上海天文台 Shanghai Astronomical Observatory CVN in Chang’e-3 lunar exploration mission ZHENG Weimin Shanghai Astronomical Observatory, Chinese Academy of Sciences 3rd International VLBI Technology Workshop Nov 11, 2014, Groningen, Netherlands

上海天文台 Shanghai Astronomical Observatory 2 1.Chang’E-3 overview 2.CVN in Chang’E-3 mission 3.Orbit and position determination 4.Summary Outline

上海天文台 Shanghai Astronomical Observatory 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

上海天文台 Shanghai Astronomical Observatory CE-1 established CVN Infrastructure CVN near real-time data flow in CE-1

上海天文台 Shanghai Astronomical Observatory 5 CE-1 CE-2 A. Direct insertion of the 100km lunar orbit after braking New Challenge of CE-3 mission CE-1 CE-2

上海天文台 Shanghai Astronomical Observatory 6 B. Powered descent procedure

上海天文台 Shanghai Astronomical Observatory 7 C. Lander and rover moon surface positioning

上海天文台 Shanghai Astronomical Observatory 8 1.Chang’E-3 overview 2.CVN in Chang’E-3 mission 3.Orbit and position determination 4.Summary Outline

上海天文台 Shanghai Astronomical Observatory New Requirements & techniques of CVN 1.High accuracy 2.Real time ability 3.Accurate Moon surface positioning ( X band ΔDOR ) DOR – Differential of One-way Range ( e-VLBI + real time data process ) ( SBI ) SBI – Same Beam VLBI

上海天文台 Shanghai Astronomical Observatory Mission Requirements on VLBI 1.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) 2.Lunar surface working phase  Lander & Rover tracking by SBI  Lander 3D position <1km (Actuality <100m )  Rover relative position of the lander <500m (Actuality ~1m )

上海天文台 Shanghai Astronomical Observatory 11 CVN upgrade 1.New VLBI data center 2.Shanghai Tianma 65m radio telescope 3.New X-band receiver & digital terminal

上海天文台 Shanghai Astronomical Observatory ΔDOR improves VLBI delay precision Kroger et al Five-minute scan sequence: Quasar-CE3-Quasar-CE3 Angular distance between CE-3 and Quasar < 10° Remove media & system errors

上海天文台 Shanghai Astronomical Observatory 13 CE-3 DOR Spectrum Frequency span = 38.4MHz, X band

上海天文台 Shanghai Astronomical Observatory CVN data center structure

上海天文台 Shanghai Astronomical Observatory Realtime VLBI 15 Processing time distribution plan ：

上海天文台 Shanghai Astronomical Observatory Actual data turn around is 15~40 seconds

上海天文台 Shanghai Astronomical Observatory Residual statistics  VLBI group delay residuals ： ~ 1ns in trans-lunar orbit ~ 0.5ns in lunar orbit.

上海天文台 Shanghai Astronomical Observatory 18 1.Chang’E-3 overview 2.CVN in Chang’E-3 mission 3.Orbit and position determination 4.Summary Outline

上海天文台 Shanghai Astronomical Observatory  100×100km circumlunar orbit accuracy: 20m  100×15km circumlunar orbit :30m  Descent trajectory: < 100m Orbit determination results 19

上海天文台 Shanghai Astronomical Observatory Position determination results 20 Long. (°)Lat. (°) Elev. (m) VLBI NASA Position Difference 17m 24m8m  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

上海天文台 Shanghai Astronomical Observatory 21 Rover positioning by same-beam VLBI 1.VLBI group delay, near real time 2.VLBI Same beam phase reference image, postprocess 3.VLBI phase delay, postprocess

上海天文台 Shanghai Astronomical Observatory Null test by same beam phase reference image positioning Local coordinateNorthEastDownDistance Same-beam phase- referencing VLBI result True value Differences Null test error: ~ 0.6 m

上海天文台 Shanghai Astronomical Observatory Rover A B C D E E17

上海天文台 Shanghai Astronomical Observatory Rover position （ 4 ways ） Site Visual/ Inertial navigation VLBI group delay VLBI phase delay VLBI phase reference map A N E B N E C N E D N E E N m E E17 N-11.83/ / E-13.05/ /

上海天文台 Shanghai Astronomical Observatory 25 1.Chang’E-3 overview 2.CVN in Chang’E-3 mission 3.Orbit and position determination 4.Summary Outline

上海天文台 Shanghai Astronomical Observatory 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.

上海天文台 Shanghai Astronomical Observatory Thank you for your attention!