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Are Aerospike Engines Better Than Traditional Rocket Engines?
- twic 7y agoOh my god. I live aerospikes, and i love expander cycles, even though neither of them are actually practical, so the idea that each one might be able to solve the main problem with the other one has given me an enormous space boner.
- 2trill2spill 7y agoWhat about expander cycle engines is not practical? The RL-10 which uses an expander cycle has been used for a very long time(1962) and it's future looks bright as well[1]. [1]: https://en.wikipedia.org/wiki/RL10 https://en.wikipedia.org/wiki/RL10
- twic 7y agoAh, i was inaccurate, sorry. They are very practical - but there's been a limit to how big you can make them, based on the need to get enough surface area in contact with the exhaust to vapourise the fuel. AIUI, that's why they're great for upper stages, but haven't been used for first stages. Combining them with an aerospike might let them scale up to first-stage size.
- 2trill2spill 7y agoSorry for the late reply. I'm curious why you think an aerospike nozzle would help expander cycle engines scale up to bigger sizes?
- chipsa 7y agoExpander cycle engines are limited because you need heat to run the turbo pump. And the heat is provided by running propellant around engine to cool it off. The advantages Tim Dodd mentions for larger engines (propellant flow increases faster than surface area of the engine), are exactly the things that make expander cycle engines hit their limit: not enough area to heat up the propellant to run the pumps enough for the amount of propellant you need for the thrust you want. Aerospikes have more surface area, which means more area to cool... which is more area for the propellant to flow through to get heated up to run the engine, which means more power available to give more fuel.
- aeleos 7y agoEveryday astronaut has some of the best space content on YouTube, which is even more impressive given that he has doesn't have any kind of formal training in it. If you are into space and especially spacex I would highly recommend his channel. This video has been in the works for many months and knowing his work it is probably one of the most comprehensive works on aerospike engines outside of academia.
- theothermkn 7y ago> ... given that he has doesn't have any kind of formal training in it. As someone who does have some training in it, I can say that "best space content on YouTube" is akin to "best brain surgeon in a room full of circus clowns." He gets a lot of stuff right, don't get me wrong. But the appearance of credibility is down to enthusiasm, specialty of focus, and editing and delivery. It's fine as far as it goes, but it's infotainment. It's more important that you be entertained and feel smart than sit down and struggle with the actual application of engineering principles and achieve any kind of reliable knowledge.
- exar0815 7y agoIf you like his content, Go with Scott Manley. He has at least some formal training as he is an astrophysicist by trade. Massive knowledge and in-depth bits of info.
- gopalv 7y agoSSTO would probably more relevant to return from Mars rather than to go there in the first place - building a solid booster or building a mars recoverable one might be crazy. However, the atmospheric pressure in Mars is a lot lower than on earth, which means the same diameter scale issues don't apply.
- DuskStar 7y agoAnd the orbital velocity is also much lower, which makes talking about Mars SSTOs kind of weird in the same sense that talking about Lunar SSTOs is rather weird. (If you need a multi-stage rocket to get off of the Moon, I really want to see your mission architecture) I think Starship is intended to go SSTE (Single Stage to Earth) from Mars, for instance.
- m4rtink 7y agoYep, Starship should be definitely SSTO from Mars, Moon and likely about any non-Earth survivable (hello Venus!) landing spot in the Solar System.
- deleted 7y ago[deleted]
- tempguy9999 7y agoWhat an extraordinarily comprehensive, comprehensible and informative article. I don't think I've read anything quite like it before.
- blakes 7y agoHere's an interesting interview the author did with Elon Musk: https://www.youtube.com/watch?v=cIQ36Kt7UVg https://www.youtube.com/watch?v=cIQ36Kt7UVg Fun to see how interested Elon is with the engineering of rockets, looks like he could talk for days if he had the time.
- tgtweak 7y agoThis is such a good interview. Lots of engineer philosophy dropped here. Love his approach on thinking things are always wrong and to constantly question interfaces and standards.
- wolfram74 7y ago"All models are wrong, but some are useful" https://en.wikipedia.org/wiki/All_models_are_wrong https://en.wikipedia.org/wiki/All_models_are_wrong
- AmericanChopper 7y agoApart from climate models of course. Science is settled.
