The orbiter would not be heavy enough to require the three-meter thick (or more) runway the carrier wing and orbiter stack would require, nor would the orbiter need a 4 or 5 kilometer long runway, which a large, heavily loaded aircraft requires.
My goal with this idea is to use the atmosphere instead of fighting it, by using air-breathing engines and aerodynamic lift to gain as much altitude as possible, providing as many ways as possible to recover the entire launch vehicle in case of a failure, and to make a space plane the default mode of transport for people.
Of course, if we never develop large space stations, interplanetary manned spacecraft, or other projects requiring lots of people in space, than all of this is moot. But I want to believe that someday there will be hundreds of people working in space, and getting them there and back will be a big deal.
No, the recovery concept I am proposing is untried. But I can’t think of another way of getting a large aircraft back on the ground safely when it has lots of lift and large amounts of surface area. The stall speed will be very low, but the vehicle will be easily pushed around by the wind.
At the time of the Solid Rocked Booster separation, the space shuttle was going about one mile per second. Half of the fuel in the external tank had already been used, which means that the other half provided enough acceleration to reach 5 miles per second.
Several factors prevent air launch of large vehicles from being worth the tremendous development cost and risk:
(1)The kinetic energy required for orbit is a squared term (KE = 1/2mv2), so a booster (whether mother ship, mag rail, etc) achieving subsonic speed doesn’t help much.
(2) In a baseline surface launch at sea level, total air drag losses aren’t that high. For the space shuttle it was 1% of delta V. So it doesn’t save much drag loss to lift the 2nd stage to, say, 50,000 ft.
(3) Gravity losses from the vertical component of ascent are higher than air drag losses, but still relatively modest.
(4) The cost and technical risk of developing an air-breathing mothership capable of replacing the 1st stage of a conventional reusable booster (e.g, SpaceX) is huge. We already have reusable conventional first stages and they work fine. THAT is what a mag rail or airbreathing booster is competing against.
The total ET propellant (LOX+LH2) is about 735600 kg. The SSMEs on average burn 1440 kg/sec over the 8.5 min ascent. So by SRB separation at 120 sec, about 1440*120 or 172,200 kg of ET propellant has been used, which is 172200/735600 or 23.4%. About 76.6% or 563,400 kg of ET propellant remains at SRB sep, which is at about 130,000 ft altitude (24 miles) at about 5,000 ft/sec.
The shuttle stack mass just after SRB sep is about 563,000 kb of ET propellant, 26,500 kg for the ET, and 109,000 kg for the orbiter, or a total of 698,500 kg or 1.54 million pounds.
So the question is what kind of air-breathing mother ship would be required to lift an orbiter the same size and mass as the shuttle stack at SRB sep to an altitude of 50,000-100,000 ft at either subsonic speed or the shuttle’s 5,000 ft/sec speed?
That stack weighs 1.54 million pounds. The largest and heaviest aircraft ever to fly was the AN-225 which could lift a single internal payload of about 416,000 pounds. It could lift the empty Buran shuttle which weighed about 130,000 pounds but not very high: https://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Antonov_An-225_with_Buran_at_Le_Bourget_1989_Manteufel.jpg/800px-Antonov_An-225_with_Buran_at_Le_Bourget_1989_Manteufel.jpg
So you’d need something vastly larger than the AN-225, and which could lift a 1.5 million pound external payload to over 50,000 ft, and the faster the better. Picture something 10 times the size and weight of an XB-70. The development cost and technical risk would be incredibly high, and you’d still have to separately develop the orbiter.
