[Wade, 1971]
Mezger, 1969 (Photo courtesy of NRAO/AUI/NSF)



NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Interview with Peter G. Mezger
At the Max Planck Institute, Bonn, Germany
November 22, 1973
Interview Time: 1 hour, 7 minutes
Transcribed for Sullivan by Bonnie Jacobs

Note: The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History or Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web.

Sullivan

22 November 1973 and this starts the interviewing of Peter Mezger at Max Planck Institute in Bonn. Now you actually began in France, is that correct?

Mezger

Yes, I began in France and, in fact, I was studying at the technical Hofschule in Munich which was an institute for technology and I didnít hear one single lecture in astronomy. But then I got a scholarship for France, and at the time I was working as a summer student at the Seimens Research Laboratory, and my boss, Professor Clain, who is well known in electronics.

Sullivan

Yes, Iíve seen his name on a couple of old German, Clain, yeah.

Mezger

He was primarily concerned with the development of electronic tubes and later on with traveling wave tubes and things like this. So after the war in France, he had pretty good connections, he in fact wanted to get me into a laboratory at the CSF, a combination of [?] and [?] but those guys didnít feel like taking a German from their competitors. And so Clain remembered that he knew Rocard, who was then director of the Ecole Normale. He talked to him and Rocard [told him if he gets it going?] and heíll see what he can do. It turned out that at that time at Ecole Normale, nearly all laboratories did classified work for the Marine Nationale or similar institutions and there was only institute which more or less did free work and this was the laboratory which was headed by Denisse on radio astronomy.

Sullivan

So you didnít go there specifically to do radio astronomy?v

Mezger

Oh, not at all. I didnít have the foggiest idea then Clain told me about something, that they are looking at old stars which have exploded some hundred years ago, and I didnít foggiest idea about this whole thing. But I of course knew a lot about electronics so the laboratory accepted me and the people with whom I was involved with most with was Denisse, Steinberg, and Blum.

Sullivan

And you went there what year?

Mezger

It must have been in 1954. í53 or í54, Iím no longer exactly certain but I could look it up if it is of interest. And the laboratory at that time was primarily working on solar. In fact, I think exclusively working on solar radio astronomy. They didnít have the telescope in NanÁay. Their prime instruments were some small solar interferometers and a WŁrzburg telescope which was of the leftovers of the German Airforce. A 7.5 meter telescope, a very deep reflector which was mounted in Marcoussis. With this telescope, we made observations at 30 cm if I can remember. We had some of these dipole walls for observations at lower frequencies.

Sullivan

Where was this located again?

Mezger

In Marcoussis.

Sullivan

And where is that?

Mezger

That is sort of a suburb of Paris. I canít even tell you what direction it is. I think south or southwest and it was probably some research from the observing station where they had their telescopes. Now Denisse was primarily working on theoretical problems. He had, at that time, a very good reputation. [?] was primarily concerned with radiation from the Sun and from plasma. And Steinberg was involved in observations and construction of receivers. I think he was the first man who had roughly looked into and measured some of the problems related to Dicke switch receivers. And Blum was concerned with the development of receivers for lower frequencies. I think he had already at that time some interest in interferometers. I think they were in the process of constructing a two element interferometer, although again with two of the WŁrzburg dishes, which later on was used by Lequex to measure a number of radio sources. But it was already at that time, they prepared the move to NanÁay. There was another guy involved in those days with radio astronomy. Heís named Laroux and heís not very well remember in radio astronomy although he is a highly intelligent man. He didnít speak one word of a foreign language so he didnít ever go to any meetings. Highly original man; was involved in the development of low noise mixers and later on parametric amplifiers but he switched as easily to theory. But he sometimes got sidetrack and wanted to reinvent quantum mechanics from the Maxwell equations. Things that obviously other people had looked into and he got lost to radio astronomy. Heís now a professor of theoretical physics in, I think, University of [?] or somewhere.

Sullivan

I see. Iíve seen his name. He left the picture when? The early Ď50s, mid Ď50s?

Mezger

Middle or end í50s. I think it was rather end Ď50s. As a paper, he is probably best known for; he was the first man to settle this question of the polarization of synchrotron radiation. That was his contribution. Well, I worked there for one year and at least, I got some ideas about astrophysics. I still can remember one evening, we were sitting on the roof of the Ecole Normale and Denisse outlined to me the Milky Way system. Thatís why you see this narrow strip. And at that time, I was primarily interested in instrumentation, and then I came back to Germany and I wanted to go back to Siemens Research Laboratories when I came home. And at that time, Germany had gotten the money to build a 25 meter radio telescope.

Sullivan

The only other radio astronomy going on was at the Heinrich Hertz Institute, is that correct?

Mezger

Yes, at the Heinrich Hertz Institute. A department of the Heinrich Hertz Institute, under Hachenberg, worked, I think, rather exclusively in those days at solar.

Sullivan

Heís told me about that of course, but was there any other radio astronomy going on?

Mezger

Yeah, there were two small groups. One in Kiel with UnsŲld.

Sullivan

Oh, thatís right. They did do some observations there. Priester told me a little bit.

