Liquid-propellant rocket
A liquid-propellant rocket or liquid rocket utilizes a rocket engine burning liquid propellants. (Alternate approaches use gaseous or solid propellants.) Liquids are desirable propellants because they have reasonably high density and their combustion products have high specific impulse (Isp). This allows the volume of the propellant tanks to be relatively low.
Types
Liquid rockets can be
Most designs of liquid rocket engines are
Advantages and disadvantages
The use of liquid propellants has a number of advantages:
- A liquid rocket engine can be tested prior to use, whereas for a solid rocket motor a rigorous quality management must be applied during manufacturing to ensure high reliability.[2]
- Liquid systems enable higher specific impulse than solids and hybrid rocket motors and can provide very high tankage efficiency.
- A Liquid rocket engine can also usually be reused for several flights, as in the Space Shuttle and Falcon 9 series rockets, although reuse of solid rocket motors was also effectively demonstrated during the Shuttle program.
- Liquid rocket engines can swivel throughout flight, whereas solid rocket motors point in one direction. Swiveling allows the rocket engine to be pointed in different directions, which allows for finer-tuned control over the trajectory of the rocket.[3]
- The flow of propellant into the combustion chamber can be throttled, which allows for control over the magnitude of the thrust throughout the flight. This enables real-time error correction during the flight along with efficiency gains.[3]
- Shutdown and restart capabilities allow for multiple burn cycles throughout a flight.[4]
- In the case of an emergency, liquid propelled rockets can be shutdown in a controlled manner, which provides an extra level of safety and mission abort capability.[4]
Use of liquid propellants can also be associated with a number of issues:
- Because the propellant is a very large proportion of the mass of the vehicle, the center of mass shifts significantly rearward as the propellant is used; one will typically lose control of the vehicle if its center mass gets too close to the center of drag/pressure.
- When operated within an atmosphere, pressurization of the typically very thin-walled propellant tanks must guarantee positive gauge pressureat all times to avoid catastrophic collapse of the tank.
- Liquid propellants are subject to slosh, which has frequently led to loss of control of the vehicle. This can be controlled with slosh baffles in the tanks as well as judicious control laws in the guidance system.
- They can suffer from pogo oscillation where the rocket suffers from uncommanded cycles of acceleration.
- Liquid propellants often need ullage motors in zero-gravity or during staging to avoid sucking gas into engines at start up. They are also subject to vortexing within the tank, particularly towards the end of the burn, which can also result in gas being sucked into the engine or pump.
- Liquid propellants can leak, especially hydrogen, possibly leading to the formation of an explosive mixture.
- Turbopumpsto pump liquid propellants are complex to design, and can suffer serious failure modes, such as overspeeding if they run dry or shedding fragments at high speed if metal particles from the manufacturing process enter the pump.
- Cryogenic propellants, such as liquid oxygen, freeze atmospheric water vapor into ice. This can damage or block seals and valves and can cause leaks and other failures. Avoiding this problem often requires lengthy chilldown procedures which attempt to remove as much of the vapor from the system as possible. Ice can also form on the outside of the tank, and later fall and damage the vehicle. External foam insulation can cause issues as shown by the Space Shuttle Columbia disaster. Non-cryogenic propellants do not cause such problems.
- Non-storable liquid rockets require considerable preparation immediately before launch. This makes them less practical than solid rocketsfor most weapon systems.
Principle of operation
Liquid rocket engines have tankage and pipes to store and transfer propellant, an injector system and one or more combustion chambers with associated nozzles.
Typical liquid propellants have densities roughly similar to water, approximately 0.7–1.4g/cm3. An exception is
For injection into the combustion chamber, the propellant pressure at the injectors needs to be greater than the chamber pressure. This is often achieved with a pump. Suitable pumps usually use centrifugal
The major components of a rocket engine are therefore the
Pressurization
Liquid propellants are often pumped into the combustion chamber with a lightweight centrifugal turbopump. Recently some aerospace companies have used electric pumps with batteries for this. In simpler small engines an inert gas stored in a tank at a high pressure is sometimes used instead of pumps to force propellants into the combustion chamber. These engines may have a higher mass ratio, but are usually more reliable, and are therefore used widely in satellites for orbit maintenance.[1]
Propellants
Thousands of combinations of fuels and oxidizers have been tried over the years. Some of the more common and practical ones are:
Cryogenic
- Liquid oxygen (GSLV Mk-III. The main advantages of this mixture are a clean burn (water vapor is the only combustion product) and high performance.[6]
- Liquid oxygen (LOX) and Raptor (SpaceX) and BE-4 (Blue Origin) engines. (See also Propulsion Cryogenics & Advanced Development project of NASA, and Project Morpheus.)
