7/12/20011 Observing Sequences in View of the SECCHI Science Goals From the EUVI Perspective J-P. Wülser

7/12/20012 Introduction It is not too early to plan observing strategies: S/C separation angle and telemetry change  character and focus of STEREO evolves  missed opportunities don’t reoccur  need mature observing strategy at launch Observing strategy influences flight software design Telemetry constraints call for innovative observing strategies to achieve science goals

7/12/20013 Science Goals (1) Science goals “Physical Evolution of CMEs” (especially through the outer corona), and “CME Interaction with Heliosphere” need long duration, uninterrupted observations at modest image cadences  Synoptic observing program Science goals “Initiation of CMEs”, and “Physical Evolution” through chromosphere and low corona need high cadence, high spatial resolution data The CME initiation process is critical for understanding the CME as a whole

7/12/20014 Science Goals (2) What image cadence is needed? Phase A report states 60 s cadence at 3” pixels as a requirement for CME initiation studies SXT observations with 23 s cadence show acceleration of erupting structure TRACE observations during CME initiation show rapid changes in the low corona that are barely resolved at s cadences  Difficult to achieve at 42 kbit/s telemetry rate

7/12/20015 Synoptic Observing Sequence (modified from Phase A report)

7/12/20016 Event Driven Observing Sequences (1) High cadence only required during relatively short CME initiation / early acceleration period Automatic detection of CME feasible w/C’graph Strategy: Observe at high cadence into a rotating buffer Stop overwriting buffer after CME detection (or x minutes after CME detection) S/C has agreed to provide two SECCHI partitions within its Solid State Recorder: one for synoptic data, and one for event data (overwritable)

7/12/20017 Event Driven Observing Sequences (2) Rotating buffer downlinked at every DSN contact (contains either event, or most recent data) At 300 km/s, CME travels 1.5 R sun in 1 hour, or in 2 hours, in case of constant acceleration Overwritable rotating buffer should be sized to hold at least 2 hours worth of high cadence data Examples assume the following partition sizes: 80% synoptic, 20% rotating event buffer

7/12/20018 Synoptic + Event Observing Sequence Example 1: Nominal Telemetry

7/12/20019 Synoptic + Event Observing Sequence Example 1: Nominal Telemetry Table shows –Sum of event buffer telemetry and synoptic telemetry –Synoptic telemetry alone Synoptic EUVI & Cor1 cadences slightly reduced Rotating event buffer receives telemetry for –Full resolution 1600x1280 EUVI images every 37.5 s –Double cadence in 3 other EUVI channels –Quadruple cadence (2.5 min) in Cor1 Capacity of rotating event buffer: 2.2 hours

7/12/ Synoptic + Event Observing Sequence Example 2: High Rate Telemetry

7/12/ Synoptic + Event Observing Sequence Example 2: High Rate Telemetry Example assumes that twice the nominal telemetry is available early in the mission Higher synoptic EUVI, Cor1, Cor2 cadences. 1/4 resolution EUVI data replaced with 1/2 resol. High cadence buffer receives telemetry for –Full resolution (1600x1280) EUVI images every 30 s –Half resolution (800x640) EUVI images every 90 s in additional channel Capacity of rotating event buffer: 2.4 hours