SCRAM jets... get rid of the C, have a easier time?

[KerikBalm]

So, if the claims on wikipedia are to be believed for scramjets:

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

They could get right up to the edge of orbital velocity.

The main challenge of them, is designing them to allow combustion in supersonic airflow.

By we don't need combustion, do we?

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

Would it be simpler to design a "SRAMjet"? using nuclear power?

Sure, running a nuclear reactor in hypersonic flight in Earth's atmosphere is quite dangerous... but suppose we had working fusin reactors.

What sort of thermal "SRAMjet" could we make in the case of a polywell device? a torus? a fusor? a DPF?

If we had a fusion powered SRAMjet getting up to mach 24... well then, it would only need a tiny push with an NTR, and its in orbit...

The mass ratio of the craft could be ridiculously low, no?

Or... would the heat exhange system/ whatever method used to heat and expand the incoming air be more complicated than combustion?

[ZetaX]

A tokamak is nothing to be put on a plane, they are just way to big. Also, fusion power plants often cause radiation, too, e.g. from tritium. You would need a reaction that does not produce neutrons; possible, but even more complicated and less effficient.

And the mach 24 is rather theoretical, that's not the speed your plane will have a chance to survive at, and I also doubt that anything that is more than just engines with small wings will be able to get that fast this way.

[KerikBalm]

>"A tokamak is nothing to be put on a plane, they are just way to big."

Yea, I'm not optimistic for tokomak reactors at all, but DPFs and poly wells... could probably be made to work on a scale that would fit on something like an an-124 or C-5 galaxy.

>Also, fusion power plants often cause radiation, too, e.g. from tritium.

Radiation from tritium is of little concern. Not that much tritium would be needed. Also, presumably It wouldn't be too hard to do D-D fusion.

The main radiation source is not the fuel (much like Uranium is not that much of a radiation hazard, particularly U238), but rather the products from operating the reactor.

Still, while a fusion reactor would produce some radiation, the amount is orders of magntude less. If there were a mishap in flight, the radiation hazard would be minimal

And of course... if you could do P-B11 fusion (DPFs have acheived the conditions needed for this, but to get the fusion rate high enough, and capture usable amounts of power, still requires a lot of work), you'd have almost no radiation at all (there would be some side reactions, but negligible)

We don't need to consider only Fusion. Fission could do it, but it would be rather risky having a nuclear reactor that has been running at full power for a while, building up a lot of fission products, repeatedly going through the atmosphere at very high mach numbers (both on ascent, and reentry)

If the plane can survive the speed on the way down, its not unreasonable to expect it to survive a similar speed on the way up - of course the air density at which it attains those speeds is very relevant.

Mach 24, mach 20, mach 16... any of the above would still be a massive benefit when trying to make an SSTO. An of course, the rocket stage would be NTR, so there should still be a rather nice payload fraction.

[Ralathon]

Yea, sure that'd work.

We could also use antimatter annihilation to heat the air. Or we could use beamed power from power stations in orbit. Or maybe just skip the plane altogether and just build a space elevator with our nuclear bomb powered heavy lift vehicle.

The technology just isn't there yet. We don't even have fusion running here on earth, building a fusion powersource that fits inside a spaceplane is far future technology. There are plenty of ideas for cheap spaceflight, but they all require technology we simply do not have right now.

[Streetwind]

We don't even have fusion running here on earth

*BZZZZZZZZT!*

We have had fusion running just fine here on earth, even sustained over relatively long periods of time (more than just a couple seconds), for many years now. The actual problem, and what I'm sure you meant to say, is that we can only sustain the fusion reaction using external energy input. We have not yet been able to build a reactor that can power itself (much less something else in addition).

It's important to be precise, though.

[KerikBalm]

But we do have fission power, and if we were talking operation in an atmosphere anywhere but Earth, there'd be not nearly as many potential problems with the radiation.

Say a Venus ascent vehicle (see the other thread about a mission to venus), or titan... I don't know about Mars, I doubt its atmosphere is dense enough to make use of it, even in a scramjet.

If we could devlop a Fission powered SRAMjet, then if/when fusion power becomes suitably advanced, the SRAMjet technology should be readily adaptable.

If you're having a problem with the hypotheticals, just think Fission only.

We've made fission powered turbotjets, fission powered ramjets, Fission powered thermal rockets, we could easily make fission powered ion/electric propulsions....

All that is needed is something to bridge the gap between the relatively low speed ramjets we've made, and space where there is no significant atmosphere to make use of.

Sure, you could try SSTOing on NTR alone (or from a reusable carrier aircraft, or from simply... say mach 2 on turbojets/Ramjets), but if a SRAMjet could be designed to take the vehicle past mach 10, we could get orbital craft with some really good mass frations.

*BZZZZZZZZT!*

We have had fusion running just fine here on earth, even sustained over relatively long periods of time (more than just a couple seconds), for many years now. The actual problem, and what I'm sure you meant to say, is that we can only sustain the fusion reaction using external energy input. We have not yet been able to build a reactor that can power itself (much less something else in addition).

It's important to be precise, though.

Well you could say its not really running if its not self sustaining.

And we do have self sustaining fusion reactors (though for very short durations), that produce much more power than is put into them.

They're called hydrogen bombs...

But I'm looking for something a little more ... shall we say.... "elegant"? than an Orion drive.

Edited September 28, 2014 by KerikBalm

[Idobox]

An alternatie to nuclear for a SRAMjet is beamed power, and people are actually looking into it.

[ZetaX]

I am not aware of any tehcnology that could "beam" an amount of energy comparable even to normal jet turbines, even less for SCRAMjets. Can you give any sources¿

[Idobox]

I am not aware of any tehcnology that could "beam" an amount of energy comparable even to normal jet turbines, even less for SCRAMjets. Can you give any sources¿

Lots of work has been done on the subject. You can check lightcraft or the recent Japanese microwave rocket.

But my favourite one is this: http://nextbigfuture.com/2011/05/beam-powered-space-propulsion-work-from.html

The idea is to beam microwaves at a slab of silicon carbide with channels for hydrogen fuel. The silicon carbide converts microwaves to heat and can also be used as a heat shield for reentry.

None of these is for a SRAMjet per se, but could be used in such a concept.

[Hodo]

The primary problem with Nuclear propulsion is the radioactivity vs shielding trade off. The US and the USSR both toyed with the concept during the 60s and 70s. The Skunkworks managed to get a working nuclear jet engine, but the engine was lethal to the crew without shielding, but required no fuel. Once you added shielding it became to heavy for the power it was generating. The other method was to have the ignition caused by the reactor itself, but this lead to a heavy radioactive exhaust which is just bad all around. The project was scrapped in favor of more conventional methods.