DEVELOPMENTAL TESTING OF A CANDIDATE SECOND-STAGE MOTOR FOR THE SS-N-20 SLBM FOLLOW-ON

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP91T01115R000100100002-2
• Release Decision: RIPPUB
• Original Classification: T
• Document Page Count: 11
• Document Creation Date: December 28, 2016
• Document Release Date: November 23, 2010
• Sequence Number: 2
• Publication Date: March 1, 1984
• Content Type: REPORT

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Directorate of Top Secret
Developmental Testing of a
Candidate Second-Stage
Motor for the SS-N-20
SLBM Follow-On (s)
Top Secret
lI RA_/Mt/IY
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or Methods Involved
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Abbreviations
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NOCONTRACT (NC)
PROPIN (PR)
ORCON (OC)
REL...
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Directorate of Top Secret
Developmental Testing of a
Candidate Second-Stage
Motor for the SS-N-20
SLBM Follow-On (s)
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Developmental Testing of a
Candidate Second-Stage Motor
for the SS-N-20 SLBM Follow-On (s)
Summary
Ton Secret
Preparations for developmental testing of a candidate second-stage motor
for the SS-N-20 follow-on SLBM were observed at the Pavlograd Motor
Development Corn lex in September 1983. The motor involved in this test
has the same diameter as the original SS-N-20 second stage, but
The development of larger motors for the SS-
N-20 follow-on would allow the Soviets to deliver more or heavier reentry
vehicles to the SS-N-20's present range, to increase the SS-N-20's present
range, or some combination of these possibilities. Special intelligence
indicates, and analysis of satellite imagery substantiates, that land-based
testing of the new missile will begin in late 1985 and that it may reach ini-
tial operating capability in Typhoon-class submarine launchers about 1988.
This information is Top Secret
Top Secret
LA 84-1003 f
March 1984
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Too Secret
Developmental Testing of a
Candidate Second-Stage Motor
for the SS-N-20 SLBM Follow-On (s)
The SS-N-20 SLBM/Typhoon SSBN weapon system
consists of the SS-N-20 submarine-launched ballistic
missile (SLBM) and its 20 launchers on the Typhoon-
class nuclear-powered ballistic missile submarine
(SSBN). The MIRVed SS-N-20 has an estimated
maximum booster range of about 9,000 kilometers. It
is about meters lone and has three solid- ro ellant
stages
space, about 4 meters, is occupied
postboost vehicle, reentry vehicles,
package. (Ts
The remaining
by the third stage,
and guidance
Special intelligence has indicated since early 1980
that the Soviets were planning a follow-on to the
SS-N-20 SLBM that would be deployed on the
Typhoon-class SSBN. Special intelligence further in-
dicates that land-based testing was to begin in late
1985 and sea-based testing a year later and that the
system would reach initial operational capability in
1988. This information also indicates that changes to
all three missile stages were being considered. One
specific proposal was to increase the length of one of
the motors, possibly the second-stage motor, by 0.234
meter. The development of larger motors for the
SS-N-20 follow-on would allow the Soviets to deliver
more or heavier reentry vehicles to the SS-N-20's
present range, to increase the SS-N-20's present
ranee, or some combination of these possibilities. (Tr
This study analyzes the motor at the test facility as a
candidate second-stage motor for the SS-N-20 follow-
on SLBM. It also discusses the test preparations being
made, the type of test they suggest, and the reasons
such a test may be required. (Ts
test preparations were observed
at the test facility of the Pavlograd Motor Develop-
ment Complex (figure 1). A motor at the facility's
(The nozzle throat dimension could not be
accurately measured.) A diffuser (a device used to
simulate the environment at altitudes above sea level)
consisting of four 5-meter-long segments, with water-
coolant lines attached, was in position behind the
motor. The assessed thrust capacity for this diffuser is
about 1,250 kilonewtons,' providing it with the capa-
bility to test the maximum thrust expected to be
produced by this large second-stage motor (appendix).
