RUNNING CALL FOR PROPOSALS FOR THE CHEOPS GUEST OBSERVERS (GO) PROGRAMME

The CHEOPS Running Call for Proposals solicits proposals for observations to be carried out as part of the CHEOPS Guest Observers (GO) Programme during CHEOPS' second extended mission (EM2). The overall observation window of the Running Call extends from 1 October 2026 to 31 December 2029 inclusive.

Observers may submit proposals at any time during the Running Call. Proposals are evaluated by the TAC in monthly cycles: proposals received by the SOC between the first and last calendar day of a given month are evaluated during the first weeks of the following month. The results of the TAC evaluation will be communicated to the observers shortly afterwards. While the TAC is evaluating proposals from one submission cycle, observers may submit new proposals for the following cycle.

Observing programmes awarded time by the TAC will ideally start three months after the closing date of the relevant submission cycle, subject to observation constraints. For example, proposals submitted during the July 2026 cycle will typically start observations from October 2026.

The table below provides an example timeline for the first proposal submission cycle in July 2026, followed by TAC evaluation in August 2026. The submission deadlines for the remaining 2026 cycles are also listed below.

Milestones for the July 2026 Proposal Submission and Evaluation Cycle

Proposal Submission Deadlines for the Following Cycles

Regular and Large Programmes

Regular programmes may request up to 120 CHEOPS orbits per proposal and may be submitted during any month of the Running Call.

Large programmes may request 121-500 CHEOPS orbits per proposal and may only be submitted twice per year, during the April and October submission cycles, from 2026 through 2029.

HST/JWST coordinated fast-track programmes may request up to 25 CHEOPS orbits and may be submitted during any month of the Running Call. These proposals skip the TAC evaluation and proceed directly to feasibility evaluation and scheduling.

Important Notes

Prospective observers are asked to take note of the following points:

• Read the Policies and Procedures document carefully before starting the preparation of a proposal, as it is the definitive document for this opportunity. It provides details of the CHEOPS science programme, the observing time available to the community, the observing strategy and constraints, and the required contents of observing proposals. It also lists the tools and documents available to support proposal preparation and submission. All proposal material and file names must be fully anonymous. Failure to comply with the anonymisation requirements will result in rejection on formal grounds. Prospective observers should also consult the Observers Manual and all other relevant documentation available on this website.
• Follow these seven steps:
  1. Registration: Register immediately if you do not already have a Cosmos user account. Waiting until the submission deadline may prevent you from submitting your proposal on time.
  2. Coordinates: Familiarise yourself with the required coordinate format. Use the Target Checker, SIMBAD, or MAST. Do not copy and paste coordinates directly from ExoFOP or the Gaia catalogues, as they use a different format.
  3. Visibility checks: Consult the visibility maps to identify targets that may be observable. Then verify whether and when your targets are observable using the Visibility Tool or the Scheduling Feasibility Checker.
  4. Target status checks: Confirm that your target is eligible by consulting the publicly available list of CHEOPS targets, including both reserved and unreserved targets, and the GTO programme information. Check the CHEOPS Mission Archive to determine whether CHEOPS has already observed the target and to ensure that the proposed observations will provide new information.
  5. Exposure-time calculation: Use the Exposure Time Calculator to confirm that the required signal-to-noise ratio can be achieved.
  6. Proposal templates: Download and complete the required proposal templates.
  7. Phase 1 submission: Submit the proposal through the Proposal Handling Tool for Phase 1 (PHT1).

Please also note that:

• Updates relating to the Running Call and its supporting material will be published on this webpage.
• The Alpha Cen system, including Alpha Cen A and Alpha Cen B, is a special case. The system was included in the Reserved Target List (RTL), but because of its high proper motion and orbital motion, the Target Checker did not resolve the RTL coordinates when queried by name. The coordinates provided for Alpha Cen in the RTL CSV file must therefore be used for Target Checker queries.
• Detailed examples illustrating how to prepare a dual-anonymous proposal are available on the FAQ pages.
• The CHEOPS team makes every effort to observe and complete awarded programmes. However, an award of observing time does not guarantee that all observations can be carried out, even when a programme is considered high-priority science. Because of the nature of the science addressed by CHEOPS, demand for observing time can be high, unforeseen events may occur, and some observations may not be feasible to schedule.
• CHEOPS is a small mission with a correspondingly small team supporting the GO Programme. Observers are encouraged not to leave proposal preparation until the last moment, as answering support requests may take several days.

Phase 1 Step-by-Step Tutorial

Please find below a one-minute video presenting the seven steps required to submit a Running Call proposal.

Key Documentation

• Announcement of Opportunity (Running Call) - invitation letter from the Director of Science
• Policies and Procedures (Running Call)
• Observers Manual (Running Call)
• GTO Programme (Running Call)
• GTO Reserved Target List (Running Call, July 2026)

This page was last updated on 2 August 2026.