I was just wondering if anyone could point me in the direction of anywhere that it talks about just how fast a suborbital shuttle in SR is?

Trying to figure out some travel times is all.

http://en.wikipedia.org/wiki/Suborbital_fl...Flight_duration

Thanks.

I was wondering if there was any info canon wise for SR on this?

A point of interest: LEO (Low Earth Orbit) has a satellite circling the planet once every 45 minutes. Suborbitals, by definition, are lower than that but moving at close to the same speed.

Well, considering that time getting through security on the in-process and customs/baggage claim on the out-process is bound to be significantly longer when taken together in comparison to the actual FLIGHT time, it's essentially "handwavium" I think somebody called it.

Now, as another side note: as your body has virtually NO time to compensate for the time zone changes, a SB/SO flight is going to be positive MURDER for "jet-lag". At least flying in one direction you can "sleep" through part of the journey to partially reset the internal clock.

Agreed!

So, since I will be employing 'handwavium' for the flight times any thoughts on how numerous these types of flights would be from international airports?

If you go by the Wikipedia entry, you get something like an hour for every 5000 km or so.

This is an amazingly ballpark figure.

Hmmm, that's a trickier question. It would depend on two factors, the most important one being flight cost to the carrier.

If the cost of fuel is comparable between a standard aircraft and the exo-atmospheric one, then the exo-atmospheric is going to win every time, and here's why: pilots make the same amount of money per x number of hours of flying. If the flights are shorter, you can get more flights per unit of money. In the same way, though exo-atmospheric vehicles will be much more expensive up front, so too will be their ticket prices, and the more flights per day you can achieve the more effectively you can finance those up-front costs. Large numbers of people still need to travel great distances. If the demand is high enough, then the ticket prices could be low enough relative to standard fares that normal intercontinental flights could conceivably entirely disapear. If that is the case, the number of flights could eacily rival what we see today (Exo-atmospheric vehicles would probably carry passengers equivalent to a Boeing 777 of modern flight, as opposed to the old Concorde SST, especially if demand made such capacity a necessity.)

As a final point, even if they are very expensive, they justify that cost on the convenience to the traveller, so I would expect a MINIMUM of two flights daily to and from each "spaceport" around the globe; Call is an AM and a PM flight. And that would be PER exo-atmospheric carrier (this is Shadowrun, remember competition?). So the number of flights would actually probably be pretty substantial.

Does that help?

Rigger3 specified the exact air speeds of a semiballistic and suborbital, along with the effective ground speeds. Unfortunately, I have no clue where my copy is.

Aaron, that is pretty amazing. You would probably spend more time going through the airport routine than you would in flight to go to the far side of the world!

Doh! I just found what I was looking for in Neo Anarchists Guide to Real Life, page 26 second column 'The Service'. "Semiballistics travel at Mach 30...(22,000mph)!" Ok, that is fast.

It isn't cheap though...2,500 !!!

When all else fails look in the NAGRL.

Thanks, I will check in there to corroborate the other book.

Be very careful how much of a parallel you draw between semi-ballistic / suborbital flight and the flight characteristics of the X-20 DynaSoar (Dynamic Soarer). That vehicle lifted off at the top of a Titan ballistic missile and then used an aerodynamic effect to partially re-enter the atmosphere but then skip back off like a rock on a pond. That means it was limited by the initial velocity imparted by the booster and whatever it could recover during the skips. As a side note, one of the things that was a major concern during the Apollo program was that a returning capsule if it re-entered at too shallow an angle could skip off the atmosphere and back out into space in an uncontrolled and irrecoverable manner.

Now, the semi-ballistic / suborbital vehicles proposed as super-airliners in the future have engines on board which means they are not limited to the speed of thier booster(s), and can power themselves to just under minimum nominal orbital speeds where their long ballistic arc spends the majority of the distance above the drag and friction of the atmosphere. Without the need for the "skips" the DynaSoar used you could make a lot better time. Like I said: a LEO satellite only takes 45 minutes to cicumnavigate the globe. No point would be more than halfway around the globe. Allowing for taxi, rollout, takeoff, ascent, exo-atmospheric cruise, re-entry, decent, approach and landing, I can't see that requiring more than an hour, tops (25 minutes for the cruise segment and 35 for everything else. The Space Shuttle is in orbit after less than ten minutes, and is already well out over the Atlantic; Re-entry takes half an orbit the way they do it, but wouldn't be required that way for a sub-orbital / semi-ballistic craft since they're already right there, and are essentially in re-entry from the moment their arc hits perigee). And you would NOT want to keep one of these things on the ground in delays. They would have top priority for departure.

