FRITZ ZWICKY
Oral history interview on artificial meteor project
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Zwicky at Schmidt telescope on Mt Palomar |
In this interview, conducted by historian R. Cargill Hall on May 17, 1971, Cal Tech astrophysicist Fritz Zwicky recounts the events leading up to his 1946 artificial meteor experiment and its aftermath. His concept of firing a projectile into the Moon at high velocity in an attempt to liberate water was finally achieved in July 1999 when NASA's Lunar Prospector spacecraft was deliberately crashed into a crater where water was believed to exist.
Interview courtesy Jet Propulsion Laboratory Archives
HALL: Okay. Well, why don't we turn from the solid work to your first ideas for the artificial meteors and the upper atmosphere and who in the Army you had proposed this to and how that work developed and why the first flight failed in 1946?
ZWICKY: Now the story of the artificial meteors essentially is based on the following idea, that in astronomy I had the idea that so far we have been just passive observers. For thousands of years we were just passive observers. Things come to use like light and cosmic rays. [sound of telephone ringing; tape interrupted] That means in making theories we only know half the things or maybe one tenth of the things compared with a theoretical physicist who can go to an experimental physicist and tell him to make such and such and such tests and make them many times. We couldn't make the tests. We had to decide what was on the Moon, what was on the Sun, what was on the stars just from insufficient evidence and we could not do any experiments. So the idea was at least get the stars and even the top of the atmosphere, we only could observe and not experiment. Well, so it was quite clear if we could shoot something through the upper atmosphere, out away from the Earth, something which would react with the upper atmosphere, with the ionosphere, a charged particle, a particle of lithium, a particle of beryllium, a particle of carbon. Let it react with the components in the upper atmosphere. Give it enough speed, what we call ultra speed. There is aerodynamics, there is supersonic aerodynamics but ultra aerodynamics, ultra speed is when the particles themselves do not conserve their initial properties any more but undergo physical, chemical changes. In aerodynamics the plane does not undergo physical, chemical changes. But we wanted to have ultra fast particles which would themselves evaporate and which would ionize and excite the atoms and molecules in the upper atmosphere. So the idea was to shoot very fast meteors, artificial meteors through the atmosphere. The opportunity for that came when the V-2 rockets became available at White Sands and that is where von Kármán and General Barnes helped. Von Kármán supported that program very heavily and General Barnes then gave us the permission to make a first night firing of a German V-2 rocket at White Sands.
HALL: You had proposed this to General Barnes?
ZWICKY: I had proposed this to General Barnes.
HALL: This was before the Upper Atmosphere Committee was active?
ZWICKY: Yes, it was a long business; many letters were written back and forth, General Barnes and Colonel Toftoy--later General Toftoy--and these people, Van Allen also, they supported us heavily and so we received permission to install nine shaped charges on a V-2 for the first night firing on December 16. December 17, was it?
HALL: 1946.
ZWICKY: 1946. We were down there, lined up with the eight inch Schmidt telescope and all kinds of small cameras and objective gratings in a thirty mile triangle around White Sands. [sound of telephone ringing; tape interrupted] Well, the night before from the rocket tank there at White Sands on that little hill, we shot some test shots, marvelous looking shots of these artificial meteors. So it was certain that we would have seen them and we had installed the timing, three of the shaped charges to eject ion particles at 120,000, 150,000 and 180,000 feet respectively. Now for some reason when we were out in the desert, some people we had invited from Harvard who themselves had observed natural meteors all their lives, they somehow got the idea that we wouldn't see these meteors at the heights that I wanted to fire them.
HALL: Had Dr. Whipple seen the firing the night before?
ZWICKY: Dr. Whipple had seen the firing the night before. But anyway he was a guest of ours and he and his men they met together out in the desert. They got the idea that the timing should be changed and brought down to lower heights. The engineers apparently at the installation there, they didn't know who was who and they listened to them and the timers were changed and I think that was the reason that nothing fired. We had a most beautiful shot of all times and a marvelous spectra of the jet, even of the graphite vanes after propellant cutoff; everything could be seen. But nothing happened. The shaped charges did not fire and I am fairly certain they did not fire because people who were not competent had tampered with our firing circuits. Then afterwards Whipple wrote a report that this was just actually a silly expenditures of money and nothing could be seen and the whole thing was useless and it got so bad that they wanted to haul me into court for having wasted the taxpayers money. Then the Navy found out that we had come there with our own trucks. Dr. Wilson, I think Dr. Pickering was there and our mechanics from Aerojet that we had paid everything ourselves and that there was no taxpayers' money involved at all and they dropped the charges. But the sad thing was it took then eleven years before we had a second chance to repeat the experiment.
HALL: The Upper Atmosphere Research Panel would not permit you to launch again?
