Permanently magnetized ion engine casing construction for use in spacecraft propulsion system

Sohl, G.

English

NASA Technical Reports Server

REPLY TO 
ATTNOF GP 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
April 5 ,  1971 
TO : USI/Scientific & Technical Information Division 
Attention: Miss Winnie M. Morgan 
FROM a GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U.S. Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8 ,  1970, 
the attached NASA-owned U.S. patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U.S. Patent No. : 3,412,559 
Corporate Source : Electro-Optical Systems, Inc. 
Supplementary 
Corporate Source 
NASA Patent Case No.: XNP-06942 
Gayle Parker 
Enclosure: 
Copy of Patent 
NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710013817 2020-03-17T03:01:41+00:00Z
Nov. 26, 1968 G. SOHL 3 4  12,55 
ION ENGINE CASING CONSTRUCTION AND 
METHOD OF MAKING SAME 
Filed July 6 ,  1966 4 Sheets-Sbeet 1 
' I  
G .  SOHL 3,412,559 
ION E N G I N E  CASiNG CONSTRUCTION AND 
METHOD OF MAKING SAME 
Nov. 26, 1968 
Filed J u l y  6, 1966 4 Sheets-Sleet i; 
PRiOR A R T  
2 8  
20 
Nov. 26, 1968 G. SOHL 3,412,559 
ION ENGINE CASING CONSTRUCTION AND 
METHOD OF MAKING SAME 
F i l e d  July 6 ,  1966 4 Sheets-Sheet 3 
INVENTOR. Gonoohl S O H &  
Nov. 26, 1968 G. SOHL 3,412,559 
ION ENGINE CASING CONSTRUCTION AND 
METHOD OF MAKING SAME 
Filed July 6, 1966 4 Sheets-Sheet 4 
38 
INVWVTOR. 
G O R U O ~  SOHL 
STATES PATENT 
IFICATE 0 
Patent No. 3,412,559 November 26, 1968 
James E. l'iebb Administrator of The National 
Aeronautics and Space Administration 
It i s  c e r t i f i e d  t h a t  e r r o r  appears i n  t h e  above i d e n t i f i e d  
pa ten t  and t h a t  s a id  L e t t e r s  Pa ten t  are hereby corrected as 
shown below: 
In the heading to the drawings, line I, Sheets 1 to 4, . SOHL" should read - -  JAMES E. WEBB, ADMINISTRATOR OF THE 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION - - .  In the heading 
to the printed specification, line 4, "Gordon Sohl, 84 S. Craig 
Ave., Pasadena, Calif. 91107'' should read - -  James E. Webb, 
Administrator of the National Aeronautics and Space Administration, 
with respect to an invention of Gordon Sohl - - .  
Signed and sealed this 24th day of March 1970. 
ward M. Fletcher, Jr. WI 
~te~ting Officer ~iss iQner of 
3,4 12,559 United States Patent ffice patented 26, 1968 
1 
3.412.559 
ION ENGINE CAS~G-CONSTRUCTION AND 
METHOD OF MAKING SAME 
Gordon Sohl, 84 S. Craig Ave., Pasadena, Calif. 91107 
Filed July 6, 1966, Ser. No. 563,651 
10 Claims. (CI. 60-202) 
ABSTRACT OF THE DISCLOSURE 
An improved ion engine, the casing of which is perma- 
nently magnetized to generate a desired magnetic field. 
Origin o f  the invention 
The invention described here in was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National Aero- 
nautics and Space Act of 1958, Public Law 85-568 (72 
Statute 435; 42 U.S.C. 2457). 
Background o f  the invention 
This invention relates to ion engines, and more partic- 
ularly to an improved electron bombardment ion engine 
that is more efficient, weighs less, and is less complicated 
in construction than previous engines of this type. 
Ion engines are being extensively investigated in the 
field of propulsion for spacecraft for long space missions. 
An ion engine for the above type of mission must be able 
to operate for very long periods of time unattended. As 
an example, it is contemplated that an ion engine will 
have to operate 10,000 to 20,000 hours on some of these 
space missions. 
Ion engines, of course, are not new. An example of one 
type of ion engine may be seen in the U.S. Government 
Publication, NAS SP-22, titled “Electric Propulsion for 
Spacecraft,” dated December 1962, page 28, FIG. 48(c)-5. 
This publication is available from the Superintendent of 
Documents. 
