phx1138 wrote:
That much freight is way more than I need, as noted. So swap for seats & call it, what, 20 men? Maybe a bit of "luggage"?
E of Pi wrote:
I'm not sure that 10,000 lbs for the t/Space concept isn't (again) the orbital vehicle's total mass, including structure. The vehicle they depict seems to be about the size of SpaceX's Dragon, and was stated to carry 4. Also, the CXV airlaunch platform (a "custom Scaled carrier aircraft" were actually based on early Rutan concepts for Stratolaunch's Roc. Stratolaunch, when publicly released a year or so later, only managed 6,100 kg of total launch mass--which would include both payload and the vehicle itself.
The link is to the old concept which required either the "Custom" carrier or serious modification to an existing (747) aircraft. Their new concept (see:
http://www.nasa.gov/offices/c3po/partners/tspace/) had a new configuration that fit under a less modified 747.
It's explained in this paper here:
http://mae.engr.ucdavis.edu/faculty/sarigul/papers/AIAA-2008-7835.pdf, along with showing the older configuration on a "long-gear" 747 concept. The original design was 13.5ft in diameter, and had a launch weight or about 290,000lbs and was a "single-barrel*" TSTO. The new concept was only 7.25ft in diameter but was much wider (a bit over 51ft) as it was a "three barrel*" TSTO with a launch mass of around 207,000lbs. Now the launch mass is the whole vehicle weight at launch time recall, but from what I understood the basic payload was the same in both versions, which I mis-typed as it's supposed to be 4 crew OR around 10,000lbs of "payload" (with no capsule) and around the same up-mass of cargo as the Dragon.
The capsule may in fact be a bit "smaller" than the one cited and closer to the size of the HMX HX Transfer Vehicle proposal for launch on surplus Titan-II missiles as proposed by Gary Hudson. (Sorry no links I can find but mentioned/shown here:
http://www.hobbyspace.com/AAdmin/archive/Interviews/Systems/GaryHudson.html, similar itself to the Phoenix CEV concept for the Falcon-V here:
http://rascal.nianet.org/wp-content/uploads/2015/07/2006-RASC-AL-UMD-Tech-Paper.pdf)
*- The difference is the "one-barrel" is a traditional two stage rocket design, while the "three-barrel" has two outer boosters with a central "core" stage that is the second stage.
Something to keep in mind is that both designs were built around the VAPAK self-pressurization system so the LV is of the pressure-fed variety which was to keep the design and operation simple and cheap. Arguments can be made for using a similar but more efficient pump-fed design though my personal preference is to keep the propellant combo (LOX and Cryogenic Propane) in order to keep the bulk of the LV smaller.
phx1138 wrote:
All of which had me thinking the top-carry/launch was the better option to begin with. (Hell, I've seen pix of the loading of the X-1 into an NB-29: they park the 'fort over a pit.)
If that's what you got out of my explanation then I obviously failed to highlight the disadvantages

See the above cited paper for an experts opinion, (on the other hand there are a lot of other experts, the DARPA Air Launch report comes to mind, who continue to assume that top-launch is always better anyway

) on the tradeoffs.
As for the loading, they did that with the early atom bombs too and for the same reason; Not enough clearance under the aircraft to roll the item under the airframe. If the X-15 wasn't carried on a wing pylon but in a centerline mount they would have had to figure out a way to raise the B-52 or put the X-15 in a pit to load it
The Mach-6 BETA-II had the Orbiter being towed with its own landing gear under the carrier vehicle, which had landing gear that could lift it higher off the runway. Once mated using on-board hoists the carrier would lower it's gear to a "normal" position. Note that the AirLaunch/T-Space concept now simply over-fills the landing gear olos which is within acceptable maintenance and operations procedures to allow the same thing.
Top loading requires something like the Shuttle/747 mate/de-mate stands to accomplish.
RanulfC wrote:
No what he's describing IS insanely risky The aircraft is stalling, fast, (unless as in the cited air-launch concepts above you do something even MORE crazy like putting a Space Shuttle engine in the tail of the 747 and light it up to keep the 747 flying while you release the LV) meanwhile once you release you carrier aircraft is trying to "push-over" (with a top-mounted LV) or pull into a loop (with a bottom mounted LV) and did you remember to seriously reinforce the whole airframe to actually pull off this maneuver in the first place? No? Well not to worry, firing the SSME probably tore your wings off anyway, if not the negative (push-over) or positive (loop) Gs will probably do that anyway...
phx1132 wrote:
That does depend, to some measure, on the engine the L/RV is using, doesn't it? I'd guess an X-15 (or something close) wouldn't produce the exhaust blast of an SSME.)
That's not even the engine of the LV we're talking about but the rocket engine in the tail of the carrier aircraft to push it up to an acceptable AoA for launch

Remember your "sweet-spot" is an angle to the local horizon of between 35-and-70 degrees which is what the carrier aircraft has to pull up to be in a proper launch position.
Or you put wings on the LV and have IT perform all the needed maneuvering, (which is how Pegasus does it), or use something like T-Lad.
But the cited proposal actually had the carrier aircraft doing the maneuver (it's called a "Gamma maneuver" for some reason, maybe because "Omega" maneuver would have been off-putting for the flight crew?

