Colloidal particle generator for electrostatic engine for propelling space vehicle

Norgren, C. T.

English

NASA Technical Reports Server

6. T. NORGREN 
COLLOID PROPULSION METHOD AND APPARATUS 
FLled March 12, 1963 
FIG.  I 
F IG .  2 
~ N V ~ N T O R ~  
CARL T. NORGREN 
https://ntrs.nasa.gov/search.jsp?R=19700023954 2020-03-17T01:30:37+00:00Z
1 
3,173,246 
COLLOID PROPULSION METHOD AND 
APPARATUS 
Carl T. Norgren, North Olmsted, Ohio, 
United States of America as repre 
Administrator of the National Aeronautics and Space 
Administration 
Filed Mar. 12,1963, Ser. No. 264,735 
10 Claims. (C1.60-35.3) 
(Granted under Title 35, US. Code (19521, sec. 266) 
The invention described herein may be manufactured 
and used by or for the Government of the United States 
of America for governmental purposes without the pay- 
ment of any royalties thereon or therefor. 
T h i s  invention is concerned with a method and appara- 
tus for propelling space vehicles, and more particularly 
with an onboard colloidal particle generator for an elec- 
tro static engine. The invention is especially concerned 
with an improved thrustor which utilizes a colloidal par- 
ticle generator. 
Colloidal particle electrostatic rocket engines have been 
proposed as propulsion systems for space missions where 
specific impulses from 1,000 to 10,000 seconds are re- 
quired. High power efficiency, high propellant utiliza- 
tion, reasonable field strengths, physical and electrical 
reliability, light weight, and long-duration operation are 
all required of these engines. 
Various methods have been used to form colloidal 
particles such as expanding material into a cooling or 
calming chamber through a high presscre nozzle. Chem- 
ical reactions such as the action of ammonia vapor in 
hydrogen chloride have likewise been utilized along with 
the oxidation of a particle forming material. Colloidal 
particles have also been produced by physical grinding 
such as mechanical disintegration in a colloidal mill. 
These techniques have disadvantages when applied to 
propulsion systems. For example, the atomization of a 
material, such as a liquid, 'tends to produce a very poor 
size distribution which is completely unsuitable for an 
electrostatic engine. Other devices which provide good 
size distribution of the particles do not produce a suffi- 
cient quantity of particles to be useful. Also methods 
which produce relatively uniform prepared particles 
often require a carrier, and it can be quite difficult to  
separate the particles from the carrier. Moreover, even 
when the particles are separated from the carrier they 
tend to form aggregates which are very difficult to sepa- 
rate. 
These problems have been solved by the present in- 
vention which utilizes the condensation of a homogenous 
vapor in a supersonic nozzle to  obtain sub-micron sized 
colloidal particles. In this manner vaporization, nuclea- 
tion, condensation, aggregation and possible revaporiza- 
tion occur at an extremely rapid rate, on the order of 
one millisecond. According to the present invention 
a material is vaporized and then passed through a con- 
vergent-divergent nozzle wherein adiabatic expansion 
of the vapor produces the required supersaturation for 
particle growth. The collision rate of the particles is 
controlled by the physical properties of the vapor as well 
as the dimensions of the apparatus, and in this manner the 
particle growth rate and size is controlled so that the 
particles have atomic mass units (a.m.u.'s) that are nar- 
rowly distributed in a predetermined mass range. The 
system is operated at a maximum pressure determined 
by the vapor pressure of the material; consequently the 
exhaust pressure can vary from a hard vacuum to a rela- 
tively high pressure and still produce colloidal particles. 
The method and apparatus for generating colloidal 
Particles according to the present invention can be used 
in numerous types of spacecraft. The colloidal particles 
are charged at the nozzle exhaust by any convenient 
means, such as a corona discharge. The resulting padi- 
cles are then accelerafed by suitable means such as an 
electrostatic accelerator. It is likewise contemplated that 
[i the colloidal particles can be charged in an electron bom- 
bardment engine and then accelerated. In an alternate 
embodiment of the invention the colloidal particles are  
accelerated in the nozzle alone to  supply small corrections 
to planned orbits. 
It is, therefore, an object of the present invention to  
provide an improved method of propulsion in which sub- 
micron sized particles are utilized which enables realistic 
accelerating potentials to be used. 
