Why Don’t They Launch Rockets From Aircraft?

Air launching is perhaps one of the most tantalizing concepts for launch vehicles. Use an aircraft while in the atmosphere so we use the atmosphere to our advantage to lift and accelerate a rocket and then just start the rocket in the upper atmosphere while already at a high velocity!
It honestly feels like a no-brainer. So why don’t we see more companies pursuing this? Or for that matter, why are pretty much all the programs that utilized air launch for orbital rockets no longer in existence?
00:00 - Intro
01:39 - Prerequisite
02:15 - Pros Of Air Launching
06:05 - Cons Of Air Launching
20:05 - Summary
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[@EverydayAstronaut]

There is an error in the graphic with the 747 which accidentally still shows the weight in pounds as 172,000 pounds instead of the 904,000 pounds its supposed to be. 410,000 KG is correct though. It was accidentally carried over from the previous graphic from the 737.

[@eamonia]

Fool!

[@112313]

Maybe just use SI units...instead of imperial...

[@YodaWhat]

@@112313 - But then the many 'Muricans who can't tell Treason from Reason might not understand. 😕

[@YodaWhat]

Tim - All very interesting, but when are you coming out with the video you previously mentioned, on maglev-assisted launch? @EverydayAstronaut

[@kaiariarti3789]

they do....

[@NuisanceMan]

17:01 "Liftoff! Disregard." A classic line.

[@Point_Particle]

This was my senior design project in the last semester of my aerospace engineering undergrad. We were tasked with designing an air-to-orbit rocket that would be launched from a modified U-2 (which we reverse-engineered the previous semester) carrying a payload to low Earth orbit. We were given full control over the parameters of the rocket, launch altitude, launch site and direction, with a focus on comparing how beneficial altitude delta was to the performance gains of launching at higher initial velocities. Our team was split into various disciplines (Performance, Aerodynamics, Structures, Controls, etc.) so we all had to work in tandem, cross-sharing data. Performance was my area. I used data and telemetry from other existing vehicles, like Orbital ATK's Pegasus, to validate my results. In the end, we established that air-launching definitely allowed for a performance gain, but the gains were obviously not linear with increasing altitude. There's a point where flying higher and higher wasn't really worthwhile. More importantly, though, we learned that initial velocity is where the true performance gains were at. Launch a rocket from a hypersonic platform and altitude is almost irrelevant. Now spend the next hour destroying your brain cells on all the reasons that such a feat would be nearly impossible...especially if you want your rocket to carry any kind of meaningful payload into LEO. [LOL]

[@HappyBeezerStudios]

How fast was the carrier? Were you also able to adjust those parameters? What if your rocket would launch from a mach 3 jet at 25 000 m? Which basically means rebuilding the SR-71, but with payload capacity.

[@alexanderjones7196]

My condolences to your struggles...

[@dyinglight7994]

I'll bite. Why couldn't you launch it from a hypersonic platform, like one drawn by a plate using steam or another compressible gas, from zero to hypersonic in a couple of hundred meters? I'm not talking something carrying human, just incompressible building materials. I'm pretty sure you could have such a platform with very finite and realistic values of pressure, and do in the hundred's of metric tonne a launch.

[@uwuowouwu4846]

@@dyinglight7994 that would basically be firing the rocket out of a cannon, which given that there are artillery shells with electronics, it might be possible, if payload limiting?

[@spvillano]

Your closing statement was summarized by the opening with using a U-2 (modified or not). Launching an orbital lift rocket from a glider. Yeah, serious brain cell destruction for that analysis! It'd make more sense to strap wings, tanks and engines onto the rocket for early lift, then jettison the lot. With, of course, any failure in separation resulting in a mission, equipment and if present, crew loss. The closest we came to doing such a thing was two SRB's and fuel tank on the shuttle and we saw what baggage that brought along.

[@EarlHare]

I started this video like, "YEHH!?? WHY DON'T WE AIR LAUNCH??" and ended like "oh that's why" Thanks buddy, good work o7

[@Secretlyanothername]

You can tell from the time stamps. 4 minutes about the pros of air-launch, and 14 minutes about the cons.

[@garyc1384]

Yep - you were ready to swallow anything you were told to - don't attempt to understand it yourself.

[@kindlin]

@@Secretlyanothername Tho, to be fair, the pros are easy to understand, some of the cons are a bit more nuanced. Tho, double granted, most of the cons are very obvious as well.

[@john_hind]

Yea, this leaves the question 'why do people keep trying it then'? I get why some billionaire thinks it seems like a good idea, but when you do the design study and the rocket turns out to perform no better than a ground launch one, why go ahead and actually build it?

