aerodynamic reasons (see the DC-X demonstrator). Here:

http://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X
Secondly, a craft with a form factor like that is not going to be very efficient in *horizontal* flight. It may be very effective in vertical take-off and landing, but not reallly useful when you want to make short hops in the atmosphere.

My idea is more like a craft that can take off from a regular airfield (or meadow) and travel through the atmosphere or ascend to orbit at will.
I do not care much for horizontal performance. The highest efficiency of ascending to reaction drive throttle-up is what I'm after. Please, runways? wings? So early twentieth century! "Got a runway in your backyard, Mr. Gates?"

Also, this heavy vehicle is going to destroy any meadow in lands in. Think about the exhaust velocity of the eight fans. This is why we use helicopters to land in backyards...
Isn't the magic number here just 'power to weight ratio'? I mean, if you have enough grunt to get 1kg off the floor, you will also have enough if you scale it up 1000-fold and lift a ton. The equation is a bit iffier with chemical rockets, as they will lose weight over the course of the trajectory, but with a craft powered by a Polywell, the power output is (in theory) constant.
Pardon, my pedantry is about to show: Thrust/mass or thrust/weight ratios are what we are hoping to maximize. The electrical/thermal power coming out of the Bussard must be coupled to the environment. At low speeds, larger airfoils will do a better job than ducted fans. By way of comparison, look at the best jetpack in the world. Here:

http://www.martinjetpack.com/

Mr. Martin dedicated his life to building a jetpack and for all its wonders, it doesn't do well at horizontal performance (it also doesn't use a jet engine, but I digress). Take a look at the videos, instructive.

Wanna go fast in the atmosphere? Build the REB screamer.

I'm afraid we will have to agree to disagree.
"Aqaba! By Land!" T. E. Lawrence

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zapkitty
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Post by zapkitty »

rjaypeters wrote:By way of comparison, look at the best jetpack in the world. Here:
http://www.martinjetpack.com/
That sure is one badly designed skycycle :)

... when I understood the limitations of chemically-powered rocket and jet packs I thought that the best solution offered was Heinleins "'copter-pack" ... which is the old open-rotor backpack helicopter concept (presumably with a futuristic power source)...


As fot the subject at hand... as I've noted here before if the multi-gigawatt polywells work out then I favor an air-augmented VTOL with ducted fans... with the fans being pulled out of the airstream when the going gets heavy and relying on ram air-augmentation from that point up to vacuum...

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Post by DeltaV »

Long, thin blades are difficult to stow cleanly for high speed ascent/reentry. While the blades are stowing, are you planning to freefall or accelerate under rocket thrust?

All big airplanes use hinged doors of some sort. Sliding doors are a little more difficult, but not that hard for a large planform vehicle.

Sealing VTOL fans is known tech...
http://www.youtube.com/watch?v=ZD-J1KksHUQ
...just add the requirement for metallic TPS and better seals.

F-35B/P&W_F-135 power into the forward lift fan drive shaft is about 26MW. F-35B lift fan thrust is about 20,000 lbf. 5GW/26MW = 192 of those for 3,840,000 lbf. Factor in realistic losses (which would not be bad for an all-electric system) and you still have millions of pounds of vertical lift available if needed.

Polywell fuel mass is insignificant. Reaction mass hopefully won't be needed until after the air thins out during REB boost. Polywell enables VTOL+Cruise+LEO for a reusable vehicle with no runways, launch towers, flame trenches, etc., as long as radiation shield and down-converter mass can be kept low enough.

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Post by rjaypeters »

DeltaV wrote:Long, thin blades are difficult to stow cleanly for high speed ascent/reentry. While the blades are stowing, are you planning to freefall or accelerate under rocket thrust?
Freefall? Accelerate? Neither, use the rocket to maintain altitude while the rotor blades decelerate and stow (alongside the body). Oh, I reckon some vertical speed could be maintained. Stowage is no problem if the aero loads are low. Ask the USN how it works on a carrier flight deck. All we need here is for the hub to align in a certain orientation and then for the blades to fold down.

Coming down: again use the rocket to hold altitude (or maintain a slight sink rate) while the blades spin up.

Before re-entry, we have the choice of lifting the blades away from the body and aligning them above the hub before starting their rotation or just leaving them along the body. I'd prefer to leave the blades along the body and use the sink rate airflow to help lift and auto-rotate them.
DeltaV wrote:All big airplanes use hinged doors of some sort. Sliding doors are a little more difficult, but not that hard for a large planform vehicle.
Yeah, the sliding and hinged technology is well established for wing flaps.
DeltaV wrote:Sealing VTOL fans is known tech...
http://www.youtube.com/watch?v=ZD-J1KksHUQ
...just add the requirement for metallic TPS and better seals.

