Reagan’s Impossible Dream: The X-30 National Aerospace Plane
thehighfrontier.wordpress.com
thehighfrontier.wordpress.com
Getting rid of the heat was the biggest problem. Rockets which launch vertically don't spend much time in the atmosphere. Aircraft which accelerate horizontally do. Hypersonic in-atmosphere travel means having to get rid of huge amounts of heat with no place to dump it. Running liquid hydrogen fuel over the vehicle exterior for cooling was considered and rejected for the SR-71. (Many rocket engines run the cryogenic fuel and oxidizer through cooling channels in the engine bell before using it as propellant. That's not a totally unreasonable idea.)
The X-30 was supposed to have a big cabin, which would have to be kept cool. Only a small part of the SR-71 is kept cool; the pilot is in a space suit. Even cooling the pilot was hard. Remember, at hypersonic speeds in atmosphere, there's no place to dump the heat; you have to bring your cold with you.
The only real advantage of this approach over rockets which get out of the atmosphere as soon as possible is that you don't have to carry oxidizer. That improves the mass fraction (rockets to orbit are > 90% fuel). Not enough to be a win, though.
Also, they went on to the X-33 in the mid 90's so clearly felt confident in a suitable "something stronger" thermal protection system by then
I've long held the opinion that the real lesson to take from NASP is that the higher the level of decision making, the more detached it is from physics or business.
Air breathing works for cruise (limited speed and altitude range, long duration, low thrust requirements).
Rockets work for acceleration (wide speed and altitude range, short duration, high thrust requirements).
Orbital missions are only about acceleration. Bringing very heavy air breathing engines to orbit doesn't make sense at all.
The lowest dry mass (=lowest cost) single stage to orbit vehicle designs tend to be dense propellant pure rockets.
In Finnish there's a saying "ajaa käärmettä pyssyyn": make the snake go into a gun barrel. An organization trying to achieve a needlessly hard thing because of political reasons. Closely related to Not Invented Here.
Personally, I find the X-33 more frustrating as this got far closer to flight and although it may never have led to VentureStar it would have been a great hypersonic testbed
I think the problem with X-33 was that it was too big and risky for an experimental-only platform. If you want to develop things like aerospike engines or composite multilobe tanks, you should first have ground tests and then relatively small demonstrators using a lot of off the shelf technology. It makes no sense to bet so much stuff on a multi-faceted big expensive program that can fail when any of it components doesn't deliver. Or if you want to build something big, either use proven technology or retire risk in smaller programs first.
I guess people were emulating Apollo and the Space Shuttle. They had high performance but were not flexible or low cost, for a reason.
Staging is immensely important because it lowers the "order complexity" of carrying additional payload. In order to add payload you need to add fuel, and then you need to add more fuel to carry that fuel, and so on. This is immensely easier if you don't need to drag the dead weight of your initial stages along with you.
Single-stage is barely even feasible to orbit. Anything past that is just flatly science-fiction.
"The Tyranny of the Rocket Equation": https://www.nasa.gov/mission_pages/station/expeditions/exped...
Think of what suborbital, zero-G, would be like in a plane with 100 passengers. Given the forces involved I cannot see suborbital transport ever replacing first class seats on BA.
https://en.wikipedia.org/wiki/Project_Pluto
Choice Quote edit:"After delivering all its warheads, the missile could then spend weeks flying over populated areas at low altitudes, causing tremendous ground damage with its shock wave. When it finally lost enough power to fly, and crash-landed, the engine would have a good chance of spewing deadly radiation for months to come"
https://en.wikipedia.org/wiki/HOTOL http://www.reactionengines.co.uk/
So Wiki says a fully-loaded B-52 can carry 35 tons of bombs.
Everybody knows 1) re-entry after achieving orbital speeds is non-trivial, and 2) doing a stationary drop from orbital heights is possible. There is even some talk of "skydiving from orbit"
So you take a B-52 out over the ocean. At 50,000 MSL, you extend two rocket pods, point the nose straight up, and take yourself out of the atmosphere post-haste. Somewhere around 200-400,000 MSL, you roll over into a standard orbit configuration.
Burn about half your fuel. Once you get to where you want to go, burn the other half, reach a dead stop, then parachute into the lower atmosphere, do an engine re-start, and be on your way.
I'm not saying it wouldn't be a helluva ride, but I'm failing to see the part where we couldn't have done this 20 or 30 years ago. Perhaps the problem was that folks tried to imagine some sort of new propulsion system -- and the numbers just don't work out. Instead of solving SCRAMJET, maybe that money would have been better spent on truly reusable rockets and high-performance, plane-rated parachutes?
ADD: This comment was meant to address the problem of sub-orbital flight from point A to point B, not getting completely to orbit. Both SSTO and suborbital flight were mentioned in the article. My point was that suborbital flight doesn't have as many problems as we might think it does.
I think that would require a shit ton of fuel. If you want to actually achieve orbit, that's at least 7.8 km/s of Δv to do it, and that much again to reach "dead stop". Your B-52 would have to be carried on a booster rocket, as opposed to carrying one.
A suborbital trajectory would make more sense, but that's generally what the US has ICBMs for.
You cannot make orbit, but you should be able to go a long ways ballistically.
Add: A great way to learn about the energies involved is to create your own simulator in your programming language of choice. The ballstic/orbital math isn't that hard, and you don't run into a huge number of problems just modeling how to get to orbit.
I did this many years ago, and concluded that for non-biological items, mass drivers win hands-down. Unless the magic of field propulsion finally happens, taking your own fuel along with you sucks.
SCRAMJETS are interesting because they can get up to a significant fraction of the required delta-v while in air-breathing mode. They can do that because unlike a traditional jet engine, they don't have to slow air down to subsonic speeds for combustion. That's what drives the maximum speed of traditional jet engines.
