Using atmosphere as propellant

[WizWom]

There is a reason Bussard's high-thrust (ARC) engine design used the polywell only for energy production, and preliminary heating of the reaction mass.

His high-ISP design, though - that one he planned to focus the fusion products out the exhaust bell.

[DeltaV]

There is a reason Bussard's high-thrust (ARC) engine design used the polywell only for energy production, and preliminary heating of the reaction mass.

His high-ISP design, though - that one he planned to focus the fusion products out the exhaust bell.

We were talking about no-down-conversion methods to drive "electrostatic" fan motors (before QED-ARC altitude and speed are reached), not about using alphas directly for thrust as in high-Isp, low-thrust QED-DFP.

[93143]

What about using the 1.5MV DC for an electro-static air breathing ION engine?

...

I'm sure with 1.5 million volts as a source, an air breathing ion engine would have quite a bit more thrust if designed properly. Maybe even circumvent the need for massive apparatus for stepping down the 1.5MV to something lower in voltage. Any thoughts?

I tried to design a Polywell-powered air-breathing ion engine a few years ago. As I recall, arcing was a major problem, and the required voltage stepdown was tied to the ionization rate, which was tied to the forward speed of the engine. I concluded it wasn't worth it.

I might have been wrong - the entire exercise was pretty much BoE...

[GIThruster]

That's a very nice summary but it's fair to note that we can do things like fly turbines faster than Mach 1. The HTV-3X or Blackswift intended to fly it's turbines to Mach 3 and then ram to Mach 6. That's still a long way from an orbital vehicle. I don't think there's anything that was ever proposed for FALCON or Falcon that was a true orbital vehicle. For orbit you need Mach 25-26 and something like ACES:

http://www.andrews-space.com/images/vid ... 00307).pdf

And I will also beg to differ that we don't know how to make a reactionless drive. We do. If the funding at Marshall for Woodward's M-E thruster work had not been interrupted by Bush's VSE, we might already have viable commercial thrusters or at the least, prototypes. They would not necessarily have the thrust efficiency necessary for human spaceflight, but I think it's most likely we'd have low efficiency thrusters suitable for satellite station keeping, and robotic interplanetary missions.

Now that Constellation is cancelled, I'd like to know where NASA intends to spend its money. We need to see Tony Robertson back working on M-E thrusters.

[KitemanSA]

How are you going to keep the skin of the craft cool?

The distinction between the SR71 and an SSTO is that th eSR71 is an atmospheric vehicle. It STAYS in the relatively dense part of the atmosphere for a long time heating up, and has wing loads etc to withstand with hot metal. On the other hand, the SSTO accelerates as rapidly thru the atmosphere as possible. A decent TPS tile or blanket will protect the skin long enough for the SSTO to leave the atmosphere and remove the heat/aerodynamic load combination that is the problem.

At least that is MHO.

[D Tibbets]

How are you going to keep the skin of the craft cool?

The distinction between the SR71 and an SSTO is that th eSR71 is an atmospheric vehicle. It STAYS in the relatively dense part of the atmosphere for a long time heating up, and has wing loads etc to withstand with hot metal. On the other hand, the SSTO accelerates as rapidly thru the atmosphere as possible. A decent TPS tile or blanket will protect the skin long enough for the SSTO to leave the atmosphere and remove the heat/aerodynamic load combination that is the problem.

At least that is MHO.

I'm not sure you can trivialize heating in the atmosphere if you are using atmospheric gas as your reaction mass. You have to stay within the atmosphere to use it. Rapid acceleration through increasingly less dense atmosphere might accommodate some tolerable heat load, but I'm sure it will be a challenge. Because of this I'm skeptical (from an ignorant perspective) that an air breathing engine could provide all the thrust necessary to reach orbit. The question I would consider more relevant, is how much velocity could be obtained before switchover to exoatmospheric on board reaction mass had to take over. Any gain past some point where additional engine weight was factored in would be profitable. In conventional rockets, the first stage, large fuel loads and structure have a huge impact on the requirements needed. Eliminating that early costly acceleration would decrease volumes/ weights and presumably costs needed for a SSTO. This is why I think some supplimental strap on boosters on an otherwise SSTO vehicle is not a terrible thing. If, some early or mid range acceleration can be done without the use of onboard fuel, it is a disproportionate gain. Then the question becomes , for the rest of the acceleration , which is better, a hybird engine that can convert to pure rocket mode, or seperate, hopefully light rocket engines that can finish the job. If something like a powerful ark jet or dilluted fusion product rocket works, the ISP will be significanly better than a chemical rocket and thus significantly less fuel tankage will be nessisary. If enough power can be delivered by these engines, the added complications of air breathing engines may not be worth the effort.

