PROMOTING A LOW FREQUENCY RADIO OBSERVATORY IN THE

PROMOTING A LOW FREQUENCY RADIO OBSERVATORY IN THE LUNAR SPACE J. S. Ping 1, Y. C. Ji 2, M. H. Huang 1, Y. H. Yan 1, G. Y. Fang 2, M. Zhang 1, M. Y. Wang 1, L. J. Chen 1, H. B. Zhang 1, C. L. Li 1, & X. L. Chen 1 1 National Astronomical Observatories of CAS, Beijing, China, jsping@bao. ac. cn, 2 Electronic Institute of CAS, Beijing, China.

CHANG’E-4 Lunar Mission The Chang’E 4 explorer is a mission to the lunar far side which will be designed, manufactured, assembled, integrated and tested by CNSA. The mission includes a relay satellite orbiting the Earth-Moon L 2 point, a lunar lander and a lunar rover. The Chang’E 4 explorer will be launched by Chinese carrier Long March rocket at China's satellite launch center. The relay satellite will operate in the orbit around the Earth-Moon Lagrange point L 2, the lander and rover will be landed on the far side of the Moon. The Chang’E 4 mission will be launched between 2018 and 2019. Lander & Rover_back up of CE-3 Relay Communication Satellite

Chang’E-4 lander mission tracking link: Embedded 2 -way in 4 -way to save hardware Carriers (S/X) and software resource onboard. L 2 Point ~65 KKM TT&C stations 4 -way link between the Earth tracking station, Relay S/C and lander was established with S-band/X-band signals.

Low Frequency Spectrometer on lunar far-side lander of CE-4 After ~10 years preparation of a radio astronomical team from National Astronomical Observatory of Chinese Academy of Science, a very low frequency radio astronomical detector will be settled on the far side surface of the Moon[1], in Chinese Chang’E-4 lunar lander mission. The 3 monopole detector of 5 meter long each will mainly investigate the type II and type III solar burst, and will also to investigate the possible lunar ionosphere above the landing site[2], by means of taking the advantage of radio quiet environment of lunar far side. Figure 1 shows the concept of the lander with radio astronomical payload. Similar antenna will be set on board the relay satellite.

Fig. 1 Three monopole HF antenna onboard lander And on board relay satellite To the Earth To the Lunar Lander Low frequency radio astronomical detector will be firstly settled on the far side surface of the Moon to detect the solar burst, and to investigate the lunar ionosphere. Additionally, it will be tested technically as a pathfinder mission for the future lunar surface low frequency radio observatory.

1. Scientific Objectives Exploration：（1）Solar radio burst exploration at HF & MF; Type II, Type III, CME event （2）Lunar plasma environment exploration; lunar ionosphere, exosphere （3）Space low frequency exploration beyond the Sun Due to the absorption by the Earth’s ionosphere and hampered by the man-made low frequency signals (RFI), the radio sky below ~15 MHz cannot be viewed from earthbased facilities. In fact, up to date the range from several k. Hz to 15 -30 MHz remains the least explored electromagnetic frequency range and is expected to conceal many scientific discoveries. Hence, the future advent in radio astronomy is expected by the realization of low-frequency radio space-based facilities to open up this frequency domain for astronomical exploration.

Solar Burst Solar radio burst may cover whole radio spectrum, with strong CME event. Low frequency spectrometer may track the CME travelling from the outside solar corona to 2 AU，may supply more information of the CME structure and dynamics.

Lunar Ionosphere Lunar plasma environment above the surface has been still an open question. Luna-19 and 22 obtained several profiles in 1970 s, SELENE have more after 40 years. A dawn exosphere of dust may contribute of 80% of the possible lunar ionosphere. This sphere may block the radio wave below 1 MHz. Low frequency spectrometer may have chance to do in-situ observation during the solar burst observation. Dr. Mingyuan Wang (in this meeting) also found the similar phenomeonen.

2 History in China Ø 1990 s, BAO/CAS suggested HF payload on geo-satellite; Ø 2001，Using a ballon SST platform, a pre-research being carried out to study the CME at 1 -30 MHz，HF imager for space radio astronomy was suggested by NAOC/CAS. Ø 2008, under the support of national 863 S&T project，IER/CAS developed test mode of low frequency explorer for 10 KHz～ 25 MHz, based on this work, a lunar surface HF radio receiver was suggested to work at 0. 1～ 30 MHz band, in early CE missions.

