. Launch Propulsion Systems
... Solid Rocket Propulsion & Liquid Rocket Propulsion Systems
. In-Space Propulsion Technologies
... Chemical Propulsion
. The Propulsion used by Rockets
. Why Russian rocket engines are so popular?
"The Saturn Propulsion System" of Project Apollo. Rocket Engines, 1962, NASA Marshall Space Flight Center.Credit: Jeff Quitney
Produced by the Atomic Energy Agency and NASA, this film details the Project NERVA- the Nuclear Engine for Rocket Vehicle Application. This was a joint program of the U.S. Atomic Energy Commission and NASA, managed by the Space Nuclear Propulsion Office (SNPO) at the Nuclear Rocket Development Station in Jackass Flats, Nevada U.S.A. Between 1959 and 1972, the Space Nuclear Propulsion Office oversaw 23 reactor tests.
This documentary explores the use of nuclear propulsion to complement the chemical fuels used in today's rockets. The film shows a Saturn V rocket on its launchpad, its launch and flight. Credit: PeriscopeFilm
NASA's Game Changing Development Program is developing new batteries, fuel cells and solar electric propulsion systems to move mans and machines through space. Credit: NASA X
Hybrid Rocket Propulsion Systems
A hybrid rocket is a vehicle with a rocket motor that uses propellants in two different states of matter: solid or liquid.
In its simplest form, the rocket have a pressure tank containing the liquid oxidizer, a chamber with the solid fuel, and a valve isolating them. When thethrust is desired, a suitable ignition source is introduced in the combustion chamber and the valve is opened. The liquid oxidizer flows into the chamber where it is vaporized and reacts with the solid fuel.
Traditional Hybrid propellants used are HTPB and wax. Performance can be enhanced with additives such as Aluminum particles.
In-Space Propulsion Technologies
The space propulsion begins where the launch vehicle upper stage leaves off, performing the functions of primary propulsion, reaction control, station keeping, precision pointing, and orbital maneuvering. The main engines used in space provide the primary propulsive force for orbital transfer, planetary trajectories, and extra planetary landing and ascent. The reaction control and orbital maneuvering systems provide the propulsive force for orbital maintenance, position control, station keeping, and spacecraft attitude control.
LOX Methane Reaction Control System (RCS) Testing. Credit: NASA
The Chemical Propulsion operate through chemical reactions to heat and expand a propellant (or use a fluid dynamic expansion, as in a cold gas), and so, provide thrust with a relatively low Isp.
The Liquid Storable propellants can be bipropellant or monopropellant and nay be stored for long periods of time. The nitrogen tetroxide (NTO) and monomethyl hydrazine (MMH) are the most common propellants that can be stored.
In a bipropellant system, because propellants are generally hypergolic, they can initiate instantaneously upon the contact. This is the reason why that system is widely used on large main propulsion systems making orbital insertions and maneuvers or surface descent/ascent operations.
For now, NASA needs to develop of non-toxic variants from 220 to 30,000 Newton engines to achieve high Isp, an throttle capacity, durability, and reliability performance. And, as always, can improve safety and handling efficiency for use in reaction control thrusters and orbital maneuvering.
In the monopropellant configuration, a propellant such as Hydrazine is decomposed through a catalyst bed to create a high-temperature gas for the thrust and providing a cold start capability. Generally, these systems are used by spacecrafts for their attitude and reaction control systems (RCS).
Like the bipropellant system, monopropellant needs to develop a non-toxic variant from 1 to 500 Newton for thrusters to achieve higher specific energy performance. That is, improve the safety and efficiency when used as reaction control thruster, which provide small accelerations to maintain or adjust the spacecraft attitude. The propellants could potentially also be used as spacecraft' main propulsion.
An High-Energy Propulsion system uses an oxidizer and a fuel that, together, undergo combustion to generate thrust. One of the two propellants may be a cryogenic fluid and will also require spark ignition systems. Liquid oxygen/ hydrazine (LO2/N2H4) is a propellant option that has comparable performance to liquid oxygen/methane (LO2/ LCH4). So, higher energy propellant combinations can increase rocket engine performance and increase vehicle payload mass. An example is the mix of liquid oxygen/hydrazine (LO2/N2H4) with a 340 to 350 seconds of Isp.
