Review of the (TECHNICALLY DONE) Aerospike Engine video

I blew it and hit the return button on this old laptop, let me continue. With a traditional 2 stage rocket, you put one rocket on the top of the other. Obviously the vacuum rated nozzle goes on the upper stage. The problem with this is that the rocket on the upper stage is dead weight for the first couple of minutes of acceleration. It is advantageous to stick the flamey end out the bottom of the rocket, along with all the sea level rated engines and let it carry the second stage weight and its own weight up to the point where the stages separate. Obviously the booster must wrap around the second stage to do this and imparts a drag disadvantage, but in the case of the Falcon nine, not really. When the falcon 9 lifts a satellite to orbit it has a 17-foot diameter fairing which puts way more drag than a dragon capsule would plus the point where the fairing necks down to the 12-foot diameter second stage body there is a massive drag penalty being applied. To keep the same internal volume for fuel and payload the outer diameter would only need to be about 21.5 feet as opposed to the 17 foot with neck down the drag penalty is practically the same. This would allow a much smaller fairing atop the entire structure which ould open to eject the second stage fully fueled rocker and the merlin vac engine. Granted there would have to be a hose and disconnect to detach it from the booster fuel supply and an electrical buss but those are not difficult engineering challenges. This configuration then allows the same number of merlins powering the vehicle at sea level, and the same number powering the second stage, but the total number of engines is 9 instead of 9 plus 1 on the second stage. Thus the payload would be improved by the weight of the 10th engine, the weight of the fuselage as the entire structure would be shorter, and the fairing would not be needed at all so another several thousand pounds of advantage. That is why you would want to fire a vacuum engine at sea level. Now as to how to do it, by putting the vacuum engine in the center of eight sea-level engines and positioning them around the vacuum bell the fast-flowing exhaust of those engines would decrease the air pressure trying to force against the side of the vacuum bell. (Bernoulli principle of fast-moving gas being a lower air pressure than a slow-moving one) thus in principle, you could avoid the damage caused by flow separation and ice buildup in the vacuum bell. (I know it sounds dumb, but it is a real issue, ice in a rocket nozzle who woulda thunk?) But there you have my answer to your question about why you would want to run a vacuum engine at sea level.

Hi Tim, at the end of the aerospike video you asked a question about why you would want to operate a vacuum rated bell nozzle at sea level. I will do you one better, first I will show you why, then I will show you how I think it can be done and should be done.

Hi Tim, here is why temperatures do not ADD. When combining two fluids of differing temperatures, the resulting mixture will have a temperature between the two. That is the temperatures do not add, but instead average. Sort of like if the bath tub water is 120F and you want to cool it down, you just add tap water of around 70 to lower the temperature. Hence the new temperature is between 70F and 120F and not 190F. If you add equal amounts of water, then the new temperature will be the average (95F). Otherwise it is the weighted average of the two (assuming same fluids, or fluids with same specific heat capacity). BTW great job on video.

Do you know if there is a significant energy loss at the two open ends of the linear aerospike that would make it less advantageous than the circular / toroidal aerospike? BTW great job!!

Do you think you have learned enough to built a rocket in your garage? You really go deep on this stuff.

I love the way you explain everything, quite fascinating really... thanks Tim for all your hard work putting these well thought out and executed videos together. Better understanding just increases our stoke!!

I would like this post but a little jealous of the hoodie thing. Kinda sad they sold out before I had a chance at one.

Just got finished watching. Excellent job, Tim! Well worth the watch!

The entire planet should be donating to these efforts

Fredrick

This is why I became a Patreon subscriber.

Great work Tim! I don’t know if it’s just me - but the sound seems slightly out of sync to the video and this is noticeable when you speak

This is literally rocket science. Will need to see this video several times until I will get it fully.

Best video I have watched this year ! Gonna have to watch it again !

Wonderful video - thanks! It makes me wonder why no one has tried harder at changing the shape / size of the bell to get better efficiency. Too hard to do, as it has to be cooled? Too much extra weight?

Big Car

There was the Falcorn Heavy... Will there be the IowaSpike Engine???

Chris B.

Tim, your work is incredible. I still can't wait for the Raptor Aerospike... Oh baby. I always thought it was one of the more innovative engines when they were working on it for X33 & Venture Star. After studying Aerospace Engineering WAY back in the day I always was fascinated by it. Congratulations on all the hard work and MAYBE someone will pick it up and prove it to Elon. ;-)

Tim, Well you've done it! It's finished-ish. :) And well worth the wait. I found the introductory information about how engine bells work very helpful in understanding the interplay between bell nozzles and aerospike. That helped frame my *very* limited aerospike "experience" (cough...cough...KSP) where since it was all virtual, the challenges that physics present are not sufficiently modeled to limit the game's aerospike performance. All in all, I found this every bit as informative as your Raptor video, and I will no longer scratch my head and wonder "Why isn't anyone flying aerospikes?!?" Thanks so much for all of your hard work and determination to make the best video possible. I think it's clear you've definitely hit your intended mark. Well done. P.S. Maybe now that this is done we can do the Midwest meet up? ;-)

Bill & Robin Korb (QISC)

Can someone explain me what exactly is the problem of cooling if we use highest melting point alloy?

Really nice video Tim! Two questions: Why do you say that using higher temperature materials for the linear Aerospike will reduce performance? You can use alloy for the Aerospike with melting temp 600 degrees higher than your methalox combustion temperature and not need cooling at all. Combustion temperature being the highest temperature of any part of the engine. Use of staged rockets is more efficient use of energy but if you always get to use SSTO you don't need to build a first stage for every planet with similar gravity well you visit. Just produce more fuel in space. I guess producing more fuel is easier than building first stage for every bigger planet u visit, right?

Can't believe I watched it all :) Didn't feel like an hour long video at all.

