Bryan Palaszewski

Glenn Research Center, Cleveland, Ohio

Solid Hydrogen Experiments for Atomic

Propellants: Particle Formation Energy

and Imaging Analyses

NASA/TM—2002-211915

December 2002

AIAA–2002–4092
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Bryan Palaszewski

Glenn Research Center, Cleveland, Ohio

Solid Hydrogen Experiments for Atomic

Propellants: Particle Formation Energy

and Imaging Analyses

NASA/TM—2002-211915

December 2002

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

38th Joint Propulsion Conference and Exhibit

cosponsored by the AIAA, ASME, SAE, and ASEE

Indianapolis, Indiana, July 7–10, 2002

AIAA–2002–4092
Acknowledgments

I’d like to thank the people who assisted in the construction and execution of the experiments conducted at NASA

Glenn Research Center: Maureen Kudlac (GL), Henry Speier, Joan Hoopes, Ernie Bell, Donald Metcalf, and Robert

Vanek. Thanks to Hugh Aylward for the image capturing and pixel measurements of the particle sizes. I’d also like

to thank John Cole, head of Space Transportation Research (STR) aspects of the NASA Advanced Space

Transportation Program (ASTP), led by NASA Marshall Space Flight Center. Extensive cooperation

with the USAF Research Laboratory (Edwards, California) was also a critical part of this testing.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Available electronically at http://gltrs.grc.nasa.gov
NASA/TMó2002-211915 1 

SOLID HYDROGEN EXPERIMENTS FOR ATOMIC PROPELLANTS: 

PARTICLE FORMATION ENERGY AND IMAGING ANALYSES 

Bryan Palaszewski*

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Phone: 216ñ977ñ7493, Fax: 216ñ433ñ5802 

Email: bryan.a.palaszewski@grc.nasa.gov 

 

*

AIAA Associate Fellow, Leader, NASA Advanced Fuels, 

Fuels and Space Propellants Web Site 

http://sbir.grc.nasa.gov/launch/foctopsb.htm

ABSTRACT

This paper presents particle formation energy balances 

and detailed analyses of the images from experiments 

that were conducted on the formation of solid hydrogen 

particles in liquid helium during the Phase II testing in 

2001. Solid particles of hydrogen were frozen in liquid 

helium, and observed with a video camera. The solid 

hydrogen particle sizes and the total mass of hydrogen 

particles were estimated. The particle formation 

efficiency is also estimated. Particle sizes from the 

Phase I testing in 1999 and the Phase II testing in 2001 

were similar. Though the 2001 testing created similar 

particles sizes, many new particle formation 

phenomena were observed. These experiment image 

analyses are one of the first steps toward visually 

characterizing these particles, and allow designers to 

understand what issues must be addressed in atomic 

propellant feed system designs for future aerospace 

vehicles. 

NOMENCLATURE

ASTP Advanced Space Transportation Program 

DOE Department of Energy 

FCC Face centered cubic 

FOV Field of view 

GLOW Gross lift off weight 

GRC Glenn Research Center (formerly known as 

Lewis Research Center (LeRC)) 

H Atomic hydrogen 

HCP Hexagonal close pack 

H2 Molecular Hydrogen 

He Helium 

LLNL Lawrence Livermore National Laboratory 

NASA National Aeronautics and Space 

Administration 

NLS National Launch System 

O/F Oxidizer to fuel ratio 

SMIRF Small Multipurpose Research Facility 

STR Space Transportation Research 

USAF United States Air Force 

wt% Weight percent 

x/L Non-dimensional distance from dewar lid 

INTRODUCTION

For over 69 years, the promise of atomic propellants 

has been pursued (Refs. 1 to 33). Using atoms of boron, 

carbon, or hydrogen, maintained at cryogenic 

temperatures, very exciting advances in rocket 

propellants and airbreathing fuels can be created. 

Atomic propellants are composed of atomic species 

stored in cryogenic solid hydrogen particles. These 

particles are stored in liquid helium to prevent the 

recombination of the atoms into molecules. Once the 

hydrogen is warmed, and the atoms allowed to 

recombine, the recombination energy heats the 

hydrogen and helium to high temperatures, and the 

resulting gases can be directed in a traditional 

converging-diverging nozzle to create thrust and, 

theoretically, high specific impulse (Refs. 3 to 7). 

Over the decades, many details of the physics of storing 

such propellants have been analyzed and 

experimentally determined. Current research is 

underway with a team from the USAF, NASA, the 

DOE, university, industry, and small business partners 

(Ref. 2). The extensive data that has been amassed over 

many decades have shown increasing storage densities 

for atoms in solid cryogenic storage media, and that 
NASA/TMó2002-211915 2 

there may be future breakthroughs that allow the more 

routine use of atoms for fuels. 

Characterizing solid hydrogen particles is required 

before any practical propellant feed system can be 

created. Solid hydrogen particles were selected as a 

means of storing atomic propellants in future launch 

vehicles. When storing atoms of boron, carbon, 

hydrogen, or other atomic materials, a solid hydrogen 

particle is preferred. Very low temperature (T < 4 K) 

cryogenic particles have the ability to stabilize and 

prevent the atoms from recombining and controlling 

their lifetime. The particles and the atoms must remain 

at this low temperature until the fuel is introduced into 

the engine combustion (or recombination) chamber. 

WHY ATOMIC PROPELLANTS?

In the future, rocket and airbreathing propulsion 

systems may be able to gain great benefits from the 

enormous power of atomic propellants. A summary of 

atomic hydrogen rocket gross lift off weight (GLOW) is 

shown in Figure 1 (Ref. 3). Using a 15-wt% atomic 

hydrogen fuel, the gross lift off weight of the launch 

vehicle can be reduced by 50% over the National 

Launch System (NLS) using O2/H2 propellants. The 

baseline rocket and payload weight for the comparison 

is an oxygen /hydrogen rocket taking 96,000 kg of 

payload to Earth orbit. For the atomic hydrogen fuel, 

the oxidizer to fuel (O/F) ratio is 0.0, using the fuel as a 

monopropellant Additional analyses and suggested 

optimal fuel selections for atomic rocket vehicles are 

presented in Refs. 3 to 7. 

SOLID HYDROGEN EXPERIMENTS

Solid hydrogen particle formation in liquid helium was 

experimentally investigated. Experiments were planned 

to do visual characterizations of the particles, estimate 

their masses, and estimate the production efficiency. 

