Why are Russian ballistic missiles Ukraine’s biggest air defense problem? Two reasons – Russian ballistic missiles are a powerful weapon, and the main system countries use to defend themselves against ballistic missiles is made by the US, and the US has cut Ukraine off from supplies of interceptor missiles that the defense system uses. The reason a ballistic missile is hard to stop is that it reaches speeds of Mach 6-7, and climbs to altitudes of up to 50 km (31 miles, 164k ft) before diving in