OTRAG Rocket
Encyclopedia
The OTRAG rocket was a modular satellite-delivery rocket
developed by the OTRAG
company in the 1970s and 80s. The OTRAG rocket was to become a rocket built up from several mass-produced units, intended to carry satellites with a weight of 1-10 tons or more into orbit. Mass production meant that the vehicle was projected to have been 10x cheaper than conventional vehicles of similar capability.
would bundle four or more CRPUs in parallel, topped with the payload. An orbital launcher would use dozens to hundreds of CRPUs, depending on payload mass. The launcher would then stage by dropping outer CRPUs, leaving the interior ones to continue with payload.
A CRPU was essentially a steel tube, 27 cm in diameter and 16 meters long, joined from a few shorter tubes. The CRPU was divided into three sections by aluminum bulkheads, with additional stiffening rings between bulkheads. Forward, the majority of the tube contained a mixture of nitric acid
and nitrogen tetroxide
oxidizers. Next was a section of kerosene
fuel. This was commercial-grade kerosene, not the more expensive RP-1
. Last was the engine section. A fuel line carried nitric acid around the kerosene, into the engine.
The design of the CRPU was extremely simple. The tubing was strong enough that the propellants were fed to the engine by pressure alone
. This eliminated the need for turbopump
s. The engine was ablatively cooled
, eliminating the need for fine fuel passages and heat-resistant kerosene. The engine did not gimbal
; instead, the vehicle was steered by throttling one side's CRPUs versus the opposite side. Thus, the engine was simply built into the tube walls, with the only mechanisms being the throttling valves. No separate pressurizing system was included; the tanks were simply left with an ullage space, which was then filled with gas to a few hundred psi. Because of the narrow tubing, the bulkheads between sections could be simple plates, instead of domes like virtually all other rocket stages. There was no ignition system; instead, a slug of furfuryl alcohol
was injected before the kerosene. The furfuryl alcohol ignited spontaneously
upon contact with the nitric acid.
The use of ablative cooling, high-pressure steel construction, and large "empty" spaces meant that a CRPU was heavy, with relatively low performance. The diameter of the tubing also put a hard limit on the engine diameter, preventing use of an efficient, high-expansion nozzle for the upper stages. However, ganging CRPUs into three stages was sufficient to reach orbit. Meanwhile, the low cost of each CRPU, after the economies of scale gained by producing hundreds or possibly thousands of them per year, would have still left the vehicle cheaper than its contemporaries. Additionally, the large number of small engines firing simultaneously would have given a high degree of reliability and a relatively smooth ride.
The company's baseline launcher design claimed to lift one metric ton to orbit. It would have consisted of a third stage core of four CRPUs, surrounded by a second stage of twelve CRPUs, in turn surrounded by the first stage's 48 CRPUs. Larger vehicles and capacities would be achieved with greater numbers of CRPUs, possibly including several hundred per flight for a heavy launcher.
The company forecast that CRPUs would eventually be so cheap, recovering and refurbishing a launcher would be no better than simply building more units. The use of storable propellants and few moving parts meant that launch-site operations would also be very simple. These advantages were expected to overcome the disadvantages of small specific impulse
and payload fraction
.
Small, 4-unit vehicles were built and tested in Shaba North, Zaire
and Seba Oasis, Libya
, where heights of 20 to 50 kilometers were reached. The rockets used there were 6 and 12 meters long. The basic CRPU concept was shown to be workable, though some rockets experienced guidance or component failures. The last launch of an OTRAG rocket took place on September 19, 1983 in Esrange
. Following this launch, the OTRAG rocket was to be used in high altitude research.
Political pressure then shut down the project, as discussed in the OTRAG
article.
After the company had left Libya in 1987, some remaining equipment was confiscated by the government. However, enough parts and knowledge were missing to prevent Libya from continuing the project.
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
developed by the OTRAG
OTRAG
OTRAG , was a German company based in Stuttgart, which planned in the late 1970s and early 1980s to develop an alternative propulsion system for rockets. OTRAG was the first commercial developer and producer of space launch vehicles...
company in the 1970s and 80s. The OTRAG rocket was to become a rocket built up from several mass-produced units, intended to carry satellites with a weight of 1-10 tons or more into orbit. Mass production meant that the vehicle was projected to have been 10x cheaper than conventional vehicles of similar capability.
Design
Various OTRAG rockets could be built up from the company's CRPUs (Common Rocket Propulsion Unit). A sounding rocketSounding rocket
A sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The origin of the term comes from nautical vocabulary, where to sound is to throw a weighted line from a ship into...
would bundle four or more CRPUs in parallel, topped with the payload. An orbital launcher would use dozens to hundreds of CRPUs, depending on payload mass. The launcher would then stage by dropping outer CRPUs, leaving the interior ones to continue with payload.
A CRPU was essentially a steel tube, 27 cm in diameter and 16 meters long, joined from a few shorter tubes. The CRPU was divided into three sections by aluminum bulkheads, with additional stiffening rings between bulkheads. Forward, the majority of the tube contained a mixture of nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and nitrogen tetroxide
Dinitrogen tetroxide
Dinitrogen tetroxide is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen dioxide; some call this mixture dinitrogen tetroxide, while some call it nitrogen dioxide.Dinitrogen tetroxide is a powerful oxidizer, making it highly...
oxidizers. Next was a section of kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
fuel. This was commercial-grade kerosene, not the more expensive RP-1
RP-1
RP-1 is a highly refined form of kerosene outwardly similar to jet fuel, used as a rocket fuel. Although having a lower specific impulse than liquid hydrogen , RP-1 is cheaper, can be stored at room temperature, is far less of an explosive hazard and is far denser...