High-Energy Oxidizers, such as fluorinated compounds, include chlorine trifluoride (ClF3), chlorine pentafluoride (ClF5), and oxygen difluoride (OF2). These oxidizers have a long history of testing, with the most recent testing conducted in the 1980s. Stages for interceptors were created for flight testing using hydrazine/ClF5. They offer much higher energy and Isp for rocket than Earth-storable nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellants.
Fluorinated compounds can increase rocket Isp by 10 to 70 seconds. An example is fluorine/ sp hydrazine (F2/N2H4) with 360 to 370 seconds of Isp.
The new propellants (e.g., AF-M315 and LMP-103S) are examples of ionic liquids that are safer to handle and offer improved performance.
Source: NASA Technology Roadmaps TA 2: In-Space Propulsion Technologies, May 2015 Draft
Launch Propulsion Systems
Space lift to Earth orbit involves escaping the gravitational field to deliver a spacecraft for its mission in the LEO starting at about 200 miles high. The launch propulsion system’s challenge is to impart at least the orbital insertion velocity to the spacecraft in the most affordable and effective manner. To this end, it uses systems as solid, liquid, or air breathing rockets or an combination of them. Further, whatever the type used, ancillary propulsion systems are necessary to provide certain functions such as aborts and thrust vectoring.
Solid Rocket Propulsion Systems
Chemical solid and liquid rocket propulsion systems uses fuel and oxidizers in solid or liquid form.
Over the liquid systems, Solid Rocket Motors (SRMs) provide higher energy density and long-term stability and storage. But, they gives lower specific impulse (Isp), a lack of throttling on demand, an inability to shut down on command, and ground operations costs for safety issues about large solid segments.
Meanwhile, because their rapid acceleration to near maximum thrust, SRMs minimizes the volumetric size of propulsion systems, provides low inert masses and high mass fractions. Very short boost phase reduces greatly the performance requirements for thelaunch vehicles because they minimize gravity loss.
Mass fraction is the % of the rocket that is transferred into energy compared to total mass including inert mass (structures, insulation, tanks, etc.). SO, higher mass fractions lend to less energy losses with Earth’s gravity, which translates into more volumetric and gross-mass efficient vehicles.
For NASA, without SRMs and their high thrust potentials and impulse density, it would be difficult to develop an optimal solution for a heavy-lift vehicle with a capability of 130 mt or greater to LEO. This is was is required for the new Space Launch System (SLS).
Solid Rocket Motors exist in monolithic and multi-segment designs, and includes igniter, case, liner, insulation, nozzle, propellants.
The current SLS five-segment design uses the same propellant binder, Polybutadiene Acrylic Acid Acrylonitrile Prepolymer (PBAN) than the old Space Shuttle. Most other large solid rocket motors developed after the reusable solid rocket motor (RSRM) use Hydroxyl Terminated Polybutadiene (HTPB).
Solid propellants are composed of an oxidizer—usually ammonium perchlorate—a fuel like aluminum, a polymeric binder, and a rubber. The type of polymer binder used classifies composite propellants. In the case of the Shuttle SRB, PBAN was used as the binder.
An improvement in the HTPB propellant formulation have the possibility to increase the performance, the Isp, and the density of rockets. Then, reaching a Isp range of 265-300 seconds and an density > 0.68 lbm/inch3 will be game changing. Currently, the HTPB is used on smaller missiles and tactical systems.
Liquid Rocket Propulsion Systems
Liquid Rocket Engines (LRE) give generally a higher Isp and a better thrust control for throttling and restart than Solid Rockets. It is a carefully designed machine with components including gas generators or pre-burners, turbo-pumps, combustion chambers, engine controllers, and flow valves. They have three predominant variants of engine thermodynamic cycles, namely the expander cycle, the gas generator cycle, and the staged combustion engine cycle.