[@Metal0sopher]

Here's an idea. Why not use jet engines like a turbo boost in cars. Create two or four specially designed jet engines that independently attach to the outside of the rocket. Power the jets at launch to "essentially decrease the weight of the rocket" at take off. After reaching the right altitude the jets can then detach like boosters and parachute down, to be reused later. They would only need fuel for about 5 minutes, and if it can save 30% than it might be something.

[@heartofdawn2341]

A couple more points you missed: 1) The ability to launch from anywhere is massively hamstrung by needing to meet all of the licensing and regulations for each and every new area. Launching from a fixed pad allows the red tape to be a lot more easily handled. 2) The small launch segment is basically dead, thanks to the likes of the Transporter missions. Companies like Rocket Lab, Relativity, and Firefly all see the writing on the wall and are pivoting to medium lift, but there's just no way for Virgin to do that with an air launch system.

[@MrAwyork]

Yes. Virgin Orbit only had two places where it was cleared to launch. That was not "anywhere". Part of relocating the 747 was to get it to an available airspace. The payload would have to have been moved launch zone too. There were only two launch zones ever used. This makes the claim that money was wasted by flying the 747 to the customer is not accurate. That might have happened once. It would have been the only launch form a place other than the Mojave complex. I read the the UK launch location made it easier to get the payload to the correct inclination.

[@Vatsyayana87]

After watching from your orange flight suit days, i can still say that every single video you put out is worth getting excited about. I cant tell you how much your content is appreciated and needed, especially for people that dont just watch rocket stuff everyday.

[@CarlosAM1]

Hah, would be kinda funny if he used it once again for a short video or something.

[@Vatsyayana87]

Or on his Dear Moon flight hahaha.@@CarlosAM1

[@chrislaf89]

I was thinking it would be cool to see Tim in his spacesuit again.

[@hbh3144]

By the time Dear Moon is really a thing custom suit themes may also be a thing. That mission is all about art right :)

[@BeechSportBill]

…new ground to earth expert

[@Zeett09]

I worked on Pegasus in the 1990’s. We had a couple of stage separation issues early in the program but we solved those. Fun times.

[@lxndrlbr]

What about safety? As Tim said, this must have been nightmarish for the safety of the crew and the airframe (separation could be done over unpopulated area ofc)! I mean the insurance cost of the aircraft must have been ... astronomical! 😂

[@Zeett09]

@@lxndrlbr yeah I’m sure the failure mode analysis was a nightmare. I’d love to read it. That said those very Pegasus rocket stages are loaded into 18 wheelers and traverse our US highways posing a risk of detonation in the event of a traffic collision. Every safety scenario is evaluated. The DOT approval usually is the most difficult part of the rocket manufacturing timeline. They let that Pegasus free fall for kind of a long time before ignition. That analysis would be interesting. How far away must the rocket be such that if it detonated at ignition the pilots are safe? Would shrapnel hit the plane? Dangerous business.

[@ganeshanguruswamy7111]

What about crew dragon? They sit on top of a rocket. Everything will be risky. Again why is he comparing the 747 and the complete rocket. Compare that to the payload faring.

[@lxndrlbr]

@@ganeshanguruswamy7111 crew escape from a rocket has been well studied: a small rocket tower above the capsule or rockets embedded in or below the capsule can separate and take them away to parachute altitude. Unless you put ejector seats for the crew in the 747, I don't see them have the time and mobility to escape a disintegrated aircraft.

[@Crunch_dGH]

@@Zeett09​​⁠Out the back of C-17/C-130s on reusable steered/powered pallets?

[@johnlynch5007]

Great Video Tim. I love the way you make things easy to understand for all. So glad I was able to meet you in Austin. That was a fantastic weekend. I hope to do it again next year.

[@pauldietz1325]

One thing to add is that the Isp advantage would only be for the first stage, as later stages already operate in vacuum. And Isp is relatively unimportant on the first stage, since staging velocity is not very high. This is especially the case if you want to recover the first stage, as Falcon 9 does (and if you do propulsive landing, those engines have to operate at sea level or close to it.)

[@cube2fox]

Did he even talk about "ISP"?

[@ASAVSP]

​@@cube2foxSpecific impulse yes he did

[@Crunch_dGH]

⁠Out the back of C-17/C-130s on reusable steered/powered pallets?

[@ddopson]

@@Crunch_dGH Only if you are a Rapid Dragon missile.