Another object to the invention is provide an improved 
15 thrustor which utilizes a colloidal particle generator 
having a supersonic nozzle. 
Other objects of the invention will be apparent from 
the specification which follows and from the drawings 
in which like numerals are used throughout to identify 
FIG. 1 is a schematic view of an electrostatic engine 
having a thrustor constructed in accordance with the in- 
vention, and FIG 2 is a perspective view of a colloid 
particle generator of the invention. 
Referring now to the drawings there is shown in FIG. 1 
an electrostatic engine 10 for rockets and the like that 
may be used with electric spacecraft. The electrostatic 
engine 10 comprises a power supply 12 and a thrustor 14. 
The power supply 12 may be any of a number of different 
30 types such as a nuclear reactor that is used to drive a 
turbine or a nuclear battery. 
The thrustor 14 comprises a propellent vaporizer 16. 
a supersonic nozzle 18, charging means 20, and accel- 
erators 22 and 24. An electron trap 26 is provided where 
35 the vaporizer 16 and the nozzle 18 are operated at ground 
potential to prevent the back streaming of electrons from 
the charging means 20. 
The vaporizer 16 and the nozzle 18 compnse a colloidal 
particle generator which is indirectly heated in a con- 
40 ventional manner for supplying sub-micron sized particles 
to be charged and accelerated. By way of example, an 
A.C.' Nichrome heating unit 28 wound around the va- 
porizer 16 and a similar heating unit 30 wound around 
[he nozzle 18 have been successfully used. Heat shields 
4.j 32 and 34 are provided to reduce radiation heat losses. 
The heating units 28 and 30 are connected to an auxiliary 
power supply 36 and the entire colloidal particle genera- 
tor is maintained at  a zero potential with respect to 
ground. 
In operation, a supply of propellent is enclosed in the 
vaporizer 16 and heated by the heating unit 28 t o  form 
a homogenous vapor which is then expanded in the nozzle 
18 to form sub-micron sized colloidal particles. The 
heating unit 30 prevents condensation of these particles 
The particle formation on a nozzle condensation prw- 
ess is highly complex, and is dependent primarily on 
reaching a critical nucleation rate in the vapor flow. 
This rate is a function of the supersaturation, tempera- 
GO ture, and physical properties of the propellent in the 
vapor stream. 
Supersaturation is controlled by the flow rate in the 
nozzle 18. Because the nozzle throat functions as a 
critical flow orifice, the vapor pressure of the propellent 
6.j in the vaporizer 16 must be high enough so that adiabatic 
expansion can occur in the nozzle 18. This expansion 
creates the necessary conditions for the supersaturation 
required in nuclei formation. The vapor pressure of 
the propellent in the vaporizer 16 is controlled by regulat- 
A predetermined supersaturation is required for nu- 
cleation, and for some materials this state is reached 
10 
20 likeparts. 
25 
50 
5.j on the nozzle surface. 
i o  ing the power input to the heating unit 28. 
= r  / .  
3,173,246 
3 
ahead of the nozzle throat. In this situation subsequent 
expansion is not required for nucleation; however, the 
expansion does cool these materials. This cooling is 
necessary to reject heat from the vapor stream to insuure 
efficient formation of sub-micron colloidal particles from 
nuclei. The process is stopped with the formation of 
nuclei if low mass particles are desired. The formation 
of the stable nuclei is quite complex and can vary from 
100 a.m.u.’s to  over 600,000 a.m.u.3 for different ma- 
terials. 
While an important function of the nozzle 18 is to  
provide for supersaturation so that nuclei can be formed 
from a given material, it further insures an adequate 
mass flow rate a t  a given supersaturation to provide a 
sufficient quantity of nuclei suitable for use in an electro- 
static engine. Also the length of the nozzle 18 is selected 
to provide the required time necessary for nuclei forma- 
tion and/or particle growth. The nozzle has an expan- 
sion ratio which not only provides the supersaturation 
required for nuclei formation but also insures cooling so 
an efficient conversion of vapor to particles can occur 
from a thermo-dynamlc viewpoint. 
