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Explore the role of China's Lunar Exploration Program phases, CVN infrastructure, & new techniques enhancing Chang'e-3 mission accuracy. Details on orbit determination, position tracking, and CVN upgrade. Summary of key results achieved.
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CVN in Chang’e-3 lunar exploration mission ZHENG Weimin Shanghai Astronomical Observatory, Chinese Academy of Sciences3rd International VLBI Technology Workshop Nov 11, 2014, Groningen, Netherlands
Outline • Chang’E-3 overview • CVN in Chang’E-3 mission • Orbit and position determination • Summary
The China’s Lunar Exploration Program (CLEP) 3 phases: Orbiting: Chang'e 1 (CE-1), 2007 CE-2, 2010 Landing: CE-3, CE-4 (2013~2016) Sample return: CE-5T1, CE-5, CE-6 2014-2020
CE-1 established CVN Infrastructure CVN near real-time data flow in CE-1
New Challenge of CE-3 mission A. Direct insertion of the 100km lunar orbit after braking CE-1 CE-2 CE-2 CE-1
Outline • Chang’E-3 overview • CVN in Chang’E-3 mission • Orbit and position determination • Summary
New Requirements & techniques of CVN High accuracy Real time ability Accurate Moon surface positioning ( X band ΔDOR ) DOR – Differential of One-way Range ( e-VLBI + real time data process ) ( SBI ) SBI – Same Beam VLBI
Mission Requirements on VLBI • Earth-Moon transfer orbit phase & Circumlunar phase • ΔDOR tracking group delay < 4ns (Actuality <0.5ns) • Orbit & angular determination and orbit prediction; • Data processing delay < 1minute (Actuality 15~40 seconds) • Lunar surface working phase • Lander & Rover tracking by SBI • Lander 3D position <1km (Actuality <100m ) • Rover relative position of the lander<500m (Actuality ~1m )
CVN upgrade • New VLBI data center • Shanghai Tianma 65m radio telescope • New X-band receiver & digital terminal
ΔDOR improves VLBI delay precision Five-minute scan sequence: Quasar-CE3-Quasar-CE3 Angular distance between CE-3 and Quasar < 10° Remove media & system errors Kroger et al
CE-3 DOR Spectrum Frequency span = 38.4MHz, X band
Realtime VLBI Processing time distribution plan:
Residual statistics • VLBI group delay residuals: ~ 1ns in trans-lunar orbit ~ 0.5ns in lunar orbit.
Outline • Chang’E-3 overview • CVN in Chang’E-3 mission • Orbit and position determination • Summary
Orbit determination results • 100×100km circumlunar orbit accuracy: 20m • 100×15km circumlunar orbit :30m • Descent trajectory: < 100m
Position determination results • Get Lander position in 30 minutes after soft landing • 3D Lander position difference between by LRO (Lunar Reconnaissance Orbiter, NASA) and VLBI < 50m Lander Rover
Rover positioning by same-beam VLBI • VLBI group delay, near real time • VLBI Same beam phase reference image, postprocess • VLBI phase delay, postprocess
Null test by same beam phase reference image positioning Null test error: ~ 0.6 m
E17 A B C D E Rover
Outline • Chang’E-3 overview • CVN in Chang’E-3 mission • Orbit and position determination • Summary
4. Summary (1)Real-time and high accuracy VLBI has demonstrated it ability and played an important role in CE-3 Mission. (2)The lander position accuracy better than 100m. (3)The Yutu Rover relative position accuracy is ~ 1 m. (4)Fast ΔDOR and same beam VLBI hope to be used in the CE-5 rendezvous and docking and the Martian Lander / Rover tracking.