Scramjets !!!! It works

On Tue, 30 Nov 2004 17:40:22 -0600, Dave Logsdon wrote:
>
> From: ANTIcarrot [mailto:dante.feditech@...]
>
> "But not an orbital RLV though. I've also yet to see a design for a launch
> vehicle with a hybrid engine. Not that I'm saying that it's impossible ..."
>
> That's my point. Not yet, but not impossible. That's why I believe hybrid
> fuel systems should be used now, for anything they are currently capable of.
> First, because they're cheaper to build, cheaper to operate, and safer.

So far as I know, the cheaper to operate has not yet been show. They are
not necessarily safer either- a hybrid is a pressure vessel, and
hybrids *have* failed (pressure vessel failure- booom!)

> RE: Challenger: "I put it to you that if your biggest engine rips loose and
> damages the super-structure at high speed, you're screwed no matter what
> design you use. ;) "
>
> Well, maybe it's the way you described it. Or maybe, the SRB failure
> detonated the *explosive* fuel in the ET, but if the fuel for the SSMEs
> hadn't been explosive, the pilot *might* have had a few extra seconds to
> initiate SRB separation, and try for an emergency landing.

Nope. The studies say that the vehicle comes apart like wet tissue paper
if you do that. In fact, the ET didn't exactly explode. The real
damage was done by the loss of attitude- then the supersonic airflow
ripped off the tail and one of the wings of the orbiter. The loss of
attitude was caused by the SRB burning through on the of the struts
and then the SRB went sideways through the main tank. That's always
going to be a bad day, whatever kind of propulsion you use.

> "The only reason the tank has insulation in the first place is because if it
> didn't, ice might form and fall off during launch, damaging the shuttle's
> heatshield. Spot the irony. "
>
> Yeah, I spot the irony. Now, would you please spot the point I've been
> making? So, why was the insulation there? Because ice might form. And, why
> might the ice form? Because of the *cryogenic* fuels! *IF* we can get rid of
> cryo-fuels, we eliminate this problem.

Um. Hybrids would almost certainly use LOX if you want orbit. Nitrous
doesn't really have the ISP.

> "Watch a saturn-v launch sometime. You can see it's covered with ice that
> falls off during launch. This was never a serious issue before the shuttle."
>
> Reverting to an old-fashioned, straight-up, single-stack VTOL is, indeed,
> *one* way of dealing with the problem. But, is it the *only* way? NO. If
> not, is it the *best* way? Well, that's our current discussion.

No, he's saying that the problem is a feature of the unusual layout of
the Shuttle. It was realised quite late on in the day that this was an
issue. The fix- the foam- has turned out to be quite problematic.

> I posted:
> Even if all the safety issues could be addressed, the cost savings alone of
> hybrid systems make them worth considering.
>
> "That's like saying, 'Cars crash and are unreliable. We should all start
> using bicycles.'"
>
> I don't see how you're relating cost savings to this. If your point was
> actually in reference to the safety issue, then I'd say the comparison is
> between your fondness for an earlier model, and my preference for a later
> model that's less expensive to make, requires much less maintenance, and is
> safer to `drive'. No matter if it's cars or spacecraft, anything that's
> cheaper *and* safer is an improvement.

The performance of current hybrids are lower than the performance of
liquids, and IRC solids. That usually means that your payload ends up
costing more per kg, even if the rocket is cheaper.

> "In case of systems failure. Would you really like to tell your astronauts,
> "We're pretty sure it's safe, but on the off chance we're wrong you're
> completely screwed?"
>
> My analogy was to current, commercial aircraft, that fly *thousands* of
> times a day without any need for any escape mechanism. But, if you want to
> insist on an evacuation system, then the ejection systems used in some
> military aircraft could easily be added to the jet-powered lifter/first
> stage, and the orbiter/second stage could be equipped with an ejectable
> `survival module', similar to the one in the FB-111.

As I understand it, these modules are not very successful. The
designers of the ill-fated European manned vehicle fought long and
hard to avoid these modules being used. Even the designers of the
capsules were unhappy with them.

> "Where as VTOL has the advantage of making any patch of concrete anywhere
> into a space-port."
>
> You *know* it takes more than a "patch of concrete" to create a spaceport!
> On the physical side, you'll need a gantry, a complete cryogenic system to
> process your fuel and oxidizer, possibly a VAB, maybe a `crawler' to carry
> the assembled ship into position... whatever.

As you say, whatever that particular vehicle needs, you need.

> As I've mentioned before, HTOL
> systems will be able to use the infrastructure already in place for
> aircraft.

Apart from different fuels, different airports, different runways, a
different regulatory position, a different safety, a different
passengers and a few more things, yes, exactly the same!

> HTOL looks and
> sounds like just another aircraft taking off.

No.

> This isn't a real issue for a
> nat'l gov't space program, but for a private company?
>
> "Consider the Harrier and the A-10. Which needs more
> concrete? Which has greater flexibility?"
>
> You know as well as anyone reading this that the Harrier uses the same
> resources and infrastructure as any other aircraft.

No, he's right, Harrier can take off from a very small area, even
grass at a push (although it tends to blow soil away). You only really need
a tanker of kerosene.

> "Vertical take off is the way every rocket has ever worked."

Actually, no. Pegasus is horizontal takeoff. And either X1 or X15 took
off horizontally atleast once.

> And your point is?
>
> "The design shapes are very simple. Hence easy to build and maintain."
>
> Hybrid-fueled systems are simpler and cheaper than cryo-fueled systems. HTOL
> systems -- aka aircraft -- have been built and maintained longer, and at
> lower costs, than any VTOL system.

They haven't been orbit capable though. You might be able to use it as
a booster though.

