The really fun part about watching SpaceX land their first stage on either their ASDS Barge (JRTI or OCISLY) or Landing Zone 1 on land, is they drew a nice target on the surface.

There is a literal X that marks the spot for the first stage to hit.

Reports have been that the stage has landed within 4 feet of the center of the target. If so, which has a greater CEP (Circular Error Probability)? The Minuteman ICBM missile or the first stage of a Falcon 9 landing?

  • 3
    $\begingroup$ Technically, the accuracy of the Minuteman ICBM is irrelevant; it's the accuracy of the reentry vehicle which matters; modern RVs are unpowered but highly maneuverable via aerodynamic control surfaces. The question is really about apples and oranges, as other answers have noted - a hypersonic warhead bus that's destined to explode versus a soft-lander. $\endgroup$ – Russell Borogove May 8 '16 at 1:02

There are a few differences. The most notable difference is the much larger distance that a Falcon 9 must go to achieve it's orbit. Also, the fact that Falcon 9 does a soft landing as compared to the fast landing required by a BM. Also, the Falcon 9 relies on GPS navigation, whereas a military system cannot be solely reliant. Lastly, these systems won't actually give their real accuracy, just vague terms like "pinpoint precision", but an open source claims the Tomahawk missile has an accuracy of about 30m. This is the most comparable weapon I know of to the Falcon 9.

As was noted, the accuracy of the Minuteman is estimated to be around 100m. Given an estimated 6 km/s, that means that it had to explode within 1/60th of a second, assuming pinpoint precision. Furthermore consider that a Minuteman doesn't have to be more accurate, 100m won't make much of a difference, so they don't have the required precision that a Falcon 9 landing requires.

The most directly comparable landing would be for the Dragon's landing back on the ground, but again, the speed at landing will be quite different. I suspect still that SpaceX will be more accurate, but as declared above, that doesn't matter.

Another compatible value is the orbital insertion error, which is estimated at 500m for the ORBCOMM mission in 2014.

| improve this answer | |
  • $\begingroup$ The Tomahawk has to be a lot more accurate than 30m. We saw plenty of shots of maneuvers in Desert Storm that would simply have been a wasted missile if it only had a 30m accuracy. $\endgroup$ – Loren Pechtel May 9 '16 at 1:21
  • $\begingroup$ Overcoming initial position error (think of nuclear submarines that have been submerged for six months or more) and orbit insertion error were the primary reasons GPS was invented. $\endgroup$ – David Hammen May 9 '16 at 10:50
  • $\begingroup$ @DavidHammen This is true, however, one can't expect a GPS guided solution the entire path of an ICBM, GPS can be jammed. $\endgroup$ – PearsonArtPhoto May 9 '16 at 11:44
  • $\begingroup$ @LorenPechtel I have no doubt you are right. The military likes to keep the exact accuracy for that kind of stuff secret. I suspect the error is more along the lines of 5m, but I'm really not sure about that. $\endgroup$ – PearsonArtPhoto May 9 '16 at 11:46
  • $\begingroup$ @PearsonArtPhoto - GPS was initially invented to address the huge position error of a submarine submerged for six months in the middle of the ocean combined with the equally huge orbit insertion error. A single star sighting made it so SLBMs could take out Russian train stations and industrial sites (as opposed to taking out Russian women & children). Taking out hardened silos demanded something more than a single star sighting. You don't need GPS all the way down. Just part of the way up will do, preferably during the powered portion of the flight. $\endgroup$ – David Hammen May 9 '16 at 11:56

Open sources have the Minuteman III CEP on the order of 100 m. Falcon 9 needs to be on the order of ~20 m to not miss the deck of the barge.

There are big differences in targeting: The Minuteman gets its destination programmed in before launch. You usually can't send in a surveying team, so there may be some uncertainty of the target's position.

The Falcon has a cooperative target: it can get live updates of the barge's position during flight.

| improve this answer | |
  • $\begingroup$ Hmm, seems like they could contract out the nuclear mission? $\endgroup$ – geoffc May 6 '16 at 20:31
  • 2
    $\begingroup$ No, for a number of reasons... $\endgroup$ – PearsonArtPhoto May 6 '16 at 20:55
  • $\begingroup$ @geoffc: F9 lands practically empty and with 0 payload, at speed that makes intercept with defense rockets easy. No room for warheads. OTOH the nuclear explosion's fireball - total obliteration radius - is greater than 100m, so the target will be hit by it regardless. $\endgroup$ – SF. May 6 '16 at 20:56
  • $\begingroup$ Is FAR greater than, you mean. The fireball is estimated at 1.35 km according to nuclearsecrecy.com/nukemap $\endgroup$ – PearsonArtPhoto May 6 '16 at 20:58
  • $\begingroup$ @PearsonArtPhoto - It depends on what the nuke is trying to nuke. A ten km error is fine if the goal is to take out enemy women and children. To take out enemy train stations and industrial sites, one needs one km accuracy. To take out critical enemy stations, 100 meter accuracy. To take out hardened enemy nuclear silos, on the order of ten meter accuracy. $\endgroup$ – David Hammen May 9 '16 at 10:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.