REENTRY PHYSICS AND TERMINOLOGY
A de-orbit burn is the firing of a spacecraft's engine against the direction of motion to cut the spacecraft's orbital speed. The speed reduction places the spacecraft in a lower orbit. If this lower orbit passes through Earth's atmosphere, the spacecraft reenters.
In spaceflight, a plasma sheath is an envelope of ionized gas, or plasma, that surrounds a body moving through an atmosphere at hypersonic velocity. A plasma sheath forms around a spacecraft during reentry and interrupts or interferes with communication with the ground.
More generally, a plasma sheath is the boundary layer of charged particles between a plasma and its surrounding walls, electrodes, or other plasmas. The sheath is generated by the interaction of the plasma with the boundary material. Current flow may be in only one direction across the sheath (single sheath), in both directions across the sheath (double sheath), or when the plasma is immersed in a magnetic field, it may flow along the sheath surface at right angles to the magnetic field (magnetic current sheath).
Reentry (test program)
Reentry was a series of suborbital tests carried out by NASA in the 1960s to evaluate various types of heat ablative materials (see ablation) and atmospheric reentry technology, particularly in preparation for the Apollo program. The nose cones of the Scout rockets used in these tests were coated in heat-shield ablators and then caused to reenter the atmosphere at around 28,000 kilometeres per hour – the speed of reentry after a lunar excursion.
Reentry Flight Demonstrator
RFD (Reentry Flight Demonstrator) was two spacecraft, launched on suborbital flights in 1963–64 to test reentry effects on nuclear reactor mock-ups supplied by the United States Atomic Energy Commission (AEC). The tests were carried out at a time when NASA and AEC were engaged in the NERVA (Nuclear Engine for Rocket Vehicle Applications) program.
Sweat cooling is a method of controlling the excessive heating of a reentering body. Surfaces subjected to excessive heating are made of porous material through which liquid of high-heat capacity is forced. The evaporation of this coolant completes the sweat-cooling process.