One of the most efficient mixtures,
Liquid methane/LNG has several advantages over LH2. Its performance (max.
Semi-cryogenic
- Liquid oxygen (LOX) and first stages.
- Liquid oxygen (LOX) and alcohol (Redstone
- Liquid oxygen (LOX) and Robert Goddard's first liquid rocket
- Liquid oxygen (LOX) and Zirconia electrolysis from the Martian atmosphere without requiring use of any of the Martian water resources to obtain Hydrogen.[9]
Non-cryogenic/storable/hypergolic
Many non-cryogenic bipropellants are hypergolic (self igniting).
- Ba 349 Natter crewed VTOinterceptor prototypes.
- SRBM
- Inhibited red fuming nitric acid (ISS-1-c,-d,-e
- Nitric acid 73% with
- High-test peroxide (H2O2) and kerosene – UK (1970s) Black Arrow, USA Development (or study): BA-3200
- Hydrazine (N2H4) and red fuming nitric acid – MIM-3 Nike Ajax Antiaircraft Rocket
- Unsymmetric dimethylhydrazine (Long March 2 (used to launch Shenzhoucrew vehicles.)
- Aerozine 50 (50% UDMH, 50% hydrazine) and dinitrogen tetroxide (N2O4) – Titans 2–4, Apollo lunar module, Apollo service module, interplanetary probes (Such as Voyager 1 and Voyager 2)
- Dragon spacecraft.
For
Injectors
The injector implementation in liquid rockets determines the percentage of the theoretical performance of the nozzle that can be achieved. A poor injector performance causes unburnt propellant to leave the engine, giving poor efficiency.
Additionally, injectors are also usually key in reducing thermal loads on the nozzle; by increasing the proportion of fuel around the edge of the chamber, this gives much lower temperatures on the walls of the nozzle.
Types of injectors
Injectors can be as simple as a number of small diameter holes arranged in carefully constructed patterns through which the fuel and oxidizer travel. The speed of the flow is determined by the square root of the pressure drop across the injectors, the shape of the hole and other details such as the density of the propellant.
The first injectors used on the V-2 created parallel jets of fuel and oxidizer which then combusted in the chamber. This gave quite poor efficiency.
Injectors today classically consist of a number of small holes which aim jets of fuel and oxidizer so that they collide at a point in space a short distance away from the injector plate. This helps to break the flow up into small droplets that burn more easily.
The main types of injectors are
- Shower head
- Self-impinging doublet
- Cross-impinging triplet
- Centripetal or swirling
- Pintle
The pintle injector permits good mixture control of fuel and oxidizer over a wide range of flow rates. The pintle injector was used in the
The RS-25 engine designed for the Space Shuttle uses a system of fluted posts, which use heated hydrogen from the preburner to vaporize the liquid oxygen flowing through the center of the posts[10] and this improves the rate and stability of the combustion process; previous engines such as the F-1 used for the Apollo program had significant issues with oscillations that led to destruction of the engines, but this was not a problem in the RS-25 due to this design detail.
Valentin Glushko invented the centripetal injector in the early 1930s, and it has been almost universally used in Russian engines. Rotational motion is applied to the liquid (and sometimes the two propellants are mixed), then it is expelled through a small hole, where it forms a cone-shaped sheet that rapidly atomizes. Goddard's first liquid engine used a single impinging injector. German scientists in WWII experimented with impinging injectors on flat plates, used successfully in the Wasserfall missile.
Combustion stability
To avoid instabilities such as chugging, which is a relatively low speed oscillation, the engine must be designed with enough pressure drop across the injectors to render the flow largely independent of the chamber pressure. This pressure drop is normally achieved by using at least 20% of the chamber pressure across the injectors.
Nevertheless, particularly in larger engines, a high speed combustion oscillation is easily triggered, and these are not well understood. These high speed oscillations tend to disrupt the gas side boundary layer of the engine, and this can cause the cooling system to rapidly fail, destroying the engine. These kinds of oscillations are much more common on large engines, and plagued the development of the Saturn V, but were finally overcome.
