"Mine's bigger and better than yours"...
By the way, which one will perform better - His Muskness's Heavy launcher or Allen's aeroplane in lifting heavy stuff?
The world's largest aircraft, designed to one day fling rockets into space, has tested out its taxiing capabilities at the Mojave Air and Space Port in New Mexico. The 500,000lb (227 metric ton) "Stratolaunch" is the brainchild of Microsoft co-founder Paul Allen and advanced materials aviation wizard Burt Rutan. The pair plan …
If Wikipedia is to be believed, it's intended to carry a payload of 250t, which is less than half the mass of a fully fuelled Falcon 9. That's also about ten times the mass of a Pegasus XL, but it's designed to carry only three of those.
Air-launched rockets might have a 12 km head-start in terms of altitude but they still have to burn a lot of fuel to reach orbital velocity.
Meanwhile, a Falcon 9 launch (heaviest demonstrated payload: 9,600 kg) costs less than twice as much as a Pegasus XL launch (maximum payload: 443 kg)...
"Air-launched rockets might have a 12 km head-start in terms of altitude but they still have to burn a lot of fuel to reach orbital velocity."
Have a read of a mad (doesn't imply bad) idea to mount a space shuttle main engine on the back of a 747, allowing it to fly (for a short time) at very high speed/altitude before launching a rocket carried on its back:
http://www.thespacereview.com/article/1608/1
But it is the payload that counts, not the fuel on the rocket required to lift the fuel to lift the fuel.
High altitude launch allows using gravity, instead of fighting it, to gather some speed and there is less air resistance to fight against.
Buzz Aldrin laid out the idea for an air launch system, back in the 70s and has been trying to raise interest in it ever since.
at some point it may need JATO bottles or some other kind of 'rocket booster' to assist taking that really freaking heavy rocket up to altitude...
but who knows, if it costs less than a "pure rocket" 1st stage...
the other alternative might be a hybrid air-breather for the 1st stage rocket.
Impulse is basically mass times delta-velocity of the stuff being ejected out of the tail end. If you double the delta velocity, it takes 4 times the energy to do it. OR, if you DOUBLE THE MASS, it only takes TWICE the energy. In both cases, you get twice the thrust.
So if you can breathe air {and use that as a significant part of the exhaust) the rocket itself becomes more efficient. It's only when you get to an altitude where air breathing isn't practical any more that you have to use 'fuel only' to propel you.
[it's the same basic reason why turbofan engines are so much more efficient than turbojet engines]
In any case, strap on hybrid rocket/air-breather engines could be a third option to increase payload capacity of the aircraft. Strap them on next to the rocket you're taking up to altitude, and land with them still attached (minus fuel weight). More hybrid hybrid solutions.
/me points out that extra booster rockets burning jet fuel + LOX could be fueled by extra 'drop tanks' carried by the aircraft. Hybrid hybrid hybrid hybrid I guess
> If you double the delta velocity, it takes 4 times the energy to do it. OR, if you DOUBLE THE MASS, it only takes TWICE the energy. In both cases, you get twice the thrust.
No. If you double the velocity you do not "take 4 times the energy to do it" if the mass flow (kg per sec) remains the same. However, if the nozzle is the same size then the mass flow will also double and thus it will "take 4 times the energy to do it", but it will give you FOUR TIMES the thrust
> So if you can breathe air {and use that as a significant part of the exhaust) the rocket itself becomes more efficient. It's only when you get to an altitude where air breathing isn't practical any more that you have to use 'fuel only' to propel you.
The only advantage of 'breathing air' is that you get to use the oxygen in it to burn the fuel rather than having to use the LOX that otherwise has to be carried. A rocket engine using fuel + LOX is completely incompatible with an air breathing engine and so there would have to be 2 completely different systems. in order to get sufficient thrust to make air breathing worth while for the short time the rocket is within the atmosphere the weight and cost are prohibitive.
The Falcon Heavy Lift produces around 23,000Kn. - about the same as 100 747 engines - each weighing 4 tonnes just for the engine.
Merely processing air for its mass without using the oxygen would produce no benefit at all, it would take more energy to accelerate the air than would be obtained in thrust.
