Space Foundation & Warrior Maven By John Warnock, Warrior Senior Fellow You Might Want to Know: What are “re-entry vehicles”? Why do we need them? How do they work? What are MIRVs? How do they work? If you know what happened to the Space Shuttle Columbia in 2003, you know why nuclear warheads need re-entry vehicles. Anything that gets going fast enough to get into orbit, which is 17,500 miles an hour, will still be going thousands of miles an hour when it comes back into the atmosphere. At that speed, friction with the atmosphere generates temperatures of thousands of degrees on the surface of the vehicle. Without a heat shield, the vehicle will burn up. On its way up into orbit, Columbia lost some tiles in the heat shield that was supposed to protect it when it came back and re-entered the atmosphere. Where the tiles were missing, the friction heated the Shuttle up past what it could take. It broke apart. We saw pictures of the white trails of the fragments streaking across the sky. All seven astronauts were killed. A terrible thing. Intercontinental Ballistic Missiles don’t go into orbit but they propel their warheads far above the atmosphere. Different ICBMs propel their warheads to different altitudes but the apogee (high point) can be more than seven hundred miles above the earth. Coming back, the warheads re-enter the atmosphere at about sixty-two miles above the earth (Our atmosphere extends only that high, did you know? That’s not very high.). When the warheads re-enter the atmosphere, they are still travelling at many thousands of miles an hour. Fifteen thousand miles an hour, it could be. Much faster than any bullet. They will keep most of that speed all the way down. If the warheads weren’t protected against the heat, the friction with the atmosphere would heat them up so much they couldn’t be counted on to work the way we want them to. Re-entry Vehicles use different special materials developed by materials scientists to keep the warheads from overheating. Some RVs “ablate” (partially vaporize) their surfaces coming in. This carries off some of the heat. Our first RV—the Mk-2--was developed by General Electric in 1955, two years before the first flight of the Atlas, our first ICBM. With our warheads as big and heavy as they were at first, it was all our Atlas could do to get one warhead in its RV up there. The warhead used for the Atlas, the W49, weighed three-thousand seven-hundred pounds, close to two tons. It yielded the equivalent of one-million four-hundred forty thousand tons of TNT. A thousand Hiroshimas. But we were finding ways to make lighter warheads that still had the yield we thought we needed. By 1964, we had developed the W-58 warhead that weighed just under two-hundred sixty pounds and yielded the equivalent of two-hundred thousand tons of TNT, thirteen and a third Hiroshimas. By 1964, we had also developed a Submarine Launched Ballistic Missile called the Polaris. We could put three W-58 warheads into the Mk 2 re-entry vehicles and mount them on top of the Polaris. The Polaris wasn’t as accurate as some of our other missiles that we thought might be targeted on something more specific, like a missile complex. So we just targeted the Polaris and its three W-58 warheads on cities and whoever lived there. By 1970, we had developed a re-entry vehicle—the Mark 12A--that allowed us not only to put several warheads on one missile, but to direct them to different targets. Our newer Minuteman III ICBMs had on them three W62 warheads—253 pounds, 170 kilotons of yield each—and each could be aimed at a different target. Within a certain “footprint,” of course. The footprint was maybe three hundred miles across. The Mark 12s had a nifty new feature. They could carry “penetration aids”--chaff and balloons that could be released as the warheads were coming in that we hoped would blind or fool radars that might be trying to find the incoming warheads. Their missiles would soon have penetration aids too no doubt. If this worked for us, it would work for them. Have you wondered how the Multiple Independently-targeted RVs worked? Here’s how. The MIRVs with their warheads inside would be mounted on a platform, called a “bus.” The bus would be fastened on top of the missile and covered with a streamlined fairing. The missile would climb up out of the atmosphere until all the rocket’s stages were spent and had fallen away. The fairing would be jettisoned. The bus with its warheads would tip over and start down. On its way down, the bus would release one RV and then use little jets in the bus to change course before it released another RV. And do this again for the third. Or for however many RVs and warheads and penetration aids the missile could carry. A few years after we deployed our Minuteman IIIs with three MIRVs on them, the Soviets developed some great big ICBMs that could carry ten MIRVed warheads. Maybe more. Yikes. I suppose we could have foreseen this. It doesn’t seem we had. We got busy and in President Carter’s administration started to develop a missile called the Peacekeeper that also could carry ten warheads. Before we got it completely deployed, the Cold War ended. At the end of the Cold War, President George H. W. Bush signed the Start II Treaty with the then leader of Russia, Boris Yeltsin. The treaty said that all our land-based missiles could carry only one warhead. Bye bye to MIRVs. Not so fast. In 2005 President Bush’s son, President George W. Bush, withdrew us from the Anti-Ballistic Missile Treaty President Nixon had signed with the Soviet Union back in the 70’s. When George W. Bush did that, Russia started to re-MIRV their weapons. That seemed a shame. President George W. Bush didn’t re-MIRV the Peacekeepers. Instead he decided to take them out of service. Packed together the way they were in that dense pack, there wasn’t much chance they would have survived an ICBM attack. Never had been, had there? There was also the fact that in 1990, right at the end of the Cold War, we’d put in service some new submarine-launched ballistic missiles, the Trident II D5s. The D5s could carry fourteen W88s in independently targetable Mark 5 reentry vehicles. Each of the W88s yielded four-hundred seventy-five kilotons, more than thirty-one Hiroshimas. Every one of our Trident II submarines could carry twenty-four D5 SLBMs. We planned to have fourteen of these submarines. You can do the math if you want. By the late 70’s, we had learned how to make MaRVs, RVs that were “maneuverable.” MaRVs wouldn’t just fall on their targets. Using navigation devices carried in the RV, they would move flaps on the RV and change course as they came in many times faster than any bullet. Track that! We’ve heard that the Chinese have recently developed re-entry vehicles that can increase their speed as they come in. I guess they think 15,000 miles an hour isn’t enough. What’s next, do you suppose?
