SNAP RTGs

The Space Nuclear Applications Program, or SNAP, was a large program looking at nuclear power sources (and related technologies), mainly in the 1950’s through 1970’s. Even numbered SNAP programs were nuclear reactors, and odd numbers were for radioisotope power sources. While we tend to focus on the reactors (SNAP-2, SNAP-8, SNAP-10 and SNAP-50, links to the pages available by clicking on the names), the RTGs developed during the program were far more commonly used.

These power systems were not only designed for space, but terrestrial and nautical use as well. As such, there will be some systems that simply don’t apply for this website, but I include them for historical interest.

Another note is on the concept of “Tasks” in the SNAP program. These appear to be specific program targets, for instance Task 3 was Nuclear Thermoelectric Generator Development.

Be Warned! This page is still very much under construction, most systems don’t have anything but a list of links for primary sources. If you aren’t afraid of primary sources, and are looking for something in particular, you’re encouraged to wade in, and I’ll fill in more information as I’m able to.

SNAP-1

The first design of the SNAP series, SNAP-1 was a very different power system than the ones initially flown, or even flown to date. This design was fueled with Cerium-144, and ran a mercury Rankine power conversion system. As such it’s more properly known as a RPS, or radioisotope power supply, rather than an RTG.

This design was meant to provide 500 watts of power at 10% efficiency. It never ended up flying, whether this was due to power conversion system development issues or not is not clear. However, it was successfully tested for 2500 hours as part of the development process. 

One curious design decision to ease ground handling radiological concerns was to have a secondary shield integrated into the fuel casing. This would be filled with mercury while on the ground and fueled, then the mercury would be drained out of the vessel before launch. This significantly reduced the dose rates during ground handling.

Overall, this design seems to be forgotten, and I have not been able to find a summary of the program to orient myself through the sparse references available. Of those, all of them relate to SNAP-3 as well, so I’ll post those with a note under the next section.

Additional Reading:

Final Safety Analysis Report – SNAP-1A Radioisotope Fueled Thermoelectric Generator, Dix 

SNAP I—DYNAMIC MERCURY LOOP TESTS OF SELECTED MATERIALS, McGrew 1960 https://www.osti.gov/servlets/purl/4131227

SNAP I POWER CONVERSION SYSTEM DEVELOPMENT 1 FEBRUARY 1957 TO 30 JUNE 1959 https://www.osti.gov/servlets/purl/4131443

SNAP I POWER CONVERSION SYSTEM TURBINE DEVELOPMENT 1 FEBRUARY 1957 TO 30 JUNE 1959 https://www.osti.gov/servlets/purl/4138690

SNAP I POWER CONVERSION SYSTEM PUMP DEVELOPMENT 1 FEBRUARY 1957 TO 30 JUNE 1959 https://www.osti.gov/servlets/purl/4138663

SNAP I MERCURY BOILER DEVELOPMENT, JANUARY 1957 TO JUNE 1959 https://www.osti.gov/servlets/purl/4067689

SNAP I POWER CONVERSION SYSTEM MATERIALS DEVELOPMENT 1 FEBRUARY 1957 TO 30 JUNE 1959 https://www.osti.gov/servlets/purl/4135509

SNAP I POWER CONVERSION SYSTEM BEARINGS DEVELOPMENT. Period covered: February 1, 1957 to June 30, 1959 https://www.osti.gov/servlets/purl/4134558

SNAP I POWER CONVERSION SYSTEM CONTROL DEVELOPMENT DAUTERMAN et al 1 FEBRUARY 1957 TO 30 JUNE 1959 https://www.osti.gov/servlets/purl/4134557

SNAP I POWER CONVERSION SYSTEM ALTERNATOR DEVELOPMENT I FEBRUARY 1957 TO 30 JUNE 1959 MORGAN https://www.osti.gov/servlets/purl/4135549

SNAP I POWER CONVERSION SYSTEM CONDENSER RADIATOR DEVELOPMENT. Period covered: February 1, 1957 to April 15, 1959 https://www.osti.gov/servlets/purl/4138661

SNAP-3

Artist’s impression of SNAP-3 powered spacecraft, image NASA

The first of the SNAP RTGs to fly, the SNAP-3 was tiny in power output by today’s standards, at only 2.4 watts of electrical power output, but it paved the way for later designs. A 210Po fuel element (total radioactivity 1495 curies, 55.3 Tbq) was used as the heat source, and a doped lead telluride thermoelectric convertor was used for power conversion. The entire unit was only 4.75 inches in diameter, and 5.5 inches in height, and weighed five pounds.