And the NAGRL was 2nd ed IIRC, so prices would probably have fallen as the technology matured over twenty years. And for those who are interested, that further supports my earlier observations: Mach 30 is actually HIGHER than typical re-entry velocity: the Shuttle only hits the atmosphere at a clip in the vicinity of Mach 25. So, yes, I would say no more than an hour total flight time to any point on the globe.

Same day shipping! I think you are right that prices would have dropped over that period of time.

Imagine, pull a run in Chiba at 0200 hours and four hours later be back at your doss in Seattle. That would really put pressure on security to nab/terminate the team at the site where they can contain it. After that they could be any where in the world.

One itsy-bitsy-leetle problem with that, Bob. Airport security. Think the corps ae wired into the system? *grin* You DID manage to deny them a good scan of your face on the run, right? You're SURE? REALLY sure?!

I guess we will find out one way or the other! But one would hope that I took the prerequisite actions.

You forget that going faster, especially over the speed of sound, significantly increases fuel use, reduces maximum capacity and increases maintenance costs on the vehicle. It isn't an arithmatic progression. If that weren't the case, concord flights would cost only slightly more than flights in an airbus of comparable length of time, not $30,000. Suborbitals will cost significantly more than sub-mach trans-oceanic flights.

Flights like this will still be pretty common out of places like Seattle. Seattle is a super-major business center, and if execs can't get a flight from A to B in the time they have available, the service isn't any use to them. Similarly, security will be significantly pared down for those luxury-class passengers. Again, if you have an hour to get from Seattle to Tokyo and Ares Sub-orbital can't get you there in less than two hours, you're going to stop flying on Ares and look for someone else who can manage it, even if it costs you more. Expect to pay through the nose for those extra minutes shaved off, but I'm sure it's available with the cash and credentials.

Ah, but there is one thing you left out: the exo-atmospheric vehicle is outside the atmosphere for a LOT of the flight, so those considerations are much less important for the majority of the flight. The total fuel usage would be comparable taken in comparison, more than likely, or the sub-orbital/semi-balistic would never have the range to reach its destination. And on maintenance, one of the reasons the Concorde got to be so expensive was that it was over four decades old, and old aircraft don't tend to age gracefully. That's one of the MAIN reasons the F-14 was retired - the plane was costing over four times as much money and man-hours to maintain per flight hour as a new-build F-18, despite the ncreased technical sophistication of the new aircraft. Consider one other thing: many of the current proposed propulsion technologies for hypersonic flight are mechanically very simple (read: low maintenance). The Concorde is a miserable example to use, because it was only useful on short distances (Atlantic, not Pacific routes for example), wasnt OVERLY fast, being not much more than 2.2x faster than a 747 when compared to a Mach 30 exo-atmospheric vehicle. You can't reap that "multiple trips" effect I mentioned for the ammortization of the purchase price of the aircraft and getting better use out of your flight crew.

And I think the Concorde was up to about $10,000 rount trip at the same time that a comparable first-class ticket was running abut $4,000.

Um, even the Salish Shide Council has regular Sub-Orbital / Semi-Ballistic flights out of their territory. I think the are a lot more common than you think. (NAN Vol 1)

Well, I remember reading that the Concorde in fact did age quite well and that the airframes were in much better shape than sub-Mach planes of the same age. This was attributed to the Concorde flying not only faster but much higher than other planes resulting in less air friction (even with the Mach 2) due to lower pressure - conventional jets travel at 10,000 - 13,000m but the Concorde flew at 15,000 - 18,000m (the other famous beyond-Mach plane, SR-71 Blackbird, routinely traveled at 20,000m and higher).

LEO is a 90-minute orbit. Low Earth orbital velocity is 17,500mph; Earth is about 24,000 miles in circumference. 24,000 / 17,500 is approximately 1.5 hours. Plug in more exact numbers than those quick-n-dirty approximations and you'll get a value closer to 90 minutes.

Doing it the hard way for a 200km orbit using Earth's mean radius:
http://en.wikipedia.org/wiki/Orbital_perio..._a_central_body

Time = 2*Pi*sqrt [ 6,571,009^3 / (6.67428E-11 * 5.9742E24) ]
Time = 5300.122 seconds
Time = 88.33 minutes



The space shuttle's half-an-orbit aerobraking maneuver is meant to keep G-forces below 3Gs, and the shuttle has a particular hot-and-hard re-entry as a consequence of meeting USAF design goals for a high cross-range re-entry. If you bulldoze into the atmosphere for an even shorter re-entry track, you're going to see even higher temperatures and higher G-forces as you shed ~17,500mph of velocity in a shorter period.