F-35B/P&W_F-135 power into the forward lift fan drive shaft is about 26MW. F-35B lift fan thrust is about 20,000 lbf. 5GW/26MW = 192 of those for 3,840,000 lbf. Factor in realistic losses (which would not be bad for an all-electric system) and you still have millions of pounds of vertical lift available if needed.
I haven't looked up the numbers for the F-35, but they sound right. I'm not saying VTOL fans won't work. I am saying for the equivalent lift, helicopter works better and is lighter. The central concept here is to reduce the disk loading so the air we accelerate downward has the lowest velocity for less noise (did you listen to the Martin Jetpack?) and wear and tear on our backyards.
DeltaV wrote:Sealing VTOL fans is known tech...
http://www.youtPolywell fuel mass is insignificant. Reaction mass hopefully won't be needed until after the air thins out during REB boost. Polywell enables VTOL+Cruise+LEO for a reusable vehicle with no runways, launch towers, flame trenches, etc., as long as radiation shield and down-converter mass can be kept low enough.
Who needs VTOL fans + REB + rocket? Save the weight (and money BTW) and complexity by having one flight transition per ascent (helicopter to rocket) rather than two (fans to REB to rocket). Descent is probably a different case for you, I imagine REB won't be needed coming down, but if you want to loiter or greatly change the LZ, REB would be handy.

The helicopter removes the weight of the REB equipment and lets us carry (in fact, requires) more reaction mass. I'm assuming water is our reaction mass, but tankage is a lot lighter than REB equipment and we can leave surplus water in orbit where it will do some good.

On another point, these vehicles are going to be heavy. I'm guessing around one million pounds. We're still going to need landing pads, but flame buckets won't be required.

I don't see loiter or atmospheric cruise as requirements which should drive the design of the first generation Polywell SSTO. I think the point is to, as cheaply as possible, lift mass and bring it back down again. IMO, high speed and/or extended flight through the atmosphere is not what we should be designing for in the first generation Polywell SSTO.

Once we understand the Bussard better (and can make it better), follow-on vehicles should have more difficult to satisfy requirements. Else, what would the engineers do?
:D
"Aqaba! By Land!" T. E. Lawrence

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DeltaV
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Post by DeltaV »

rjaypeters wrote:
DeltaV wrote:Long, thin blades are difficult to stow cleanly for high speed ascent/reentry. While the blades are stowing, are you planning to freefall or accelerate under rocket thrust?
Freefall? Accelerate? Neither, use the rocket to maintain altitude while the rotor blades decelerate and stow (alongside the body).
Hope your rocket consumes less than the SSME:
Each engine consumes 1,340 liters (340 gallons) of propellant per second. If the engine pumped water instead of liquid oxygen and liquid hydrogen, an average-sized swimming pool could be drained in 75 seconds - or 25 seconds for the sum of the three used for the space shuttle launch.
And that's not counting the solids.
rjaypeters wrote:Before re-entry, we have the choice of lifting the blades away from the body and aligning them above the hub before starting their rotation or just leaving them along the body. I'd prefer to leave the blades along the body and use the sink rate airflow to help lift and auto-rotate them.
Deploying them before reentry guarantees they melt or break off.
rjaypeters wrote:I'm not saying VTOL fans won't work. I am saying for the equivalent lift, helicopter works better and is lighter.

Polywell should have power to spare before orbit boost. Lots of lift fans if needed. Two helo rotors can't lift that much, and only give one level of redundancy, assuming they're cross-connected. Eight lift fans can tolerate losing two or three. Don't forget the complexity of rotor heads, gearboxes and cross shafts compared to Halbach rim-drive motors.
rjaypeters wrote:The central concept here is to reduce the disk loading so the air we accelerate downward has the lowest velocity for less noise (did you listen to the Martin Jetpack?) and wear and tear on our backyards.
Eh. Pour a concrete pad out back, if China doesn't buy up all the concrete first. If "disk" loading is that big a deal for arbitrary sites (dust/gravel kicked up) use more, smaller lift fans.
rjaypeters wrote:Who needs VTOL fans + REB + rocket? Save the weight (and money BTW) and complexity by having one flight transition per ascent (helicopter to rocket) rather than two (fans to REB to rocket).

Rocket? Where did you get rocket? It's VTOL electric lift fans, transitioning to electric turbines up to ~M2.5, transitioning to REB from there to orbit. See Bussard's papers on hypersonic propulsion. I'm feeding air to the REB until the atmosphere thins out, only then blending in onboard reaction mass. Jumping from helicopter to rocket means you'll need to carry a lot more reaction mass, especially with the hover time needed for blade stowage.
rjaypeters wrote:The helicopter removes the weight of the REB equipment
Huh?
rjaypeters wrote:and lets us carry (in fact, requires) more reaction mass.

Carry more, no. Sikorsky Skycrane payload is 20,000 lb. Think you're going to go orders of magnitude beyond that? Require more reaction mass to reach orbit? Yes, since you are starting to consume reaction mass much lower/slower, but it won't be able to lift it.
rjaypeters wrote:I'm assuming water is our reaction mass, but tankage is a lot lighter than REB equipment.
Maybe when it's empty.
rjaypeters wrote:On another point, these vehicles are going to be heavy. I'm guessing around one million pounds. We're still going to need landing pads, but flame buckets won't be required.
So the low disk loading of helo blades becomes moot.
rjaypeters wrote:I don't see loiter or atmospheric cruise as requirements which should drive the design of the first generation Polywell SSTO. IMO, high speed and/or extended flight through the atmosphere is not what we should be designing for in the first generation Polywell SSTO.
That's trivial compared to getting to orbit. Atmospheric cruise lets you pick your orbit and your takeoff/landing locations. So you want to limit yourself to a few orbit inclinations and one or two launch/landing sites, like Shuttle?
rjaypeters wrote:Once we understand the Bussard better (and can make it better), follow-on vehicles should have more difficult to satisfy requirements. Else, what would the engineers do?
Go for broke. Before the daggum gubmint regulates it all away.

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