The first to fly was the SNAP-3B on the Transit 4A satellite, the first geopositioning satellite system. It would also fly on the Transit 4B (which would be damaged in the Starfish Prime high-altitude nuclear test), Transit 5A3, and Transit 5B1.  

Additional Reading:

TASK 3, SNAP III NUCLEAR THERMOELECTRIC GENERATOR DEVELOPMENT 1960 https://www.osti.gov/servlets/purl/4500836

Operational and System Testing of a SNAP-3 Thermoelectric Generator, Wilson 1967 https://www.osti.gov/servlets/purl/4496406

RADIOISOTOPE FUELED AUXILIARY POWER UNIT. Quarterly Progress Report No 1, January 2-April 2, 1957 [also includes SNAP-1], https://www.osti.gov/servlets/purl/4775988

RADIOISOTOPE FUELED AUXILIARY POWER UNIT. Quarterly Progress Report No. 6, April 1958-July 1958 [also includes SNAP-1], https://www.osti.gov/servlets/purl/4667334

RADIOISOTOPE FUELED AUXILIARY POWER UNIT. Quarterly Progress Report No. 7, July-September 1958 [also includes SNAP-1] https://www.osti.gov/servlets/purl/4695722

DESTRUCTIVE EXAMINATION OF A SNAP HEAT SOURCE 1963 https://www.osti.gov/servlets/purl/4220878

Dynamic Testing of SNAP-3 Radioisotope Thermoelectric Generator 1966 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670002048.pdf

SNAP-7

Cutaway of SNAP-7, image DOE

The first on this list that wasn’t primarily designed for space use, the SNAP-7 RTG was designed for naval use, primarily for maritime weather stations. As such, these were massive units, weighing between 1870 and 6000 pounds. They used a Strontium-90 radiopower source with 225 kilocuries, or 8.3PBq, of power. Their power output increased over time, but an average output would be about 30 watts of electrical power.

SNAP-7D mounted to maritime weather station, image DOE

Another use, which was pointed out to me by Jose Solis on Twitter, is the use of the SNAP-7A for light buoys for navigation. He also provided me a link I hadn’t come across before about this application: Strontium-90 Fueled Thermoelectric Generator Power Source for Five-Watt U.S. Coast Guard Light Buoy: Final Report https://digital.library.unt.edu/ark:/67531/metadc303779/

The final report of the SNAP-7D power supply can be found here: https://www.osti.gov/servlets/purl/4713816

References and Additional Reading

Quarterly Progress Reports, Task 8 – 90Sr TEG Development, Martin Co.

November 1, 1960 Through January 31, 1961 https://www.osti.gov/servlets/purl/4030344

May 1, 1961 through July 31, 1961 https://www.osti.gov/servlets/purl/4829696

August 1, 1961 through October 31 , 1961 https://www.osti.gov/servlets/purl/4759162

November 1, 1961 to January 31, 1962 https://www.osti.gov/servlets/purl/4816010

May 1 through July 31, 1962 https://www.osti.gov/servlets/purl/4781268

SNAP-13

The SNAP-13 was a thermionic radioisotope power unit, using a mix of 241Am and Curium 242 as its radioisotope fuel. I have only found one reference for this system, which mentions problems with the fuel containment, fuel clad manufacture, and thermionic system challenges. If anyone has more information, please comment below!

References and Additional Reading

SNAP 13 THERMIONIC DEVELOPMENT PROGRAM , GENERATOR FUELING REPORT 1967 https://www.osti.gov/servlets/purl/4655700

SNAP-15

SNAP-15 cutaway display model, image DOE

The SNAP-15 was a 238Pu fueled RTG, built by General Atomics. It was designed for an output of at least 1 mW and 4.5 volts for over 5 years. This was a tiny RTG, massing only 0.85 lbs, and was 2.5 inches in diameter and 5 inches long.

