capacity, and/or survivable de-escalation capacity. This also might not apply to a "non-discriminatory" space-based missile defense system, even if it is—actually, precisely because it is—of global reach. Such a system would be designed to destroy all weapons launched by any nation in a ballistic trajectory, negating any nation's capability to launch any strike with ballistic missiles, assuming the system was sufficiently robust to repel attacks from all potential threats, and built to open standards openly agreed upon and adhered to. No such system has yet been seriously proposed. Other possible first-strike weapons systems UGM-133 Trident II missiles may carry up to 8, 100kt W76 (C4) or 12 (START-limited 8, SORT-limited 5) W76 or 475kt W88 MIRVed warheads (D5). The circular error probability of the weapons is classified but is believed to be less than 120 m (C4) and 100 m (D5). The missile attains a temporary low altitude orbit only a few minutes after launch. The guidance system for the missile is an inertial guidance system with an additional star-sighting system, which is used to correct small positional errors that have accrued during the flight. GPS has been used on some test flights but is assumed not to be available for a real mission. Trident I-C4 has a range of over 4,000 nmi, and the Trident II-D5 can surpass 6,000 nmi; however, the absolute ranges of the missiles are classified and withheld from public domain for reasons of national security. R-36 (SS-18 Satan) Mod I/II 25 megaton variant. Although it is widely accepted that Soviets never had a first-strike strategy because of their conventional arms superiority in Europe, some experts believed that the single-warhead 25 megaton version of R36-M (SS-18, CEP 250 m) was a first-strike weapon targeted against Minuteman III silos. However, a much more logical explanation comes from retired Soviet military officers, who report that the 25 megaton SS-18 was targeted against heavily fortified command-and-control facilities. The reason is that a single 25 megaton warhead could take out only one hardened missile silo if the silos are sufficiently separated—probably by only 2–4 km, depending on the amount of hardening because of the inverse square law, which predicts that the amount of energy dispersed from a single point release of energy (such as a thermonuclear blast) dissipates by the inverse of the square of distance from the single point of release. Therefore, the power of a nuclear explosion to