Civilian vehicles interested in maintainability will probably select metallic heat shields (like the X33 and Faget's early shuttle concepts), which demand a gentler (lower peak temperature) re-entry than the shuttle. This will, in turn, impose lower G loads, thus slower braking, and longer re-entry tracks. You could try some next generation ceramics for harder re-entries, but NASA was wary of 3Gs for its physically fit post-Apollo civilian astronauts. Common 6th World businessmen won't like a 10G entry at all.



A largely ballistic, rocket-type vehicle won't follow trends set by airbreathing, aerodynamic lift vehicles. You'll want to use the Rocket Equation to determine fuel requirements.

However, the fuel requirements are quite high for the orbital and super-orbital velocities given here. An outstanding hydrogen/oxygen single stage design will need to be 9 parts fuel by mass at takeoff (say, 900 tons of LOX [cheap] and LH2 [not so cheap] to 100 tons of aerospacecraft, payload, and passengers). In practice, you'll be lucky to achieve 10:1, and the 22,000mph velocities cited for semiballistics would demand closer to 12 or 13:1, which is pretty hard to achieve for low density propellants like LH2/LOX. A kerosene/LOX rocket could easily get to 20:1 owing to the greater propellant density, but it would need it, too, because of lower exhaust velocities.

Suborbital scramjets, which double or treble the specific impulse of rockets, would use proportionally less fuel. However, 3 or 5 tons of fuel per ton of aircraft is still an engineering challenge and very high compared to turbofan aircraft.

The point being: suborbitals and semiballistics will need a lot of fuel compared to HSCTs and subsonic airliners covering the same distance. They need it to reach their target flight velocities regardless of the distance they have to fly.

Cray74,

So it would be safe to say a 45 minute flight time half way around the world then? Which still doesn't seem so bad.

60 to 75 minutes. It takes 45 minutes to circle half the world at orbital speeds, but a semi-ballistic flight doesn't go from 0 to 17,500mph in an eyeblink - reaching that speed takes about 8 minutes for the shuttle (and probably more than twice as long as for a suborbital; scramjets are not high thrust engines). Braking will take at least as long as accelerating. So, 60 minutes for a semi-ballistic should be close to correct. A suborbital would be closer to 75 minutes.

Note that the braking and acceleration phases will not get longer as distance increases (or decreases). A coast-to-coast hop by a semi-ballistic in North America (or New York-to-London flight) will still need ~8 minutes to accelerate and 8-15 minutes to brake and land (in fact, for such short flights the semi-ballistic may never reach its cruising speed and will be under acceleration for the whole flight). Likewise, a circumnavigation from, say, New York to New York (just for giggles) would take 90 minutes plus the aforementioned braking/acceleration times. Only when flights get so short that a vehicle can't reach its usual orbital cruising speed will the accelerating and braking times fall.

If any of you follow BattleTech, the new Strategic Operations book addressed (with a short table) various intercontinental flight times by its semiballistics, "DropShips." Those would be close to the flight times of semi-ballistics in Shadowrun, though they assume fairly high G-forces that military flights would tolerate.

And if you'd like some roleplaying material for the launch on a semi-ballistic, here's an 11-minute ground-to-engine cut off video aboard the shuttle. There are some differences - the passengers of a semi-ballistic are unlikely to be in space suits. And the ride on the shuttle is rougher than an all-liquid-fueled semiballistic for the shuttle's first ~2 minutes of flight (solid fueled rockets have slightly erratic thrust as chunks of fuel break loose) - note that from launch (3 minutes, 30 seconds into the video) to SRB separation (5 minutes, 30 seconds) the two foreground astronauts shake and shudder a great deal more than after SRB separation, when the shuttle is propelled only by its smooth-running liquid-fueled main engines. Finally, note cabin noise from launch to about 5 minutes 20 seconds - noise starts plummeting after you hear "go for throttle-up" as the shuttle is getting into much thinner air, with less turbulence and dynamic pressure. Without the SRBs, a semi-ballistic will be quieter than the shuttle, but it will still experience a lot of aerodynamic noise. (Final random factoid of note: the two foreground astronauts are using handheld mirrors to look through the shuttle cabin ceiling windows over their heads.)

Cool video! Thanks for the RL info. Gives me something to work with so I don't get that one player who tells me that isn't how it would work.

Gak. I'm not usually that brain dead. I think I was figuring furthest distance to the opposite side, then halved it AGAIN. I can't believe I missed that. *sigh*


I was going on the assumption that they would be in a technical "re-entry phase" for a while closer to the end, but peak atmospheric heating and deceleration isn't at the top part of the arc. The S-turns at the end of the shuttle approach to landing dump an awful lot of velocity as well. Frankly, I wouldn't expect corporate captains of industry to tollerate much more than 2g, myself. I was imagining a vehicle that would be able to use aerodynamic lift to get itself to very high altitude before having to fall back on pure reaction-drive power, and by then you've already picked up a good bit of velocity.