Allen's team instead turned to Orbital ATK, which will sell off-the-shelf Pegasus XL air-launch vehicles capable of delivering 1,000lb satellites into low-Earth orbit.
And here is where this story ends. Pegasus cannot compete in cost with any launch system. It is costed on "you forgot to book a sea when you should, buy one last minute" basis.
So unless they find a cheaper launcher this whole story goes nowhere.
This doesn't save much fuel because lifting the rocket is nothing compared to bringing it up to orbital speed. It's about being able to build and ignite the rocket anywhere. The second part is important because people get very NIMBY about lighting up a rocket that could incinerate an entire town.
Actually a big part of the original plan for Pegasus was to avoid range costs.
You have to book a launch range in advance. It's not cheap and the costs don't scale on size. So Rocket Labs would pay about the same to launch 250Kg on their Electron LV as SX would pay to launch 22800 Kg on F9, which is why RL run their own launch range in NZ. Something others might follow.
Likewise running the "Flight Termination System" as special software on a separate computer on the LV (rather than have a "Range Safety Officer" follow the launch and press a BRB if it fails also saves about 100 staff (and their associated costs).
But Pegasus is still the most expensive LV in terms of $/lb to orbit on the planet.
Actually I think the BRB just got retired in favour of an fully automated system. On the last few SpaceX launches you could here someone say "ATFS enabled" just before launch - which is Autonomous Flight Termination System. Apparently this also leads to the possibility of launches on the same or consecutive days from Cape Canaveral as (I didn't realise) that one of the most time consuming bits about switching the range from launch to launch was actually re-configuring and testing all the radars/scopes/etc. - that were needed for the manual system - to the next launch trajectory. Don't know if the new ATFS will be used on manned missions though. I can imagine people still preferring the idea of having people in the loop for that. Although that can lead to "Wargames (1983)" problems and the fact that in the Shuttle era the Range Safety officers were carefully kept well away from the Astronauts and their families lest personal feelings got in the way...
You'd be surprised how much fuel this approach can save.
Firstly the aircraft can add a few hundred metres per second to the rocket,. Not much, but it's a start.
The largest help though is lifting the rocket up the first few thousand meters, because that has a relatively large effect on the air density that the rocket has to push though. It also reduces gravity losses somewhat.
As other people have noted, it also give you complete freedom in orbital inclination, and launch times and locations.
phuzz wrote the inherently self-contradictory, "You'd be surprised... ...Not much..." <- :-)
"...it also give you complete freedom in orbital inclination, and launch times and locations."
I understand that launch location and orbital inclination, if optimised for fuel, are somewhat linked. The Saturn V famously used the "Roll Program" to tune the orbital inclination to match the Moon's.
Launch times would be impacted by weather, both the rocket's limits and now this added aircraft's limits. So it unfortunately remains lacking in "complete freedom". Perhaps they could move to a different airport the night before the storm (if that's even practical, what with having to prepare a rocket).
IANA scientist, or an engineer, but the forces acting on the central section are going to be massive, yes? It suggests to me, just by looking at it, that it could split in two.
Even if the two fuselages are very light they are going to have to be robust enough also to withstand major stress, stress which the central section thus has to bear. And unlike a conventional aircraft their will be different forces to contend with such as twisting, and a few more for which there are probably technical terms.
Seem to recall even the fuselage of the Russian Concordski blew apart in mid-air because the turn was too tight.
If this thing flies I shall be gob-smacked. And impressed.
Well, I'm not an engineer* either but I don't see why having two fuselage is especially problematic. In a conventional design each wing root has to bear half the full loaded weight of the fuselage. In this design the weight of the load plus that of the fuselages is distributed across a section of the wing, which should lead to lower stresses. Sure it looks wrong, but then a 747 would probably have looked terribly wrong to the Wright brothers.
See also: the P38 and the twin Mustang. (I'll happily go up in either if anyone's offering.)
*I was however almost a physicist in another long-lost life.
Think less of the wings hanging off two fuselages joined together by a central section and instead think more of the fuselages hanging from the wing which runs from tip to tip. And the engines are on the wing not off the fuselage(s)
Twin boom aircraft have been around for years. The Germans stuck two He 111 bombers together in order to tow their largest gliders. Not a great success as still couldn't get enough power but principle not new.
but most twin boom aircraft are linked at the tail as well as the wing - e.g. Lockheed Lightning, de Haviland Vampire/Venom/Sea Vixen so reducing the risk of torsional rotation around the central wing spar.