The particle sizes were estimated from video image 

analyses, similar to those presented in Refs. 9 and 10. 

The work presented here is the detailed studies of the 

Phase II (2001) video images, which precisely 

measured the particles sizes. This set of Phase II (2001) 

test analyses includes the analyses of numerous images, 

and numerous particles in each image. A mass estimate 

of the solid hydrogen particles was conducted. Using 

the particle size analyses and dewar gas outflow data, a 

solid hydrogen production efficiency was estimated. 

EXPERIMENTAL SETUP

The experiments were conducted in the Small 

Multipurpose Research Facility (SMIRF, formerly the 

Small Multilayer Insulation Research Facility, Ref. 12). 

The facility has a vacuum tank, into which the 

experimental setup was placed. The vacuum tank was 

used to prevent heat leaks and subsequent boiloff of the 

liquid helium, and the supporting systems maintain the 

temperature and pressure of the liquid helium bath 

where the solid hydrogen particles were created. 

The experimental setup included several key 

components. Figure 2 depicts the helium dewar and the 

associated liquid hydrogen tank. A small cryogenic 

dewar was used to contain the helium bath, in which the 

solid hydrogen particles were formed. The dewar was 

711.2 mm (28 inches) in height, with a 609.6 mm 

(24 inch) inside depth and had an inside diameter of 

315.9 mm (12.438 inches). To create the solid 

hydrogen, liquid hydrogen at a temperature of 14 to 

18 K was used. To contain the liquid hydrogen, a small 

stainless steel tank was used, which was 152.4 mm 

(6 inches) in diameter, and 609.6 mm (24 inches) long. 

As shown in Figure 2, the tank was mounted above the 

dewar. To control the hydrogen flow, a precision flow 

valve was used, and a video camera recorded the 

particle formation. All of the flow control for the liquid 

hydrogen, liquid and gaseous helium, and nitrogen 

purge gases was provided by the SMIRF systems. 

The field of view (FOV) of the camera versus the 

distance from the dewar lid was computed. Figure 3 

compares the camera field of view with the dewar 

diameter. Once the liquid helium's free surface is at 

x/L = 0.43 (315.9 mm, or 12.0 inches, with L = 711.2 

mm (28 inches)), the liquidís entire surface is in the 

FOV. For runs, the helium liquid level was maintained 

at nearly 355.6 to 406.4 mm (14 to 16 inches) from the 

dewar lid. This location was chosen based on the 

knowledge of the field of view of the camera, and the 

need to observe as much of the liquid surface as 

possible. 

Table I shows the locations of the silicon diodes for the 

temperature measurements. As these temperature 

measurements were used to establish the location of the 

helium surface and overall image sizes and field of 

view, the diode locations are presented. The Phase II 

temperature profiles in the helium dewar are presented 

in Figure 4. The diodes have a temperature accuracy of 

+1 degree K, and they are attached to a non-metallic 

rake, composed of circuit board material that extended 

from the dewar lid into the liquid helium. The diodes 

were mounted on the rake. Circuit board material was 

used as it had a low thermal conductivity, it was readily 

available, and was easily cut to the proper dimensions. 

A polycarbonate screw attached the top end of the 

circuit board to a polycarbonate rod. The upper end of 

the polycarbonate rod was threaded and screwed into 

the underside of the helium dewar lid. 
NASA/TMó2002-211915 3 

Table I.óSilicon diode locations in helium 

dewar L, dewar = 711.2 mm (28 inches) 

Name Location below dewar 

lid (inches) 

SD4 0 

LL1 2 

LL2 4 

LL3 7 

LL4 10 

LL5 12 

LL6 14 

LL7 16 

LL8 19 

LL9 22 

EXPERIMENTAL PROCEDURE

During the experimental runs, a small amount of liquid 

hydrogen was dropped onto the surface of the liquid 

helium. The hydrogen flow rate selected was 1/500th 

liter per second. This flow rate was selected by 

comparing the total heat capacity of the hydrogen 

versus the helium. Selecting a high flow rate would 

create a very high helium vaporization rate, and loss of 

the liquid helium. With the low flow rate, the particles 

formation is clearly observed, and it eliminates any 

chance of the relatively warm liquid hydrogen 

vaporizing all of the liquid helium in the dewar. Only a 

small amount of the liquid helium contained in a dewar 

vaporized as it froze the hydrogen particles. 

In the first step of the hydrogen freezing process, the 

liquid hydrogen temperature was subcooled to 14 to 

18 K. This process allowed the hydrogen to be at a very 

low temperature, near its freezing point. Comparisons 

of the heat capacity of helium and the heats of 

liquefaction and fusion (solidification) of hydrogen led 

to the selection of conditioning the hydrogen to a very 

low temperature before releasing it onto the helium 

surface. Otherwise a large amount of helium would 

have been used to condense the gaseous hydrogen, 

liquefy it, and then finally freeze the hydrogen into 

solid particles. Large clouds of vapor that are created 

during higher speed hydrogen freezing would have also 

obscured the formation process, and thwarted efforts to 

see the final particles. After the hydrogen particles 

freeze, they are observed for many minutes. 

Many frames from the videotape of the experiment 

were captured and analyzed. Table II summarizes the 

timing for the experimental runs, where each solid 

hydrogen formation run began. There was an interval of 

between 25 and 65 minutes between runs. These time 

spans were chosen to allow the particles to 

agglomerate, and to observe any unusual activity of the 

solid hydrogen. 

EXPERIMENTAL APPARATUS 

IMPROVEMENTS FOR 2001 TESTING

The 2001 Phase II testing included a number of 

improvements to the experimental apparatus used in 

Phase I (1999). The lighting in the dewar was improved 

with a high intensity light, and a silvered cone to reflect 

light into spaces that were shadowed in the Phase I 

testing. The mass flow into and out of the dewar is 

shown notionally in Figure 6. The gas composition of 

the venting gases from the dewar was measured with 

increased accuracy with the addition of a Residual Gas 

Analyzer (RGA). A heat exchanger was fabricated and 

added to the gas space above the liquid helium. The 

heat exchanger was to help reduce the temperature of 

the gas above the liquid surface. The insulation and 

cooling of the precision hydrogen valve was improved. 

A more reliable operation of the valve was needed to 

assure the proper small amount of hydrogen was 

introduced into the dewar. 