How about this? Stated speed for semi-ballistics per canon is supposed to be around 9388 meters per second. 1 g is 9.8 meters per second squared. So to achieve that speed at the 3G limit specified would take about five and a half minutes of continuous thrust. At 1G it would be sixteen minutes or thereabouts. On the 1g profile, you've travelled [1/2(Vi+Vf)]*T = [1/2(9388 meters per second)]*958 seconds = 4496852 meters = 4496 Km through the air. That's the hypotenuse of a triangle, so the actual ground speed's going to be a lot less, but even there (depending on angle of ascent) at least 3,000 Km downrange, or a quarter of your way there. Allowing for a similar decent profile at 1G again under airfoil, that's another quarter of the distance to the opposite side of the world. Now you have the "sub-orbital" cruise portion at full velocity without the need for further fuel use since there's almost no friction. That portion would represent about another third of the journey. So I see 45 minutes actual flight time with no more than 1G acceleration. Let's allow for sloppy math and other things, call it closer to an hour. But it's still VERY doable that way.

You're quite right falling back on rocket formulae, but like I said, you're an airplane until you are ready to leave the atmosphere. A lot of funding got pulled in the 90's for the basic research on the technology, but I don't see why it couldn't have been ready by 2030 or so as a viable commercial system. It took less time than that to go from Kitty Hawk to 707. Add another forty years to that and you've got the A380 moving people around like bulk cargo over insane distances. So if you use more conventional aircraft math for the ascent to say 85k feet / 26 Km. Now you start to transition to pure scramjet up to say 120k feet / 36.5 Km. Now you're a rocket, but you only need to lug around the bulky and heavy oxydizer for the last jump, and you've already burned off a lot of your fuel load so mass is less of a concern to have to overcome. Once you're above the actual atmosphere, there's no more drag so you're more onto orbital transfer mechanics than rocket formulae. The coast is free. The re-entry is mostly free. The approach is powered for controlability, but it's not like you're going to be needing thrust to decelerate, since the atmosphere takes care of that for you.


You're quite right about the effect of shorter distances. At 1G, you leave New York and turn over about half way to begin the re-entry phase. Across North America coast-to-coast will be similar. Now, if you're willing to accept proportionately higher G-loads, that will improve the efficiency since you're in space longer. I would generally say, based on the math, that you can assume no more than 1 hour flight times to any point on the globe if you're willing to pay. And ast to the price you mentioned for LH2, with cheap fusion power, those costs drop to zilch, especially if you use superconducting transmission lines to move the power to the (coastal, as in near lots of water) launch sites. Crack the water with fusion power, and go. If you could have a single flight crew making 4 flights per day with about a 1 hour turn-around between flights, that's pretty productive in terms of man-hours (flight crews for ANY kind of intercontinental flight are NOT cheap) as opposed to the "one flight per two days" if you're awake sixteen hours, or worse, the cost of relief crews. You've got some great points, but I'm not sure about the math (despite my glaring and gargantuan oopsie when I started) you suggest. And I still come out about right with the "under an hour" so I think I am comfortable sticking to that.

The flight profile will be pretty horizontal with respect to the ground and not much more than 600km up (due to the lower Van Allen belt) except for the tail ends of the flight. The shuttle only spends its first 2-3 minutes doing serious climbing, and a similar period losing most of its altitude. Those large altitude changes occur at the slowest parts of its flight.



At launch, you'd be an airplane that's 90-95% fuel by mass - a severely overloaded aircraft that will have to burn a lot of fuel to stay aloft under aerodynamic lift. Farting around in the atmosphere is just a good way to demand even more fuel, possibly over-sized air breathing engines that add nothing but extra mass, and drive your wet/dry mass fraction to even more unobtainable levels. If you're going to make a rocket transport, make it a rocket transport. Launch from the ground, don't mess around with aerodynamic flight, and burn straight for orbital velocity.

H2/LOX spacecraft already suffer from high gravity- and drag-losses due to their low rate of weight loss and thus low increase in acceleration during launch, equating to a painful 1200m/s gravity/drag loss. Under the stern rule of the Rocket Equation, puttering around in the atmosphere (guzzling hundreds of m/s of delta-V) and tacking on powerful airbreathing engines that can keep such an over-fueled rocket aloft is going to be painful. LOX/LH2 rockets just don't like to be pushed beyond 10:1 mass ratios because the tanks get so large.



