Air launch capability

[PistolPete]

<i>I was going to post this last night but, of course, uplink went down for maintenace right before I was going to.</i><br /><br />Ok, I’ve had this idea for nigh on a decade and I’ve come to the realization that I will never be able to see if it would actually work or not, so I’m putting it out here for every one to see, and maybe someone can come along and pick up this ball and run with it. If not, then let’s deflate this sucker right now so I don’t have to think about it anymore.<br /><br />There has been a lot of talk on this thread about using drop aircraft for a first stage. This is fine, but if you want real airline-like flight rates then you need the air breathing stage and the exoatmospheric stage together in a single stage, ala Pioneer Rocketplane’s Pathfinder. Because of the extraordinarily high empty weight due to all of the ancillary stuff associated with this type of spaceplane: wings, landing gear, cockpit & life support equipment (optional), thermal protection, jet engines, ramjets or scramjets (pick one), rocket engines, ect., the mass fraction for a spaceplane is extraordinarily high, which means a small payload to LEO, or fewer space tourists (or passengers/cargo if you want to deliver people/things suborbitally). One of the things that weigh down an atmospherically self-propelled spaceplane is the requirement to have separate atmospheric and exoatmospheric propulsion systems. Basically, jet engines are dead weight after the rocket engine ignites, and fancy propulsion systems such as ramjets and scramjets are about as useful as a lead balloon outside of the atmosphere.<br /><br />Mikeemmert mentioned in his last post that jet engines don’t work outside of the atmosphere because, of course, there is no air for them to run on. But what if there was?<br /><br />The discussion about LOX injection into ramjets (MIPCC) has made me realize that this is the thread for my idea. It has been talked about that LOX injection at supersonic speeds would cause <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[rocketman5000]

Check out information about the GTX. A test plane that never flew (surprising isn't it?) of NASA's. It used a RBCC (rocket based combined cycle) engine as it's propulsion system. It had all of the trick componets to boost Isp, aerospike nozzles and what no. Similiar to that which you are talking about. <br /><br />In theory an RBCC engine can boost the overall Isp of the system significantly enough that it would be capable of SSTO. You would have a very high mass fraction, however because ram and scramjets were used during the accent your required mass fraction would be much lower.

 

[barrykirk]

You can't necessarily say that you need an airbreathing stage to make cheap access to space possible.<br /><br />Air breathing booster stages do have a lot of merit.... but how do they compare to a conventional rocket powered booster stage?<br /><br />Let's look at the Falcon 1 rocket.<br /><br />Stage 1 provides an altitude of 297,000 feet and a velocity of ( couldn't find that number, but it is at least mach 6 and probably a little higher ).<br /><br />No air breathing stage is going to be able to match that without resorting to exotic stuff like LOX augmentation and even than it is going to be tuff.<br /><br />That is a huge boost to provide to your second stage. In fact it makes it possible for the second stage to reach LEO all by itself and still carry a substantial payload.<br /><br />If a pure rocket booster stage like the Falcon 1 or other can be made re-usable and that looks like a real possibility, than it could be fairly cheap to fly.<br /><br />Air launch does have the advantage launch pad flexibility, especially with mid-air refueling.<br /><br />But a carrier aircraft won't be able to replace the booster stage entirely. Not without seriously compromising the payload to orbit.<br /><br />If you want to launch your two stage vehicle from the air, then yes it can make sense. Build a vehicle with conventional engines and make the target 50,000 feet and subsonic.<br /><br />Of course, you could probably get a similar effect of an air launch by adding a couple of SRB's to your core liquid first stage. And it might be cheaper to do that.

