You're right! I hadn't read through the startup method.

Hmm. It makes a big difference actually, in multiple ways; it's rather interesting.

Yeah, it's really, really old tech. But as I say, it's the L/D ratio that's key; you need it to be as high as possible to get a good glide/skip out of the velocity you have, but it's very hard to do that. The highest anyone has ever done is the shuttle.

Most of the systems that are described like Dynosaur or Sanger bomber were basically ICBMs with a reentry vehicle stuck on the nose. The costs were not very good. You do get more range, but only a few hundred miles, unless you can get the L/D ratio up to around 4-6 during the skip or glide.

The designs like the waveriders they think might work, but they sharp leading edges and need active cooling; and nobody has done anything like that.

Oh and there was a double biconic reentry vehicle mentioned in the wikipedia's 'atmospheric reentry' article that might work for this, but I believe it's pretty classified, so nobody know exactly how good it is.

There is no temporary sheath; I don't know where you got that from. The sheath is needed to be there at all times, it controls, shapes, and stabilises the rotor and is needed at start up and shutdown.

It takes days or even weeks to shut down; you just gradually bleed energy out of the rotor and the cable comes down from 80km.

Those rods would be designed to survive flight through the atmosphere. Here we would be trying to make it *not* survive flight through the atmosphere, which is easier, but not without its challenges. And it's not a solid rod, it's made up of foot-long sections, so it would break up in flight into sections and tumble; those rods from God would be designed to be very stable in flight.

No, no. The rotor can be routinely stopped without any problems (actually you can generate electricity and feed it into a power grid for really quite a while).

You would only do a rotor dump in an emergency.

And it's not quite analogous to a nuclear bomb either- a loss of containment event would continue for 4 minutes, so although the total energy is the same, the rate of release is far slower; and you can spread the energy over a much bigger area and time.

Perversely, the rotor is going too fast to cause any real damage.

If the rotor ever sees the atmosphere then the stagnation temperature is around 50,000K, and the rotor will start to vaporize incredibly quickly; once it has done that then the iron vapour will simply burn.

Basically it's a meteorite.

The nice thing about meteorites is that if they're less than a certain size, they tend to just burn up; and not only that, but the atmosphere's drag limits the maximum range they can travel. The sections making up the rotor are smaller than that size.

So it's a meteorite, that, if fired from above the atmosphere, probably won't reach the ground, and if it does, the remaining fragments will be small.

And if it misses the atmosphere entirely, then it's at escape velocity, so it's probably not coming back for a long, long time. And if it does happen to, it will very probably just burn up.

I don't know, it seems a bit safer than I had imagined.

I just checked the 1985 paper, 1.5e15 joules, according to the conversion in the wikipedia, 350 kilotons.

That's a logical guess, but actually it's the other way around, the ribbon is moving faster than the speed of sound in the ribbon, so the ribbon is supersonically slowed ("shocked down" might be a good description) to lower speed as it goes past the payload, and it gets hotter as it does this. No perturbations can go upstream from the payload. However the decrease in speed is very small, just ~3 m/s, the ribbon is going *fast*; tens of tonnes of ribbon go past the payload per second.
Mmm. The biggest problem is the heating- it gains 80 centigrade as it goes past the payload. And its in a vacuum, so doesn't lose heat very fast, and if it reaches ~1000 C then it stops levitating ;-)
It wouldn't be one piece, it would be multiple pieces less than a metre long since it needs to change length slightly, but FWIW there are continuous manufacture techniques like extrusion that can produce indefinite lengths.

I'm not sure whether the characteristic length corresponds to the diameter or the length in this case.

However, where the rotor enters the section where it is deflected in a circle, that very definitely does correspond to flow in a pipe, and the drag there at least would be expected to be huge. You could try pumping the air that enters away so that most of the deflection happens in a vacuum with reduced drag, I suppose, but it looks a bit messy at the inlet. I've never heard of a mach 60 inlet, the heating would be stupendous.

But as a sanity check, consider a rocket's exhaust. A rocket's exhaust travels at hypersonic velocities, around Mach 10 (much slower than Mach 60 the rotor travels at.)

A rocket exhaust creates *huge* shockwaves around it. and acoustic losses are about 1% of the total energy in the exhaust. Are you suggesting that a Mach 60 rotor with air surrounding it, won't create similar waves, but over a much longer distance and represent similar or greater losses and noise hazard?

The thing is you have to hold yourself up long enough to reach your destination.

Either you're holding yourself up on 'centrifugal effect', i.e. you're in a non-inertial frame at near orbital speeds; or you're holding yourself up on wings.

The first effect implies you're more or less an ICBM; with similar launch costs (most ICBMs can do orbit with a 30% or so reduction in payload and a bit of fiddling around).

The second effect implies very, very good hypersonic lift/drag ratios (around 5-6 where the space shuttle manages 1 BTW). Which is very hard, and implies very high rates of heating and very high temperatures.

In case that's not clear, the low reynolds regime is one where viscosity completely dominates. The atmosphere would be like treacle to the launch loop a really, really thick boundary layer would form, and you would be trying to drag great oceans of air around at Mach 50. That's why the drag would be horrendous.

That's the wrong calculation. The Reynolds number is low here, it's low Reynolds because of the speed of the flow relative to the size of the object.

Not really, that's only true at *very* high speeds.
No, the air next to the rotor would be carried with it in what's called a 'boundary layer', and there would exist shear flow relative to the stationary air around it, and it would lose energy due to viscosity.

Over a such long length the energy losses would be prohibitive and unfortunately it would never lift off the ground.

No, the incline is only 'short' a few hundred km(!)- the acceleration happens on the 2000km long flattish top bit. There's a loading dock at the point where the loop flattens out (actually the weight of that dock is partly what flattens out the trajectory), it looks a bit like an oil rig, there's pictures of it around.

I've no idea why the proposal is to do it that way; operationally you would prefer to load from ground level.

Absolutely, CNT would be very useful in a lot of scenarios including this one.

They winch it; there's ties up to the top of the incline; they're tapered material (ideally CNTs but the current design uses Kevlar and metal). I'm not quite sure why the payloads don't ride the incline though.
The SE is very thin and weak at low altitude, I don't think it would help enough; this thing weighs many thousands of tonnes.