Even if the Staged Combustion Engine is the highest performing, the most complex and the State-Of-Art in LRE design, for any cycle, great performance, high reliability and fault tolerance are necessary attributes.
Further, LREs must be affordable through modern technologies. To reach this, NASA need to develop a U.S. version of the oxygen-rich staged combustion cycle engine, an advanced new upper stage engine and the first methane-fueled LRE. All this can ensure current and future Earth-to-orbit launch systems. Also, the availability of a fleet of modern booster and upper stage at a more affordable cost, at 25 to 50 percent lower than today costs, will enable exploration missions for many decades.
Figure: Space Launch System (SLS) Mission Planner's Guide, ESD 30000, Initial baseline, Release date: 4/12/17, NASA
The RS-25 Engine
For now, the existing SOA reusable booster engine, the RS-25D, is adapted from its prior usage as the Shuttle Orbiter Main Engine to be used as SLS RS-25 Core Stage Engine. The SLS inlet pressures for the engine pump is higher and therefore modifies the engine operations. The evolution of this engine involve modern and advanced manufacturing methods, as the 3D Printing process, for its production and provides gains per unit of cost. All this enhancement must maintain its heritage of high performance in the Isp, which is generally 450 seconds and higher.
There are primarily two conventional fuels used in modern launch vehicle boost propulsion, the Liquid Hydrogen (LH2) and the Rocket Propellant (RP)-1. Hydrogen-fueled engines are already in wide use in the launch vehicle first stage and upper stage propulsion applications, frequently in multi-engine configurations with throttling capability and thrust vector control by nozzle gimballing.
A new common upper stage will provide a single larger upper stage engine at 60,000 lbf thrust, and preclude the need for a dual-engine RL10s or quadruple RL10 configurations currently envisioned.
The Exploration Upper Stage (EUS) of the SLS is being developed to provide ascent/circularization and in-space transportation for payloads. Four RL10-C3 LOX/LH2 engines power the stage.
Potentially, the larger 290 klbf J-2X upper stage engine can support further Earth-to-orbit and beyond capability for the 130 mt' SLS Block 2 . (At the left, astronauts survey RL10 engine in test chamber at KSC)
The Methane as Propellant!
J-2X Gimbal Testing at Stennis Space Center. Credit: NASA
With an improved RS-25 production line, the SLS 70 mt Block 1 and its future versions will rely on an wide domestic supply of these expendable engines for flight usage, spares, and additional risk-reduction and improvements in ground testing campaigns.
For upper-stage engines, the J-2X and a potential future advanced upper stage engine as the RL10, the challenges will also involve manufacturing and affordability improvements in their complex precision combustion devices, with a special emphasis on materials and their respective high-area-ratio nozzles.
If a lower-cost booster system using the relatively abundant Methane (CH4) as propellant is built, a noticeable Isp advantage over Kerosene will be possible. There is interesting for a staged combustion because it will be possible to have a Isp up to 360 seconds.
Solid Rocket Fuels - 1950's US Army Documentary "Solid Punch" : The Big Picture - WDTVLIVE42. Credit: P. O'Neill
THE ROCKET: SOLID AND LIQUID PROPELLANT MOTORS. Credit: Space and Missile Systems Center Los Angeles AFB.
Animated Documentary/Explainer Video about the Amazing Saturn V RocketDyne's F-1 Engine. After having played an essential role in sending humans to the Moon, the F-1 engine Technology is being studied using Twenty-First Century analysis tools, in the context of NASA's SLS Development. Made with Modern Manufacturing Processes and technologies, the F-1 could open the Solar System to Human Exploration. Credit: Get Effect
The Space Launch System (SLS) is a launch vehicle system being developed by NASA for the next era of human exploration beyond Earth’s orbit. The vehicle will be used to send crews of up to four astronauts in an Orion spacecraft, cargo, or large robotic scientific missions to Mars, Saturn and Jupiter.
Boeing is the prime contractor for SLS. Orbital ATK will provide the solid rocket boosters (SRB), United Launch Alliance (ULA) will provide the Interim Cryogenic Propulsion Stage (ICPS), and Aerojet Rocketdyne is the provider of liquid rocket engines.