2 History out of CHina Space HF study started from 1960~70，for example, the 3 JIEKTPOH-2和-4，RAE-1，RAE-2，WIND，Ulysses missions. Ø Outstanding mission in 1990 s：（1）WIND/Waves（launched in 1994）： 2 bands： ØRAD 1： 20 k. Hz~1. 04 MHz，256 ch of 3 k. Hz for each； ØRAD 2： 1. 075~13. 825 MHz，256 ch of 20 k. Hz for each （2）STEREO /SWAVES（launched in 2006）： 3 bands： HFR： 40 k. Hz-16 MHz； LFRIo： 10 -40 k. Hz； FFR： 50 MHz。 Ø 1997~ pre-researches for lunar far-side HF astronomy a round the world (NASA, ESA, ISAS) STEREO

3 Technical requirements 3. 1 Operations ØReceive solar and cosmic HF & MF radio signal, recorde the real-time ADC raw data; ØReal-time spectra analyzing on-board, and record the spectra information； Options: Ø analysis the radio wave direction and polarization； ØVLBI between lander and relay satellite ?

3. 2 specifications items index others Freq. 100 k. Hz~40 MHz Below and above 1 MHz， two bands Dynamical range ≥ 75 d. B sensitivity ≤ -75 d. Bm antenna Three mono-pole polarization all pointing ~2° Data rate ~100 kbps mass ≤ 14 kg Average power ≤ 15 W Life Time 6 months 4000~5000 mm Including E-box Launch in early 2019

4 Principle design Lunar low frequency spectrometer will use three monopole antenna to detect the cosmic radio signal. Receiver will be developed with the design of software. From the observations of three antenna, the direction, power, spectrum, polarization and their time variations can be retrieved.

LNA and E-box Independent E-box in side the lander， 280 mm× 160 mm× 22 mm； 3 LNA near the 3 antenna，100 mm× 30 mm for each。 E-Box LNA position

Lander and Satellite VLBI ? Ø Lander part； Ø Relay satellite； Ø Payloads are designed for VLBI and other joint observations. 1~5 s time synchronization To UTC for lander USO on lander: Stability 10 -12（~100 s）， Mean distance R=~63000 km Draft 10 -10（/day）。 5~50 ms or worse time synchronization To UTC for satellite

VLBI is suggested to be done with LOFA array VLBI principle of correlatoin: local frequency standard on lander: USO Stability 10 -12（~100 s）， Draft 10 -10（/day）。

4 -Way Link in Chang’E-4 Mission FIG. 2 4 -way & 2 -way radio link For tracking and communication In Chang’E-4 Mission PLLs will be used at all transponders With the possible 4 -way link, lander positioning and POD of relay satellite can be done at the same time. After that, with the relay communication link, a reasonable time synchronization can be carried out.

5 Communication and storage ü Using 1553 B bus pipe to communicate with onboard data sub-system, obtain commander and system parameters; ü Using LVDS pipe line to send the data to lander HDD (rather than data sub-system) for real-time tag of lander, and for using the 25 Gbits HDD of lander. References: [1]Zhang M. , (2014) Ph. D. Thesis, [2]Wang M. et al. , (2016) this meeting. [3]Vyshlov A. S. (1976) Spacecraft, Space Res. , 16, 945 -949. [4]Wolt M. W. et al. , (2016) this meeting. [5] Barrow C. H. et al. (1999) A&Ap. 344, 1001– 1013.

SUMMARY • Preliminary design is being reviewed now; • Electrical property mode will be assembled and tested since later of 2016; • Critical design will be reviewed after the test in 2016. • Flight mode will be assembled and tested in early 2018. Acknowledgement: This study is supported by a NSFC grant (No. 41590851), by the National Key Basic Research and Development Plan (Grant No. 2015 CB 857101), and by the State Key Laboratory of Astronautic Dynamics and by Chinese Chang’E-4 exploration lunar project.

Спасибо! 谢谢！ Thank You!