Observing Programmes

Observing time during the 3.5 year duration of CHEOPS nominal operations  is split 80%: 20% between the Guaranteed Time Observing (GTO) Programme, which is under the responsibility of the CHEOPS Science Team, and the ESA-led Guest Observers Programme, through which the Community can conduct scientific investigations of their own choice. 


The CHEOPS Guaranteed Time Observing Programme

The GTO Programme is based on the science case for the CHEOPS mission, which is summarised in the CHEOPS Science Requirements Document and the CHEOPS Definition Study Report (Red Book). Details of the GTO Programme can be found at this link.


The CHEOPS Guest Observers Programme

Proposals for a share of the time allocated to the CHEOPS GO Programme are solicited through ESA Announcements of Opportunity (AOs) that will be made to the Scientific Community. The first AO was forseen to be issued six months before launch, and to cover a period of the first year of nominal operations. Proposals are selected on scientific merit, by a CHEOPS Time Allocation Committee that will be appointed by ESA in consultation with the CHEOPS PI. The TAC works independently from the CHEOPS Consortium, and receive technical support from the ESA Project Scientist (secretary) and also from the CHEOPS Consortium Project Science Office. Proposals are ranked based on scientific merit, and recommendations for CHEOPS observing time made to the Director of Science who awards the observing time. 

It is important to note that the vast majority of CHEOPS observations will be time-critical, and as a result non-trivial to schedule.  Propsective obserers should be aware that the award of time on CHEOPS does not provide any guarantee that the observations will actually be scheduled and completed. 

Proposals for observing time in the Guest Observers' Programme can cover any type of science that can be shown to be both addressable by the performance capabilities of CHEOPS and to be compatible with the operational, observational and technical constraints of the mission. Observations of targets that are on the Reserved Target List (see below) are not allowed. PIs will be required to provide evidence to be submitted as part of their observing proposals that the Reserved Target List has been checked and that there are no conflicts.   

Update of the GTO Reserved Target List to include new targets takes place on a regular basis. To enable important new targets to be included in the GO programme, up to 25% of the observing time on the Guest Observers' Programme is available to through the Discretionary Programme (see below).


SUpport to Guest Observers

Tools and documentation to support the Community in preparation of proposals in response to the ESA AOs are available through the ESA webpages, and include descriptions of the mission and payload, user manuals, CHEOPS target visibility plots and an exposure time calculator. Webpages with "frequently asked questions" are available for each of the calls. 


Planning cheops observations

PIs of successful proposals will be invited to submit detailed information relating to the scheduling of their requested observations. This will be used to generate the long term schedule for CHEOPS. Observers will be informed that their observations have been scheduled no later than the time at which the relevant weekly activity plan is uploaded to the spacecraft.  


cheops data processing and data reduction

All data taken by CHEOPS will be processed and reduced at the SOC using a common CHEOPS data reduction (DR) pipeline. The DR pipeline will not be available to the user, however detailed descriptions of the reduction steps, including assumptions and algorithms that have been used will be provided as part of the SOC documentation. 


accessing cheops data

All data obtained with CHEOPS will be made available via the CHEOPS science archive which will be hosted by the SOC at Geneva Observatory. This includes the following level data products: 

  • ​Level 0 - data received from the MOC: science + housekeeping + ancilliary 
  • Level 0.5 - converted to FITS fils, sorted according to visit and pass (downlink)
  • Level 1 - calibrated/corrected images and quality reports
  • Level 2 - light curves/time series --> final CHEOPS data product

as well as on-ground calibration products (reference files), all housekeeping+ancilliary data and data taken in-orbit as part of monitoring and characterisation activities. 

WIth the exception of data taken during characterisation and monitoring activities, all CHEOPS observations will be subject to a proprietary period of 1 year. The proprietary period will be set at the level of individual observation requests: it will begin at the time that the data from the last visit in an observation request is declared to be complete by the SOC, following quality checks. The total proprietary period will not exceed a period of 1.5 years which starts from the time of successful completion of the first visit of the observation request. Only the PI of the proposal associated with the observation request, together with a second designated scientist noted in the observing proposals, will be able to see and retrieve proprietary data  from the archive; all members of the CHEOPS Science Team will have proprietary access to observations made as part of the Guaranteed Time Observing Programme, 

Beyond the proprietary period, data become public and are freely available from the CHEOPS mission archive which can be found here. 


The CHEOPS reserved target list

The first issue of the CHEOPS Reserved target List comprised targets from the Guaranteed Time Observers Programme and covered the full 3.5 years of the mission. The list is maintained in a versioned database for which all entries and changes are tracked and time-stamped/logged. The list is frozen at the time of the opening of each call.  The list at the time of the first call was available ESA to ensure transparency, but was not be provided to the Community as a whole. This was changed for the second and third calls, with the list being freely available.

A dedicated tool is available to query the Reserved Target List. It reports back on the status of a target. Scientists writing proposals to observe with CHEOPS are required to use the tool, and to provide evidence that no targts in their proposals are on the list.

Targets from GO proposals that are awarded observing time on CHEOPS are also on the Reserved Target List and similarly blocked. In all but exceptional cases, targets from the GO Programme will be removed from the Reserved Target List at the time of the next AO. 


announcements of opportunity for the CHEops Guest Observers Programme

Calls for proposals for the CHEOPS Guest Observers Programme are made through annual Announcements of Opportunity (AOs). The first AO came out on the 19 March 2019 and covered the period from end March 2020 to end March 2021. To-date (Sept 2022) two further calls have been issued to cover observing time to the end of the mission. Details can be found at this link.


The CHEOPS Discretionary Programme

Up to 25% of the total observing time available to the Community on CHEOPS is foreseen to be awarded through the Discretionary Programme. Proposals seeking time via this route can be submitted at any time of the year. As of end-September 2022, this is the only way in which scientists outside the CHEOPS Mission Consortium can apply for observing time on CHEOPS. Details of the Programme, including its constraints, can be found at this link.