Many more runs were conducted in the 2001 Phase II 

testing. The experience in the 1999 Phase I testing 

allowed for a much greater frequency of testing, and the 

new operational changes to the experimental apparatus 

gave us more repeatable and reliable flow of the liquid 

hydrogen. 

EXPERIMENTAL CONSIDERATIONS

As the liquid hydrogen fell toward the helium surface, it 

became frozen and particles formed immediately after 

hitting the helium surface. Some of the hydrogen froze 

as it fell, but some vaporized as well. The hydrogen was 

a jet of fluid, with the outer shear layer vaporizing, but 

with the central core remaining liquid for a short time, 

and finally freezing during the drop, and as it hit the 

helium surface. 

During the fall of the hydrogen onto the helium, some 

of the hydrogen went into the gas phase. Small clouds 

of hydrogen were seen forming about the stream of 

hydrogen falling onto the free surface. Additional mass 

flow rate instrumentation was included to assess the 

total mass of hydrogen that is in the gas phase versus 

the solid particles. The temperature profiles of the 

dewar will shed light on the amount of gas formed, and 

a thermal and mass balance analysis can be conducted 

to more accurately measure the distribution of hydrogen 

gas and solid hydrogen in the dewar. A mass 

spectrometer was also used to determine the mass of 

hydrogen in the helium gas above the liquid helium. 

Solid hydrogen is less dense than helium, so the 

hydrogen particles floated on the surface, simplifying 

the particle imaging. In an operational propulsion 
NASA/TMó2002-211915 4 

system, this buoyancy property will be overcome by 

gelling the helium, thus allowing the hydrogen particles 

to be suspended in the helium. During the testing, it was 

noted that the frozen hydrogen particles may also serve 

as an effective gelling agent for liquid helium. 

A more detailed listing of the events from each run are 

provided in Appendix A. Appendix B and Figure 5 

show typical images from the testing. The small 

particles were allowed to float on the helium surface for 

at least 25 minutes before adding more hydrogen. 

During that 25 minute minimum time span, they began 

to seek each other out, agglomerate into a larger 

collection of particles, and minimize their surface 

energy as they float on the helium. The particles also 

turned from clear or translucent crystals to cloudy 

crystals, implying a transition from face centered cubic 

(FCC) to hexagonal close pack (HCP) molecule 

packing (Ref. 13). After allowing the first batch of 

particles to form, the dewar pressure was lowered to 

agitate the liquid helium surface, and the particles 

quickly broke up into their original smaller 

components. The particles would then again begin to 

agglomerate. 

Table II.óSolid hydrogen video event timing 

02ñ23ñ2001: During the run, the helium level is between 

14 and 16 inches below the lid. 

12:14:44 The first drop begins 

02ñ27ñ2001: During the run, the helium level is between 

14 and 16 inches below the lid. 

14:53:46 The first drop begins 

SOLID HYDROGEN TESTING RESULTS

Three major observations resulted from these solid 

hydrogen particle runs: particle sizes, the flows into and 

out of the dewar, and the particle formation efficiencies. 

Additional observations had to do with the thermal 

profile and stratification in the helium dewar. 

Analysis Background

The images were taken with a 0.5 inch lens, charged 

coupled device (CCD) black and white camera. The 

illumination in the Dewar was created with 150 Watt 

bulb with the light introduced into the dewar with an 

optical fiber system. All of the observations were done 

with a black and white video camera, with a 56 degree 

field of view. The video images were recorded on 

Betacam and VHS tape formats. The Betacam 

recordings were used to improve the ability to obtain 

high definition frames for analysis. To analyze the 

particles, a commercially available photo manipulation 

and analysis software package was used. 

There was one effective height to the liquid level that 

were used in the image analyses. The level for the 

helium was during the runs (x/L = 0.5, 14 inches below 

the lid), and this height was used for the baseline sizes 

for the overall image area (representing the entire free 

surface helium in the dewar). The specific particle sizes 

were then measured, and the ratio of the two, with the 

overall dewar surface area, is used to compute the 

particle size. 

Particle sizes

The solid hydrogen particles were analyzed by 

digitizing the video images, and measuring the sizes of 

the particles. The particle size measurements were 

corrected for the actual size of the particles using these 

equations: 

area, particle = (area, dewar / pixels, dewar) 

 x pixels, particle 

where: 

area, particle = area of the particle (mm2

) 

area, dewar = area of the dewar free surface (mm2

) 

pixels, dewar = number of pixels in the imaged 

 free surface 

pixels, particle = number of pixels in the imaged 

 particle 

At the beginning of and during each run, a variety of 

individual particles are measured. The smallest of the 

particles is identified, as well as a representative set of 

other larger particle sizes. Figure 5 illustrates a typical 

image from the analyses. The circle encompasses a 

small set of hydrogen particles that have agglomerated. 

Appendix A contains the raw data of the video 

observations from the 2001 testing and Appendix B 

provides the 2001 video image data. These data are the 

raw measurements of the particle sizes from the video 

observations. 

In the Phase II tests, the smallest particles were formed 

during the initial freezing of the hydrogen. Figure 7 

provides data from the 2001 testing. The smallest 

particle sizes are 1.0 to 6.4 mm. In this testing, no 

control was placed on the particle formation, other than 

the helium and hydrogen temperature and pressure and 

the flow rate of the hydrogen. The simple freezing 

process is somewhat random, and the particle will vary 

in size simply due to the random breakup of the stream 

of hydrogen that fell onto the helium during the 
NASA/TMó2002-211915 5 

freezing process. The other measurement variation of 

the particles from the video images that occurred was 

that all of the particles were not perfectly spherical or 

elliptical, thus an average size was measured. The 

Phase II (2001) testing included some unique 

observations, such as tiny scintillating particles, curling 

up in strings to form larger millimeter sized particles. 

Flow out of the dewar

The flow meter at the exit of the dewar exhaust stack 

records the volumetric flow rate out of the dewar. 

Figure 8 shows a flow rate versus time plot for a 

2 second run, on 02ñ23ñ2001. Figure 9 provides similar 

data for the run of 02ñ27ñ2001. The total outflow mass 

for the 2 runs is quite different, and dependent upon the 

dewar gas temperature, and the conditions for each run. 

The time for the flow rate to settle was about 2 minutes. 

