A growing number of high-level authorities are saying that Malaysia Airlines Flight MH17 was brought down by a surface-to-air missile.
Indeed, one of those claims was made by U.S. President Barack Obama on Friday. "What we have confidence in saying is that a surface-to-air missile was fired, and that's what brought the jet down."
Obama added, "It's important for us to make sure we don't get out ahead of the facts."
Here then are some facts about surface-to-air missiles, or SAMs.
What are the origins of SAMs?
SAMs were first deployed in the 1950s, in the U.S. and former Soviet Union.
The U.S. began to deploy Nike Ajax missiles in 1953, positioned to protect cities and military installations. The missiles were developed as part of Project Nike (the name for the Greek goddess of victory), which began in 1945.
The first Soviet SAM, the S-25 Berkut (golden eagle), was deployed in 1955, eventually in several rings around Moscow.
The early SAMs replaced anti-aircraft guns.
The Vietnam War was the first serious wartime use of SAMs, beginning in 1965. They were effective, especially in the early years. About 205 aircraft were shot down with SAMs during the war
How do SAMs work?
A target is identified, usually visually or by radar, the missile fired and, with the help of a guidance system, homes in on its target. If that target is not deploying any missile defence — which civilian aircraft do not — the SAM is very likely to hit its target.
The missiles contain a warhead and a propulsion system.
They can be fired from a missile system or with a hand-held launcher for smaller, shorter-range missiles.
What guidance systems do SAMs use?
The guidance system may be on the missile or on the launch system using remote control.
The larger, longer-range SAMs usually rely on radar, although not exclusively, for guidance. In the most-common system, known as semi-active radar homing, a receiver in the missile picks up the reflections of the surface-based tracking radar and then homes in on that signal.
Smaller, shorter-range SAMs tend to use an onboard infrared guidance system to home in on targets.
Some newer systems use a laser instead of radar for guidance.
What are the types of SAMs?
SAMs are grouped according to their range, and, generally, the longer the range the larger the missile.
Short-range missiles, including MANPADS (man-portable anti-aircraft missiles) get deployed against aircraft on ground-attacks, including helicopters. They may be fired from someone's shoulder or from vehicle mounts.
Medium-range systems are usually vehicle-mounted and can be fired while the vehicle is moving.
The long-range missile systems may be fixed or semi-mobile.
From what distance can a SAM hit an airplane?
Russia’s 40N6 SAM has a range up to 400 km, although 250 km is a more common range for long-range SAMs.
Normal airliner cruising altitude, 10,000 m, would be beyond the reach of short-range SAMs but could be brought down by most medium-range SAMs.
MH17 was at 10,000 m when it vanished from radar.
What is the SA-11 Gadfly?
That is the NATO designation for the Russian 9K37 Buk medium-range SAM system. That is the system the U.S., Ukrainian officials and others say was used to shoot down Malaysia Airlines Flight MH17.
It uses semi-active radar homing and has been around since 1979. It's a mobile system consisting of two vehicles and can be ready to fire in five minutes.
Each launcher is armed with four SAMs.
The missiles travel at three times the speed of sound, are about 5.5 m in length and .4 m in diameter. They weigh about 700 kg, with a 70 kg warhead that has a 17 m lethal radius.
These missiles are usually used to defend against aircraft or cruise missiles. They can hit a target travelling up to 3,000 km/hr at altitudes from 30-14,000 m., or even 22,000 m according to some sources.
Each SAM has a range of three to 28 km.
Why is the SA-11 suspected to be the type of SAM that brought down MH17?
Both Russia and Ukraine have SA-11 or Buk systems, and there are also reports from Ukraine and rebel sources that pro-Russian rebels have acquired one or more SA-11s.
Ukraine has 60 SA-11 systems according to the International Institute for Strategic Studies' 2014 Annual Survey.
The SA-11 is definitely capable of shooting down an airliner at 10,000 m.
Its identification friend or foe system "would not give you a warning that you were tracking an airliner," according to Jane's Defence Weekly. It will only identify the particular military's own aircraft.