Developed from the earlier
space-based Missile Defence Alarm System (MiDAS) program
of the 1960s, the first DSP satellite was launched on November 6, 1970.
missile warning satellite spots the launch of a ballistic missile and
immediately relays that information to the ground, enabling the targeted
country to retaliate, take cover, or possibly shoot down the missile. The
first missile warning satellites were born in the early days of the space
race, when the 1957 Soviet launch of Sputnik atop its converted
intercontinental ballistic missile (ICBM) reminded U.S. generals that the
country had become increasingly vulnerable to attack. The U.S. military
knew that an ICBM launched from the Soviet Union to the United States
would take about 30 minutes to reach its target, but in the 1950s,
American radars located on overseas bases in Norway, Greenland, and Great
Britain could spot an ICBM only after it had travelled half its distance.
This meant that, at best, the United States would have only 15 minutes to
get their strategic bombers, like the B-52 Stratofortress, off the ground.
This was not enough time, and the generals realized that most of their
bombers would be blown up before they ever lifted off the runway.
before Sputnik, a few scientists and engineers proposed using infrared
sensors aboard aircraft to spot the hot exhaust of Russian ICBMs soon
after they blasted off. They proposed placing these sensors on high-flying
U-2 spyplanes flying around the edge of the Soviet Union. But this plan
required a lot of planes flying all the time and would have been
expensive, and the plan was not approved by the Air Force.
Joseph Knopow, an engineer at Lockheed Aircraft Corporation, proposed
putting an infrared sensor on a telescope aboard a spacecraft flying in
low-Earth-orbit. This spacecraft could spot the hot exhaust of a rising
ICBM once it lifted clear of the clouds and increase warning time of an
ICBM attack from only 15 minutes to more than 25 minutes. But because
satellites are constantly moving around the Earth, as many as 24
satellites would be needed so that several would be positioned over Russia
at any one time to spot the missiles. The Air Force adopted this proposal
and named it MiDAS, for Missile Defence Alarm System.
Force launched its first MiDAS test satellite in February 1960, but it did
not reach orbit. The next several test launches suffered various problems,
many of them pertaining to the spacecraft and not its telescope. But
committees of scientists asked to evaluate the MiDAS system were sceptical
that the telescope's sensors would ever work. In particular, they were
concerned that sunlight reflecting off of clouds would confuse the
infrared detectors and register as false alarms.
group of test satellites, known as Program 461, was launched in 1966.
These satellites had more powerful telescopes capable of spotting cooler
solid-propellant rockets like the American submarine-launched Polaris
missile. These satellites were more successful than their predecessors and
finally proved that the concept could work. But the requirement for a
large number of satellites meant that the program would be expensive, and
Department of Defence officials cancelled it.
a high-level scientific committee determined that a satellite with a big
infrared telescope and located in geosynchronous orbit could spot an ICBM
launch. The chief advantage of operating in such a high orbit was that
only a few satellites, rather than the dozen or more needed for a
low-altitude system, were needed to observe all the primary launching
sites because each satellite could now see virtually half the Earth. The
Air Force abandoned the low-altitude approach and selected satellite maker
TRW and sensor manufacturer Aerojet to build the new satellites. This
project was soon named the Defence Support Program, or DSP. The first DSP
satellite was launched in 1971 into an improper orbit, but the spacecraft
itself worked and proved that the technology worked. DSP proved to be a
very successful military satellite program.
since 1971, the U.S. Air Force has been launching bigger and more powerful
DSP satellites into orbit. The 14th satellite launched entered service in
1989 and was the first of a new class of satellites named DSP-1. In 1992,
a DSP was launched from the Space Shuttle. The satellites are
barrel-shaped, with four solar panels on extendable panels at their rear.
They spin in orbit for stabilization. They have a large telescope that is
mounted at an angle at their front end and which sweeps across the face of
the Earth six times every minute, meaning that they can detect, or
“image,” an infrared heat source, such as a missile, every ten seconds,
tracking its trajectory.
Initially two ground stations were built to receive their data, one near
Denver, Colorado, and another in Alice Springs, Australia. The Australian
site was classified because the Australian government feared public
opposition. It was closed in 2001, and now all missile warning data is
relayed to the Colorado station.
controllers soon discovered that the satellites could spot other heat
sources besides land and submarine-launched missiles. These included
forest fires, surface-to-air missiles, and even military aircraft using
their afterburners. The U.S. Navy began to use DSP satellites to warn of
Soviet bomber attacks on its aircraft carriers. Other intelligence
agencies used this information as well.
1980s, the United States began operating infrared sensors on top-secret
satellites in highly elliptical orbits that carry them high over the
northern part of Russia and low and fast over the southern hemisphere.
These sensors augmented the existing early warning system and also focused
on specialized targets, such as the anti-ballistic missile system around
with most military space technologies, the Soviet Union lagged behind the
United States by several years. The Soviet Union launched its first
missile warning test satellite in 1972, and its first operational
satellite in 1977. The Soviet satellites, named Prognoz, operated in
highly elliptical orbits that were highly inclined to the equator. These
orbits, also known as “Molniya” orbits after the first Soviet
communications satellite to use them, enabled the satellite sensors to
view a missile above the horizon of the Earth against the cold background
of space, which is easier than viewing it against the warm Earth
background. But because the satellites are always moving, more of them are
needed and the Soviets required a “constellation” of nine satellites to
provide full coverage of American ICBM launch sites. This still left other
areas of the globe uncovered, like the oceans that hide U.S. missile
submarines. The large constellation size, combined with the short
lifetimes of the satellites, meant that the Soviets had to launch up to
seven satellites in a single year to keep the system running. After the
Cold War ended, the Russian government was no longer able to maintain the
system and during the 1990s only about half of the constellation was
operating at any one time. During the mid-1980s the Soviets began
launching missile warning satellites to geosynchronous orbit, like the DSP,
but they launched far fewer of these satellites and Western space experts
believe that these satellites, called Oko (or “Eye”) have not been very
the other hand, has been tremendously successful. During the Persian Gulf
War in 1991 it provided effective warning of the launch of Iraqi Scud
missiles against Saudi Arabia and Israel. But the basic satellite design
and its sensor technology are obsolete. This led the U.S. Air Force to
begin developing a replacement. After a frustrating series of stops and
starts, by the late 1990s the Air Force was developing two different types
of satellites, known as SBIRS-High and SBIRS-Low. (SBIRS, pronounced “sibirs,”
stands for Space-Based Infrared System.) The SBIRS-High satellites will
replace DSP satellites in geosynchronous orbit. Unlike their predecessors,
they are three-axis stabilized and their sensors “stare” at the ground
continuously rather than sweeping over a specific point every ten seconds,
thereby providing much more accurate data. SBIRS-Low satellites, if built,
will operate in low Earth orbit and track missiles as they fly above the
horizon, offering much more accurate information on their trajectories.
Such information is necessary for an effective anti-ballistic missile