A new concept of a space-based-laser (SBL) defense system is proposed. It is based on a chemical oxygen laser
(COL) which has been investigated to achieve its oscillation 1-3). A COL is suitable as a high energy laser (HEL)
directed energy weapon (DEW) 4) because it could produce a giant pulse of ~0.1 ms which can damage a target by a
single shot without producing plasma during the propagation. However since the beam cannot propagate for a long
distance due to the absorption in air, it should be used in space considering the capability of operation without
electric power supply. Therefore a new SBL defense system using a COL is proposed in order to destroy a ballistic
missile in its boost phase. It is based on an SBL at geostationary Earth orbit (GEO) with the altitude of ~36,000 km.
Since the beam needs to propagate for a long distance, the focused beam diameter is ~8 m even if the initial beam
diameter is 8 m. Therefore an 8 m-diameter focusing mirror, carried by a high altitude airship (HAA) flying at the
altitude of more than 20 km, could be used to focus the beam at the target. Although such a large focusing mirror is
necessary, the focused spot size can be <1 cm at 30 km away. Thus, much less than 100 kJ pulse can cause a fatal
damage. Unlike a conventional SBL defense system based on SBLs and/or relay-mirror satellites in low Earth orbit
(LEO), the new defense system needs only a single SBL and a single relay mirror HAA (RM HAA) to intercept a
ballistic missile if the enemy is a small country since the HAA can always stay close to the enemy’s missile site.
Another concept of the defense system is also proposed, which is based on a COL equipped with anther HAA
because a COL can be lightweight. These geostationary defense systems can also intercept a submarine-launched
ballistic missile (SLBM) if the submarine’s location is monitored.