 

[PistolPete]

I never said that you <i>need</i> an airbreathing first stage to make launches cheaper, but it does help out a lot when you are trying to get the launch rate up. I doubt that any VTOL reusable rocket, like the Falcon series, could ever match the turnaround rate of an HTOL rocket. Even if an air breathing HTOL system is developed, big dumb boosters will still be around for a long time to deliver the heavier payloads. Besides, I'm looking beyond just LEO launches, I think that there is a lot of money to be made in suborbital passenger and cargo transport. The reason that the Concord didn't work is because there were only 14 of them and they only had two routes: NY/London & NY/Paris. Because an antipodial ranged air breathing suborbital spaceplane does not have to worry about sonic boom noise complaints, then they can fly practically any long range route (there is a minimum practical range). More routes means more planes, more planes means lower unit price and lower maintenance costs which translates into lower ticket prices. Sure the tickets will be more expensive than a regular airliner (expecially at first), but the more planes that are in the air, the more prices will come down.<br /><br />There is a market for this: all of the people who flew the Concord but can't now. It was a market that would have been filled by the Sonic Cruiser, but Boeing and the airlines were too chicken to take that small risk. (because of this, I lost all faith in Boeing) It sounds stupid, but if you build it, they will come. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[barrykirk]

First of all. A correction to my previous post. I meant to <br />say Mach 4 not Mach 6 for the Falcon 1 first stage.<br /><br />Question. Has ever successfully launched a re-usable liquid fueled booster stage?<br /><br />Until we have something like that flying on a regular basis, who knows what the turnaround time will be.

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Question. Has ever successfully launched a re-usable liquid fueled booster stage? <p><hr /></p></p></blockquote><br /><br />OF COURSE !!<br /><br />I think they called it.... ummm... AIR PLANES ???<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Uh. Doh!!!<br /><br />Let me rephrase that.<br /><br />A reusable liquid fueled rocket powered booster for a rocket capable of acheiving LEO.

 

[barrykirk]

Now having said all of that. For smaller stuff, a "standard" jet aircraft releasing a two stage rocket at 50,000 feet and subsonic would definitly improve the capability of that rocket.<br /><br />The question is how large a two stage rocket could you drop from an aircraft?

 

[moonmadness]

Why do so many of these air lanch scenarios involve the shuttle or a shuttle sized vehicle.<br /><br />Right after the surpassing LEO the best idea I seen from Constellation(IMHO) is the seperation of crew and cargo alluded to by the Ares designs.<br /><br />Use any available rocket to launch cargo supplies equipment et al.<br /><br />But how feasible would it be for a small reusable air launched "spaceplane" if you will. SS1 but better and not so ugly.<br /><br />no cargo nada, just crew of 10(round number) with fuel and supplies to get to ISS and/or an Earth Departure Stage. <br /> <div class="Discussion_UserSignature"> <p>I'm not a rocket scientist, but I do play one on the TV in my mind.</p> </div>

 

[PistolPete]

It all boils down to reoccurring costs. Let's take the Falcon series. It needs a specialized launch pad and gantry and a whole plethora of associated equipment and a large launch crew (which has always been a problem and one of the things that SpaceX has tried to work on). Once the first stage has done it's buisness, it has to be recovered, this means that you need a boat to tow it back and specialized equipment to bring it ashore once you've towed it. Then you have to dry it, refold the parachutes (not a small task) and replace any parts that were corroded by the salt water. With a self-propelled spaceplane all you need to do is service it, drop the payload in it, fuel it, take off, land and start the process all over again. While the development of such a spaceplane will be more expensive (perhaps by upwards of an order of magnitude), but over time the vastly lower reoccurring costs will pay for itself. This is what happened with the space shuttle. NASA copped out on development costs and payed for it with the $500 million per flight reoccurring cost. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[mikeemmert]