Particles in the range of 1 0 3  to 105  a.m.u.3 are pre- 
ferred because they can be accelerated to a desired im- 
pulse by reasonable accelerating voltages. Particles in 
this size range are formed from large nuclei or by can- 
densing vapor on a small nucleous. Particles having a 
size in the range of IO5 to IO8 a.m.u.’s are easier to 
handle and are formed by condensation and agglomera- 
tion of the smaller particles. 
Referring to FIG. 2 there is shown a typical colloidal 
particle generator constructed in accordance with the 
invention. This embodiment utilizes a convergent- 
divergent nozzle 18 that has a length of 15.5 centimeters 
and a rectangular throat 0.273 by 4.48 centimeters. The 
total turning angle for expansion is taken at the throat 
of the nozzle 18 while the remainder of the length is used 
to cancel reflecting shock waves. The nozzle 18 is char- 
acterized as supersonic because the velocity of the pro- 
pellent flow through the throat is sonic, and the subse- 
quent expansion produces supersonic velocities. 
By way of example mercurous chloride propellent 
which was vaporized in the vaporizer 16 shown in FIG. 
2 at a temperature of 480” F. gave a particle size of 106 
a.m.u.’s. Mercuric chloride vaporized at temperatures of 
400°F. and 430°F. gave particle sizes of 108  and 108 
a.m.u.’s respectively. Aluminum chloride vaporized at 
temperatures of 180°F. and 220°F. produced particles 
having sizes of 103 and 105 a.m.u.’s respectively. 
At the nozzle exit the condensed particles may be 
considered analogous to molecular flow; for example, 
pressures in the order of mm. Hg are common in 
this region. 
Upon leaving the nozzle 18 these particles are charged 
by electron attachment. In a preferred embodiment for 
use with an electrostatic thrustor the charging means 20 
comprises a negative corona discharge from a wire con- 
nected to the power source 12. A negative corona dis- 
charged is preferable for charging the particles because 
the high voltages necessary for high impulse can be placed 
on the wire without breakdown at the low pressures 
encountered adjacent the nozzle exit. In addition, be- 
cause the electrons are supplied from a relatively cold 
source no undesirable heat is added to the system which 
would affect nucleation or over-all efficiency. 
It is also possible to positively charge the particles. 
Positive charging by electron bombardment is contem- 
plated as well as positive charging by ion attachment. 
Positive static charging by particle rupture can be used 
along with static charging by contact with surfaces hav- 
ing high surface field strengths. The particles may like- 
wise be positively charged by a radioactive source. 
The accelerator 22 is connected to the power supply 
12 while the accelerator 24 is grounded. By way of 
example, the accelerator plates 22 and 24 may be formed 
4 
from metal foil that is supported on a relatively light 
frame. 
While one example of the invention has been dis- 
closed and described it will be appreciated that various 
5 modifications may be made to the structure as well as 
the method without departing from the spirit of the 
invention or the scope of the subjoined claims. For ex- 
ample, it is contemplated that water as well as carbon 
dioxide may be used as the propellent in the colloidal 
10 engine. 
What is claimed is 
1.  A method of propulsion comprising the steps of 
vaporizing a material, 
expanding said material in a supersonic n o d e ,  con- 
densing said material to form a plurality of sub- 
micron sized colloidal particles, 
15 
charging said particles, and 
accelerating said particles. 
2. A method of propulsion comprising the steps of 
heating a coloidal particle forming material to vapor- 
ize the same, 
expanding said vaporized material in a supersonic 
nozzle, 
controlling the flow rate of said vaporized material in 
said nozzle and subsequent supersaturation therof 
to form a plurality of nuclei, 
20 
23 
charging said nuclei, and 
accelerating said nuclei. 
3. A method of propulsion as claimed in claim 2 in- 
regulating the temperature of said colloidal particle 
forming material to control the vaporization pressure 
thereof. 
4. A method of propulsion as claimed in claim 2 in- 
negatively charging said nuclei by electron attachment 
5. A method of propulsion as claimed in claim 2 in- 
30 cluding the step of 
2.j cluding the step of 
with a negative corona discharge. 
cluding the step of 
&i positively charging said nuclei. 
6. A method of propulsion as claimed in claim 2 in- 
condensing material on said nuclei to form a plurality 
of particles, each have a mass in the range between 
1 0 3  to about 105 a.m.u.’s. 
