FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

NUMBER 10 221
Actually, the technology of the A-4 rocket, which
became operational 19 years later, included all
essential details of Oberth's suggestions for the first
stage of his Models B and E that he made in 1923.
But still, there was a long way to go. As to the
cooling method, the first rocket engines developed
after 1923 used much more primitive processes.
In his Wege zur Raumschiffahrt 5 Oberth still
suggested a simple sounding rocket, Model A, with
the liquid-propellant engine encased by the fuel
tank in the lower part and the liquid oxygen tank
in the upper part. Capacitive cooling was to be
applied; the pre-heated oxygen was to be fed into
the combustion chamber by its own vapor pressure
and the fuel by a pressurizing gas.
Oberth's first rocket engine test model, the "coneshaped
nozzle," built in the same year according to
the specifications of the German patent DRP
549,222, had capacitive cooling only—even without
a cooling jacket—but with oxygen-rich combustion
resulting in low combustion-gas temperatures. For
example, during the famous demonstration at the
Chemisch-Technische Reichsanstalt, the amount of
oxygen injected was 1.9 times the stoichiometric
value. According to Willy Ley's notes, one of the
combustion chambers of this series was lined with a
ceramic material (steatite magnesium). The text of
the patent did not include any details regarding the
cooling system, only the somewhat vague phrase:
"The inner lining can be of clay, asbestos, mineral
wool, platinum sponge, or similar materials. It can
also be omitted entirely, for example, when using
copper sheets adequately cooled from the outside."
Actually, the combustion tests with the lined combustion
chamber proved unfavorable. In his publication
Rakentenflug, 6 Nebel commented on the
tests with Oberth's combustion chamber models that
"Use of fireproof material did not prove to be successful,
either, and in many tests the material burnt
up." Still, this led to the development of the socalled
"Spaltduese" (slot nozzle) providing a thrust
of 2.5 kg. After the slot nozzle, the cone-shaped
nozzle was developed with a thrust of 7.5 kg. Soon,
this conical nozzle attained a constant thrust of 7.5
kg over a combustion time of 100 sec. Because of
the rudimentary equipment, the tests progressed
very slowly. Materials problems were especially
hard to solve because all "fireproof" materials
burned up at these high temperatures.
The German patent 484,064, mentioned in Ley's
chronicle, was held by Heinrich Schneider, a former
Austrian Marine officer, with whom Hermann
Oberth had corresponded for a short while in 1924.
The patent was based on an earlier Austrian patent
of 25 November 1925, and referred only to suggestions
for propellant flow, not to any cooling systems.
Entitled "Mit fliissigen Betriebsstoffen betriebene
Gasrakete" (Gas Rocket Using Liquid Propellants),
it contained no less than 16 claims. According to
the then existing state of the art in rocketry, the
sketch of the overall design of the rocket thrust
chamber, attached to the patent specifications,
showed a static liquid cooling system. The combustion
chamber and the first quarter of the nozzle
were surrounded by a jacket filled with non-circulating
liquid; the rest of the exhaust nozzle was uncooled.
The descriptive test simply mentioned that
"the space around the nozzle and the combustion
chamber may be filled by a coolant."
Ley also reported briefly on the firing of a liquidpropellant
rocket by Friedrich Wilhelm Sander,
the owner of a factory in Wesermuende, which produced
rescue and signal rockets, and since early
1928, solid-propellant rocket motors for the first
Opel-Rak test runs by Max Valier. In his book
Raketenfahrt, Valier himself wrote in 1929:
In the field of liquid-fuel rockets, Sander must be mentioned
as the most successful research engineer of the year. On
10 April 1929, he was the first who succeeded in launching
such a rocket on a free-ascent trajectory. According to his
specifications, the rocket was 21 cm in diameter, 74 cm long,
and weighed 7 kg without and 16 kg with propellants. The
burning time was 132 sec, maximum thrust 45 to 50 kg. The
propellant, which Sander keeps secret, had a combustion
heat of 2380 k cal/kg. It seems that he used gasoline and a
suitable oxidizer under special burning conditions. As construction
materials, steel and light metals were used.
This first liquid-propellant rocket took off so rapidly that
it was impossible to track its flight or to recover it. Sander
therefore repeated the experiment two days later, attaching
4000 m of 3-mm rope to the rocket and applied all precautions
known to him from his marine rescue rocket operations.
In spite of its heavy load, the rocket took off like
a bullet, taking with it 2000 m of rope, and disappeared
forever with the torn-off part.
After this success, Sander concentrated again on rocket propulsion
for manned aircraft. By May 1929, he had succeeded
in producing a thrust of 200 kg for a period of more than 15
minutes, and in July, at the Opel plant in Russelsheim, he
attained combustion times of more than 30 minutes with a
thrust of 300 kg. Sander was most concerned with achieving
operational safety and using low-priced fuels. Using a waste
product of the chemical industry, he succeeded in reducing
the price for one kilogram of fuel to 20 pfennige.