A bit of air turbulence and there's going to be a heck of a twist around that central spar, which to my (amateur) eyes looks a hell of a risk. I'd want those tails linked!
A bit of air turbulence and there's going to be a heck of a twist around that central spar, which to my (amateur) eyes looks a hell of a risk. I'd want those tails linked!
I wonder if the tails are separate to prevent being damaged by payload as it gets released, and/or to avoid getting burned by rocket exhaust (any rocket motor on the payload may get spun up before it gets released)
"any rocket motor on the payload may get spun up before it gets released"
If you've ever seen the L1011 or B52 pegasus launches you'll know that's not the case.
The launcher drops the rocket and peels back. The rocket loses around 1000-2000 feet in altiude before the rocket ignites and another few hundred feet before gaining enough speed to make up the loss.
Firing the load on-wing might sound like a good idea from an efficiency point of view but consider what happens to the carrier aircraft if the rocket engines misfire or explode.
"a heck of a twist around that central spar,"
The spar is not there to provide torsional stiffness. It is there to provide bending stiffness. In a wing made of spars and ribs the torsional stiffness is massive, provided by the actual stressed skin of the wing.
This is a much larger aircraft than the Lightning or Twin Mustang and it seems the newer twin designs are moving to independent tails like White Knight 1 & 2. Consider in a turn the outboard side is taking a faster larger turn and the inboard side is making a slower but tighter turn and especially in an aircraft this large it would likely be advantageous to compensate by differing the inputs to the control surfaces as identical inputs would induce unnecessary stress on the frame and slippage over the control surfaces as neither side will be fully coordinated. If the aircraft is small like the Lightning it probably doesn't matter so much given the distance between the tails isn't great and it probably benefits from a stiffer airframe in combat maneuvers where here it just adds extra weight. Since I imagine this is also a fly by wire plane they can take advantage of computer power and sensors to ensure the optimal operation of the control surfaces.
I'm not an aeronautics engineer either but I believe this design probably is strong enough, based on - and apologies as this is pure speculation on my part - that there was a team of suitably qualified aero engineers involved in the design of this thing ... After all, where aircraft design is involved, aircraft designers are fairly useful guys to have on your team.
It should be reasonably easy to arrange for any torsion forces to be automatically counteracted by a suitable input to the tail control surfaces on one or both of the tails. Computer or other closed-loop feedback systems are a necessary part on several types of aircraft. I believe that the Harrier would be impossible to fly if a human had to make all the control adjustments needed to keep it stable, and commercial airliners have "yaw dampers" to avoid dutch rolls.
> Computer or other closed-loop feedback systems are a necessary part on several types of aircraft. I believe that the Harrier would be impossible to fly if a human had to make all the control adjustments needed to keep it stable,
The P.1127, Kestrel and Harrier were all manual control. They did not have any computer stabilization.
From a 1972 issue of Flight International
"Command inputs from the Elliott autostabilisation system, when selected, act through the conventional surface controls. Pitch control is effected by varying the downwarddirected airflow through the nose and tail shutter valves, with the tailmounted valve carrying additional lateral shutters to control yawing moment " "in the event of an autostabilisation fault, its limited control
authority, 20 per cent, can be readily over-ridden by the pilot. While the computer - controlled autostabiliser is capable of operation at all speeds below 250kt, the handling characteristics in the jet-borne region are such that many V/Stol transitions and landings are made without using it"
@PhilipN: I wouldn't be too worried about the strength of the center wing section because I reckon they'll have done their sums re stresses etc, and remember that this isn't a long distance transport aircraft that might be expected to fly through bad weather; it'll only be flown when the weather's acceptable, and it'll more or less a case of just going up very high up and then coming back down again.
I reckon engine-out situations might be a bit more tricky than usual though. The engines are all a long way from the centerline and the turning/yaw moment provided by the rudders will be somewhat reduced due the relatively short fuselage length and also being off the centerline.
