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
RadZone
Temperature Prediction (degF)
ObsID
• 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 < -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)
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)
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.
ObsID 18201
Planning
Limit
• 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.
( 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 ) X18201 )
) ( 2016 03 08 00 00 00.000 ) X18201 )
) ( 2016 04 06 00 00 00.000 ) X18201 )
) ( 2016 05 14 00 00 00.000 ) X18201 )
) ( 2016 08 04 00 00 00.000 ) X18201 )
) ( 2016 11 13 00 00 00.000 ) X18201 )
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)