Constrained and Coordinated
Observations
Chandra Mission Planning Response to
Questions from Chandra User’s Committee
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Statistics on Constraints
“How many observations are actually constrained, and in what category (e.g.,
approved by peer review, preferences expressed in forms, constraints added
by users after their programs were approved, DDT observations, etc.)?”
The statistics are summarized in the following table. Specific items to note are:
• Nominally, the limit for constrained observations is supposed to be 20%. This
is intended to mean that constrained observations should not exceed 20% by
number or time, but things are usually tallied by number at peer review.
• Most DDT observations are constrained in some way. Some are the equivalent
of TOOs while others are the equivalent of somewhat right time windows and/or
monitoring programs.
• Tracking constraints (or preferences) that have been added after peer review
can be difficult, and some such constraints are satisfied without the constraints
ever making it into the database. Operationally this probably seems larger than
it really is.
• There is some double-counting of constrained observations in the database
compilation because of splitting of ObsIDs. This should be relatively small.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Statistics on Constraints
“How many observations are actually constrained, and in what category (e.g.,
approved by peer review, preferences expressed in forms, constraints added
by users after their programs were approved, DDT observations, etc.)?”
AO
TOT
TOTT
PRC
%
TPRC
%
AC
TAC
1
1025
22.2
188
18
4.1
18
107
2
852
21.5
236
28
6.6
31
3
929
22.5
225
24
6.0
4
889
20.0
169
19
5
830
23.9
279
37
DDT
DC
3.6
20
69
1.4
27
76
1.5
4.3
21
5
0.1
5.5
23
37
1.1
AO: Observing Cycle
TOT: Total number of targets
TOTT: Total observing time (Ms)
PRC: Targets w/ peer-reviewed constraints
(includes CAL and GTO)
TPRC: Time for targets w/ peer-reviewed constraints
AC:
Number of targets w/ added constraints
TAC: Time for targets w/ added constraints
Chandra User’s Committee Meeting (6/27/04)
PRP
AP
DP
TOTC
%
12
7.6
34
34
22
8.0
37
4
46
30
5
7.6
34
63
5
23
18
5
4.4
22
42
2
14
11
5
6.9
29
PRP: Targets w/ peer-reviewed preferences
(includes CAL and GTO)
AP:
Number of targets w/ added preferences
DDT: Director’s Discretionary Time targets
DC:
DDT observations w/ constraints
DP:
DDT observations w/ preferences
TOTC: Total constrained time
(not including preferences)
P. Slane (Chandra Mission Planning)
Constrained and Coordinated Observations
“What is the appropriate overall number of constrained observations (health
and safety vs. scientific value), and how many should be given out by the
peer review vs. DDT? This should include a discussion of the load on CXC
planning and operating staff.”
• Constrained observations do not, in general, represent a health and safety issue.
- Constraints are identified in advance and evaluated at several points in planning
process; such observations are done safely or not at all.
- TOO/DDT observations are more an issue for health and safety since these
require rapid replanning and detailed review. These are a large manpower load.
• The primary “costs” for constrained observations are:
1. Difficulty and loss of flexibility in scheduling
- All constraints (and most preferences) are met in initial long-term schedule.
- Competition between observing constraints, spacecraft constraints, & visibility.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Constraint Checks:
• Roll violations
• Sunblock
• Phase constraints
• Windows
• Radzones
• Pitch angle
• Coordinations
• Monitoring
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Constrained and Coordinated Observations
“What is the appropriate overall number of constrained observations (health
and safety vs. scientific value), and how many should be given out by the
peer review vs. DDT? This should include a discussion of the load on CXC
planning and operating staff.”
• Constrained observations do not, in general, represent a health and safety issue.
- Constraints are identified in advance and evaluated at several points in planning
process; such observations are done safely or not at all.
- TOO/DDT observations are more an issue for health and safety since these
require rapid replanning and detailed review. These are a large manpower load.
• The primary “costs” for constrained observations are:
1. Difficulty and loss of flexibility in scheduling
- All constraints (and most preferences) are met in initial long-term schedule.
- Competition between observing constraints, spacecraft constraints, & visibility.
- Future modifications difficult w/ lots of constraints (particularly if long duration).
- Constraints added after LTS is built are a burden.
- SOT/MP team has been reduced from 5 to 3 scientists, with 5 data aides.
 Increasing number of constraints will become a manpower issue
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Constrained and Coordinated Observations
“What is the appropriate overall number of constrained observations (health
and safety vs. scientific value), and how many should be given out by the
peer review vs. DDT? This should include a discussion of the load on CXC
planning and operating staff.”