) and the LV had to light off two of the 10 RL10s powering it to ensure separation.
phx1138 wrote:
I'm not opposing a dedicated "carrier", even one capable of Mach 6 & costly. I'm after something to replace throwaway (or nominally reusable) lifters like the Saturns or SRBs for crew-only missions: essentially, split the STS task in two, & make the L/RV truly "flyback" (within limits; IDK I'd demand jets for cross-range, when you'd want to return to a maintenance &/or launch base anyhow). I'm happy if it's a Citation-size crew load, rather than a DC-3 or L049.
E of Pi wrote:
If you're building a custom Mach 6 flyback carrier, you might as well just make it about 50% larger and get a payload that's actually usable for commercial cargo missions as well as just passengers.
From my readings around 10,000lbs is considered a "viable" up-mass for orbital use, but that's not clearly defined as to what all that entails as the definition varies. For example, Cargo-Dragon, Cyngnus, and CST-100 all are supposed to deliver about the same mass to ISS/orbit but they are shown to only be delivering around 5,000lb to 7,000lbs (2,268kg to 3,175kg) of the launch vehicles "payload" capacity which varies between 21,610lbs (9,800kg) to 63,450lb (28,790kg) and that last is a Delta-IV I might add. On the other hand you'll note that the Beta and proposals like the Black Horse specify 10,000lbs of "payload" in addition to at least two crew members. (That would "work-out" to something like 20 people including the crew but without things like seats, extra life support, etc. So offhand I'd figure no more than 15 and most likely 10 including crew) However your other constraint is physical space as most concepts have a "bay" or housing that's not designed for people but a general "cargo" configuration. The generally circular configuration is going to have a lot of space eaten up by seating arrangements that allow functional use of the space either in orbit or on the ground. (If you've ever seen the pictures of the mockup for the Big Gemini capsule, take a close look at where the astronaut is sitting in the aft-upper-left side seat. As the vehicle is on the launch pad and his back is "down" getting into the seat is pretty easy. Now look at the angle it's at in the mockup and then notice that the capsule is still not "landed" yet and he's got about another 10-15 degrees of "face-down" angle to deal with AND he's like 6 ft off the "floor" in the horizontal position. How the heck does he get out of his seat without lots of help or killing himself?

)
And just to stir things up even more, why build a 'dedicated carrier aircraft" at all even if you want to use air-breathing propulsion?
May I introduce the "Spacejet" LV concept:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780003229.pdf
http://www.secretprojects.co.uk/forum/index.php?topic=11026.0
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810020560.pdf
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810024617.pdf
Your building "aircraft" to house your jets engines but the lift and flight control comes mostly from your LV. The design only addressed an orbital vehicle with "Shuttle" capacity payload and a staging speed of around Mach-3.5 but the overall idea is scalable. (I've done some really rough BOTE stuff on using a Black-Horse sized Orbiter with smaller versions of this concept that stages at similar velocity and it shows a real solid payload of a bit over 10,000lbs, though how you actually fit that in something that's supposed to be the size of an F-15 I'm not at all sure

) And you can in fact get the turbojets to operate up to around Mach-6 with some additional systems installed (Mass Injection, Pre-Compressor Cooling using water and lox doubles your jet compressor face Mach number capability and thrust for example) and if you build a Beta-like "over-under" or combined turbo-ramjet system...
As long as you're not concerned with cost, (and that's really the rub because costing-aeronautical/aerospace systems is a pretty well defined art and going supersonic is expensive, while hitting hypersonic really starts to cost money) and as long as you don't demand excessive air-breathing time, (lets fact it do you really NEED to go faster than Mach-6 with all the structure and costs that go with it? Most times the answer is a definite "no") or exotic propulsion (SCramjets for a really good example) the whole concept is probably feasible. If you've got the money.
On the other hand a more "reasonable' approach was a concept called "CRoSSBoW" which can be seen here:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070002822.pdf
Which supposes (again) to reduce your carrier aircraft to the smallest (and therefore cheapest) possible platform. Here it's a subsonic platform but all flight control is from the LV with only enough to autonomously return to the launch site. The LV provides the thrust (and that way you check out the rocket engine before release) for the gamma-maneuver and then releases the carrier to fly back to base while it continues on to orbit.
The study is actually more of a general study of Air Launch options and trades than a full-up concept and quite an educational read overall.
Randy