Mezger

The instrumental man had the name DrŲge and the Priester was the astrophysical man and they made a survey of the whole sky at 150 MHz. I think this was a pretty good contribution to German radio astronomy, in those days. And about the same time when this money was given for the 25 meter telescope, then Becker, who was the director of the Bonn University Observatory in those days, looked around for people to work on this project and he got Priester from Kiel as sort of the astrophysical man and he hired me at that time as the instrumental man. Now the driving force behind the 25 meter telescope was Brant, Secertary of State of the North Rein Westphalia, for basic research, the only position I knew of in any of the German states. He was a member of the Socialist Party and had very good connections to everybody. During the war, he was the head of the radar development. I think first of Telefunken but if I remember correctly, then he headed the whole operation at Telefunken. He coordinated the efforts of the whole company. So he was actually too high up in the hierarchy, he was an administrator, no longer a technical man. But then after the war, of course, any German activity on radar or anything connected with radar, I think even wave guides, the building of magnetrons or klystrons was highly forbidden and then came up this radio astronomy.

Sullivan

When was this allowed to begin microwave work again?

Mezger

I could not tell, I think at the time when I started most of the restrictions had fallen. The only restrictions I can still remember in those days were for electronical tubes, tubes where you measure very weak currents and it needs primarily nuclear physics but I think the wave guide restrictions had already fallen.

Sullivan

So they were able to do the solar astronomy with just dipoles?

Mezger

Well, there is an interesting part. Because Hachenberg Institute, Heinrich Hertz Institute was in East Germany not in West Germany and as far as I know the Russian gave a darn about any restrictions. That was the amazing factor. When I first met Hachenberg at the URSI Meeting in Den Hogue which must have been í54 or í55.

Sullivan

You had to meet him outside the country?

Mezger

Yes, yes. And he talked about an eclipse which just had happened before and he strange enough said it was the best solar measurements of this eclipse at high frequencies at short wavelengths 3 centimeter so they must have been very much advanced but they had a lot of problems of getting tubes and I remember one day giving an overnight visit to East Germany. I brought him over a few diodes, 1N21C, though it probably wasnít the best thing and I brought him a few of the low noise input stage tubes, cascade tubes and things like this. So they obviously didnít have many restrictions, he should know better but they didnít have much material so it was quite a performance to get things running.

Sullivan

Now what about Priesterís survey though? Was that held down by restrictions?

Mezger

No, no, no.

Sullivan

So dipoles and TV antennas and so forth, there was no restrictions on that sort of thing?

Mezger

No and of course all the receiver for 150 MHz was not exactly classified. It started only when you get into the higher range.

Sullivan

So Brant was the driving force for getting the money for the Stockert Telescope and why was he interested? Was it just a matter of looking at other countries and saying this was a good field to work in?

Mezger

Yeah, I mean he saw the possibility to get somehow back into this radar business through...

Sullivan

Radio astronomy. I see.

Mezger

Radio astronomy. In fact, when eventually our 25 meter telescope was built and ready, we had to give away a certain percentage of a certain time for active radar work because at that time the restrictions had fallen completely and they had installed one of these high powered 21 cm radar systems and made experiments which were classified so when these people worked, we were not allowed to come into the Stockert building and if they had ever done anything useful or not, I donít know. After two years I left the place and Rocard takes the instruments over.

Sullivan

And that was under Brantís control, the experiments?

Mezger

No, I think it was the German Minister of Defense who controlled it somehow but loosely and what they actually did, I donít know. Well, though the 25m was planned in either í53 or í54. It must have been í54. I went back to Munich and finished my diploma. Then I started to work with the University of Bonn, early in í55 or late in í54 if I remember correctly. At that stage, the initial planning had already been done. They had decided for a 25 meter telescope primarily because at that time the plans for the 25 meter telescope at Dwingeloo had also been advanced. And so Germany felt that they should have at least an equal telescope, and the work which they primarily wanted to do was 21 cm line observations.

Sullivan

And who set that decision?

Mezger

Well I think this decision was made by Becker although before I came. In fact, when I looked into the planning of the receiver I was a bit shocked to see that there were only provisions for measuring the line and there were no provisions whatsoever for measuring the continuum. I sneaked in sort of a continuum channel in order to make some continuum measurements. I think one of the basic mistakes which they made here was that they did not have any electronics development here at the university itself. Everything was done by industry outside.

Sullivan

By contract?

Mezger

Yes, they had the chief contract was Telefunken and then they had Zeppelin and [?] which built the telescope or the reflector and the company Alket in Berlin who built the machine parts and so on. Telefunken itself built the radio receiver and so I had quite some influence on the way this receiver was built. I sneaked in this continuum channel. I worked for about one and a half years at [?] with Telefunken and then when the telescope was ready and the receiver was ready, we moved it out to the Stockert and then it took us another half a year at least until the electronics ran smoothly. This must have been in the early í57 or so. And that time I still didnít have much feeling for what this whole thing was good for. I was relying that the people here at the University of Bonn would know what to do.

Sullivan

Where to point it.

Mezger

Yes, and this was a bit disappointing in the end, we did not get very much support. Priester who was supposed to be the leading man got sidetracked by Sputnik, the early days of Sputnik. And one of our technicians was a ham and he had some equipment and we really started to observe Sputnik and the TV people called in and the journalists and so on, Preister did some of the early interpretations of satellite work and he got completely so completely sidetracked that he is now...

Sullivan

Heís still in space.

