LADEE Mission Lunar Atmosphere and Dust Environment Explorer LDEX

1. LADEE MissionLunar Atmosphere and Dust Environment ExplorerLDEX Payload Accommodation Study (PAS) 5/14/09

2. Payload Accommodation Study 1. Instrument Description 2. Driving Instrument Interfaces • Electrical Power Interface • Command and Data interfaces • Software Interfaces • Mechanical Interfaces (mass & CG) • Thermal Interfaces 3. Instrument FOV Requirements 4. Driving Environmental Interfaces (inc. radiation, contamination, EMI) 5. Driving Operational Requirements • OPS Concept (including instrument modes, etc) • Operational Constraints 6. Programmatic Requirements • Schedule (including payload I&T and System I&T support) 7. Potential Trade Studies:

3. 1. Instrument Description • Electronics and detector packaged in the same ‘box’ with the c.g. approximately in the geometric center

4. 1. Instrument Description • LDEX detects dust particle impacts over an aperture of approximately 100 cm2 • LDEX determines the mass of individual particles with radii ~ 0.3 < r < 5 mm • LDEX sets an upper limit for the number density of particles with radii ~0.1 < r < ~0.3 mm • LDEX measures the charge generated by dust impacts • The aperture must point within 5° of ram direction for primary science • Measurements are not possible when sun is in the UV FOV (damage to instrument if HV is on)

5. 2. Driving Instrument Interfaces • Electrical Power Interface • Command and Data Interfaces • Software Interfaces • Mechanical Interfaces (mass & CG) • Thermal Interfaces

6. 2a) Electrical Power Interface

7. 2b) Command & Data Interfaces • Asynchronous RS-422 • One Hertz Pulse (separate lines to instrument) for time sync • 33.6 kbps will allow full-resolution science data during I&T and any other opportunities during mission • 57.6 kbps also acceptable • Telemetry rates • 1000 bits/sec (science mode) • 300 bits/sec (standby mode) • 5.2 million bits/orbit • Assuming 65% science and 35% standby for a 113 min orbit

8. 2c) Software Interfaces • Will need time synchronization signal from S/C • Need to understand plan for spacecraft clock to design LDEX telemetry processing system – UTC, MET, other? • A “sun in FOV” warning message from S/C is desired to protect the instrument if stored commands run out • Instrument has built-in sun detection and autonomous switch to safe mode when sun in UV FOV as a backup • Return to science mode only via ground command • We have a strong preference to use CCSDS TC and Telemetry Packets to simplify the interface to the S/C • Allows reuse of existing ground and operations software • S/C will not have to do any manipulation (compression, etc) on the LDEX telemetry data

9. 2d) Mechanical Interfaces

10. 2e) Thermal Interfaces • LDEX will be thermally isolated from S/C bus using passive thermal design to stay within instrument operating temperature range under nominal (powered) conditions • A thermostatically controlled survival heater (separate power line from S/C) will be used to maintain the instrument within its survival temperature range

11. 3) Instrument FOV Requirements • Primary concern is to prevent, as much as possible, UV reflections from the lunar surface from entering LDEX aperture, which has a 60° half-cone UV FOV • Minimum required dust FOV for science is simply the aperture area extended to infinity • Required pointing: normal to ram +/- 5 deg • Pointing knowledge (from post-processing) +/- 1 deg

12. 4. Driving Environmental Interfaces • Nominal Launch Environment • Vibration, shock, acoustics: need environment description to complete the design • Nominal Space Environment • Radiation, charging: need environment description to complete the design • I&T Environment • Cleanliness • Contaminants on impact target surface can degrade UV rejection • Aperture cover provides mitigation (also helps with purging, described below) • Humidity • MCP can be damaged by water vapor • Instrument maintained under N2 purge except for brief durations (tests, whenever precluded by S/C movement, etc) • Will be an issue during encapsulation in LV fairing • See Trade Studies slide for more details

13. 5. Driving Operational Requirements • LDEX cannot be pointed at the sun while in science mode (HV ON) • Planning should schedule commands to revert to standby mode when the sun is predicted to be within 5° (TBR) of the UV FOV • Therefore, LDEX data rate will probably (depending on orbit b angle) be reduced when LADEE crosses the night-to-day terminator and for some time after that (again, depending on orbit properties) • Instrument detects when the sun is in the FOV and protects itself from accidental sun pointing • Request the S/C to alert instrument within 5 sec of a sun pointing event (if feasible) • Instrument would like to be powered and in science mode as much as possible, even when not pointed in ram direction (useful science data can be acquired in most orientations)

14. 6. Programmatic Requirements • TBD

15. 7. Potential Trade Studies • Deployable aperture cover for contaminant and water vapor protection • Status: hinged, spring-driven, one-time actuation aperture cover is now included in mechanical design • Mass and cost included in instrument lien list • MCP and/or target heater for contamination mitigation • Status: under investigation • T-0 (flyaway) purge would aid contamination mitigation and risk of MCP damage during launch activities • Status: under investigation at mission level • Techniques to safe instrument when sun in aperture • Status: under investigation to determine if S/C can provide an HV-OFF command if Sun nears LDEX FOV

16. Backup Slides …