Dan Tibbets

[DeltaV]

The task as I see it is how to get 1.5MV DC electric power to provide lift in a flight envelope that goes from 0 fps at sea level, to 25,000 fps in a vacuum and everything in between.

What has been kicked around here for a while is VTOL-capable electric fans to ~M1, electric turbines to M2-3 with indefinite cruise, and QED-ARC (relativistic electron beam) from there to orbit (propellant injected for this mode). This avoids the REB's ozone production at low altitude. A vehicle mass issue (beyond radiation shielding) is the HVDC down-converter mass (needed if you want to use some evolution of modern, high-power-density, low-voltage, brushless motors, probably involving magnetic bearings and superconductors). MV-level "electrostatic" motors would avoid the down-conversion mass, but are also an entirely new R&D project (the REB likes high voltage).

Since we don't know how to make an inertia-less drive (i.e. no reaction mass) then we are going to need some kind of reaction mass to propel our craft.

Plan A is Mach Effect. Plan B above is a backup, until MLT research yields sufficient thrust.

So you have to switch to a method that can heat the air in a supersonic air stream, i.e. a scram-arc-jet. Once you are out of the atmosphere, (i.e. above 100,000 ft) then you have to use reaction mass you have carried along with you.

QED-ARC using a REB above ~100K ft, maybe lower.

How are you going to keep the skin of the craft cool?

Cruise slower than an SR-71. Use REB(s) as an "aerospike" ahead of the vehicle. Possibly more options, like aspirated metallic TPS or magnetocaloric cooling. Use air-only as propellant for this mode, to avoid expending cryogenics or onboard propellant, allowing indefinite cruise pre/post-orbit (only small amounts of H, B11 consumed).

These are all the problems we are facing trying to build a SSTO craft. Yes Polywell may give of lots of power, but having adequate power is only an answer to a small part of the problem of getting to orbit.

Agreed. It's a fun problem though.

Now that Constellation is cancelled, I'd like to know where NASA intends to spend its money.

On improving relations with the Muslim world:
Former NASA Director Says Muslim Outreach Push 'Deeply Flawed'

On the other hand, the SSTO accelerates as rapidly thru the atmosphere as possible.

If it's chemically fueled, it has to. It will run out of fuel quickly. There are definite operational (economic) advantages to a Polywell SSTO capable of long-duration atmospheric cruise both before boost and after reentry.

[DeltaV]

http://www.masbret.com/asc08.html [dead link]
http://masbret.com/asc2008-plenary/ [new link]

Current HTS electric motor technology (low-voltage of course) is roughly equivalent to gas turbines for power density. With more research, they claim it can reach 50 kW/kg.

About a factor of 5 improvement in power density relative to a GE-90-115B turbofan.

Check out the section on airframe-integrated distributed propulsion (many HTS electric fans driven by low-voltage cables from a few power sources). I keep seeing that Blended Wing-Body airframe morphing into a flatter, wider variant of the X-33 shape for SSTO, with a Polywell in the middle and embedded, sealable VTOL fans (nice and fluffy for reentry with metallic TPS, if radiation shield and down converter mass can be kept low enough). The boundary-layer ingesting upper surface propulsors might then get it to M2-3, REB zone, without that somewhat bulbous BWB forward section and the long wings. Nice thing about that location for the propulsors is that they don't see much reentry heating.

[Edit] Fixed dead link.

[KitemanSA]

On the other hand, the SSTO accelerates as rapidly thru the atmosphere as possible.

If it's chemically fueled, it has to. It will run out of fuel quickly. There are definite operational (economic) advantages to a Polywell SSTO capable of long-duration atmospheric cruise both before boost and after reentry.

