Spherical solid propellant rocket engine desig

Styles, C. M.

Swain, R. L.

Thibodaux, J. G., Jr.

English

NASA Technical Reports Server

t. J. Ah 
SPHERICAL SOLID-PROPELLANT ROCKFP MOTOR 
3 Sheets-Sheet I 
https://ntrs.nasa.gov/search.jsp?R=19700024020 2020-03-17T01:33:43+00:00Z
J. G. P 
SPHERICAL SOLID-PROPELLANT ROCKET MOTOR 
Filed March 4, 1958 3 Sheets-Sheet 3 
ATTORNEYS W 
,.... 
the charge in place and showing a part of the igniter; 
6. 7 is a curve showing the performance in thrust 
chamber pressure for a tested rocket; and 
FIG. 8 is 8 detail sectional view of a casing formed 
Refemng to FIG. 1 there is shown a rocket 10 incor- 
porating the invention, this rocket including a spherical 
11 and a nozzle 12 connected to  the shell. The shell 
preferably formed in hemispheres 13 and 14 of 
inch S A E  4130 steel, the diametric openings hav- 
The invention described herein may be manufactured an inner flange 17 and 18 projecting over and welded to  
a~(i u s d  by or for the Government of the United States the half-shell edges. Spaced a b e d  holes are drilled 
of America for governmental purposes without the pay- through the sides of the bands 15, 16, the holes in band 
ment of any royalties thereon or therefor. 15 15 being threaded to  receive cap screws 19, whereby the 
This invention relates to solid propellant rockets with bands and hence the shell halves are held firmly together 
particular applicability to  rockets of spherical shape. to form a spherical unit. 
Solid propellant rockets have been devised for propelling The trailing shell half 14 is formed with an exit open- 
brllistic missiles, earth satellites and space craft but these hg 22 for the outlet nozzle, the opening edge being rein- 
rockets have generally taken the form of cylinders, which, 20 forced by an annular plate 23 overlying the shell edge 
it: comparison with spherical motors of comparable and attached thereto, as by welding, and centrally ter- 
thrust, burning time and operating pressure, are heavier, minating in an internally threaded cylindrical coupler 24. 
have lower loading densities, lower impulse to weight Screw threaded t o  this coupler is a cylindrical tube 25, 
ratios and are more difflcult to stabilize inertially by rota- the inner end Of which is externally threaded to engage 
tion about their axes. 25 the coupler 24, an annular flange 26 on the tube 25 form- 
The general object of the invention therefore is to ing a terminating abutment to  screw movement. Integral 
produce a rocket which is lighter than a cylindrical with and in extension of the exit end of tube 25 is a 
rocket of comparable operating characteristics and 'ballis- tubular flared section 27, which with the tube 25 forms 
tic performance and, at the same time, has higher loading the exit nozzle 12. TO complete the nozzle structure, the 
dencities, higher impulse to weight ratios, higher vacuum 30 inner surface Of tube 25 is provided with a graphite insert 
velocities for a given payload, and greater ease in achiev- 28, the thickness of which varies so as t o  continue the 
ing inertial stabilization. An important object also is to taper Of ~ O z Z l e  Section 27 to a point short of the inner 
provide a rocket container in which solid propellant end of tube 25, at which point the thickness diminishes 
masses may be inserted of intricate form and substantial in a sharp Curve to  the inner tube end. By use of this 
burning areas without disassembly or disturbance of the 35 insert, the appropriate throat area of the nozzle for most 
container. Still another object is to provide structure in effective action i s  determined. 
a rocket shell for forming the propellant charge and sub- The propellant or charge for the rocket is a solid which 
sequently remove the forming structure without container iS contoured for effective burning action. While any solid 
or propellant disturbance. An object also is to provide Propellant meeting rocket requirements may be used, 
means for removing support structure film from the 40 tests were carried on  with polysulfideperchlorate (Thio- 