- jamiek88 7y agoRelativity is a model. Yet it is settled. Still 'wrong' though.
- AmericanChopper 7y agoSeems like a pretty creative use of the word ‘settled’.
- Retric 7y agoF = M * A is never correct. Yet, it’s simple and useful enough in most situations to be ‘settled’ and people will probably still use it in 10,000 years. Thus, demonstrating these are different qualities when it comes to models.
- avmich 7y ago> Throughout history, there have been a number of aerospikes that have made it really far in development, but to date, none have ever really flown http://www.astronautix.com/g/garveyaerospike.html http://www.astronautix.com/g/garveyaerospike.html During 2005, GSC and California State University, Long Beach (CSULB) conducted several notable small launch vehicle R&D activities through their partnership in the California Launch Vehicle Education Initiative. Using a single-chamber, liquid-propellant, annular aerospike engine concept developed by CSULB, the GSC/CSULB team validated the basic design and ignition sequence with a successful static fire test at the Reaction Research Society's Mojave Test Area (MTA) in June 2003. The team then mounted one of these 4,444-newton thrust LOX/ ethanol ablative engines onto their Prospector 2 vehicle and proceeded to conduct the first-ever powered liquid-propellant aerospike flight test at the MTA in September 2003. In response to several issues observed during that flight, modifications were made to the engine fabrication process. Another flight test with the Prospector 4 vehicle followed in December 2003. Performance was entirely nominal, resulting in complete recovery of the vehicle and key trajectory data.
- jessriedel 7y agoWhat altitude did it reach?
- vilhelm_s 7y ago1370 meters (4,500 feet), apparently. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.7636&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544...
- jessriedel 7y agoThanks. The air pressure is about 85% of sea level pressure at that altitude. Maybe that's enough to get some data about how the engine responds, but it's nothing like a real launch, and I think it's borderline fair for Tim Dodd to say these that "none have ever really flown" in the context of orbital rocketry.
- basementcat 7y agoThe Pan-Am spaceplane in Kubrick's 2001: A Space Odyssey featured an aerospike.
- theothermkn 7y agoIt is a pet peeve of mine that people call all spike engines "aerospikes." An aerospike engine has a truncated physical spike that is replaced with expanding gasses. In other words, it has an aerodynamic spike, or aerospike. Spike engines that taper to a line (for linear engines) or a point (for cylindrical engines), are just "spike engines." I know I've lost this one among popular and lay audiences. It's just way too cool to say 'aerospike.'
- foota 7y agoI was under the impression that the linear spike engines also used the mechanism of the air pressure keeping the gases in the right shape?
- theothermkn 7y agoThe issue is that an aerospike engine is a spike engine that has been truncated, with the truncated portion replaced with an aerodynamic "spike," which also eliminates base drag.
- catalogia 7y agoIs it even practically possible to have a non-truncated spike engine? If you don't truncate the spike, won't it get so thin that it'd just burn/melt off? It seems like all spike engines are truncated to at least a minimal degree. Or is the matter whether or not the truncation has aerodynamic effects? (Do any truncations not?)
- mLuby 7y agoPet peeve of mine is that you could have a missile propelled by an aerospike that also uses an aerospike to decrease drag.
- buboard 7y agoFor a TL;DR this is a good video: https://www.youtube.com/watch?v=-SGIiO1APig https://www.youtube.com/watch?v=-SGIiO1APig I remember EverydayAstronaut had a chat with Elon Musk about aerospikes recently, don't know if it was featured in the video.
- tony 7y agoAnother one https://www.youtube.com/watch?v=K4zFefh5T-8 https://www.youtube.com/watch?v=K4zFefh5T-8
- InTheArena 7y agoThis has been a labor of love for Tim - and most of the space community has been watching for this to come out. He recently had a interview with Bridensteine at NASA (who despite expectations seems to be doing a amazing job at NASA) and a geek out moment with Elon Musk. He's shifting the reporting of space news.