At sea level, the ambient air keeps the exhaust tight against the nozzle. In a vacuum, the fact is ANY nozzle (AS or not) would bleed out all edges, so at least having the chambers pointing inwards and having most of their flow directed along the spike, is the same as a vacuum optimized bell.

Everyday Astronaut

You warned us that it was long, but every moment seems relevant and of value. (possible exception being your talking about being confused about mixing gasses of different temperatures. They always meet somewhere in the middle. :-) Perhaps someone in your audience would benefit from that too. ) I'd say you are condition green with this video. :-) ...most thourogh aerospike YouTube presentation out there and you made it. :-) ...definitely not for the sleep deprived but excellent. Sometimes a project just has a natural size and that size deviates from your initial expectations, but it is best to let the project guide the process for excellence when practical. :-)

@34:29 ya cut yaself off before finishing "tubes"

TBthegr81

Awesome stuff! Great to be a patron today! I was too much into the video to notice much. Only thing that hit me, just as it did in the Raptor video, was the kilometers per liter analogy since that's not what we use here in Europe. It's actually 100km/L, so how many liters you use within 100 kilometers. BUT your analogy is perfectly valid, although might hit some non-US ears. But the video was so good that no one will remember such a thing in the end. I've watched Raptor video several times, and I think this will also get couple of view from me!

Mikko

Time-stamps are always appreciated. Keep up the good work. I hope you get enough support to afford to hire an assistant (or several someday) I grew up with the space race near White Sands Missile Range. Yes, that was exciting, and your channel has brought back that excitement for me and so much more! I think this is just the beginning of Everyday Astronaut. The sky's the limit, oh wait, it's not! Think big.

Great video! Not too long at all - to my taste ;-) Summary summing up the balancing of the different aspects, I think one of the most complex ones is cooling. Almost everything about making rocket engines work is about cooling. And this is where the aero spike engine have it's biggest challenge. Edit: UPS, sorry, I guess this is a (minor) script change.

Jens Krabbe

Oh yes, an even longer video! (Not sarcasm)

OR, when more technical terms or acronyms show up, write down the meaning over the video, whoever needs to will stop for a moment and get the info when they need it

MrElizondo

Him too 😂

MrElizondo

Phew - My brain hurts ! So much info in a sold chunk. Good Job EA. Very Well Done. Thanks...

That video really turned out great! I just noticed a few very minor things: At 2:23 there is an artifact when the video scrolls through the document. In your room in the upper left corner the lamp looks a little weird (looks like a blown out highlight that was pulled down and some artifacts). At 28:04 there is a black spot in the graphic that doesn't seem to belong there. And at 30:26 there is a reflection of a person moving in the glass in front of the aerospike which distracts a little.

Yes, but that relates to a classical nozzle, not an AS. After the AS burner spits out the gases there is only half a nozzle that can do the conversion from pressure to velocity. Why doesn't the gases expand outwards as it would have done without a classical nozzle at the same pressure? I realize they 'direct' the AS nozzles inward, but is that all it takes?

Bernoulli Equation and how it relates to the flow in the divergent portion of our nozzle. Here it is: Absent other factors, when fluid is accelerated, its pressure drops. You can think of this in terms of energy. Pressure is like stored energy, as in electrical energy in a battery. Velocity is active energy, as in electrical energy spinning a fan. Absent any other input or output, when you show more active energy (velocity), you then have less stored energy (pressure).

Not sure if I missed something, but why doesn't the exhaust from the AS nozzle spread out in all directions? Isn't it very high pressure right after the waist?

But I think it would be advantageous to start of, after the intro, with explaining some of the most common names and short words used in the video. I'm not sure that the average person will be able to decipher what an SSTO is for example. Just mention a few of them, and that would probably make the most of the video more clear to the viewer.

AkeBjorn

I loved this video, it's always great to see how involved you get into a project and how much fun you have presenting your learnings to us.

AkeBjorn

I would need to watch numerous times to fully understand things to offer any technical feedback, which would be too late anyway. Nothing jumped out at me, and it usually does. Very WELL DONE! As an Engineer it's all about optimizing tradeoffs, while being cool, the areospike engines with today's technology just don't offer enough benefits to offset the engineering cost. Maybe some day when when material science produces substances close to Unobtainium.

Go for launch. Put it away for a day or two and watch again. Good for many different levels of knowledge, including mine. Thanks!!

Aerospike Engines are like your vids! Cool, interesting, technical, and worth waiting for! Great work!

Brell Persovin

I was only able to watch the first half on my lunch break, but so far it's great! One thing I saw is it looks like the black and white video showing flow separation is missing a source.

Andrew Luchenbach

Everything is great. If you had asked me to nit pick I would have found nothing to say still. This like your other rocket videos will be one I will watch over and over to grasp all the intricacies. Thank you for such excellent work!

Tim, You have put together an AMAZING video. I was engaged from start to finish. ❤️

I know that feeling! At least the Elon interview made perfect sense this time! lol

Steve Childs (MGSteve)

Epic it is! Watched the whole thing. I was just going to sample the first five minutes, got sucked into the massive flow of data.

Awesome vid Tim - No show stoppers as far as I can see - although perhaps the only suggestion (and I know you said its too late now), but at 22:43 when talking about temperatures adding together, a good metaphor would be adding warm water to boiling water, yes they're both hot, but the cooler water cools down the boiling water, just as the less hot air cools the hotter air. Awesome though Tim, glad to see you're 99.9% there now. :D

Steve Childs (MGSteve)

Fantastic! I've been looking forward to this for a long time.

Pål Ellingsen

Maybe a small pause at 23 second, or a lets jump in! (if possible)

Going to be epic. I will be watching in my limited addition Starman hoodie! It's out for delivery today!

Joe Rader