Mission Planning Updates Chandra Users Committee Meeting 092915
- Slides: 8
Mission Planning Updates Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)
Thermal Balance: A Reminder Maximum Dwell for Sample S/C Component Brown: maximum exposure before exceeding temperature limit Note that this is only for one of the multiple spacecraft components with temperature limits Blue: minimum cooling time required to return to state from which another max dwell possible Complete Science Orbit Rad. Zone Temperature Prediction (deg. F) Obs. ID • Scheduling is a balance of heating and cooling multiple s/c components - Observations often split to accommodate temperature limits Chandra User’s Committee Meeting (09/29/15) 2 P. Slane (Chandra Mission Planning)
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)
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 < -14 C • 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)
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 < -14 C • 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)
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)
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. Obs. ID 18201 Sunblock Planning Limit • If Tobs, max is above the planning limit (-14 C), then we are assured of getting stars as long as the observation can be scheduled at all. • Time intervals with Tobs, max > -14 C are identified as window constraints for placement of observations. ( window (2015 10 30 00 00 00. 000 ( window (2016 02 28 00 00 00. 000 ( window (2016 04 05 00 00 00. 000 ( window (2016 04 26 00 00 00. 000 ( window (2016 08 01 00 00 00. 000 ( window (2016 10 29 00 00 00. 000 Chandra User’s Committee Meeting (09/29/15) ) ( 2015 11 14 00 00 00. 000 ) X 18201 ) ) ( 2016 03 08 00 00 00. 000 ) X 18201 ) ) ( 2016 04 06 00 00 00. 000 ) X 18201 ) ) ( 2016 05 14 00 00 00. 000 ) X 18201 ) ) ( 2016 08 04 00 00 00. 000 ) X 18201 ) ) ( 2016 11 13 00 00 00. 000 ) X 18201 ) P. Slane (Chandra Mission Planning)
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)