If you keep the rocket system simple and don't mess around with lots of atmospheric flight, sure. There were good concepts feasible with 1970s hardware for semi-ballistic transports.
http://www.astronautix.com/lvs/pegvtovl.htm
http://www.astronautix.com/lvs/hypnssto.htm
http://www.astronautix.com/lvs/ithacus.htm
http://www.astronautix.com/lvs/kanhmaru.htm

The key feature, though, is to avoid frills. Even wings can be bad, since they're really only useful for a few minutes at landing and are a non-contributive deadweight during launch. Something that guzzles fuel like pre-launch aerodynamic flight is a catastrophe for the engineers designing the aircraft.



Not a fair comparison. There's a lot more involved in a semiballistic and suborbital than a Wright Flyer and 707 - subsonic flight, supersonic flight, hypersonic flight, orbital mechanics, re-entry behavior, life support, extremes of environment that make escape damned difficult, etc. It took 2 dudes in a bicycle shop to make the first heavier than air flight. It took an army of engineers to make minimal headway on the National Aerospace Plane. The engineers behind the X-43 were chanting the hot fusion mantra of "only 20 years away" when that program was cancelled.

The lesson of aerospace history? Rockets and airplanes are easy and can even be built by slave labor if you keep the frills away. Trying to combine them, though, turns into multi-billion dollar boondoggles. Only one (1) spaceplane has ever flown repeatedly and successfully. There have been a number of contenders that even made flights, but they were the results of large, complicated development programs.




Don't fall prey to the Airbreathing Engine Mafia.

Here's an important secret about fuel: it's structurally light (caveat: unless it's hydrogen). Sure, a purely rocket spacecraft might need hundreds of tons of oxidizer more than a combined-operation turbojet/scramjet/rocket, but the key metric for getting a ship into space is its mass in orbit, not its fueled mass on the ground. Adding another hundred tons of liquid oxygen only calls for a ton or two of tankage, airframe, and heat shield. Adding a scramjet calls for an elaborate, convoluted heat shield (part of the engine, really) designed for extended hypersonic flight.

A simple kerosene/oxygen rocket can easily achieve a 15:1 ratio between fuel and dry structure, which is what you need for a kerosene/LOX SSTO. The Saturn IC (first stage of the Saturn V) had better than 20:1 despite have 1000 tons of upper stages on its shoulders. Even with all the elements of a reusable SSTO, a dense fuel vehicle would be able to achieve about 16:1. On the other hand, a scramjet will be damned lucky to manage 5:1, given its high surface area, large heat shield mass, and incredible low thrust-to-weight scramjet engine (it's quite easy for 1960s dense fuel rockets to achieve a 120:1 thrust-to-weight ratio, while a scramjet is lucky to make 1:1; even airbreathing turbojets with afterburners have trouble reaching 10:1). A 5:1 fueled:dry ratio is brutal on the folks trying to make the aircraft work, since it sets very high standards for the propulsion system.

Screwing around with scramjets and atmospheric flight is putting an incredible amount of time, labor, energy, and research into an area that doesn't actually save you much. I'd point out this study again - note how the vehicle that's heavier on the launch pad is simpler to build and lighter in orbit than the more fuel efficient hydrogen/oxygen rocket. A scramjet is worse than the H2/LOX SSTO - it has an engine with lower thrust per unit mass, heavier airframe (because it has to optimized for sustained hypersonic flight, not quick rocket ascents), heavier heat shield, etc.
http://yarchive.net/space/rocket/fuels/hydrogen_deltav.html



...the Rocket Equation is used for orbital mechanics. If you need to know the delta-V for an orbital transfer, then the mass of fuel required will come from the rocket equation.

Turning into an interesting discussion, now.

Do you think you'd actually need to boost as high as 600 km?

If it's as all obvious to you, why did they even bother trying in the first place? I just can't see it as being that overloaded in terms of fuel. Certainly more than the equivalent airliner, even a good bit more. Let's say you go with a hydrocarbon fuel source for a turbine engine for takeoff, you're suggesting it would take more fuel to fly an equivalent payload to altitude under wing and turbine than using pure rocket power? I understand your argument but I don't buy it. Convince me, I'm a skeptic, not a complete jerk.


I conceed to you entirely on the up-and-down-under-thrust concept in terms of numbers, so leave that aside. I'm more focused on the "spaceplane" for now.

