{"id":31914,"date":"2017-05-18T14:30:58","date_gmt":"2017-05-18T04:30:58","guid":{"rendered":"https:\/\/www.aspistrategist.ru\/?p=31914"},"modified":"2017-05-18T09:14:06","modified_gmt":"2017-05-17T23:14:06","slug":"ballistic-missiles-%c2%bd-rule","status":"publish","type":"post","link":"https:\/\/www.aspistrategist.ru\/ballistic-missiles-%c2%bd-rule\/","title":{"rendered":"Ballistic missiles and the \u2018\u00bd rule\u2019"},"content":{"rendered":"

\"Image<\/p>\n

North Korea\u2019s ballistic missile tests are indeed a roller-coaster ride. After a string of failures in its recent ballistic missile testing program, with some missiles failing almost immediately after launch, last Sunday it conducted what some are calling its most successful ballistic missile test to date<\/a>. The test provides a shot in the arm for Pyongyang\u2019s WMD programs. It also signals to the broader international community that the North\u2019s ballistic-missile capabilities are definitely improving. Yes, the missile flew to a range of 787 km<\/a>\u2014on the face of it, nothing startling. But over at 38North, John Schilling noted<\/a> that the test represents \u2018a level of performance never before seen from a North Korean missile\u2019 and suggested that the missile\u2019s range is better seen as 4,500 km, not 800 km. He\u2019s not making a wild guess.<\/p>\n

The test provides an excellent opportunity to remind readers of an important general rule about missile range. The rule can be found in a useful\u2014and free\u2014little publication called The physics of space security: a reference manual<\/em> (which can be downloaded here<\/a>). In their chapter on space launches, the authors take the reader through what\u2019s called the \u2018\u00bd rule\u2019.<\/p>\n

\u2018A useful rule of thumb is that a ballistic missile that can launch a given payload to a maximum range R on the Earth can launch that same payload vertically to an altitude of roughly R\/2. This relation is exact in the case of a flat Earth and therefore holds for missiles with ranges up to a couple thousand kilometers (the Earth appears essentially flat over those distances, which are small compared to the radius of the Earth). But the rule continues to hold approximately for even intercontinental range missiles.\u2019<\/p><\/blockquote>\n

Broadly, the rule states that if a missile is fired straight upwards into space, it will achieve an altitude of \u00bd its maximum range. A Scud missile with a maximum range of 300 km, for example, would\u2014if fired straight up\u2014reach an altitude of 150 km before falling back to earth.<\/p>\n

So the interesting statistic from the recent North Korean test is not the missile\u2019s range but its altitude. That\u2019s been reported<\/a> at 2111.5 km\u2014a figure that, had it been achieved by firing the missile straight up, would point to a range of 4,223 km. That altitude was achieved while using some of the missile\u2019s thrust to go almost 800 km downrange, which points to a range figure a little greater than that.<\/p>\n

Of course range also depends on payload, so perhaps it would be more accurate to say that the test missile might have flown to a range in excess of 4,223 km with that particular payload. North Korea has emphasised that the missile is capable of carrying a large, heavy warhead. From publicly-available sources, it\u2019s hard to tell how large the actual payload was.<\/p>\n

Several analysts have pointed to the fact that this missile is not an ICBM. That\u2019s true. An ICBM is defined in the strategic arms control agreements between the US and Russia as any ballistic missile with a range of, or above, 5,500 km. That range wouldn\u2019t actually allow North Korea to target the continental US\u2014or, at least, not the 48 contiguous states. But President Trump has said that North Korea will not be allowed to develop an ICBM, without providing any different definition of such a capability.<\/p>\n

Some commentary on Sunday\u2019s test has observed that the North Koreans might well be testing ICBM \u2018subsystems\u2019 in their current program. By flying the missile on a highly-lofted trajectory, for example, the North Koreans have been able to subject their re-entry vehicle to a more stressful heat test than could have been achieved by a standard trajectory. William Broad and David Sanger, writing in the New York Times<\/em>, suggest that such gains show a Pyongyang tip-toeing over the line<\/a> that the US has attempted to draw in relation to ICBM-applicable technologies.<\/p>\n

As North Korea makes greater efforts to field an arsenal of longer-range missiles, we might begin to see a pattern of more frequent lofted missile tests. If so, that\u2019s going to set Washington\u2019s teeth on edge, not to mention Tokyo\u2019s and Seoul\u2019s. Australia itself has already been threatened with nuclear attack by North Korea, and the credibility of that threat can only grow as Pyongyang\u2019s missile capabilities increase.<\/p>\n

If we\u2019re witnessing the start of a new wave of longer-range missile tests, we might all soon be paying much greater attention to the \u2018\u00bd rule\u2019. Pyongyang needs to be particularly careful about conducting a test where the missile reaches an altitude suggestive of a 5,500-km range. If that were to occur, the \u2018\u00bd rule\u2019 might end up being a trigger for war.<\/p>\n","protected":false},"excerpt":{"rendered":"

North Korea\u2019s ballistic missile tests are indeed a roller-coaster ride. 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