Transcript

Report on a Conversation

I came to Aerospace from NACA, as an fluid dynamicist and aeronautical engineer. This was in 1961. I headed the aeronautical heat transfer group, which worked on launch and re-entry problems and heat transfer. Our mission was advanced test facility concepts.

In the mid-1960s, a major problem was the creation of a satisfactory ground facility to test nose tip materials under conditions corresponding to the severe re-entry conditions. No such facility then existed for both the heating and mechanical shear conditions. The failure mechanism of nose tips was not understood, so a facility was much wanted.

Our concept was to use a wind tunnel to achieve the mechanical aerodynamic shear and high pressures encountered, and to use a radiation source to irradiate the tip and duplicate the heat load. A cone experiences about 100 atmospheres and 10,000 degrees Kelvin, causing material to burn off.

Our original thought was to use an arc heater, to be built by Electro-optical of Pasadena. It may have been a xenon electrical arc. NASA had already used radiation loads for the simulation of thermal loading. In this situation, the wavelength is not important but the heat is. The entire facility was to be the Radiation and Cold Flow Facility (RASTA).

The pressure was to be created by a shock provided by supersonic flow past the nose cone. A contract was let to AVCO-Wilmington to build the tunnel.

We then became aware that AVCO-Everett had demonstrated the gas dynamic laser. AVCO-Everett suggested to AVCO-Wilmington that we use a laser with the tunnel. We therefore started a program to study the CO gas dynamic laser. Don Spencer was to do the experiments. We built an arc with nitrogen and carbon-dioxide to test the concept.

We went to AVCO-Wilmington to discuss these concepts; and after that trip, George Sutton carne from AVCO to make a presentation to the Air Force, and to convince it to change the contract. The meeting was held in San Bernardino, and we were present in the role of advisors. Since we had already been studying the feasibility of AVCO's scheme, we were able to agree with Sutton. The Electro-optical contract was terminated, so that we could have AVCO build the device.

AVCO had shortly before demonstrated the CO laser at a power of 10Kw. They had wanted the Avionics Laboratory to fund a project to reach 100 Kw. The Avionics laboratory had felt that this was premature and thought that they should do more work on the science. Since we needed orders of magnitude higher power, we in effect gave AVCO the possibility they sought of building a larger laser.

This program was ultimately classified 8th card because of the laser's power. At the start, however, it was either unclassified, or had very low classification. And our part of the program never was under 8th card.

During this time, the Aerodynamics and Propulsion Laboratory was directed by Joseph Logan. He eagerly promoted advanced concepts and facilities. Both my group in Aerodynamics and Heat Transfer, of which Spencer was a member and Ted Jacobs' Chemical Kinetics group, with Gross and Giedt were under Logan.

We had a common background in fluid dynamics with the AVCO people. Like them, we knew about nonequilibrium flow because of its association with re-entry phenomena. And we learned the necessary optics and laser technology. We did not have appreciable interaction with the Aerospace Electronics Research Laboratory. There was too large a power level difference between our work and theirs, and the lasing materials were different. We were also not in touch with Pratt-Whitney in Florida and Hartford, who was independently working on this. Abraham Hertzberg was a consultant for us, and may have been the source for us as to what was happening at AVCO.

The chemical kinetics group and my group were located in the same part of the same laboratory. We saw each other all the time. In the course of this contact, Ted Jacobs suggested to me that we join forces to demonstrate the CW chemical laser, using our Radiation and Cold Flow facility.

The idea was that nitrogen would get heated in the arc. We would then add SF₆ which, since it was hot, would dissociate into SF₅ and F. We would put a source of hydrogen on the other side of a porous material and flow the hydrogen out, and get lasing action in the reaction zone between the fluorine and hydrogen.

The first experiment did not work. But we at one point moved the hydrogen source up to the edge and put the mirrors in place and it did work. At that point, we realized that what was needed was hydrogen flowing in from the edge.

The discovery was something of an accident, but we had the right techniques in the right areas. I am proudest of the fact that we understood the CW laser in a matter of months, how it scales, how it operates. We were able to exploit the capabilities of the chemical kineticists and the fluid dynamicists. We could come up with design criteria.

The division of labor was that my department had the responsibility for device development. Chemical Kinetics did the science, primarily kinetics, optics, mixing, modeling; when they ventured away from that area they made bad mistakes.

The variety of skills that were involved — chemical kinetics, fluid dynamics, mechanical design, analytic modeling on the computer — are all involved in rocket launch and re-entry science; it's the same technology.

Logan encouraged us on the chemical laser. He had read Pimentel's article in the Scientific American. Shortly after we started, Dick Hartunian replaced Logan. Then Wally Warren came in. There was, however, about a year when there was no head, and that is actually when most of the work took place.

In the early 1960s, for example, in 1961, this laboratory had an academic atmosphere. 20% of our effort directly supported the Air Force while the rest of our mission was to be a recognized science center, capable of attracting good people. We were to be knowledgeable about advanced technology in order to help in both current program development and future technology.

Over the years, our discretionary funds have been reduced, and we have shifted more and more to direct support to the AF. However, the progressive tightening of money did not affect this program. It was always funded, although as a low scale, marginal effort, with 1-2 people.

Interestingly, I remember that I had to fight at one point for the use of the laser. A review was called by management. Essentially, our upper management knew about the 8th card effort, whereas we didn't. They wanted to know what we were doing. There was some opposition when we presented our ideas to the review group. We were asked, "Why use an arc? It's not practical. Eventually, you are going to have to use combustion excitation. “I was the one to give that presentation explained that in this way, we could separate the heating from constituent phenomena.

It was that flexibility, given by the arc, which led to the HF laser. We already had the leads in the apparatus f or the CO₂ and so were able to just substitute a bottle of SF 6 for the CO_2. On the other hand, the RASTA facility itself never proved practical. The fluid dynamics — heating relationship was not properly simulated by it. Part of the problem was that the heating was sharpening the nose cone.