[@onebronx]

Yep, for the first stage the thrust and mass flow are much more important. It would make more sense just to increase a diameter of the first stage and add more cheap engines with a relatively slow exhaust velocity and use the transom pressure excess they create more effectively.

[@ShubertReads]

Because the flamey end is pointed the wrong way! Duh

[@cmelton6796]

The Up-goer program has learned much from this concept.

[@koleoidea]

The air-fed booster engine concept at least removes sensitive biological components from the equation. To cut down on complexity from a turbine engine, just use fuel injected into aerodynamic pressure fed scramjet. They wouldn't work at launch time but you could throttle down or discard the launch engines and still get decent thrust once you are moving a few hundred m/s through the atmosphere. Appreciate it Tim. Great work as always.

[@MusikCassette]

are we talking about 3 stages before the Rocket stage? 1. turbine engine to get to the speed to start the ramjet 2. Ram jet to the speed to start the scramjet 3. scramjet

[@ehtuanK]

@@MusikCassettePerhaps it's possible develop some engine that can be used successively as a launch rocket AND ramjet AND scramjet, so you could combine those three stages into one stage before the rocket stage.

[@juliankoch9921]

Yea But you want the engine at launch time. The time when a rocket is fast enough for scram jets AND the atmosphere is thick enough might be just a few seconds

[@davegrenier1160]

Just off the top of my head, but this seems more complex and more costly (and possibly less reliable or at least unproven) compared to some strap-on solid fuel boosters.

[@juliankoch9921]

I guess that will be the answer for the whole Jet Engine idea anyway. But its interesting to think about the possibilities :D

[@samedwards6683]

Thanks so much for creating and sharing this informative and timely video. Great job. Keep it up.

[@pete3000]

Why don't they fly the booster and starship to their pads on their own power instead of moving them down the street ;D

[@josephrileyosullivan]

Cost of fuel

[@Scooterdude01]

Are you serious or delirious

[@mrandersen6872]

Because moving them down the street is cheap and effective.

[@just_archan]

​@@Scooterdude01it was a joke. Look at emote at end.

[@Scooterdude01]

@@just_archan sorry, I thought you were a Democrat.

[@AscendDynamics]

Per the Pizza Analogy... Colin Furze recently made that work quite well... we just need to get him to make an Air Launch system. Then it would work great and be a huge advantage... LOL! 🤣 Love the video Tim and how well you can make these complex concepts easy to understand. Keep up the great work!

[@AlRoderick]

This was actually also the premise of a technology startup that wanted to drive pizza kitchens around in vans. Like most technology startups, once interest rates rose above zero percent and money became expensive again, they went incredibly bankrupt.

[@benlewis4241]

I was thinking the same thing!

[@paulcarpenter999]

Great video! I remember a 1980s air launch concept drawing with a Space Shuttle Main Engine mounted in the tail of the 747 carrier aircraft, to get extra boost and trajectory. Cool in concept, prohibitive in practicality and economics.

[@ksd593]

Hi Tim, great reaserch. Looking forward to part two. Yours, everyday person.

[@JohnboyCollins]

Variable geometry intake and nozzle would probably be my big gamble. One engine that transitions from ram jet, to scram jet, to pure rocket. Awesome video.

[@MichaelWinter-ss6lx]

Variable nozzle = _aero-spike_

[@JohnboyCollins]

@@MichaelWinter-ss6lx Well just enough to optimize pressure. Basically make a simplified version of John Bucknell's NTTR rocket. Something like the SABRE engine is probably the most promising truly "next gen" launch tech.

[@bricefleckenstein9666]

Much easier said then done. The SR-71 used that concept to a serious degree - and had a lot of issues with the engines "flaming out".

[@hypertectonics7009]

With a variable geometry flying wing. Just to make things extra hard. Would be cool, but insane.

[@JohnboyCollins]

@@hypertectonics7009 F35 can change it's nozzle orientation by over 90 degrees... Variable intake goes all the way back to the MiG-21 from the 50s.

[@danoosterhous4933]

Tim, thanks for putting out this video, always have loved your features, learned so much from you!

[@TomUlcak]

Finally, you're back. Haven't been watching your videos (won't go into why), but, keep this up and I'll keep coming back.

[@AdamTizzdall]

Awesome Classic EDA video, Thanks Tim and Team

[@AuthenticAfricanAdventures]

Let's goooo! Another Tim deep-dive. I am all here for it!

[@MattLowne]

11:59 💀

[@maniek0156]

We nerd ksp2 blundrebirss🎉😮😅

[@tylerfinch9491]

Thanks! These videos are super helpful and add context for first principles thought experiments. Lots of comparisons I was unaware of

[@dawidcham]

Tim, great that you're making 'back to the basics' content that got me hooked in the first place!

