Yesterday, I noted that images of the debris from the Unha launch might provide insights into the design of the missile. We have such an observation already! The fuel tank appears to have four feed pipes coming out of the fuel tank.
This answers a long-standing question about whether North Korea might try to redesign the first stage of the Unha, which comprises a cluster of four Nodong engines, to reduce its weight. North Korea might have, for example, designed a single turbo pump to service all four engines. Geoff Forden has written before on this blog about the weight savings (about 100 kilograms) from such a redesign:
As can be imagined, a missile’s engines constitute a major portion of the “dead” weight contribution outside of the payload. Engine weights have, therefore, been a major area of research with much work going into reducing the weight per ton of thrust.
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Finally, a cluster of four Nodong engines—such as has been reportedly used in the first stage of the Tae’podong II—saves well over 100 kg in weight if it uses a single turbopump developed and optimized for that configuration. Is that enough to justify a proliferator developing a new turbopump? Perhaps we will only know for certain when we start seeing images of that stage appear in public.
Well, now we know! Four feeds would imply four turbopumps, one for each engine. The answer, at least for North Korea, appears to be “no.”