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The Unha-3 Second Stage (Analysis)
Source:
Explaining_the_Musudan_Schiller_Schmucker_v1.2.pdf
"In April 2012, North Korea launched a rocket
designated Unha-3, with the first and second stage apparently the same as
Unha-2. High resolution photos of the second stage now allow a detailed
analysis."
"The Unha-3 second stage..........shows an area with several rivet joints
in the lower half of the stage. This is a clear sign for an empty space
between the oxidizer tank and the fuel tank, meaning that there is no common
bulkhead. The rivets indicate the use of internal stringers to stiffen this
part of the structure. This is further underlined by a retro rocket that
is mounted at this position. The different sizes of the tanks and the color
scheme of the filling or draining valves (typical Soviet color code: red
for oxidizer, yellow for fuel), as well as the Korean markings/abbreviations
at these valves all indicate that the upper tank is the oxidizer tank, and
the lower tank is the fuel tank."
"The tank dimensions are clearly visible. Assuming standard domes for these
tanks that extend beyond the visible cylindrical parts ......, the propellant
volumes are easily calculated with close to
6.2 m³ for the upper tank and around 3.8 m³ for the lower tank."
"...the effective propellant volumes are estimated with around 6 m³ and
3.5 m³. The resulting effective volume ratio is 1.7 – a number that is far
from the typical value of around 1.4 for the NTO/UDMH propellant combination
...... However, values around 1.7 are typical for the IRFNA/kerosene combination...."
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