The Missiles of Spring: 2012 Edition

Stick around any job long enough and pretty soon you’ll find a pattern of repetition or cycles will emerge.  When on active duty, it was inexorably tied to the CVW turnaround training cycle.  This year we are now on the threshold of the 3rd North Korean space launch vehicle (SLV) attempt since 2006 and the 4th overall since 1998 and my third participation in one form or another thereof (for the record, they are batting .000 with an Oh-for-3 record since 1998 – kind of like how the Red Sox and Yankees started the year, eh?).  At least this time they had the good grace not to screw with a 4-day holiday weekend.  Given this Northeast Asian 21st century meme, I thought we might take a moment and breakdown aspects of the launch and the SLV as it will provide a basis for comparison with the next in the series on the Atlas – our first ICBM and workhorse SLV from almost a half-century ago.

So – to review:

• What: Launch of a 100kg “earth resources” imaging satellite (Kwangmyongsong – or “shining star” ) into a sun-synchronus (polar) orbit at 500 km x 500 km
• How: Three stage, liquid-fueled SLV (“Unha-3”)
• From: A new launch site on the west coast of North Korea (Tongchang-ri Space Launch Center/Sohae Satellite Launch Center)
• When: sometime between 12-16 April 2012

And then of course – ‘Why?’ Ah, now there’s the rub — why indeed would a country with a large balance of its population on the brink of starvation, seem to deliberately carryout a course of action that would certainly ensure the cancellation of food-aid from the West (and US in particular) and engender another round of condemnation and possibly sanction from the UN (depending on how the Chinese and Russians vote)? Some say there is an internal, domestic dynamic at work rooted in direction from Kim Jong Il for a launch as part of a celebration of the 100th anniversary of Dear/Founding Leader and Father, Kim il Sung and KJU is in no position to delay or postpone it (and, if reports are correct, plans for yet another nuclear test too) – all this despite the “leap day” agreement as a precursor to resuming talks on the North’s nuclear weapons program.  Part of that agreement entailed acceding to “no long range missile launches of any kind” – from which there appears to be a bit of back-and-forth over who said what and a modern day “how many angels can dance on the head of a pin” argument over what constitutes “long-range missile launches” and if “peaceful” space launches fit that category.  As one writer has put it – The short version is that there is no important difference from a testing standpoint. A moratorium on missile launches that includes an exception for space launches is like a moratorium on nuclear testing that permits “peaceful nuclear explosions” — pointless. (Note: following today’s Party conference, it appears KJU has solidified his standing, gaining appointment to the new position of First Secretary of the Worker’s Party and succession to chairman of the Central Military Commission along with elevation to the Politburo – all on the eve of the internationally condemned SLV launch)

SLV – ICBM Comparison	Trajectories Comparison
Click on thumbnail to enlarge	Click on thumbnail to enlarge

If we agree with a number of open source reports, including a statement by then Secretary of Defense Robert Gates, that North Korea is indeed in the process of either building or has built and is waiting to test a road-mobile ICBM, and if, in examining the US and former Soviet space program’s extensive use of IRBM/ICBMs as space launch vehicles, then the question may be asked if the reverse is true.  Namely, can a space launch be used to test an ICBM?  The answer would be a qualified ‘yes’.  Using the SLV-ICBM Comparison and trajectories  illustrations for reference,  we note that there are a couple of distinctive differences between the two, foremost of which is that the terminal phase of flight for each is radically different; the ICBM is made to return its payload to a target on Earth, the SLV’s goal is to ensure delivery of its payload to a secure orbit.  With that in mind though, there are a number of parallels in technology and operations between the two that may be tested to validate design and operational concepts.

