Range safety

In the field of rocketry, range safety may be assured by a system which is intended to protect people and assets on both the rocket range and downrange in cases when a launch vehicle might endanger them. For a rocket deemed to be off course, range safety may be implemented by something as simple as commanding the rocket to shut down the propulsion system or by something as sophisticated as an independent Flight Termination System (FTS), which has redundant transceivers in the launch vehicle that can receive a command to self-destruct then set off charges in the launch vehicle to combust the rocket propellants at altitude. Not all national space programs use flight termination systems on launch vehicles. In the field of rocketry, range safety may be assured by a system which is intended to protect people and assets on both the rocket range and downrange in cases when a launch vehicle might endanger them. For a rocket deemed to be off course, range safety may be implemented by something as simple as commanding the rocket to shut down the propulsion system or by something as sophisticated as an independent Flight Termination System (FTS), which has redundant transceivers in the launch vehicle that can receive a command to self-destruct then set off charges in the launch vehicle to combust the rocket propellants at altitude. Not all national space programs use flight termination systems on launch vehicles. In the US space program, range safety is usually the responsibility of a Range Safety Officer (RSO), affiliated with either the civilian space program led by NASA or the military space program led by the Department of Defense, through its subordinate unit the Air Force Space Command. At NASA, the range safety goal is for the general public to be as safe during range operations as they are in their normal day-to-day activities. RSOs are also present in the hobby of model rocketry and then are usually responsible for ensuring a rocket is built correctly, using a safe engine/recovery device, and launched correctly. Some launch systems use flight termination for range safety. In these systems the RSO can remotely command the vehicle to self-destruct to prevent the vehicle from traveling outside prescribed safety zone. This allows as-yet-unconsumed propellants to combust at altitude, rather than upon the vehicle reaching the ground. Space vehicles for sub-orbital and orbital flights from the Eastern and Western Test Ranges were destroyed if they endangered populated areas by crossing pre-determined destruct lines encompassing the safe flight launch corridor. To assist the RSO in making a flight termination decision, there are many indicators showing the condition of the space vehicle in flight. These included booster chamber pressures, vertical plane charts (later supplanted by computer-generated destruct lines), and height and speed indicators. Supporting the RSO for this information were a supporting team of RSOs reporting from profile and horizontal parallel wires used at lift-off (before radar could capture the vehicle) and telemetry indicators. After initial lift-off, flight information is captured with X and C-band radars, and S-Band telemetry receivers from vehicle-borne transmitters. At the Eastern Test Range, S and C-Band antennas were located in the Bahamas and as far as the island of Antigua, after which the space vehicle finished its propulsion stages or is in orbit. Two switches were used, ARM and DESTRUCT. The ARM switch shut down propulsion for liquid propelled vehicles, and the DESTRUCT ignited the primacord surrounding the fuel tanks. In the case of manned flight, the vehicle would be allowed to fly to apogee before the DESTRUCT was transmitted. This would allow the astronauts the maximum amount of time for their self-ejection. The primary action performed by RSO charges is rupturing the propellant tanks down the middle to spill out their contents. In the case of boosters with cryogenic propellants, the RSO system is designed to rupture the tanks in such a way as to minimize propellant mixing, which would result in an extremely violent explosion, specifically by having the charges split the sides of the tanks open like a zipper, which spills out the propellants and minimizes mixing. On boosters with hypergolic propellants, the opposite happens—mixing is encouraged as these propellants burn on contact rather than mix and then explode. In addition, the toxicity of hypergolic propellant means that it is desirable to have them burn up as fast as possible. The RSO system used on these boosters works by rupturing the common tank bulkhead so the oxidizer and fuel immediately contact and burn. Just prior to activation of the destruct charges, the engine(s) on the booster stage are also shut down. For example, on the 1960s Mercury/Gemini/Apollo launches, the RSO system was designed to not activate until three seconds after engine cutoff to give the Launch Escape System time to pull the capsule away. American rockets have often a Range Safety destruct system since the early launch attempts conducted from Cape Canaveral in 1950. As of 2016, a total of 32 US orbital launch attempts have ended in an RSO destruct, the first being Vanguard TV-3BU in 1958 and the most recent being Cygnus CRS Orb-3 in 2014. Some launch vehicles (for example, the Titan family) have included an automatic destruct system to activate in the event that the solid rocket motors or upper stages separate prematurely; this is separate from the standard RSO system which is activated by manual command.