Hi, Pistol_Pete <img src="/images/icons/laugh.gif" /><br /><br />Well, you're the third person I know of who has independently invented the cramjet engine and has posted on this forum!<br /><br />The way I set the launch angle of a cramjet; first of all, atmospheric density (d) at some altitude (a) {in meters, I like metric} is 1/e^(a/8000) X density at sea level (but I usually use density at the launch point because you get a number more relevant to what you're trying to do). Note that this is a rate of change, a derivative.<br /><br />A ram/scram/cram-jet at supersonic speed eats all the air in front of the air intake, because it can't get out of the way, so the amount of air the intake eats depends on velocity. The derivative of that is acceleration. Setting the two combined derivatives equal to zero gives the maximum airflow.<br /><br />Playing around with these figures reveals that high acceleration is good for an airbreathing or partially airbreathing booster; the higher, the better.<br /><br />This requires maximum chamber pressure. The problem with purely airbreathing engines is that they need to be designed for peak airflow; before or after that is acheived, the chamber is overdesigned and is too heavy. Thus a cramjet has a higher average T/W ratio. It can operate at a pretty much constant thrust over a wide range of speeds and altitudes, whereas a purely airbreathing engine has a short stay at peak thrust, only to see the thrust drop as the ship climbs.<br /><br />So far, I've wound up with two designs. Both accelerate at 6 g's. One I call a "jumpjet", max airflow is at mach three and the rate of climb needs to be about 460 meters per second. Climb is steep enough at that point so that the downward vector of thrust causes it to acclerate in the upward direction. It quickly runs out of air, but builds up enough speed to leave the atmosphere. This takes more rocket to get it into orbit.<br /><br />Another trajectory would have it travelling at mach 5 at maximum a

 

[moonmadness]

747<br /><br />max. Altitude:13,700 m<br />Cruising Speed:920 km/h<br />Average Cargo Capacity:100,000 kg<br /><br />Could any worthwhile vehicle weighing 100,000 kg or less reach orbit from that height and speed?<br /> <div class="Discussion_UserSignature"> <p>I'm not a rocket scientist, but I do play one on the TV in my mind.</p> </div>

 

[barrykirk]

Well, a Falcon 1 has a launch mass of 27,200 Kg.<br /><br />The Falcon 5 has a mass of 154,500 Kg.<br /><br />So the answer is that a 747 could carry almost 4 Falcon 1 rockets.<br /><br />The question is much of a performance gain would a Falcon 1 gain from air launch?<br /><br />I'm sure it would be substantial, but I don't know the exact numbers.

 

[moonmadness]

But the Falcon 1 is strictly a sat launcher. No??<br /><br />By vehicle I meant something that transports people. <div class="Discussion_UserSignature"> <p>I'm not a rocket scientist, but I do play one on the TV in my mind.</p> </div>

 

[barrykirk]

A Falcon 9 weighing in at 290,000 Kg can launch a dragon capsule to orbit, but it exceeds the 747 mass limit by a factor of about 3.<br /><br />What if the launch vehicle aircraft takes off with a Falcon 9 with empty fuel tanks.<br /><br />Use midair fueling to fill up the tanks.<br /><br />If the aircraft has it's own fuel tanks almost empty at the point of launch, then it should have a much greater weight capacity for cargo.<br /><br />For a 700-400ERF wikipedia lists<br /><br />Maximum takeoff weight as 413,636 kg<br /><br />Empty weight is 164,382 kg<br /><br />This provides max cargo mass of 249,254 Kg not including fuel.<br /><br />This is getting close.<br /><br />For the Airbus A380F version<br /><br />Maximum takeoff weight is 590,000 kg<br /><br />Empty weight is 252,200 kg <br /><br />This gives 337800 kg lifting capacity.<br /><br />So. With midair fueling and a Airbus A380F there is the possibility of air launching a falcon 9.<br /><br />That would have to increase the payload capacity tremendously.<br /><br />

 

[rocketman5000]

something that just sprang into my mind. we talk about one aircraft dropping another. <br /><br />What if the "rocket" composed the fuselage of the aircraft? Have all control surfaces of the aircraft attached to the wings. After droping the "rocket" The wings and control surfaces would esentially be a flying wing. This would more or less make the takeoff plane a giant KC-130 with a rocket attached to the back end of it. <br /><br />The aircraft would initiate pitchup to a lauch attitude. Ignite Rocket engines prior to stall, detach control surfaces at rocket ignition. The stalled wing would tumble behind the booster and regain flying control after losing significat altitude<br /><br />I haven't thought this all through obviously as I was writing as it came to me but, maybe its something others can build on.

