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SCATHA

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SCATHA Credit: Manufacturer Image

AKA: Spacecraft Charging at High Altitude. Status: Operational 1979. First Launch: 1979-01-30. Last Launch: 1979-01-30. Number: 1 . Gross mass: 360 kg (790 lb). Height: 1.80 m (5.90 ft).

SCATHA's primary mission was to obtain information about the processes and effects of spacecraft charging, a phenomenon known to have contributed to several on-orbit satellite failures. The mission's specific objectives were to (1) obtain environmental and engineering data to allow the creation of design criteria, materials, techniques, tests and analytical methods to control charging of spacecraft surfaces and (2) collect scientific data about plasma wave interactions, substorms, and the energetic ring. (Spacecraft shown in stowed configuration, with experiment booms stowed). The spacecraft was also known as P78-2.

The spacecraft was spin stabilized (~1 rpm) with 5 deg pointing accuracy. The hydrazine propulsion system had 8 thrusters and 2 tanks. Body mounted solar cells generated 290 watts and recharged three 8 Ahr NiCd batteries. Downlink was at 8.2 kbps at S-Band from redundant 10 W transmitters. The aluminum, titanium, magnesium, and glass fiber structure supported seven deployed experiment booms. Two tape recorders provided ~350 Mb storage each.

The twelve experiments had a total mass of 87 kg and consumed 110 W. They were:

• SC1 - Engineering Experiments plus VLF and HF Receivers - measured surface potentials of various spacecraft materials, measured RF waves between 0-300 kHz, 2-30 Mhz.
• SC2 Spacecraft Sheath Fields Plus Energetic Ions - measured low energy electrons and ions, energetic protons, and electrons.
• SC3 High Energy Particle Spectrometer - measured high energy electrons and protons.
• SC4 Satellite Electron and Positive Ion Beam System - used ion and electron beam guns to control spacecraft surface potential.
• SC5 Rapid Scan Particle Detector - measured electrons and ions.
• SC6 Thermal Plasma Analyzer (failed soon after initial turn on) - designed to measure thermal electrons and ions.
• SC7 Light Ion Mass Spectrometer (failed soon after initial turn on) - designed to measure light ion density, temperature and composition.
• SC8 Energetic Ion Compositions Experiment - measured low energy electrons and the ion composition of energetic plasma.
• SC9 UCSD Charged Particle Experiment - measured electrons and ions.
• SC10 Electric Field Detector - measured DC and ELF electric fields and satellite potential.
• SC11 Magnetic Field Monitor - measured DC and ELF magnetic fields.
• ML12 Spacecraft Contamination Plus Thermal Control Materials Monitoring -measured contamination rates and property changes of several thermal control material samples.
• TPM Transient Pulse Monitor - supported the other experiments by providing supporting data about the electromagnetic pulse environment.

• Contract for Space Test Program Flight P78-2. - . Spacecraft Bus: Space Test Program Payloads. Spacecraft: SCATHA. Effective on this date, Martin Marietta "Corporation was awarded a $12.36 million contract to develop a spacecraft for Space Test Program Flight P78-2..

• SCATHA - . Payload: P 78-2. Mass: 360 kg (790 lb). Nation: USA. Agency: USAF. Class: Technology. Type: Communications technology satellite. Spacecraft Bus: Space Test Program Payloads. Spacecraft: SCATHA. Completed Operations Date: 1991-05-28 . USAF Sat Cat: 11256 . COSPAR: 1979-007A. Apogee: 42,860 km (26,630 mi). Perigee: 28,018 km (17,409 mi). Inclination: 10.20 deg. Period: 1,418.40 min.

  Flight P78-2 was successfully launched by SAMSO's Space Test Program. The mission was designated SCATHA (Spacecraft Charging at High Altitudes) and gathered data on the build-up of electrical charges on satellites operating at geosynchronous altitude. It was sponsored jointly by NASA and the Air Force. Spacecraft charging experiments. The SCATHA spacecraft had two charged particle injection systems, one of which was the Satellite Positive-Ion-Beam System (SPIBS). This was a xenon ion source which included some of the technologies used in thrusters: however, the discharge chamber was not performance optimized as was done with ion engines. Maximum operating power was 0.045 kW, and the ion source could produce a thrust of about 0.14 mN at a specific impulse of 350 s. Ions could be ejected at 1 keV or 2 keV. Neutralization was accomplished by a tantalum filament. The specific impulse was low because there was no attempt to optimize the propellant efficiency. The SPIBS system was ground-tested for a period of 600 hours. The SCATHA spacecraft was placed in a near geosynchronous orbit. Ion beam operations were performed intermittently over a 247 day period. The SCATHA flight demonstrated that a charged spacecraft, and the dielectric surfaces on it, could be safely discharged by emitting a very low energy (<50 eV) neutral plasma -- in effect shorting the spacecraft to the ambient plasma before dangerous charging levels could be reached. As of 28 August 2001 located at 153.98 deg W drifting at 4.513 deg E per day. As of 2007 Mar 8 located at 19.65W drifting at 4.513E degrees per day.