The ion engine shown in the above publication, and as 
will be more fully explained later on, operates to cause 
an electron to collide with an expellant atom. The colli- 
sion results in the formation of two electrons, and an ion 
that is accelerated and used for thrust. To increase the 
probability of an electron colliding with an atom, a field 
coil is placed around the ion engine’s casing and is used 
to create a magnetic field to influence the path of travel 
of the electrons. The magnetic field causes the electrons 
to travel in a spiral path to increase the likelihood of 
collision with an atom. If the magnetic field were omitted, 
the electron would be drawn generally in a straight-line 
path to the ion engine’s positive anode, and the chances 
of its colliding with an atom would be greatly diminished. 
Another example of an ion engine, that will also be 
more fully described hereinafter, is shown in the above 
publication on page 28, FIG. 48(c)-6. This figure shows 
an ion engine having a plurality of permanent bar magnets 
around the outer casing of the engine in the place of the 
magnetic field coil. Bar magnets eliminate the power for- 
merly required by the field coil. They also reduce the 
need for a separate power supply previously required to 
energize the field coil, thus further simplifying the engine. 
While the engine with bar magnets is an improvement 
over the engine with a field coil, both engines weigh ap- 
proximately the same amount. This is because the bar 
magnets themselves add weight to the engine. 
With the above in mind, it is apparent that an ion 
engine that can be made lighter than ion engines of the 
field coil, or bar magnet type, and still deliver the same 
amount of thrust, would provide a distinct advantage for 
a successful space mission. Along the same line, it would 
2 
be an even greater advantage in space flight if the engine 
could also be made more efficient, and less complicated 
structurally. 
Summary of the invention 
An ion engine that is constructed as taught by this in- 
vention, as discussed hereinafter, is more efficient than 
prior art types. It is capable of providing the same or 
greater thrust than previous ion engines of the above type. 
It is less complicated structurally. And, it is lighter in 
weight. 
The above is accomplished by eliminating the bar mag- 
nets and field coil of the ion engine entirely. This inven- 
tion teaches using the casing of the ion engine to create 
According to the teaching of this invention, the outer 
casing of the ion engine is made out of a magnetizable 
material. It is then selectively magnetized to create a per- 
manent magnetic field that provides increased efficiency 
20 for the ion engine. That is, one circumferential section of 
the casing can be made with a weaker or stronger mag- 
netic field relative to another circumferential section of 
the casing to vary the magnetic field axially along the 
length of the casing. 
The casing is easily fabricated by rolling magnetic sheet 
stock into a cylinder. Then the casing is placed within a 
magnetizing coil and magnetized. The magnetizing coil 
is connected to a DC power supply whose current can be 
varied or reversed so the strength of the magnetic field 
30 can be adjusted to vary the magnetization in selected por- 
tions of the casing. Thus a tailer-made magnetic field can 
be created having any selected characteristics desired. 
The invention also teaches a preferred way of magnet- 
izing the casing so as to create the desired magnetic field. 
36 The casing is magnetized to its highest magnetization and 
then the portions of the surface, where weaker magnetic 
fields are desired, are slightly demagnetized. This provides 
very accurate control over the magnetic field. 
With the above in mind, it is therefore an object of this 
40 invention to construct an ion engine that is more efficient 
than prior art types. 
Another object of this invention is to provide an ion 
engine that can be made lighter than prior art types, yet 
will yield the same or a greater amount of thrust. 
It is another object of this invention to provide an ion 
engine that is less complicated structurally than prior art 
types. 
Another object of this invention is to teach a preferred 
method of magnetizing an ion engine casing to provide ac- 
50 curate control of the magnetic field being created. 
Brief description of the drawings 
Other objects and advantages will appear from the fol- 
lowing description considered in conjunction with the ac- 
FIG. 1 is a sectional view of a prior art ion engine 
FIG. 2 shows a simplified portion of prior art ion 
FIG. 3 is an overall exterior view of the ion engine 
FIG. 4 is a sectional view of FIG. 3 taken in the di- 
FIG. 5 is an end view of FIG. 4 taken in the direction 
FIG. 6 shows how the chamber of the ion engine can 
5 
15 the magnetic field. 
25 
45 
55 companying drawings: 
utilizing a field coil; 
engine that employs bar magnets; 
of this invention; 
rection of arrows IV-IV; 
6o 
65 of arrows V-V; and 
be magnetized. 
