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What Brought Down the Malaysia Airlines Jet Over Ukraine?

Experts say portable surface-to-air weapons can reach Malaysia Airlines flight 17's cruising altitude, but shoulder-fired missiles cannot.

U.S. officials now say that Malaysia Airlines flight 17, which crashed in Ukraine Thursday with 298 passengers and crew aboard, was brought down by a surface-to-air missile. At a convention of liberal bloggers and activists, Vice President Joe Biden said that the plane had apparently been "shot down" and "blown out of the sky."

Officials said they do not know, however, who fired the missile. And others in the intelligence community, including Rep. Mike Rogers, R.-Michigan, chair of the House Intelligence Committee, say there is still no official determination of what caused the downing. Right now, said Rogers, "anything you see is speculation."

The Boeing 777, which was flying from Amsterdam to Kuala Lumpur, was flying above the contested area of eastern Ukraine where Russian separatists are battling the Ukrainian government when it crashed into a field 31 miles west of the Russian border. Earlier Thursday a Ukrainian government official said that it was brought down by a surface-to-air missile.

Ukrainian President Poroshenko initially labeled it a “terrorist act,” according to his press secretary, but later put out a statement that called for an international investigation into the cause of the crash.

The “Manpads,” or shoulder-fired surface-to-air missiles, commonly used by footsoldiers in modern conflicts are capable of taking down passenger jets like the 777. But shoulder-fired missiles are largely ineffective above 20,000 feet. Flight 17 was traveling two miles higher, according to Ukrainian officials.

Portable surface-to-air missiles batteries like the Russian Buk, however, can intercept aircraft up to 72,000 feet. Earlier this week, the AP reported it had seen a Buk system on the ground in a separatist-controlled area of eastern Ukraine. Video posted on the website on Tuesday also purports to show Russian S-400 missile batteries traveling into Ukraine at night, but NBC News could not confirm the accuracy of the video.

Flight 17, which was flying from Amsterdam to Kuala Lumpur, hit the ground 31 miles west of the Russian border.

In a five day period ending Wednesday, air combat has dramatically increased, according to both Russian and Ukrainian reports.

Ukrainian officials said that a military transport plane was shot down by a missile fired from Russian territory.

Ukrainian officials said they did not believe that shoulder-fired missiles could have reached the transport plane’s altitude.

The Voice of Russia, a Russian government owned news service, said that Russian separatists in the Donetsk region had downed two Ukrainian jets, one of them with a “portable air defense system” near Horlivka. Horlivka is about 30 miles west of MH17's crash site.

NBC News analyst Michael Leiter, former director of the National Counterterrorism Center, said that “with intelligence assets clearly focused in this area, it should not take long before we understand what happened” to MH17.

The key to discovering what kind of missile hit the plane is a family of U.S. satellites that use infrared sensors to detect heat sources on the ground, such as rocket or missile plumes

The satellites, called the U.S. Space Based Infrared (SBIR) satellite system, fly 22,300 miles above the Earth in geosynchronous orbit, meaning that they move at the same speed as the earth revolves and thus "hang" over a single location. Their field extends thousand miles and their sensors are among the most sophisticated in the U.S. intelligence community's inventory.

The principal mission of the satellites is to detect the launches of intercontinental and submarine-launched missiles via their plumes. In the 1970s, as the Vietnam War progressed, officials found that the satellites could also detect large surface-to-air missiles. As the satellites were replaced and ground computers upgraded, smaller and smaller signatures could be identified and traced to specific locations -- including smaller and smaller missile launches and even small arms fire.

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The satellites have over the years been able to detect and provide data on things like nuclear tests, arms depot explosions, midair explosions and even some heat-generating industrial processes. The sensors can distinguish between missile systems, and could differentiate between a shoulder-fired missile and a Buk, for example.

The satellites were used to determine that there was no mid-air explosion of MFH370, the Malaysia Airlines. jet that vanished over the Indian Ocean four months ago.