> I wouldn't be too worried about the strength of the center wing section because I reckon they'll have done their sums re stresses etc
Nah, we just increased the redundancy.
Now instead of two wings we have three wings, in case any two of them fail.
An issue Reaction Engines have modeled with Skylon, since the engines (each roughly the power of 4.5x Trent 1000s on an A380) are on the wing tips.
Yes there is a yaw component but it was manageable with the fin and throttling down the other engine. In practice
Since this has 6 engines a single engine out would only unbalence the vehicle by 1/6, rather than 1/2 (probably 1 quarter, as SABRE in air breathing mode has 2 parallel channels from the precooler).
PhilipN was worried, "...it could split in two."
From a Project Management point of view, this is trivial to avoid. Open DOORS database, insert new Requirement 'Structural#1837': BY THE WAY, IT SHALL NOT SPLIT IN TWO. Save, close file, go for lunch.
Absolutely trivial. Takes only a minute.
> insert new Requirement 'Structural#1837': BY THE WAY, IT SHALL NOT SPLIT IN TWO. Save, close file, go for lunch.
Then come back to find that the engineer in charge of structural aspects¹ has added a series of weak points along the fuselage, to ensure that it will split in at least three pieces.
¹ If he is anywhere as literalist as my developers.
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I always wondered why the tyres of lifting body 1 weren't scuffed when the wing-tips angled down. The main body was not still on it's stilts when LB1 was attached.
I made a mean Lego model of Zero-X when I was a kid. It was about 15" long, and used nearly all of the Lego that we had. The colours were wrong, of course, and as all large Lego models were, it was a bit fragile.
Unfortunately, I did not take any pictures, because I didn't have a camera at the time.
"even now, this bit of film has me spellbound
https://www.youtube.com/watch?v=x8PR3QIwXHs "
Me too, but with many more years of life behind me than at the time of first seeing it, it looks massively over-engineered, hugely over-complex and I not that some of the landing gear, on retracting, looks like it ends up inside some of the engines :-)
"Sadly not true. To me, the Supermarine swift is the epitome of "looking right" but the Hawker Hunter was the better plane
https://en.wikipedia.org/wiki/Supermarine_Swift
https://en.wikipedia.org/wiki/Hawker_Hunter"
Interesting retro look...
If you like a bit more of a modern vibe, this is my favourite:
https://cdn.airplane-pictures.net/images/uploaded-images/2010/9/20/102986.jpg
https://1.bp.blogspot.com/-hsnevsNYoug/V8m1JV6IS8I/AAAAAAAAGG8/6w_yqsOPHIIstMwaRNaWMNTiTmhATYSswCLcB/s1600/Gripen%2BF.jpg
The lower end of the one-off space launch market is pretty small. SpaceX gave up on the original Falcon1 as soon as the Falcon9 appeared, because it only got a trickle of orders and piggybacking on the spare capacity of a Falcon 9 turned out far cheaper. I think Pegasus are going to hit the same wall. What this beastie needs is a 250-ton second stage tailored to shifting the heaviest possible load into low Earth orbit. And only Stratolaunch will be willing to restrict their first-stage options to the present beastie. They may well have to go it alone.
The Bagger isn't truly self-propelled, though (it doesn't carry its own power source). For big self-propelled land vehicles, consider "haul trucks", although it's worth noting that they, too, are used in open-cast mining.
https://en.wikipedia.org/wiki/Haul_truck
Whether this flies or not, the investment in space technology is worth taking note of.
If you'd done a survey of the world's rich in, say, 1990 or 2000, you would have found very few that were investing in space in any real way. People like Larry Ellison and Warren Buffet have had bucketloads of cash, but have kept it to themselves.
The change in the last ten or fifteen years is incredible. Musk, Bezos, Allen, Branson, and others are all pouring millions into space companies, all with very clear aims of bringing the costs down for access to space. It's a really dramatic sea change, and it is producing real results.
There's a real chance that some of these billionaires will lose their shirt on this. That's the risk you take when you spend this kind of money on this kind of project. But I do genuinely wish them all well, because even the ones who are falling behind like this project are still pushing the boundaries and discovering stuff. Exciting times.
