So - can anyone tell me why this needed to be the world’s largest airplane when a modified Boeing 747 would have done the trick?
Where on a 747 would you hang a big-ass rocket?
“Modified”.
Where on a 747 would you hang a big-ass space shuttle?
It’s not the world’s biggest airplane. It has the longest wingspan, but that’s all.
The Antonov is longer and carries more.
God Damn it! I am getting sick of people half-assing stuff.
For a rocket that isn’t supposed to glide back to earth, it won’t have wings; the only way to separate it from the carrier vehicle is to drop it, which means it won’t be riding piggy-back.
The rockets intended to be carried by this thing are significantly big-asser than a space shuttle. And you also don’t drop-launch space shuttles from the carrier aircraft. (Especially since the shuttle goes on top.)
The original Pegasus II design (since cancelled, but that’s what the Stratolaunch was designed for) would have had primary stages roughly the same size as the Space Shuttle SRB (about 12ft in diameter and 140ft long), with a fat payload stage about 16ft in diameter, and filled to the brim with heavy rocket fuel.
The shuttle itself is big but empty when transported by the carrier aircraft. An empty space shuttle weighs about 165,000 pounds; a loaded Pegasus II would have been in the neighborhood of 465,000 pounds.
So what’s the point of giving it a cockpit - selling the seats to tourists? I can’t imagine “commonality of tooling” extends to leaving in the windshields etc. unless there’s some practical purpose.
That was my thought. I’m sure the engineering is impeccable, but… not even a tail-boom spar to stabilize the fuselages and take some loading off the wing spars?
On a treadmill?
“I bet you an M1 tank could break the U-2s altitude record.”
“Are you joking?”
“Well, there would have to be modifications made.”
As I pointed out, for the purpose stated (LEO, 100lb satellite) the rocket weight is around 200,000 lb. Easily done by existing planes.
Maybe I missed it but is the cost of the plane mentioned?
Why have two planes joined instead of doing the plane equivalent of this type of cargo helicopter?
It could look something like this with the space rocket instead of a bomb: http://defense-update.com/wp-content/uploads/2012/12/laser-sdb.jpg with some adaptation for the cabin.
Come to think of it, the plane doesn’t need to be manned so it could do without a cabin.
How many emergency landing options would this bad boy have? Or, how many parachutes would it take when it’s fully loaded?
The Stratolaunch was not built to launch cubesats.
From that height you are avoiding something like 90% of the atmosphere.
I mistyped. 1000lb LEO satellites require a rocket that weighs around 200,000lb. That’s what the article says this plane was created to do. A Boeing 747 has 300,000lb payload capacity.
I suppose you’re right, since they’ve launched the Pegasus rocket from the underbelly of an L-1011 aircraft before.
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But the purpose stated in the article (launching Pegasus XL rockets) does not reflect the initial design intent of the vehicle. As friedo says, it was initially supposed to carry the massive Pegasus II rocket, which would have weighed in at 465,000 pounds and been able to put up satellites as big as 13,500 pounds. No existing plane could have managed that.
For the time being, the Stratolaunch vehicle is apparently going to be used for the much smaller Pegasus XL rockets, which seems like a pretty poor utilization of its capability.
In a way, the stratolaunch kind of is the plane equivalent of the Sikorsky Skycrane. It’s an airplane designed to carry a heavy load attached underneath. They’re both designed and built around a large open area where the cabin (or cargo hold) would usually be. And you couldn’t just take a regular 747 and cut out the lower fuselage; where the wings connect together through the body is the strongest part of the plane.
Dr. Strangelove is correct that the amount of speed added to the vehicle is negligble (less than 1% of the total orbital speed), and while there are some gains in getting above the first 30 kft of atmosphere it does not offset the difference in impulse between an air-breathing subsonic “stage” and an expendable first stage rocket booster. The bigger advantage for an air launched rocket is the ability to launch from any azimuth and latitude the aircraft can reach within range, and also select a launch position to maximize trajectory over broad ocean area or uninhabited land to reduce the Expectation of Causulty to an acceptable minimum, thereby opening up a wider array of potential orbits than would be available from any fixed launch site. Getting above low altitude wind shear also provides some advantages, but that is offset by the requirement for the vehicle to be robust enough to withstand takeoff and contingency landing loads as well as having reinforcements for mounting points, so at best it is a wash.
The differences in performance between solid and liquid propellants are not as great as just looking as propellant specific impulse values would lead you to believe, particularly for the lower stages where propellant-specific performance (generally cited as total impulse or I[SUB]sp[/SUB]) is less critical than being able to tailor thrust to get an optimal rate of ascent. Although solid propellants generate less thrust per unit mass of propellant than most common liquids, they are stable (don’t require cooling or regeneration systems), don’t have the complexity of turbopumps, ullage gases, et cetera, and also forms a reinforcing part of the the motor case structure prior to being pressurized; all of this results in a reduced inert mass fraction, so more of the stage is propellant rather than dead weight carried throughout flight. Solids also generate more thrust per unit volume by dint of their higher operating temperatures and pressures, and so the launch vehicle gets going faster and doesn’t lose as much impulse to gravity drag (the amount of impulse expended just keeping the rocket from falling down to Earth before reaching orbital velocities); in fact, the propellant grain profile of solid motors often have to be tailored to limit thrust both near maximum aerodynamic loading (max-Q) and near end of burn to prevent generating excessive drag and accelerations. Propellant specific performance is far more important on upper stages where the reduction in carried weight counts directly against payload fraction; even then, there are several upper stage deployment systems that use solid motors (e.g. the Payload Assist Module) because of their simplicity and the reduced potential for propellant contamination (most of the products are heavy with lower ratios of specific heat, and therefore less propensity for turnback of exhaust). Some solid propellant boost systems, such as the Orbital Science Pegasus and Minotaur vehicles offer a small liquid final stage (e.g. Hydrazine Auxiliary Propulsion System) to provide final maneuvering into the desired orbital parameters.
Solids are logistically easier to handle once emplaced, as once the grain is cast there is no unloading or topping off of propellants, though the offset is that the motor has to be handled intact at full weight from the production facility to the launch site and handled carefullly to protect the integrity of the propellant, case, and any field joints. Liquid stages also have to be handled carefully, often with reinforcements placed inside tankage or a handling frame (strongback) outside the stage to prevent it from being damaged, but the dry weight is a fraction of its total loaded weight so it can be lifted with lighter cranes or other handling fixtures. For air carry, solids eliminated the problem of propellant slosh, and also issues with expansion or potentially hazardous venting with changes in ambient pressure and temperature.
However, despite the launch azimuth and altitude advantages, I’d reserve expectations of cost reductions until they are demonstrated. Orbital Science has been flying the much smaller Pegasus air launched rocket for over twenty-five years, originally with the expectation that air launch would be much cheaper and open up a market for smaller satellites that couldn’t afford or obtain a launch on then government launch vehicles such as Thor-Delta or Atlas, but it was never as profitable or required as little ground crew support as expected, and combined with some teething problems and the increasing cost of solid propellant constituents did not really foster the market for small satellites. Stratolaunch seems to be aiming for much larger payloads which seems curious because there are several notable options both foreign and domestic, and unless they can seriously cut costs or offer some other capability not currently on market they’re going to have a difficult time distinguishing their capability, especially given conservatism of the large satellite market and the payload launch “insurance” money behind it.
Stranger