. Last was the engine section. A fuel line carried nitric acid around the kerosene, into the engine.
The design of the CRPU was extremely simple. The tubing was strong enough that the propellants were fed to the engine by pressure alone
Pressure-fed cycle (rocket)
The pressure-fed cycle is a class of rocket engine designs. A separate gas supply, usually helium, pressurizes the propellant tanks to force fuel and oxidizer to the combustion chamber. To maintain adequate flow, the tank pressures must exceed the combustion chamber pressure.Pressure fed engines...
. This eliminated the need for turbopump
Turbopump
A turbopump is a gas turbine that comprises basically two main components: a rotodynamic pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together...
s. The engine was ablatively cooled
Ablation
Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. This occurs in spaceflight during ascent and atmospheric reentry, glaciology, medicine, and passive fire protection.-Spaceflight:...
, eliminating the need for fine fuel passages and heat-resistant kerosene. The engine did not gimbal
Gimbal
A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain immobile regardless of the motion of its support...
; instead, the vehicle was steered by throttling one side's CRPUs versus the opposite side. Thus, the engine was simply built into the tube walls, with the only mechanisms being the throttling valves. No separate pressurizing system was included; the tanks were simply left with an ullage space, which was then filled with gas to a few hundred psi. Because of the narrow tubing, the bulkheads between sections could be simple plates, instead of domes like virtually all other rocket stages. There was no ignition system; instead, a slug of furfuryl alcohol
Furfuryl alcohol
Furfuryl alcohol, also called 2-furylmethanol or 2-furancarbinol, is an organic compound containing a furan substituted with a hydroxymethyl group. It is a clear colorless liquid when pure, but becomes amber colored upon prolonged standing. It possesses a faint burning odor and a bitter taste. ...
was injected before the kerosene. The furfuryl alcohol ignited spontaneously
Hypergolic fuel
A rocket propellant combination used in a rocket engine is called hypergolic when the propellants spontaneously ignite when they come into contact. Strictly speaking it is the combination that is hypergolic, but in less precise usage the individual propellants are also referred to as hypergolic....
upon contact with the nitric acid.
The use of ablative cooling, high-pressure steel construction, and large "empty" spaces meant that a CRPU was heavy, with relatively low performance. The diameter of the tubing also put a hard limit on the engine diameter, preventing use of an efficient, high-expansion nozzle for the upper stages. However, ganging CRPUs into three stages was sufficient to reach orbit. Meanwhile, the low cost of each CRPU, after the economies of scale gained by producing hundreds or possibly thousands of them per year, would have still left the vehicle cheaper than its contemporaries. Additionally, the large number of small engines firing simultaneously would have given a high degree of reliability and a relatively smooth ride.
The company's baseline launcher design claimed to lift one metric ton to orbit. It would have consisted of a third stage core of four CRPUs, surrounded by a second stage of twelve CRPUs, in turn surrounded by the first stage's 48 CRPUs. Larger vehicles and capacities would be achieved with greater numbers of CRPUs, possibly including several hundred per flight for a heavy launcher.
The company forecast that CRPUs would eventually be so cheap, recovering and refurbishing a launcher would be no better than simply building more units. The use of storable propellants and few moving parts meant that launch-site operations would also be very simple. These advantages were expected to overcome the disadvantages of small specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
and payload fraction
Payload fraction
In aerospace engineering, payload fraction is a common term used to characterize the efficiency of a particular design. Payload fraction is calculated by dividing the weight of the payload by the weight of the otherwise empty aircraft when fully fueled...
.
Flight History
The engines were tested extensively on ground rigs, on both German and African test sites. Experiments were run with varying fuel and oxidizer formulations, as the general design was quite robust.Small, 4-unit vehicles were built and tested in Shaba North, Zaire
Zaire
The Republic of Zaire was the name of the present Democratic Republic of the Congo between 27 October 1971 and 17 May 1997. The name of Zaire derives from the , itself an adaptation of the Kongo word nzere or nzadi, or "the river that swallows all rivers".-Self-proclaimed Father of the Nation:In...
and Seba Oasis, Libya
Libya
Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west....
, where heights of 20 to 50 kilometers were reached. The rockets used there were 6 and 12 meters long. The basic CRPU concept was shown to be workable, though some rockets experienced guidance or component failures. The last launch of an OTRAG rocket took place on September 19, 1983 in Esrange
Esrange
Esrange Space Center is a rocket range and research centre located outside the town of Kiruna in northern Sweden. It is a base for scientific research with high altitude balloons, investigation of the aurora borealis, sounding rocket launches, and satellite tracking, among other things...
. Following this launch, the OTRAG rocket was to be used in high altitude research.
Political pressure then shut down the project, as discussed in the OTRAG
OTRAG
OTRAG , was a German company based in Stuttgart, which planned in the late 1970s and early 1980s to develop an alternative propulsion system for rockets. OTRAG was the first commercial developer and producer of space launch vehicles...
article.
After the company had left Libya in 1987, some remaining equipment was confiscated by the government. However, enough parts and knowledge were missing to prevent Libya from continuing the project.