charge surfaces without opening the rocket container. kol T-211, as this propellant is easy to mix and cast, 
Other objects include means for providing radially burn- good Performance, is within the specified burning 
ing charge surfaces in a spherical rocket container, for time Over the entire operating-pressure range, and has a 
providing a spherical rocket in which the contained low Pressure exponent n. To place this charge in the 
charge is self-supported, and for providing a spherical 45 shell and at the same t h e  form the charge so as to obtain 
rocket in which the charge contours are such as to the desired burning surfaces, use is made of a mandrel 
minimize resonance. which may be inserted securely inside the shell and be 
Other objects and many of the attendant advantages subsequently removed by fusion after the charge has 
of this invention will be readily appreciated as the Same been pumped into the cell chamber and cured. While any 
becomes better understood by reference to the following ' O  desired shape of mandrel may be used, the form shown 
c;-tailrd description when considered in connection with in FIG. 2 has been found adequate for the desired pur- 
the accompanying drawings wherein: pose. This mandrel 30 is cast of an eutectic alloy of bis- 
I-IG. 1 i s  a side view of the rocket with parts broken muth, lead, tin and cadmium (known as Cerrobend) 
:*way to show the internal shell and nozzle structure; which may be in the proportions of bismuth 50.00, lead 
FIG. 2 is a side view of the mandrel which is insertable 55 26.70, tin 13.30, and cadmium 10.00, the alloy having 
m i d e  the rocket shell for forming the propellant charge; a melting point of 158.0" F. As indicated in FIGS. 2 
and 3, the mandrel 30 consists of a group of flat semi- 3 is a section of the mandrel taken along lines circular disks or plates edged by perimeter strips 32, 
these disks being cast in one piece about a common core 
forwrd half of the shell removed showing the mandrel in and the threaded terminal shank 35. The mandrel 30 
is inserted in the rear shell hemisphere 14 of the rocket, 
FIG. 5 is a perspective view of the rear half of the as shown on FIG 4, with the cylinder 34 lying in the 
, the nozzle tube 25-26 having been 
FIG. 6 is a perspective view of the completed rocket 65 removed. A centering device 36 (FIG. 5) is now placed 
.Yo 
5 of glass fibres. 
United States of A r n e ~ c ~  as repre- 
swted hy the Administrator of the National Aero- 
nantirs 2nd Space Administration 
Piled Mar. 4, 1958, Ser. No. 719,173 
2 Claims. (C1. 60-35.6) 10 
(6ranted under Title 35, u.9. code (19521, set' 266) ing bands 15 and 16, each band having 
3-43 of FIG. 2; 
FIG* 4 is a perspective View of the rockc% with the 60 33. The core is extended at one end to form cylinder 34 
piacc; 
rocket shell; 
I 
3,001,363 
10 Sphericd racket motor 
over coupler 24 and secured thereto by any appropriate 
means, this device being shaped as a cap with a central 
hole 37 for reception of the mandrel shank 35 and a ring 
of holes 38 through the plate surface between the center 
hole 37 and the cap edge, the number of these holes, and 
their position, corresponding to the position of the spaces 
between mandrel plate sections abo 
The cap structure is provided with 
for holding the mandrel and mandre 
The leading shell section 13 of the sphere is now at- 
tached to thc other section 14 by means of cap screws 19. 
The propellant, in an uncured liquid state, is forced into 
the shell through end cap openings 38 and cured in an 
oven for 4 days at a temperature of from 140" P. to 
150" F.  After cure is completed, the shell is inverted 
with the cap opening 38 down and the oven temperature 
raised to a value of from 160" F. to 165" F., thus melting 
the mandrel, the molten fluid escaping through cap open- 
ings 37 and 38 and leaving the solid propellant in its 
molded form. FIG. 6 illustrates the mold formation, 
this figure shouing the radial cavities 40 which conform to 
the shape of disks 31 aild perimeter strips 32 of mandrel 
