杏吧原创

THE GULF WAR may have seemed like a triumph for high technology but behind
the scenes it was a communications nightmare. The satellite network that
linked troops to their commanders took days to set up. Once the ground forces
began to attack Iraqi positions, American troops had to transport giant 6-
metre satellite dishes across the desert. And although secret orders had to be
encoded before being broadcast, not every unit was equipped with a computer
that could decode them. This meant hand delivering battle plans for air
attacks which ran to 800 pages.

The Pentagon says the next generation of military communications systems
will solve these problems. It has in mind the Military Strategic, Tactical and
Relay system (Milstar), a network of four communications satellites and around
1200 portable ground terminals that will combine sophisticated encryption
methods with the convenience of a civilian telephone network.

But question marks hang over the need for Milstar. The system was conceived
in the early 1980s to allow limited communication during a nuclear attack.
Critics say such a Cold War capability is no longer needed and that a cheaper
system could do a better job. Already engineers are working to modify the
design of the Milstar satellites that have yet to be built. Some say Milstar
should be scrapped altogether.

Large footprints

At $17.3 billion, Milstar will be the largest and most expensive
communications system ever built. The first Milstar satellite was launched in
February and is now operating high over the coast of Ecuador. Another is due
for launch next year. The system requires two more satellites. These have been
ordered and are due to be launched later this decade. And since the satellites
have a seven-year life cycle, the Pentagon has ordered two replacements to be
ready early next century.

Each satellite will weigh 4700 kilograms and requires a US Air Force Titan
4 rocket to put it in orbit at a cost of more than $300 million per
launch. The satellites will orbit 35 000 kilometres above fixed locations on
the equator. Their communications footprints will each cover a third of the
Earth鈥檚 surface and together they will cover the entire globe except for the
North and South poles.

Milstar will be worth every penny of its hefty price tag, according to
Leonard Kwiatkowski, the Air Force officer in charge of the programme. Instead
of 6-metre satellite dishes, soldiers in the next war will carry 60-centimetre
dishes in their backpacks. The portable terminals will encrypt broadcasts to
prevent eavesdropping and the satellites will be able to foil enemy attempts
to jam their signals.

Perhaps the most significant advantage is that each Milstar satellite has
on-board computers which automatically route signals from satellite to
satellite or to the ground. Kwiatkowski calls it the first switchboard in the
sky. Existing communications systems use ground stations to process and route
signals. The satellites simply relay the signal. Military strategists have
never liked the idea of relying on ground stations in remote or unfriendly
regions to process critical communications. Milstar, on the other hand, will
be run from a single control centre at Falcon Air Base in Colorado.

Once a message has been sent, Milstar needs no more help from the ground.
Each signal is tagged with an encrypted digital address that is decoded by one
of nine computers on each satellite. Armed with this information, the
satellite searches an on-board database similar to a telephone directory and
routes the message accordingly. The control centre can instantly modify the
database so that communications networks such as those used during the Gulf
War, can be set up or torn down in minutes. If a Milstar terminal falls into
the wrong hands, the control centre can wipe its entry from the database
making the terminal useless. And as if encryption were not enough to confound
eavesdroppers, the satellite also hops between frequencies during
transmissions.

Milstar makes it possible for isolated or remote units, such as submarines,
to talk to their bases at a moment鈥檚 notice. Existing defence communications
satellites have a limited number of antennas to receive signals, so commanders
must book time on the satellite and wait for their slot. Each Milstar
satellite has up to 25 antennas and the on-board computers can distinguish
between almost 40 messages received simultaneously at the same antenna. This
means that Milstar can link hundreds of users at the same time. In future,
submarines will carry 13-centimetre satellite dishes which require more power
than the 60-centimetre models. The advantage is that these dishes will fit
inside a mast to allow the submarine to communicate at periscope depth rather
than from the surface as is now the case.

Radiation fog

Milstar is also designed to work during a nuclear war. Nuclear explosions
create enormous bursts of radiation which can damage microelectronic
components. To protect the satellites鈥� circuitry the computers are surrounded
by tens of kilograms of the metal tantalum and an aluminium honeycomb to
absorb the radiation. Some theorise that Milstar has other protective
measures. John Pike, an analyst with the Federation of American 杏吧原创s in
Washington, believes that in the event of a nuclear war, Milstar can boost
itself into a higher orbit, perhaps halfway to the Moon, as further protection
from this radiation and from missile attack. Kwiatkowski acknowledges Milstar
has thrusters which can move the satellite but refuses to say whether it is
more manoeuvrable than other military satellites.

Part of the radiation generated by a nuclear explosion is in the form of an
enormous electromagnetic burst which swamps conventional radio broadcasts,
preventing communication. Milstar, however, operates in the extremely high
frequency (EHF) radio band at up to 44 gigahertz. (In comparison, existing
defence satellites operate at up to 8 gigahertz and civilian short-wave radio
at about 0.3 gigahertz.) The higher the frequency of a signal, the greater its
energy. Engineers believe Milstar鈥檚 transmissions will have enough energy to
pierce the electromagnetic fog created by a nuclear explosion and so maintain
communications.

