Chandra X-Ray Observatory

Chandra Observation Scheduling and Observer Support


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.

Cycle Transitions and Early scheduling of Targets

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.

Reviewing Target Information

Observers can review observation parameters in the Chandra database at any time using WebChaSeR.

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.

Uplink Support (USINT) for Observers

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:

  1. The uplink scientist sends a letter to the user, which asks for a response within a certain time frame based upon a projected observation date.
  2. Upon response from the user, the uplink scientist requests any necessary changes to the observation configuration and releases the observation for scheduling. Should the user not respond by the specified deadline, the observation cannot be scheduled and may be significantly delayed.
  3. The observation is selected as a candidate for observation in a specific STS and enters the scheduling process.
  4. Should the observation be confirmed, it will appear in the current STS on the CXC web pages.
  5. After the observation setup is confirmed, Uplink Scientists will only contact the observation PI/observer again if the scheduled observation is not actually done (e.g., due to radiation, safe mode, TOO, or other unforeseen circumstances).
  6. When the observation is completed and the data received on the ground, the PI/observer is informed by the CXC data systems group, who forward the quick look images and, later, the complete data.

Observation Planning Schedule

This table applies to observations scheduled during the nominal cycle and may not apply to targets chosen for early observation. Early targets may undergo an abbreviated schedule, with faster required response times.

ActionUsual Timing
(days are counted back from the first day of the target's STS)
First Contact from the Director's OfficeWithin 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 required32 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 database25 days
Observation request is submitted for scheduling23 days

Long Term Schedule (LTS)

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.

Short Term Schedule (STS)

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.

TOO/DDT support

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.

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The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email: Smithsonian Institution, Copyright © 1998-2016. All rights reserved.