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 ( ) ( ) X18201 )
( window ( ) ( ) X18201 )
( window ( ) ( ) X18201 )
( window ( ) ( ) X18201 )
( window ( ) ( ) X18201 )
( window ( ) ( ) X18201 )
Chandra User’s Committee Meeting (09/29/15) P. Slane (Chandra Mission Planning)

8. MLI: Long-Term Trends Chandra Spacecraft+Y
Chandra Spacecraft -Z +X
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)