Mezger

Still in space research especially in high atmospheres; thatís where came in, I think, and his Chair which he holds nowadays is for theoretical astrophysics and space research but what he is doing is primarily physics of the high atmosphere.

Sullivan

I see. What was he doing with Sputnik? Calculating the orbit and things like this?

Mezger

Yes, calculating the orbit, calculating the slowing down, and they found the inversion layers and the interpretation of the thing. I think he worked pretty closely together with the Goddard Institute, not in Greenbelt but in New York and these people.

Sullivan

In New York.

Mezger

Yeah so he was more or less lost for radio astronomy and for those 21 cm line profiles, there was not too much interest here for the rest of the people. They were this type of classical stellar astronomers with not much of a basis in astrophysics; and I just didnít understand enough to do any interpretation of the work.

Sullivan

But who made the decision originally for the hydrogen line or because thatís because the Dutch were very gung ho on that and then they felt...?

Mezger

Ok, this could be the reason. As Becker explained it to me, it was that he and especially his brother Wilhelm, who was still in Bassel. He did a lot about investigating, exploring the structure of the Galaxy. It was Wilhelm Becker with all the classical associations. O stars and HII regions always find the three arms so it was anthing and they saw it was [?] but I mean the whole matter of radio waves and receivers and so on was so far from these people here and Becker himself was no longer active. He had suffered from a heart attack and from that time I think he was more or less a teacher and an administer. The group was practically endless.

Sullivan

Yeah, I see what you are saying. Let me just verify what this personís name is? Is it Becker? B-E-C-K-E-R?

Mezger

Yes, the name here was Frederic Becker and Wilhelm...

Sullivan

And Wilhelm is still one active with galactic structure?

Mezger

Yeah. Well and then in 1959 I got so fed up with this 21 cm business that I had some talks with Westerhout in Leiden whom we had visited several times and he had visited us, and so I started continuum work. In fact my first measurements was I got interested in the variations, the count variations of the map, the horizon of Stockert, and we actually got a picture of the thermal radiation from the count and then I found out that this could be used to calibrate the telescope.

Sullivan

A la Kootwijk.

Mezger

Yeah with one exception, we were aware of the effects of side lobes and the back lobe where the people in Kootwijk did not. So I calibrate the telescope and made at that time one of the first accurate measurements of Cassiopeia A and then four other sources which we connected to it and I think this value still stands today. I mean the large error bar of course. That was one of the first accurate measurements.

Sullivan

Thatís at 21 cm?

Mezger

At 21 cm and then I decided this continuum I understand more about it and I understand how to make maps and so I started to build an 11 cm superheterodyne receiver.

Sullivan

Let me just ask about the hydrogen line work. Was that ever published, any of that work anywhere?

Mezger

No.

Sullivan

Iím not familiar with it at all.

Mezger

I think they published it in the end in some obscure publication. I mean it never was in the standard at Bonn or something like this. It never made any great hit.

Sullivan

OK, so you built an 11 cm?

Mezger

Yeah, I built an 11 cm. I again made some absolute calibrations of the antenna and so on but primarily what we were setting out was a survey of the galactic plane at 11 cm. I was joined in this effort by two graduate students from the University of Muenster. Ok, I should perhaps say another work which perhaps I published which I think was quite successful in those days was thermal radiation from the moon at 21 and 11 cm and thatís another story. I teamed up with Strossel who is a complete positional astronomer because I couldnít...

Sullivan

Librations and such?

Mezger

Yeah, heís just gave me a table and he also gave me the diameter of the moon and I was very much amazed to see that the diameter of the moon changes. So I started my plots and I saw the thermal radiation of the moon was changing and of course, it was what I was expecting because Minent had published the measurements at high frequencies had changed and they attached this beautiful theory of the dust layer and so on so I suspect itís the same thing. But Akabani had done a similar thing at 11 cm and also found that it changed.

Sullivan

In Japan.

Mezger

In Japan. And then I did the same thing, you know, the diameter changed but I also had this table where I found that the diameter of the Moon also changes and I did the convolution into a Gaussian beam with the disk and after I did the thing and corrected it, it came out a perfectly flat line and we went back and checked Akabaniís measurements in France and what he was observing was just the effects of the variation of the diameter of Moon.

Sullivan

And you donít get as much of an amplitude as you do at 1 cm.

Mezger

Itís completely flat. There is no amplitude whatsoever. And we got a good mean value of the Moon. Ok but since we are assigned things then we set out for this 11 cm survey and I was showing to my two graduate students from Muenster, where Strossel had gone as a professor and Altenhof and Wenker.

Sullivan

Strossel was first here at Bonn?

Mezger

Strossel was first here at Bonn as an associate professor and then went to Muenster where he became a full professor of astronomy and he still continued including in his courses radio astronomy. He had, of course, no instrument himself but he had an arrangement whereby he could send his students including the first two of mine Altenhof and Wenker and they got involved first in the 21 cm line observations and then I got them interested in this survey.

Sullivan

What year is this now? Just to see where we are.

Mezger

Hmm?

Sullivan

What year is this?

Mezger

It was 1959. So we got about 3 months time on the 25 meter telescope and we surveyed the Galactic plane completely, and then in the interpretation we teamed up with Gart Westerhout who just was on his way to Maryland and we got out a paper as quick as possible. And after this thing I left astrophysics disgusted and went back to the Siemens Research Laboratory.

