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Where Should Space Exploration Go From Here?
Since Congress has been steadily cutting back on support for NASA, Nick suggests this idea: "I'm sure there are many taxpayers out there like me that would love to see NASA's budget doubled. The problem is there isn't enough support to get congress to increase the budget by that amount, and I really don't want people to pay that don't care to. I propose an opt-in, one-time contribution box added to tax returns. I would require that my money be used only to advance the space program with either a shuttle replacement, an extra crew compartment for the space station, or a launch vehicle for a manned trip to Mars. Would you support a bill that would allow taxpayers to voluntarily contribute money to NASA? Are you ready to put your coin where your Dreams are?"
Although some of his arguments are not convincing or even insulting ("Did Israeli astronaut Ilan Ramon really have to be there to push a couple of buttons..."), the article makes several important points. Here's one of them:
China is planning on becoming a lot more active in space shortly. I sort of feel this will give the US a huge incentive to give more funding to NASA, there's nothing like competition to get the money pumping in.
Uh, no. Nobody's figured out how to keep a scramjet lit. The Australians did it for about six seconds, which is a record for a free-flying vehicle.
Last semester my classmates and I wrote a draft for the AIAA design paper competition for a reusable, air breathing single stage to orbit "rocket" plane.
Bottom line? Unless we get a lot better fuels, or radically lighter structures, it's not going to work. That's even assuming that you can keep the scramjet lit. (which would get you a PhD, if not a Nobel prize)
X-30 is not the way. Venture Star was much closer. A shuttle-oid with Boeing's fly-back boosters might be a really good short term solution.
Why yes, I AM a rocket scientist!
Money certainly is the problem. NASA, and space exploration needs to be a higher priority than some of the garbage we pour money into. Here's some numbers -
NASA's budget for 2003 - now $15.5 billion after the Columbia tragedy
Military budget for 2003 - $396 billion
Now of course I think the military needs a massive amount of money, but they spend it like water, and on things that we do not need.
Here's an example of new weapons we are buying that are included in the 2003 budget -
the Army's RAH-66 Comanche helicopter (Boeing and the Sikorsky Aircraft Division of United Technologies, $941 million); the Air Force's F-22 Raptor (Lockheed Martin, Boeing, and the Pratt and Whitney Division of United Technologies, $5.2 billion); the Navy's F-18E/F fighter plane (Boeing, General Electric, and Northrop Grumman, $3.3 billion); Joint Strike Fighter/F-35 (Lockheed Martin and Northrop Grumman, $3.5 billion); the V-22 Osprey (Boeing Vertol and the Bell Helicopter Division of Textron, $2 billion) the DDG-51 destroyer (Bath Iron Works and the Ingalls Shipbuilding Division of Northrop Grumman, $2.7 billion); the Virginia class attack submarine (Electric Boat Division of General Dynamics and the Newport News Shipbuilding division of Northrop Grumman, $2.5 billion); the Trident II Submarine-Launched Ballistic Missile (Lockheed Martin Missiles and Space, $626 million); and the Crusader artillery system (Carlyle Group/United Defense, $475 million).
Total - $21.2 billion
These are known as "cold-war relic" programs. In fact, many of these systems were mentioned as candidates for major reductions or cancellation during the Bush campaign and during the early months of Secretary of Defense Donald Rumsfeld's defense review. In addition they have been criticized in the past by Bush advisors or independent advocates of military reform as being too heavy (the Crusader), redundant (the three new fighter plane programs), or otherwise out of step with our current situation.
If our space shuttles could bomb Iraq we would be getting new ones all the time.
Anti-social? My code is just platform-specific.
It gets a little hairier than that. : )
A scramjet is a Supersonic Combusting Ramjet. Let's back up a step. A ramjet is an engine that uses shock waves, instead of fan-shaped compressors, to compress the air to mix with your jet fuel. If you don't grok why you need to compress air, go thou and Google search for a description of turbojets or any other internal combustion engine. This is going to be a long enough post as it is. : )
As the ramjet passes air through the shock wave system in its inlet, the air a) heats up and b) slows down. The speed of sound increases with temperature, and the speed of the gas goes down (from the Mach 3 to Mach 6 where ramjets can typically be operated). At some point, the air is actually subsonic. At that point, fuel is introduced and ignited. Hot air go out back of motor, airplane go forward.