The view on the camera however shows that the view 

remains cloudy, and does not clear for 21 minutes with 

the 02ñ23ñ2001 run, and 13 minutes with the 

02ñ27ñ2001 run. The temperature in the helium dewar 

for the 2 runs is shown in Figure 4. The dewar liquid 

and gas temperature was generally lower in the run on 

02ñ27ñ2001. However, the lid temperature was higher 

for this run. 

Flow into the dewar

During the range of runs conducted in the 2001 Phase II 

test, the mass flow rate of liquid hydrogen into the 

dewar is maintained for 1 to 3 seconds. The nominal 

flow rate desired was 1/500th to 1/100th liter per 

second. These flow rate correspond to the precision 

flow valve being 15 and 30 percent open, respectively. 

Based on the calibration of the precision control flow 

valve, the flow rate is not linear, but somewhat sharply 

peaked. Figure 10 shows the notional comparison of the 

planned flow rate and Figure 11 depicts the typical 

valve percent open data from the liquid hydrogen valve, 

and it is related to actual flow rate from the test 

configuration. The instantaneous flow rate is therefore 

significantly different than the planned rate, and this 

difference led to creating a better planning for 

conducting the experiments. Average flow rates were 

not able to be used in the calculations but an integrated 

total mass of liquid hydrogen flow could be estimated. 

Particle formation efficiency

The efficiency (eta) of particle formation can be 

expressed as: 

Eta = mass of hydrogen frozen / total mass of hydrogen 

(frozen plus vented) 

From the analyses of the test images, the mass of frozen 

hydrogen was estimated (using the technique discussed 

in Ref. 10). The area of the hydrogen particle is used 

with the average thickness (of 4 mm) of the hydrogen 

particle on the liquid helium to compute a hydrogen 

volume. A hydrogen density of 90 kg/m3

 was used for 

the analyses. This density was selected based on testing 

conducted by the USAF (Ref. 28). In the data from the 

run on 02ñ23ñ2001, the mass of hydrogen that was 

frozen was 2.55 grams. The hydrogen mass frozen in 

the run on 02ñ27ñ2001 was 1.32 grams. 

For the testing on the run on 02ñ23ñ2001, the 

efficiency (eta) was: 

Eta = 2.55 / (2.55 + 1.1464) = 0.69 or 69 percent 

The efficiency for the run on 02ñ27ñ2001 is 

Eta = 1.32 / (1.32 + 0.695) = 0.66 or 66 percent 

Comparing the frozen mass with the mass lost out of 

the dewar, is appears that the efficiency of production is 

somewhat low. For a small scale system, it may be 

typical to assume that that the efficiency of production 

may be low. In this experimental configuration, there is 

a relatively static production of solid hydrogen. There is 

little of no flow of the solid hydrogen particles away 

from the main formation point, and hence there is no 

way to demonstrate that a continuous production rate 

would be more efficient. 

There is a large volume of warm gas above the liquid 

helium surface, which will tend to vaporize part of the 

liquid hydrogen, and make it unavailable for forming a 

solid. In many cases during formation, we see particles 

that have frozen onto the sides of the dewar, and slump 

into the liquid helium. Some of these particles are 

exceedingly small (much less than 1 mm diameter), and 

are hard to see directly. They reflect so much light they 

seem to scintillate, and the brightness obscures their 

direct observation. 

The large gas volume above the liquid helium was 

required for the camera that was chosen for the testing. 

Filling to a higher level in the dewar does not allow us 

to image the full liquid helium surface. Without seeing 

the full surface or the full mass of frozen hydrogen, we 

are unable to predict the particle sizes, and observe and 

ultimately measure the full mass of frozen hydrogen. 

Much of the gas that was obscuring the view is finally 

the frozen onto the walls, and becomes the tiny 

scintillating particles. This seems evident from the 

observations for longer flow times, and higher flow 

rates. 
NASA/TMó2002-211915 6 

Timing event influence

During the testing there are several time scales that 

affect the solid hydrogen formation. The first is the time 

of flow for the liquid hydrogen, the second the time for 

the hydrogen outflow to be completed, and the time for 

the gas in the ullage to liquefy, and then solidify. There 

are different time scales for the different processing to 

occur. The flow of liquid hydrogen in the tank is about 

1 to 4 seconds, the time for the outflow to stabilize is 

about 60 seconds, and the time for the freezing of the 

hydrogen gas in the dewar ullage is about 1 to 

30 minutes. 

The flow of liquid hydrogen is controlled by the 

precision flow rate hydrogen valve and the pressure 

difference across it. This flow rate is computed using 

standard techniques. During the testing, care was taken 

to prevent the hydrogen tank pressure from exceeding 

the helium dewar pressure. A small amount of 

unplanned leakage of hydrogen into the helium dewar, 

creating particles before an experimental run was 

planned to begin. 

The freezing of the ullage gas was influenced by the 

rate of flow into the dewar, and the temperature of the 

dewar ullage gas. These values can be controlled more 

rigorously in future experiments, but they were not 

controlled precisely in these experimental runs. 

COMPARISON OF PHASE I 

AND PHASE II TESTING

There were some interesting similarities and differences 

between the Phase I and Phase II testing. Figure 12 

shows the Phase I (1999) particle sizes results. Overall, 

the initially formed particles were 1.8 to 4.6 mm (0.07 

to 0.18 inches) in diameter. These sizes are very similar 

to those from Phase II: 1.0 to 6.4 mm. 

Particle compaction was found in this set of 

experimental runs, as with the Phase I testing in 1999. 

The compaction trends seen in the Phase I and Phase II 

testing were similar. The smallest particle sizes were 

very small (almost microscopic) in most cases, and 

much smaller than those seen in Phase I. The lower 

dewar temperatures were able to freeze particles onto 

the walls of the dewar, and these particles flow down 

the walls and enter the liquid helium. 

Many additional images and other temperature data are 

available for analyses, and these additional images and 

data can lead us to more insights into the formation 

process. Initial analyses of the video and flow rate data 

showed many new phenomena that were not previously 

observed. These phenomena include the formation of 

what appear to be microscopic hydrogen particles, the 

formation of long coiled structures of hydrogen that 

curl up to form small particles, and the formation of 

long bars of solid hydrogen. Additional data and video 

analyses will show the precise conditions under which 

the new phenomena occur. 

CONCLUSIONS

The solid hydrogen testing described in this paper was 

the Phase II testing of a program to characterize solid 

hydrogen particles. The improvements to the test article 

allowed a better measurement of the flow rate into and 

out of the dewar. These measurements allowed the 

computation of a production efficiency, and showed 

that the formation efficiency is related to many aspects 

of the event timing for the experiment. 

