FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

NUMBER 10 233
appears non-feasible because of the unavoidable detonations
connected with the combustion of the said propellants.
February 3, 1934 For the State Secretary
Dr. Leitner, Superintendent General.
Not even was an effort made, prior to returning the
manuscript, to erase the reviewer's vitriolic pencil
notes from the submitted pages.
The youthful research team, however, could not
be discouraged; from that time on they began to
look more and more beyond the border, especially
toward Germany, as the defiant name of a "German"
Rocket Flight Yard demonstrated.
On 7 February 1934, preliminary tests were run
again, of which the very first established the trend
for future cooling methods. Sanger's log book reads:
Half-inch steel and copper tubing with a wall thickness of
1 to 2 millimeters is connected to a water line and water is
passed through. An attempt is made to melt the tubing by
heating it on the outside with a welding torch (largest available
burner No 22-30). But as long as running water completely
fills the tube, the torch can cut neither copper nor
steel tubing.
At the end of the detailed test report it says: "The
experiments are considered decisive for testing
thrustor models with metallic combustion chamber
walls cooled by fuel."
The next combustion chamber design, SR-3, was
first hot-fired on 14 March 1934, after completion
of the test set-up. It no longer had a liner, only bare
steel walls which were still water-cooled during the
first test series. Otherwise, SR-3 consisted of a cylindrical
combustion chamber and an attached Laval
nozzle with a 6° half-angle, a 1.2-mm throat diameter
and a nozzle-area ratio of 10:1. A cylindrical
cooling jacket surrounded chamber and nozzle. The
total length of the thrustor was 180 mm and its outside
diameter 57 mm. During Sanger's first test
series, Shell diesel fuel from a three-cylinder, manually
operated pump was burned with gaseous oxygen
supplied from bottles with a volume of 6 m 3
and under storage pressure of 150 atm. During the
test the thrustor was suspended from the ceiling in
a hinged frame which could move only in the direction
of the horizontal thrustor axis. A horizontal
spring dynamometer, firmly braced to the ground,
accepted the full thrust. Also recorded, in addition
to thrust, were chamber pressure, flow rate, and
cooling-water temperature, fuel and oxygen consumption,
total thrustor operating time, and overall
test duration. By 6 April 1934, this type of thrustor
was tested 60 times and combustion chamber pres­
sures up to 45 atm, thrust levels up to 1 kg and
exhaust velocities up to more than 830 m/sec were
measured during test runs exceeding 26 min. Thereafter,
for some tests, the throat diameter was varied
between 1.2 and 2.5 mm—and correspondingly the
nozzle area ratio—with the result that the exhaust
velocities increased up to at least 1460 m/sec and
the thrust levels up to 2.80 kg.
On 20 March 1934, while still running these tests,
Sanger—drawing from his experience gained on
February 7—conceived the first thrustor featuring
forced regenerative cooling with the cooling coils
wrapped around the smooth walls of the combustion
chamber and nozzle. By 14 April 1934, this
concept was incorporated into the design of SR-4.
Copper tubing of 8/10 mm (id/od), tightly wound,
with wall-to-wall contact, was to be brazed to the
3-mm-thick cylindrical combustion chamber shell
and the adjoining nozzle. The total thrustor length
was to be 283 mm and the maximum outside diameter
95 mm. For the first time, a short nozzle with
an 8° half-angle, a 2.4-mm throat diameter and
again an area ratio of 10:1 was proposed.
However, on 23 April 1934, based on analytical
studies, Sanger terminated the work on SR-4 in
favor of a new design (SR-5) with thrustor walls
made up solely of coiled tubing welded on the
outside; thus, the load-carrying shell portions were
exposed to lower temperatures and the heat-dissipating
surfaces enlarged in comparison to those of
a smooth inner wall. The shell of the elongated
cylindrical combustion chamber of SR-5 consisted
of coiled double tubing with the coolant in counterflow
so that both coolant inlet and outlet were close
to the injector. The short nozzle with a 4° halfangle
had a 2.3-mm throat diameter and a 4:1 area
ratio. SR-5 tests were run between 7 and 14 May
1934. During a burning time of 260 sec at a chamber
pressure of 47 atm this model realized an exhaust
velocity of 1750 m/sec comparable to a theoretical
value of 1913 m/sec.
During one of these firings Sanger, for the first
time, thought about vapor as a potentially feasible
coolant and on 9 May 1934, wrote about test run
83 in his log book:
For the time being, since a water pump is not available and
cooling by vapor to be investigated, partial evaporation of
cooling water is acceptable. . . . During the test run, strong
evaporation at the cooling water outlet can be observed, and
at times reading of the dynamometer is difficult. After 260
sec, at test cut-off, the nozzle is thrown out; at the top,