Seminar BELA STAR SIMULATOR

Transcription

1 Seminar BELA STAR SIMULATOR Sumita Chakraborty, Michael Affolter, Jakob Neubert (external contractor), Stefan Graf, Daniele Piazza and many more Universität Bern

2 Content > Mercury > BepiColombo > MPO and BELA > Star simulator Lab setup Receiver and Transmitter co-alignment Planetary Background Straylight 2

3 Mercury > Highly cratered surface (moon like) > High density iron > 3:2 resonance tidal flexing > Recent evidence for volcanism from MESSENGER (Head et al. 2009; Prockter et al., 2010) > Difficult to observe from Earth > Until today only 2 missions to Mercury: > Mariner 10 (flyby) > MESSENGER (orbit insertion 2011) ½ day 2 days 2 ½ days 1 day 3 days 1 ½ days 3

4 Bepi Colombo Why a mission to Mercury? Many unsolved questions: > How did Mercury form? > Why is the mean iron density higher than on Earth? > Characterization of surface geology > Characterization of interior structure > Surface composition > Surface age crater counting > What is the origin of the magnetic field? > Origin, composition and structure of Mercury s exosphere 4

5 Bepi Colombo > Launch: > Journey: 6 years, nominal mission: 1 Earth year ( 5 Mercury years) Flyby at the Moon, Earth and Mercury > The Bepi Colombo mission consists in two orbiters : Mercury Planetary Orbiter (MPO) From ESA, focused on planetary remote sensing Mercury Magnetospheric Orbiter (MMO) From JAXA, focused on magnetic field and plasma studies The Mercury Transfer Module (MTM) provides power and propulsion for the journey to Mercury. 5

6 Mercury Magnetospheric Orbiter MOSIF Mercury Planetary Orbiter Mercury transfer module 6

7 MPO Mercury Planetary Orbiter > Minimum distance to Mercury: 400km > Maximal distance to Mercury: 1 500km > Orbital period: 2.32h > Nadir pointing: The same side of the spacecraft is always facing the surface of Mercury Mercury Mercury orbit Sun Spacecraft orbit 7

8 List of Instruments on MPO BELA ISA MERMAG MERTIS MGNS MIXS MORE PHEBUS SERENA SIMBIO-SYS SIXS Laser Altimeter Accelerometer Magnetometer Thermal IR Spectrometer Gamma ray and neutron Spectrometer X-ray Spectrometer Radio Science Experiment UV Spectroscopy Neutral and ionised particle analyzer Camera and IR Spectrometer X-ray Spectrometer 8

9 BELA Bepi Colombo Laser Altimeter BELA is measuring: > The topography of the planet surface < 1m range resolution > Tidal deformation of the surface > Roughness variation > Slope variation > Active albedo measurements at = 1micrometer Are there ices inside permanently shaded craters near the poles? 9

10 BELA Bepi Colombo Laser Altimeter One goal of the experiment is to obtain a profile of Mercury s surface. This is done with a Laser Altimeter. Laser Altimeter h =1/2c t Surface 10

11 BELA Signal from the detector T From Kilian s PhD thesis 11

12 BELA Track on Mercury surface Example from MLA/MESSENGER Zuber et al.,

13 BELA - Transmitter part: Laser > Nd:YAG Laser (1064nm) > Energy : 50mJ > Pulse width: 5.5ns (FWHM) > Pulse rate : 10Hz > Divergence : 60 rad (0.003 ) Spot diameter on Mercury between 24m and 66m 10MW 13

14 BELA - Receiver part Telescope Avalanche Photodiode Focal length = 1 250mm One pixel with diameter = 0.8mm The field of view of the receiver is maximal ±320 rad (±0.018 ). 14

15 BELA - Laser footprint and Field of View of the telescope 24 m 260 m 133 rad of movement is allowed. The position of the transmitter and the receiver may move. What are the errors? 15

16 BELA Alignment error sources In flight > SC moves during the travel time of the laser light aberation angle depending the height of the SC > Offset between Tx and Rx in absence of gravity > Thermal gradient (inside spacecraft: -20 C to +50 C) 73 rad On ground > Mounting errors 60 rad (Tx vs. Rx) Knowledge of the mounting error 10 rad (goal) 16

17 Star simulator > Co-alignment Transmitter (laser) to receiver (telescope) > Measurement of mounting error to an accuracy of 10 rad > Simulation of planetary background > Straylight measurement Laser Off axis parabola Telescope Light source and detector 17

18 Setup of the lab Fiber to focus CCD Linearity Wave front test Fiber to focus of off axis parabola with Shack-Hartmann Wavefront sensor (iterative process) Flat mirror Fiber exit Wave front sensor RMS = 2.6 mu RMS = 0.04 mu 18

19 Setup of the lab Fiber to focus CCD Linearity Wave front test CCD in focus Flat mirror CCD Diffraction limited spot (resolution of the optimal optical system): f Airy _ radius d m 19

20 Setup of the lab Fiber to focus CCD Linearity Wave front test Verification of tilt angle measurement linearity Flat mirror Autocollimator CCD x f tan The effective focal length is not constant! 20

21 deviation of the effective focal length [mm] Star simulator Effective focal length f eff f off axis decenter [mm] 21

22 Setup of the lab Fiber to focus CCD Linearity Wave front test Analyzing the test wavefront fiber collimator travelling pentaprism (oversized) cw laser diode monomode fiber Y large folding mirror X Z beamsplitter CCD paraboloid 22

23 Co-alignment of Transmitter and Receiver > Alignment of Receiver line of sight to zero tilt angle > Alignment of Laser to Receiver line of sight Laser Off axis parabola Telescope Light source and detector Beamsplitter and attenuator 23

24 Attenuation glass and coating Window glass Corning 24

25 Beam splitter and attenuator Beam trap 1:1 beam splitter Light source Tx beam attenuator Beam trap detector R = 1064nm R > 635nm 25

26 Prisma group With this setup it will be possible to align the laser and the telescope within the requirements. 26

27 Other test in Star simulator-planetary Background simulation laser telescope 27

28 Flux [W/m 2 ] Star simulator Other test in Star simulator-planetary Background simulation Heat flux along spacecraft orbit. Mercury is at perihelion. Time from periapsis [s] Two tests, one for the flux and one for the spectrum 28

29 Other test in Starsimulator-Planetary Background simulation 29

30 Other test in Starsimulator-Planetary Background simulation LED s or cw Nd:YAG Diffuser mask Diffuser, integrating sphere Off axis parabola Monomode fiber Lense Mulitmode fiber Planetary background mirror Laser spot on Mercury 30

31 Other test in Star simulator-straylight Aphelion: =38.9 Perihelion: 51.6 Mercury Detector on y-z table Turning table Off axis parabola Integrating sphere 31

32 Other test in Star simulator-straylight Requirement: Straylight < 1% 32

33 Results of Straylight test 1.00E % 5.00E E % 3.00E E E E % 1.50E E E E+00 33

34 Conclusions and future work > Design of the lab is done and proved on paper > Now we will start building and assembling > Assembly should be done by 2011 > EQM delivery to ESA in January

35 END THANK YOU! 35

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