Edit: saw your other response. Delta-v is still an issue for suborbital trajectories. Hitting 100 km altitude requires a speed of about 3,200 mph. If you've got a subsonic air breathing stage, you're still not getting much benefit. The big benefit of SCRAMJETS for suborbital flight is that they can hit the required speeds in air-breathing mode the whole way. No need to carry around heavy oxidizer.
The reason your proposal doesn't work is that during the portion of the trajectory outside the atmosphere, you either need to be ballistic (and therefore suborbital if you're traveling intercontinental) or you need to be constantly directing a portion of your rockets thrust downward. The latter is fantastically inefficient, which is why planes operate in the atmosphere (where they can use air to convert efficient horizontal thrust to lift) and why suborbital rockets are ballastic for the large majority of their flight.
You see, to accelerate straight up (or nearly so) your thrust must be greater than your weight. To get enough acceleration to be useful, you usually need an amount of thrust that's more like 1.2x your mass. For example, the fully loaded Saturn V weighed about 6,500,000 lbs and the first stage had 7,650,000 lbs of thrust.
So your fully loaded B-52 (~265,000 lbs) needs around 320,000 lbs of thrust from the rockets. This is more than double the amount of thrust produced by the jet engines. By the time you've accounted for your rocket engines, strengthened the airframe to survive the rocket thrust, and added a reaction control system (to turn around for deceleration), you've lost a good chunk of your 35 tons of rocket fuel.
It's about this time you realize that even 35 tons of rocket fuel is a laughably small amount. A single space shuttle main engine is a bit more powerful than what you'd need (~420,000 lbs of thrust), but it's good enough for ballpark numbers. It will consume 35 tons of fuel in about a minute... meaning your mission profile is probably something like 30 seconds of vertical acceleration, 15 second horizontal acceleration, 15 seconds horizontal deceleration. Not enough to take you very high or very far.
It's not that we can't do it, it's that it's woefully inefficient.
For the latest developments: https://en.wikipedia.org/wiki/Skylon_(spacecraft)
Which, as it turned out, was anything but trivial and took 14 years. Their main competitors – ULA and Arianespace – already announced they won't be able to manage similar capabilities this decade; and their plans for the next decade are still not as sophisticated as SpaceX's approach (they only want to recover the engines and build a wholly new stage around them).
Skylon is a massively more ambitious undertaking compared to that – if it works, it'll be the first practical SSTO, the first horizontal takeoff spaceplane, the first vehicle to use multi-mode engines, the first practical space plane to use a novel heat shield technology, …
That's an awful lot of challenges to tackle. If it turns out to work, and if it then turns out to be as re-usable as hoped (something that did never panned out for the Shuttle, and which SpaceX will only learn over the next years for their Falcon), then it could beat SpaceX… in a decade or two.
The main advantage Skylon would have over the Falcon 9 is the fact that the Falcon 9 is not fully reusable because they don't and can't recover the second stage, while the entire Skylon is recovered.
That's significant, of course. The second stage makes up about 25% the cost of the rocket, so that places a ceiling of about 75% on how much Falcon 9 reusability can save..
But then, starting from where the Falcon 9 is now, building a new rocket that can also recover the second stage doesn't seem too difficult. It's a big challenge, to be sure, but relative to Skylon it's not too bad.
Skylon is certainly much more ambitious in terms of how it works, but it doesn't seem to be very ambitious in terms of what it can do, which is not a promising combination.
Plus, payload fraction is another thing like SSTO, horizontal takeoff, novel heat shields, and all the rest that are cool but just don't matter except for how they affect the end result. All that matters in the end is how much you can launch, and how much it costs.
That's the critical point. Skylon is still vaporware, and they've really assumed the best case in published numbers.
So, afterwards, it needs another 8000 m/s Δv on rocket engines to reach LEO.
Skylon is a neat trick, but it's not magical.
NASA on the other hand had lot's of issues.
Challenger: "[W]e're only qualified to 40 degrees ...'what business does anyone even have thinking about 18 degrees, we're in no man's land.'"[2]
Columbia had 27 successful missions and went though several redesigns one of which resulted in failure.
How, when the cost was limited by the refurbishing costs after each launch?
https://en.wikipedia.org/wiki/STS-61-B Had a 54 day turnaround time which is not 'great' still. That's 6+ short missions per year per orbiter call it 5 including missions and some unscheduled down time.
They started with 6 orbiters * 5 missions a year ~= 30 missions per year. The shuttle actually did 135 over 30 years or 4.5 per year * (~0.75 per orbiter per year).
PS: At even 1/2 that 30 mission per year rate they would have finished 135 missions in under 10 years.
If your engines burn out after 5 instead of the planned 55 flights, I damn well hope you're going to invest into more R&D on them!
> Had a 54 day turnaround time which is not 'great' still.
And the pressure to keep up that break-neck pace directly led to the Challenger disaster.
Still, the point is they did not need to wait over a year reusing launches from design constraints. Instead, NASA simply did not need that many manned launches per year.
Now, I am not saying it was a great or even that good of a design. It was simply a poor fit for what they used it for. NASA would have been better off with either a much smaller shuttle that only sent crew up, or an unmanned system for hauling cargo. Instead, they tried to do both which caused a lot of problems.
- why do today what you can wait for a national crisis tomorrow?
In other words, the Federal government isn't responsible for most of what is out there and many state and local governments refuse to fully fund their own obligations.
Wow. No kidding that "no one also ever seems to mention"! That puts things in perspective a bit, doesn't it?
State governments in particular love federal infrastructure spending, since it is more or less a direct cash transfer to a) their own budgets, where local infrastructure spending can crowd out other priorities and b) the politically potent building and construction trades.