[@cyclesingsleep]

Thank you, Tim (all everyone behind the scenes)!!! These videos are fantastic - Go Team Space!!!

[@Zeyervv]

Pro’s of air launch explained in 3:50 minutes. Con’s of air launching explained in 14 minutes. Seems pretty clear why people don’t do it that much

[@callenclarke371]

Excellent content. I've been mulling this question over for years. Thank you for your detailed and cogent explanation. I think you put this issue to bed fairly handily.

[@reconstructo]

Brilliant I loved it! What you can do versus what you can do at a certain price, in certain time, at a certain success percentage, is a whole other question.

[@Jatheus]

You read my mind! Haha! I was thinking, why not make SRB style jet engines to help the first stage and ditch the aircraft altogether. I look forward to that next video!

[@MichaelWinter-ss6lx]

Solid Rocket Boosters were prohibited from human space flight; for good reasons. After the moon missions, every cutdown in budget was meat with insane security breeches. The Challenger could have simply shut down a liquid booster and separate for landing. SRBs can't be shut down, once ignited. If at all, one could use small firework crackers for a rocket chair, like in _KungFu_ _Panda_

[@Jatheus]

@@MichaelWinter-ss6lx Indeed, I have never been a fan of SRB’s, I referenced them only for the style of how they attach and function to give a kick off the ground. So… I meant replace them with liquid fueled air breathing jet engines. Banned? I know many countries will not use SRB’s for manned space flight because of the higher risks, but NASA decided once again that “it’ll be fine”, and they made the SRB’s even larger on SLS.

[@dufkers]

Using jet engines as boosters is a cool idea and this got me thinking, but it probably is not worth it. The F135 engine on an F-35 fighter makes about 20 tons of thrust (at sea level), it weighs about 2 tons and then you would need a pod to hold it and the fuel it needs so about 3 tons in total per engine. So about 17 tons of additional thrust. Jet engines are dependant on air pressure so thrust decreases rapidly with altitude so I wonder how high the jet booster could go before it is no longer helping at all. Also a single Merlin rocket engine makes 100 tons of thrust and a rockets thrust increases as air pressure decreases. So jet boosters are probably not great.

[@jamskinner]

@MichaelWinter-ss6lx Solids are perfect but using challenger as an example is ridiculous. The problem was fixed.

[@jamskinner]

@Jatheus They aren’t dangerous. They do have drawbacks though. Cost seems to be one of them. I actually worked at ATK for a year assisting the inspectors for the boosters.

[@Digital-Dan]

Tim, you are a true national treasure/resource. Thanks for the work you put into these.

[@andrewpearse53]

International treasure too.

[@charlesvandeweghe5002]

Well done Tim. Really interesting and educational.

[@Juanito3978]

Thank you for this clear and comprehensive analysis on this very counter intuitive topic. Having often to explain it, I can now use this video as reference 👍😁

[@Spearhead-ke8kd]

This seems like a great way to develop cruise missiles under the guise of not developing weapons. But that's par for the aerospace course by now.

[@wim0104]

but more like ICBM size payloads.

[@Spearhead-ke8kd]

​@@wim0104 technically, that has already been tested. During the cold war, I know the US tested launching ICBMs out of cargo aircraft. Though the Rapid Dragon system doesn't exactly deploy ICBMs, it's still a way of air deploying long range missiles out of cargo aircraft.

[@Vatsyayana87]

How is that "par for the aerospace course by now"? Par means the average, so i can say with 100% it isnt anything close to par. But id like you to give me even a couple examples of when this was done in aerospace. 100 examples would be less then 0.0001% of aerospace, can you give me 5? Can you give me 1?

[@ShubertReads]

​@@Vatsyayana87You challenge them to give you just 1 example (I can think of a couple off the top of my head) but also say 100 examples would not be enough to meet your definition of "on par". It seems like you have already decided that any amount below 50% would not be enough. If that's the case, is asking for 1, 5 or even 100 cases disingenuous, since you already stated you won't accept those numbers? Would it be a good use of someone's time to give you examples? How many examples would you need?

[@NickFajardo]

​@@Vatsyayana87 "Once the rockets are up, who cares where they come down? That's not my department!" says Wernher von Braun

[@nowhereman1046]

The Soviet Union before it collapsed floated the MAKS system that was a mini-shuttle on a mini-external tank that in turn were mounted and carried up in altitude by the AN-225 Mirya. And speaking of SpaceX, for a few years, they worked with Stratolaunch on launching the (now cancelled) Falcon 5 from the Roc.