The particle sizes formed in the Phase I (1999) and the 

Phase II (2001) testing were of very similar sizes. In the 

Phase I (1999) tests, the sizes ranges from 1.8 to 

4.6 mm in diameter. The Phase II (2001) testing 

produced particle sizes of 1.0 to 6.4 mm. However, 

there were many more interesting phenomena that 

occurred in the freezing processes in Phase II. These 

phenomena included microscopic scintillating particles, 

and particle that froze onto the dewar walls and slid into 

the liquid helium. 

The particle formation efficiency is in the range of 66 to 

69 percent for the 2 runs analyzed. This efficiency 

though relatively low, shows that a large fraction of the 

hydrogen is frozen. However, for future propulsion 

systems, a better method of particle formation is 

needed. Using recirculation systems, recovery and reuse 

of the vented hydrogen is likely. 

CONCLUDING REMARKS

The data analyzed thus far shows that the formation 

process must be done slowly to allow for the most 

efficient solid hydrogen particle formation. A fast flow 

will create a large cloud of hydrogen, much of which 

will go out of the vent stack. Additional experiment 

analyses will reveal the best flow rates from these 

experiments. 

Future propulsion systems using atomic rocket 

propellants with solid hydrogen will likely require 

massive facilities for creating particles and many 

complex processes to trap atoms. Though the 

complexities seem daunting, the potential of these 

propellants is great, and the capacity for reducing 

vehicle lift off weight and increasing payload capacity 

is theoretically unmatched. In some future vehicles and 

energy systems, atomic propellants in solid hydrogen 
NASA/TMó2002-211915 7 

may allow us to store and controllably release large 

quantities of energy, and allow the final Human 

expansion into the Solar System. 

REFERENCES

1) Palaszewski, B., ìAtomic Hydrogen Propellants: 

Historical Perspectives and Future Possibilities,î 

NASA Lewis Research Center, AIAA 93ñ0244, 

NASA TMñ106053, presented at the 31st AIAA 

Aerospace Science Meeting, Reno, NV, January 

11ñ14, 1993. 

2) Palaszewski, B., Ianovski, L., and Carrick, P., 

ìPropellant Technologies: Far Reaching Benefits 

for Aeronautical and Space Vehicle Propulsion,î in 

the Special Edition of the AIAA Journal of 

Propulsion and Power, September/October 1998, 

pp. 641ñ648. 

3) Palaszewski, B., ìLaunch Vehicle Performance for 

Bipropellant Propulsion using Atomic Propellants 

with Oxygen,î NASA Glenn Research Center at 

Lewis Field, AIAA 99ñ2837, presented at the 35th 

AIAA/ASME/SAE Joint Propulsion Conference, 

Los Angeles, CA, June 1999. 

4) Palaszewski, B., ìLaunch Vehicle Performance 

with Solid Particle Feed Systems for Atomic 

Propellants,î AIAA 98ñ3736, NASA/TMó1998-

208498, presented at the 34th AIAA/ASME/SAE 

Joint Propulsion Conference, Cleveland, OH, July 

1998. 

5) Palaszewski, B., ìSolid Hydrogen Testing and 

Analyses for Atomic Rocket Propulsion,î 

presented to the Propulsion Engineering Research 

Center (PERC) 11th Annual Symposium on 

Propulsion, The Atherton Hotel, State College, PA, 

November 18ñ19, 1999. 

6) Palaszewski, B., ìAtomic Propellants for 

Aerospace Propulsion Systems: Solid Hydrogen 

Experiments and Vehicle Analyses,î presented at 

the 1999 USAF High Energy Density Materials 

Contractors Conference, Cocoa Beach, FL, June 8ñ

10, 1999. 

7) Palaszewski, B., ìAtomic Hydrogen as a Launch 

Vehicle Propellant,î NASA Lewis Research 

Center, AIAA 90ñ0715, NASA TMñ102459, 

presented at the 28th AIAA Aerospace Science 

Meeting, Reno, NV, January 8ñ11, 1990. 

8) Lubell, M., Lue, J., and Palaszewski, B., ìLargeBore Superconducting Magnets for High Energy 

Density Propellant Storage,î presented at the 1996 

Applied Superconductivity Conference, Pittsburgh, 

PA, August 25ñ30, 1996. 

9) Palaszewski, B., ìSolid Hydrogen Experiments for 

Atomic Propellants,î NASA Glenn Research 

Center at Lewis Field, AIAA 2000ñ3855, 

presented at the 36th AIAA/ASME/SAE Joint 

Propulsion Conference, Huntsville, AL, July 2000. 

10) Palaszewski, B., ìSolid Hydrogen Experiments for 

Atomic Propellants: Image Analyses,î NASA 

Glenn Research Center at Lewis Field, AIAA 

2001ñ3233, presented at the 37th AIAA/ASME/ 

SAE Joint Propulsion Conference, Salt Lake City, 

UT, July 2001. 

11) Sanger, E., Rocket Flight Engineering, NASA 

Technical Translation, NASA TTñFñ223, 

Translation Into English of the book 

ìRaketenflugtechnikî' Berlin, Verlag Von 

Oldenburg, 1933, translation published 

September 1, 1965. 

12) Dempsey, P., and Stochl, R., ìSupplemental 

Multilayer Insulation Research Facility,î NASA 

Lewis Research Center, NASA TMñ106991, July 

1995. 

13) Silvera, I., ìThe Solid Molecular Hydrogens in the 

Condensed Phase: Fundamentals and Static 

Properties,î Reviews of Modern Physics, Vol. 52, 

No. 2, Part I, April 1980, pp. 393ñ452. 

14) McCarty, R.D., ìHydrogen Technology Survey: 

Thermophysical Properties,î National Bureau of 

Standards, NASA Technical Reports, NASA SPñ

3089, January 1975. 

15) Fajardo, Mario, USAF Research Laboratory, 

Edwards, CA, personal communication, July 1999. 

16) McNellis, N., et al., ìA Summary of the Slush 

Hydrogen Technology Program for the National 

Aero-Space Plane,î NASA TMñ106863, AIAA 

Paper 95ñ6056, presented at the Hypersonics 

Technologies Conference, Chattanooga, TN, 

April 3ñ7, 1995. 

