Like so many other questions one could ask about space travel, the
answer is not yet, but soon. All current military, commercial and scientific launches use decades-old rocket technology. The most popular is a solid rocket booster, so called because its oxidizer and fuel--a blend of volatile and hazardous chemicals--are pre-mixed inside the rocket, where they cure into a solid. Once fired, these rockets cannot be shut off or even throttled down. At its core, launching a manned
capsule or satellite on a solid rocket booster is the space travel equivalent
of tying a green plastic Army man to
a bottle rocket and hoping it doesn't blow up. The main exception in the U.S. space program is the troubled shuttle, which uses liquid hydrogen and oxygen in addition to solid fuels (see story "Space Shuttle: The Next Generation"). Soyuz rockets burn liquid oxygen and kerosene fuel.