# How Do MIRVed ICBM's Work? **URL:** \ **Category:** Factual Questions\ **Created:** [April 10, 2002, 2:20am UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766 "2002-04-10T02:20:32Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![tsunamisurfer](https://avatars.discourse-cdn.com/v4/letter/t/a698b9/32.png) [@tsunamisurfer](https://boards.straightdope.com/u/tsunamisurfer)\ **Post date:** [April 10, 2002, 2:20am UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766/1 "2002-04-10T02:20:32Z")
I am at a loss as to how MIRVed ICBMs/SLBMs deploy their warheads during the re-entry phase, as well as to how the guidance systems work. Regrettably, good technical information on this matter is rather difficult to come by. I understand that MIRVed re-entry vehicles use spin stabilization and gyroscopic guidance–and that said spinning is obscenely rapid–but in what manner are the individual warheads guided, once deployed? Obviously, each has its own inertial (?) guidance system, but I’m also left wondering what kind of propulsion each missile has. Obviously a gravity-based system would not work. At what approximate height are the warheads deployed? By what mechanism are they ejected? How do the warheads maintain their course when ejected from a rapidly spinning re-entry vehicle? Feel free to throw in any additional technical details. I’m sure the North Koreans won’t learn anything new. ---
**Author:** ![Tranquilis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tranquilis/32/3639_2.png) [@Tranquilis](https://boards.straightdope.com/u/Tranquilis)\ **Post date:** [April 10, 2002, 2:24pm UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766/2 "2002-04-10T14:24:23Z")
As you say, there’s little good web-based info on the behavior of ICBMS. [Here is a primer](http://www.fas.org/nuke/intro/missile/icbm.htm), at least. ICMBs use either inertial or stellar navigation, and if equiped with MIRv, the warheads will deploy during the “flight” phase (post “boost”; exo-atmospheric). Each warhead will be targeted to it’s own meeting with destiny. Once a MIRV’d ICBM is past the ‘boost’ phase, it still has a ‘bus’, which is a liquid-fueled third stage and which contains the separate warheads and the guidance package. Using inertial or stellar navigation, the Bus will position and release the individual warheads. One of the issues with ICBM warheads is that any kind of accuracy requires a high ballistic coefficient (low coefficient means cheap heatshield, slow reentry, and much drift: Perhaps as much CEP as 20,000 meters), meaning that you’ve got to have one hell of a good heatshield, and that shield can’t errode or deform at all during reentry, or the aerodynamic forces will shift the warhead in unpredicatble directions, dropping your bomb pretty much any ol’ place. Few nations have the tools, knowledge, skill, and money to achieve decent accuracy, which is why so few have proper ICBMs (much less MIRV’d ICMBs). Obviously, shorter-ranged weapons are easier to aim, having lower thermal stresses, and thus requiring less exotic materials and processes. IRBM’s and SRBMs also have less _time_ to go astray, further increasing their ease in targeting. Does this answer any of your questions? ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [April 10, 2002, 3:57pm UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766/3 "2002-04-10T15:57:59Z")
[http://www.gwu.edu/~nsarchiv/nsa/NC/mirv/mirv1\_1.html](http://www.gwu.edu/~nsarchiv/nsa/NC/mirv/mirv1_1.html) ---
**Author:** ![Kamandi](https://avatars.discourse-cdn.com/v4/letter/k/5daacb/32.png) [@Kamandi](https://boards.straightdope.com/u/Kamandi)\ **Post date:** [April 10, 2002, 4:10pm UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766/4 "2002-04-10T16:10:27Z")
I love this Board! What a cool topic! The issue of MIRVs and their launch bus is what caused all the brouhaha with China a few years ago when Lockheed Martin was passing them information on busses for launching multiple commercial satellites on one rocket. The US gub’mint said that the technology could be applied to ICBM MIRVs, and so could not be exported. It got commercial satellite exports put on the State Department’s “munitions” list (with a corresponding increase in red tape) and put a real hurtin’ on US satellite manufacturers. ---
**Author:** ![tsunamisurfer](https://avatars.discourse-cdn.com/v4/letter/t/a698b9/32.png) [@tsunamisurfer](https://boards.straightdope.com/u/tsunamisurfer)\ **Post date:** [April 11, 2002, 2:07am UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766/5 "2002-04-11T02:07:04Z")
> [@](#): > > \*Originally posted by tsunamisurfer \* > \*\*At what approximate height are the warheads deployed? By what mechanism are they ejected? How do the warheads maintain their course when ejected from a rapidly spinning re-entry vehicle? Feel free to throw in any additional technical details. I’m sure the North Koreans won’t learn anything new. \*\* These are the specific technical issues I am most interested in. Any other information available? ---
**Author:** ![JMRossi](https://avatars.discourse-cdn.com/v4/letter/j/74df32/32.png) [@JMRossi](https://boards.straightdope.com/u/JMRossi)\ **Post date:** [April 11, 2002, 2:47am UTC](https://boards.straightdope.com/t/how-do-mirved-icbms-work/102766/6 "2002-04-11T02:47:37Z")
The exact height is classified,I would say to help the pen-aids(penetration aids)clutter radar to disguise the RV from the bus while re-entering the atmosphere.The RS(reentry system or bus ,holds the warheads-3 for Minuteman 3,10 for Peacekeeper))doesn’t spin,small spin rockets at the base of the RV ignite after seperation giving it stability during re-entry.What the system does is basically like throwing rocks at long distance.Stage seperation and thrust termination have a lot to do with it,but the bus has to release the RVs at the correct time to get the best CEP.Even tho this system is old it is still a vital part of our national defence and a lot is still classified.When I was in SAC, RV serial numbers were classifed for 20 years,I have no idea why. A former SAC Master Missileman and ICBM Master Technician.