Some combustion chambers, such as those of the
To prevent these issues the RS-25 injector design instead went to a lot of effort to vaporize the propellant prior to injection into the combustion chamber. Although many other features were used to ensure that instabilities could not occur, later research showed that these other features were unnecessary, and the gas phase combustion worked reliably.
Testing for stability often involves the use of small explosives. These are detonated within the chamber during operation, and causes an impulsive excitation. By examining the pressure trace of the chamber to determine how quickly the effects of the disturbance die away, it is possible to estimate the stability and redesign features of the chamber if required.
Engine cycles
For liquid-propellant rockets, four different ways of powering the injection of the propellant into the chamber are in common use.[11]
Fuel and oxidizer must be pumped into the combustion chamber against the pressure of the hot gasses being burned, and engine power is limited by the rate at which propellant can be pumped into the combustion chamber. For atmospheric or launcher use, high pressure, and thus high power, engine cycles are desirable to minimize
- Pressure-fed cycle
- The propellants are forced in from pressurised (relatively heavy) tanks. The heavy tanks mean that a relatively low pressure is optimal, limiting engine power, but all the fuel is burned, allowing high efficiency. The pressurant used is frequently helium due to its lack of reactivity and low density. Examples: SPS, and the second stage of the Delta II.
- Electric pump-fed
- An electric motor, generally a brushless DC electric motor, drives the pumps. The electric motor is powered by a battery pack. It is relatively simple to implement and reduces the complexity of the turbomachinery design, but at the expense of the extra dry mass of the battery pack. Example engine is the Rutherford designed and used by Rocket Lab.
- Gas-generator cycle
- A small percentage of the propellants are burnt in a preburner to power a turbopump and then exhausted through a separate nozzle, or low down on the main one. This results in a reduction in efficiency since the exhaust contributes little or no thrust, but the pump turbines can be very large, allowing for high power engines. Examples: Merlin.
- Tap-off cycle
- Takes hot gases from the main J-2S and BE-3.
- Expander cycle
- Cryogenic fuel (hydrogen, or methane) is used to cool the walls of the combustion chamber and nozzle. Absorbed heat vaporizes and expands the fuel which is then used to drive the turbopumps before it enters the combustion chamber, allowing for high efficiency, or is bled overboard, allowing for higher power turbopumps. The limited heat available to vaporize the fuel constrains engine power. Examples: RL10 for Atlas V and Delta IV second stages (closed cycle), H-II's LE-5 (bleed cycle).
- Staged combustion cycle
- A fuel- or oxidizer-rich mixture is burned in a preburner and then drives turbopumps, and this high-pressure exhaust is fed directly into the main chamber where the remainder of the fuel or oxidizer undergoes combustion, permitting very high pressures and efficiency. Examples: .
- Full-flow staged combustion cycle
- Fuel- and oxidizer-rich mixtures are burned in separate preburners and driving the turbopumps, then both high-pressure exhausts, one oxygen rich and the other fuel rich, are fed directly into the main chamber where they combine and combust, permitting very high pressures and high efficiency. Example: SpaceX Raptor.
Engine cycle tradeoffs
Selecting an engine cycle is one of the earlier steps to rocket engine design. A number of tradeoffs arise from this selection, some of which include:
Cycle type | ||||
---|---|---|---|---|
Gas generator | Expander cycle | Staged-combustion | Pressure-fed | |
Advantages | Simple; low dry mass; allows for high power turbopumps for high thrust | High specific impulse; fairly low complexity | High specific impulse; high combustion chamber pressures allowing for high thrust | Simple; no turbopumps; low dry mass; high specific impulse |
Disadvantages | Lower specific impulse | Must use cryogenic fuel; heat transfer to the fuel limits available power to the turbine and thus engine thrust | Greatly increased complexity &, therefore, mass (more-so for full-flow) | Tank pressure limits combustion chamber pressure and thrust; heavy tanks and associated pressurization hardware |
Cooling
Injectors are commonly laid out so that a fuel-rich layer is created at the combustion chamber wall. This reduces the temperature there, and downstream to the throat and even into the nozzle and permits the combustion chamber to be run at higher pressure, which permits a higher expansion ratio nozzle to be used which gives a higher ISP and better system performance.[12] A liquid rocket engine often employs regenerative cooling, which uses the fuel or less commonly the oxidizer to cool the chamber and nozzle.
