Heaob

X-ray astronomy

X-ray telescope & instruments

540 km circular inclined 22.75 deg

Atlas-Centaur launch; 12 mo in LEO

Atlas-Centaur

NASA S-band GSTDN network

to be pointed anywhere and stabilized to 1 arcmin accuracy, with 30 arcsec stability over one hour. A slew rate of 10 deg/min was required. The orbit was circular at 540 km altitude inclined at 22.75 deg. HEAO-B was launched on an Adas-Centaur in late 1978 and had a design life of one year. It interfaced with NASA's GSTDN S-band ground network.

Table 10-33 presents the key design decisions for configuring the two spacecraft. Weight dominated the FLTSATCOM design. The payload was large and complex, and mission-reliability goals required complete payload redundancy. The Atlas-Centaur's launch capability limited the weight, thus requiring tight weight control. Because the FLTSATCOM payload required over 1,000 W, designers selected an oriented planar solar array. The Adas-Centaur's fairing diameter also limited the spacecraft's folded size. The spacecraft employs two attitude-control modes: spin stabilization for orbit injection and 3-axis stabilization for on-orbit .control. All communication components are body-fixed, and the body is controlled to point the antennas toward nadir. A planar solar array is articulated about one axis to point toward the Sun. Liquid-hydrazine propulsion provides attitude and orbit control; a solid apogee kick motor injected the spacecraft into orbit.

TABLE 10-33. Initial Design Decisions for FLTSATCOM and HEAO-B (See Table 104).

Design Aspect

FLTSATCOM Design Approach

HEAO-B Design Approach

Spacecraft Weight and Power

Dominated by heavy weight and high-power payload; constrained by booster capability

Large margins established Initially; not tightly constrained by booster capability

Spacecraft Size

Folded configuration limited by fairing; deployed configuration dominated by antenna size and solar array area

Folded configuration Dmlted by fairing diameter; large déployables not required

Attitude Control Approach

Spin stabilization for kick motor firing; 3-axis control on orbit

3-axis control used to provide precision

Solar Array Approach

Planar-oriented array

Planar body-fixed array

Kick Stage Use

Solid AKM used for orbit Insertion

Not required

Propulsion Appmach

Liquid hydrazine thrusters used for attitudel

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