[@andrewpearse53]

As usual a well laid out arguement with lots of "oh, I guess so" moments. Thanks Tim.

[@danieltiema]

Thanks for another great explanation as always

[@xymaryai8283]

Scaling up sometimes does fix problems. if you had a large enough, Mach 2-4 capable vehicle that can pitch up hard enough in high atmosphere to get the space vehicle to almost the right angle, it could breakeven, but of course the scale of maintenance and operations would be delicate to keep balanced. but even with that high cost, being able to eliminate 75% of a booster's job would be worth it. also keep in mind, MaxQ at higher altitudes is far less stressful, so the structure could be lighter but honestly, i don't think it would make sense for cargo, as for a manned or mixed mission, the abort procedures get a lot more flexible when you have wings or start far from the ground

[@user-jx5cj8xh5e]

hey tim i am 12 yr old from india, bangalore i have always loved your videos and they have taught me alot, thanks for fueling me to become an aspiring astronaut

[@OhmsLoLEnforcement]

We missed you, Tim. Great video, as always!

[@frankgulla2335]

Thanks, Tim. Nice job and great illustrations and videos.

[@derekmcdonald2168]

I actually work on Pegasus! What a great video AS ALWAYS

[@derp8575]

Is your work classified and compartmentalized?

[@efulmer8675]

@@derp8575 No. The Pegasus was privately developed so it wouldn't be classified but anything rocketry related is export-controlled. Payloads are almost always the thing that's classified.

[@derp8575]

Wait a stinking moment, I asked that question to @derekmcdonald2168, not you. Allow the OP to respond or STFU. LOL!!!! You will be waiting a looooooong time, LOL!!!@@efulmer8675

[@derp8575]

Are you Derek?@@efulmer8675

[@derp8575]

My reply was deleted, so I will reply again, are you @derek? I'll wait..........@@efulmer8675

[@ecdcrew]

Your detailed yet pragmatic approach is so refreshing. These videos are bringing advanced principles to us, and you and the team deserve high praise for this content. Keep 'em coming 🎉

[@pearl3293]

I really love this format!

[@finoxb944]

Really good breakdown, keep this series going, it's interesting to know why some things don't work.

[@nonsequitor]

You just made a great argument for turning a 747 (or Antonov) into a stick plane with an H tail and mounting the rocket on top so it's fully supported pre-launch. You could fly rockets longer than the launch fuselage. The problem is people thinking too small 🙌😉

[@tristanridley1601]

I hear the humour here, but honestly this sounds like something that might resemble an eventual solution. The issues mentioned here are all hypothetically solvable, with future ideas and future materials.

[@MrCateagle]

Consider using an AN225 or equivalent for air launching.

[@spamcrud5639]

Yes. an Antonov, or H tailed 747 could have a rail down its back to fully support the vehicle and help in its deployment, as it rolled off the back. Also the rocket could be fueled and/or oxidisered (new word alert!) in air from a tanker aircraft, so Max take-off weight limits and stresses need not apply.

[@MrCateagle]

@@spamcrud5639 If you do both fuel and oxidizer by AAR, I would suggest using different methods for transferring the two. Perhaps flying boom for fuel and probe and drogue for oxidizer; you want to minimize chances for problems.

[@leptok3736]

Take say the wings from an A380, redesign the bits between the wings to turn it into a flying wing that could mate to the rocket and remove as much unneeded structure as possible. Given the slop in places like the flight profile and dropping from test equipment, it doesn't seem completely far fetched, just who wants to pay to do it.

[@phlipschnodt]

Well done, Tim. Videos like this one are why I became a Patreon sponsor a couple years ago.

[@pruephillip1338]

Well researched. Thank you. Quite enjoyed this.

[@allenhansen9093]

Awesome thanks! I was wondering about this.

[@DrEdit-ol4nc]

Love the video Tim! Buuuuuuut, I see someone didn't get the correct translation for the 747-400 at 8:43 in the video you've got the weight right for the Falcon 9 but not the 747. Just to let you know! Still love the videos.

[@user-ro1ov3bk7b]

I have always be fascinated by air launching... I always imagined a space plane that was carried by a large cargo air plane like how they once planned to use the mriya..

[@VikingTeddy]

In the end, a launcher aircraft is needlessly complicated and imo, a technological dead end. I wonder if it would be simpler to just make a semi-space plane. A rocket that takes off like an airplane, with the first stage/boosters being jet engines. After enough altitude, it would drop its wings and engines and switch to rocket propulsion. Maybe you could increase efficiency even more by using hybrid ram/scramjets.