Well, if you're wanting timeline comparisons that are a better fit, let's call it "Goddard to Ballistic Missile / early manned space flight (Mercury)" and "from there to the Shuttle's reusable replacement that never was". Goddard wasn't that much more advanced than the wright brothers in terms of his access and materials. And the other thing to consider is the rapid evolution of computer design and modelling. When the NASP was under development, the models were crude and the modern IPhone can compete for processing power. An EXCELLENT example would be the difference in development times between the F/A-22A Raptor and the F-35X Lightning II. Or the parallel development of the SSN-21 Seawolf attack submarine and the follow-on Virginia class. The follow on was in both cases designed in a mere fraction of the time based on the earlier work and engineering, and were brought in at a lower cost as well. The one thing that has dissapointed me is that without strong government backing, the space program in the United States has languished since even before the end of Project Apollo. The shuttle, marvel that is still is, was a compromise design, less than it could have been. The international space station is nothing compared to the original plans for Space Station Freedom, and was built using the same basic technology but arrived decades late. HOW long did Japan have the Kibo module in the works? The current generation of lift vehicles: Atlas V, Delta V, proposed Orion lifters, Ariane V, Energia; all are evolutions of technology and designs from the late seventies, at best. The SSME, unique in it's design and function (that hybrid turbo-pump is something else), is fundamentally almost forty years old at the heart. What if a true revolution were to hit the aerospace (empasis on the "space" part) industry the same way electronics were altered by the arrival of the integrated circut? Something revolutionary to kick things over? The Aerospike had interesting potential but I haven't heard what was done after cancellation. Are we content to rely on the same basic designs and philosophies of the last half century? Do you think Goddard or Von Braun Korolev would have been satisfied with where we are today?

STRUCTURALLY light, yes. But you have to (obviously, since you're not talking completely casually here) have picked up on my observation about LIFTING that oxidizer in the first place. The tanking isn't my concern in the least. It's the mass of all that liquid, and breaking inertia's hold on it, that has me thinking.


You know, I am noticing something here: you aren't allowing for much in the way of materials science improvements here. I don't see why in twenty or thirty years they couldn't find a material that wouldn't be able to serve as both structure and heat shield, at least as far as was needed to get out of the atmosphere and re-enter safely. It MIGHT even wind up being pretty light. If you're lifting under wing, you can make do with a much lower thrust system and just take more time to pick up initial speed. The A380 has a TTW at Max GTO of something like less than 2:10, but manages to get itself up to 30,000 feet. Ok, so we're dealing with a vehicle designed exclusively for the high trans-sonic environment and carrying a conventional long swept wing. And a high bypass turbofan isn't a good cantidate for a spaceplane. But essentially, I am asking why you say a wing would be such a bad idea for the intial climbout? OK, so the numbers scale back quite a bit: instead of 45 minutes world wide, the climb out might take a good bit longer, perhaps twice as long as I stipulated. What if you had a vehicle able to get up to 3.0 Mach and 100,000 feet on wings and air breathing engines? Then you start introducing stored oxidizer and take off from there? You're telling me it would take more fuel to get that far than the shuttle burns in the same ascent? How much fuel has the shuttle burned to get to 100,000 feet? To be economical in any way, a spaceplane would need to have at LEAST that much cargo space/mass availability. Anything less would be too little to be practical.


So you are saying that in your opinion, the entire concept of a reusable spaceplane that is SSTO (Single Stage To Orbit fot the uninitiated) is essentially both unfeasible and impractical? That no amount of development in engine design, aerodynamics or materials science, with the full support of modern (and expanding) computer aided design and modelling, would be able to create such a vehicle? Because the way you describe the thing, it's at best a technology demonstrator. It would be cheaper to ride a normal rocket to LEO (and that's SAYING something right there) and better to fly on a future SST? Because there is no WAY humanity is going to ever achieve a meaningful, long term, and broad presence in space without better and cheaper launch capability than conventional chemical fueled expendable rockets provide. That's the equivalent to me of telling Von Braun that he would never get enough thrust and a light enough structure to get to the moon in 1942. He never stopped believing, and in the end, he was right.

From a purely 6^th World perspective, they HAD to have come up with a way, because they have Lagrange Point stations, and there's no way you're going to build and maintain those with conventional rockets.

So like I said, convince me. I am convinced that there's got to be a way. Remember what they said about single stage to the moon, until some "crackpot" came up with Lunar Orbit Rendezvous? 95% mass fraction to fuel just seems improbable in the long term. There HAS to be an answer. We just haven't thought of it (materials, fuel, science, aerodynamics, structure, design, propulsion) yet. I can't keep the A-12 Blackbird out of my head, either. They designed everything on those birds from the hydraulic fluid to the fuel to the paint custom for the job, and nobody believed it was possible then, either.

Not a rocket scientist, here, but it seems to me that the advance that would be the most linchpin-y advance for commercial sub-orbital flight would be in propulsion and fuel technologies, ne?

Nope, which makes ground speed even closer to flight speed.