References and Additional Reading

SNAP-15A THERMOELECTRIC GENERATOR FINAL REPORT May 6, 1963, through September 30, 1964 https://www.osti.gov/servlets/purl/4472063

FINAL SAFETY AND HAZARDS REPORT FOR THE SNAP-15A GENERATOR 1964 https://www.osti.gov/servlets/purl/4618122

SNAP-19

SNAP-19 cutaway, image DOE

Of all the SNAP RTGs, the SNAP-19 is the second best known after the SNAP-27 used by the Apollo astronauts. This 238Pu fueled RTG was the first that I know of to use the TAGS-85 thermocouple material currently being used by the MMRTG.

Note the RTG between the panels. Image DOE

Its first use was on the Nimbus-3 satellite – both of them. The first exploded on the launch pad, but the RTG was recovered, and the fuel (not sure about the generator) was placed on the Nimbus-3B satellite. Two other Nimbus missions used RTGs as well.

Artist’s impression of Pioneer 10 at Jupiter. Note the RTGs on the upper left. Image NASA

The next missions to use the SNAP-19 was on Pioneer 10, one of the first missions to the outer Solar System. This spacecraft was the first to return on-site data on Jupiter, which it flew by in December 1973, returning an incredible amount of scientific data. Two SNAP-19s were used for the spacecraft, mounted to a boom on the side of the spacecraft.

Its twin, Pioneer 11, was the next probe to use the power supply. It also passed by Jupiter and then went on to Saturn, helping pathfind the flyby trajectory for the Voyager probes only a few months behind. The debris situation between Saturn’s rings were an unknown, so Pioneer 11 was a perfect chance to make sure that the Voyagers would not be damaged during their flybys.

Viking 2 Lander. RTG blade barely noticeable on right side. Image NASA

The last use of the SNAP-19 was on the Viking missions. Both landers used two modified SNAP-19s each, with the heat sinks designed to utilize the thin Martian atmosphere for more efficient heat transfer.

Additional information available below.

References and Additional Reading

OPERATION AND FIELD MAINTENANCE TECHNICAL MANUAL, 1968 https://www.osti.gov/servlets/purl/4513086

SNAP 19 TAGS 85/2N RTG POWER SYSTEMS THIRD SEMI-ANNUAL PROGRESS REPORT (July 1, 1970 to December 31, 1970) https://www.osti.gov/servlets/purl/4065539

SNAP 19 Jupiter Pioneer Application Study Program Plan 1969 https://www.osti.gov/servlets/purl/5322915

SNAP 19-C2 SITE HAZARDS ANALYSIS AND SAFETY REPORT 1966 https://www.osti.gov/servlets/purl/4197495

SNAP 19 PROGRAM GENERATOR PROTOTYPE QUALIFICATION ENVIRONMENTAL TEST REPORT ELECTRICALLY HEATED SYSTEM NO, 2 PART I – HUMIDITY AND DYNAMIC TESTS https://www.osti.gov/servlets/purl/4621341

DYNAMICS AND LOADS ANALYSES OF SUPPORT STRUCTURE FOR SNAP-19 GENERATORS (NIMBUS APPLICATION) 1964 https://www.osti.gov/servlets/purl/4602181

THERMAL ANALYSIS OF THE INTACT SNAP-19/NIMBUS B/AGENA SYSTEM https://www.osti.gov/servlets/purl/4724391

ON THERMAL STRESS FAILURE OF THE SNAP-19A RTG HEAT SHIELD 1974 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740022225.pdf

SNAP-19/NIMBUS B INTEGRATION EXPERIENCE 1968 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680022615.pdf

Pioneer F and G

PIONEER F/SNAP 19 HEAT SOURCE THERMAL ANALYSIS 1972 https://www.osti.gov/servlets/purl/4269349

SNAP 19 PIONEER F & G Final Report 1973 https://www.osti.gov/servlets/purl/5352675
also (different report)
SNAP 19 PIONEER F & G FINAL REPORT
https://www.osti.gov/servlets/purl/4441003

Viking SNAP-19

A Summary of Neutron Measurements for the Viking Program M. E. Anderson August 15, 1975 https://www.osti.gov/servlets/purl/4211668

TAGS-85/2N RTG POWER FOR VIKING LANDER CAPSULE 1969 https://www.osti.gov/servlets/purl/5415537