[@chrislaf89]

@@VikingTeddy A plane capable of going suborbital on it's own, and thus becoming the entire first stage on it's own? Launching only the "upper stage."

[@MichaelWinter-ss6lx]

The SpaceShuttle2.0 was planned this way, but with _aero-spike_ engines, and of course not dropping its wings. How's it supposed to land without wings? Developement of the _aero-spikes_ lost its funding. NASA never even got into their first assignment. They're a dead weight on tax payers purse.

[@krumuvecis]

@@VikingTeddy yes, and an ion engine for the final stage

[@pplusbthrust]

@@VikingTeddy All's it takes is 💲💲 .

[@charleswolfgram6670]

Your content is as valuable as a college degree for some of which I’m great full to congeal this way. Thank you for your expertise. Value such as you share is rising the bar. Thanks

[@GarranGossage]

Great video as always. Thanks!

[@marco-jg4hi]

I'm working in a startup on a project very similar to the vehicle you put on the video cover; I think you should have focused more on systems similar to that, where the first stage is the air-carrier with its own detachable wings and air-breathing engine like the SABRE instead of the old design with an aircraft-launchpad-carrier systems.

[@peps9839]

Can you share the name of the startup?

[@skysurferuk]

Thunderbirds "Zero-X"? 🤣

[@marco-jg4hi]

@@peps9839 It’s called Rocketech Systems

[@ItimDave]

I was wondering why this wasn't a thing. Seems silly to use an off-the-shelf aircraft with all of it's mass instead of creating a custom air breathing first stage.

[@cube2fox]

Yeah the thumbnail is really misleading. Would have been a more interesting topic.

[@DanJanTube]

I remember having this idea (and thinking it was a novel approach) back in the late 90s. I sketched it out and then started doing some math and quickly realized it just doesn't pay off. Humbling experience.

[@efulmer8675]

It did actually pay off for Orbital Sciences in the 1990s and 2000s. They launched the Pegasus (across three variants) 45 times.

[@DanJanTube]

@@efulmer8675 for small payloads, to low orbits. Not useful for much else

[@CloudSpecter]

Awesome video great explanation! Thank you

[@michalhaubner2104]

Nice and clean educative video. You've improved your presenting a lot! :)

[@swag247]

Gotta say I really enjoy the topics and the simple (for non-tech guys like me) explanations that cover complex topics, well done.

[@siedliko]

What about a mile long steep hill with a launcher. They could propably speed it up to 400mph, that could save at least 20% of fuel. Maybe using a magnet train?

[@linecraftman3907]

a train/cannon is a good idea, but on the moon where there is no air resistance and low orbital velocity

[@caldodge]

Already addressed by Tim. Look for his video on "why don't they launch rockets from a mountain?" And with a first stage going about 5000 mph at MECO (typical for a Starlink launch), 400 mph represents about 1/(12.5^2) (1/156) of the total kinetic energy. So the fuel savings would be less than 1%. How are you launching it up the hill? You can't use the rocket itself with a mass driver, because rockets are largely made from non-magnetic materials (aluminum/lithium or stainless steel). So now you need a structure large enough to support the rocket, using either its own engines (like in "When Worlds Collide" or "Fireball XL-5") or some external force (like mass driver rings). And now you have all that additional structure to design and maintain ("structure is expensive, fuel is cheap" - Jerry Pournelle). That could work on the Moon (lower escape velocity, no need to use a hill), but for launching people it's useless. There's at least one guy working on launching with a hydrogen gas gun on a hillside (it would need a solid motor kick stage to get to orbital speed), but that would be good only for cargo that doesn't mind LOTS of Gs.

[@pauldietz1325]

Fuel is cheap. Liquid oxygen is extremely cheap (it's the second cheapest industrial liquid, after water). Making things complex and difficult to save really cheap propellant is not a win.

[@siedliko]

@@pauldietz1325 there is a weight limit? Would you rather take more fuel or food?

[@Soulleey]

@@caldodge your kinetic energie calculation is right but you forgot the simple rocket equation... you need much more propellant/energy to gain a bit more payload because you have to carry all the propellant as well. Thats why it is not as bad as you said.

[@anderscavallini8517]

Great video as usual! I believe the next monumental shift in getting things into orbit will be a space elevator. I did my thesis on the feasibility of a MEO space elevator and we are still a long way away from that.

[@MrAltairantares]

Really great video, thanks.

[@bmobert]

Three deep dive video suggestions: 1) the SERJ engine; 2) Black Horse, stage and a half to orbit; 3) attempts to orbit before sputnik, there were several.