This issue was discussed in this AIAA paper which said: *“a typical straight and level subsonic horizontal air launch such as used by the X-15 research rocketplane does not
result in any significant changes in the delta V requirement”. *“A Study of Air Launch Methods for RLVs” (Sarigul-Klijn, 2001): Mechanical and Aerospace Engineering
Anybody wanting to know more about why hypersonic air-breathing launch vehicles have thus far been unsuccessful should read these three documents:
The Hypersonic Revolution, Volume III by Dr. Larry Schweikart: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=2ahUKEwjtgKrc9pflAhWLVN8KHdZJCxkQFjADegQIBxAC&url=https%3A%2F%2Fwww.usaf-sig.org%2Findex.php%2Freferences%2Fdownloads%2Fcategory%2F63-general%3Fdownload%3D198%3Athe-hypersonic-revolution-vol-3-the-quest-for-the-orbital-jet-the-national-aero-space-plane-program-1983-95&usg=AOvVaw1HLl4d2n2Q4CCT9NhWUhx9
Facing the Heat Barrier: A History of Hypersonics by T.A. Heppenheimer: https://history.nasa.gov/sp4232.pdf
Single Stage to Orbit: Politics, Space Technology, and the Quest for Reusable Rocketry by Andrew J. Butrica. This book is available free if logged into Scribd.com (Amazon link shown here): https://www.amazon.com/dp/B002CZP1TQ/
A constant wind pushes all airborne vehicles around equally.
Given that space-based industry will become common, people will be needed in space in numbers far larger then six. Partial crew rotations will involve carrying at least ten people, plus shuttle craft crew. Think of an off-shore oil rig. And I find it hard to believe that capsules are the ultimate technology for carrying people to and from space.
Yes, my concept would be more expensive than conventional vertical launching.
A refused take-off can occur for a variety of reasons. The launch track would be able to stop the stack from take-off speed without destroying either vehicle. This will require a longer track, but that is acceptable.
I use the term ‘wing’ to refer to the carrier wing, which would be supported at its center by the launch track.
Launching straight up with a large payload requires a thrust-to-weight ratio of greater than 1 to 1. Accelerating horizontally is possible with thrust-to-weight ratios of less than 1 to 1.
Large wings are a problem during launch and ascent, because of turbulence, but landing with small wings requires very high speed. So wings that can be extended to reduce landing speed are desirable.
Having one engine that can be restarted during landing would allow a go-around.
Unless you have a dry lake bed which allows landing in any direction, cross wind landings will happen. A large, very light plane will have a lot of problems landing in a cross wind. A retrieval system which allows for recovery of the aircraft at speeds of 500 kph would make cross wind landings easier, I believe.
This whole concept is based upon a perceived need many years in the future. We may end up not needing people in space, or only very small numbers, in which case this concept is worthless.
Put the end of your track high up, outside of most of the atmosphere, and forget the wing, now you have a magnetic launch system.
Capsules kinda are the best thing for getting people to and from space. Anything else increases complexity, and complexity is more stuff to go wrong. If you have infrastructure already there, then all you need is life support for the time to rendezvous, and a robust craft that can handle re-entry.
The Space Shuttle was somewhat useful before we had a space station to go to. It provided many of the amenities that are needed for survival in space for up to two weeks at a time. It also weighed about a third of what the ISS weighs. For every three shuttle missions, we basically launched the entirety of the ISS. Now that there is somewhere to go, there is no need for such a complicated human transport system.
I don’t understand what this would do that Starship and Super Heavy don’t have well coverered. I assume you are familiar with Starship and Super Heavy from SpaceX? They are fully reusable and will enable huge payloads to LEO and beyond.
Now what might be handy for putting stuff into orbit at low cost might be some sort of ground-based linear accelerator (mass driver) set up in some kind of mountainous region that could get your payloads going pretty fast and fairly high before their own rockets kick in.
The whole trick to getting into orbit after all, is going fast enough to basically fall past the Earth. Your orbital height is determined by your speed- the faster you go, the larger circle you describe as you fall around the earth and vice-versa. Deorbiting and re-entry is basically slowing down such that you quit falling past the earth and start falling into it.
So anything you could do that would get you going faster without actually having to burn onboard fuel would probably be a good thing.
Where earth orbit is concerned, a ground based accelerator is going to have to impart a lot of energy to be useful.
