The European Space Agency
Observing with CHEOPS - CHEOPS Guest Observers Programme
Observe with CHEOPS:
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Observing with CHEOPS
Overview
CHEOPS' science programme consists of two main components: the Guest Observers (GO) Programme, which gives the worldwide scientific community access to CHEOPS observing time, and the Guaranteed Time Observing (GTO) Programme, which is under the responsibility of the CHEOPS Science Team. The table below summarises the nominal science observing-time allocation.
| Mission phase | Period | GO observing time | GTO observing time |
|---|---|---|---|
| Nominal Mission (NM) | 25 March 2020 – 24 September 2023 | Up to 20% | At least 80% |
| Extended Mission 1 (EM1) | 25 September 2023 – 31 December 2026 | Up to 30% | At least 70% |
| Extended Mission 2 (EM1) | 1 January 2027 – 31 December 2029 | Up to 30% | At least 70% |
Guest Observers (GO) Programme
GO Programmes can cover any type of science addressable by CHEOPS' performance capabilities and compatible with the operational, observational and technical constraints of the mission.
ESA solicits proposals for GO Running Call, with deadlines the last natural day of every month starting in July 2026 for regular programmes (of up to 120 orbits) and deadlines at the end of October and April from 2026 to 2029 for large programmes (from 121 to 500 orbits). You can see the details at the Running Call website.
Proposals are selected and ranked on scientific merit by an independent CHEOPS Time Allocation Committee (TAC), which is appointed by ESA in consultation with the CHEOPS Principal Investigator. The TAC works independently from the CHEOPS Consortium and receives technical support from the ESA Project Scientist, acting as secretary, and the CHEOPS Consortium Project Science Office (PSO). The TAC makes recommendations for CHEOPS observing time to ESA's Director of Science, who then awards the observing time.
Observations of targets that are on the Reserved Target List (RTL; see below) are not allowed. Updates of the RTL to include new targets take place on a regular basis. In the Nominal Mission, the RTL was technically unlimited, but in practice constrained to approximately 150–200 targets. With the start of Extended Mission 1, the RTL is limited to 50 targets and for Extended Mission 2, the RTL will be limited to 20 targets.
PIs of successful proposals are invited to submit detailed information relating to the scheduling of their requested observations. This information is used to generate the long-term schedule for CHEOPS. Observers are informed of their observation schedules when the relevant weekly activity plan is uploaded to the spacecraft.
ESA supports the community in the preparation of proposals via tools and documentation available on this website.
Guaranteed Time Observing (GTO) 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). The CHEOPS Science Team, chaired by David Ehrenreich, defines the programme.
An overview of the GTO Programme as it stood at the opening of the various AOs is available below:
- GTO Programme at the Running Call opening
- GTO Programme at the AO-6 opening
- GTO Programme at the AO-5 opening
- GTO Programme at the AO-4 opening
- GTO Programme at the AO-3 opening
- GTO Programme at the AO-2 opening
- GTO Programme at the AO-1 opening
Reserved Target List (RTL)
The RTL comprises targets, i.e. lines of sight, from the GTO Programme that cannot be proposed through the GO Programme. The list is frozen at the time of the opening of each AO Call. A dedicated Target Checker is available to query the RTL, along with unreserved GTO targets and GTO programmes.