i'ltrajast particles extruded f r o m 1%-inch copper con,. liner o f a commercial shaped charge, m c h 0,s is used i n oil-well drilling operation:.. /'holograph was made with a rotating camera. The great plume of luminous particles whose paths appear flattened out because of the camera's relation are fragnzt1~1.s of the container of the shaped charge. The few particles whose tracks are alnwsl vertical have tremendous speed; tracks are hardly hen/ despite fast rotation o f camera.

'd into the atrtiosj iip and then melt which cause them I

ere the artificial meteor r evapo cool do

rotating the camera. perature- could be determined. The latter were found I I, <;pen from the ciiazratn below (rixhtl t h d ~ ~ M O to be of thy order of 2900° for A1 uellets moving

I n particular. three objections were raised against any further experimentation with artificial meteorsf"'. These objections are: 1 ) Artificial meteors are too slow and too small to lie seen in the tenuous upper parts of the atmosphere since they cannot he expected to heat up enough. 2 ) They are also too slow to leave the earth or even to reach great heights. 3 It was feared thai the launching of artificial meteors within the United States might conceivahlv endanger people hecaiise of falling fragments.

The great progress which has been made toward the elimination of objections 1 and 2 w i l l he described elo ow. As far as objection : S is roncerned. artificial meteors could tie fired at sea. on the extended Australian rocket range. or in the Sahara desert. if this type of ex- ~erimentation is not rlesirahle in this coimtry. For this tuityose 1 have already established siiccessful contar'ts i t 1 Australia and i t 1 France.

Intensification of brightness

For a particle o f given size and speed the brightness can he increased in t w o ways. First. one may choose ar t ic les (Tracers 1 which. when heated by the initial extrusion process, w i l l react vigorously with the oxygen or with the nitrogen of the air. Secondly. when air is coml>letely absent this method will not work: hul one may heat the meteors through the initiation of internal solid-solid chf>?nicnl reactions in order to make them v isible.

This ran easily he accomplished through the choice of liner's i n the shaped charges which are made up of

lighly compressed mixtiires of suitable solid fuels and ~xidizers. The reaction i n the liner is initiated hy the detonation of the shaped charge. Therrnit. composed of aluminum arid of iron oxide. is a well-known reactive mixture of ihi's kind. which on ignition become? ex- trernelv hot.

Chemical heaters

Much more potent "chemical heaters" are available. however. even if we do not tap the resources of T r a g - rnent (:hemistry" or "Metart~emistry"('~'. For instance.

suitable element's rnay be mixed stoichiorr~etricall y with solid oxiclizers such as k(-;1O4. or similar compounds. Through the choice of the proper fuel component it is possible to produce intensely hot solid. liquid or paseous jets from the explosion of lined shaped charges. Using elements at the two ends of the periodic system one may. for instance. mix Boron with kCIOi and achieve an average density of 2.51 gr/crn" and a heat of reaction of about 12 hcal/crri-": or mix tungsten with KC10, and get an average density of 5.7 gr/cmC' and a heat o f re- action of 3.8 Kcal/cm".

The two mixtures will produce gaseous and solid par- t ide jet's respectivel!. The study of the reaction of jets of these tvpes wi th air of different density. or with solid and liquid media, promises to open u p some interesting new fields. In particular. i t is to he foreseen that he-

cause of internal rhernicai heating the drag of projec-tiles through different media may. interestingly enough. he both decreased or increased.

Particles which are internally heated during their flight produce luminous trajectories even when flying i n high vacuum outside of the earth's atmospherp. Through the ejection from shaped charges of ~uitahly chosen materials one also has the means to experiment reactively with the various constitt~erits o f the impel atrnosphere(lO).

Increase of speed

V(- ith cornmerciallv available shaped charges and liners one may eject Fast sol id particles whose speeds seldom surpass 10 krn/sec. The velorbity of esrape frorn the earth at the pole? i s 1 1.2 km/sec. Obviously, in at- tempting to project small sings into interplanetary space one would prefer to have some extra speed available.

r 7 I here are two general nosqihili~ies to speed ~p the jets frorn lined shaped r'harges :

1 I Higher speed o f the ejected particles can he achieved with conventional explosives and proper liners if one improves on their design and the rnethod of iriitiat- ing the detonation. Wiih this approach velocities as high as 90 km/sec have now been achieved w i ~ h beryllium linersf'". 2 1 I n the not-too-far future. conventional chemicals in shaped charges wil l no d n o h t hp replaced by much more potent explosives which liberate more energy. at detonation velocities superior to those which can now be achieved. These unconventional explosives w i l l he made up of fra&ments or radicals of chemical inolecules or of m~tastabh' states of such niolerules, The stabilization of macroscopic density of such frag- merits and metastable molecules is the tack of two new branches of chemistry for which F haxe proposed the designations F ra gm e n t Chemistry and Metachemis- try('". Rork in these fields was initiated only a short time ago. hut important results may be forthcomi~~a' shortly.

REFERENCES

( 1 l F, Zwicky. Pub. 'I. S. F'.. 58. 260. 1940: ,W. 32, 1947: 9. b l . 1947. rrit~r Ordnance. J uly-dugiict i w i w 1947. See d i n 4nnual Report, Calif. Inçti of Terhrtoloav. 1946-47, p. 57,

(21 Rirkhoff. MarDougall. Puph. Taylor. .IT. 4 p p l . Ph\s.. 10. 563. 1948.

( 3 1 F. Zivivky. Helvetica Ph^ff (1 -irta. 2.3. 223. 1950. f 4 1 F. Zwic-ky. Pro(. Int . Asfr. Hninn and Int . Union for Theor.

urld ''tppl. Me( h(ini(s. Syrnpo-ium. Paris 1919. Pnhl. ( prl-

ter. 4ir Dorument= Office. ( hapter 31. .Fiine 1951. f 5 1 F. Zwick! . ( I / ) Y P ~ I Y U O ~ J . ff8, 845. 1948. ( f t l R. W. Wood. P/~?.s. R P ~ . . 71, 471 f i l l . 1917. ( 7 ) W. \. 4llen. J. S. Ririehart. W. ( . White, . fr . '4ppI. Ph"ii(s

23. lX. 198. 297. 1952. (81 F. Zwirky, Mis(el1arieoi~ M'emriran(la No. 3. Aerojet E n -

gineering ( orpoiation. 'Vzusa. Calif.. December 18, 1946, ( 9 ) F. L. Whipple. Hanard M ~ t e o r Program. T ~ r h . Rpt.. No.

1 , ( ambritIge, 1947. ( Kit F. Zwicky. Chenti(a1 am! Engineering Ven~s. 28. 156. 1950:

Engineering rind Sf ien( P f ( alif. Inqt. of Te<-h. I . I .? . 10-1 4. Nov. 1949. 3. .Ian. 1950. 4 1 ~ artif Ie o n "Future F'ro-ipect~ of ,Jet Propul'iion." imprint for t h e En/ vclopedin of H i g h Speed +lerod\rifirrtir<s and .lei Propiihion. f Prinr~ton l rrtiv. F1rei.s i .

( 1 l F. .I. Willie, F. ('I. Lur-y and R , G. Shreffler. Bull~-tin No. 1. of the h. Phvc . S ~ I - i r t v V. 2F, Jiiw .'SO, 1952