The Plesetsk launch center was discovered publicly by the Kettering space observers group in London. It was built in 1960, south of Archangel in the northern USSR (62.8° N 40.1° E) near the city of Mirny (Peaceful). Origionally, only a military garrison existed there until the military built an SS-6 ICBM base which later evoloved into a full fledged cosmodrome. The center was roughly 100 km. long with four different types of launch complexes which are heavily defended with surface to air missiles.
In its hay-day Plesetsk launched more satellites than any other base in the world. Roughly two thirds were recoverable military reconnaissance satellites which orbit for one week. Others were weather and communication satellites. Inclinations for the launches are between 62.8° and 82.9°. The center also tests many ICBM's each year (for example 128 in 1973).
Plesetsk is used for polar or high inclination flights to reduce risk of boosters falling in populated areas around Baykonur and the base is also much closer to Moscow's scientific centers than Baykonur allowing easier assess for development organizations around the capital. In 1983, the Soviets publicly admitted the launch centers existence after wide spread UFO reports in the area from people really seeing rocket launches.
The center contains all the necessary assembly, launch, computer, telemetry and communications services for launching spacecraft. Mirnyy also includes most of the comforts of a small city with a bakery, food markets, apartment blocks, and greenhouses.
It was the second major launch site for the R-7 booster. Plesetsk has the same type of launch pads for the R-7 as does Baykonur, and in addition has more modern launch pads. These pads are similar to Titan launch pads at Cape Canaveral where the booster is assembled on the launch pad, surrounded until launch by a moveable building or service structure. The service structure is 100 meters tall, covers 200 square meters, weighs 450 tons and moves on rails. The Plesetsk complex compares well to Vandenburg AFB in the U.S. except for the much larger number of launches per year.
Western journalists admitted to the site in 1989 were told of two fatal accidents at the launch center. On June 26 1973, nine technicians were killed in a launch pad accident and on March 18 1980, 50 technicians were killed by an explosion while fuelling a Soyuz booster.