EHF broadcasts have other advantages too. The higher frequency means
shorter wavelengths, which can be broadcast in a narrower beam. Such signals
are more difficult to intercept or trace than wider beams. But satellites can
be spotted at night with a telescope because they reflect the Sun鈥檚 light in
the same way as the Moon. Should an enemy spot the satellite and attempt to
jam its signal, Milstar can respond.

Built into each of its satellites are two nulling antennas connected to
powerful computers that can distinguish friendly signals from the noise
broadcast by jamming devices. These act as a backup when Milstar鈥檚 other
antennas are overwhelmed. The computers work by assuming that jamming signals
are always more intense than friendly ones. With this knowledge they search
for weak signals while ignoring stronger ones. Air Force officials admit the
solution isn鈥檛 perfect because any friendly signals that appear strong can
also be ignored.

The Milstar design originally had another big disadvantage. It was designed
to cope with tiny amounts of information. The first Milstar satellite, which
was launched in February this year, and the second, which is due for launch
next year, transmit data at between 75 and 2400 bits a second. The minimum 75
bits is equivalent to only 10 letters on a teletype machine, 2400 allows
mildly distorted voice communications. The low data rate is designed to send,
for example, nuclear launch codes to submarine commanders, or brief messages
telling special forces when to start an action. But it would have been
insufficient to carry the amount of information generated during the Gulf
War.

Science fiction

So in 1991, the US Congress ordered the Pentagon to take another look at
the Milstar specification. At the time, part of Milstar鈥檚 specification was a
fleet of mobile command and control vans which could control Milstar while
cruising the countryside. The idea was that a nuclear war could still be
directed if fixed command posts were wiped out. This fleet was judged to be
obsolete and cancelled. In addition, the Pentagon decided to fit a new
communications payload to the final four satellites that could handle much
higher rates of information (the first two being too near completion to
modify). The modified Milstar satellites will transmit up to 1.5 million bits
per second, more than 600 times more than the first two satellites and enough
to send satellite pictures and complex battle commands, such as the 800-page
plans used during the Gulf War. To make room for the new package, engineers
will have to remove the nuclear shielding and a top secret 360 kilogram
payload.

Although defence officials in the US see the Gulf War as proof that Milstar
is needed, others say the war proves just the opposite. 鈥淒uring the Gulf War,
we managed perfectly well using commercial communications satellites,鈥� says
Joseph Cirincione a member of the Henry L Stimson Center, a defence think-tank
in Washington DC. 鈥淢ilstar has outlived its mission, if it ever had one,鈥� he
says. Meanwhile, Pike has dubbed Milstar 鈥淏attlestar Galactica鈥� after the
1970s science fiction television series because of its enormous size and its
Cold War price tag.

Other criticism comes from within the Air Force, which is responsible for
building and launching military satellites. Some officials say that Milstar is
using valuable funds that could be used to build more aircraft and that the
Pentagon has spent closer to $30 billion than the original $17.3
billion budget when development costs are taken into account. They want the
Pentagon to make better use of commercial communications satellites, which
lack Milstar鈥檚 security features but can transmit data at a higher rate. The
critics have yet to persuade Congress. In August, an effort to cancel Milstar
was defeated.

Sweeping review

But some defence officials in the Alr Force, who accept the need for
Milstar, say that a smaller, leaner satellite might prove better value for
money. The US Senate agrees. It has told the Pentagon to look into the
possibility of replacing the fifth and sixth Milstar satellites due for launch
in 2001 and 2002, with spacecraft known as advanced EHF satellites based on
the Milstar design but weighing no more than 2000 kilograms. At less than half
the weight of their predecessors, these satellites could be launched on much
cheaper rockets. The Pentagon says such a satellite could not be built before
2006 and so would not be ready to replace the early Milstar satellites. The
General Accounting Office, which evaluates projects like this for Congress,
disagrees, saying that the advanced EHF satellites could be ready by then if
the development programme was accelerated. Rahul Gupta, an analyst at the GAO,
says such a strategy could save up to $2.1 billion because smaller,
lighter satellites are generally cheaper to build and launch.

To save weight, Air Force engineers want to combine Milstar鈥檚 nine
computers into one. But a smaller satellite leads to other problems. 鈥淲e know
how we can miniaturise Milstar. The problem is coming up with enough space for
all the antennas, says one Air Force official on the programme.

But the advanced EHF satellites may never get further than the drawing
board. The GAO recently announced that the Pentagon is planning to buy more
weapons than it can pay for. To save the $150 billion needed to make up
the difference, the Pentagon has ordered a sweeping review of all its main
programmes. Whether Milstar can survive this latest round of cuts remains to
be seen.