For reference, an aircraft carrier catapult can fling a 40,000-pound aircraft off of a level deck at 150 MPH - provided that aircraft is already operating at something close to max thrust.
The Soyuz rocket weighs in at 672,000 pounds, and 150 MPH is a flea fart compared to the 17,000+ MPH needed for low earth orbit. If you want to justify the cost of your accelerator program, you had better substantially reduce the cost of the vehicle, which means you had better give that vehicle a lot of takeoff speed.
Except you can’t, not at ground level. The space shuttle hit max Q at about 35,000 feet altitude, at a speed of 1000 MPH. If you try to go 1000 MPH at ground level - even assuming ground level is up in the mountains at 10,000 feet - you’ll shred your vehicle unless you toughen it up, i.e. make it heavier. But if you can’t even impart 1000 MPH of speed from your ground-based accelerator, then you can’t make your rocket much smaller than the Soyuz. Your rocket won’t be cheaper.
All of this is without considering the g-loading imparted by the accelerator. Orbital launch vehicles typically don’t exceed 3 g. If you want to avoid adding additional mass to your rocket to have it tolerate higher g loads, then your accelerator can’t exceed 3 g. Want to achieve 1000 MPH takeoff speed? You’ll need 16 seconds and 11,250 feet of rail. Not including additional length to allow for decel of whatever will remain attached to the accelerator rail.
This is not practical.
This overall concept was discussed in a video posted yesterday by Fraser Cain, publisher of Universe Today. It is called AstroClipper. There is an actual company behind this, albeit a tiny one: https://youtu.be/qWfkW2y-hAQ
The problem is very few details are given. It is easy to make a compelling graphic, e.g: https://photos.smugmug.com/photos/i-2tBk3CN/0/1f54f426/O/i-2tBk3CN.jpg
But it’s not too different than a child making a crayon drawing of a rocket and saying “this part goes here”. When you ask the actual engineers and managers tasked with implementing that in the real world, reaching affordable, workable solutions is a lot harder.
E.g, NASP, which initially looked very promising based on Tony Du Pont’s original design. Further engineering scrutiny using real-world numbers and margins and more detailed modeling indicated it was just not possible. Neither AstroClipper or other similar paper designs have yet been subjected to that.
The additional problem all novel launch systems face is – if they ever fly – they will be competing with SpaceX’s super-low prices. This was known years ago: Spaceplanes vs reusable rockets – which will win?
SpaceX projects the price per kg to LEO for Starship and Super Heavy will be less than a fully recoverable Falcon 9, so the task for airbreathing, magnetic rail or other novel launch systems is more difficult than ever.
As several people have pointed out, getting into orbit is all about going fast. Accelerating in a horizontal direction. Getting above the bulk of the atmosphere is necessary because turbulence will destroy a vehicle traveling at high speed. Max-Q is the region in a launch trajectory where speed and atmospheric density combine in their most destructive potential. As long as aerodynamic lift is possible, turbulence can be encountered, but max-Q speeds go into the hypersonic range before lift disappears.
A space craft launched at 15 kilometers can accelerate horizontally while using aerodynamic lift to gain altitude. As the speed increases, the vehicle will ascend as the Earth curves away beneath it. A space craft capable of landing horizontally will have sufficient lift to fly off of a carrier vehicle that is traveling at twice the stall speed of the space craft. Putting the carrier wing in a slight dive would assist with separation, as well as reducing chances of a collision. The carrier wing would have shielding to deflect the exhaust of the space craft.
The amount of engine power needed to accelerate a given mass horizontally is less than the amount of engine power needed to lift that same mass vertically, so a vehicle launched horizontally at high altitude will not require engines as large as would be needed for a vertical launch.
Much of what I propose is based upon an orbiter that would resemble the space shuttle orbiter, but would be considerably lighter. The space shuttle was a heavy lift launch vehicle, which launched vertically. This meant that the engines had to be extremely powerful, which means using lots of fuel. Reducing the payload requirements to a value around 6,000 kilograms would mean that the orbiter could be as much as half the weight of the space shuttle, given that composite materials are available now.
