Electron bombardment ion rocket engine with improved propellant introduction syste

Kaufman, H. R.

Reader, P. D.

English

NASA Technical Reports Server

= * a .  
LECTROSTAPIC ION ROCKET ENGINE -%%--%\ 
=. Piled Jan. 18, 1965 \ 
s 
https://ntrs.nasa.gov/search.jsp?R=19710006186 2020-03-17T02:39:10+00:00Z
g the reverse feed feature 
FIG. 3 is an enlarged sectional view of an alternate 
embodiment of the invention having a cross fecd feature; 
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. 
This invention is concerned with electrostatic ion rocket 
engines and, more particularly, with an electron bom- 
bardment ion rocket engine having an improved propel- 
lant introduction system. 
An electron bombardment ion rocket engine of the type 
shown in Patent NO. 3,156,090, has a through-feed pro- 
pellant supply system wherein a vaporized propellant is 
fed to a flow distributor prior to entering an ion chamber 
where it is ionized by high velocity electrons emitted by 
a cathode. The ionized propellant is accelerated by a 
positive screen and negative accelerator grid located at 
the downstream end of the engine. It has been found 
that a major portion of the total ion beam of such an 
electron bombardment ion rocket engine is located in a 
central area near the axis of the engine because of the 
position of the cathode and the resulting radial distribu- 
tion of high velocity ionizing electrons. This causes non- 
uniform erosion of the accelerator grid which decreases 
the useful life of the engine. 
This non-uniform erosion problem has been solved by 
the present invention without relying on a plurality of 
cathodes whose use is mechanically and electrically com- 
plex. In the electrostatic ion rocket engine constructed 
in accordance with this invention, propellant vapor is in- 
troduced into the ion chamber about its periphery ad- 
jacent the accelerator system which results in lower dis- 
charge power losses and produces a uniform ion-current 
profile across the grids which increases the useful life 
of the engine. ahis uniform current profile enables the 
current density as well as the thrust density to increase 
significantly for a given accelerator lifetime. This is 
achieved by matching the propellant distribution and the 
ionizing electron distribution to more closely approxi- 
mate a uniform ion production rate a t  the plane of the 
accelerator system. 
It is, therefore, an object of the present invention to 
provide an electrostatic ion rocket engine having an im- 
proved propellant introduction system for feeding an 
ionizable propellant into the ion chamber. 
Another object of the invention is to provide an im- 
proved electron bombardment ion rocket engine wherein 
the propellant distribution is matched with the ionizing 
electron distribution for a more uniform ion production 
rate adjacent the accelerator system. 
A further object of the invention is to provide an elec- 
trostatic ion rocket engine in which the propellant is 
introduced into the ion chamber about the periphery of 
the accelerator system to produce a uniform ion current 
profile across the grid. 
Other objects of the invention will be apparent from 
the following detailed description taken with the draw- 
ings in which like numerals are used throughout to iden- 
tify like parts. 
In the drawings: 
FIG. 1 is an axial quarter section of an electron bom- 
bardment ion engine shown in perspective utilizing an 
improved propellant introduction system constructed in 
accordance with the invention: 
FIG. 2 is an enlarged sectional view taken along the 
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20 
25 
30 
35 
40 
45 
BO 
85 
GO 
(hi 
TO 
FIG. 4 is an enlarged sectional view of another alter- 
nate embodiment of the invention having an angle feed 
feature. 
Referring now to the drawings there is shown in FIG. 1 
an improved electron bombardment ion rocket engine 10 
constructed in accordance with the present invention. 
This rocket engine includes a cylindrical casing 12 that 
is closed at the forward end by a centrally apertured end 
plate 14. An accelerator system 16, whose operation will 
be described later in greater detail, is niounted at the 
opposite end of the casing 12. 
A propellant supply conduit 18 is located at the for- 
ward end of the rocket 1 and forms a source of ionizable 
propellant. One end of the conduit 18 is in conimunica- 
tion with the interior of the casing 12 through the central 
aperture in the end plate 14 while the opposite end is 
connected to a container of propellant (now shown), 
such as mercury. The propellant container may be a 
steam jacketed boiler of the type shown in Patent No. 
3,156,090 having a calibrated orifice at the entrance to 
the supply conduit 18. 
A tubular anode 28 is mounted in the casing Pt and 
forms the peripheral wall of a chamber 22 for contain- 
from the source 18. 
ch as a tantalum or 
center of the cham- 
y a pair of electrically conducting support arms 
8 which are maintained out of electrical contact 
anode 2B by insulators 30 and 32, respectively. 
Those portions of the arms 25 and 28 within the chamber 
22 between the cathode 24 and the insulators 30 and 32 
are generally normal to the axis of the ion rocket engine 
18. The arms 26 and 28 are curved at the insulators 
30 and 32, and the sections outside the chamber 22 ex- 
tend toward the front of the engine 80 in an annular pa.s- 
sage 34 formed by the space between the anode ZQ and 