Please note; Bernoulli's Principle is not how aircraft produce large amounts of lift. It's mostly angle of attack and Newton's third law blasting air downwards off the wing to send the aircraft upwards in an equal and opposite direction. Otherwise planes couldn't fly upside down. Everyone gets taught in school that planes fly because of Bernoulli but that effect just adds a little efficiency to the cruise more than anything else. You can fly a plane with a completely flat wing if you get the angle of incidence right. The guy writing your aviation / space based articles should really know this stuff.
Bernoulli's and Newton's principles as applied to flight are two sides of the same coin and are both correct, confusion generally arises due to oversimplifying the problem. See ...
https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html
or
http://www.planeandpilotmag.com/article/bernoulli-or-newton-whos-right-about-lift/
Thanks for pointing this out, OP, I just came to do the same. Every time someone feels inclined to show off their superior aviation chops out comes that stupid "because Bernoulli" nonsense and I'm not quite sure what happens after that because all I see is red by that point. Fair warning: I'm one more "because upper and lower flows must meet at the end of the wing" away from a full berserker mode rampage.
I think part of this is also reducing the stresses caused by the MaxQ.
A lot of engineering goes into stopping a rocket being crushed between the dense low altitude air and its own motors.
By starting the launch at altitude the air is ruffly a 5th as dense hugely reducing vibration and friction allowing for a simpler lighter rocket to do the same job.
At the moment they are limited by having to work with off the shelf gear not really designed for their application, with any luck this will get resolved and thy will be able to make a run of this.
PS not a rocket scientist if i have goofed this please tell me i am a Muppet ;->
Is there any research (or any point into researching) using some sort of balloon to do the heavy lifting to 100Km, and then launching a rocket from that altitude ?
It's a question, not a suggestion.
If we can get a relatively cheap reliable way to get things into LEO, there's the possibility of building factories or really big moon/mars landers ?
In theory, you could build an entire moonbase in orbit, and gently drop it onto the moon, ready for habitation ?
Not being au fait with the science, how easy would it be to rig up a true conveyor (think paternoster lifts) between earth and a point in LEO. Mechanical stress issues about obviously. But you'd think that the descending weightpretty much matching the ascending weight would mean quite low energy to get a lot of stuff up there.
I recall Arthur C. Clarke seriously proposed a space elevator ... and he was worth listening to.
Low earth orbit is not a particular height, but a height and speed. The height is not really where all the energy go, most go into obtaining the speed.
A conveyor belt can't be built up to LEO without anything supporting it, so basically you have to build a couple of hundred kilometres tall structure. Our current record is about one. Then there is the space elevator which is a theoretical possible idea. The basic principle is that if you go further out the orbital velocity decreases and the length of the orbit increases. Both of these contribute to the length of the orbital period increases also. At some point it goes up to 24 hours instead of one and a half which is about what it is in LEO. At equator the ground also "orbits" the centre of earth in 24 hours. Thus an object that far out over the equator will seem to stay put or as we say synchronous. Call it geosynchronous if you will. Since you then have an object seemingly floating out there you could tie a rope to it and lower it down to the ground. This will of course shift the centre of mass of the object downwards which you compensate by having a more massive object and also place it a little outside GEO so that the rope and the object combine has a centre of mass in GEO. Pull yourself up along that rope and you have an space elevator.
First problem, it doesn't go to LEO, but GEO. You could get something to height of LEO using it, but you still need the velocity afterwards.
Second building it. At the moment we are not sure if there even exists a material strong enough to hold it's own weight while stretched out so far. The distance to GEO is about 36 thousand kilometres.
> Pull yourself up along that rope and you have an space elevator.
You would also need to accelerate laterally. At ground level at the equator your velocity will be 1600kph. At geostationary orbit it will need to be 11,000 kph. You cannot take energy for acceleration from the tether as this would slow down the satellite.
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> In theory, you could build an entire moonbase in orbit, and gently drop it onto the moon, ready for habitation ?
How would you get it to be "gentle"? You couldn't use a parachute. Think: dropping a piano off the Empire state Building.
> Not being au fait with the science,
That is obvious.
> how easy would it be to rig up a true conveyor (think paternoster lifts) between earth and a point in LEO.