Oh, heck no. I'm saying that trying to using airbreathing engines to reduce oxidizer mass is penny wise and pound foolish. I KNOW hardware has flown with the correct fueled:empty mass ratios to be SSTOs - the Saturn V and Atlas first stages, for two examples. And once you get past achieving the critical mass ratio, the rest is details. I think the Kankoh Maru and Phoenix SSTO proposals were quite reasonable, and I'd love to see a dense fueled SSTO put together like the one I linked in in my last post.



Most don't try. The serious aerial launch concepts for SSTOs fall into one of two categories:

1) Launch by a mother ship, like Pegasus (which is actually a multi-stage expendable, but air launched).

2) Launch without all possible weight, like Blackhorse.
http://www.islandone.org/Launch/BlackHorse-PropTransfer.html



If you're combining it with rocket power, yes. A purely rocket vehicle might have a larger fuel mass than one with airbreathing assistance, but the pure rocket vehicle's dry weight will be lighter (not to mention simpler). The number you're trying to beat to get into orbit is (Fuel Mass / Empty Mass), which plugs into the rocket equation to tell you how much velocity you'll get from the vehicle. Installing low thrust-to-weight airbreathing engines, heavy wings, and flying high-drag ascents only shrinks that ratio, undoing the benefits of a higher engine efficiency and does nothing to make use of the oxidizer weight savings, since that'll all be thrown overboard by the time you get to orbit.



See: rocket equation. Yes, I'm going to have to get into numbers, both speed and mass.

It goes like this: puttering around in the atmosphere with turbojets, rockets, whatever gives you maybe 300m/s to 450m/s (factoring in bypassed drag losses by effectively launching at high altitude), unless you bother with the engineering headache of sustained supersonic flight (which might give you a 600 to 900m/s). However, the target cruise velocity of a suborbital or semiballistic is 7800m/s. Add in 900m/s in gravity losses that you won't avoid, and your target delta-V is about 8700m/s - above and beyond whatever you need from airbreathing system. But that's an overly convoluted way to approach a back-of-the-envelope evaluation of a spaceplane. The easy way to start is in orbit and work backward to the ground.

Let's say your suborbital or semiballistic masses 100 tons in orbit (counting airframe, tankage, crew, passengers, orbital maneuvering and landing fuel, heat shield, etc.) Basically, 100 tons after all the launch fuel is expended. You can pick another mass; the values will scale linearly for this quick approximation. This vehicle has been lofted to 7800m/s (orbital speed).

To get to 7800m/s in orbit from a turbojet launch, you need about 8700m/s to accomodate drag and gravity losses (vs 9000-9100m/s for a purely rocket launch from the ground). Figuring you used hydrogen/oxygen rockets (not my first choice because of the heavy tankage required, but it has good efficiency) that averaged a specific impulse of 430 from air to vacuum, you need 700 tons of LH2 and LOX to reach orbit from your aerial launch (Rocket equation: 430 x 9.8 x LN [800 / 100] = 8762m/s). (Incidentally, 700 tons of LH2/LOX is the shuttle's external tank payload, so you'll have an idea of how big this vehicle will be, and start to see why I prefer dense fuels.) So at the point it lights its rockets, the spacecraft is 800 tons.

Now we have an idea of what the airbreathing engines have to battle with: an 800-ton fuel tank with people strapped to it. So, our multi-mode flying machine is as big as a future derivative of the A380. Getting 800 tons of payload aloft on turbofans or other airbreathing engines is not trivial especially when there's only 100 tons of vehicle weight available. The A380 is 250 tons "dry" (vs. 560 tons fully loaded and fueled), and this aerospace vehicle not only has to at least duplicate the flight characteristics of the A380 in 100 tons (to get the 300-450m/s launch boost), but also has to fit in fuel tanks for 700 tons of H2/LOX (which would be about 25 tons, based on the shuttle's 30-ton example), rocket engines for 800 tons (12-15 tons for H2/LOX rocket engines with a questionably high 75:1 thrust-to-weight ratio - dense fuel rockets could easily manage 120:1 or better), a heat shield (about 15% of the re-entry mass: 15 tons), landing gear fit for 800 tons (~2.5% of takeoff mass: about 20 tons), crew and passenger facilities, etc. When you cut out the largest "rocket ship" items, you've got 25 tons to share between the passengers, airbreathing engines (assuming you pick afterburning, low efficiency military-rated screamers, you might need 20 tons for an airliner-like 1:4 takeoff thrust-to-weight ratio), airframe, loitering fuel to putter around in the atmosphere, etc.

In other words, it's damned hard to fit in all the hardware. More rocket fuel, though, is structurally light compared to all this horizontal takeoff, airbreathing engine trouble. So, let's look at a purely rocket vehicle.