[@mriguy3202]

Also, a track-and-ramp launch like the old children's TV show Fireball XL5

[@MrCateagle]

​. That goes all the way back to Sanger's Silbervogel concept.

[@MrCateagle]

Consider a combination of Black Horse with a hypersonic air-breather as a SSTO vehicle.

[@bmobert]

@@MrCateagle According to my (very crude) calculations, if Skylon used the Black Horse flight profile, it could get 30 tonnes to LEO rather than 15. So, yeah. I have. Edit.. and what's more, the original black horse paper did too. Part of the estimation was about a mach 5.5 Black Horse. They estimated that 40% of the dry-mass would be payload with a mach 5.5 airbrushing blackhorse powered by hydro-lox.

[@Thissapunyo]

What about the additional drag induced by the missing doors?

[@iandennis1]

Great documentary Tim! Very interesting

[@jiripertl821]

Thanks Tim, this is really informative. Maybe you can talk about launches from water, water platforms in some next episode.

[@olafmesschendorp147]

What about the Skylon spaceplane concept? A jetengine that turns itself into a rocket engine at higher altitudes. Single-stage-to-orbit

[@AKbamoida]

It bothers me how overlooked skylon is. Its potential is collosal.

[@thamiordragonheart8682]

maintainance cost. that engine requries a precooler that has thousands of nickle tubes pressurized with ulta-cold helium with wall thicknesses measured in micrometers, a counter rotating tip driven comperssor with a pressure ratio of 150:1, and an oxydizer system that can run equally with liquid oxygen and supercritical air (which have vastly diffrent properties even if the denisties are similar). I think it also needs a varieable throat plug nozzle, and it has the ramjets that also need maintainance. It's also size limited because it has to take off from a runway, so it can't be heavier than a 747 or C5

[@pricelessppp]

It would have tl start as a small sat launcher.​@AKbamoida

[@Joe-xq3zu]

Extremely limited payload capacity from everything I've seen. It has its niche, but it will never be a replacement for traditional rockets.

[@Soulleey]

too complex and too much dry mass... single stage to orbit is not practical with traditional propulsion methods...

[@fabrb26]

Best plan is to build the Death Star first and launch from there. Simple.

[@chrisstevens2]

The Empire approves!

[@johndoepker7126]

I got friends who are curious about space stuff and are constantly asking questions....Thanks to your "why don't we just," series.....and of course all your other episodes..... I know exactly how to answer them 🤟

[@woutdel]

amazing video! thank you so much

[@bensharpe64]

Pointy end front, flamey end back!

[@bluestraveler2980]

Space elevator.2042

[@Allan_aka_RocKITEman]

Great video, Tim...👍

[@danko6582]

Good analysis, delivered well.

[@AKTROOPER1]

20:37 I forgot that starship actually flew 😂 And also how beautiful it is

[@Hydrogenior]

When I hear the practicality argument, I can't help but be reminded of what was said about reusability before everyone was proven wrong. I am not saying that it is the same here, it might be true that airlaunching is actually not practical, but I still think we should try. There is a saying that to do what is possible you have to dare trying the impossible. This is one of the things for me aerospace engineering is about, pushing the boundaries of what is possible and daring to go further, daring to try even if everyone says it's impossible.

[@trimeta]

We did try. Or rather, Virgin Orbit tried. As Tim noted, they used the best possible carrier aircraft and built a rocket using established technologies, and ended up with something that was basically Falcon 1. There was no advantage over ground-launch in terms of performance.

[@Hydrogenior]

I disagree that Virgin Orbit was the best try we could do. A plane built for passenger transport is compromising a lot in a lot of ways. The limit due to imbalance due to the rocket being under one of the wings, the flight limitations for a better start angle, the unnecessary drag from the big useless cabin. @@trimeta

[@trimeta]

@@Hydrogenior It was the best insofar as it wasn't a massively expensive hypersonic vehicle which would cost more to develop than the rocket itself. Remember, part of the problem with Virgin Orbit is they somehow spent over a billion dollars getting to orbit, and would need to earn all that back selling flights for $12M each. Increasing the upfront cost isn't a path to success.

[@nuance9000]

​@@trimetaIt's like saying the Soviet's moon rocket was inferior to the Saturn V. Sure, you're correct, but SpaceX was influenced by both ventures

[@trimeta]

@@nuance9000 If your program is so expensive that it gets cancelled before it achieves any of its goals, I'd call that a failure, yes. That doesn't mean every element of that program was individually a failure (and so a later project could pull out just the "good parts"), but in the case of air-launch, spending hundreds of millions of dollars on a custom airplane isn't one of the "good parts."