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The otor observed in September had the same' 7F. X1
diameter as the original SS-N-20 SLBM sec- 25X1
and-stage motor
original motor
when it was observed being prepared for production-
related testing at the Biysk Solid Motor Complex
(figure 2). This increase in length and the motor'
' A newton is defined as the standard meter-kilogram-second unit of
force, equal to the force that produces an acceleration of 1 meter
per second per second on a mass of 1 kilogram. (u)
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observation
Special intelligence and imagery have indicated that
the Utkin design bureau and its associated test facili-
ties in Pavlograd were involved in developing the
SS-N-20 propulsion system. In late 1978, approxi-
mately 26 months prior SS-N-20 land-
based test, two motors were ob-
served at the test facility in Pavlograd. Their lengths
suggested they were related to the development of the
SS-N-20 first-stage motor. Developmental testing of
motors for the SS-N-20 follow-on SLBM at Pavlo-
grad and the timing of these tests are therefore
consistent with previously observed practices. The
timing of the recent test preparations suggests that
this new missile is on a schedule that will lead to flight
testing beginning in late 1985 and deployment about
1988 in accordance with the Soviet proposal. (TsF-
Construction to support simulated altitude testing of
large motors at Pavlograd began in July 1980, proba-
bly as part of an effort observed at other Soviet solid-
propellant facilities to improve the effectiveness of
their static test programs. An assembly and control
building, rail lines (required for the movement of
diffuser segments), and a water reservoir (required for
er to cool the diffuser segments) were
near the test stand. In August and Sep-
1, compatibility tests of the diffuser were
using four of five diffuser segments, each 5
and 3 meters in diameter.2 25X1
cility appeared to be preparing to use t25X1
a static test for the first time, although an
tal cover at the thrust block precluded
der in
the fa
conducted
tember 198
storing wat
of the motor. (s 25X1
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In the September 1983 preparations, however, the
environmental cover had been removed and the motor
was in the test stand with the water-cooled diffuser
behind it. Diffusers are used in various configurations
to simulate the environment at altitudes above sea
level for static testing of motors. Testing a motor in a
simulated-altitude environment provides data that
otherwise would be available only through flight
testing. Altitude environments, in relation to missile
stages, differ from a sea-level environment in two
primary effects: lower ambient pressure and reduced
heat transfer. These changes affect motor ignition,
chamber pressure, nozzle design, insulation, thrust
termination, and structural integrity. 025X1
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In the September test preparations, we could not
determine if the diffuser would have been attached to
the motor nozzle prior to testing. If it were not, the
Soviets could have measured motor thrust and burn
rate in the simulated-altitude environment that wc25X1
be created after the motor was ignited and began to
exhaust through the diffuser. The Soviets then could
have extrapolated their measurements to reflect the
same parameters at a given altitude. The effectiveness
of the thrust vector control systems in altitude envi-
ronments could also have been tested. (sF25X1
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Alternatively, the diffuser could have been attached
to the motor nozzle and evacuated of air prior to 125X1
test to simulate ignition at high altitude. Solid-prc2bX1
lant motors are ignited by filling the propellant cavity
with hot gas produced by an igniter. More gas is
required to ignite a motor at higher altitudes than at
sea level because of the lower ambient pressures at
z The fifth segment appears to be a spare, probably to replace the
segment closest to the nozzle during a static firing because it
probably will receive the most ablative force from the motor's