Bimonthly Technical Progress Report

October 1979 and November 1979 https://www.osti.gov/servlets/purl/5284287

SNAP-21

Another naval RTG, the SNAP-21 was meant for deep-sea installations such as SOSUS arrays and other sonar fixtures. This RTG used 90Sr fuel to produce 10 watts of power for at least 5 years. Check the references below for more information

References and Additional Reading

PRELIMINARY DESIGN DESCRIPTION 10-WATT SYSTEM 1967
https://www.osti.gov/servlets/purl/4645483

THERMOELECTRIC GENERATOR PERFORMANCE EVALUATION AND DESIGN DESCRIPTION 1968 https://www.osti.gov/servlets/purl/4802495

FINAL SUMMARY REPORT SNAP-21B Phase I 1966
https://www.osti.gov/servlets/purl/4794421

NONDESTRUCTIVE TESTING OF ISOTOPE CONTAINMENT CAPSULES PHASE I SNAP -21 AND SNAP -23 1958 https://www.osti.gov/servlets/purl/4565214

BIMONTHLY REPORT I January 1965 to 28 Febmary 1965
https://www.osti.gov/servlets/purl/4634045

CHARACTERIZATION OF SNAP~21 AND SNAP~23A THERMOELETRIC MATERIALS 1968 https://www.osti.gov/servlets/purl/4501582

THE DESIGN, DEVELOPMENT, AND DELIVERY OF HIGH TEMPERATURE VACUUM INSULATION SYSTEMS FOR SNAP-21 THERMOELECTRIC POWER SYSTEM. Final Report. 1970 https://www.osti.gov/servlets/purl/4091262

ELECTROCHEMICAL CORROSION STUDIES OF GALVANICALLY COUPLED SNAP-21 MATERIALS 1968 https://www.osti.gov/servlets/purl/4533560

SNAP 21A Ten-Watt Deep Sea Isotopic Power Supply Second quarterly progress report June through August 1964 https://www.osti.gov/servlets/purl/4528855

PHASE I DEEP SEA RADIOISOTOPE-FUELED THERMOELECTRIC GENERATOR

QUARTERLY REPORT NO. 3 1 October 1964 to 31 December 1964 https://www.osti.gov/servlets/purl/4655728

QUARTERLY REPORT NO. 10 April 1, 1969 through June 30, 1969
https://www.osti.gov/servlets/purl/4759648

PHASE II DEEP SEA RADIOISOTOPE-FUELED THERMOELECTRIC GENERATOR POWER SUPPLY SYSTEM

QUARTERLY REPORT NO. 1 https://www.osti.gov/servlets/purl/4354911

QUARTERLY REPORT NO.2 July 1, 1964 – September 30, 1964
https://www.osti.gov/servlets/purl/4634071

QUARTERLY REPORT NO. 3 September-November 1964
https://www.osti.gov/servlets/purl/4538941

QUARTERLY REPORT NO. 5 July 1, 1967 to September 30, 1967
https://www.osti.gov/servlets/purl/4518297

QUARTERLY REPORT NO. 7 January 1, 1968 to March 31, 1968
https://www.osti.gov/servlets/purl/4520358

Quarterly Report No. 8, April 1, 1968–June 30, 1968 https://www.osti.gov/servlets/purl/4505331

Quarterly report no 10 October to December 1968
https://www.osti.gov/servlets/purl/4796573

QUARTERLY REPORT NO. 12 April 1, 1969 to June 30, 1969
https://www.osti.gov/servlets/purl/4756894

SNAP-23

The SNAP-23 was another terrestrial RTG, designed to output 60 watts of DC power using 90Sr fuel elements similar to the SNAP-21, but in a larger generator. More information can be found below.

References and Additional Reading

SNAP-23A PROGRAM: THERMOELECTRIC CONVERTER DEVELOPMENT PROGRAM. Final Report 1970 https://www.osti.gov/servlets/purl/4071791

QUARTERLY REPORT NO. 1 February 1, 1967 through March 31, 1967 https://www.osti.gov/servlets/purl/4330003

QUARTERLY REPORT NO. 2 April 1, 1967 through June 30, 1967
https://www.osti.gov/servlets/purl/4263738

QUARTERLY REPORT NO. 3 July 1, 1967 through September JO, 1967
https://www.osti.gov/servlets/purl/4492886

QUARTERLY REPORT NO. 4 October 1, 1967 through December 31, 1967
https://www.osti.gov/servlets/purl/4546038