7. A method of propulsion as claimed in claim 6 in- 
agglomerating said condensed material to form a plu- 
rality of particles. each having a mass in the range 
between about 1 5 5  to 10s a.m.u.’s. 
8. Propulsion apparatus comprising 
a generator for forming a plurality of sub-micron 
sized colloidal particles having a relatively narrow 
distribution in the range about lo3 to about lo* 
a vaporizer having meanse for controlling the tem- 
perature of a colloidal particle forming material to 
heal the same thereby forming a vapor, and 
a nozzle for receiving said vapor, 
a relatively cold wire having a voltage thereon to form 
a negative corona discharge for charging said par- 
ticles by electron attachment, and 
means for accelerating said particles electrostatically. 
9. An electrostatic engine comprising 
a power supply, and 
a thustor including 
cluding the step of 
4 3 
cluding the step of 
50 
55 a.m.u.’s, said generator comprising 
6” 
0 3 
a colloidal particle generator for forming sub- 
micron sized particles, each having a mass in 
the range between about lo3 t o  about 1Ds 
a.m.u.’s, said colloidal particle generator com- 
prising means for heating a material to vapor- 
ize the same and a nozzle for receiving said 
a wire connected to said power supply for pro- 
i 0 
vapor, 
* -  
I .) 
3,173,246 
5 6 
viding a negative corona discharge to charge 
said particles, and 
acclerator means for accelerating said charged 
par tides. particles. 
an electron trap positioned between said nozzle 
accelerator means for accelerating said charged 
and said wire, and 
6 10. An electrostaiic cngine comprising 
a power supply, and 
a thrustor including 
eferences Cited by the ep 
UNITED STATES PATENTS a colloidal particle generator for forniiqg sub- 
micron sized particles, each having a mas6 in the 2,754,442 7/56 Boutry et al. _-________ 313-62 
range beiween about 103 to zbout 108 a,m.u.'s, 10 2,880,337 Langmuir et al. _ _ _ _ _ _ _ _ _  6 6 3 5 . 5  
said colloidal generator comprising meqns for 2,883,568 4/59 Beam et al. - -__________ 60-35.5 
heating a material to vaporize the same and a 3,073,984 1/63 Eschenbach et al. _ _ _ _ _ _  313-63 
nozzle for receiving said vapor, 3,120,736 2/63 Gignoux _ _ _ _ _ _ _ _ _ _ _ _ _ _  60-35.5 
a wire connected to said power supply far pro- 3,122,882 3/64 Schultz et al. _ _ _ _ _ _ _ _ _ _  60-35.5 
viding a negative corona discharge to charge 15 
said particles, 
3/59 
SAMUEL LEVINE, Primary Examiner. 
ATENT OFFICE 
CORRECT 
P a t e n t  No. 3 , 1 7 3 , 2 4 6  March 1 6 ,  1965 
Carl  T .  Norg ren  
I t  is hereby ce r t i f i ed  t h a t  e r ro r  appears i n  the above numbered pat- 
e n t  r eq l i r ing  c x r e z t i o n  and tha t  the sa id  Let ters  Patent s h o d d  read as 
Column 4 ,  l i n e  2 0 ,  f o r  " c o l o i d a l "  r e a d  - -  c o l l o i d a l  --; 
co:*rer: ted , below. 
l i n e  4 4 ,  f o r  "have" r e a d  - -  h a v i n g  - - ;  l i n e  5 0 ,  f o r  r r 1 5 5 "  read 
column 4 ,  l i n e  5 6 ,  f o r  "meanse" r e a d  - -  means --;  column 5 ,  l i n e  
11, a f t e r  " c o l l o i d a l "  i n s e r t  - - p a r t i c l e  - - .  
- _  1 0 5 '  - - .  , l i n e  5 4 ,  a f t e r  " r ange"  i n s e r t  - -  be tween  - - ;  same 
S i g n e d  and  s e a l e d  t h i s  2 4 t h  day  o f  Augus t  1965 .  
(SEAL) 
Attest: 
ERNEST W e  SWTDER 
Attc4ng Officer 
EDWARD J .  BRENNER 
Commissioner of Patents 


Colloid propulsion method and apparatus Patent

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