Sullivan

Thatís this one right here. Altenhof, Mezset, Stossel, Wenker, and Westerhout.

Mezger

Yeah and Westerhout went to the University of Maryland and Altenhof and Wenker went back to Muenster to finish the thesis, I think Altenhofís work was on the refraction and attenuation of radio waves by the atmosphere. It was on the sideline of this 11 cm survey.

Sullivan

And Wendkerís thesis, was that?

Mezger

He did his thesis much later on. Iíll come back to this thing. The one thing I should mention, already with the 11 cm survey someone had turned my attention to a paper by Kardashev on the possibility of seeing the recombination lines and when we considered what can we see at 11 cm, of course, HII regions and one looked at those HII regions and one saw that they were all over the sky, out to the... Then someone showed me this paper by Kardashev and I realized that if we could recombination line, we may be in a position to also get kinematic distances of the HII regions so I had built in this 11 cm receiver, one channel spectrometer, which just scans the channels to look for these lines, but this experiment would get never off the ground because we first wanted to complete the survey and once the survey was completed there was no observing time left and I wanted to leave astrophysics anyhow so we never got the chance to look for the recombination lines.

Sullivan

And that was in í61?

Mezger

No, this was in í60. In í60 eventually I left in September of í60. I left radio astronomy, I went back to Siemensí Research Laboratories and there I worked primarily on the development of parametric amplifiers, and my only connection then to radio astronomy was because I worked in a research laboratory I was not obliged to do anything that directly related for commercial use so we had an agreement that I was supposed to build a 21cm paramp for the Stockert as a sort of something you would like to see how it works. And during that time I had quite some good connections with Brian Robinson, at that time worked in the Netherlands also in the development of parametric amplifiers. He worked on upconverter or downconverter and I worked on directly on a straight parametric amplifier [isolators?]...

Sullivan

Circulator.

Mezger

Circulator. Anyway, it was a two stage parametric amplifier which had a gain stabilization by servo loop which controlled the diode, current, and it was a quite successful thing. We finished it after two years and brought it up to the Stockert and built it in; and I think it worked there for three or four years approximately, again for 21 cm line measurements. Shortly after I had left Bonn, Hachenberg took over, first as an associate professor, later as a full professor. What had happened was at his institute where he worked was in East Berlin and he himself in West Berlin and they built the Berlin Wall on a Sunday and he was in the right part so he had some negotiations and they forced him to either resign or move his family over. So he resigned and then Becker got him the job here and Hachenberg had to take it over.

Sullivan

He did get to bring his family?

Mezger

Hmm?

Sullivan

He did get to bring his family with him?

Mezger

Yes, I mean his family was in West Berlin.

Sullivan

They were in West Berlin. Oh thatís right, the whole family was in West Berlin.

Mezger

So he didnít have any problems. Ok, then what has happened here, they started this 80 to 100 meter telescope. Thatís the story which I donít know, Hachenberg should know all about. My personal fate was that I already worked at Siemens and got a few offers from the United States. One was from Kraus, other was from another place and eventually I got this offer from Heeschen; and at the time, I was decided to make an industrial career. But anyhow it was interesting to go to the United States so I negotiated with Heeschen that I was coming for one year as an associate scientist or research associate and I was primarily interested at that time in instruments, so I set out and developed testing of the NRAO Green Bank telescopes. They had this beautiful photometric, no, not photometric, photogrametry. Anyhow, it was a survey from a helicopter where they could measure actually the best fit deviations of the paraboloids.

Sullivan

From a helicopter?

Mezger

Yeah, from a helicopter. They made stereometric photographs.

Sullivan

I see.

Mezger

So they had surveyed all the different reflectors of the 300 foot telescope and on the 85 foot Tatel telescope. So they knew what the deviations were and I, of course, knew with John Ruzeís theory which was never published. I thought, My God, you have a fantastic possibility to check the theory and so we did measurements and Heeschen was very sympathetic for the experiment and he gave me all the help and we checked the 300 foot telescope down to 10 cm and the Tatel telescope down to about 1.9 cm and we found we could confirm Ruzeís theory and we checked out the telescopes and at the same time we continued some work on high resolution observations of Galactic sources; and now if I say we, this mean who at that time had come over and I also had gotten Wenker from Muenster who wanted to do his thesis work, so we got him over to Green Bank and he worked with me and Wenker with Jason Baars, who was instrument minded.

Sullivan

Now when did you go to the states?

Mezger

It was í64. I think both of us arrived in í64.

Sullivan

And let me just also ask, did this 21 cm paramp that you built that was used for several years, I guess that was used mainly while you were in the States?

Mezger

Yes, I didnít have to do anything.

Sullivan

You never took part in those observations?

Mezger

No, no. Altenhof and I did some measurements with the paramp just to check it out, published just these results as a proof how parametric amplifiers work what this was the end. I was completely disconnected.

Sullivan

Who were the people who worked with it mainly? Just for my information.

Mezger

Well I think there was Rolfs and Gernstein, who is now mainly into computer engineer here, and Felton. I think all the people who are still around but never published very much.

Sullivan

Right, I mean these things are not known at all.

Mezger

No, itís more or less the effort was completely lost and ok, I really donít know the reason why the thing never got off the ground.

Sullivan

Ok but anyway back to the States. So you worked first on the parabolas, the surfaces of them at Green Bank?