2. Competing/Conflicting space for TOO/DDT observations
- LTS is heavily subscribed with constrained observations.
- Interruption of schedule for TOO or DDT often means working around
or moving a constrained observation.
- Long constrained observations are particularly difficult in this regard,
as are long TOO/DDT observations.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Chandra Long-Term Schedule
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Constrained and Coordinated Observations
“What is the appropriate overall number of constrained observations (health
and safety vs. scientific value), and how many should be given out by the
peer review vs. DDT? This should include a discussion of the load on CXC
planning and operating staff.”
2. Competing/Conflicting space for TOO/DDT observations
- LTS is heavily subscribed with constrained observations.
- Interruption of schedule for TOO or DDT often means working around
or moving a constrained observation.
- Long constrained observations are particularly difficult in this regard,
as are long TOO/DDT observations.
3. Efficiency and conflicts w/ spacecraft constraints
- As spacecraft constraints become more restrictive, constraints are more
difficult to accommodate. Example: EPHIN pitch constraints and need
for “cool” targets. (This now dominates scheduling difficulties.)
- Minimizing slew time is more difficult with large numbers of constrained
observations. Pre-launch simulations indicated 20% was ok; we aim for that.
• Current number of constraints awarded at peer review is probably a bit high.
Higher levels would certainly be a burden.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Constrained and Coordinated Observations
“What is the appropriate overall number of constrained observations (health
and safety vs. scientific value), and how many should be given out by the
peer review vs. DDT? This should include a discussion of the load on CXC
planning and operating staff.”
• Time available for DDT observations: 1 Ms for Cycle 1-4; 700 ks in Cycle 5
- full allotment not used in Cycles 1, 2, 4
- large single segments (~500 ks) used in Cycles 1, 2 – not highly constrained
- overall percentage of constrained budget is this not large; primary difficulty is
more along lines of TOO-like nature of many DDT observations
• Coordinated observations require more effort than typical constrained targets.
- Planning/negotiation with planners from other observatories
AO #
is manpower intensive (and often iterative).
- Number per cycle is shown in table; this does not include a fair
1
49
number of “preference” coordinations that have been supported.
2
51
- Pitch angle restrictions introduce additional complications
3
31
because many observatories have pitch angle restrictions very
near 90 degrees (Chandra’s “bad pitch” zone).
4
26
- Increasing number beyond current levels would be a
5
55
considerable burden.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Changing Allowed Constraints and Formats
“Can the constraints be changed for the ease of users (e.g., allow setting
time constraints in GST)?”
The short answer is “Yes, if necessary, but it can be a large task.” Here’s why:
RPS: The proposal submission software requires modification to accommodate new constraints
or new ways to specify existing constraints. Our version of RPS is under CXC control and
modifications are performed by CXC staff.
Databases: If modifications require new fields, new ranges, or multiple values, the proposal and/or
observation databases require restructuring. New elements must be added to databases, software
to populate/query these must be modified, and many individual scripts need to be updated.
Spike: The long-term scheduling software has a fixed set of constraints that it can handle. New
constraints require modification of the software. Spike is maintained and modified by STScI
through a support contract.
OFLS: The off-line system scheduling software is used for generating the detailed schedule (and
also the spacecraft command loads). In general, new constraints need to be added here as well.
Changes to this software are expensive, and the turn-around time is very long.
To date, modifications have been made to support multiple roll ranges, multiple
window constraints, grouping constraints, nonlinear monitoring intervals, and
preferences. All have required significant software changes.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)
Changing Allowed Constraints and Formats
“Can the constraints be changed for the ease of users (e.g., allow setting
time constraints in GST)?”
With specific regard to modifying the allowed constraints to support the
specification of time constraints in Greenwich Sidereal Time:
• Note first that Chandra does not support constraints for coordinated
observations with ground-based observatories. In RPS, such a request can
be made as a preference only.
• Addition of such support would require modifications to RPS, the Proposal
database, ObsCat, Spike, and the OFLS. Modifications to the two scheduling
software packages could be significant.
• While not technically supported, to date we have coordinated a significant
number of observations with the VLA. In a very small number of cases,
tight restrictions on the sidereal time have been required. These have been
handled “by hand.” The number of such instances have been very small. A
large software modification does not seem warranted for this.
Chandra User’s Committee Meeting (6/27/04)
P. Slane (Chandra Mission Planning)