
Are Aerospike Engines Better Than Traditional Rocket Engines? - wolfram74
http://everydayastronaut.com/aerospikes/
======
orbital-decay
A 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.

------
blakes
Here'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
This 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
"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
Apart from climate models of course. Science is settled.

~~~
inamberclad
That's why researchers should always report uncertainty bounds. On that note,
I don't think I've ever heard a researcher give a definitive answer as to what
climate change _will_ do. We can very precisely measure the change in ocean
surface temperature and acidity and come up with reasonable guesses for the
amount of CO2 added to the atmosphere every year, but the future always
involves additional uncertainty.

~~~
AmericanChopper
This simply isn’t true. Climate science has an incredibly long history of
failed predictions, with the less specific predictions being obviously more
resilient to falsification. If you care about the existence of climate change
deniers, then you should know who Competitive Enterprise Institute are, most
writing on climate change denial can be traced back to their publications. The
reason being that they have an essentially limitless supply of alarmist
predictions that have been falsified.

[https://cei.org/blog/wrong-again-50-years-failed-eco-
pocalyp...](https://cei.org/blog/wrong-again-50-years-failed-eco-pocalyptic-
predictions)

[https://cei.org/blog/manufacturing-alarm-dana-nuccitellis-
cr...](https://cei.org/blog/manufacturing-alarm-dana-nuccitellis-critique-
john-christys-climate-science-testimony)

[https://wattsupwiththat.com/2017/10/30/some-failed-
climate-p...](https://wattsupwiththat.com/2017/10/30/some-failed-climate-
predictions/)

Just look at all the other child comments, most of them immediately jumped to
the defence of supposedly irrefutable climate models. The reason climate
deniers have so much support is that climate scientists, their communicators
and their advocates have little credibility outside the true believers. If you
don’t want to take my word on it, here’s a Stanford study on this exact topic:

[https://www.sciencedaily.com/releases/2019/10/191018112145.h...](https://www.sciencedaily.com/releases/2019/10/191018112145.htm)

------
aeleos
Everyday 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
> ... 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.

~~~
mikenew
You're conflating "doing brain surgery" and "learning about how the brain
works". No one is claiming to be an aerospace engineer after watching one of
his videos.

Taking an esoteric concept and making it understandable for the masses takes
far more talent and dedication than you might think, and it's something that
experts often fail at (or don't attempt). This guy makes no false claims about
his credentials or the intended purpose of his videos, and your condescending
gatekeeping shows a real lack of understanding for what this guy is actually
doing and why it's so valuable.

~~~
theothermkn
What I'm saying is that the video contains numerous misconceptions, errors,
and dubious bits of hand-waving. _I 'm not saying that people think they're
engineers after watching. I'm saying that he is not trained as one, and that
it shows in his work._ I'm also saying that "what this guy is doing" and "why
it's so valuable" are both undermined by his lack of training.

Long ago, some cranky academic wrote on his very well-sourced and specialized
website, back when there was still that sort of thing, something like,
"Everybody said that the internet was going to let anybody say anything at
all. It turns out they were right."

I'm fine with the backlash from what you call my "gatekeeping." (I imagine
that some gates need to be kept, but I suppose that's another story.) My point
is that "the best on YouTube" is not as grand a qualification as one might
suspect, and is certainly not a guarantee of accuracy.

~~~
thatswrong0
I’d be curious about the errors and inaccuracies - I’m not trained in the
field, and to me it didn’t seem like he got into any real detail about how the
aerospike actually worked from a physics perspective other than that it did
indeed work. Seemed magical.

------
InTheArena
This 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.

------
theothermkn
It 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
I 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
The 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
Is 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?)

------
avmich
> 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
What altitude did it reach?

~~~
vilhelm_s
1370 meters (4,500 feet), apparently.

[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544...](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.7636&rep=rep1&type=pdf)

~~~
jessriedel
Thanks. 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.

~~~
avmich
I think Tim didn't know about that launch, that's why decided to add to the
discussion. Not having data is not the same as not having flown; not only the
flight has symbolic value but also, I'm sure, the flight serves as an
incentive to all participants, especially students. 1.3 km altitude for a
liquid fuel rocket is a very real launch, believe me, for amateur
participants.

~~~
jessriedel
In the context of the video, which focused on technical details, I personally
don't think the symbolic or incentive value is relevant. I'm glad you raised
the point though.

------
Robotbeat
Tim 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).

------
spectramax
I 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
As 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
Nuclear 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_\(SSN-597\))

------
basementcat
The Pan-Am spaceplane in Kubrick's _2001: A Space Odyssey_ featured an
aerospike.

------
makerofspoons
Rest in peace Lockheed VentureStar :(

~~~
JanSolo
Amen. 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
A 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.

------
gopalv
SSTO 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
And 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
Yep, Starship should be definitely SSTO from Mars, Moon and likely about any
non-Earth survivable (hello Venus!) landing spot in the Solar System.

------
deepnotderp
This 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.

------
tempguy9999
What an extraordinarily comprehensive, comprehensible and informative article.
I don't think I've read anything quite like it before.

------
ryanthedev
Wow. 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.

------
buboard
For 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
Another one
[https://www.youtube.com/watch?v=K4zFefh5T-8](https://www.youtube.com/watch?v=K4zFefh5T-8)

------
THWars
Incredible Video!

------
twic
Oh 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
What 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
Ah, 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
Sorry for the late reply. I'm curious why you think an aerospike nozzle would
help expander cycle engines scale up to bigger sizes?

~~~
chipsa
Expander 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.