 

[moonmadness]

So it would seem the answer is NO.<br /><br />Thank you. <div class="Discussion_UserSignature"> <p>I'm not a rocket scientist, but I do play one on the TV in my mind.</p> </div>

 

[halman]

BarryKirk,<br /><br />For want of hard numbers to reference, we look to existing, or planned aircraft. But air launching requires unusual airframes. (Witness the White Knight.) Lift comes from the wing, which also induces drag. The wing for all production aircraft supports a fuselage, which is where the cargo is carried, (passengers count as cargo,) and the fuselage adds weight and induces substantial drag.<br /><br />To minimize drag, and reduce weight, we dispense with the fuselage. The control cabin is placed under the leading edge of the wing, for visibilty at landing, and to protect it when the second stage flies off the back of the wing. The size of the wing is determined by the payload to be carried, the altitude the payload is to be carried to, and the length of time to reach the altitude. The number of engines is determined by the size of the wing and the altitude to be reached.<br /><br />By building both stages from composite materials, we are able to reduce weight considerably from classical designs. Modern engine design allows total aircraft weight to be substantially higher than existing aircraft. The GE90-115B produces 115,000 pounds of thrust, while weighing only 18,000 pounds. The C-5 uses four GE TF39 engines, which produce 43,000 pounds of thrust, while weighing 7,900 pounds. With 172,000 pounds of thrust, a C-5 can lift off carrying 840,000 pounds. With 8 GE90-115B engines, 1,240,000 pounds of thrust can be produced. Using flaps, Boundry Layer Control, and a catapult, a vehicle weighing 4,500,000 pounds would be able to take off.<br /><br />Even though a catapult limits launch site options, it is desirable because it will produce the acceleration needed to reach take off speed without consuming large amounts of onboard fuel. It also is desirable because an undercarriage able to support 4,500,000 pounds would be massive, yet, when landing, the wing will only weigh about 600,000 pounds. A catapult also can be designed to allow an abort witho <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[barrykirk]

We can save a lot of weight by launching the aircraft and rocket portion with the tanks empty or nearly empty. Midair fueling aircraft can be used to load the weight on after takeoff.<br /><br />Isn't it much safer to take off and possibly abort with tanks nearly empty.<br /><br />Also, if the jet engines don't have to develop much thrust at takeoff because the weight isn't there yet, can't they be designed for peak performance at higher altitudes.<br /><br />The same goes for the wings and control surfaces.

 

[scottb50]

Which is pretty much the idea I have been proposing for quite some time. It seems to be the best alternative and is pretty much what the Shuttle was intended to be to begin with indicating the basic concept has gone through a lot of anylisis already.<br /><br />The basic difference between Shuttle and a flyback wing is instead of the ET separating and crashing the First stage, containing the tanks and engines separates and returns and the Second Stage and Payload continue to orbit. <div class="Discussion_UserSignature"> </div>

 

[halman]

BarryKirk,<br /><br />Certainly, airbrorne fueling is an option, but I am not sure if it is going to make things that much easier. The reason that I say that is that the carrier wing will have to remain airborne while the tanker(s) transfer the fuel, which would take some time for fueling a vehicle to reach orbit. Also, transfering liquid oxygen is going to be a bit different than transferring JP-4. And I don't even want to think about transferring liquid hydrogen. Because of the volume requirements, as well as safety, it might be necessary to launch two tankers. In any case, transferring both propellent and oxidizer is going to be time consuming, which might offset the benefits of the concept. Or, perhaps one component could be loaded before take-off, and the other one transferred while airborne.<br /><br />I have based my proposal on the simplest, most direct method I can think of to get the orbiter to launch altitude ready to go. Because this requires building an aircraft far larger than anything which has been flown before does not, in and of itself, make the proposal unworkable, I believe. The history of aeronautics is one of overcoming negativity and skepticism, with people who are considered experts saying that something cannot be done, only to be proven wrong. Just because something has never been done before does not mean that it cannot be done.<br /><br />I am also inspired by the original proposal for a reusable space transportation system, which used a fly-back booster. The whole purpose of the system was to develop specialized vehicles for each part of the ascent to orbit, which passes through at least two different regimes, the lower atmosphere, where oxidizer is available for the taking, and air density is such that rockets are inefficient, and lift from a wing is possible, and the upper atmosphere/low Earth orbit region, where oxygen is not available (broadly speaking), and rockets operate efficiently. The concept of using a catapult to get the <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[barrykirk]

