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Chandra Uplink Support

All approved Chandra observations need to be carefully scrutinized by both the Program Principal Investigator (PI) or the official Observer, and also CXC Technical staff (the Chandra Uplink Support team) to make sure the scientific objectives are achieved. The steps involved between program approval and a successful observation are summarized below.

Mission Statement

Correctly configure the Chandra Observatory to carry out each observation. This process helps carry out the CXC requirements to maximize the scientific return, and to ensure a broad scientific usage.

Scheduling Process


Long Term Schedule (LTS), see: We use SPIKE to sort observations into one week time bins. This sorting satisfies the time and roll angle constraints, and the visibility window of the target (if any).

Pool Targets

The LTS process also selects ``pool" targets, for which all constraints are satisfied anywhere within a 4 month window, or even anywhere during the entire year.

These targets are used for ``oversubscribing" the observation requests (ORs) made during any one week, in order to improve scheduling efficiency.

User Support Interface

The official OBSERVER for every target is assigned an uplink support contact. (The PI is also the OBSERVER, unless another person is named.) We include all targets, GO, GTO, TOO. The OBSERVER receives a personalized form letter from their contact, with instructions to check the observation parameters and to note issues that might be relevant to the chosen instrument. (See, where acis is to be replaced with hetgs, letgs, or hrc when those are used.)

All OBSERVERS need to check:

$\bullet$ the target name,

$\bullet$ the target coordinates (in decimal degrees),

$\bullet$ the target offset (in arcminutes),

$\bullet$ the defocus (in mm),

$\bullet$ the SIM-Z offset (in mm),

$\bullet$ the roll constraint (in degrees),

$\bullet$ the time constraint.

ACIS observers especially need to consider pile-up, the desired energy resolution, choice of ACIS-I vs ACIS-S, possible use of a subarray, the telemetry throughput, and the choice of faint versus very faint mode. HRC observers especially need to consider back- ground rates, telemetry throughput, and the use of HRC-S for observations of msec pulsars. The above considerations may depend on whether the target is a point or an extended source, or a survey of a field.

Schedule of Events

This section is most important to understand.

The OBSERVER is contacted by their uplink support scientist either

$\bullet$ 60 days before the week in which the target is listed, or

$\bullet$ at the start of the period for which the target is ``pooled."

The OBSERVER is asked to confirm the parameters planned for their observation, by looking at the web page

and where the 984 is replaced by the OBSID of the target in question.

The request is to be answered 32 days before the start of the week in which the observation is scheduled, or within 2 weeks if it is a pool target. The OBSERVER response may request allowed changes, or provide missing information, but even if the configuration is perfect the OBSERVER must reply with a positive confirmation. Please copy all email to our Chandra Uplink Support archive at This allows us to use a search engine to retrieve information. The OBSERVER will receive a second email reminder, and one phone call, before the target is removed from the LTS and deferred for one year.

The following changes are not allowed in general:

$\bullet$ adding any constraints,

$\bullet$ changing exposure time or target,

$\bullet$ adding or removing a grating, or

$\bullet$ switching between ACIS and HRC or LETG and HETG so that the target and instrument configuration end up being the same as in someone else's observing proposal.


Please be responsive to your uplink support contact. They are a knowledgeable member of the Operations Science Support or Calibration groups. We can help provide information and flexible adjustment of your observation, up until the time limits stated above.

- Dan Schwartz

next up previous contents
Next: Communication with the CXC
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Previous: The Chandra Data Archive