The Engines That Came From The Cold - And how The NK-33/RD-180 Came To The USA / Credit: Matthew Travis
Channel 4 Equinox Documentary explain the history of the NK-33 engines, originally developed for the Soviet N1 moon rocket. The U.S. Atlas V RD-180 generation of rocket engines is now applying this 'closed cycle' or staged combustion principle. Contains rare interviews with veterans of the early Soviet Space program: including Vasily Mishin and Boris Chertok. http://www.imdb.com/title/tt0872854/ei
Why Russian rocket engines are so popular?
Russian and American rocket engines using liquid oxygen as oxidizer and kerosene or RP-1 (some kind of kerosene) as fuel. It is clear that the specific impulse (Isp) for the Russian engines is much higher, offering a significant reduction in propellant mass. Russia Insider website https://www.russia-insider.com/en
The Propellant used by Rockets
RP-1 (Rocket Propellant-1 or Refined Petroleum-1) is a highly refined form of kerosene outwardly similar to jet fuel used as rocket fuel. RP-1 has a lower specific impulse than liquid hydrogen (LH2), but are cheaper, stable at room temperature, far denser, more powerful and has a fraction of the toxicity and carcinogenic hazards of Hydrazine.
RP-1, commonly burned with the oxidizer liquid oxygen(LOX), is a fuel in the first stage boosters of the Soyuz-FG, Zenit, Delta I-III, Atlas, Falcon 9, Antares and Tronador II rockets. It also powered the first stages of the Energia, Titan I, Saturn I
and IB, and the historic Saturn V.
Unlike the hydrogen-fueled equivalents, powered boosters are always more compact due to the order-of-magnitude higher density of the propellant. Booster stage configurationsare multi-engine and include thrust vector control by nozzle gimballing. Kerosene is hardly ever used for upper stage in the United States.
Additive Manufacturing can reduce cost & time!
One example of NASA's challenge and focus on future materials development is the manufacturing capability to replace 12 ft diameter metallic Solid Rocket Motor (SRM) case with up to a 13.4 ft diameter composite case. This latter one have to maintain high reliability for human-rating, reduce recurring hardware production costs, and increase mass fraction. This is the Additive Manufacturing (AM) concept.
In fact, AM such 3D printed or free form methods are being developed to manufacture SRM cases, domes, and joints. Currently, we use it for small-scale hardware but scale-up to booster class is required to reduce recurring hardware costs and production schedules.
Today, only 2 ft diameter cases have been printed but larger ones could be fabricated using free form electron beam fabrication. The technology challenge is the scale-up of 3D printing technology and incorporating another material printing to create hybrid metallic or composite structures.
Traditional methods of casting synthetic rubber and wax fuels to form solid grains can be challenging, requiring mold tools, and some designs incorporate extensive use of internal webbing materials to improve the grainʼs ability to withstand stress.
Current research is conducted to provide enhancement in AD, notably, in its ability to create complex structures with unprecedented accuracy, to manufacture high-performance hybrid rocket fuel grains.
For J-2X Gas Generator Duct: 70% of Cost Savings & 50% of Time Savings
RS-25 Engine Flex Joint: 45 parts count from Heritage Design to 17 of SLM Design & Welds Pass from +70 to 26 & Machining Operations, to 147 at 57. Results: Reduce Cost & Time.
Current Additive Manufacturing work with acrylonitrile butadiene styrene thermoplastic. It may be developed to offer the ideal combination of an industrial-scale fabrication platform capable of producing large grain sections in a high modulus, chemically stable polymer with excellent accuracy and throughput. Additive Manufacturing is also used to print other hybrid motor parts, such as motor cases and domes .
Powder Bed Fusion (PBF) technologies enable rapid manufacturing of complex, high-value propulsion components.
Flexibility inherent in the AM technologies increases design freedom; enables complex geometries. Designers can explore lightweight structures, integrate functionality, customize parts to specific applications and environment concerns.
Glenn Research Center (GRC) and Aerojet Rocketdyne tested an additively manufactured injector in 2013 under the Manufacturing Innovation Project (MIP)