Aerospike Engines - Why Aren't We Using them Now?

Ever since the earliest rockets we've seen them working with a bell-shaped engine nozzle from the first German v2 rockets right up until the spacex falcon heavy but the ubiquity of the bell shaped rocket nozzle doesn't mean to say that it's the best way to do things in fact they have a major drawback which is one of the reasons why we use multistage rockets, however since the early 1970s there has been an alternative rocket engine which has much greater efficiency and was to power the next generation of single-stage-to-orbit spacecraft to replace a space shuttle but if it's so good why hasn't even been flown yet. The engine in question is the aerospike, a design that goes back to the 1950s when it was first developed by Rocketdyne. Now whilst this might sound like an exotic new type of propulsion the aerospike is not actually a whole new engine it's actually just a different way to contain and control the thrust but any rocket be that liquid or solid fuel produces and it replaces the Bell type combustion chamber. Now if we've been using the Bell type rocket nozzle combustion chamber since the very first Rockets right up until now and what's wrong with them. For a rocket to work correctly and produce enough thrust to lift it into orbit then you have to control the burning rocket fuel. If there was no rocket nozzle then the burning rocket fuel would just expand uncontrollably in all directions and very little of it will be converted into useful thrust. What the rocket nozzle does is convert the high-pressure combustion of a rocket fuel into an ultra-high speed flow of gas exiting the nozzle in one direction and at atmospheric pressure. The ratio of the size of a narrow end to the wide end of the nozzle must also allow for the atmospheric pressure where the rocket will operate. Now this sounds complicated but it's actually quite simple. Everything including you, me the ground and rocket engines has atmospheric pressure pressing on us in all directions due to the weight of the atmosphere as the air is pulled down by the Earth's gravity. If you imagine a column of air measuring one square inch or 2.54 square centimeters from sea level to the top of the atmosphere, that air would have a mass of 6.67 kilograms or 14.7 pounds.we don't feel it because we have evolved to live at that pressure but if you were to go up to 12 kilometers that pressure would be just one-tenth of sea level and at 50 kilometers it will be one hundredth of sea level simply because the column of air is now much shorter and thus weighs much less. That air pressure also pushes on the gases exiting the rocket nozzle. For a rocket to work at its most efficient and produce the most amount of thrust the gases exiting the rocket nozzle must be at atmospheric pressure so where they exit out as straight as possible. This is fine if your rocket is traveling sideways through the atmosphere like a air to air missile then the air pressure doesn't change much. A rocket going into orbit however starts at sea level with a lot of air pressure and ends up in a vacuum with no air pressure. Because a bell nozzle has a fixed shape and size its maximum efficiency and thrust will only be achieved at one altitude. Design it to have maximum thrust at sea level and takeoff and the exhaust gases will over expand and lose thrust at high altitudes because of a lack of air pressure, design it to have maximum thrust at high altitudes and at takeoff the air pressure is so much but it constricts the gas flow inwards which leads it to separating from the nozzle wall and becoming unstable usually resulting in the engine blowing up. In an ideal rocket nozzle it would change its shape as the altitude and air pressure changes this is what an aerospike does. It uses the pressure of the air surrounding it air surrounding it to have the same to have the same effect as the bell of a traditional rocket engine. The two main types of aerospikes which have been developed are the annular or round ones and the linear or straight ones. The round ones are where we get the name from, if you imagine an inverted bell shape it becomes a round spike, this spike becomes one side of a virtual Bell whilst the air pressure surrounding it compresses the exhaust gas against the inner spike, although many now use a truncated spike which has a much shorter design than the equivalent engine bell. As the rocket goes from takeoff at high air pressure to the low air pressure at high altitudes the shape of the exhaust flow changes due to the changing air pressure to keep it at its optimum shape and optimum thrust. This is what's called an altitude compensating rocket nozzle. Although it might not be as efficient as a bell any given altitude it outperforms them at all others. The Space Shuttle main engines which were used from takeoff to space were much less efficient at sea level than they were in space. With a rocket engine like the aerospike you could use just one engine that will work efficiently from takeoff to space and avoid the need for multiple stages with different rocket engines optimized for different altitudes effectively becoming an SST o or single-stage-to-orbit. So if these are so good why aren't they used to date no major rocket launches have used an aerospike despite much research and development being done during the 1960s and 70s and then in the 1990s. As a follow-on to the successful J-2 engine which was used on the Saturn third stage Rocketdyne set about developing and building both toroidal and linear aerospikes using the turbo pumps and engine infrastructure of the J-2. one of the biggest problems with a aerospike engine is the cooling of the spike. in the toroidal or round design the spike is long and heavy which makes