Mezger

Yes and then I was always interested in observations at very high frequencies so, ok, so at that time there was Frank Low, who worked at 1 mm and I [?], Heeschen, and Hvatum, who was at that time head of the electronics division, that you show make an effort to bridge the gap between 1 mm and say 2 cm and we started a millimeter wave laboratory where I was the head of the thing and Rama Menon, Menonís wife, was working as an engineer and Neil Albaugh, who is still at the 36 foot telescope out in Tucson, were my first people and later on we got some technicians. And however, we ordered the spare parts for the millimeter wave receiver but there always is time delaying up for about half a year and so in the mean time we thought what else can we do. And at Green Bank at that time we had a maser at 6 cm which was a horrible thing. It was built by Airborne Instruments and it never got off the ground. We raised it weekends and nights and so on to get it to work and it never worked. I mean, it would hang on the telescope then itíd work for ten minutes. In this ten minutes, one got beautiful fantastic measurements and then it broke down. And so again everybody was disgusted. The maser was put in some corner. And I had this millimeter wave laboratory, we didnít really know what do to so I asked Hvatum if he had anything against if we dismantled this maser and took the second stage. It was a high noise paramp, so to say, 400į or so and then I wanted to look again for the recombination lines and because Hoglund had just completed a 20 channel receiver for Mort Roberts to look for 21 cm lines in extragalactic systems, we had the right channels widths and I decided weíd work together and built a receiver and we made it together and at that time the 140 foot telescope just got into operation. This was in 1965 and I must say, ok, I told you in the beginning I first came over for only for one year but when I had seen the 140 foot telescope, I immediately fell in love with it and I realized that when this instrument is in operation, itís the biggest instrument, so when Heeschen offered me to stay, I decided immediately to stay. And ok, my people at Siemens werenít too happy about my decision but on the other hand, they took it nicely and so after this one year was over, I took all my furniture and everything in a big box and became a permanent staff member. It was at the time when just before I left to go back to Germany, we had completed the first version and we had put it in the Tatel telescope and I was there for the first measurements but then I had to leave and Hoglund took over and when I came back I saw the results. It was rather strange. Sometimes there was something that looked like a line but then at other stages...

End of Tape 22B

Sullivan Tape 23A

Sullivan

So you came back and the results looked puzzling on the 85 foot?

Mezger

Yes, and then we waited on the 140 foot telescope to get into business; however, at the time there was one of the IAU meetings in Hamburg, and Heeschen came back and told us about measurements done by the Russians, and it was so noisy and horrible looking that nobody took them serious and it was quite a situation and I will come back to this thing later. So then we got the 140 foot telescope into operation and we installed the 6 cm receiver as the first system but it should first be used for pointing measurements which was done by a guy named DeYoung and then Kellermann, of course, wanted already to look for extragalactic sources and we could see that time pressure would become bigger and bigger and we wouldnít get much time to do our line experiments but then something that was fortunate for us and unfortunate for them happened because when DeYoung made the pointing measurement, he saw that the pointing was changing from day to day and this ,of course, was a rather horrible story and they found out after about one week what had happened. The encoder was rigidly coupled to the declination axis and there was a bend in the thing and the coupling couldnít take it so the bend translated into the encoder and somehow broke, the encoder so to say, and in the process until we realized the thing, the encoder was damaged and it was damaged so much that we had to bring it back to, not to Feranti, I forgot the real name, to get the thing fixed and it took them at least 14 days to fix it and during this time, we had only an encoder which was accurate to about 1 degree and so nobody wanted to use it, at least not Kellermann. So we had the telescope for about 14 days for us. We, of course, didnít have any problems. We could pick up on strong sources like M17 and Orion. So we got the receiver fixed and we found out what the reasons was that we did not find the recombination lines on the 85 foot telescope. There was a servo loop on the local oscillator which worked intermittently and sometimes it locked the local oscillator to the standard frequency and sometimes it did not and when it did we could see a line and when it did not, of course, the local oscillator would run away and we couldnít see anything.

Sullivan

So you were out of lock essentially when you werenít seeing the line?

Mezger

Yeah. After the thing was fixed then in the first night, we worked on it and we integrated on M17, it was the first source. We could already see it on the analog records and Hoglund took the thing back into the computer which we still had at Green Bank at that time after he came back and you can see the line sticking out like a sore thumb. It was quite fantastic and then the next thing was Orion but I just didnít believe in it. I stayed at that telescope until the morning around 10 or 11 oíclock until we got Cassiopeia and Virgo and we didnít see a line then I believed we did it and we actually had the line. In fact, when I go back to my, our, publications in Science where we announced the detection of this line and we also showed the spectra of the non-thermal source, we showed for the first time, at that time we didnít know what it was, but baseline ripple.

Sullivan

Yeah, baseline ripple little did you know that many years later.

Mezger

So this was the story of the recombination lines and there I just want to mention the following thing. Of course, later on I was interested in why did nobody else look at those recombination line before Kardashev had published this paper in í59 and he had already communicated the results at the IAU meeting in...

Sullivan

The URSI Meeting in Ď58, no, the IAU Meeting in Moscow in Ď58.