Ignition
Ignition can be performed in many ways, but perhaps more so with liquid propellants than other rockets a consistent and significant ignitions source is required; a delay of ignition (in some cases as small as a few tens of milliseconds) can cause overpressure of the chamber due to excess propellant. A
Generally, ignition systems try to apply flames across the injector surface, with a mass flow of approximately 1% of the full mass flow of the chamber.
Safety interlocks are sometimes used to ensure the presence of an ignition source before the main valves open; however reliability of the interlocks can in some cases be lower than the ignition system. Thus it depends on whether the system must fail safe, or whether overall mission success is more important. Interlocks are rarely used for upper, uncrewed stages where failure of the interlock would cause loss of mission, but are present on the RS-25 engine, to shut the engines down prior to liftoff of the Space Shuttle. In addition, detection of successful ignition of the igniter is surprisingly difficult, some systems use thin wires that are cut by the flames, pressure sensors have also seen some use.
Methods of ignition include
Ignition with a
History
Russia–Soviet Union
The idea of a liquid rocket as understood in the modern context first appeared in 1903 in the book Exploration of the Universe with Rocket-Propelled Vehicles,
From 1929 to 1930 in
During this period in Moscow Fredrich Tsander, a scientist and inventor was designing and building liquid rocket engines which ran on compressed air and gasoline. Tsander used it to investigate high-energy fuels including powdered metals mixed with gasoline. In September 1931 Tsander formed the Moscow based 'Group for the Study of Reactive Motion',[20] better known by its Russian acronym "GIRD". [21] In May 1932, Sergey Korolev replaced Tsander as the head of GIRD. Mikhail Tikhonravov launched the first Soviet liquid propelled rocket, fueled by liquid oxygen and jellied gasoline, the GIRD-9, took place on 17 August 1933, which reached an altitude of 400 metres (1,300 ft).[22] In January 1933 Tsander began development of the GIRD-X rocket. This design burned liquid oxygen and gasoline and was one of the first engines to be regeneratively cooled by the liquid oxygen, which flowed around the inner wall of the combustion chamber before entering it. Problems with burn-through during testing prompted a switch from gasoline to less energetic alcohol. The final missile, 2.2 metres (7.2 ft) long by 140 millimetres (5.5 in) in diameter, had a mass of 30 kilograms (66 lb), and it was anticipated that it could carry a 2 kilograms (4.4 lb) payload to an altitude of 5.5 kilometres (3.4 mi).[23] The GIRD X rocket was launched on 25 November 1933 and flew to a height of 80 meters.[24]
In 1933 GDL and GIRD merged and became the Reactive Scientific Research Institute (RNII). At RNII Gushko continued the development of liquid propellant rocket engines ОРМ-53 to ОРМ-102, with ORM-65 powering the RP-318 rocket-powered aircraft.[18] In 1938 Leonid Dushkin replaced Glushko and continued development of the ORM engines, including the engine for the rocket powered interceptor, the Bereznyak-Isayev BI-1.[25] At RNII Tikhonravov worked on developing oxygen/alcohol liquid-propellant rocket engines.[26] Ultimately liquid propellant rocket engines were given a low priority during the late 1930s at RNII, however the research was productive and very important for later achievements of the Soviet rocket program.[27]
Peru
Peruvian Pedro Paulet, who had experimented with rockets throughout his life in Peru, wrote a letter to El Comercio in Lima in 1927, claiming he had experimented with a liquid rocket engine while he was a student in Paris three decades earlier.[28][29] Historians of early rocketry experiments, among them Max Valier, Willy Ley, and John D. Clark, have given differing amounts of credence to Paulet's report. Valier applauded Paulet's liquid-propelled rocket design in the Verein für Raumschiffahrt publication Die Rakete, saying the engine had "amazing power" and that his plans were necessary for future rocket development.[30] Hermann Oberth would name Paulet as a pioneer in rocketry in 1965.[31] Wernher von Braun would also describe Paulet as "the pioneer of the liquid fuel propulsion motor" and stated that "Paulet helped man reach the Moon".[28][32][33][34][35] Paulet was later approached by Nazi Germany, being invited to join the Astronomische Gesellschaft to help develop rocket technology, though he refused to assist after discovering that the project was destined for weaponization and never shared the formula for his propellant.[36][37] According to filmmaker and researcher Álvaro Mejía, Frederick I. Ordway III would later attempt to discredit Paulet's discoveries in the context of the Cold War and in an effort to shift the public image of von Braun away from his history with Nazi Germany.[38]
United States
The first flight of a liquid-propellant rocket took place on March 16, 1926 at Auburn, Massachusetts, when American professor Dr. Robert H. Goddard launched a vehicle using liquid oxygen and gasoline as propellants.[39] The rocket, which was dubbed "Nell", rose just 41 feet during a 2.5-second flight that ended in a cabbage field, but it was an important demonstration that rockets utilizing liquid propulsion were possible. Goddard proposed liquid propellants about fifteen years earlier and began to seriously experiment with them in 1921. The German-Romanian Hermann Oberth published a book in 1922 suggesting the use of liquid propellants.
