The document discusses the advantages of aerospike nozzles over traditional De Laval nozzles in rocket engines, particularly for single-stage-to-orbit (SSTO) vehicles. Aerospike nozzles provide consistent efficiency across varying altitudes by allowing for altitude compensation, which mitigates performance losses seen in conventional nozzles. The piece also highlights the challenges and complexities surrounding aerospike technology, including heat management, manufacturing costs, and a lack of flight experience.

1. Naveen S Yankanchi
ME Aerospace Engineering
MIT, Chennai
01
AEROSPIKE ENGINE

2. Nozzle used in the launch vehicles to produce a thrust. In modern vehicles
mostly the nozzle used is de Laval nozzle. The major drawback using the the
CD nozzle is it is fail to provide same efficiency under varying condition of
the flight. Modern rocket usually uses 2 stages one is sea level optimized and
another is vaccum optimized nozzle. Because of using 2 stages there will be
increase in weight as well as more operating cost. Solution for this is using
altitude compensating nozzle, i.e., using Aerospike nozzle. The Aerospike
nozzle provide same efficiency throught the flight under varying ambient
conditions so this makes possible to use SSTO ( single stage to orbit vehicle )
having a single Aerospike nozzle with potential of being completely
reusable.
02
INTRODUCTION

3. 03
A high efficient propulsion system is one of the key factors to realize an
advanced launching vehicle. Research and development of reusable
propulsion system characterized by lightweight, low cost and high
performance is the inevitable trend of future aerospace propulsion
technology.
Conventional bell nozzles are not suited for Single Stage To Orbit (SSTO)
missions on account of the fixed geometry which cannot compensate
performance at varying altitudes. The performance is reduced at low
altitudes due to overexpansion and at high altitudes due to under expansion
inturn reducing efficiency.

4. 04
The most popular altitude-compensating rocket nozzle to date is the
aerospike nozzle, the origin of which dates back to Rocket dyne in the 1950s.
This type of nozzle was designed to allow for better overall performance
than conventional nozzle designs
Aerospike nozzle is a type of nozzle with capacity of continuous altitude
compensation. Aerospike nozzle is considered to have better performance at
off- design altitudes compared with that of the conventional bell shaped
nozzle since its plume is open to the atmosphere outside and free to adjust,
allowing the engine to operate at its optimum expansion at all altitudes.

5. 05
The aerospike nozzle comes with a uniquely designed set of combustion
chambers arranged in specific manner. Many types of aerospike engines are
seen among them are the linear type, Plug type, Annular Multi-thruster etc.
XRS-2200 linear aerospike engine Multi – thruster Aerospike Nozzle

6. 06
Plug Type Annular Aerospike Nozzle

7. 07
A linear aerospike has rows of combustion chambers that all point
onto a flatter wedge shaped ramp and has at least two sides, and the
exhaust ends up meeting each other at the tip.
Plug type (figure), the central plug is surrounded annular type of
combustion chamber through which the flow is expanded through a
series of expansion waves on the spike.
The Combustion Process takes place in an enclosed chamber similarly as
that of a Conventional bell nozzle, Initially there is a converging section
where the flow is accelerated to M=1, in the throat section.

8. 08
Then it is further accelerating in the diverging section, but this is where
it varies from the bell nozzle. The bell nozzle has a continuous geometry
of wall in the diverging section to direct the flow downwards, but in case
of a aerospike nozzle plug acts as an inner wall and the length of the
outer wall is small compared to the spike.
In an aerospike nozzle the flows in directed downwards as the ambient
pressure pushes the flow on to the inner wall i.e. the aerospike where it
expands. Initially the flow has a curvature moving downwards, but it
straightens out along with the geometry of the spike.

9. 09
As the ambient pressure reduces the same process would repeat but
a greater expansion of the gases. Due to the aerospike geometry the
exhaust would be relatively straight, unlike the bell nozzle where in
this condition under expansion takes place. This property of the
nozzle to maintain a perfectly expanded exhaust with the variation
of the ambient pressure makes it an Altitude Compensating nozzle.
The idea behind aerospikes is you allow the ambient air pressure
to actually form the walls containing the flow of the exhaust so it’s
always in nearly ideal conditions at any altitude.

