shockonlip said:
mz said:
Flexible perhaps in low fuel consumption in their speed range, that's good for missile use. Anything else - extremely inflexible. Large dry mass, huge size, low thrust, using them always dictates the whole vehicle's aerodynamic and all other design. Very complex and hard to design inlets, practically unknown at this point and hard to test, narrow speed range. And they need rockets both before and after. (Or alternatively turbines before.)
It's like trying to plow a field with a Ferrari. It's a nice vehicle when on the road and a technological marvel but it's practically useless for that purpose.
Well, I'm not tring to plow a field with them. And I don't know if you've ever driven
a Ferrari, but I have and they're really competent. In fact, I've owned two of them in
the past! These kinds of vehicles are the safest and fastest vehicles I've every driven!
And I never gotten tired or sleepy driving one, and I've taken them on long trips and
driven them at speed in bad weather. In fact you should have heard the comments from
my passenger, on a business trip, in bad wether: "this thing feels better the faster we go".
Anyway to end the anology, but all cars should be as competent!
Well, trying to space launch with an air breather
is like trying to plow a field with a Ferrari.

For all it's quality and high technology, it's not the right tool for that. A 50 year old Fordson would beat it any day.
Haven't driven one, I'm very envious, but the ever more competent a vehicle gets on the road, probably the less competent it gets on the field, that's what I'm aiming at.
It reminds me of the other age old canard: about ion engines and VASIMR. Usually it's the "give NASA money so they can continue this program and then people can fly to Mars in weeks" style argument. Getting technical, they say look how great high specific impulse (which they say is like fuel efficiency in a car) we get with these designs, when in reality the ISP is only a detriment because you need an external power source which is much heavier than the fuel expended. With electric propulsion, for the same thrust and impulse, higher ISP results in
higher total mass for practically all missions that don't last for decades and require tens of km/s delta vees.
You have to understand the technology to say that the ISP rules of thumb that apply with chemical rockets don't apply in this very different case.
Incidentally, the same ISP argument is used as a motivation for air breathers. Here ISP really helps but it's the other factors (that don't really count in rockets since they are negligible) that are bad with air breathers that just go unmentioned.
So we will stop using supersonic airbreathers and use rockets instead ?
Why am I bringing that up? Because we successfully developed supersonic (Mach 3+)
airbreathing technology because we needed to.
We haven't built a hypersonic airbreather because we haven't ever needed one.
Probably useful in a missile (or even a reconnaissance craft) that cruises long distances at that hypersonic design point.
That's the Ferrari.
Practically useless in space launch.
That's where the tractor, the rocket, shines.
Different usage.
A number of companies have proposed them, and have shown that they could be built,
but they were never funded.
So you're basically saying that the technology has all these problems, but we
haven't finished developing the technology and funded building one, except for a SSTO,
which is like von Braun or Goddard trying to build the orbital rocket first.
Those problems don't matter for *cruise* because you don't need wide speed range or high thrust for that.
They are killers for space launch missions.
NASP was a crazy program. As was X-33 the way it was done. You can often bench test technologies to at least some confidence level far far quicker and less expensively than trying to use billions to just build a vehicle straight out with some idealistic materials. That's just wasting taxpayer and investor money. And employee efforts and public trust.
As proper development occurs, the technology problems will be solved.
It's stupid to try to push a bad solution for a problem when better ones exist.
Use tractors for plowing the fields and Ferraris for road driving, ok? Both suck at each others' uses.
Let's use another analogy: the toilet seat and the bathtub. One is good for putting dirty things to, the other one is good for washing yourself. You don't want to use one for the other's functions, nor would you want to develop either further towards the other, although they might look a bit similar to some observers and share some technology like perhaps coatings and plumbing connections.

One might say "oooh but the bath tub is sooo big, a toilet seat would be much cheaper and take much less space". Yes but you can't actually get into the toilet seat. You'd have to sit down on it. All the water from the shower would spill all over the place. And you couldn't bathe at all. It would be useless. The toilet seat is very good as a toilet seat, much better than the bathtub. But it's much worse as a bathtub.
Why did jet aircraft not replace propeller aircraft in all uses? Because propellers are simply better for some uses while they are worse for others. Why are there still helos, why didn't we transition to VTOL jets for sightseeing, SAR and police work instead? Because the physics is against that. It's not a question of improvements required in VTOL jet technology, it would be pointless. I mean, why would someone try to do that? They'd need to be technically illiterate. Maybe if we have antimatter technology so we can waste power with abandon...
Rockets are extremely good for very high thrust, very light weight, they don't care about the speed of the vehicle they're on at all, they can operate in the vacuum, they don't have any effect on vehicle aerodynamics... None of which hypersonic airbreathers are good at, they're not even decent, they are absolutely horrible in these issues. And all of these are very relevant for launchers.
You can go around some of them if you stage a lot and only use (sometimes different) air breathers in some stages so the speed ranges are narrower and the high dry mass doesn't have to be carried that far.