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higher altitudes. If the original second-stage igniter
(or a minor modification of it) were being used on the
second-stage motor for the SS-N-20 follow-on, an
altitude-simulation test would be required to assure
that enough gas would be produced to ignite the
additional of propellant. (Ts F
Another purpose for an attached nozzle test at Pavlo-
grad could have been to test specially configured
nozzles for use at higher altitudes. Gases escaping the
nozzle of a burning motor expand more rapidly at
high altitude than at sea level. Upper stage nozzles,
therefore, are configured with a higher area ratio to
obtain the greater efficiency in performance available
at altitude.' Simulating the altitude at which the
motor is expected to operate allows these specially
configured nozzles to be tested on the ground prior to
their use on flight test missiles. Improving nozzle
design is an option the US has pursued for several
years, resulting in specially configured nozzles being
used on the third stage of the Peacekeeper (MX)
missile. The test activity observed at Pavlograd may
be an indication that the Soviets are also attempting
to improve their nozzles. (s
' The nozzle area ratio is equal to the area of the nozzle exit divided
by the area of the nozzle's throat: Ae/At. (u)
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Top Secret
Appendix
Calculating the Thrust
Capacity of the Diffuser
The measured thrust of a motor (Tm) is the sum of the
momentum thrust and the pressure thrust:
Tm = m Ve + (Pe - Pa) Ae
where m is the propellent mass flow, Ve is the velocity
of the exiting gases, P. is the pressure at the nozzle's
exit plane, Pa is the ambient pressure, and A. is the
area of the nozzle's exit (figure 3).',Z Assuming the
diffuser is connected to the nozzle and is evacuated of
air, Pa in the formula decreases and will be represent-
ed by Pa'.' The steam thrust at the diffuser exit (TSe) is
the pressure thrust in the diffuser factored by the
ratio of specific heats (Y) relative to the Mach number
(M):
TSe = Pd Ad (1 + YMZ)
where Pd is the pressure in the diffuser and Ad is the
area of the diffuser and M is the Mach number
(figure 4). Finally, the steam thrust at the diffuser
inlet (Ts) of a vacuum test cell is the sum of the
velocity thrust (rn Ve) and the pressure thrusts relative
to the nozzle and to the test chamber:
T51=mVe+PeAe+Pa'(Ad-Ae)
where Pa' is the ambient pressure at the diffuser inlet Summarizing, we have:
if connected to the nozzle. (u)
' For more information on the origination and use of these formulas,
see Rocket Propulsion Fundamentals, L. K. Isaacson, July 1981. (u)
In measured thrust, the effect of the gravitational constant (G)
from Newton's second law of motion, F = Ma/GC , is negligible.
The formula for the calculation of measured thrust thus becomes
F = Ma. (u)
' If the diffuser is not connected to the nozzle, Pa' would more
closely approximate Pa, thereby reducing the capacity of the
diffuser. (u)
T. = tit Ve + (Pe - Pa') Ae
TSe = Pd Ad (1 + YM2)
TS, = mVe + Pe Ae + Pa' (Ad - Ae).
Rearranging for TS; produces:
Ts;=mVe+(Pe-Pa')Ae+AdPa'
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Ton Secret
and the formula for motor thrust becomes T. = TS;
- Ad Pa'. For purposes of this estimation, friction
effects on the steam thrust can be neglected, resulting
in TS; being roughly equal to TSe . Substituting
produces:
T. = Pd Ad (1 + YM2) - Ad Pa'
This quantity is only slightly less than diffuser thrust
and can be used to estimate the diffuser capacity (Tm
Td). Y can range from 1.16 to 1.34, so 1.25 will be
used; Pd for solid motors is usually about 1 atmo-
sphere, or 101.33 kilopascals' (kPa); and Pa' is as-
sumed to be no greater than 0.1 atmosphere or 10.133
kPa, the pressure at 50,000 feet. (u)
Using M = 1, a nominal value for diffuser operations,
and the 3-meter diameter diffuser (estimated 2.7-
meter inner diameter):
Td = (101.33) it (1.25)2 (1 + (1.25) (1)2) - a (1.35)2
10.133
Td = 1,247 kilonewtons (S NF REL UK CAN WN)
4 A pascal is defined as a unit of pressure or stress; 1 pascal equals 1
newton per square meter. (U)
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