10. 10
Exhaust plume pattern at different altitudes of Aerospike Nozzle

11. 11
Thrust Characteristics of Aerospike Nozzle

12. 12
Firstly, the converging diverging annular thruster section
(toroidal chamber), placed at the base of the nozzle, produce
thrust as the fuel is combusted and exhausted. Let the thrust
produced by this annular thruster be denoted by 𝐹𝑡ℎ𝑟𝑢𝑠𝑡𝑒𝑟. As
the thruster is at an angle to the normal the cosine component
(𝑐𝑜𝑠𝜃)
The Aerospike Nozzle Produces Thrust in three distinct form

13. 13
We use the bell nozzle primarily for combustion, the exhaust
gases from the nozzle lip are pressed against the centerbody of the
aerospike by the ambient. As it presses against the centerbody it
exerts a force 𝐹𝑐𝑒𝑛𝑡𝑒𝑟𝑏𝑜𝑑𝑦 onto it.

14. 14
The aerospike nozzle is so named because an "aerodynamic spike" is
created through the addition of a secondary, circulating flow aft of
the flat nozzle base. As the supersonic primary flow, consisting of
the high-pressure gases exhausted from the thrusters, expands
downstream of the base, the primary flow interacts with the
subsonic, secondary flow causing it to circulate. This low-pressure
flow then re-circulates upward to exert an additional thrust force on
the base.

15. 15
Summing up these three thrust components yields the following
relationship for the total thrust force (T) generated by an aerospike
nozzle:

16. 16
AEROSPIKE FLOWFIELD
AEROSPIKE FLOWFIELD
AEROSPIKE FLOWFIELD

17. 17
The exact nature of the exhaust flowfield behind an aerospike
nozzle is currently the subject of much research. The most notable
features of a typical aerospike nozzle flowfield are shown in more
detail below.
The primary exhaust can be seen expanding against the centerbody
and then around the corner of the base region. The interaction of this
flow with the re-circulating base bleed creates an inner shear layer.
The outer boundary of the exhaust plume is free to expand to ambient
pressure.

18. 18
Expansion waves can be seen emanating from the thruster exit
lip, and these waves reflect from the centerbody contour to the
free jet boundary. Compression waves are then reflected back
and may merge to form the envelope shock seen in the primary
exhaust.
At low altitude (high ambient pressure), the free boundary
remains close to the nozzle causing the compression waves to
reflect onto the centerbody and shear layer themselves.

19. 19
The waves impacting the centerbody increase pressure on the
surface, thereby increasing the centerbody component of thrust.
The waves impacting the shear layer, on the other hand, increase
the circulation of the base flow thereby increasing the base
component of thrust.

20. 20
Shadowgraph flow visualization of an ideal isentropic spike at
(a) low altitude and (b) high altitude conditions

21. 21
As the vehicle ascends, the pressure decreases and the free boundary
expands further and further away away from the nozzle contour, as shown
above. As it does so, the compression waves also move downstream and
eventually cease to impact on the centerbody. The pressure profile on the
contour becomes constant and no longer varies with ambient pressure.
However, the secondary flow remains under the influence of ambient
pressure for a much longer period. Only at very high altitudes do the
compression waves impact downstream of the sonic line, at which point the
base pressure becomes constant. The primary exhaust is then said to have
enclosed the wake.

22. 22
COMPARING AEROSPIKE ENGINES TO BELL ENGINES
COMPARING AEROSPIKE ENGINES TO BELL ENGINES
COMPARING AEROSPIKE ENGINES TO BELL ENGINES

23. 23
The most notable and promising aerospike was an aerospike version
of the J-2 engine that powered the second and third stage of the Saturn
V. This was called the J-2T and on paper it seemed to be a nice and
compact version of the J-2 while offering even greater vacuum
efficiency than the standard J-2. Although it hit the test stand 34 times
and had some promising potential, it was shelved alongside the
Saturn V and any potential upgrade path thereof once the Space
Shuttle program began. BUT it was actually considered for use as the
space shuttle main engine, but as we know, NASA went with a closed
cycle bell nozzled engine, the RS-25.

24. Rocketdyne also took spare parts from the J-2 and the simplified J-2s
rocket engines and developed a linear aerospike engine known as
the L-1 linear test bed from 1970 to 1972 and had 44 tests with 3,113
seconds of operation.
It would be almost 30 years before the concept would be dusted off
again and looked at with any serious consideration, and this time it
was for a space shuttle replacement known as Venture Star.
VENTURE STAR WAS PROPSED BY LOCKHEED MARTIN
24

25. In order to minimize risk, Lockheed Martin began the development of
a suborbital demonstration version of the Venturestar called the X-33
which was to use a smaller testbed version of the RS-2200 called the
xRS-2200.
The Venture Star was a rocket nerds ultimate dream rocket, a single
stage to orbit or SSTO, fully reusable space plane that was to utilize
linear aerospike engines called the RS-2200, that not only made it
look like the millenium Falcon, but it also promised nearly the same
payload capability to low earth orbit as the space shuttle it was
intended to replace.
25