Preferred embodiment of the invention 
To help explain the invention, a prior art field coil 
ion engine and a prior art bar magnet ion engine will first 
70 
3,412,559 
3 4 
be briefly described. These will help to point out ap- semblies 44 and is in turn connected to rim 40 by screws 
plicant’s invention over the prior art. 46. Referring to FIG. 5, accelerator electrode 30 is pro- 
Referring to FIG. 1, there is shown a sectional view vided with a terminal 48 for electrical connections. 
of a prior art electron bombardment ion engine 2 of the It will be noted, in comparing the prior art ion engines, 
field coil type. Essentially the engine operates to ionize 5 illustrated in FIGS. 1 and 2 of the invention, that field 
an expellant material, such as cesium vapor (not shown) coil 26 in the ion engine, shown in FIG. 1, as well as 
and to eject the ions out of the engine, using a high nega- bar magnets 32 and enlarged plates 14, 28 of the ion 
tive voltage, so as to provide thrust. Generally the cesium engine shown in FIG. 2, have been eliminated. The pres- 
vapor is admitted from reservoir 4 through opening 6 ent ion engine is constructed so that outer casing 36 alone 
in cathode 8 through orifice plate 10 to ionization cham- produces the magnetic field. 
ber 12 at a controlled rate. Cathode 8 is supported by a One example of the construction of casing 36 follows: 
cathode plate 14. The cathode includes a tubular emitter A permanent magnetic casing with a coercive force of 
16 made, for example, of tantalum, that emits electrons about 20 oersteds was needed when c o n s t h i n g  the ion 
when heated. A heater 18 is imbedded in and is coaxial engine. A sheet stock of magnetizable material (such as 
with the emitter to heat it. The electrons and vapor enter 15 Vicalloy) was used for the ion engine casing. According 
ionization chamber 12 through orifice plate 10. to calculations it was determined that the casing could 
The electrons are attracted to the peripheral cylin- be made to a design minimum thickness of .007 inch. 
drical anode 20. Anode 20 is carried by an anode sup- However, for convenience, the thickness actually used 
port comprising feed-through bolts 22 that are connected was .016 inch. 
to cylindrical casing 24. Anode electrical connections are 20 The casing was rolled from the magnetizable sheet 
made through strap 23 connected to bolts 22. stock into cylindrical form and electron beam welded to 
A field coil 26 surrounds casing 24 and creates an axial the iron rims. The casing was then heat-treated to develop 
magnetic field that acts on the electrons to give them a the magnetic properties, and then magnetized. 
spiral path 25 to facilitate collisions between the elec- Referring to FIG. 6, there is shown one method of 
trons and atoms so as to create ions as explained pre- 25 magnetizing ion engine casing 36. Only rim 38 can be 
viously. For comparison purposes, the path of an elec- seen in this figure, although rim 40 is connected to the 
tron, if the magnetic field was omitted, is shown by dotted other end. A charging coil 50, connected to a DC sup- 
lines 27. ply 52, is used. Any DC supply can be used whose cur- 
The ions are extracted by a high potential difference rent and polarity can be varied. This is deemed desirable 
pressed across the perforated plate-shaped screen elec- 30 because considerable difficulty was initially encountered 
trode 28 and perforated plate-shaped accelerator elec- in properly magnetizing the engine casing. This difficulty 
trode 30 to provide thrust. was caused by iron rims 38 and 40 distorting the coil’s 
With respect to this type of engine, it is emphasized charging field. The iron rims ended up with significantly 
that casing 24 is surrounded by field coil 26. One of the higher magnetization than the center of the casing. It was 
principal power losses in this type of engine is the energy 35 discovered that the results desired could be obtained by 
that is used to energize field coil 26 to maintain the mag- charging the center of the casing to the point where it 
netic field. was properly magnetized and then reversing the field to 
An ion engine employing a field coil has just been de- demagnetize the ends slightly. 
scribed, An ion engine utilizing bar magnets will now A magnetic field was selectively created within the 
be described. 40 engine casing that was slightly weaker at the cathode 
Referring now to FIG. 2, a simplified illustration of end, increased in strength to the center and then decreased 
a second type of prior art ion engine 30’ is shown. Like in strength axially from the center toward the screen 
parts are similarly numbered. This type is like the type electrode by about 15%. A field of this nature, with a 
shown in FIG. 1 except that a plurality of bar magnets weaker field at the screen electrode end, tends to exert 
32 have been placed around outer casing 33 and are used 45 a down stream force on electrons; this sets up a potential 
in place of field coil 26 of the prior art engine shown in gradient that accelerates ions toward the screen electrode, 
FIG. 1. To accommodate the bar magnets, cathode plate The ends result of the electrons colliding with the atoms, 
14 and screen electrode plate 28 have been enlarged in and also moving toward the screen electrode, is for the 
diameter. Magnets 32 induce a magnetic field through- electrons to essentially sweep the ions toward the screen 
out ionization chamber 12. 
