Free APIs
Free Space & science APIs
| Free tier | Docs | ||
|---|---|---|---|
APOD, Mars photos, near-Earth objects, EPIC and more
Catch: DEMO_KEY has much lower limits | Free key: 1,000 requests/hour by default | API key | docs |
Rocket launches, agencies and spacecraft
Catch: Low hourly limit; Patreon for more | Free: 15 requests/hour without key | No key | docs |
ISS position, pass times and people in space
Catch: HTTP only | Free, no key | No key · no HTTPS | docs |
Current ISS position and satellite positions
Catch: Rate limited | Free; about 1 request/second | No key | docs |
Real-time and historical earthquake events
Catch: Queries returning over 20,000 events are rejected | Free, no key | No key | docs |
Space weather: solar wind, aurora, Kp index
Catch: Public JSON products; no formal SLA | Free, no key | No key | docs |
Confirmed exoplanets and stellar data
Catch: TAP/ADQL query interface | Free, no key | No key | docs |
Sunrise, sunset and twilight times by coordinates
Catch: Attribution required | Free, no key | No key | docs |
| Free, no key | No key | docs | |
Scholarly article, DOI and citation metadata
Catch: Add a mailto in requests for the faster polite pool | Free, no key | No key | docs |
Open index of scholarly works, authors and institutions
Catch: Daily request limits; key recommended | Free; no key for light use, API key for more | No key | docs |
Paper, author and citation graph data
Catch: Unauthenticated use shares a pool and may throttle | Free; API key gives 1 request/second | No key | docs |
Chemical compounds, substances and bioassays
Catch: 5 requests/second, 400 per minute | Free, no key; max 5 requests/second | No key | docs |
Nature observations, taxa and places
Catch: Hard cap 100/minute; keep under 10,000/day | Free, no key for reads; keep under 60 requests/minute | No key | docs |
FAQ
What is the best free space & science API?+
NASA Open APIs, Launch Library 2, Open Notify (ISS) are good places to start. Compare the free tiers and catches in the table; they differ mostly in limits and whether commercial use is allowed.
Is there a space & science API without an API key?+
Yes: Launch Library 2, Open Notify (ISS), Where the ISS at?, USGS Earthquake API, NOAA SWPC Data Service work without a key.
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