the casing 12. The forward end of the nrm 26 extends 
through an insulator 316 in the end plate 14 while the 
extends through a similar insulator, and 
nd 28 are connected to suitable power sup- 
own in Patent No. 3,156,090. 
The particle densities of the plasma in the chanihcr 22 
are sufficiently small that the incan free path for ioniza- 
tion is quite long therchy necessitating the cont:iinment 
of the high velocily ionizing elcctrons within this ch:im- 
ber. An axial magnclic ficliJ is ulili;.c.tl to lcnglhcn the 
path of the high vclocily elcdron.; th:it :trc cniittctl froin 
the cathode 24 to incr.c:isc the proh;ihility of clcctron- 
propcllant collisions, This magnetic field is proviilcd by 
an electromagnet 38 which surrounds the ca.;ing 12. If 
desired, a plurality of permanent magnets OF the type 
shown in application Serial No. 312,269, now U.S. Patent 
No. 3,238,715, may be utilized instead of the electro- 
magnet 38. 
The accelerating system I6 includcs a grid 4Q in the 
form of an apertured plate which is positioned at the 
downstream or exhaust end of the chainbcr 22 to accel- 
in the p lwna  that move to this end 
0. The grid 40 is sccurcd to and is in 
electrical contact with an annulus plate 42. A screen 41 
containing a plurality of apcrtures is positioncd between 
the chamber 22 and the grid 40. The apcrtures in the 
screen 44 are aligned with the apertures in the grid 40 
is spaced from the bcreen 44 by sapphire 
insulating balls 46 carried by brackets 48 niountcd on 
mpingemcnt of the ions on the grid. 
5,262,262 
insulating balls 56) and osed with respect to the 
casing 112. The grid extends into the annular 
matched-drilled mol passage 34 to direct the ant through a peripheral 
structure of the engine slot in the anode 20 along paths that are angularly dis- 
I@ is fabricated of nonmagnetic stainless steel with the 6 posed with respect to both longitudinal axis of the 
chamber 22 and the screen 4 
While several embodiment the improved propellant 
introduction system have been described, it is apparent 
that various structural modifications may be made to 
10 these systems without departing from the spirit of the 
invention or the scope of the subjoined claims. tially equal to that of a cathode 2% while the grid 40 
has a relatively high negative potential relative to the 
screen. The thrust producing mechanism of the engine 
I@ is the momentumchange of the ions as they are a&el- 
erated by the electrostatic field which is applied between 15 
nvention, propellant from 
the source I8 is introduced into the chamber 22 adjacent 
the screen 42 to provide a uniform current profile across 
10. This is achieved by matching the propellant distribu- 
tion and the ionizing electron distribution to more closely 
approximate a uniform ion production rate at the plane 
of the accelerator system 86 which results in a relatively 
uniform erosion of the grid 40. 
In the embodiment shown in FIGS. 1 and 2 having a 
reverse feed feature propellant from the source IS  enters 
the casing 12 through the end plate 14 and passes around 
a circular plate 54 mounted on the forward end of the 
which increases the useful life of the engine 20 
25 
. Thereupon the gaseous propellant passes 30 
0. Rearward flow of 
3% is limited by an 
the rear end of the 35 
As the propellant 
r 22 through a slot 
formed between the rear end of the anode 20 and the 
lip 56, it contacts a tubular member 58 in the form 
of a cylindrical wall mounted at the rear of the anode 20 *O 
on the inner edge of the lip 56. The tubular member 58 
has an outside diameter smaller than the inside diameter 
of the tubular anode 2Q and this cylindrical wall extends 
into the anode to direct the propellant away from the 
screen 42 toward an impervious wall 60 which forms 45 
the forward end of the chamber 22 as shown in FIG. 1. 
The periphery of the wall 60 is insulated from the 
anode 30. The wall 60 is mounted on a plurality of 
electrically conducting rods 62 which extend through 
insulators 44 and 66 in the circular plate 54 and the 50 
end plate 14 respectively. The rods 62 are connected 
to a suitable electrical power source, and the wall 60 
o the same potential as the cathode 24 and 
Axial movement of the wall 60 to alter the 
the chamber 22 is ac 
0 in the insulators 64 
may be utilized to pcrfo 
urn location for a particular engine 
feed feature, a plurality of annular plates 68 are mounted 
in the annular passage 34 adjacent the screen 44. The 
plates 68 are spaced from one another and are parallel 
to the screen 44 with their flat faces extending perpen- 
dicular to the longitudinal axis of the engine BO to direct 65 
the propellant into the chamber 22 through openings in 
the anode 20 along paths perpendicular to the axis. The 
outside diameter of each plate 68 is greater than that of 
the adjacent upstream plate and smaller than that of the 
adjacent downstream plate while the inside diameters 70 
of the plates 68 are the same as the inside diameter of 
In the embodiment shown in FIG. 4 having an angle- 
feed feature, an outwardly directed flange 70 is provided 
on the rear end of the anode 20 adjacent the screen 44. 75 
fn  the embodiment shown in FIG. 3 having a cross- 60 
We claim: 
I. An electrostatic ion rocket engine comlprising 
a source of ionizable propellant, 
a chamber for containing said propellant, 
an anode, 
a thermionic emitting cathode wilthin said chamber 
