WEBVTT

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How does the Orbital Maneuvering System work? At main engine cutoff for the Space Shuttle, it doesn't have sufficient speed to

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stay in orbit. So it must use its Orbital Maneuvering System, as well as its Reaction Control System, or "OMS RCS" as we call it.

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These are hypergolic systems. What that means is, you have two chemicals -- monomethyl hydrazine and nitrogen tetroxide -- who

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really, really hate each other. I don't need a spark-ignition device, they're not cryogenically stored. I just open up two valves,

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they flow into the combustion chamber, boom! I have rocket propulsion; a very, very simple system.

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The downside to these chemicals is, they're very, very toxic. Whenever you see people working with them here on the ground, you'll

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see them essentially wearing a spacesuit to protect them from these chemicals. Because if you got a deep enough whiff of these

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things, you would have to go to the hospital and you could have some significant lung damage.

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So we trade that ease of use on orbit for the problems we have handling it here on the ground. Now you use the Orbital Maneuvering

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System to give you that tiny, extra boost of speed to get you up into space, and then you also use it on the day you come home in

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order to slow the orbiter down just enough so that it will reenter the Earth's atmosphere.

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And that's how we use the OMS RCS system.

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