VEx – Akatsuki co-ordinated observations VMC team meeting MPS Lindau 29-30 April

Akatsuki payload overview VMC Akatsuki payload overview VIRTIS-M-VIS VIRTIS-H SPICAV Imaging at 11 wavelengths No spectrometers

Relative positions of the Akatsuki (VCO) and VEX orbits Relative positions of the Akatsuki (VCO) and VEX orbits. Inserted plot shows the orbital time range when VCO is in co-rotation with the main cloud deck super rotation.

Relative position of VEX and VCO orbits at VCO arrival ψ VCO orbit insertion: 13 December, 2010 VCO Apocenter is above the ecliptic (~10° ) Major axis of the VCO orbit is almost perpendicular to the VEX orbit plane This configuration will not change Earth VCO orbit VEX orbit N 70 Venus

Akatsuki (Planet-C) arrival

Example VEX-VCO orbit (orbit #1) Time-steps duration: 4 hours Japan GS Japan GS Japan GS CEB CEB CEB VEX: VPER -12 VEX: VPER -20 VEX: VPER -16 VCO: VPER -15 VCO: VPER -23 CEB VCO: VPER -19 CEB CEB Japan GS Japan GS Japan GS CEB CEB CEB VEX: VPER VEX: VPER -4 VEX: VPER -8 VCO: VPER -3 VCO: VPER -7 VCO: VPER -11 CEB CEB CEB

The VEX-VCO 5 day cycle Conclusions: #2 Day #1 #3 #5 #4 #1 VCO is shown in the VEX fixed frame (VEX S/C is fixed at apocentre) – 24 hour time steps. Note that VCO moves back-wards because of 24 time samples in sketch CEB Japan GS Japan GS CEB CEB Japan GS Day #1 #2 #3 CEB CEB CEB Japan GS Japan GS CEB CEB Japan GS #5 #4 #1 CEB CEB CEB Vex-VCO 5 day cycle Limitations on simultaneous observations due to downlink to 2 antennas Conclusions:

4.1 VEX-AKATSUKI CROSS-CALIBRATIONS (DAY SIDE) Scientific Rationale: Cross check of the radiometric calibration of the Venus Express and Akatsuki optical instruments is an important task for joint observations. Instruments: VEx: VMC, VIRTIS, SPICAV VCO: UVI, IR1, IR2 Geometry: This task requires specific geometry when both spacecraft observe Venus simultaneously from the same direction that ensures similar illumination conditions (see figure). Akatsuki Figure 4.1: VEx-Akatsuki cross-calibrations (Day side)

4.2 VEX-AKATSUKI CROSS-CALIBRATIONS (NIGHT SIDE) Scientific Rationale: Cross check of the radiometric calibration of the Venus Express and Akatsuki optical instruments is an important task for joint observations. Instruments: VEx: VMC, VIRTIS, SPICAV VCO: IR1, IR2 Geometry: This task requires specific geometry when both spacecraft observe Venus simultaneously from the same direction that ensures similar illumination conditions (see figure). Akatsuki Figure 4.2: VEx-Akatsuki cross-calibrations (Night side)

4.3 GLOBAL 'SNAPSHOT’ OVER LARGE RANGE OF LATITUDES (DAY SIDE) Scientific Rationale: These observations will give an instantaneous snapshot of cloud morphology and dynamics on most of the day side, ranging from the South pole all the way to Northern high latitudes (see figure) Instruments: VEx: VMC, VIRTIS VCO: UVI, IR1 Figure 4.3: Global snapshot over range of latitudes (Day side)

4.4 CONTINUOUS MONITORING OF CLOUD MOTION (DAY SIDE) Scientific Rationale: Determination of the wind field from tracking of cloud features is one of the main goals of both missions. The maximal duration of such observation is ~10 hours for Venus Express and ~20 hours for Akatsuki. Combination of both when one spacecraft starts tracking of a certain feature and the second one takes over would result in extension of observation time to ~30 hours. Instruments: VEx: VMC VCO: UVI Geometry: The figure shows the sequence that starts with VCO observations for ~20 hours (red arc A-B-C), and when the feature disappears from the VCO field of view (point C) Venus Express takes over and continues observations for another 10 hours until point D. Akatsuki Figure 4.4: Global snapshot over range of latitudesContinuous monitioring of cloud motion (Day side)