17) Hardy, T.L., ìFLUSH: A Tool for the Design of 

Slush Hydrogen Flow Systems,î Technical 

Memorandum, NASA TMñ102467, Lewis 

Research Center, February 1, 1990. 

18) Sater, J.D., Pipes, J., and Collins, G.W., 

ìCryogenic D-T Fuel Layers Formed in 1-mm 

Spheres by Beta-Layering,î Report Number 

UCRLñJCñ128031ñABSñREV-1, Lawrence 

Livermore National Laboratory, Target Fabrication 

Meeting ë98, 1998. 

19) Collins, G.W., Sanchez, J.J., Bernat, T., Sater, J.D., 

and Bittner, D., ìForming Uniform D-T and D2 

Layers For Cryogenic NIF Targets,î Report 

Number UCRLñJCñ129969ñABS, Lawrence 

Livermore National Laboratory, European 

Conference on Laser Interaction with Matter, 1998. 
NASA/TMó2002-211915 8 

20) Bittner, D.N., Collins, G.W., Monsler, E., and 

Letts, S., ìForming Uniform HD Layers In Shells 

Using Infrared Radiation,î Livermore National 

Laboratory, Report Number UCRLñJCñ131371, 

40th Annual Meeting of the Division of Plasma 

Physics, New Orleans, LA, November 16ñ20, 

1998. 

 21) Collins, G.W., Bittner, D.N., Monsler, E., Letts, S., 

Tiszauer, D., Feit, M., Mapoles, E.R., and Bernat, 

T.P., ìForming and Smoothing D2 and HD Layers 

for ICF by Infrared Heating,î Lawrence Livermore 

National Laboratory, Report Number UCRLñJCñ

123596ñABS, European Conference on Laser 

Interaction with Matter, 24th, Madrid, Spain, 

June 3ñ7, 1996. 

22) Collins, G.W., Mapoles, E.R., Sanchez, J.J., 

Bernat, T., Sater, J.D., Bittner, D., Sheliak, J.D., 

Hoffer, J.K., ìReducing DT Surface Roughness 

For Cryogenic Ignition Targets,î Lawrence 

Livermore National Laboratory, Report Number 

UCRLñJCñ124884ñABS, Annual Meeting of the 

American Physical Society Division of Plasma 

Physics, 38th, Denver, CO, November 11ñ15, 

1996. 

23) Kozioziemski, B.J., Collins, G.W., and Bernat, 

T.P., ìSingle Crystal Growth of Solid D2,î 

Lawrence Livermore National Laboratory, Report 

Number UCRLñJCñ125981ñABS, 1997 March 

Meeting of the American Physical Society, Kansas 

City, MO, March 17ñ21, 1997. 

 24) Kozioziemski, B.J., Collins, G.W., Bernat, T.P., 

Mapoles, E.R., and Unites, W., ìCrystal Growth 

And Roughening Of Solid D2,î Lawrence 

Livermore National Laboratory, Target Fabrication 

Specialistís Meeting, 11th, Orcas Island, WA, 

September 8ñ12, 1996, Report Number UCRLñ

JCñ125121ñABS, Fusion Technology, Vol. 31, 

pp. 482ñ484, July 1997. 

25) Bittner, D.N., Collins, G.W., Letts, S., and 

Monsler, E., ìGeneration Of Uniform Solid HD 

Layers Inside Spherical Capsules Using Infrared 

Illumination,î Lawrence Livermore National 

Laboratory, Report Number UCRLñJCñ125140ñ

ABS, Conference, Target Fabrication Specialistís 

Meeting, 11th, Orcas Island, WA, September 8ñ12, 

1996. 

 26) Bernat, T.P., Collins, G.W., Mapoles, E.R., and 

Duriez, C., ìHeat-Flux Induced Changes To 

Multicrystalline D2 Surfaces,î Lawrence 

Livermore National Laboratory, Report Number 

UCRLñJCñ124261ñABSñREVñ1, 39th Annual 

Meeting of the APS (American Physical 

Society)/DPP (Division of Plasma Physics), 

Pittsburgh, PA, November 17ñ21, 1997. 

27) Kozioziemski, B.J., Collins, G.W., and Bernat, 

T.P., ìD2 Crystal Growth and Surface Energy,î 

Lawrence Livermore National Laboratory, Report 

Number UCRLñJCñ130037ñABS, Target 

Fabrication Meeting ë98, Jackson Hole, Wyoming, 

April 19ñ23, 1998. 

 28) Fajardo, M., ìCryosolid Propellants - The Last 

ìRevolutionaryî HEDM Concept,î in Berman, M. 

(editor), Proceedings of the High Energy Density 

Matter (HEDM) Contractors Conference, Scientific 

Special, June 8ñ10, 1999, January 2000. 

29) Larson, C.W., ìKinetics of Boron Carbon HEDM,î 

in Berman, M. (editor), Proceedings of the High 

Energy Density Matter (HEDM) Contractors 

Conference, Scientific Special, June 8ñ10, 1999, 

January 2000. 

30) Talroze, V.L., Gordon, E.B., Ivanov, B.I., 

Perminov, A.P., Ponomarev, A.N., ìMeasurement 

of the Hyperfine State of the Hydrogen Atom as it 

Interacts in the Gas Phase With CO, SO2, CO2 and 

N2O Molecules,î Akademiia Nauk SSSR Page: 

vol. 227, Akademiia Nauk SSSR, Doklady, 

vol. 227, Mar. 11, 1976, pp. 407ñ410. In Russian. 

Mar. 11, 1976, pp. 407ñ410. In Russian. 

31) Gordon, E.B., Perminov, A.P., Ivanov, B.I., 

Matiushenko, V.I., Ponomarev, A.N., and Tal'roze, 

V.L., ìChange In The Hyperfine State of the 

Hydrogen Atom During Its Collisions With 

Unsaturated Hydrocarbon Molecules in the 

Gaseous State,î (Previously cited in issue 23, 

p. 3317, (Zhurnal Eksperimental'noi i 

Teoreticheskoi Fiziki, vol. 63, Aug. 1972, pp. 401ñ

406.) Soviet Physics - JETP, vol. 36, Feb. 1973, 

pp. 212ñ215. Translation. 

 32) Hardy, W.N., Klump, K.N., Schnepp, O., Silvera, 

I.F. ìOptical Phonons in Solid Hydrogen and 

Deuterium in the Ordered State,î Phys. Rev. 