30 and thus have the shape of a plurality of radially ex- 
tending disks cach having a periphery defined by a sub- 
stantially semicircular arcuate edge extending inwardly 
to open into the central cavity 41. The arcuate edges of 
disk-shaped portions 40 are of greater thickness at and 
adjacent to such edge than the portion thereof between 
such edge and central cavity portion 41 and the propellant 
sections 42 are thus distributed around the spherical cham- 
ber of the casing. This figure shows also the solid layer 
of propellant adjacent the shell interior, and it is apparent 
that this layer serves as a heat protection for the shell 
metal, direct heating of the shell occurring only approach- 
ing the end of the burning operation. This fact permits 
a thin shell metal to be used, the actual thickness as used 
varying from 1/16 inch to w 5  inch. 
Aftcr the main body of the mandrel alloy has been re- 
moved there remains a thin film of alloy, coating the 
propellant surface, It is important that this film be re- 
moved as otherwise it is impossible to ignite the propellant 
successfully. It was found that the film can be completely 
dissolved by mercury; and, hence, by filling the charge 
cavity with this substance the film is removed leaving a 
clean readily ignitable propellant surface. After film re- 
moval the centering cap is removed, an igniter 50 applied 
and the nozzle 12 inserted. The igniter is fabricated from 
thin gauze strips which are impregnated with a mixture 
of magnesium powder, potassium perchlorate, Vistanex 
and toluene. 'The impregnated gauze strips are inserted 
into the T-flares 43 (FIG. 6) along the outer perimeter 
of each segment. Two match squibs, connected by a 4 
inch long, VI inch diameter cellophane tube filled with 
3 grains of FFFG black powder, are used to ignite thM 
gauze strips. A inch thick plastic blowout disk 5 
is cemented in the nozzle throat to  build up operating 
pressure quickly. 
The procedure used in making and using the rocket may 
be apparent from the above description, but a brief re- 
view c f  this piocedure is considered desirable. The man- 
drel is first formed so as to insure the desired burning 
areas on the propellant as inserted in the rocket chamber. 
The mandrel. which is of an alloy fusible a t  a tempera- 
ture below that affecting the propellant, is then mounted 
in the r x r  half of the rocket cavity, the front half of the 
cavity i5 then scaled to the rear half to form a spherical 
unit, and propcllant in liquid form forced into the cavity 
and cured. Affcr curing. the propellant has solidified and 
on heating thc charged shell to the temperature of alloy 
fusion but helo:v the temperature of propellant disintegra- 
tion, the mandrel substance is removed through the shell 
openings. The igniter materials are then inserted, and 
the rocket nozzle attached in the exit opening formed in 
the rear shell hemisphere. 
The described construction lends itself to effective Op- 
Approxi- 
mate pro- Total Charge Propellant 
pellant impulse, weight, impulse 
tempers- 1b.sec. lb. lb.-sec./d. 
we, O F. 
eration. FIG. 7 shows the thrust obtainable for varying 
values of chamber pressures for a 10 inch spherical rocket 
motor and Table I below gives firing test data for three 
separate charges 1,2, and 3. 
TABLE I 
Firing test data: 
I I 
Taking test 1, for example, an average thrust of 1350 
pounds for a duration of 4 seconds was obtained. Addi- 
tionally, it is noted that the spherical one-unit shell form 
20 permits a charge with a volumetric loading factor of 95 
percent or over and a variation from a mean value of 
burning surface of less than 210 percent. Also, by ad- 
herence to the spherical form, an incremental velocity 
greater than 24,000 feet per second can be obtained at alti- 
26 tudes above 150,000 feet. In addition, the removable 
mandrel permits a three-dimensional, radial-burning me- 
piece propellant charge, the charge having an internal 
surface area greater than that of the interior surface of the 