4.5 SIMULTANEOUS IMAGING AT DIFFERENT SPATIAL RESOLUTIONS (DAY SIDE) Scientific Rationale: Akatsuki provides global views of low-latitude regions; on the other hand, Venus Express is always close to the planet when it observes low-latitude regions and thus provides high-spatial resolution imagery (roughly one order of magnitude higher spatial resolution). Akatsuki will provide context imaging for Venus Express high resolution images. Instruments: VEx: VMC, [VIRTIS] VCO: UVI, IR1, IR2 Geometry: Figure 4.5: Simultaneous imaging at different spatial resolution (Day side)

4.6 SIMULTANEOUS IMAGING AND SPECTROSCOPY (DAY SIDE) Scientific Rationale: VCO will track cloud-top features on the dayside using UVI and LIR cameras. Venus Express can provide spectra of the objects being tracked, using VIRTIS-M-VIS, VIRTIS-H, and/or SPICAV. This allows study of both the microphysical properties of the cloud and its evolution through time. In particular, VIRTIS-H spectra can be used to validate the cloud-top height retrieval made with Akatsuki IR2. Instruments: VEx: VIRTIS, SPICAV VCO: UVI, IR2, LIR Geometry: Dayside. Venus Express should follow a cloud feature which is in the VCO field of view.(Cloud feature should be assumed to move westwards with a velocity of 100 m/s, as it is the upper cloud being observed in this observation). Figure 4.6: Simultaneous imaging and spectroscopy (Day side)

4.7 SIMULTANEOUS IMAGING AND SPECTROSCOPY (NIGHT SIDE) Scientific Rationale: Akatsuki will use 2.26 and 2.32 um filters to map CO below the clouds. VIRTIS-H and SPICAV spectrometers can be used to measure spectra of these emissions, to help validate the VCO retrievals of CO abundances. Instruments: VEx: VIRTIS, SPICAV VCO: IR2 Geometry: Nightside. Venus Express pointing should follow a cloud feature which is in the VCO field of view. (Cloud feature should be assumed to move westwards with a velocity of 60 m/s, as it the lower cloud which is being observed in this observation) Figure 4.7: Simultaneous imaging and spectroscopy (Night side)

4.8 SIMULTANEOUS IMAGING ON THE NIGHT SIDE FOR DE-CLOUDING Scientific Rationale: Surface imaging requires correction for variations of cloud opacity. Since the failure of the VIRTIS-M cooler in October 2008, this correction is not possible anymore. With arrival of Akatsuki spacecraft that carries near-IR cameras such correction will become possible again. Simultaneous observations by the JAXA spacecraft will help both VIRTIS and VMC to “de-cloud” the night images. This is envisaged on an occasional (case-by-case) basis rather than on a regular (routine) basis. Instruments: VEx: VMC, VIRTIS VCO: IR2 Geometry: Nightside. Venus Express should be observing regions of the planet also observed by VCO. Both VIRTIS-M-VIS and VMC will require long integration times to see the surface, so this would probably be a Case 2 (ascending branch) observation for Venus Express. Feature tracking mode is not necessary for these observations. Figure 4.8: Simultaneous imaging on the night side for declouding

4.9 DAY SIDE IMAGING AT DIFFERENT PHASE ANGLES Scientific Rationale: VEx and VCO can observe the same regios at different phase angles, which could allow constraint of phase functions. Note that VCO can measure, during a single orbit, a complete phase function from 0-180°. Instruments: VEx: VMC, VIRTIS VCO: UVI, IR1 Geometry: This task requires specific geometry when both spacecraft observe Venus simultaneously from the same direction that ensures similar illumination conditions (see figure). Figure 4.9: Dayside imaging at different phase angles

4.10 SIMULTANEOUS OBSERVATIONS OF NIGHTGLOW (VEX IN LIMB GEOMETRY) Scientific Rationale: Simultaneous observations of airglow with Akatsuki LAC and VEx VIRTIS. Both VIRTIS and VMC are capable of seeing the nightglow; VIRTIS can add spectral information to airglow observed by LAC. VMC has higher spatial resolution than LAC but probably a much lower sensitivity (TBC). Instruments: VEx: VMC, VIRTIS VCO: LAC Geometry: Oxygen airglow occurs mainly towards antisolar point. Limb tracking would allow mapping of spatial distribution of airglow and would achieve long integration time. Akatsuki LAC operated only when VCO in shadow of Venus. Akatsuki (in Venus shadow) Figure 4.10: Simultaneous observations of airglow (Vex in limb geometry)

