Spacecraft Systems Henry Heetderks Space Sciences Laboratory, UCB

2 SNAP CD0 January, 2001 System Engineering H. Heetderks System Electrical Block Diagram

3 SNAP CD0 January, 2001 System Engineering H. Heetderks Observatory Mechanical Layout EXPLODED VIEW

4 SNAP CD0 January, 2001 System Engineering H. Heetderks Baseline Spacecraft Configuration 3-axis stabilized, 4 Reaction wheels, IRUs, no torquer bar Sun side w/ rigid body mounted solar arrays & anti-sun side w/ radiators Standard Hydrazine propulsion system, 5 N thrusters, ~150 kg total propellant required: 50 kg for attitude and station keeping, 100 kg for disposal 5.6 Tbits SSR, storage for science data. (Avg. data rate ~40 Mbps; 300Mbps downlink). Ka band 300 Mbps to Berkeley and Perth Gimbaled.5m Ka band HGA; S-band omnis; S-Band T&C thru omni antennas

5 SNAP CD0 January, 2001 System Engineering H. Heetderks Pointing Accuracy »Yaw & Pitch : 1 arc-sec (1  ) »Boresight Roll:100 arc-sec (1  ) Attitude Knowledge »Yaw & Pitch :0.02 arc-sec (1  ) »Boresight Roll:2 arc-sec (1  ) Jitter/Stability -Stellar (over 200 sec) »Yaw & Pitch :0.02 arc-sec (1  ) »Boresight Roll:2 arc-sec (1  ) Sun Avoidance Earth Avoidance Moon Avoidance ACS Driving Requirements

6 SNAP CD0 January, 2001 System Engineering H. Heetderks ACS Component Recommendation --Fine pointing is achieved by taking guide star data from the instrument telescope

7 SNAP CD0 January, 2001 System Engineering H. Heetderks Electrical Power System Selected Configuration Solar Array. Selected 2.47 M 2 solar array area using Triple Junction Gallium Arsinide (TJGaAs) solar cells to reduce solar array area and weight. MAP type PSE. This PSE can be adapted easily for the study phase. Battery. NiH2 IPV (individual Pressure Vessel) at 100 ah this is a EPT stock item SAR Note a EPT SAR may also work. The mass of either of these batteries is 81 kg and further search for NiH2 SPV’s (Single Pressure Vessel) and development of large ampere hour LiIon batteries could provide a mass savings.

8 SNAP CD0 January, 2001 System Engineering H. Heetderks Transponder & Antenna Selected Configuration Ka-Band —Gimbaled 0.5m antenna antenna movement does not overlap with science data taking Beamwidth of 1 deg is large enough to provide adequate coverage without movement during observation periods (will stay close enough to main beam so as not to degrade the link) —Ka-Band modulators(2)-modification to existing L3 X Band transmitter —Data rate = 300 Mbps continuous (includes science, Hskpg, CCSDS & R/S encoding) S-Band —Omni antennas —Transponders(2) —Command rate = 2 Kbps —Telemetry rate = 1 Kbps

9 SNAP CD0 January, 2001 System Engineering H. Heetderks Transponder Selected Configuration Observatory Control Unit S-Band XPNDR OMNI 1 OMNI 2 CMD/TLM Science HGA S-Band XPNDR Hybrid K-Band Modulator(2) Diplexer K-Band Amplifier(2) Switch

10 SNAP CD0 January, 2001 System Engineering H. Heetderks SNAP Ka-Band 10 M Downlink (300 Mbps)

11 SNAP CD0 January, 2001 System Engineering H. Heetderks SNAP Propulsion System F/D Valve N2H4 Tanks w/ AFE-332 or PMD Pressure Transduc er P Filt er Latching Isolation Valve LVLV LVLV Primary & Redundant 22 N Thrusters with Dual Seat Valves SNAP N2H4 PROPULSION SYSTEM N2H4 Propulsion System Design N2H4 mass (10% contingency) = 130 kg “Dry” mass (4 Tank Design) = 34.1 kg Three 48.3 cm dia tanks with AFE- 332 elastomer diaphragm Primary & Redundant set of 22N thrusters mounted on –X axis & canted 15 o off X-axis Orbit Ave Power D.C.) = 23 W Catalyst Bed + Thruster Power (During Firing) = 10.2 W per thruster 15 o XY ZZ

12 SNAP CD0 January, 2001 System Engineering H. Heetderks SNAP Propulsion System

13 SNAP CD0 January, 2001 System Engineering H. Heetderks Preliminary Bus Subsystems Mass [kg] Bus Structure (Custom to accommodate instrument) Payload Mount 9.0 Antenna support30.0 ACS50.0 S/C Processor12.0 Power Electronics15.0 Battery81.2 Solar Arrays10.5 Thermal Hardware67.0 RF Communications53.0 Bus Harness 8.0 Separation System, spacecraft side 8.0 Bus Subsystems Total 486.7