Mezger

The IAU Meeting in Moscow and people were questioning if this was correct and Shklovskii got up and told that he had already checked the computations himself, Kardashev was one of his students, and he thinks that he is right. And why did people not search for these lines, the reason was they that assumed that stark effect would wipe out the thing completely and this came just by applying a theory which was developed for the optical region extrapolating it to radio range and even when the Russians announced the detection of these lines in Hamburg and all the American radio astronomers were around, again nobody believed it because when Lilley came home and talked to Menzel, he reported they canít see the line and after we had announced the detection of this line, it took Lilley about four or five days to retune his 18 cm maser for the OH line and see the lines again. It was a rather strange thing. As far as the stark effect goes, a couple of months later I was invited for a colloquium at the University of Maryland by Westerhout; and I was talking to Westerhout over a glass of something, the strange thing was the stark effect and he told me, ok, talk to the expert on this thing. Who is the expert? This Hans Green, his little daughter is just here for a birthday party and he will pick her up and talk to him. So I talked to Hans Green and I got to even talk to him in German because he was coming from Germany, and I told him to come to my office tomorrow and I will explain what the problem is so when I came, he had already filled eight sheets of paper with equations and he told me itís not as simple as I thought and it turned out it was not that simple. It took about three months to work out the theory of stark broadening. I hoped to understand. Today it looks like we still had overestimated the stark effect. Yeah, this was the early days of Green Bank and then of course, after the detection of the recombination lines we did these surveys of recombination lines primarily in cooperation with Bernie Burke and his students Tom Wilson and Ted Riffenstein. These surveys which we first did with NRAO telescopes on the northern hemisphere and then later on Tom Wilson and I went to Australia and did it again with Frank Gardner and Doug Milne for the southern HII regions with the aim of investigation the large scale structure of the Milky Way. In other efforts as far as the helium lines and the carbon lines were concerned I cooperated with the people from Harvard, Ed Lilley, Zuckerman and Pat Palmer. This was the setup. We also continued our work on continuum observations of HII regions especially on high resolution observations.

Sullivan

Before you go any further, let me just ask about the early days at NRAO. So you were there after Struve had gone?

Mezger

Yes.

Sullivan

So you werenít that early but I was just trying to get a feel for what sort of place did it seem like when you were there? Was it all working well or?

Mezger

I came there in í63 and just a couple of months ago Heeschen, had been named Director at NRAO. You know, Pawsey was supposed to come and got this brain tumor and never could take over. So at that time the NRAO was apparently very heavily under attack by other American radio astronomers and they had a visiting committee and this visiting committee convenes, they obviously only said very nasty things about the radio astronomy as a sink of money and so on and so on.

Sullivan

Money should only go to the universities.

Mezger

Yes. Yes. So ok, when I came, the situation had still these very heavy attacks from outside but inside the organization, I met an organization which impressed me very much. Heeschen was a man, a very strong minded man, who had a big idea about how to organize this place. I did not agree fully with all his decisions. For example, that he felt the receivers for the telescopes had to operated in a way so that an outsider observer who would come and use the thing without diving into the details of this instrument and so on. I did not agree with this thing but later on I found out it was the only right thing to do because this was a national institute and it had to serve a purpose. I think although in the opinion of the outside the NRAO had gone through its lowest point with the successful operation of the 300 foot telescope. It was a cheap instrument. It was built in a very short time and it was primarily to have the instrument working and it just had started to work a couple of months before I arrived.

Sullivan

When was the lowest point?

Mezger

It must have been in probably in í61 or í62.

Sullivan

Before the 300 foot?

Mezger

Before the 300 foot, yeah. The 300 foot was the first thing where you had an instrument in place in Green Bank which was outstanding and people came. In fact, when I was around at that time the first people to use the instrument officially was Bernie Burke and Ken Turner.

Sullivan

Yeah, he told me he was the first on to use it, I think.

Mezger

Yeah. They had their spectrometer in a van. They had a something which scans the channels and Westerhout was around too and wanted to use the scanning feed; however, with this scanning feed they had forgotten there is a beam factor when they scan to higher rates. The tilt angle of the feed and the tilt angle of the beam are not the same. The tilt angle of the beam is smaller. At that time, Frank Drake left for JPL and then later on for Cornell. Yes but I had a feeling that they were an organization that was over the hump and you could see how the spirit was improving. Every day they got people with good reputation like Morton Roberts came in. So I must say that I never saw the inside of the observatory in the low days. I only saw it on the up.

Sullivan

But what created these? The fact that they only had the 85 foot and it wasnít so great a telescope after all?

Mezger

It was the 85 foot telescope, it was not a very good telescope. The place was horrible. I mean you just couldnít get a good man to come to Green Bank for a long time.

Sullivan

To live there?

Mezger

Yes, I mean itís a small place and it was very underdeveloped at that time. You had to drive 80 miles to Elkins in order to go shopping so wives didnít like it. They had some troubles with the school. All kinds of thing right together.

Sullivan

And when was the move to Charlottesville?

Mezger

It was in í66 or í67. I think í67. [Move to Charlottesville was in 1965.]

Sullivan

So that was after things started going up?

Mezger

And then of course, the big chunk came with taking in the operation of the 140 foot. This was really the big thing. Now of course, the construction of the 140 foot telescope was marred with problems, all kinds of problems, and the last one which I remember still very lightly was when they had to turn the reflector around which was built face down. In order to mount it, they had to turn it around.

Sullivan

You mean they had to pick it up like so?