Quarterly Report No. 5, January 1–March 31, 1968
https://www.osti.gov/servlets/purl/4500441

Quarterly Report No. 6, April 1–June 30, 1968
https://www.osti.gov/servlets/purl/4477268

Quarterly Progress Report September 1, 1969 through November 30, 1969
https://www.osti.gov/servlets/purl/4137513

QUARTERLY REPORT NO, 13 January 1, 1970 through March 31, 1970
https://www.osti.gov/servlets/purl/4155138

SNAP-27

SNAP-27 cutaway drawing, image DOE

The SNAP-27 RTG was the power source for the Apollo Lunar Surface Experiments Package, which was placed by each lunar Apollo crew during their surface missions.

Fuel capsule cutaway diagram, image DOE

This RTG used 238Pu microcapsules in an annular cylindrical shape, with a void in the center of the fuel cask. These fuel pellets were unclad, allowing for He (in the form of alpha particles) to fill the void in the center of the annulus and prevent materials failure.

Alan Bean removing the fuel cask from the LM. The generator and some of the ALSEP package can be seen. Image NASA
LM fuel cask cutaway, image DOE

Rather than have the astronauts handle the relatively bulky generation system, the fuel capsule was shipped to the moon in a special carbon sleeve, removed by the astronauts after the generator and associated experiments were placed on the lunar surface, and then inserted into the generator itself.

This RTG design flew on every Apollo lunar mission, and continued to power many experiments left behind by the astronauts for years to come.

References and Additional Reading

SNAP-27 RELIABILITY MEASUREMENT PLAN, Breen et al 1966 https://digital.library.unt.edu/ark:/67531/metadc1036069/

SNAP-27 Radioisotopic Heat Source Summary Report, Prosser 1969 https://www.osti.gov/servlets/purl/4758004

SNAP-27 FUEL CAPSULE ASSEMBLY RADIANT HEAT TESTS, Keller 1969 https://www.osti.gov/servlets/purl/4791556

SNAP-27 follow-on quality assurance plan, Mason et al September 1970 https://www.osti.gov/servlets/purl/5422370

RADIOLOGICAL CONTROL PROCEDURES APPLICABLE TO RADIOISOTOPE THERMOELECTRIC GENERATOR SNAP-27 VOLUME 1 NORMAL OPERATIONS 1966 https://www.osti.gov/servlets/purl/4493938

RADIOLOGICAL CONTROL PROCEDURES APPLICABLE TO RADIOISOTOPE THERMOELECTRIC GENERATOR SNAP-27 VOLUME II RADTOIOGTCAL EMERGENCIES 1966 https://www.osti.gov/servlets/purl/4494722

Examination of SNAP~27 Heat Source FCA4 and Preparation of Fuel for FCA8 1971 https://www.osti.gov/servlets/purl/4761339

SNAP-29

Image DOE

The SNAP-29 was a spacecraft-mounted RTG designed by Martin Marietta and Mound Laboratory. The RTG was fueled with 210Po, and had a serpentine form, unlike others looked at up to this point. Meant to be mounted to a spacecraft for onboard power, the RTG was always designed to be for short mission durations only.

This RTG was looked at for powering both the Saturn-V and the Agena spacecraft. It is also one of the first systems I’ve found to use heat pipes for thermal rejection. Unfortunately, very little information is available online about this RTG, but I will continue to look for more information. For those who are willing to dig, I’ve linked the quarterly progress reports I’ve found below (the only info that’s been digitized that I’ve seen).

References and Additional Reading

Second Quarferly Progress ReportApril 28, 1967
https://www.osti.gov/servlets/purl/4232480

SNAP 29 POWER SUPPLY SYSTEM THIRD QUARTERLY PROGRESS REPORT, Aug 1967 https://digital.library.unt.edu/ark:/67531/metadc1016451/m2/1/high_res_d/4223844.pdf

SNAP 29 POWER SUPPLY SYSTEM FIFTH QUARTERLY PROGRESS REPORT, January 1968 https://digital.library.unt.edu/ark:/67531/metadc1022692/m2/1/high_res_d/4232443.pdf

SNAP 29 POWER SUPPLY SYSTEM SIXTH QUARTERLY PROGRESS REPORT, April 1968 https://digital.library.unt.edu/ark:/67531/metadc1021350/m2/1/high_res_d/4218569.pdf