26. It was fully operational and had accumulated 17 tests and about
1,600 seconds of test stand operation. But because of the overly
ambitious use of super-advanced carbon composite tanks, a few
other technologies that had yet to be perfected, and some
interesting politics, Lockheed Martin may have bitten off more
than they could chew. The Venturestar program and the X-33
along with the RS-2200 and xRS-2200 linear aerospike engines
were put on the shelf in 2001.
RS-2200 KING OF ROCKET ENGINE
26

27. WORKING OF AEROSPIKE ENGINE

28. 27
At sea level , the high ambient pressure pushes on the exhaust gas of
a conventional rocket engine keeping it in a straight line.
But as the altitude increases the ambient pressure decreases causing
the exhaust gas to expand that actually is disadvantage because
rather than going straight down and pushing the rocket along the
exhaust goes sideways, making the rocket engine less efficient.

29. The Aerospike doesn't have that problem the air and spike
work together creating virtual nozzle, which shape changes
as altitude increases. It is adapting to keep the efficiency
high at all altitudes.
To ensure proper flow we add pumps to power the pumps we
add a turbine which itself is powered by a gas produced inside a
gas generator. After powering the turbine, the gas flows
through the holes at the base of the spike, producing some
additional thrust.
28

30. 30
Tory Bruno, the CEO of ULA who actually worked on the X-33 and
Venturestar program has to say.
WHAT THE EXPERT SAY
WHAT THE EXPERT SAY
WHAT THE EXPERT SAY
The toughest part about the design and operation of an aerospike engine is
thermal management. A traditional AS engine is conical in shape and can
really struggle with heating as the spike tapers down. The linear AS design,
together with the strategy of truncating the taper, goes a long way to
simplifying this problem, but it is still there. However, this linear AS thermal
advantages are accomplished in exchange for having to use many smaller
engines arrayed in two lines, which adds significant complexity over a single
(larger) engine conical (sometimes called “toroidal”) configuration.

31. 31
Elon Musk why he hasn’t opted to use an aerospike engine for
anything at SpaceX and here’s what he said. Elon’s biggest focus is on
combustion efficiency. It seems like he’s focusing and his engineering
team’s work on combustions efficiency over the advantage of an
altitude compensating nozzle.
The next technology issue is the management of the flow field across
and around the truncated end. We usually want to flow some gas
through the truncated surface to keep it organized and not be
disruptive of the flow along the termination of the ramps, while also
collecting a little additional thrust at higher altitudes.”

32. 32
Peter Beck, the CEO and co-founder of Rocket Lab. Not only has Peter
built aerospikes himself, but he has a great view of why a company
like Rocket Lab hasn’t pursued them.
They are attractive for all the right physics reasons but a pain
for all engineering reasons and it is kind a cancels it's out.
And the mess and complexity you end up designing into them is
too high.

33. 33
VECTOR AEROSPACE
VECTOR AEROSPACE
VECTOR AEROSPACE
But perhaps the best summary of the aerospike comes from Vector
Aerospace who worked on several aerospike engines, including one of
their first engines in April 2002 which was test fired in front of Elon
Musk and Tom Mueller of SpaceX.
The engine unfortunately only lasted 200 milliseconds before it
blew the graphite plug right off the injector face. But this wasn’t
their last attempt. They continued to pursue different aerospikes
including a 10 chamber, 1,300 lbf thrust aerospike engine which
also, unfortunately, failed on it’s 2009 flight test.

34. 34
In 2016, Vector released this statement, which I think summarizes
aerospikes perfectly “While aerospike engines can provide performance
advantages, the larger number of parts and components means that they
are usually heavier than their regular bell-nozzle counterparts in terms of
thrust-to-weight and, more importantly, require very high component
reliability.”

35. 35
COMPANIES ARE CURRENTLY WORKING ON AEROSPIKES
COMPANIES ARE CURRENTLY WORKING ON AEROSPIKES
COMPANIES ARE CURRENTLY WORKING ON AEROSPIKES
ARCA has a pretty intriguing video series called “Flight of the
Aerospike” and they are promising to make a low cost and simple
SSTO aerospike rocket.
The other company currently working on an aerospike is RocketStar
who is pursuing an aerospike, but so far their engines seem to only be
in the high powered model rocket category, although they do have
plans for a Starlord rocket which would use an aerospike.