it difficult to cool the tip of a spike to stop it from melting. This was mostly overcome with the development of the new copper alloy called NARloy-Z in the 1970s which allowed longer use of high temperatures. The design were also changed with a truncated spike with some of the exhaust gases being passed through the center to achieve a similar result of a long spike but with much less mass. However the linear version was even more flexible. In this the round spike is straightened out into a v-shape with the combustion chambers on either side, the beauty of this design is that can be made modular so that it can have more combustion chambers added to make a longer a more powerful engine. Back in the 70s they use combustion nozzles made into small banks which were stacked side-by-side on both sides of the "V" center. Although aerospikes were proposed for the space shuttle, as the Apollo program was wound up in the early 1970s development work on the aerospikes also stopped and the space shuttle went on to use conventional Bell engine nozzle designs. Things stayed pretty much like this for the next 20 years until NASA was looking to develop the next generation of space shuttle using an all-new single-stage-to-orbit design. The design brief was to be able to come up with a completely new launch vehicle that would be fully reusable and would greatly reduce the cost of getting into space from $10,000 per pound to $1,000 per pound. Lockheed Martin won the contract to build the revolutionary design designated the X-33 and one of the key features was the use of the linear aerospike engines. Development work continued on the XRS- 2200 linear aerospike and by now with the use of electricmagnetic nozzles it meant that the fuel system could be controlled on a nozzle by nozzle basis a bit like the fuel injection on a car. This allowed for much greater throttling control and allowed for the thrust vectoring by turning off different sections of the engine. This also removed the need to have heavy complex engine gimbals. Work progressed well up until 2001 when due to issues with the X-33's composite fuel tank and cost overruns the project was cancelled again taking the aerospike engines with it. Progress has been made with NASA testing small scale solid rockets with a toroidal full-length aerospike in 2004 but since then there have been no large aerospike engine developments. So why don't new companies like SpaceX and Blue Origin use the aerospike engines with all the efficiencies they bring wouldn't they be the perfect match for a low-cost route to space. As far as we know SpaceX has looked at using aerospikes but given the fact that no large-scale aerospike has ever been flight tested it would be a very big risk when you're looking to set up a commercial orbital space company. One of the driving principles of the space race was "To do the job good enough and no more", basically mainly that once you have developed your spacecraft or your rocket engine to do what it was designed to do then that's it you stop there. The technology SpaceX and others are using is well known and tested. The way they use it might be different like relighting the main angels descend back to earth but the engines themselves are a known quantity. Commercial companies have to make a profit in the end and taking on a major task like developing a new untested engine design is something but could quickly sap those profits away. Although the X-33 project almost got them to flight testing, it's still new technology and needs more money and more development. It would also mean completely redesigning the Rockets away from the tried and trusted but yet limited traditional bell nozzle engines. All this takes time time which could be used launching with traditional engines and getting money into the companies. Although there would be a saving of up to 40%, the fuel is actually one of the cheapest parts of a rocket launch, Elon Musk said himself that the Falcon 9 costs $60 million to build but only $200,000 to fuel. The bringing back of the boosters and the central core with the engines brings far greater savings than could be achieved with a change to aerospike engines. It seems as though until the price of launches has been driven down to as low as conventional Bell nozzle engines will allow that arrow spikes will remain on the drawing board. The single-stage-to-orbit vehicles which perfectly compliment the aerospikes capabilities seem a long way off since the cancellation of the X-33 and the renewed interest in returning to the moon using variations of conventional engines that date back to the early 1960s. There are smaller companies like Arco space which are developing small-scale aerospike engines for single-stage-to-orbit satellite launches but unless there is a radical change in the space market only time will tell if arrow spikes will ever get used for future space vehicles. So what does it take to design a rocket engine how much thrust does it take to lift a spacecraft and how fast must we launch an object from the surface of the earth to get it to leave. You can look up the answer if you want but if you like me then you want to create things by yourself our sponsor for this video, brilliant.org is dedicated to doing just that turning you into a living breathing and most importantly calculating scientist head on over there and prove for yourself just what it takes to get a rocket into orbit. Having a strong math and science skills set is crucial because it opens up so many ways to explore the universe. To support curious droid and learn more about brilliant go to brilliant.org/curiousdriod and sign up for free. so if you're ready to launch off a planet the first 200 people will get 20% discount off of the annual premium subscription