The advantages in the use of bar magnets 32, as men- An engine, constructed as above, has operated with in- 
tioned previously, is that they eliminate the power re- creased performance due to the magnetic field configu- 
quired by the previous field coil. They also reduce the ration. Operation at high mass utilization efficiency, that 
need for a separate power supply to energize the field is, number of ions accelerated to obtain thrust, was in- 
coil. 55 creased, and this was possible with a lower degree of 
Having ‘the above two prior art ion engines in mind, arc power required (arc power = cathode to anode 
the ion engine of the present invention will be described. voltage X anode current). Much greater efficiency was 
Referring to FIGS. 3, 4, and 5, there is shown an thus obtained with reduced power, 
exterior view, a sectional view and an end view of ion Additionally, it has been found that the use of the mag- 
engine 34 of this invention. This ion engine is generally 6o netized casing 36, as taught by the invention, eliminates 
similar to the prior art engines except that it does not various distortions of the megnetic field that were present 
contain a field coil or bar magnets. Like parts have been in the magnetic field created by field coil 26 and bar mag- 
similarly numbered and will not be described again. nets 32, so the magnetic field created is now more effi- 
Outer casing 36 (that corresponds to outer casings 24 cient. 
and 33 of the prior art engines) has been magnetized to 65 An idea of the weight saving of the engine of this in- 
replace the magnetic field formerly created by the field vention, which construction was previously described, com- 
coil and bar magnets. pared to a bar magnet ion engine, may be helpful. The 
outer casing 36 is of cylindrical shape. At one end (to bar magnet engine had approximately the same diameter 
the left in FIG. 4), is connected an iron rim 38. The rim outer casing as the engine of this invention and weighed 
acts as a pole piece, and is used as a support to which 7o approximately 4.3 pounds, The engine of this invention 
cathode plate 14 is connected by screws 39. weighed approximately 2.45 pounds, a weight reduction 
Casting 36 has a second iron rim 40 connected to its of almost half. Additionally, even further weight re- 
other end that also acts as a pole piece and as a sup- duction could have been made by using the calculated 
port. Screen electrode 28 is connected to rim 40 by screws design minimum for the material of the magnetic casing. 
42. Accelerator electrode 30 is carried by insulator as- 75 It will be obvious to those skilled in the art that the 
5o and eccelerator electrodes. 
cylindrical permancait magnet, said perni?.cent magnet 
having a magnetic ficld that varies axially from a 
nianen! magnet; 
a qlincirical afiode, ccaxid wiih and supported within 
?h3 interior of said anode; and 
screen 2nd accelerator electrodes supported from one 
20 end of said casing. 
19. A device, as set forth in claiin 7, wherein said 
Wliai is claimed is: 
1. In ;IT? icn cngine, of the electron bombardment type 
h;:ving i:n accelerator electrode, the improvement com- 
, for said ion engine that is a permanent 
30 magnetizing the center of said casing to the point where 
slightly demagnetizing the end of said casing adjacent 
PIP. A method, as set forth in claim 9, innciuding the 
35 step of slighily demagnetizing the other end of said casing, 
but a less amount than the acceferator end of said cas- 
ing. 
eferennees Cited 
UNITED STATES PATENTS 
it is properly magnetized, and then 
said accelerator electrode. 
:s set forth in claim 2, wherein said cy- 
m 1 c c ~ t  magnet casing includes a pole piece 
4 0 
ice, as set forth in claim I? wherein said outer 2,460,664 211949 Farrow _ _ _ _ _ _ _ _ _ _ _  317-157.5 
I m a g e t  casing is constructed with a magnetic 3,149,957 12/1954 Webb _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  60-202 
&creases in strength toward the end of said 3,162,398 12/1964 Clanser et ai. _ _ _ _ _ _ _ _  60-202 
3,171,081 2/1965 Garwood _______-_____ 313-7 
45 3,238,715 311966 et ai. _ _ _ _ _ _ _ _  60-203, 
3,273,336 911966 _ _ _ _ _ _ _ _ _ _ _ _ _  60-202 
a i  oukr  caqing for said ion engine that is a hollow CARLTON 13. CROULE, Prirnnry Exnnziner. 


Ion engine casing construction and method of making same Patent

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