Letters, Vol. 21, No. 5, July 29, 1968. pp. 291ñ294. 

33) Agosta, C.C., Silvera, I.F, Stoof, H.T.C., and 

Verhaar, B.J., ìTrapping Of Neutral Atoms With 

Resonant Microwave Radiation,î Technische 

Univ., ìFew-Body Collisions in a Weakly 

Interacting Bose Gas,î reprinted from Physical 

Review Letters (American Physical Society), vol. 

62, no. 20, 15 May 1989, pp. 2361ñ2364. 

 
NASA/TMó2002-211915 9 

Figure 1. Atomic hydrogen rocket vehicle GLOW 

Figure 2. Solid hydrogen test configurationóLiquid helium dewar and liquid hydrogen tank 

Atomic hydrogen rockets: no helium addition

0

500

1000

1500

2000

2500

NLS: Isp 430

s

H: Isp 612 s H: Isp 750 s H: Isp 1282 s

Propulsion technology

GLOW (1000's of kg)

Propulsion

Payload
NASA/TMó2002-211915 10

Figure 3. Solid hydrogen experiment: camera field of view (FOV), dewar diameter = 315.9 mm 

Figure 4. Temperature distribution in helium dewar: 02ñ23ñ2001 and 02ñ27ñ2001 
NASA/TMó2002-211915 11

Figure 5. Image of solid hydrogen 2001 (full mass on helium surface) 

Figure 6. Flow in and out of the Helium Dewar 

Exhaust: Vent gases 

of helium and 

hydrogen 

Liquid 

helium 

Input: liquid 

hydrogen 

Gaseous helium 

and hydrogen 
NASA/TMó2002-211915 12

Figure 7. Solid hydrogen particle diameter versus timeóSolid hydrogen run: 02ñ27ñ2002 

Figure 8: Gaseous hydrogen flow rate out of dewar: 02ñ23ñ2001
NASA/TMó2002-211915 13

Figure 9: Gaseous hydrogen flow rate out of dewar: 02ñ27ñ2001 

Figure 10. Notional flow rate for solid hydrogen 

Solid Hydrogen Testing : Liquid Hydrogen Mass Flow Rate 

Computations ñ 2001 Testing

Planned experimental mass flow rate

time (s)

Mass flow rate

(liters/s) 1/500

time (s)

Mass flow rate

(liters/s) 1/500

Theoretical mass flow rate

Solid Hydrogen Testing : Liquid Hydrogen Mass Flow Rate 

Computations ñ 2001 Testing

Planned experimental mass flow rate

time (s)

Mass flow rate

(liters/s) 1/500

Planned experimental mass flow rate

time (s)

Mass flow rate

(liters/s) 1/500

time (s)

Mass flow rate

(liters/s) 1/500

Theoretical mass flow rate

time (s)

Mass flow rate

(liters/s) 1/500

Theoretical mass flow rate
NASA/TMó2002-211915 14

Figure 11. Liquid hydrogen valve opening versus time: for flow rate into helium dewar 

Figure 12. Solid hydrogen particle sizes, Phase I testing (1999) 
NASA/TMó2002-211915 15

Appendix A 

 Solid Hydrogen Video Observations: February 27, 2001 

Tape 1

Event timing 

(hh:mm:ss:ff) 

Observations 

14:48:01:25 Beginning of tape. This is a null 

image, before 1st H2 drop. Small 

amount of boiling at 

temperature rake 

14:48:59:05 Calm Helium surface. 

Liquid Helium level ~ 16î 

below lid 

14:53:45:16 Begin drop of liquid H2 to form 

solid hydrogen. Flow rate is 

approximately 1/100th liter/sec, 

t, open = 2 sec (corresponding to 

30% open for H2 valve) 

14:53:50:03 Clouds form, but many particles 

are visible (through the clouds) 

14:54:05:12 Many small particles visible 

14:54:22:09 Flurries of small particles, but 

very cloudyÖ. 

14:54:41:22 Large agglomerate to visual 

rake. Very cloudy, but clearing 

up. 

14:58:07:11 2 tiny particles swirl at center of 

field of view (FOV) 

15:01:26:13 Fog about 1⁄2 gone, agglomerate 

is quite visible, attached to 

visual. RakeÖ 

Much of it is out of FOV 

(agglomerate not visible, fully) 

15:06:22:27 Boiling visible off of 

temperature rake 

15:10:30:06 Fog mostly cleared up, 

agglomerate is unmoving 

15:21:55:16 Agglomerate is still 

immobilized 

15:28:10:21 Agglomerate moves, dropped 

pressure in dewar o psia to 

attempt to move agglomerate 

(at ~ 15:27:00) 

15:28:37:15 Agglomerate breaks loose, but 

reattaches to visual rake. 

Reduce pressure in dewar. 

another o psia (at ~ 15:29:00) 

15:29:28:04 Agglomerate begins rotating 

about the visual rake. 

15:29:24:27 good image of complete mass of 

solid H2 

15:31:01:22 Good image of ice edges 

15:32:25:10 Agglomerate is arrested by 

visual rake in new configuration 

15:36:28:11 More boiling at bottom of 

dewar, Lower pressure again to 

dislodge solid H2 

15:36:42:27 More violent boiling dislodges 

solid H2 

15:37:03:07 Agglomerate is almost 

completely in FOV 

15:37:48:02 Agglomerate is back in FOV in 

new configuration 

15:41:09:11 Agglomerate moves OUT of 

FOV 

15:42:44:06 Agglomerate moving due to 

induced boiling 

15:43:50:16 Part of agglomerate (that is free 

floating) has dark & light 

sections ñ good for study 

15:44:30:22 End of tape 
NASA/TMó2002-211915 16

Tape 2

Event timing 

(hh:mm:ss:ff) 

Observations 

15:44:54:04 Beginning of tape, solid H2 

still arrested by visual rake 

15:46:51:11 Boiling evident from 

lowered P., Solid H2 is 

tenaciously hanging on, 

only small portion is 

moving. 

15:51:00:09 *Piece breaks free to 

circulate on surface 

15:52:14:05 Good image for aging 

study (light and dark area 

to be calculated). 

15:54:32:17 Another good image for 

aging studyÖ 

15:54:40:28 *Piece rejoins larger 

agglomerateÖ 

15:55:37:00 Static, Clam View 

15:55:38:29 *Piece moves up, out of 

fov 

15:56:31:27 Lower pressure to agitate 

complete agglomerate, 

breaking it up. 