Channel: Curious Droid

Views: 2,956,620

Rating: 4.8940973 out of 5

Keywords: aerospike engine, aerospike engine test, aerospike rocket engine, aerospike nozzle, aerospike rocket, nasa, x-33 space plane, x-33 venturestar, rocketdyne, j-2 engine, lockheed martin, paul shillito, paul shillito curious droid, curious droid, curious-droid.com, apollo, rocket nozzle, rocket nozzle design, rocket engine bell, aerospike nozzle solid rocket, aerospike nozzle solid rocket motor, aerospike rocket nozzle, aerospike nozzle test, aerospike nozzle working

Id: K4zFefh5T-8

Length: 13min 38sec (818 seconds)

Published: Sun May 27 2018

Reddit Comments

[u/DaBlueCaboose]

At work so I can't watch the video but from what I remember from Launch Vehicle Design aerospikes are prohibitively expensive if they're gonna get dumped in the ocean like most rocket engines, and wouldn't really be as useful since their main strength is optimal thrust at all ambient pressures, and they'd get dumped 1/3 of the way through.

Aerospikes on a new Space Shuttle would make a whole lotta sense, but we're done doing spaceplanes so I'm not sure when they'll really come back into vogue.

[u/AresV92]

Aerospikes are expensive and heavy. If you put an aerospike on a rocket you save some fuel efficiency. You could just put a few stages with differently optimized nozzles and save a whole lot of money and weight. Aerospikes make sense if you plan to fly the engine repeatedly through atmospheres at wildly different pressures and you are unable to add more stages. Even the engineers of BFR opted to go with a stage and differently optimized nozzles even though the BFS looks like it could benefit from an aerospike on paper. This leads me to believe they did the math and found it was not the right choice.

[u/TheNewBlue]

I would be a regular viewer of a Lord Varys hosted science show.

[u/Decronym]

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
AR	Area Ratio (between rocket engine nozzle and bell)
	Aerojet Rocketdyne
	Augmented Reality real-time processing
AR-1	AR's RP-1/LOX engine proposed to replace RD-180
ASAP	Aerospace Safety Advisory Panel, NASA
	Arianespace System for Auxiliary Payloads
BE-4	Blue Engine 4 methalox rocket engine, developed by Blue Origin (2018), 2400kN
BFB	Big Falcon Booster (see BFR)
BFG	Big Falcon Grasshopper ("Locust"), BFS test article
BFR	Big Falcon Rocket (2018 rebiggened edition)
	Yes, the F stands for something else; no, you're not the first to notice
BFS	Big Falcon Spaceship (see BFR)
COPV	Composite Overwrapped Pressure Vessel
ESA	European Space Agency
FAA	Federal Aviation Administration
GEO	Geostationary Earth Orbit (35786km)
GNC	Guidance/Navigation/Control
ICBM	Intercontinental Ballistic Missile
ITS	Interplanetary Transport System (2016 oversized edition) (see MCT)
	Integrated Truss Structure
Isp	Specific impulse (as explained by Scott Manley on YouTube)
KSP	Kerbal Space Program, the rocketry simulator
LEO	Low Earth Orbit (180-2000km)
	Law Enforcement Officer (most often mentioned during transport operations)
LES	Launch Escape System
LH2	Liquid Hydrogen
LOX	Liquid Oxygen
MBA	Moonba- Mars Base Alpha
MCT	Mars Colonial Transporter (see ITS)
MFR	Medium Fu- Falcon Rocket (Falcon 9/Heavy), contrast BFR
	Manipulator Foot Restraint, support equipment for Hubble servicing
NERVA	Nuclear Engine for Rocket Vehicle Application (proposed engine design)
NTR	Nuclear Thermal Rocket
OTV	Orbital Test Vehicle
RD-180	RD-series Russian-built rocket engine, used in the Atlas V first stage
REL	Reaction Engines Limited, England
RLV	Reusable Launch Vehicle
RP-1	Rocket Propellant 1 (enhanced kerosene)
RTLS	Return to Launch Site
SABRE	Synergistic Air-Breathing Rocket Engine, hybrid design by REL
SECO	Second-stage Engine Cut-Off
SLS	Space Launch System heavy-lift
	Selective Laser Sintering, contrast DMLS
SSME	Space Shuttle Main Engine
SSTO	Single Stage to Orbit
	Supersynchronous Transfer Orbit
STS	Space Transportation System (Shuttle)
TSTO	Two Stage To Orbit rocket
TWR	Thrust-to-Weight Ratio
ULA	United Launch Alliance (Lockheed/Boeing joint venture)
VTOL	Vertical Take-Off and Landing