Germany
In Germany, engineers and scientists became enthralled with liquid propulsion, building and testing them in the late 1920s within
By the late 1930s, use of rocket propulsion for crewed flight began to be seriously experimented with, as Germany's
Post World War II
After World War II the American government and military finally seriously considered liquid-propellant rockets as weapons and began to fund work on them. The Soviet Union did likewise, and thus began the Space Race.
In 2010s 3D printed engines started being used for spaceflight. Examples of such engines include SuperDraco used in launch escape system of the SpaceX Dragon 2 and also engines used for first or second stages in launch vehicles from Astra,[46] Orbex,[47][48] Relativity Space,[49] Skyrora,[50] or Launcher.[51][52][53]
See also
- Comparison of orbital launch systems
- Comparison of orbital launchers families
- Comparison of orbital rocket engines
- Comparison of solid-fuelled orbital launch systems
- List of space launch system designs
- List of missiles
- List of orbital launch systems
- List of sounding rockets
- List of military rockets
References
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- ^ NASA:Liquid rocket engines, 1998, Purdue University
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- ^ ISBN 978-3-540-22190-6, retrieved 2023-11-29
- ^ "Thomas Mueller's answer to Is SpaceX's Merlin 1D's thrust-to-weight ratio of 150+ believable? - Quora". www.quora.com.
- ^ a b c "About LNG Propulsion System". JAXA. Retrieved 2020-08-25.
- ^ a b Hagemann, Dr. Gerald (November 4, 2015). "LOX/Methane The Future is Green" (PDF). Retrieved November 29, 2022.
- ^ "Methane Engine Just for Future Space Transportation" (PDF). IHI Corporation. Retrieved November 29, 2022.
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- ^ Sutton, George P. and Biblarz, Oscar, Rocket Propulsion Elements, 7th ed., John Wiley & Sons, Inc., New York, 2001.
- ^ "Sometimes, Smaller is Better". Archived from the original on 2012-04-14. Retrieved 2010-06-01.
- ^ Rocket Propulsion elements - Sutton Biblarz, section 8.1
- ^ Russian title Issledovaniye mirovykh prostranstv reaktivnymi priborami (Исследование мировых пространств реактивными приборами)
- ^ Siddiqi 2000, p. 1.
- ^ Siddiqi 2000, p. 27.
- ^ Siddiqi 2000, p. 6–7,333.
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- ^ Siddiqi 2000, p. 4.
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- ^ Chertok 2005, p. 167 Vol 1.
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- ^ a b Paulet de Vásquez, Sara (2002). "Pedro Paulet: pionero peruano del espacio". Ciencia y tecnología. Lima: 5–12.
- ^ Ordway, F. I. (September 1977). "The alleged contributions of Pedro E. Paulet to liquid-propellant rocketry". Nasa, Washington Essays on the History of Rocketry and Astronautics, Vol. 2. NASA.
- ^ Mejía 2017, pp. 115–116.
- ^ Fitzgerald, Michael (2018). Hitler's Secret Weapons of Mass Destruction: The Nazi Plan for Final Victory. pp. Chapter 3.
Paulet was clearly a pioneer in the field of rocketry and it is unsurprising that the Nazis were keen to recruit him to assist their efforts. The German Astronautical Society invited him to Germany to become part of a team of researchers into rocket propulsion and he was initially interested, but when he discovered that the intention was to construct a weapon that would be used for military purposes he declined the invitation. As late as 1965, Oberth described him as one of the true pioneers of rocket science.
- ^ "El peruano que se convirtió en el padre de la astronáutica inspirado por Julio Verne y que aparece en los nuevos billetes de 100 soles". BBC News (in Spanish). Retrieved 2022-03-11.