[D, FOV ~ 11 3/8î] 

15:56:47:03 Edge of FOV 

15:57:30:27 Good image of complete 

mass of solid H2 

15:59:21:15 Many good images of solid 

h2 floating (2 pieces) 

16:02:54:23 Tiny particle seen.. 

Analyze! 

16:03:31:04 Small doughnut seen 

16:04:53:07 Better doughnut image 

16:05:16:08 Many tiny particles are 

evidentÖ 

16:06:23:09 Straight ìBEAMSî of solid 

H2 evident Ö VERY 

DIFFERENT!! 

16:07:36:19 MANY New Tiny Particles 

Everywhere 

16:12:06:23 MANY tiny particles 

persist, do not appear to be 

agglomerating 

16:12:50:10 Particle appear to repel 

each other, HUMM! 

16:13:15:28 Lower pressure to break up 

solid H2 ñ KA Boom! 

16:13:46:18 Good edge of FOV 

16:15:27:00 Many smaller agglomerates 

danceÖÖ 

16:22:29:00 1/ [1/23/2002] 

Particles move slowly, not 

fully agglomerated, mass 

of H2 by rake (visual) and 

one in open space 

16:25:05:22 Many tiny (super tiny) 

particles, dead center, FOV 

16:27:20:26 More tiny particles 

16:29:33:24 Many tiny particles scoot 

about the surface 

16:31:55:05 H2 mass from visual rake 

breaks away 

16:33:10:10 More motion on helium 

surfaceÖ 

16:34:50:17 H2 agglomerate hits Visual 

rakeÖ 

16:34:53:01 Boiling at temperature rake 

small waves of clouds 

appearÖ at bottom of FOV 

16:36:27:08 Small H2 mass breaks 

away from Temperature 

rake 

16:36:30:08 Small H2 mass attaches to 

larger H2 mass 

16:37:31:18 End of tape 
NASA/TMó2002-211915 17

Tape 3

Event timing 

(hh:mm:ss:ff) 

Observations 

16:37:54:10 Begin tape 3 

16:40:37:02 H2 agglomerate is very 

stable, attached to visual 

rake. 

16:41:42:00 Boiling at the temperature 

rake 

16:51:54:18 Begin lower pressure, 

blasting particlesÖ. 

16:51:58:27 GOOD FOV Edges 

16:51:58:28 GOOD FOV EDGE 

16:52:03:18 GOOD FOV EDGE 

16:53:13:05 Clouds forming at tank is 

evacuated at end of runÖ. 

16:53:36:00 Waves of gas mesmerized 

the viewerÖ ☺

16:55:28:07 Hundreds of tiny particles are 

seen over the next few 

minutes, dead center of FOV. 

It is not clear if they are new 

particles reforming form 

agitated H2 mass, or H2 

frozen on wall that is coming 

off the wall 

16:57:56:21 Tiny particles continue to 

appearÖÖ. 

16:58:55:06 H2 agglomerate 

reforms/regroupsÖ. 

16:59:01:10 Many tiny particles still 

visibleÖ 

17:00:48:21 Image to determine 

area/mass difference from 

16:41:42:00 

17:00:58:21 ìClearerî image of H2 Area 

17:02:57:12 Very few tiny particlesÖ. 

17:04:21:25 Agitation clearly shows 

clumps of h2 (aged) 

17:07:53:21 ClumpsÖ. 

17:17:02:23 Clumps and more clumps 

17:34:27:22 Clumps appear more 

rounded, uniformÖ.. 

17:36:48:08 Large particle appears clear 

or very clear 

17:39:01:26 End of tape 

Tape 4

Event timing 

(hh:mm:ss:ff) 

Observations 

17:39:30:17 Beginning of tape 

17:40:17:23 Particles Agitated as 

Gas Departs Dewar 

17:46:28:04 View becomes more 

cloudy 

17:47:24:17 See reflections of 

particles on wall of 

dewar. 

17:50:33:01 See particle reflections 

on dewar wall 

17:51:47:29 Reflected images seem 

enlarged, and distorted 

17:54:10:28 Helium level in dish of 

dewar, only 

17:54:15:04 Particle reflections 

look like Georgia 

OíKeefe cloud 

painting ☺

17:55:42:17 Small, tiny particles 

Seem to reappear in 

dewar dish, may be 

boiling 

17:58:12:03 Many tiny sites for 

boiling at top of FOV 

18:00:35:12 Beached H2 particle 

nearly evaporated 

18:02:29:29 Helium level receding 

quickly 

18:02:59:02 Last H2 particle is 

vaporized / vaporizing 

18:03:07:29 All H2 is gone. 

18:04:02:17 All helium is 

vaporized 

18:11:26:24 End of tape

NASA/TMó2002-211915 19

Appendix B 

Solid hydrogen images from testing: February 27, 2001 
NASA/TMó2002-211915 20
NASA/TMó2002-211915 21
NASA/TMó2002-211915 22
NASA/TMó2002-211915 23
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29

Solid Hydrogen Experiments for Atomic Propellants: Particle Formation Energy

and Imaging Analyses

Cryogenics; Gelled propellants; Solid hydrogen; Helium; Rocket propulsion; High energy

density fuels

Unclassified -Unlimited

Subject Categories: 15, 20, and 28 Distribution: Nonstandard

Bryan Palaszewski

Prepared for the 38th Joint Propulsion Conference and Exhibit cosponsored by the AIAA, ASME, SAE, and ASEE,

Indianapolis, Indiana, July 7–10, 2002. Responsible person, Bryan Palaszewski, organization code 5830, 216–977–7493.

This paper presents particle formation energy balances and detailed analyses of the images from experiments that were

conducted on the formation of solid hydrogen particles in liquid helium during the Phase II testing in 2001. Solid

particles of hydrogen were frozen in liquid helium and observed with a video camera. The solid hydrogen particle sizes

and the total mass of hydrogen particles were estimated. The particle formation efficiency is also estimated. Particle sizes

from the Phase I testing in 1999 and the Phase II testing in 2001 were similar. Though the 2001 testing created similar

particles sizes, many new particle formation phenomena were observed. These experiment image analyses are one of the

first steps toward visually characterizing these particles and it allows designers to understand what issues must be

addressed in atomic propellant feed system designs for future aerospace vehicles.