After the Peer Review, the Chandra Director's Office (CDO) sends a message to observers of approved programs, requesting that they confirm basic observing parameters for their targets.
After observers confirm basic parameters, a long-term schedule (LTS) can be generated. The LTS includes all observations for the given cycle. This consists of both targets that need to be assigned to specific time intervals, plus targets assigned to a "pool" (but not targets without sufficient scheduling information, such as Targets of Opportunity selected through peer review). Pool targets are unconstrained observations that are used to fill out short-term schedules (STS), which are generally spaced at one to two week intervals.
The LTS is updated as each new STS is generated to incorporate changes as the cycle progresses.
After the initial LTS is built for a cycle, the Chandra uplink support Interface scientists ("USINT", or "uplink scientists") contact observers to request a more detailed second confirmation of observation parameters. If these parameters are not confirmed in a timely fashion, the target may need to be rescheduled, sometimes after a considerable delay.
Each final planned short-term schedule (STS) is posted on the public web soon after the schedule is approved for upload to Chandra.
Targets are placed in the LTS according to constraints imposed by both science and spacecraft requirements. Observers should be aware that these constraints result in an interleaving of cycles: an extensive period -- of order months -- during which schedules are built drawing on targets from both the earlier cycle and the later cycle in a transition. In particular, some targets will be scheduled early, which will require an accelerated schedule of contact with the CXC to finalize observing parameters.
Currently the cycle turnover (at which about 50% of targets are chosen from each of the earlier and later cycles) takes place approximately during the February of the year following the proposal due date for targets in the later cycle.
Observers can review observation parameters in the Chandra database at any time using ChaSeR.
Observers are encouraged to review these pages to confirm the observation setup well in advance of their LTS observation date and either submit changes or else confirm that the configuration is correct to their uplink contact scientist.
After the initial parameter confirmation done by CDO, each Chandra observation is assigned an uplink support (USINT) scientist from the DOSS or Calibration groups at the CXC based upon the selected instrument. Uplink scientists are responsible for contacting all observers to confirm their observation configurations in more depth in advance of releasing the observations for scheduling in an STS.
The support process includes a series of steps:
| Action | Usual Timing (days are counted back from the first day of the target's STS) |
| First Contact from the Director's Office | Within one month of the announcement of approved targets for the new cycle |
| USINT Contacts the Observer | Beginning after LTS is built, continuing through cycle |
| Observer Response to USINT contact required | 32 days (Failure to respond to USINT can cause significant delays in the scheduling of an observation, possibly as long as a year in extreme cases.) |
| Observing Parameters are finalized in the CXC database | 25 days |
| Observation request is submitted for scheduling | 23 days |
This is generated for each observing cycle. It places over half of the targets into one STS bins, taking note of all observing constraints. In order to achieve an efficient final schedule, the remaining unconstrained targets are placed in the pool and are selected for observation by the Mission Planning team as they become visible to Chandra and as they are needed given the Chandra operating requirements.
The LTS is generally updated when a new STS is developed, and is available on the LTS page. Pool targets, which are those most likely to move around, are labeled clearly in each schedule.
A new STS is generally developed at one to two week intervals in preparation for upload to Chandra. Each STS is also made available on the public web site soon after notification of final approval for that STS goes out.
This is the official observation plan but we note that unanticipated events -- such as TOOs, increased solar activity, or satellite problems -- can interrupt the schedule, resulting in some of the observations not being completed. In this case, an updated STS is generated and posted on the web and affected observers are notified.
Due to the unpredictable nature of the observations, TOO and DDT targets are not usually assigned an uplink scientist until after a trigger has been approved. If they have not been assigned a USINT person before triggering an observation, the observers of these proposals may request help from the CXC through the HelpDesk.