shell. It is pointed out, also, that the radial charge forma- 
30 tion resembles internal bafiles and acts to suppress res- 
onance. The described structure lends itself to multiple 
propellants to give two step control, for example; or a uni- 
form thrust with a large surface charge may be used. In 
addition, progressive or regressive charges may be em- 
86 ployed: spheres within spheres of charge may be used; and 
off-center charge cores may be utilized to control surface 
area as a function of time. An additional use of the 
described spherical structure is an i d o w  turbine during 
burning, if the rocket is spun up to an initial rotational 
40 velocity. While a solid metal shell is described for the 
rocket, it is important to note that moditied structures may 
be used, such, as a shell 60 formed of wrapped Fiberglas 
filaments 61 with a plastic binder 62, such as acrylic 
resin, as indicated in FIG. 8. 
Obviously many modifications and variations of the 
present invention are possible in the light of the above 
teachings. It is therefore to be understood that within 
the scope of the appended claims the invention may be 
practiced otherwise than as specifically described. 
1. A solid propellant rocket motor comprising a pair of 
hemispheroidal casings rigidly secured together to brrn 
a substantially spherical casing, an aperture formed in 
one of said hemispheroidal casings, an internally threaded 
65 cylindrical annular plate secured to said one of said 
hemispheroidal casings adjacent to  and surrounding said 
aperture, a nozzle for said motor comprising an external- 
ly threaded frusto-conical body having an axis and being 
in threaded engagement with said annular plate, an an- 
50 nular graphite insert of predetermined cross-sectional area 
mounted internally of said frusto-conical body; and a 
solid propellant filling said substantially spherical casing, 
said solid propellant forming a continuous layer of pro- 
pellant adjacent the interior surface of said substantially 
(35 spherical casing and having a cavity therein, said cavity 
having the shape of a central portion having an axis which 
is collinear with a diameter of said substantially spherical 
casing and coaxial with said nozzle axis, and further !?av- 
ing the shape of a plurality of semi-circular disks extend- 
70 ing radially outwardly from said central portion, each of 
said disk-shaped portions having an outer periphery de- 
fined by a substantially semi-circular arcuate edge and 
extending inwardly to open into said central cavity por- 
tion, and each of said disk-shaped portions being of greater 
thickness at and adjacent to said arcuate semi-circular 
45 
$0 What is claimed is: 
1 
9,061,868 . 
edge thereof than at the n thereof between said 2,603,061 Avery ___- .-7-v----- July 15, 1952 
arcuate semi-circular edge and said central portion. 2,709,890 Goddard ______________  June 7, 1955 
2. The rocket motor as set forth in claim 1, and includ- 2,771,212 Effinger --___-_------ Nov. 20, 1956 
ing an igniter disposed in said thick m u a t e  semi-circular 2,816,721 Taylor __________-____- Dec. 17, 1957 
edge portions of said cavity. 5 2,849,860 Lowe _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  Sept. 5 1958 
2,900,168 Nyborg _ _ _ _ _ _ _ _ _ _ _ _ _ _  Aug. 18, 1959 
e ~ ~ ~ e n c e ~  Clted in the file of this patent 2,902,822 McKiernan _ _ _ _ _ _ _ _ _ _ _ _  Sept. 8, 1959 
UNITED STATES PATENTS 2,920,443 Higginaon _ _ _ _ _ _ _ _ _ _ _ _ _  Jan. 16, 1960 
A Quasi-Morphological Approach to the Geometry of 
charges for Solid Propellant Rockets: The Family Tree 
of Charge Designs, by J. M. Vogel, published February 
1956, in Jet Propulsion, pp. 102 to 105, vol. 26, No. 2. 
2,395,406 Ooddard ____ __________ Feb. 26, 194 OTHER REFERENCES 
2,435,610 
2,448,658 
2,500,334 
2,555,080 
Schneider __-__________ Feb. 10, 1948 lo 
Carey -----..- __- - ---.. Sept. 7, 1948 
Zucrow --_---_-_-_..-- Mar. 14, 1950 
aoddard -_---__----I -- May 29, 1951 


Spherical solid-propellant rocket motor Patent

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