Jargon	Definition
EMdrive	Prototype-stage reactionless propulsion drive, using an asymmetrical resonant chamber and microwaves
Starlink	SpaceX's world-wide satellite broadband constellation
apogee	Highest point in an elliptical orbit around Earth (when the orbiter is slowest)
deep throttling	Operating an engine at much lower thrust than normal
hydrolox	Portmanteau: liquid hydrogen/liquid oxygen mixture
iron waffle	Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large; also, "grid fin"
kerolox	Portmanteau: kerosene/liquid oxygen mixture
methalox	Portmanteau: methane/liquid oxygen mixture
monopropellant	Rocket propellant that requires no oxidizer (eg. hydrazine)
quess	Portmanteau: Qualified Guess (common parlance: "estimate")
retropropulsion	Thrust in the opposite direction to current motion, reducing speed
tripropellant	Rocket propellant in three parts (eg. lithium/hydrogen/fluorine)
turbopump	High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust

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[u/wolfe1947]

Did most people commenting even watched the video?

[u/Rock3tman_]

Already a lot of good comments on "why not" but I figured I'd share my two cents:

Like pointed out above, aerospikes are too expensive to realistically be considered on expendable rockets, which makes them more useful on reusable rockets because theoretically most of that high cost will be recouped. However, the reason an aerospike isn't a "must have" for reusable rockets is because they come with other disadvantages:

• Mass. Aerospikes, especially the linear variety seen in the VentureStar video, carry a significant dry mass penalty

• Complexity. Space launch is hard no matter what, but de Laval nozzles are much easier to manufacture than the innards of the Aerospike.

• Thrust vectoring on an aerospike engine is more complicated than normal nozzles and may require differential thrust

So the design trades for a rocket that never loses its efficiency are pretty substantial, and that leads the aerospike to be viable in really only one application: SSTO rockets. And I think the illustration above shows perfectly why SSTO is a flawed idea to begin with. Hear me out.

SSTO is cool in concept. No staging events, just launch, land and reuse like an airplane. But to get there with any significant payload is much harder, and always takes a "hack" of the Tsiolkovsky rocket equation. This isn't Kerbal where the solar system is 10x smaller. To attain SSTO you have to worry about ballooning design complexity, and don't forget that your payload mass to orbit in an SSTO will be pitiful. Even if you can launch, land, recover, and relaunch in, say, a day, you'll have to field many many missions to get anything of significance to orbit.

A two stage reusable launch vehicle like SpaceX's BFR is far better and more practical than an SSTO ever will be. By adding one more stage to your SSTO, the payload you get to orbit scales up by perhaps an order of magnitude and allows for far more flexibility in your missions. The addition of your lower stage need not increase ground processing time either: Design your connections between the tow stages to easily mate and you can easily process a vehicle as fast as an SSTO. Not to mention you don't have to rely on ultra-complex technologies like aerospikes, air augmented rockets, or tripropellant engines. And just for clarification: I'm not saying here that SpaceX is the only way to do rapidly reusable rockets. Two stage fully reusable rockets could be two spaceplanes stacked on top of each other, or other combinations of stages that are brand new. Point is, stop fixating on SSTO because it's really hard and the trades are enormous.

[u/[deleted]]

[removed]

[u/not-a-fox]

Anyone else notice he said 1 sq inch = 2.54 sq cm?

I believe bad things happen to spaceships when you mix up imperial and metric units ...

[u/therealgurneyhalleck]

If the space program was allowed the same blank check policy as the "defense" industry, we'd have a practical space plane by now.