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(SBIRS) in low earth orbit is another

sors. Developing software for BM/C3 is more

component of the mature NMD sys-

of a challenge than is developing hardware.

tem, likely to be available after 2004.46

According to BMDO:

The GBI is a hit-to-kill system (the inter-

All elements of the NMD system will

ceptors physically smash into the incoming

work together to respond to a ballis-

warheads) designed to intercept incoming

tic missile directed against the United

warheads in the midcourse (or exoatmospher-

States. The U.S. Early Warning Sys-

ic) phase of their trajectories. The GBI con-

tem, consisting of Defense Support

sists of a rocket booster and exoatmospheric

Program (DSP) satellites, and its fol-

kill vehicle (EKV), which has its own set of

low-on capability, the Space Based

sensors, propulsion, communications, and

Infrared System (SBIRS) satellites,

guidance to complete the intercept.

will detect the launch of enemy mis-

To support NMD, the UEWR is an

siles and will subsequently track

upgrade to the existing large, fixed, phased

these missiles while also gathering

array early-warning radar network. According

information on them. After confir-

to BMDO, "Prior to deployment of the SBIRS

mation, this information will be

(Low) early-warning satellites, the UEWRs

passed to the Battle Management/Com-

will be used to detect and track objects during

mand, Control, and Communications

their midcourse phase, primarily to cue the

(BM/C3) system while groundbased

more precise X-Band Radars."47 Cueing is

radars acquire and begin to track the

when less precise long-range sensors tell more

missile. After defense engagement

precise shorter-range sensors where to search

authority is granted, one or more

for the target as it gets closer.

interceptors will be launched on com-

SBIRS is being developed by the Air Force

mand to engage the threat. The

as part of an upgrade to the early-warning sys-

BM/C3 system will continue to

tem that will eventually replace the current

process radar and other system data

Defense Support Program (DSP) satellites.

in order to provide more information

SBIRS will provide "over-the-horizon" acqui-

to the interceptor so it, in turn, can

sition and tracking of ballistic missiles

better discriminate between debris,

throughout their flight trajectories. Both

false objects (penetration aids), and

DSP and SBIRS satellites use infrared sensors

real warheads.

to detect the exhaust plumes of missile

The interceptor will use its on-

launches.

board sensor to acquire the threat,

Sophisticated

The XBR (also referred to as GBR or

select the target warhead, and guide

countermeasures

ground-based radar) is a forward-deployed

to a direct, high-speed collision using

are unlikely to be

radar designed to acquire incoming warheads,

on-board computers and divert

track them, distinguish them from decoys,

propulsion systems. During and after

easily deployed

and assess whether they have been destroyed.

the engagement, the radars continue

by rogue states.

According to BMDO, "XBRs use high fre-

to collect data, and observe the inter-

quency and advanced radar signal processing

cept results in order to provide "kill

technology to improve target resolution,

assessment" information which eval-

which permits the radar to perform more

uate[s] the interceptor's success or

effectively against closely-spaced warheads,

failure.49

debris and penetration aids."48

Ground-Based NMD

BM/C3 is the "brains" of the NMD system.

It provides the capability to plan, coordinate,

In 1996, the Congressional Budget Office

direct, and control NMD weapons and sen-

(CBO) estimated that an initial defense con-

15