CHEOPS  "Frequently Asked Questions" :  AO-3


Below is a collection of Frequently Asked Questions (FAQs), with answers, relating to the preparation and submission of proposals for CHEOPS AO-3. The page will be updated to include quesions that come up in the run up to the Call and during the period that the Call is open.

Please send an email to with any questions that you have.  Note that it may take a few days for questions and answers to be posted on this webpage.

In case of problems with the email address noted above, please contact cheops-ps at esa dot int, replacing "at"  with "@" and  "dot" with "."

Lastst updated 3 March 2022



You will need to register for the Guest Observrs Programme in order to submit proposals as well as to download the scheduling feasibility checker required to make a detailed assessment of the visibility of your targets with CHEOPS. Instructions on how to register can be found at


Q2   which targets (lines of sight) are already reserved and thus blocked?

There are two ways in which you can find out which targets, or more precisely which lines of sight, are already reserved or blocked, and thus may not be included in observing proposals: 

  1. target by target, one-by-one, using the so-called reserved target list checker tool which is available at: Thia provides access to the most up-to-date version of the target list.
  2. a csv file which contains the target name and coordinates for all targets on the reserved target list at the time the AO opens. This will be made available on the webpage for the AO shortly days before the AO opens. This list may evolve during the period that the AO open - as observations of targets in the GO programe are completed (no longer reserved) and as programmes are awarded time in the discretionary programme (become reserved) - so it is important to check using the status of a target using the online tool also.


Q3   Are there any restrictions on the science topics that can be put forward in CHEOPS proposals, or any quotas for science areas?

Observations can be proposed that cover any science topic, including exoplanets. There are no quotas for time that will be allocated to different science topics. All proposals will be evaluated by the Time Allocation Committee according to the following criteria:

  • The scientific excellence and relevance of the proposed observations;
  • The uniqueness and applicability of CHEOPS to achieve the proposed scientific objectives of the proposal;
  • The technical feasibility and robustness of the proposed observations and data analysis.

There are some constraints on the types of observations that CHEOPS can be used to do. These are summarised below and will be elaborated on in more detailed in the Policies and Procedures document for the AO:

  • Simultaneous observations with other facilities can be done in exceptional cases but are very challenging to schedule on CHEOPS.
  • CHEOPS does not support non-sidereal tracking. Solar system objects may be observed in exceptional circumstances by providing static time-dependent RA and Dec values. This approach is definition extremely time-critical and makes scheduling of such observations correspondingly challenging.

In both cases above the scientific justification for the request needs to be made in the proposal and will be considered by the TAC in the proposal evaluation process. 


Q4   Are there limits to the number of orbits that CAN Be requested in a proposal?

There is no maximum number of orbits that can be requested in a single proposals. There are restrictions on the number of orbits that can be requested for a single observation/visit:

  • There is a minimum visit duration of 5 orbits outside of transit which is enforced to ensure that efficient and effective detrending of the resulting lightcurves is possible.
  • There is a maximum visit duration of around 100 orbits (around 1 week) which is set by the length of the observing schedule that is uplinked to the satellite. Longer duration observations can be made by scheduling two consecutive visits.


Q5   I am UNABLE TO run the scheduling feasibility checker on a virtual machine on the UBUNTU OS

A user has reported difficulties using the scheduling feasibility checker (SFC) in combination with the Ubuntu OS. They were able to isolate the issue to the Virtual Box installation based on the solution proposed here:

By removing the VirtualBox version downloaded from the VirtualBox website, and using that provided in the Ubuntu software source (reply 7):

sudo apt-get install --reinstall virtualbox



Q5   When is it useful to use CHEOPS imagettes rather than subarrays, and how do I do so ?

Photometry on imagettes typically performs as well as photometry on subarrays, with the added advantage of the higher cadence. This can be advantageous when de-trending but also for resolving rapid phenomena such as flares in active stars and for timing measurements (e.g. better resolution of ingress and egress).

PIPE is a photometric extraction package, developed by members of the CHEOPS Science Team, that uses PSF photometry on 60 pixel diameter CHEOPS imagettes. The package complements (but does not replace) the official Data Reduction Pipeline (DRP), which uses aperture photometry on the 200 pixel diameter subarrays. Details of the PIPE package can be found at this link (GitHub). The package currently requires detailed tuning - interested users are therefore advised to contact the author of the package directly to discuss possible collaborations.