High resolution middle infrared spectrometer, a part of Atmospheric Chemistry Suite (ACS) for ExoMars 2016 Trace Gas Orbiter

Transcription

1 High resolution middle infrared spectrometer, a part of Atmospheric Chemistry Suite (ACS) for ExoMars 2016 Trace Gas Orbiter Alexander Trokhimovskiy, Oleg Korablev and ACS team Space Research Institute (IKI), Moscow, Russia ICSO 2014

2 Launch in 2016 Trace Gas Orbiter ExoMars EDL Demonstrator Module (EDM) The Rover Launch in 2018 Landing Platform

3 ExoMars TGO mission phases and timing Launch window 7-27/1/2016 Near Earth Commissioning Cruise Phase L + up to 1 month Approx 250 days EDM release and Mars orbit insertion 19/10/2016 Aerobraking into 400-km circular orbit On-orbit commissioning Science Operations Beginning of Relay Phase Approx 230 days Approx 2 weeks 1 Martian Year From ~July 2017 (MY34, Ls=30) January 2019 (rover arrival) End of Mission 31/12/2022

4 TGO operational orbit near-polar 400-km altitude circular orbit, with an inclination of 74 T ~ 2 hr orbital period 12 orbits per day 12 sunrises and 12 sunsets 24 occultation s per day 72 s 100 km

5 Space Research Institute(IKI) NOMAD High resolution occultation and nadir spectrometers Atmospheric composition (CH 4,O 3, trace species, isotopes) dust, clouds, P&T profiles TGO science instruments (since 2011) UVIS ( mm) l/dl ~ 250 SO Limb Nadir IR ( mm) l/dl ~ 10,000 SO Limb Nadir IR ( mm) l/dl ~ 20,000 SO CaSSIS High-resolution camera Mapping of sources; landing site selection ACS Suite of 3 high-resolution spectrometers Atmospheric chemistry, aerosols, surface T, structure Near IR ( mm) l/dl ~ 20,000 SO Limb Nadir IR (Fourier, 2 25 mm) l/dl ~ 4000 (SO)/500 (N) Mid IR ( mm) l/dl ~ 50,000 SO Nadir SO FREND Collimated neutron detector Mapping of subsurface water All resolving power figures l/dl are calculated at mid-range

6 ACS Atmospheric chemistry, aerosols, surface T, structure Atmospheric Chemistry Suite Set of 3 high-resolution spectrometers Near IR (Echelle+AOTF, mm) l/dl ~ 20,000 SO Limb Nadir IR (Fourier, 2 25 mm) l/dl ~ 4000 (SO)/500 (N) SO Nadir Mid IR (Cross dispersion, mm) l/dl ~ 50,000 SO

7 ATMOSPHERIC CHEMISTRY SUITE (ACS)

8 MIR: Mid-IR Echelle/cross-dispersion Spectral range: μm Instantaneous coverage: nm ranges per measurement Spectral resolving power: > FOV: 0.1 x 2.9 mrad Aperture ratio 1:3 Mass/ Power / Data: 12 kg / 20 W / 1.2 Gbit per day Size 460 x 200 x 440 mm Operation modes: Solar Occultation Operation rate 1-2 images/s S/N >500

9 MIR spectrometer High spectral resolution ~ SNR >500 Vertical resolution in SO ~5 km sec for measurements 1-2 position of secondary grating angle 72 sec for occultation km in the atmosphere CO 2 measurements for density and temperature from 10 to at least 140 km Known species CH 4, H 2 O, СО at km Isotopic ratios HDO/H 2 O, 13 CO 2 /CO 2, CO 18 O/CO 2 etc. Search of minor gaseous species С 2 H 2, С 2 H 4, С 2 H 6, SO 2, HO 2, H 2 O 2, H 2 CO, HCl, OCS etc.

10 MIR / occultations CH 4 measurements Ground-based observations Variable values from 0 to 30 ppb Krasnopolsky et al. (2004, 2007, 2011), Mumma et al., 2009, Villanueva et al. (2013) PFS on MEX: 10 ppb Formisano et al. (2004); Geminale et al. (2011) TLS on Curiosity: 0.18 ±0.67 ppbv corresponding to an upper limit of only 1.3 ppbv Webster et al. (2013) Future instruments: NOMAD on TGO MIR-ACS on TGO the orders between µm (secondary grating angle=53.6 ) The detection limit is better than 0.3 ppb for target altitude of 20 km (without averaging) CH 4 10 ppb at 20 km

11 A simplified optical scheme of the MIR channel. 1, 3- folding mirrors; 2- entry telescope; 4- slit; collimator of the main spectrometer: 5- primary mirror, 6- secondary mirror, 7- echelle diffraction grating, 8 folding convex, 9- collimator of the secondary grating; 10- two steerable secondary gratings; detector s focusing lenses; 14- cold filter; 15- detector array. Not shown entry filter and periscope mirror

12 MIR key components AMOS custom echelle grating 3 gr/mm Blaze angle Dimensions 107 x 240 mm Gold coating Sofradir Scorpio MW detector 640 x 512 HgCdTe MWIR (15 μm PITCH) Mechanical cooler RICOR K508 adapted for operation in space custom band-pass filter μm Rotating unit NIIKI Diamond turning aspherical mirrors collimator ZnSe and CaF2 optics

13 AMOS custom echelle grating 3 gr/mm Blaze angle Dimensions 107 x 240 mm Gold coating Diffraction orders SFE

14 MIR rotating unit NPP «Astron Electronics» Stepper motor Phytron VSS ,6-High Vacuum Two secondary cross-dispersion diffraction gratings (180 and 361 gr/mm) 1,8 0 step 100 ms per position change

15 Mechanical design (pic of not flight, but close to it)

16 0,5 sec per position MIR spectral coverage position Relative angle Grating Min wavelength Max wavelength Coverage, nm center Single frame Transmittance with absorption lines of different molecules at 22 km during occultation nm

17 Example of MIR/ACS single frame Line height mkm Order mkm Typical line spread functions Order mkm

18 Thermal noise issue Back trace analysis Cold filter 1 (detector), Mirror aperture 2 and 3 Mirror insert inside secondary grating Bright slit Controlled instrument cooling Pix and frames averaging S/N ratio on a single pix (instrument 300К) For λ = 2.3 mkm S/B 361 = 106 For λ = 4.2 mkm S/B 180 = 11 + averaging over slit height (up to 20 pix) + averaging frames (up to 32 every 0.5 s) + prior cooling (D30 К => order better S/N)

19 Current status and schedule STM being tested these hours Last flight hardware is very late, but arriving October-November March 2015 PFM ACS to be delivered for TGO integration October 2015 TGO to Baikonur

20 Current status and schedule STM being tested these hours Last flight hardware is very late, but arriving October-November March 2015 PFM ACS to be delivered for TGO integration October 2015 TGO to Baikonur Thank you!