Mezger

Yes, they had to pick it up like so and turn it around and they had fixed two cranes to pick up at the center of gravity and took a small one to turn the thing around and they didnít get the center of gravity right so the pull on this little crane which had to pull the thing over was much too large. The rope broke and the reflector was swinging back and ran into the ground. This is all very dramatically shown in a movie.

Sullivan

Iíve seen that movie a long time ago but I didnít remember that scene was in there.

Mezger

Ok, perhaps they have taken it out. It wasnít very much appreciated.

Sullivan

No, it was when I was an undergraduate in í65.

Mezger

Ok, there are two movies. One which is shown to the normal spectators and one which was done on the request of the project manager of the 140 foot, what is his name, [Max] Small.

Sullivan

But the real story.

Mezger

The real story which was all the problems and they were not very much liked by Associated Universities but there you see this beautiful color picture and you see this little thing and you also hear the sound and then you hear how the alarm bell starts to ring because there is an overload and you see the crane operator jumping out of his crane and flying then you hear the bang when the rope breaks and the receiver swings back.

Sullivan

I guess itís not really funny.

Mezger

Nothing happened. This machine was so heavy.

Sullivan

So it didnít damage the reflector?

Mezger

No, it didnít damage the reflector. And otherwise the thing went very smoothly apart from this pointing and encoder business.

Sullivan

Did that get straighten out quickly?

Mezger

It was about 14 days. It was straighten out and they put in a belly coupling which then could take the strain and so on. We had always constantly had problems with the 140 foot telescope with the hydraulic system but the operators knew how to solve these problems. So I think it turned out to be one of the most successful and most efficiently operated telescopes.

Sullivan

So once it was built then there were not many problems? It was only in the actual building that..?

Mezger

Yes, in the actual building. I think at several stages, as far as I know, they wanted to terminate the construction; and once it turned out that they used the wrong steel which then started to crack at low temperatures and all kinds of things. You could still see all the spare parts which they had taken out still lying around the 140 foot telescope. But then the thing went up and I think that Heeschenís policy paid off that he was leaning over backwards to give service to the universities. It was so that sometimes the staff members were quite fed up with the thing seeing that the outside people came and didnít know too much about observations but got the bulk of the observing time. But on the long run I think Heeschenís policy paid off, which changed this wave of hate against NRAO and gave support and eventually led to the result that the whole astronomical community was supporting the VLA.

Sullivan

I forgot what I was going to say, oh yes, I donít want to take it much later than í67 or so. I think thatís about where youíve gotten to I think because I got to stop somewhere. It gets a little too much out of hand but now were you involved at all with the 100 meter telescope in the mid Ď60s? I mean can you tell me anything about that from your point of view?

Mezger

No, I can only tell the story as far at von Hoerner was involved. Von Hoerner was involved so far in I think it was in í65 probably, í64 or í65. He was the professor for astronomy and the director of the observatory in Tubingen. [?] had died and Sebastian von Hoerner was invited for this chair of university and von Hoerner at that time was deeply involved and fascinated by cosmology and he found out at moon occultations was a good way of measuring at high angular resolution and then he realized the existing antennas were not big enough and so he looked how can you build antennas and then in typically von Hoerner way, he started to get involved in the construction of antennas himself and went down to the basis and started again. In fact, he later on worked for five or six years on this problem and came out with a solution of homology. But any how when they asked him if he wanted to come back to Germany, he made it clear that he would only come back if he got a radio telescope and then some people pointed out to him that the best way to get some money would be through the Volkswagen Foundation. Now obviously at the same time, the people in Bonn like Hachenberg, got all the plans to build a large radio telescope and then they heard about von Hoerner and they also applied to the Volkswagen Foundation and so there were two proposals for two large antennas. One in the conservative construction by Krupp and MAN at Bonn and the other one in using homology construction by Sebastian von Hoerner.

Sullivan

Were they as big as 100 meters?

Mezger

I think he was even talking about a 150 meter telescope or something like this. He wanted it only for lower frequencies. He was not interested in high frequencies. Well and so the Volkswagen Foundation was faced with two proposals and they had to make a choice. And they asked an institution which is called Rich Sternwarten where all the directors get together and they should give advice. And their advice was, of course as you can expect, was that you build both instruments. The Volkswagen Foundation was again faced with the problem and then they made a rather clever decision. They told the two parties you get some money provided you find an institution which gives you the operational budget, which was about 10% of the investment cost. Both of them wanted 18 million deutschmarks so they had to find a yearly budget of 1.8 million deutschmarks which even at that time was a very high amount of money. So it was clear that no university, neither Tubingen nor Bonn could bring up this money and von Hoerner who originally came out of the Max Planck, got his thesis from Von Weiziger and Heidenberg.

Sullivan

Which Max Planck Institute?

Mezger

It was the Max Planck Institute for Physics and Astrophysics, Heisonberg-Beirman Institute. He applied to the Max Plank to try to interest them. It must have just been a lucky time because the Max Planck Institute realized that radio astronomy was one of the bigger interests and so they immediately reacted and within a short time they started to found the Max Planck Institute for Radio Astronomy. However, then they did the reasonable thing because it is impossible to have two large observatories in Germany so we are going to support an institute but Bonn and Tubingen have to work together and the idea was probably that the telescope design from Bonn was the more realistic design. On the other hand, the scientific support from Sebastian von Hoerner would make the better scientific use of the instrument. So I think from the Max Planck point of view, it was a reasonable thing to get the two groups together but von Hoerner didnít like the idea. So after one year of negotiating, he just told them that I am no longer interested. And he was already appointed as the first director of this Max Planck Institute in and Hachenberg the second and so von Hoerner decided no and then Hachenberg was for two years or so the only Director of the Institute.

