Difference between revisions of "Rocket Engines"

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==Design Structure Matrix (DSM) Allocation==
==Design Structure Matrix (DSM) Allocation==
[[File:Liquid Rocket Engine DSM|thumb]]


==Roadmap Model Using OPM==
==Roadmap Model Using OPM==

Revision as of 23:34, 7 October 2019

Technology Roadmap Sections and Deliverables

Roadmap Overview

The primary function of rocket engines is to convert chemical energy to kinetic energy. This means that a rocket engine would be placed squarely on the cell “Transforming Energy” in our 5x5 technology matrix. There are several different styles of rocket engines that are used today (all of which meet the primary functional requirements) but the perform those functions in slightly different ways with slightly different architectures. These architectures are all determined by their fuel type and their fuel consumption method. The rocket engines we will examine here include: solid rockets, open cycle liquid fuel, closed cycle full flow liquid fuel, and nuclear. Below is a generalized OPD describing the operation of a liquid fuel rocket engine.
Generalized Liquid Fuel Engine - Copy.png
Generalized Liquid Fuel Engine Text.png

Design Structure Matrix (DSM) Allocation

Roadmap Model Using OPM

Solid Rocket Boosters

Solid rocket boosters are a comparatively simpler system. However, once ignition starts, there are no ways to stop the process. Ammonium perchlorate acts as the oxidizer, and aluminum powder acts as the fuel source.
Solid Rocket Engine.png
Examples of solid rocket boosters getting used in large quantities are the space shuttle and the lower stages of the Ariane-6 rocket.

Gas Generator Open-Cycle Engine

A gas generator open cycle engine is one of the simplest forms of liquid fueled rocket engines. In order to supply more fuel and oxidizer to the combustion chamber – which in turn increases pressure of combustion, and generally higher thrust – turbopumps are installed in the lines of the engine. The turbopumps are rotated by a small rocket engine called a preburner which is itself fueled by the same liquid fuel and oxygen. The spent preburner exhaust is directed outside of the main throat and bell as exhaust.
Gas Generator Open Cycle Engine.png
Examples of this style of rocket engine are the F-1 and the Merlin Engine.

Oxygen-rich, Closed-Cycle, Staged-Combustion Engine

An oxygen-rich, closed-cycle, staged-combustion engine is one of the more complex than open cycle gas turbine engines, but they are more efficient because they use more fuel and oxidizer in the main combustion chamber. In these engines, all oxidizer is pumped into the preburner, with some fuel. The remainder of the fuel is pumped directly to the main combustion chamber. The preburner exhaust is oxygen rich, and is pumped into the main combustion chamber where it supplies the required oxidizer for combustion.
Oxygen Rich Close Cycle Engine.png
Examples of this style of rocket engine are the RD-180 and the BE-4.

Fuel-rich, Closed-Cycle, Staged-Combustion Engine

A fuel rich dual staged combustion closed cycle is similar in concept, but much more difficult in execution to the already complex oxygen rich staged combustion closed cycle engine. In the fuel rich closed cycle engine design, all of the fuel is sent to the two preburners, and the oxidizer is sent to the preburners as well as the main combustion chamber. Super-heated, fuel-rich exhaust is then directed from the preburner to the main combustion chamber. The advantage to this setup is that it is very efficient and generally has a high thrust to weight ratio as it is quite compact in its dimensions.
Fuel Rich Dual Chamber Closed Cycle Engine.png
An example of this engine is the RS-25.

Full-flow, Closed-Cycle, Staged-Combustion Engine

A full flow staged combustion closed cycle engine takes advantages of oxidizer rich and fuel rich closed cycle designs. This design is technically the most difficult to successfully built, and only one engine has ever been flight tested with this configuration. The key differentiator is that flowing fuel and oxidizer are never directly connected to the main combustion chamber. Instead, they are all directed through turbopump assemblies. One assembly is responsible for producing an oxygen rich exhaust – which drives the oxidizer turbopump – and the other assembly produces a fuel rich exhaust – which drives the fuel turbopump.
Full Flow Staged Combustion Cycle.png
There are only three engines which have ever attempted this design, and only one has ever flown. The soviet RD-270, the Rocketdyne integrated powerhead demonstrator (never tested), and the Raptor engine, which was first flown in August 2019 for a 1 minute 150m flight demonstration.

Nuclear Engine

Nuclear propulsion is slightly different then chemical rockets, in that chemicals are not getting combusted, but rather chemical reactions are taking place. A nuclear rocket uses the expansion of liquid hydrogen to gaseous hydrogen in confined spaces to generate thrust. The heat required to generate this expansion is achieved by forcing hydrogen through a nuclear core. Nuclear rockets have significant advantages to chemical rockets in their Isp values, but the major downside is their very low thrust to weight ratios.
Nuclear Rocket Engine.png
The NERVA rocket is one of several examples that have ever been built.

Figures of Merit

Tsiolkovsky Rocket Equation (m/s)

       Δv = ve*ln(m0/mf)
  • ve = effective exhaust velocity
  • m0 = initial total mass including fuel and oxidizer
  • mf = final mass without fuel and oxidizer

Specific Impulse (s)

       Isp = ve/g0 
  • ve = average exhaust speed along the axis of the engine (either at sea level or vacuum)
  • g0 = standard gravity in m/s2

Net Thrust (N)

       Fn = M*Ve
  • M = exhaust gas mass flow
  • Ve = effective exhaust velocity

Thrust-to-weight ratio (N/kg)

       TTW = Net Thrust (N)/m (kg)
  • m = dry mass of the engine

Comparison of FOMs Across Platforms

Engine Name Engine Type Use Case Year of First Development Isp vac (s) Thrust vac (kN) Dry Mass (kg) Thrust/Weight Ratio Cost ($Million) Isp/Weight (s/kg) Thrust/Cost (kN/$) Isp/Cost (kN/$)
Raptor Full flow staged combustion closed cycle Starship 2019 330 3,297 1,700 198 1 170 3,297 330
BE-4 Oxygen rich staged combustion closed cycle New Glenn 2020 340 2,400 Unknown Unknown 8 Unknown 300 43
Merlin Gas generator open cycle Falcon 9 2007 305 981 470 213 0.75 146 1,308 407
Vinci Gas generator open cycle Ariane 6 2017 465 180 93 197 Unknown 240 Unknown Unknown
Vulcain 2 Gas generator open cycle Ariane 6 1995 431 1,140 1,800 65 Unknown 682 Unknown Unknown
P120 Solid rocket booster Ariane 6 2018 279 4,500 11,000 42 Unknown 682 Unknown Unknown
Space Shuttle SRB Solid rocket booster Space Shuttle 1975 242 12,000 91,000 13 8 1,835 1,500 30
RS-25 Fuel rich staged combustion closed cycle Space Shuttle 1980 452 2,297 3,177 73 50 630 46 9
RD-180 Oxygen rich staged combustion closed cycle Atlas V 1989 338 4,150 5,480 77 25 446 166 14
F-1 Gas expansion open cycle Saturn V 1964 304 7,770 8,391 94 30 328 259 10
NERVA Nuclear solid core Test Only 1964 850 334 18,144 2 Unknown 46,175 Unknown Unknown