> "Heatshields can be kept small (with only the base being armored) which
> allows heavier but more reliable technology... Multiple landing options,
> including parasail or powered landing."
>
> This brings up something I've been concerned about re: VTOL systems, but you
> might have just addressed it. Just how accurately can your preferred system
> park itself where it's needed? Gov'ts can afford to chase all over the place
> to recover their space capsules, but private companies can't.

Well, the Roton could have landed with pinpoint accuracy.

> An HTOL craft
> landing at an airport/spaceport has access to any facilities needed to deal
> with it's passengers and cargo. Are VTOL craft able to do this? Roton and
> the DC-X were intended to be controllable-descent designs, but the
> parachutes all the *successful* VTOL designs have used just drop the capsule
> somewhere in the general vicinity of a awfully big `landing site'. Maybe
> current VTOL systems can deal with this? How accurately can a parasail land
> a capsule?

As accurately, in principle, as the Shuttle.

> "Small VTOLs can operate from almost anywhere."
>
> *After* you build the infrastructure to operate from, which can cost
> millions per location.

AFAIK all orbital HTOLs would use specially built runways anyway. It's not
like you are going to get these things landing at JFK. Suborbitals can
probably use normal runways.

> HTOL can operate from existing airports,

Suborbitals yes, orbital no. These vehicle take off carrying *large*
quantities of LOX.

The technique for extinguishing a fire from a vehicle containing fuel
and LOX involves running shoes- you run the other way very fast, and
wait for it to burn itself out. There's no way you can put it out, and
there's no way that large LOX vehicles can mix it with 777s. Ain't gonna
happen in a million years. Or, it might, until the first accident. It
makes that crashed Concorde look like a camp fire.

The problem with LOX is that it tends to expand more than a 1000x in a
fire (density goes from 1 tonne per m^3 to less than 1kg per m^3),
whilst adding oxygen to the fire, and carrying the fire with it,
starting secondary fires. LOX and cold oxygen gas itself are also
heavier than air, so hug the ground, as does the fuel. *Really* nasty.
AFAIK nitrous is similar, but not quite as bad.

I saw some footage of somebody putting a bucket full of LOX onto a
barbeque. A camera 20-30 feet away rapidly caught fire. The barbeque
itself was flattened, the sausages on it vanished; the coals were just
gone.

> saving
> millions in creating said infrastructure. In addition, VTOL can operate
> "almost anywhere" only *IF* they're certified and permitted to operate. NASA
> and the U.S. military -- and their equivalents in other countries -- do what
> they want, wherever they want. But private companies have to answer to the
> FAA, OSHA, other Federal agencies, and a host of local bureaucrats and
> agencies. Spacecraft that launch like an airplane, and land like an
> airplane, are more likely to be thought of as airplanes. This second point
> *might not* be an issue, but it strikes me as something that needs to be
> looked at.

No, that is pretty much how it has gone for the last few years. New
regulations are coming in now. I think that aeroplanes that
essentially can stand on their tail for most of their powered flight are
treated as launch vehicles now.

> "They can be sold commercially, because the design doesn't lend itself to
> weapons deployment."
>
> Oh, you *GOTTA* be kidding me! What do you call a VTOL suborbital? I call it
> an ICBM!

Nope!

ICBMs (*Intercontinental* Ballistic Missiles) are usually orbital
capable with about 30% less payload, given modifications to the
guidance system of course. Suborbitals typically have a range of ~50
miles or so; if it is capable of 100 miles vertically. Surprising,
huh? It's because they leave the atmosphere and go ballistic.
Attempting to go sideways scrubs off too much speed, and so range is
low.

> "With very slight modifacations and refueling in orbit, the VTO can go to
> Luna, Mars or GEO."
>
> Assuming there would ever be a reason to use the *same* craft for those
> missions -- and I make no such assumption. Why would we ever want to try to
> create a craft that's supposed to climb in and out of Earth's atmosphere
> into the edge of space, and then expect that *same* craft to go voyaging off
> somewhere else?

Correct! You'd be carrying a lot of unnecessary weight around, that
costs fuel. On-orbit fuel is very expensive.

> "Greater flexibility in positioning the base of operations."
>
> See my infrastructure points above. The `bases of operation' for HTOL
> already exist, all over the world.

I suppose you might be able to use a military base, but there aren't
many that are
suitable. These vehicles are much, much more unreliable than
conventional aeroplanes, so very few airports will allow takeoff.

> "Able to land and take off in bad weather."
>
> Aircraft regularly take off and land in weather that grounds rocket
> launches.

Correct. It's got a lot to do with the low speeds at takeoff- they
usually worry about it striking a tower if there is one; there can
also be problems with windshear.

> "Fewer enviromental (sound) problems."
>
> Interesting point. I've never been around for a major rocket launch, so I
> can't compare it to the countless aircraft launches I have been near. The
> impression I've always had was that rockets were much louder, but if they
> do, in fact, require a smaller `sound abatement zone', then this would be a
> legitimate point in your favour, *if* you're building a completely new
> spaceport. So, *once again*, we're back to my point that HTOL systems will
> be able to utilize the infrastructure of *existing* airports, avoiding the
> need to build a new, separate, very expensive spaceport.

Depends on the exhaust velocity. If you assume that the rocket is far
noisier than an equivalent thrust jet engine you won't go far wrong at
all. Most orbital rockets are atleast 160 dBA.

The noise is actually caused by the wake. Decent rockets have
incredibly fast exhaust, much, much faster than an equivalent jet, so
they are much, much noisier.

> Dave

--
-Ian Woollard

"In theory there is no difference between theory and practice, but in
practice there is."
"a society in which people can do and say what they want will also
tend to be one in which the most efficient solutions win" - Paul
Graham