Propulsion: Both vehicles in this comparison use a “storable” liquid propellant (fuel + oxidizer), though the nitric acid oxidizer combination (AK27: nitric acid 73% with dinitrogen tetroxide 27%)  attributed to use in the Unha-3 is highly corrosive and limits the hold on a missile thus fueled to about 24-48 hours of “use it or lose it.” There are a myriad of other issues attendant to liquid propulsion missiles – sloshing, shifting center of gravity that requires the larger of the two tanks (containing the oxidizer) to be stacked above the fuel tank, pogo oscillation and of course, leaks.  That said, there are a number of benefits to liquid propulsion that accrue from an ability to throttle the engines, higher energy density and their engines, even with the added weight of turbo-pumps, still  provide the highest thrust-to-weight/specific impulse when compared to solids.  Additionally, if your development model is to grow from the mother SCUD, as is the case for North Korea (with one or two notable exceptions), it makes sense that the first large SLV/ICBM platform would also be liquid-based propellant; just as the US (Atlas) and Soviet (R-7) programs – though those early missiles used a LOX/Kerosene oxidizer/fuel configuration.  It should be noted though, that almost all ICBMs today are solid fuel (with the exception of the SS-18 and SS-19) owing chiefly to the long-term storage capability, level of toxicity (liquids, especially hypergolics like UDMH, and nitric acid can be extremely toxic).

Guidance:Maneuvering a missile, whether it is an ICBM or SLV, requires pretty much the same guidance package and ability to vector thrust to adjust the trajectory, optimizing either CEP or to hit a specific window for satellite placement. The rather crude system that the SCUD employed worked, in a fashion, for the SCUD as it was an SRBM and not considered a precision-strike weapon, even with a nuke.  The shorter distances involved did not amplify range error as one finds with ICBM distances (+5,000 KM).  The Unha-3 sitting on the pad today most likely has a system derived from the Musudan IRBM – itself a derivative of the former Soviet SS-N-6 Sawfly SLBM.  A successful launch of the Unha-3 and placement of the KM3 satellite on orbit would validate the (presumed) navigation and guidance package that in turn, could be transferred to a notional ICBM.

Staging: it seems simple – for so many years now we’ve watched manned and unmanned launches lift from the pad and shed stages on their way to space with little problem.  ‘Twasnt always so.  One of the major bugbears for the North Korean program has apparently been staging.  So many things can go wrong in staging — early ignition of the upper stage, failure to cleanly separate, early shutdown or asymmetric thrust in the booster, among other things, that clearly one of the mechanisms to be tested on an SLV launch, staging, has direct application to a multi-stage ICBM.  As with guidance – success here helps to validate the design for an ICBM.  A subset of this is final staging and separation of the payload, whether satellite or RV.

Payload: With the exception of the aforementioned final staging/separation of the payload from the missile, there isn’t much more to be gained in weighing an SLV payload vs an ICBM for test results – unless a re-entry body is part of the SLV shot (which, in the case of a return-to-Earth payload of film from the satellite).  Clearly, as we found out in our own RV tests early in the development of ICBMs, the dynamics present and forces acting on a body re-entering the atmosphere are much more severe than that experienced by an SRBM as it or its payload re-enters after a relatively short flight.  (BTW, Yengst’s monograph is an excellent reference if you want to learn more and I highly recommend it, especially his history on early MaRV development).

We shall see in the next day or two a couple of noteworthy events.  First – will the shot be successful (and note that one way or the other it will undoubtedly be claimed as such to the North Korean people).  More telling will be what follows in the big celebratory parade – namely, will a successful Unha-3 shot embolden the North Koreans to unveil the road-mobile ICBM that former SECDEF Gates referred to above?  Recall that last year we finally saw the Musudan (actually, what may have been training shapes of an extended range variant or Musudan ER) revealed at the parade.  Will a nuclear test follow – and if so, to what real (geo-political, vice technical) end?  One thing is for sure – the attention this has garnered has offset the chatter over a potential Israeli strike on Iranian nuclear facilities – a discussion which has suddenly, and curiously, gone comms silent on the part of the Israelis these past few weeks…

Interesting times indeed.