The Unha-3 Second Stage (Analysis)
"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...."
Note: My calculation of the tank volume O/F results in a ratio of about
chosen a different variant of the tank design.
Comparison between Unha, Simorgh and Safir upper