I agree that special purpose aircraft are the way to go.<br />Also, I agree that it might be easier to preload the LOX<br />and load the RP-1 and possibly the carrier jet's fuel later<br />in the flight.<br /><br />I was assuming that the point of rocket launch might be<br />many miles away from the runway. Possibly 1000's of<br />miles. The carrier aircraft doesn't have to take off with<br />all of its fuel.<br /><br />Obviously, igniting a rocket from 50,000 feet and mach<br />0.8 is going to help a lot. For one thing, the booster<br />engine can be designed for efficiency at a higher<br />altitude.<br /><br />The question is, how much of a gain is there in payload<br />to orbit, by launching from an aircraft?<br /><br />If you double your payload to orbit, then this could very<br />well be worth it.<br /><br />If you increase your payload by 1%, then it is not worth<br />it.<br /><br />I don't know what the break even point is that would<br />make air launch worthwhile and I don't know what the<br />increase in capacity from air launch is.

 

[rocketman5000]

I think the biggest advantage would be the increase in orbit options without having to build another pad facility. I am sure with proper design that cost could be reasonably managed

 

[argosy]

<< The question is, how much of a gain is there in payload<br />to orbit, by launching from an aircraft?<br /><br />If you double your payload to orbit, then this could very<br />well be worth it.<br /><br />If you increase your payload by 1%, then it is not worth<br />it.<br /><br />I don't know what the break even point is that would<br />make air launch worthwhile and I don't know what the<br />increase in capacity from air launch is. />><br /><br />To partially answer your question... I believe that some time ago I've read a article concerning the Ishim concept and launching micro and nanosats from an MiG-31, while doing more than Mach 2 and around 70 000 feet... I think the number is 30% propellant less to same orbit(for same mass)<br />Now, is it really worth it? It certainlly isn't cheap using such high performance airplanes... Around 15-20 tons of jet fuel per each flight, paying the pilots and the ground crew...<br />It sure would be fun, but would it pay off?

 

[halman]

BarryKirk,<br /><br />Maybe airborne launching is one of my obsessions, but I will say in my defense that it has been championed by people with a lot more knowledge of launch systems than me. For instance, the engineers at NASA back in the late 1960s, who were considering building a totally reusable launch system. Their concept of reusable was not parachuting into the sea, but flying back to a runway, refueling, and launching again. To make travel into space on a regular basis economical, we have to make launching a process which is easily repeatable, on a frequent basis.<br /><br />Vertical launching demands extreme performance, large numbers of people to oversee every aspect of the launch, the launching range, perfect weather, critical timing, and incredible amounts of energy. But it is the only way we can do it at the moment. Changing that requires taking risks, vision, and willingness to believe in our engineering. Airborne launching will probably never equal vertical launching in capacity to orbit, and there will probably be heavy lift launch vehicles around for many years.<br /><br />But I have to believe that the time will come when going into space will be simple, involving a small number of people, in most any weather, and routine. So I seek a system which does not involve co-ordinating tanker launches, airborne transfer of voitile liquids, and precise flying by two aircraft in extremely close proximity. So that means buildng an aircraft several times the size of anything flying today, and launching it using a catapult several miles long. I have flown in a 1929 Stearman open cockpit byplane. I have also watched a Japan Airlines 747 freighter taking off fully loaded for a non-stop flight from Seattle, Washington, to Japan. To the builders of the Stearman, the 747 would have been imcomprehensible, yet they both operate on the same principles. The difference is in the level of technology used. We have technology available to us now which far excedes wha <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>