36. 36
SMALLER NOZZLE
SMALLER NOZZLE
SMALLER NOZZLE
Aerospike Nozzles are substantially shorter than CD nozzles figure. This results
in a lot of weight savings which is essential when sending payloads, reduces
vehicle length and vehicle inert mass.
SIZE COMPARISON OF A BELL
SIZE COMPARISON OF A BELL
SIZE COMPARISON OF A BELL
AND A PLUG NOZZLE
AND A PLUG NOZZLE
AND A PLUG NOZZLE
ADVANTAGES OF AEROSPIKE NOZZLE
ADVANTAGES OF AEROSPIKE NOZZLE
ADVANTAGES OF AEROSPIKE NOZZLE

37. 37
THRUST VECTORING
THRUST VECTORING
THRUST VECTORING
Because the combustion chambers can be controlled individually, the vehicle
can be maneuvered using differential thrust vectoring. This eliminates the
need for the heavy gimbals and actuators used to vary the direction of
traditional nozzles.
AEROSPIKE THRUST VECTORING CONTROL [FROM ROCKETDYNE, 1999]
AEROSPIKE THRUST VECTORING CONTROL [FROM ROCKETDYNE, 1999]
AEROSPIKE THRUST VECTORING CONTROL [FROM ROCKETDYNE, 1999]

38. 38
The figure shows the proposed experimental SLV (Space Launch Vehicle) X-33 ,
as shown the aerospike is positioned inside the base portion of the SLV which
reduces a type of drag known as base drag.
LOWER VEHICLE DRAG
LOWER VEHICLE DRAG
LOWER VEHICLE DRAG
AEROSPIKE NOZZLES INSTALLED
AEROSPIKE NOZZLES INSTALLED
AEROSPIKE NOZZLES INSTALLED
ON X-33[ROCKETDYNE, 1999]
ON X-33[ROCKETDYNE, 1999]
ON X-33[ROCKETDYNE, 1999]

39. 39
LOWER FAILURE RISK
LOWER FAILURE RISK
LOWER FAILURE RISK
The aerospike nozzle being comparatively small uses a simple gas generator cycle having a
lower chamber pressure than a conventional CD nozzle, thus reducing the risk of a failure.
Although this also means reduction in performance which is again compensated by the high
expansion ratio.

40. 40
HEATING OF THE SPIKE
HEATING OF THE SPIKE
HEATING OF THE SPIKE
DISADVANTAGES OF AEROSPIKE NOZZLE
DISADVANTAGES OF AEROSPIKE NOZZLE
DISADVANTAGES OF AEROSPIKE NOZZLE
The working of the aerospike majorly involves the exhaust plume
being pushed against the spike, this results in the heating of the
spike, to an extent which cannot be easily cooled by the conventional
methods (passing cryogenic fuel about the geometry of the nozzle in
case of F-1 engines). Hence the aerospike needs to be truncated
which reduces its performance.

41. 41
FLIGHT EXPERIENCE
FLIGHT EXPERIENCE
FLIGHT EXPERIENCE
MANUFACTURING
MANUFACTURING
MANUFACTURING
The aerospike is more complex and difficult to manufacture than
the bell nozzle. As a result, it is more costly.
The aerospike only has achieved ground tests, and never flown on the
actual flight. This lack of flight experience is a major disadvantage, as
this design has potential.

42. 42
There’s two pretty promising ideas or technologies that might
actually help aerospikes find their place on the bottom end of an
orbital rocket. The first being 3D printing.
FUTURE AEROSPIKE PROSPECTS
FUTURE AEROSPIKE PROSPECTS
FUTURE AEROSPIKE PROSPECTS
3D printing allows for advanced designs that can help make cooling
channels and combustion chamber shapes, that would normally be
physically impossible to manufacture. There are companies like
Amaero who have built additively manufactured aerospikes out of
Hasteloy X which is a high strength nickel based superalloy.

43. 43

44. 44
The other concept, that very well might work hand in hand with 3D
printing is a dual expander cycle aerospike engine and one in
particular is known as the Dual Expander Aerospike Nozzle or
DEAN.
The cool about DEAN is it takes the biggest problem of
aerospikes, which is heat, and makes use of it in the expander
cycle.

45. 45
DEAN CONICAL AEROSPIKE CONTOUR
DEAN CONICAL AEROSPIKE CONTOUR
DEAN CONICAL AEROSPIKE CONTOUR

46. 46
But to date, the DEAN concept has only existed in theoretical
papers which targets an engine with 111 kN, 383s of impulse in a
vacuum and a TWR ratio of 108, which should note these
specific impulse and TWR numbers would put it on par with
the Raptor engine.

47. THANK YOU