SNAP 29 POWER SUPPLY SYSTEM NINTH QUARTERLY PROGRESS REPORT, Jan 1969 https://www.osti.gov/servlets/purl/4183615

Task-2 RTG

Task-2 RTG, image DOE

This was an unknown to me until I began research for this paper. A space-based RTG, the Task-2 used 3440 grams (0.88 megacuries) of Cerium-144 fuel to provide 250 watts of power for one year. Lead telluride (with sodium and boron doping of unknown amount) thermoelectric convertors were buried within the outer thermal insulation of the generator. The overall unit was 34.1 inches long and 24 inches in diameter, and was meant to be launched on a standard launch vehicle. 

Prototype Task-2 fuel capsule, image DOE

This unit used double shielding: a tungsten shield was mounted above the fuel to protect the payload from radiation coming off the source during decay, and a temporary biological shield was incorporated for ground handling. This shield was made up of 4000 pounds of mercury, which filled the void around the core of the RTG and reduced the radiation to acceptable levels. This mercury would be drained immediately before launch. Thermal control shutters would be used to shed excess heat during the beginning of the mission, slowly closing over time to maintain the appropriate thermal environment for the convertors to work reliably and efficiently.

Additional reading:

Preliminary Operational Hazards Summary Report for the Task-2 Thermoelectric Generator, Dix 1959 https://www.osti.gov/servlets/purl/4056522

Task 7

SNAP RADIOISOTOPE SPACE PROGRAMS QUARTERLY PROGRESS REPORT

April 1 through June 30, 1961 https://www.osti.gov/servlets/purl/4823309

July 1 through September 30, 1961 https://www.osti.gov/servlets/purl/4741658

April 1 through June 30, 1962 https://www.osti.gov/servlets/purl/4777535

Additional and General References

Power from Radioisotopes by Williaim R. Corliss and Robert L Mead https://www.osti.gov/servlets/purl/1132525

Bibliography on Sadioisotope Power Supplies August, 1963 https://www.osti.gov/servlets/purl/4096792

INVESTIGATION OF GAS PRESSURE BUILDUP IN THERMOELECTRIC SNAP GENERATORS, McDonald et al 1964 https://www.osti.gov/servlets/purl/4082219

RADIOISOTOPE FUELED AUXILIARY POWER UNIT QUARTERLY PROGRESS REPORT NUMBER 7 JULY – SEPTEMBER 1958 https://www.osti.gov/servlets/purl/4695722

PRELIMINARY DESIGN AND SAFETY STUDIES OF LARGE RADIOISOTOPE HEAT SOURCES FOR SPACE POWER(U) Mid-Term Technical Progress Report APRIL 15, 196 5 throug h JULY 31 , 196 5 https://www.osti.gov/servlets/purl/4690052

Aging Effects of US Space Nuclear Systems in Orbit Bartam et al 1982 https://www.osti.gov/servlets/purl/6237635

RADIOISOTOPE FUELED AUXILIARY POWER UNIT. Quarterly Progress Report 

January 2 to April 2, 1957 https://www.osti.gov/servlets/purl/4775988

APRIL 1958-JUlY 1958 https://www.osti.gov/servlets/purl/4667334

JULY-SEPTEMBER 1958 https://www.osti.gov/servlets/purl/4695722

April-June 1959 https://www.osti.gov/servlets/purl/4599705

Mixed Quarterly Status Reports with Task #s

Report No 1 Tasks 3, 5 and 6, October 22–December 31, 1959
https://www.osti.gov/servlets/purl/4079689

Report No, 2^ Tasks 2^ 3, 5 and 6 January f© March 31^ 1960
https://www.osti.gov/servlets/purl/4036289

Report No 5 Tasks 2, 3 and 7, October 1 through Decembe r 31, 1960 https://www.osti.gov/servlets/purl/4064004

Report No. 6 Task 6 January 1 through March 31, 1961 https://www.osti.gov/servlets/purl/4811922

SUPPLEMENTARY INFORMATION ON SNAP BY ATOMICS INTERNATIONAL BEFORE THE SUBCOMMITTEE ON RESEARCH & DEVELOPMENT OF THE JOINT COMMITTEE ON ATOMIC ENERGY MARCH 13, 1962 https://www.osti.gov/servlets/purl/1240149