![]() This autonomy system was responsible for preparing the spacecraft for first contact, monitoring component health, monitoring overall spacecraft attitude and maneuver health, and maintaining proper spacecraft component on/off configurations and other autonomous actions to support the recorder and hardware-based reactions. The ACE autonomy system, in conjunction with hardware-based fault detection and reaction and together with the command and data handling (C&DH) and power subsystems, formed the overall ACE safing strategy. The subsystem is a hydrazine blowdown unit that uses nitrogen gas as the pressurant and is made up of four fuel tanks, four axial thrusters for velocity control along the spin axis, and six radial thrusters for spin plane velocity control and spin rate control.įigure 2: Block diagram of the ACE observatory (image credit: JHU/APL)įor APL developed spacecraft - the 1 st generation autonomy capability began with the ACE mission, during which autonomy was first separated from hard-coded software. The ACE propulsion subsystem (of Primex) corrects launch vehicle dispersion errors, injects the spacecraft into the L1 halo orbit, adjusts the orbit and spin axis pointing, and maintains a 5 rpm spin rate. The FPGAs are designed with triple voting cells to minimize the probability of SEUs. Both RAM and EEPROM utilize error detection and correction (EDAC) circuitry to correct single errors and detect double errors. ![]() The EEPROM can be reloaded on the ground, and the RAM can be patched in flight. Code is stored in electrically erasable/programmable read-only memory (EEPROM) and downloaded into random-access memory (RAM) for execution. The RTX2010 is fabricated in a CMOS/SOS process that is exceptionally hard to single-event upsets (SEUs), making it suitable for operation through solar flares. It utilizes a Harris RTX2010 processor executing the FORTH language. The C&DH (Command and Data Handling) subsystem is of JHU/APL design. 3) 4) 5)įigure 1: Line drawing of the ACE spacecraft Nominal life of the mission is 2 years with a five-year goal. There are two deployable magnetometer booms (magnetometer sensors on ends of boom). A NiCd battery (18 cell 12 Ah) is being used. S/C launch mass = 785 kg (includes 189 kg of hydrazine fuel for orbit insertion and maintenance), peak power = 443 W (EOL with EOL defined as 5 years) from four deployable solar panels (each 86.4 cm x 149.9 cm). The nominal spin rate is 5 rpm, the S/C is oriented in the Earth/sun direction. ![]() Attitude is measured by a star tracker (CT-632 solid-state scanner of BATC) and sun sensors, attitude knowledge is within ± 0.7º (goal of ± 0.5º for the magnetometer). The S/C is spin stabilized with the spin axis Earth/sun pointing (star and sun sensors). ![]() The S/C structure (decks and panels: honeycomb with aluminum alloy facesheet) has two octagonal decks, 1.6 m across and 1 m high the overall wing span is about 8.3 m. The ACE spacecraft was designed and built at JHU/APL, Laurel, MD. A NASA solar-terrestrial space weather mission in the Explorer Program (Explorer-71) with the prime objectives to determine: the elemental and isotopic composition of matter, the origin of the elements, the formation of the solar corona and acceleration of the solar wind.
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