having a negative potential relative to said anode for 
bombarding said propellant with high velocity elec- 
trons to form ions, 
a screen adjacent said chamber having a voltage poten- 
tial substantially equal to that of said cathode, 
an apertured grid spaced from said screen away from 
said chamber and having a relatively high negative 
potential relative to said screen to accelerate said ions 
away from said engine, said screen being in substan- 
tial alignment with said grid for shielding the same 
from the ions to reduce erosion, 
magnetic means positioned around said casing to form 
a magnetic field about said propellant and said 
cathode whereby the paths of said high velocity 
electrons are lengthened to increase the rate of 
collision of said electrons with particles of said 
propellant, and 
means for introducing said propellant from said source 
into said chamber adjacent said screen whereby said 
erosion is relatively uniform across said grid. 
2. An electrostatic ion rocket engine comprising 
an anode forming a peripheral wall of a chamber for 
containing an ionizable propellant, 
a thermionic emitting cathode within said chamber 
having a negative potential relative to said anode for 
bombarding @aid propellant With high velocity elec- 
trons to form ions, 
a screen at one end of said chamber having a voltage 
potential substantially equal to that af said cathode, 
an apertured grid spaced from said screen away from 
said chamber and having a relatively high negative 
potential relative to said screen to accelerate said 
ions away from said engine, said screen being in  
substantial alignment with said grid for shieldink 
the same from said ions to reduce erosion, and 
means for introducing said propellant into said chamber 
adjacent said one end thereof to  provide a uniform 
current profile across said grid. 
3. An electrostatic ion rocket engine comprising 
a casing, 
a tubular anode within said casing forming a peripheral 
wall of a chamber for containing an ionizable propel- 
lant, 
a thermionic emitting cathode wtihin said anode for 
bombarding said propellant with high velocity elec- 
trons to form ions, 
a screen at one end of said chamber having a voltage 
potential substantially equal to said cathode, 
an apertured grid having a relatively high negative 
potential relative to said cathode positioned on the 
opposite side of said screen from said anode and 
spaced therefrom {to accelerate said ions away from 
said engine, said screen being in substantial align- 
ment with said grid for shielding the same from said 
ions to reduce erosion, and 
means for introducing said propellant into said chamber 
at said one end thereof about the periphery of said 
anode to provide a uniform current proNe across said 
screen and grid so that said erosion is relatively 
uniform across said grid. 
4. An electrostatic ion rocket engine as claimed in 
claim 3, wherein 
the tubular anode is spaced from the inner wall of the 
casing, 
a source of ionizable propellant in communication with 
the space between said anode and said w i n g ,  said 
space being in communication with said chamber 
at the one end thereof adjacent the screen. 
5. An electrostatic ion rocket engine as claimed in 
a plurality of annular plates mounted in the casing at 
the end thereaf adjacent the screen, said plates being 
spaced from one another with their flat faces extend- 
ing substantially perpendicular to the longitudinal 
axis of said chamber and parallel to the screen for 
directing the propellant into said chamber along paths 
generally perpendicular to said axis. 
6. An electrostatic ion rocket engine as claimed in 
a tubular member having a diameter smal,ler than that 
of the tubular anode mounted at lthe end thereof 
adjacent the screen, said tubular member extending 
into said tubullar anode and being spaced inwardly 
therefrom to direct the propellant along the inner 
surface of the tubular anode away from said screen. 
7. An electrostatic ion rocket engine as claimed in 
an outwardly directed flange on the end of the tubular 
anode adjacent the screen, said flange being angularly 
cltaim 4, including 
claim 4, including 
claim 4, including 
disposed with respect to said tubular anode and add 
screen for directing the propellant along paths that 
are angularly disposed with respect CS the, longitudinai 
axis of ,the chamber. 
. An eleotrostatic ion rocket engine comprising 
chamber for containing an ionizable propellant, 
means ifor introducing said propellant into said chamber 
about .the periphery thereof adjacent one end, 
means within said chamber for bombarding said propel- 
lant with high velocity electrons to form ions, 
means positioned at said one end of said chamber 
adjacent said propellant supply means to accelerate 
said ions away from said engine. 
. In an electrostatic ion rocket engine of the type 
ing a chamber for containing an ionizable propellant 
and a grid for accelerating ions away from the engine, 
the improvement comprising 
an impervious wall at one end of the chamber remote 
from the grid, and 
means for introducing $the ionizable ,propellant into the 
chamber about the priphery thereof a t  the end 
opposite said wall. 
10 
20 
UNITED STATES PATENTS 
3,075,115 '1/1963 em et al. _ _ _ _ _ _ _ _  3 1 3 4 3  
3,156,090 11/1964 man _ _ _ _ _ _ _ _ _ _ _  60-35.5 
25 
30 
E, Assistant Examiner. 


Electrostatic ion rocket engine Patent

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