FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

NUMBER 10 231
Rudolf Nebel, who had somehow heard very
quickly of the contract signed on 11 March 1933
between Sanger and the publishing house Oldenbourg,
wrote Sanger on 25 March 1933:
Dear Dr. Sanger:
We heard that you are planning to complete your manuscript
on rocket technology by April 1. Herewith, we are
taking the liberty of forwarding you some informational data
and asking whether you might need additional material for
your book. We could also supply photographic material. We
assume that you are interested in including in your book
the latest research and are looking forward to hearing from
you.
Sincerely yours,
Berlin Rocket Field, Nebel.
Attached to his letter was Nebel's paper "Rocket
Flight" dating from the year 1932. Eugen Sanger, on
April 5, sent the following thank-you letter:
Dear Mr. Nebel:
This is to thank you for your letter of March 25 and your
paper "Rocket Flight" which I read with very great interest.
I am continuing with my work and would, of course, be
glad to accept your kind offer, should you be able to relate
to an outsider some of your apparently considerable experience.
First of all, I would like to mention that my book
"Technology of Rocket Flight" that has already gone to print,
discusses in a purely theoretical manner the scientific aspects
of the indicated subject. Structural details and photos of
structural elements are not included. My studies are limited
to liquid-propellant rockets. In comparison to your practical
experiments a difference exists in that I have eliminated on
the basis of my theoretical studies any static liquid cooling
of the rocket because of the chill-down problems that would
occur at high flight speeds. Partly, this is due to the fact
that I have considered the rocket purely from the standpoint
of a propulsion system for aircraft.
Thus, it would be of special interest for me to hear of the
experience that you gained earlier when still using heatblocking,
highly refractory materials for nozzle walls, in
particular I am interested in the type of materials used.
For lecture purposes I would appreciate receiving from
you some technical slides and detail drawings showing the
actual configuration, if these can be made public.
May I thank you again for your kind offer. With best
regards,
Sincerely yours,
E. Sanger.
No reply to this letter was ever received from Berlin,
perhaps because of the poltical changes occurring at
that time.
On 10 October 1933, Sanger presented a comprehensive
plan, "Testing Models of Constant-Pressure
Rocket Engines," to Professor Rinagl, his superior
and the director of the Technical Research Institute
of the Technical University in Vienna; to Professor
Katzmayr, chief of the Department of Aeronautics;
and also to the Association of Friends of the Technical
University in Vienna, asking for their support
for his efforts. With regard to the cooling problem
he mentioned in this paper:
A key problem in building a rocket thruster burning at
constant pressure is the thermal design of the combustionchamber
wall. It essentially consists of a load-carrying outer
shell, which has to withstand the very high combustion
pressures, and of an inner liner, which has to meet the following
requirements:
1. Adequate high-temperature service life, i.e., sufficient
mechanical strength at temperatures around 3500° C.
Because of low heat transfer and a very thin temperature
boundary layer, the inner surfaces of the combustion
chamber liner attain almost the same temperature as the
combustion gases.
2. Adequate resistance against chemical reactions with hightemperature
combustion products, thus assuring that a
liner lasts at least for a maximum operating time of 20
minutes.
3. Adequate thermal insulation assuring that the penetrating
heat can be absorbed by the propellants; the use of propellants
as coolants is feasible if the heat flux through the
liner is less than 1% of the liberated chemical propellant
energy.
4. Minimum weight.
Because of the first requirement, from the currently known
high-temperature resistant materials only a few metals, metallic
oxides, carbides and pure carbon may be considered,
mainly: thorium oxide, rhenium, zirconium carbide, titanium
carbide, tungsten, tantalum carbide, niobium carbide, hafnium
carbide, a mixture of hafnium and tantalum carbide,
and carbon. A final selection from among these materials
would have to be based on screening tests. . . . To cool the
walls of the combustion chamber and nozzle directly by air
stream during flight or by circulating a coolant around the
combustion chamber wall and through an air-cooled heat
exchanger, as used for internal combustion engines, is impossible.
The huge amount of heat to be dissipated in a very
short time approximates 150,000 kilowatts for an aircraft
weighing only 10,000 kilograms at take-off. . . . Direct or
indirect air-cooling must be ruled out because the air streaming
past the aircraft is heated by stagnation and friction.
. Consequently, the temperature difference between ambient
air and cooled wall at first diminishes and at very high
flight speeds turns zero or negative. . . . The walls exposed
to the burning gases must be highly heat-insulating and
without cooling withstand chemical reactions of hightemperature
combustion gases. Cooling of the combustion
chamber and heat flux across its walls is limited by the
heat-ingesting capability of the propellants serving as coolants
prior to their evaporation and injection into the combustion
chamber. . . . The design considerations valid for
the combustion chamber apply also to the structural and
liner materials of the nozzle. ... Of course, even the most
careful precautions cannot prevent relatively rapid wear of
the liner material of the combustion chamber and nozzle