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Chandra Mission Planning Updates - Thermal Constraints and ACA Considerations

Learn about the thermal balance and ACA constraints in Chandra mission planning, including temperature predictions and spacecraft orientation limitations.

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Chandra Mission Planning Updates - Thermal Constraints and ACA Considerations

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  1. Mission Planning Updates Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  2. Thermal Balance: A Reminder Maximum Dwell for Sample S/C Component Brown: maximum exposure before exceeding temperature limit Blue: minimum cooling time required to return to state from which another max dwell possible Note that this is only for one of the multiple spacecraft components with temperature limits Complete Science Orbit RadZone ObsID Temperature Prediction (degF) • Scheduling is a balance of heating and cooling multiple s/c components • - Observations often split to accommodate temperature limits 2 Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  3. ACA Constraints on Mission Planning • Chandra uses Aspect Camera to determine • attitude, maintain pointing, and provide • post-facto image reconstruction data • Typically, 8 acquisition stars are used to • acquire target attitude. • - practical minimum brightness is M ≈ 10.6 • For guide and aspect reconstruction, typical • configuration is 5 guide stars and 3 fiducial • lights Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  4. ACA Constraints on Mission Planning • Increasing temperatures for aspect camera result in increase in hot/warm pixels • - Effective background increases, making it more difficult to detect faint stars • - Planning constraints needed to limit camera temperature; TACA < -14C • Result is a limitation on continuous dwell time at particular spacecraft orientations • - In addition, post-observation cooling attitudes required before returning to • such “hot” orientations. Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  5. ACA Constraints on Mission Planning • Increasing temperatures for aspect camera result in increase in hot/warm pixels • - Effective background increases, making it more difficult to detect faint stars • - Planning constraints needed to limit camera temperature; TACA < -14C • Result is a limitation on continuous dwell time at particular spacecraft orientations • - In addition, post-observation cooling attitudes required before returning to • such “hot” orientations. Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  6. ACA Constraints on Mission Planning • Increasing temperatures for aspect camera result in increase in hot/warm pixels • - Effective background increases, making it more difficult to detect faint stars • - Planning constraints needed to limit camera temperature • Result is a limitation on continuous dwell time at particular spacecraft orientations • - In addition, post-observation cooling attitudes required before returning to • such “hot” orientations. Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  7. ACA Constraints on Mission Planning • For given target, star field is investigated • for each day of year to determine how warm • camera can be (Tobs,max) while still ensuring • sufficient detectable stars. • - Both nominal (red) and off-nominal • (blue) roll angles are considered. • If Tobs,max is above the planning limit (-14C), • then we are assured of getting stars as long • as the observation can be scheduled at all. • Time intervals with Tobs,max > -14C are • identified as window constraints for • placement of observations. ObsID 18201 Sunblock Planning Limit ( window (2015 10 30 00 00 00.000 ) ( 2015 11 14 00 00 00.000 ) X18201 ) ( window (2016 02 28 00 00 00.000 ) ( 2016 03 08 00 00 00.000 ) X18201 ) ( window (2016 04 05 00 00 00.000 ) ( 2016 04 06 00 00 00.000 ) X18201 ) ( window (2016 04 26 00 00 00.000 ) ( 2016 05 14 00 00 00.000 ) X18201 ) ( window (2016 08 01 00 00 00.000 ) ( 2016 08 04 00 00 00.000 ) X18201 ) ( window (2016 10 29 00 00 00.000 ) ( 2016 11 13 00 00 00.000 ) X18201 ) Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

  8. MLI: Long-Term Trends Chandra Spacecraft -Z +X +Y • Thermal effects result from the slow degradation of • thermal multilayer insulation (MLI). • Initial trends suggested eventual flatting of temperature • increase. With more data, trend appears linear. • - Current data indicate linear increase • for remainder of mission. Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

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