Sullivan

When was the institute created? What year?

Mezger

Let me see. It must have been í66 or í67. Thatís when the final decision was made.

Sullivan

Thatís when it was officially created?

Mezger

Yes.

Sullivan

But it had no staff or anything?

Mezger

Well, they just had a staff but a small one. They still didnít have the computer people or their own computers or they didnít have a large electronics division. I think the first real electronic man they had was Zinz, who is now head of the electronics division, and Nigel Keen who came in his various way, floated into Bonn.

Sullivan

But the money for the telescope wasnít guaranteed yet or was it?

Mezger

They got money to continue their study and Hachenberg had first asked for two separate studies from Krupp and MAN. Then it turned out that Krupp had the better idea, this sort of inverted umbrella which is the Krupp idea however then they forced the two companies to work together. Krupp, of course, got the chief contract but MAN had to be involved too. I think this turned out to be very good and very clever because Krupp is very good in steel construction and MAN is good at all the machinery parts.

Sullivan

Who forced them to work together?

Mezger

Volkswagen or whoever gave the money. I donít know exactly what the management organization was. So when I finally got involved and I was offered a directorship here at the MPI in the beginning of í69 when I just came back from Australia, after a year in Australia. Ok the basic plans for the telescope were done. There was not much you could change and I felt it would have been silly to do any changes. I saw some weak points, how to put in the receivers and the primary focus box.

Sullivan

But this was a conventional design still?

Mezger

Yeah, yea so when I first visited the place here had just had the concrete basement and I saw this square frame on which the telescope was built on the wheels but that was all. But then within, I think, nine months or so it was actually built and constructed.

Sullivan

But what happened for the homology design?

Mezger

Well, von Hoerner was of course very outspoken about the homology idea and so Krupp and Hachenberg heard of this idea and so they applied it but they did not apply it in von Hoernerís way who actually obtained an analytic solution. In homology you take a given construction and you optimize this construction by fiddling around the various members and trusses until the deflection produces a paraboloid again.

Sullivan

Right, no matter what the...

Mezger

The thing is this, homology does not prevent you having a good idea about the construction. Only once you have selected a construction then it helps you to optimize the thing.

Sullivan

Was this actually applied then?

Mezger

It was not applied in von Hoernerís way but what they did was something rather similar, namely a trial and error. They just got this grand program from IBM at this time and they applied it to the construction and they computed the deflection and then they saw that it did not exactly deflect like a paraboloid so these were very experienced engineers, they just knew what to change and they iterated the thing four times and they got the homology solution which may not be the optimum but it is good enough. But I think was the reasons that this telescope is so close to homology telescope in this way is because Krupp, in its basic construction, had built in this radial symmetry in the trusses all around so it is a homology telescope but it does not go directly back to von Hoernerís.

Sullivan

Not from the beginning. It was a little bit accidental that it had this design that worked out well.

Mezger

I think if you go like this intuitively all the constructors had felt that they had to introduce some spherical symmetry if they wanted... although I always face a problem when you have a reflector with radial symmetry and then you have to support it.

Sullivan

Like the Jodrell Bank.

Mezger

And I think Hachenberg was aware of this thing too because he was looking into construction of whether you can support of reflector on four points or eight points and so on. So the idea was in the air. Krupp did it on a trial and error basis. Von Hoerner looked for an analytic solution and I think, nowadays von Hoernerís solution is widely used even by people like Krupp but at that time it was not used.

Sullivan

Are there any other telescopes that have been used homology telescopes?

Mezger

Oh yea, we built a 25 meter telescope for space tracking and then in the design study for the millimeter wave telescope which Krupp did in parallel with the NRAO after I had arrived here. Homology was widely used in telescopes and so all millimeter wave telescopes which are at the moment offered by Krupp or maybe they are built one day are all derivatives of our design study which again is based on the homology.

Sullivan

I see.

Mezger

So the homology has found wide application.

Sullivan

How did it happen? Let see Krupp was the contractor for the Parkes dish or was it [?].

Mezger

No. MAN.

Sullivan

Ok, I get them mixed up. I see, it was KruppĎs basic design you said, thatís why it doesnít look like the Parkes dish even though...

Mezger

No. Ok, you have to be aware that MAN was not the designer. The designer of the Parkes dish was Freeman and Fox.

Sullivan

Oh yea, thatís right.

Mezger

So, MAN stuck more to the very heavy, rigid design. For example they built a 36 meter for the German Ministry of Defense which is probably an excellent telescope even down to 8 mm but boy itís heavy and sitting in a raydome so they didnít trust in homology.

Sullivan

So in both cases they were mainly the people who built is as opposed to designing it?

Mezger

Yes.

Sullivan

Ok, well I think that covers things pretty well unless you think of anything. Thank you very much. That finishes the interview with Peter Mezger on 22 November 1973.


Modified on Monday, 11-Mar-2013 13:07:46 EDT by Ellen Bouton, Archivist (Questions or feedback)