- ^ Von Braun, Wernher; Ordway III, Frederick I. (1968). Histoire Mondiale de L'Astronautique. París: Larousse / Paris -Match. pp. 51–52.
- ^ Fitzgerald, Michael (2018). Hitler's Secret Weapons of Mass Destruction: The Nazi Plan for Final Victory. pp. Chapter 3.
Even Wernher von Braun described Paulet as 'one of the fathers of aeronautics' and 'the pioneer of the liquid fuel propulsion motor'. He declared that 'by his efforts, Paulet helped man reach the Moon'.
- ISBN 9781136257902.
Peru holds a special place among Latin America's EMSAs because the country was home to Pedro Paulet, who invented the world's first liquid-propelled rocket engine in 1895 and the first modern rocket propulsion system in 1900. ... According to Wernher von Braun, 'Paulet should be considered the pioneer of the liquid fuel propulsion motor ... by his efforts, Paulet helped man reach the moon.' Paulet went on to found Peru's National Pro-Aviation League, a precursor of the Peruvian Air Force.
- ^ "El peruano que se convirtió en el padre de la astronáutica inspirado por Julio Verne y que aparece en los nuevos billetes de 100 soles". BBC News (in Spanish). Retrieved 2022-03-11.
- ^ Fitzgerald, Michael (2018). Hitler's Secret Weapons of Mass Destruction: The Nazi Plan for Final Victory. pp. Chapter 3.
Paulet was clearly a pioneer in the field of rocketry and it is unsurprising that the Nazis were keen to recruit him to assist their efforts. The German Astronautical Society invited him to Germany to become part of a team of researchers into rocket propulsion and he was initially interested, but when he discovered that the intention was to construct a weapon that would be used for military purposes he declined the invitation. As late as 1965, Oberth described him as one of the true pioneers of rocket science.
- ^ "Un documental reivindicará al peruano Paulet como pionero de la astronáutica". EFE (in Spanish). 2012-04-05. Retrieved 2022-03-11.
- ^ "Re-Creating History". NASA. Archived from the original on 2007-12-01.
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- ^ "Fritz von Opel, Speech at Deutsches Museum, April 3, 1968, re-print in "Opel Post"" (PDF). May 1968. p. 4ff.
- ^ Frank H. Winter, "1928-1929 Forerunners of the Shuttle: the 'Von Opel Flights'", SPACEFLIGHT, Vol. 21,2, Feb. 1979
- ^ Boyne, Walter J. (September 2004). "Rocket Men" (PDF). Air Force Magazine.
- ^ Magazines, Hearst (1 May 1931). Popular Mechanics. Hearst Magazines. p. 716 – via Internet Archive.
Popular Mechanics 1931 curtiss.
- ^ Volker Koos, Heinkel He 176 – Dichtung und Wahrheit, Jet&Prop 1/94 p. 17–21
- ^ "Astra Rocket Engine — Delphin 3.0". June 2020.
- ^ "Orbex builds single-piece rocket engine 3D printed on SLM 800 - Aerospace Manufacturing". 13 February 2019.
- ^ "Orbex unveiled largest 3D printed rocket engine in the world". 13 February 2019.
- ^ "Relativity Space will 3D-print rockets at new autonomous factory in Long Beach, California". Space.com. 28 February 2020.
- ^ "Launch startup Skyrora successfully tests 3D-printed rocket engines powered by plastic waste". 3 February 2020.
- ^ "A tiny start-up based in Brooklyn has a 3D-printed rocket engine it says is the largest in the world". CNBC. 20 February 2019.
- ^ "Air Force funding keeps Launcher development on track". 14 November 2019.
- ^ "Meet Launcher, the rocket engine builder with just eight employees". 9 November 2020.
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- Baker, David; Zak, Anatoly (9 September 2013). Race for Space 1: Dawn of the Space Age. RHK. Retrieved 21 July 2022.
- Chertok, Boris (2005). Rockets and People Volumes 1-4. National Aeronautics and Space Administration. Retrieved 21 July 2022.
- Mejía, Álvaro (2017). "Pedro Paulet, sabio multidisciplinario". Persona & Cultura (in Spanish). 14 (14). Universidad Católica San Pablo: 95–122. S2CID 258143557.
- Siddiqi, Asif (2000). Challenge to Apollo : the Soviet Union and the space race, 1945-1974 (PDF). Washington, D.C: National Aeronautics and Space Administration, NASA History Div. Retrieved 21 July 2022.