ZWICKY: No, for eleven years there seemed we could not get the permission to launch anything again. Actually that report--I've forgot the title of it but I have it lying on my desk at home; I just took it out. I think from the Naval Research Lab--just put thumbs down on the whole thing. Well, to be sure that next time we would succeed and see them, I then developed the idea of coruscative inserts. That is an entirely new notion, namely heat explosives, that is not like ordinary explosives which develop gases and blow apart. It is simply a detonation in a solid body but which does not produce any gases. One of the best ones is the reaction between solid titanium and solid carbon, compressed, which escapes titanium carbide and I showed then by experiments at Edwards Air Force Base and at Inyokern that these things do detonate. There we had a great trouble with the chemists for a long time. They simply did not think that the solid body could detonate if it did not develop gases. These were not explosives but what we call coruscatives, that is, heat detonators which just give heat but do not blow apart. I only could convince some of the professional chemists later on by showing them that in Bichowski and Rossini's standard book from the Bureau of Standards was mention that antimony can be detonated from one crystalline formation into an allotropic formation and not blow apart. Not much energy but it did show us the phenomenon. Then we developed quite a few coruscatives and we were ready to launch then luminous at the start, luminous artificial meteors so we would not have to rely on the friction in the atmosphere of the fast particles getting heated by friction and we would even see them when launched in absolute vacuum. Well, we had nevertheless several friends like Maurice Dubin and Knox Milsaps in the Air Force and they promised to watch for an occasion when some little space would be available in an instrument head of an Aerobee rocket which were then being launched at that time at Alamogordo. In August 1957 they called me up and said there would be a launching in October of that year and there would be one cubic foot of space if I could use that to install these coruscative shaped charges. Mr. Cuneo who used to be our patent attorney at Aerojet and a professional chemist, he and I then developed these coruscative inserts to be installed in that instrument head of this Aerobee rocket and on October 16, twelve days after Sputnik 1, this was suppose to take place then at Alamogordo. Now to be sure that nothing would happen, when we got down there I told General Hook this time to send all the visitors two hundred yards away, back of a fence and let Cuneo and me do the whole thing which we did from twelve noon until ten at night when the firing took place and then it was just perfect although we had the following difficulty. There was a guy there, a physicist by the name of Yagoda who had cosmic ray plates under the instrument head and he was beefing that if our charges exploded, his plates would not come back. So then we told him okay, in that case we have to kick off the instrument head, the dunce's cap at 40 kilometers height and install our charges looking backwards, shooting backwards which meant that we had to change the dunce's hat, the position on the next stretch from 40 kilometers to 90 kilometers height just by 180 degrees and we achieved that by having three little springs of different strengths on the periphery of the flange and that thing worked perfectly. Exactly at 91 seconds as we had timed it on our timer, the charges went off and registered with all the telescopes including the 48 inch Schmidt at Palomar at a distance of a thousand kilometers and the speed measured with the propeller shutter of the Schmidt telescope on Sacramento Peak, the fastest particle showing about 49,000 feet, 15 kilometers per second, higher than the escape velocity from the Earth of 11.2 kilometers per second.
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Aerobee rocket equipped with three coruscative shaped charge launchers for October 1957 test |
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Telescopic
photo of pellets streaking from rocket at 15 km/s
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Actually if we had fired the thing along the trajectory of the Earth in the forward direction, the trajectory of the Earth along its orbit around the Sun, the particles almost could have left the planetary system. At 16.2 kilometers per second speed they would leave the planetary system when fired in addition to the 30 kilometers speed of the Earth on its orbit. [tape interrupted] Now beyond using artificial meteors for testing the composition and the physical conditions in the upper atmosphere, one of the most important aspects is to test the lunar surface down to considerable depths for various constituents and particularly for crystal water. Here on the Earth in granites or basalt or so, we have 1 to 5 or 6 percent crystal water and with artificial meteors consisting of a reducing agent such as aluminum, that aluminum in penetrating the granite at the speed of 10-15 kilometers per second will dehydrate the crystal water in the granite. Dehydrating the crystal water means that the H20 will be split and hydrogen will be liberated at pressures of a million atmosphere or more and explode out the parts around the track you see which has been pierced by the artificial meteor. Well, for us it is exceedingly important for a life sustaining installation on the Moon to know how deep down is the crystal water because then if it is say only one, two, or three feet down, it would be very easy to explode it out in the focus of a solar furnace and with a very small solar furnace, an individual could produce for himself enough water and oxygen to live on the Moon without taking it along from here. Therefore it was exceedingly important to find out how deep down is the crystal water. If it should be a hundred feet down, then the situation will be very difficult but still not hopeless. Well, what we wanted to do first was from an Aerobee rocket shoot a large shaped charge--and we had figured out that we could shoot a slug into the Moon at 10-15 kilometers per second of a reducing agent such as beryllium, aluminum, boron, or something like that which would dehydrate that crystal water, explode it out, and actually make a flash due to the heat of reaction liberated and that this flash we could have seen with an objective grating strapped into the zero corrector of the 200 inch telescope which would give over a relatively large area the spectrum of every luminous object. We could have calculated closely enough where the impact would be; we could have observed through the 200 inch telescope directly if there was any crystal water because we would have seen the Balmer lines in emission in the flash. In spite of the fact that some agencies, some private donors wanted to mobilize $500,000 for us to do that, we were not allowed to make this shot. Then later on when the Rangers came with the television cameras -approaching the Moon we proposed that a shaped charge should be shot from the Ranger for the particle to get ahead of the Ranger impact on the Moon and the television camera again with some optical grating would record if there was an explosion of hydrogen with the flash of the Balmer lines. That also was not honored. Then later on when actually landings took place on the Moon, we again suggested to have an arm stretched out from the landing device and a shaped charge shot with a reducing fast particle penetrating the Moon's surface to a few feet to find out whether any crystal water was there within three or four feet.
HALL: But NASA would not accept.
ZWICKY: None of these things have been done. So to this very day we do not yet know can we rely on a life sustaining installation using solar furnaces and magneto-hydrodynamic generators such as we had proposed and actually as pilot devices built at Aerojet twenty-five years ago to develop water, oxygen, CO2, and so on and propellants out of the Moon's surface. To this very day we have not yet gotten the information which we could have obtained in this fashion. [tape interrupted] . . . .
The following was added at this point as a footnote to a transcript prepared by the Historian's Office in the 1970s: Zwicky first made a mosaic grating of 18 inches diameter consisting of six five by seven inch replicas. In order to cover the full aperture of the Schmidt, R.W. Wood and Zwicky plastered fourteen five by seven inch replicas on the 18 inch circular plate. Three were made. Two were 800 lines per inch, one was 1440. They were etched gratings. This grating provided the spectrum of each luminous point in the field while existing gratings gave only one point.