An open, versioned, verifiable catalogue of the observability parameters of space observatories — field of regard, roll convention, roll slack, orbit — each value carrying the primary source it was checked against.
Ground-based observing sites are trivially described: a latitude and a longitude, and anyone can create one. Space telescopes are not. What gates their visibility is a pointing envelope defined in mission documentation, and those numbers are spread across proposer handbooks, help pages, and reference code — mixed with presentation, easy to mis-transcribe, and impossible to check at a glance.
A wrong number here does not fail loudly. It produces a visibility window that looks authoritative and is silently false. So this repository does for space-telescope constraints what standard-stars-catalogues does for photometric standards: it decouples the data from any one presentation, puts it under version control, and — crucially — attaches to every value a provenance record naming the source, the date it was checked, and whether a human has verified it.
If you think a number is wrong, you can see exactly where it came from and open an issue.
facilities.json manifest of every facility
schema/facility.schema.json JSON Schema (draft 2020-12) every file validates against
facilities/<key>/
parameters.json the structured, machine-readable values
README.md the same values in prose, with source URLs and quotes
scripts/validate.mjs validates every file against the schema + manifest
| Facility | Field of regard (solar elongation) | Status |
|---|---|---|
| JWST | 85°–135° | operational |
| Roman | 54°–126° | planned |
| Euclid | 87°–110° | operational |
| Chandra | 46.2°–178° | operational |
| XMM-Newton | 70°–110° | operational |
| ARIEL | 70°–120° | planned |
The field of regard is the range of Sun–observatory–target angle in which a target is observable. For observatories in high or low Earth orbit (Chandra, XMM-Newton), it is the coarse annual constraint — per-orbit Earth occultation, radiation-belt passages and duty cycle are recorded under unmodelled_constraints, not in the field of regard.
Every value sits under a provenance object:
{
"source": "STScI JDox — JWST Field of Regard (FoR): \"must remain in the range 85° to 135°…\"",
"url": "https://jwst-docs.stsci.edu/...",
"retrieved": "2026-07-20",
"verified": true
}verified: true means a maintainer has confirmed the value against the cited primary source. Consumers should surface verified: false as a warning rather than presenting a guessed number as fact. A value is preferably corroborated by an independent cross-check (e.g. the field of regard reproduced from the documented sky-coverage fraction).
Constraints that are real but deliberately not encoded — because no number is published, or they need scheduling detail — are listed under unmodelled_constraints, so consumers know the model is planning-grade, not scheduling-grade.
npm install
npm run validateCI runs this on every push and pull request. A change that does not validate cannot merge.
Open an issue if you find a mistake — quote the source that contradicts the value. To add a facility:
- Create
facilities/<key>/parameters.jsonand aREADME.mdbeside it. - Add it to
facilities.json. - Every value needs a
provenancewithverified: falseuntil someone confirms it against the primary source. Prefer versioned, machine-readable sources (as Roman provides) over prose pages. npm run validatemust pass.
@onekiloparsec/night-explorervendors a pinned snapshot and builds its space-facility catalogue from these files.
The compiled catalogue is offered under CC BY 4.0 (see LICENSE). The underlying figures are facts drawn from public mission documentation and are not themselves copyrightable; attribution covers this compilation and its prose.