Again, let's say the vehicle is 100 tons in orbit. To get there, it needs 9100m/s (with LH2/LOX). Because of the low altitude launch, let's lower the average efficiency of the engines to 410 seconds. Per the rocket equation, 9100 m/s = 410 * 9.8 * LN (970/100). So, this vehicle will need 870 tons of LH2/LOX to get into orbit. The fueled mass is, yes, heavier on the ground - but rocket fuel and fuel tanks are *cheap* compared to airbreathing engines (both in terms of weight and money).

By making this a vertical takeoff, horizontal landing all-rocket vehicle, you get enormous savings on structural mass that can go into payload. A straight stretch of the fuel tanks from the airbreather would, yes, call for 5 extra tons of tankage to accomodate 870 tons. Rocket engines grow a bit (to 17 tons) because of the higher launch mass. However, the vertical takeoff means that the thrust structure can support the 970-ton launch mass, so you don't need landing gear to handle 970 tons - you only need landing gear to handle 100 tons. That's 2.5 tons of landing gear instead of 20. You can shrink the wings since they only need to keep 100 tons aloft, not 800. You can completely remove the mammoth airbreathing engines, saving ~20 tons there. Or, if you'd like, add some jet engines for safety in the landing phase (to avoid a purely glider landing), but those only need about a 1:10 thrust-to-weight ratio to keep the vehicle aloft (vs 1:4 for takeoff), and they're only keeping 100 tons aloft, not 800 - so the landing jet engines might only be 2 tons.

In short, by going to a purely rocket launch and flight, you've saved nearly 30 tons for the vehicle (assuming you can fit all the airbreathing stuff into 30 tons) and sidestepped serious engineering problems, like how to make 800 tons fly with only 100 tons of airplane (that has to double as a spaceship). The cost? Larger fuel bills, which are very cheap compared to all the R&D and construction costs you're saving. Aluminum fuel tanks are much cheaper than giant airbreathing engines.



Well, using the examples above, look at what saving oxidizer gets you.

By going from a subsonic aerial launch to orbit, you delete 170 tons of propellant (including 146 tons of LOX) compared to a purely rocket launch from the ground. In doing so, the spacecraft ends up burdened with 25 to 30 tons (optimistically) of extra hardware related to atmospheric flight. When the challenge is optimizing a vehicle's fueled:empty mass ratio to appease the Dark God named "Rocket Equation," why would you want to add more structural mass?

This situation is even clearer when you look at dense fueled SSTOs. Dense fuels, while requiring an even heavier launch weight (about 1600 tons for a 100-ton orbital weight), can further reduce structural weight. The rocket engines would be lighter (16 tons with a conservative 1960s kerosene/LOX design) and fuel tanks lighter and smaller (you need less tankage at lower pressurization to hold 1500 tons of kerosene and oxygen than to hold 700 tons of LH2/LOX - the value of density). Despite adding 800 tons of fuel compared to the airbreathing option, the vehicle is much more capable of meeting even stricter fueled:empty mass ratios demanded by its lower fuel efficiency (300-350 seconds) than the airbreathing or H2/LOX pure-rocket vessels.

A scramjet is an even more extreme case. While it promises high efficiencies and reduction of oxidizer mass, you're paying in spades for "saving" something that's structurally and economically cheap (oxidizer). The problems are summarized here:
http://en.wikipedia.org/wiki/Scramjet



Yes, and the funny part is that I'm a materials engineer currently working on an aerospace weightsaving project. I'm going to spend most of the week laying up carbon fiber composites for a test article.

The reason I'm not explicitly allowing for materials science improvements is related to the reason I'm not addressing the typical 10-20% weight bloat of aerospace projects: I'm hoping they cancel each other, though that may be optimistic.

It's probably in structural weight, actually. Chemical rockets mostly hit a wall in fuel efficiency and weight in the late 1960s to mid-1970s; there's simply no more energetic chemicals than are currently used in rocket engines** and engines don't have room to get much lighter than some rockets that were on the drawing boards as improvements to existing Apollo/Shuttle/Rooskie hardware. Airbreathing propulsion like scramjets comes with significant penalties (see my above post), though canonically Shadowrun made them work.

(**Except some weird things like hydrogen/lithium/fluorine rockets, which balance high efficiency with incredible structural penalties.)

The place to save weight is improvement in structures. Lighter heat shields, combined heat shield/structures, composite airframes, etc. may make it possible to achieve the 10:1 fueled:empty ratio needed by LH2/LOX single-stage-to-orbit vehicles, and would almost certainly make dense fueled SSTOs (which need 15:1 ratios) reusable and robust.

I logged on to the boards this morning to talk about what sort of blinged out SMG a gang banger might use, and got a lesson in flying spaceships. This place is AWESOME!