Scramjet is basically the same idea, except without the slowing the air down to subsonic part. The entire combustion process happens in a supersonic airflow. While the physics of "low speed" combustion are pretty well understood, doing the same thing in a high speed flow is seriously non-trivial. In the paper we wrote, we adopted a technology called a "hyper-mixing injector" to dump fuel into the stream, and we actually let the high temperature air ignite the fuel all by itself. Keeping that fire going is, well, hard. Stick a Zippo out your sunroof. You get the idea.
Scramjets are way tricky. If you don't manage the airflow very precisely by varying the geometry of the intake section and not maneuvering the aircraft EVER, you might get a condition called an "unstart". Basically, all the nice shock waves you've been using to compress your gas glom together into a big strong shock wave perpendicular to the gas flow directon in your inlet, and basically at that point the temperature and pressure in your combustion chamber go from really really improbably high (which is good, and you've designed for that) to freakin' nutty crazy blow-up-spaceship now high, and you start collecting pieces of the thing across three states.
See recent Columbia accident for a much less violent example of what would happen. It would be far worse.
Scramjets are scary. Yeah, they might work, but they're REALLY finicky, and I don't believe our flight control systems are sufficiently advanced to fly them reliably and safely.
And forget about having a guy driving the plane. If you pitch the nose a few degrees off the trajectory, or roll the airplane at all, the shock system will change formation, and very likely you won't even know what hit you. No way to do it without computer control end-to-end.
You might have observed that the low speed for a ramjet is Mach 3. In order to have the shock waves in the inlet, you already have to be going really fast. You might be interested to know that the SR-71 used a partial ramjet cycle at its Mach 3 cruise condition. It also had a turbojet engine core to accelerate it to ramjet operating speeds.
Nuclear powered plasma would work great in an atmosphere...if you don't mind dumping a very highly radioactive plume all over Florida.
Actually, even though the specific impulse of the nuclear rockets is really good (specific impulse is a good measure of the fuel efficiency of a rocket. It tells you the number of pounds of thrust you get per pound of fuel) the peak thrust values are not very high. In other words, it'll be a good interplanetary drive, but really not ideal for launch systems (bad environmental issues aside).
Why yes, I AM a rocket scientist!
Orbital insertion? Equivalent speed is Mach 25. (of course, in orbit, there is no speed of sound, so Mach numbers don't apply, but for purposes of this discussion...)
SR-71? Mach 3. Teeny payload. However, the design we worked out used upgraded J-58 engine cores from the SR-71 to get up to scramjet operating speeds. And yes, having to fly for a long time while you accelerate is a big problem. You're burning just incredible amounts of fuel the whole time, and burning fuel to accelerate the fuel you need to burn to accelerate fuel that you need to burn to accelerate. Ad nauseam.
The other problem with air breathing rocketry is wave drag. In order to get the same thrust as a rocket, an airbreathing space craft's cross-sectional area has to be about 1.5 to 4 times as large as the rocket is to ingest enough air. Since wave drag (the primary drag force at high speeds) is very strongly dependant on cross sectional area, you swiftly get to a point of diminishing returns. Let's make up some numbers.
Rocket A thrusts at 100lbs, and weighs 10 lbs, and has (say) 10lbs of drag acting on it. That gives it an excess thrust of 80lbs to do the force=mass*acceleration thing.
Scramjet B thrusts at 100lbs, flys mostly horizontally so its weight isn't a factor (it's a lifting body), but has (say) 80lbs of drag on the airframe. So it only has a quarter of the thrust available to accelerate as our rocket, meaning it will take much longer to get to orbital insertion velocity.
In a nutshell, that is the problem with air breathing rocketry.
Why yes, I AM a rocket scientist!