- orbital-decay 7y agoA spike isn't the only way to compensate for altitude, it's just the most popularized one. There are also expansion-deflection nozzles, expanding nozzles and notably removable inserts for ordinary bell nozzles, which are simple, good enough and are being used on real rockets for a long time. > But all in all, I think the best way I can summarize the Aerospike is to compare it to like the rotary engine seen on cars like the Mazda RX-7 and RX-8 and their predecessors. This is a great analogy.
- deepnotderp 7y agoThis is an excellent article. This summer I read H&H and RPE as well as reading some papers and talking to rocket engineers, and this is the best article on aerospikes at a high level that I've read.
- makerofspoons 7y agoRest in peace Lockheed VentureStar :(
- JanSolo 7y agoAmen. That thing was so close to being ready; just let down by the composite tanks. The state-of-the-art in composites has advanced so much since the 80s, I'm sure if they tried again now they'd have no problem.
- garmaine 7y agoA let down by the NASA administration who testified to Congress that there was no point to it without the composite tanks. Even though the alternative Al-Li tanks already being designed were better by every relevant engineering metric. The X-33 could have launched but the funding was pulled.
- Robotbeat 7y agoTim Dodd is super charming. He's such an antidote to common cynicism. He's approachable and passionate and humble. And cool that he interviewed literally the top 3 rocket CEOs in the US, all accomplished professionals with each having a different perspective (but having sort of a consensus on this topic).
- ryanthedev 7y agoWow. One of the best articles I have read in a while. So many great analogies, made the material extremely easy to consume. That's a rare talent.
- spectramax 7y agoI have a bit of a polarizing view about the fascination for things such as aerospike engines, wenkel car engine, etc. While I think it’s cool, what’s cooler are technologies that are optimized across many dimensions from manufacturability to cost, performance to durability, across the entire spectrum. While I understand and appreciate the author’s passion, hard work and his ability to explain things so clearly; I find the fascination, almost fetishization of outlier technologies that have been proven suboptimal for many reasons, to be unexplainable. As an engineer, I am personally fascinated by practical technologies that are simple, cost effective, manufacturable, durable, etc etc, technologies that are optimized across a wide domain to be useful... such as Traditional rocket engines and Piston IC engines to be equally “cool” if not cooler. But it’s good to learn why certain technologies don’t work and why they haven’t taken off. There is definitely something to learn from failures as much as to learn from optimal designs. Overall, I applaud the author for this amazing video.
- _iyig 7y agoAs supporting technologies improve and materials science marches on, fringe technologies can sometimes leap quite suddenly into the mainstream. For example: the Stirling-cycle engine. It was a suboptimal technology compared to steam and IC engines for nearly 200 years, until Sweden found a use for it in their Gotland-class submarines. As it turns out, subs built with free-piston Stirling engines can run even more silently than their nuclear-powered competitors: https://en.wikipedia.org/wiki/Gotland-class_submarine https://en.wikipedia.org/wiki/Gotland-class_submarine
- chipsa 7y agoNuclear powered submarines can be as quiet. They aren't typically as quiet as they could be, because they have pumps to circulate coolant around the reactor spaces, and they typically have the prop being directly driven by a turbine (through a gear train). Both of those have solutions: natural circulation, and turbo-electric drive. Natural circulation is seen on the Ohio class submarines[0], in which the heat gradient inside the reactor is enough to cause it to circulate without powering a pump to move it around. It only works well at low power, but if you're trying to make a good imitation of a hole in the water, that's enough. And it's not like the Gotland-class is any better at going fast. Turbo-electric propulsion was seen on the USS Tullibee[1]. It definitely was an advantage, in terms of making the submarine quieter. But it had a disadvantage in being heavier than the machinery required for geared drive. And the USN wants nuclear submarines. A Gotland had a pair of 75kW generators onboard for power/propulsion. A S9G reactor drives a 30MW pumpjet on a Virginia class. SSNs can go faster when necessary, and have more power available to run all their systems. [0] https://en.wikipedia.org/wiki/S8G_reactor https://en.wikipedia.org/wiki/S8G_reactor [1] https://en.wikipedia.org/wiki/USS_Tullibee_(SSN-597) https://en.wikipedia.org/wiki/USS_Tullibee_(SSN-597)
- THWars 7y agoIncredible Video!