Providing a way for the spacecraft to land horizontally reduces the danger of a vertical landing, while increasing the number of potential landing sites. Much less fuel is needed for a horizontal landing as well. There has been no demand for an extremely large aircraft to carry weight to altitude. Aircraft design has focused on carrying payload internally for long distances, with the most common payload being passengers. Designing an aircraft to lift weight to altitude means using a straight wing, perhaps two, and lots of engines.
Complexity is never desirable, but safety often demands it. Multiple redundancy, abort options, and robust construction will factor into passenger space craft design, more so than payload capacity. Every fatal accident brings about questions of whether space flight is needed, and how safe it should be. Accelerating a human being to orbital velocity will never be totally safe, but every attempt should be made to try.
And as the Earth curves away underneath your accelerating vehicle, the angle of attack of that vehicle will increase. Up to the point of stalling.
Aerodynamic lift would taper off around 35 to 40 kilometers, so a stall is unlikely. The engines would be gimballed for vector control as well.
Yakamanic: the trouble with your idea is that it’s not any safer, and it’s not efficient.
In summary, you’re talking about a complex aircraft launching a rocket. Propelled by kerosene.
If you have to build a rocket, why not use the same rocket engines, but optimize the nozzles for sea level thrust, and have one rocket carry another? This is a more straightforward approach and it means less components to design.
What are you saving with the aircraft? The only savings I see is the aircraft uses less fuel, but costs a lot more maintenance since it’s a huge and complex aircraft.
It’s also not especially safe, the aircraft is carrying a rocket fully loaded with fuel.
So, each flight, you burn kerosene and aircraft components, or instead you can just burn kerosene and rocket components.
As it turns out the latter is cheaper. Also, methane is cheaper than kerosene. So the next logical thing is to build your 2 stage rocket a bit bigger, for the economies of scale, and to burn methane instead, because it costs less. (not sure how much the methane SpaceX is using actually costs, tbh - the problem is it’s not actually natural gas, it has to be purified in a gas separation plant)
SpaceX has the right idea. The biggest tweak I would make to their plans, as an armchair rocket scientist, is to go smaller. The BFR, I suspect, is too big to be cost effective. Instead, use the same Raptor methane burning engines, but use about 3-7 for the lower stage and 1 for the upper stage. Same rocket, just scaled down, and build more of these rockets. Rely on docking in orbit to put together an interplanetary mission.
Yes, but further on in that same report the authors state:
" To provide a performance benefit, the carrier
aircraft must be capable of releasing the launch
vehicle at a positive flight path angle (g) above the
local horizon. A subsonic release at g = 25o
provides about 1,600 fps delta V benefit for a
winged launch vehicle. Further increases in g
above 25o provide little additional benefit for
winged launch vehicles but does provide
additional benefit for unwinged launch vehicles."
That report describes a number of benefits which could result in using air launch.
No aircraft has ever been built expressly to carry weight to altitude, except the White Knight and WK II. No swept wing will be used, because that is to reduce drag on long flights. Fuselage would be minimal, because payload would be on top of the vehicle. There are number of methods of increasing the lift of a wing, from flaps to Boundary Layer Control, as well as using a second wing. Biplanes were abandoned when engine technology began to improve, making higher take-off speeds possible.
When the aircraft that would become the B-17 was introduced, commentators were shocked by its size and weight. Today, it seems small. The carrier wing required for lifting the orbiter would make a 747 look small. But we have engines today that are 100’s of times more powerful than the engines on a B-17. We also have materials science which can reduce weight while increasing strength.
Yes, the reusable rocket is changing many beliefs about launching things into space. But I believe that eventually we will develop a better, safer, more reliable method of putting people into space. Cargo can wait on a launch pad for days until the weather is right, the orbital angles are right, and a number of other conditions are favorable. If a rocket carrying cargo blows up 5 seconds after launch, it is a bad thing, but much worse if people are hurt.