You cannot 'rig up' a conveyor to LEO (Low Earth Orbit). The Earth takes 24 hour to rotate, LEO is around 90 to 120 minutes. It needs to be to geostationary orbit, around 25,000 miles up.
"Is there any research (or any point into researching) using some sort of balloon to do the heavy lifting to 100Km, and then launching a rocket from that altitude ?"
Ballockets were tried back in the early days. There was nothing to gain from them and payload was limited by the lifting capacity of the balloon.
You'd probably gain more with some kind of catapault mechanism under the launchpad (sproing!)
@JimmyPage
Is there any research (or any point into researching) using some sort of balloon to do the heavy lifting to 100Km, and then launching a rocket from that altitude ?
Yes... well sorta...
Check out Issac Arthurs You Tube channel... https://www.youtube.com/channel/UCZFipeZtQM5CKUjx6grh54g/playlists
Check out the orbital ring idea!
"Not being au fait with the science, how easy would it be to rig up a true conveyor (think paternoster lifts) between earth and a point in LEO. "
A space elevator needs to go all the way to geosynchronous orbit and then beyond for counterweight, either as far out again, or with a fecking big weight. ideally, a full 48,000 miles so you get the nice launch platform at the far end.
The Falcon Heavy could well end up being the platform of choice for large payloads, but I somehow doubt it'll beat the Stratolaunch for efficiency when it comes to smaller payloads. My guess is that we'll end up using different systems for different types of payloads. There is room for both.
" I somehow doubt it'll beat the Stratolaunch for efficiency when it comes to smaller payloads."
There is very little that is "efficient" about small payloads and when you have the ability to "hitchhike"(*) on a larger launch going in the same direction as you need, it's a lot cheaper to do so.
(*) "Hitchhiking" implies it's free. Unless it's a sponsored scientific payload, the charges for putting a parasitic load on a launcher are calculated at some figure slightly higher than the mass fraction being taken up.
here, older:
http://www.thedrive.com/the-war-zone/10937/stratolaunchs-massive-mothership-rolls-out-of-its-nest-for-the-first-time
and newer:
http://www.thedrive.com/the-war-zone/18816/stratolaunch-rumbles-down-runway-as-pentagons-interest-in-rapid-space-access-mounts
btw, funny how, depending on angle of this or that shot, this contraption looks both fugly and awe-inspiring :)
> using some sort of balloon to do the heavy lifting to 100Km,
You certainly couldn't get to 100Km with any useful payload. At higher altitudes the air density falls and so does its ability to lift. At 50Km the density and lifting power is about 1/1000 of that at the surface, at 100Km it is about 1/1,000,000.
https://en.wikipedia.org/wiki/File:Atmosphere_model.png
The aircraft not only takes the rocket to altitude, it also gives it an initial speed of a few hundred km/hour which a balloon could not do. Rockets are launched as close to the equator as possible because the surface speed there is about 1000mph (1600kph) which is a good start to gaining orbital velocity. Another 500 or 600 kph adds to that.
> stress which the central section thus has to bear.
When an aircraft flies the lift comes from all along the span. The wings try to go up, the heavy bits try to go down. By distributing the weight: payload, fuel, fuselage(s) , engines; over all the span you _reduce_ the bending load. It is likely that the critical structural point is when the rocket is dropped and the lift of the central part of the wing is producing lift while carrying less weight.
I would hazard a guess that this is intended to provide the first stage of a recoverable manned vehicle for tourist purposes rather than serious cargo-lifting, but that's only a guess.
Based on the fact that the released rocket still will have to do a lot of work to get up to escape velocity. A Falcon 9 first stage separation velocity can vary, figures I've seen purportedly from telemetry, claim ~6000 kph to ~8300 kph (a shade over 3700 mph to a shad over 5100 mph) or between around 5 and just under 7 times the speed of sound*.
Escape velocity is 11.2 kilometers per second, or 40320 kph or around 25053 mph, just under 34 times the speed of sound, which the other stages have to make up.
The Starotlaunch figures for maximum velocity are not anywhere I can find them, but the Scaled Composites body doesn't "look like" a trans-sonic design.
It would seem that whatever this launches would have a serious amount of oomph to make up.