Requires large/heavy anti-ballistic missiles and sophisticated powerful radar which must often be augmented by space-based sensors.

One idea presented to the Russians is to exempt all space-based sensors from treaty limits.

And while he backs space-based sensors, he opposes space-based rockets.

In tonight's launching, other critical elements of a defense shield were tested, including space-based sensors, ground-based radar and the system's command centers.

This would be primarily a ground-based missile system with space-based sensors and management satellites.

The least contentious element of the new program may be advanced, space-based sensors that could track warheads in space but also perform other surveillance duties as well.

The Russians also possess a key prerequisite for deployment of space-based antimissile sensors and weapons - a vigorous space program.

Other important elements of the system, including space-based sensors, ground-based radars, new rocket boosters and command centers, have yet to be tested.

The test would involve the use of interceptor rockets and space-based sensors.

The president has also proposed sharply increasing research financing for laser weapons, space-based sensors and digital communications.