The Aeroassist Flight Experiment validates through orbital testing the concept of aerobraking. This concept uses a planet's atmosphere to slow an entry body in order to achieve an orbit about the planet, transfer to another orbit, or reenter and land on the planet's surface. The concept's primary purpose is to reduce fuel needed for planetary operations.
The NASA AFE project proposes to deploy the AFE unmanned test vehicle from the Shuttle, after which a solid fuel rocket would accelerate it into the atmosphere at 250,000 feet. From there the AFE's blunt shape and small thrusters would fly it back to the Shuttle for retrieval.
Rail approaches to boosting payloads to space are believed to be inexpensive innovative ways of putting payloads in orbit. They are cheaper means because the payloads are launched inside shell like projectiles that do not carry fuel as rockets usually do. Most of the gun type propulsion system remains on the ground. This reduces the mass which has to be sent into orbit. Though cost reduction is cited, the length of the rail path and required accelerations place enormous stress on payloads so that humans could not survive the g-forces.
For an Earth to orbit launch, a tube about two-thirds of a mile in length would be built at an elevation of 30 degrees with respect to the horizon. The projectile would include a removable armature and a heat protecting aeroshell, a rocket motor, and the payload itself. After the shell reached 2.7 miles per second (end of gun), the projectile would have sufficient velocity to pass through the Earth's atmosphere. The acceleration of one thousand to two thousand G's would require acceleration hardened payloads. The armature would separate and fall to Earth. The aeroshell would also drop away, and the rocket motor would add a delta v of 2.7 miles per second to reach orbit.