[@wes_d]

Thanks for the video. Would like to see you do this same thought exercise for a rail launch system with track going to the ideal vertical alignment and using a rail gun concept to give the initial boost.

[@zachreyhelmberger894]

WOW!! Great stuff!

[@ntrgc89]

Really looking forward to the video about air breathing engines on a rocket. I hope Skylon gets a mention. I mean it's pretty much vaporware at this point, but it would be fun to explore the idea. Also Rapid Unscheduled Discount 😂, nice!

[@AaronSchwarz42]

Adding high performance air breathing jet engines to the rocket, as a first stage booster, in a ring that can detach & fly back for reuse sounds like a great idea!

[@chronus4421]

Good video, thank you.

[@randallcrawford1599]

Tim, you rock!

[@eamonia]

Thanks, Timbo! You da best. :)

[@keithhansen3670]

Well done, sir. Very informative. How far is that soposid space elevator away from reality?

[@nickheidersdorf2505]

I would try to fit it in a rear bay door of a large modified cargo plane so you can maximize this true size of the rocket without the air restance on the way up. Then throw some solid rocket boosters below the wings to help the plane pitch up and have the rocket drop out the rear of the plane at a better angle. And make it all remotely controlled.

[@elmofeneken4364]

Well done video.

[@seanburton5298]

Yes! I want to see that video! Using air hungry engines as launch assistance vehicles!

[@LoneStarr1979]

Great video... as more or less always 🙂 But I think there was one con missing / only scratched: You talked about the different loads the rocket has to take when air launched... but missed on the sattelite. I assume that it also adds to the complexit of the sattelite to be able to handle forces in multiple directions due to the air launch versus only in one direction via ground launch. Especially, as a sattelite does not need to handle any substantional forces once in orbit.

[@EvilTechMoments]

Good info, sometimes the way that seems the best isn’t always the best

[@jerelull9629]

Good job! I've been a proponent of air-launch since the early days of the X-prize, yet I'm coming around wth the advent of actually-reusable 1st stages.😱

[@DataSmithy]

yea, 5 to 10 years ago I was so sure air launching was a good solution that could work. Thank you for keeping our expectations realistic and in line with good engineering principles.

[@Rattiar]

Thank you for this great explanation! That said, let's use the "Why don't they just?" song from OLF! :D I know it's not your favorite, Tim, but I love, love, love that silly song. :)

[@Rattiar]

To be clear, the perfect example can be found at OLF Ep 64 at 50:20. GENIUS! :D

[@johncook538_modelwerks]

Thanks very much for explaining this in a common sense way. After I thought about it, and realized that the jet would only provide a small fraction of the final velocity needed, there's just no way an air to orbit launch can ever really work. This is a classic case of doing your homework carefully before investing, and what happens when you don't. Thanks for another great video.

[@michaelbond569]

I had a thought going through my head watching this about gutting the 747 interior, housing the rocket on the inside, and launching out of the nose by having it open and close with an exhaust exit opening in the back of the 747, but the logistics of making that work, plus the safety issues make me twitch

[@philmoore71]

brilliant... as usual

[@notheisenbear5686]

Thanks Tim

[@jlussier98]

excellent video

[@jonathanvinarskai6230]

Great video

[@Metrionz]

When you go to do Kerbal, I've found an interesting way to use jets. Vertical launch with a first stage of only J-404 Panthers (Enough to get TWR>1 with afterburners). Burn straight up, then come straight down and use retro-propulsion to land on the pad. The "flying launch pad" works in Kerbal because of its complete lack of refurbishment penalty when you Recover the full cost of the craft landing on the pad. You're only paying the price of fuel, which will be minimal and optimal using this method. And it's not even hard to do in vanilla. You get such an absurd amount of Delta V from the jets that the apogee is high enough that you can finish circularizing your orbital stage before the jet reenters the atmosphere.

[@Retro__Rocket]

Very interesting! I had always wondered if sending CubeSats or even the fairly small (260kg) Starlink Satellite into orbit via high altitude aircraft was even possible. I knew the concept was probably not even feasible just cause low orbit is still many times farther than the highest jet transport, but this really puts it in perspective. Once again another great video!

[@bobjohn-eh7cw]

Hi Tim, do you plan to do a video on SSTO's? Past and future projects?

[@Sidewinder1009oli]

This is fascinating, I did wonder what happened to all these air launch systems. I'm very glad someone tried these things, sad they failed but look forward to the future.