There is very little reason for an SSTO, chemically or otherwise fueled, to cruise at a constant high speed like the SR71. Once on track, it will accelerate as quickly as possible no matter what it's reaction mass source.

There is one other point that should be brought up. As one gets closer to orbital speed, the wing loads go down; so typically the weakening of metals with elevated temperatures is less of an issue.

[DeltaV]

On the other hand, the SSTO accelerates as rapidly thru the atmosphere as possible.

If it's chemically fueled, it has to. It will run out of fuel quickly. There are definite operational (economic) advantages to a Polywell SSTO capable of long-duration atmospheric cruise both before boost and after reentry.

There is very little reason for an SSTO, chemically or otherwise fueled, to cruise at a constant high speed like the SR71.

Sure there is. Say you want to pick up a group of wealthy venture capitalists in Beijing, take them to your Bigelow-enclosed orbital micro-g spintronics factory in a high-inclination orbit for a tour, and then take them on to Washington, D.C. so they can sign the ITAR papers. You'll need to have parts of the trajectory be atmospheric flight simply due to the combination of orbital mechanics and geography. Airline-like operations (you don't expect your benefactors to sit on the Russian steppe next to their scorched Soyuz capsule, sipping vodka from plastic bags and waiting for helicopter transport to the nearest major airport, do you?) need a combination of prolonged atmospheric flight along with boost, orbit and reentry capabilities.

Once on track, it will accelerate as quickly as possible no matter what it's reaction mass source.

Why don't you just pull the throttle back? Once drag and thrust balance, you'll be at constant speed.

[KitemanSA]

There is very little reason for an SSTO, chemically or otherwise fueled, to cruise at a constant high speed like the SR71.

Sure there is. Say you want to pick up a group of wealthy venture capitalists in Beijing, take them to your Bigelow-enclosed orbital micro-g spintronics factory in a high-inclination orbit for a tour, and then take them on to Washington, D.C. so they can sign the ITAR papers. ...

SSTO, not hypersonic aircraft. But even so, if you have SSTO capability, tooling around in the atmosphere is still dumb. Sub-orbital skipping will get you there faster and you still won't have the atmospheric dwell. Dwelling in the atmosphere only makes sense if you DON'T have man rated vacuum capability.

And PLEASE, don't now start talking about low speed atmospheric ferry capability. Yes it makes sense to have some ability to line up your craft with a specific ground track before insertion. And yes, the faster the better. But there is no NEED to have extreme skin cooling in this case.

Once on track, it will accelerate as quickly as possible no matter what it's reaction mass source.

Why don't you just pull the throttle back? Once drag and thrust balance, you'll be at constant speed.

SSTO, single stage TO ORBIT. Why would I NOT go to orbit if I want to go TO ORBIT? Makes no sense to me. If you want to talk about SSNTO (single stage not to orbit) fine, but please don't use it to attempt to denegrate my statements wrt a SSTO vehicle.

[Aero]

Turbojets (and Turbofans) have intake systems that slow the incoming air stream to sub-sonic speeds in order for them to work. Same for ramjets.

Lets assume that we do the same with our electric fan jet. So maybe the fanjet regime will be comparable to Blackswift's flight envelope of 0-3, (electric-turbofan) then 3-6 (ram-arc-jet?) Still leaves Mach 6-25 to get to orbit.

Turbojets and ramjets slow the incoming air stream to sub-sonic speeds in order for combustion to occur. Supersonic air flow will blow out the flame - The fuel can't be burned in that configuration. SCRAM jets have been designed to overcome that limitation.

Lets NOT assume that the incoming air stream needs to be slowed to subsonic in order for electric motors to work. Accelerating a supersonic air stream using a fan or propeller is a different issue. One thing is certain when using air as the reaction mass: The momentum, relative to the engine, of the air exiting the engine must be greater than the momentum of the air entering the engine. That was a big problem for propeller driven planes nearing sonic speeds.

In the early days of jet engine research one project used an IC engine to power the compressor, then burned fuel to heat the compressed air raising even higher pressure in the exhaust for thrust. It worked but was heavy compared to turbines. However, with electric motors and electric heating, a similar configuration would work. Weight will always be a concern.