4.11 SIMULTANEOUS MAGNETIC AND OPTICAL OBSERVATION OF LIGHTNING Scientific Rationale: VEx MAG regularly observes Whistler waves thought to originate from lightning. VCO LAC will look for lightning on the nightside of Venus. Simultaneous detections using these instruments would present a powerful tool for studying the lightning. Instruments: VEx: MAG VCO: LAC Geometry: Akatsuki in Venus shadow. VEx inside magnetosheath. Akatsuki (in Venus shadow) Figure 4.11: Simultaneous magnetic and optical observation of lightning

4.12 COMPARISON OF VEX AND AKATSUKI RADIO OCCULTATIONS Scientific Rationale: Comparison of co-located (or nearly co-located) VEx and Akatsuki radio occultations will allow ensure consistency between instruments. In the longer term, VEx obtains occultations mainly at high northern latitudes while Akatsuki obtains occultations mainly at low latitudes; the datasets are thus complementary. Instruments: VEx: VeRa VCO: RS Geometry: This task requires specific geometry when both spacecraft observe Venus simultaneously from the same direction that ensures similar illumination conditions (see figure). “vertical” RO/VCO complementary to grazing RO/VEX in low latitudes Figure 4.12: Comparison of Vex and Akatsuki radio occultations

4.13 VEX NADIR SPECTROSCOPY OF AKATSUKI RADIO OCCULTATION LOCATIONS Scientific Rationale: Spectroscopy using VIRTIS and SPICAV of locations where radio occultations occur allows many scientific possibilities on both dayside and nightside. For example, retrieval of lower atmospheric properties from VIRTIS-H observations of 2-2.5 um region could be constrained by temperature profile from Akatsuki radio occultations. Instruments: VEx: VIRTIS, SPICAV VCO: RS

4.14 VEX LIMB SPECTROSCOPY OF AKATSUKI RADIO OCCULTATION LOCATIONS Scientific Rationale: Spectroscopy using VIRTIS and SPICAV of locations where radio occultations occur allows many scientific possibilities on both dayside and nightside. For example, retrieval of haze properties from VIRTIS-H observations of 2-2.5 um region could be constrained by temperature profile from Akatsuki radio occultations. Instruments: VEx: VIRTIS, SPICAV VCO: RS Note: Has this been tried with VEx data?

4.15 STELLAR OCCULTATION AT AKATSUKI RADIO OCCULTATION LOCATIONS Scientific Rationale: Allows comparison of upper atmosphere properties, in particular temperature profiles. Instruments: VEx: SPICAV VCO: RS Note: Has this been tried with VEx data?

4.16 SOLAR OCCULTATION AT AKATSUKI RADIO OCCULTATION LOCATIONS Scientific Rationale: Allows comparison of upper atmosphere properties. Instruments: VEx: SPICAV/SOIR VCO: RS Note: Has this been tried with VEx data?

4.17 VEX IN SITU OBSERVATIONS AT AKATSUKI RADIO OCCULTATION LOCATIONS Scientific Rationale: Radio occultation will allow retrieval of ionospheric properties up to several hundred km. ASPERA and MAG measure in situ properties at heights down to pericentre altitude (as low as 140 km). The combined treatment of these data could prove fruitful. Instruments: VEx: ASPERA, MAG VCO: RS Note: Has this been tried with VEx data?

Questions and open issues Other possible synergies between VEX and VCO observations ? Exact determination of relative positions of orbits at VCO arrival Identification of the time slots when joint observations are possible When the joint observations can start? Strategy of the ground station use by VCO Suggestions for VEX aerobraking: what VEX period would be beneficial for joint VEX/VCO observations ?

Next steps VEX-Akatsuki co-ordinated observations document VEx draft to be E-mailed to VCO colleagues early next week. FTP server to be set up for exchange of data. First telecon to be proposed before launch (followed by monthly telecons) Face to face meeting proposed for September. VCO representative will be invited to join monthly MTP science prep telecons.