Review 08 · Live Intelligence
ORBIT.
Nearly eleven thousand satellites moving over a drawn globe, every position worked out on your machine by an engine that matches its reference to a ten-billionth of a kilometre. The elements fed to that engine were a month old.
- Tested 27 September 2026, 20:17–20:31 UTC
- Where the work happens data shipped with the page
- Against Heavens-Above, N2YO, CelesTrak
1What it is, and who it is for
ORBIT draws a globe with the space stations, about 150 of the brightest satellites and the whole Starlink shell, 10,911 element sets in all, moving in real time. Give it your location and it lists the next 48 hours of passes for the ISS or any satellite you pick, marking which are visible: satellite sunlit, sky dark. A speed control runs the clock faster and labels the result simulated.
It is for sky-watchers who want to know when the ISS or a Starlink train will cross their sky, and for anyone curious about how crowded low orbit has become.
2How it works
There is no live feed. orbit.js loads three files on demand: the engine, the element snapshot and a coastline (orbit.js 42–73). orbit-engine.js is a self-contained SGP4 near-earth propagator ported from the Vallado reference, with WGS-72 constants, earth rotation, a low-precision sun, look angles and pass prediction (orbit-engine.js 1–30). It ships a self-test on a fixed ISS element set and a 30-satellite battery checked against the python-sgp4 reference (536–550; tools/orbit-truth.json).
orbit-data.js holds a CelesTrak snapshot in TLE format, fetched on 27 August 2026 at 16:05:31 UTC, and the page prints its age on screen (orbit.js 89–99). Positions are swept 900 per frame so the frame never stalls (119–126). Passes are scanned in 30-second steps above 10 degrees of elevation for 48 hours, and the table says when the best visible moment is not the peak. Your location can be typed, remembered, or taken from the browser's geolocation when you ask.
3The test
We fetched the page and its scripts from the local 537 copy, parsed the snapshot, ran the engine against its own reference file under JavaScriptCore, and asked it for New York's ISS passes.
Fetched the page (at 20:10:50) and its four scripts.
Page 61,688 bytes; orbit-engine.js 24,385; orbit-data.js 1,833,199; orbit-land.js 56,196; orbit.js 31,830.
Ran the self-test and the 30-satellite battery.
Self-test OK on 6 checks. Battery: 90 position rows up to 720 minutes from epoch, 0 errors, worst difference from python-sgp4 9.8e-11 km (STARLINK-35832 at 720 minutes).
Parsed the snapshot.
Stations 21, visual 157, Starlink 10,733: 10,911 element sets, 10,908 unique catalogue numbers, the highest 69998. Fetched 31.2 days before the test.
ISS passes for New York (40.7128, −74.0060), next 48 hours.
12 passes. The first peaks at 13.7 degrees, lasts 3.7 minutes and is not visible, because the sun is up. The ISS elements used were 31.71 days old.
4Against the field
Each rival was read on its own pages on the test day. Pencil marks what it does better; red, where ORBIT goes further.
Heavens-Above
heavens-above.com · checked 27 September 2026, 20:19 UTC; re-checked 21:06 UTC
A long-running satellite and astronomy site: 10-day pass predictions for satellites of special interest, the ISS among them, Starlink passes for a whole launch, daily predictions for brighter satellites, interactive sky charts and a satellite database.
In pencil
- Ten days of predictions against ORBIT's 48 hours.
- Sky charts for plotting a pass against the stars.
- A long-standing satellite database; ORBIT carries three groups.
In red
- The whole Starlink shell and the brightest satellites moving at once on a globe, each position computed in your browser.orbit.js 119–126
- It states the age of its data, and what it excluded and why.orbit.js 89–99
N2YO
n2yo.com · checked 27 September 2026, 20:19 UTC
Live satellite tracking and predictions, tracking 35,435 objects on 27 September 2026 by its own count, with email and SMS pass alerts, a space-station notification tool and an API.
In pencil
- 35,435 objects tracked, against ORBIT's 10,911 element sets.
- Pass alerts by email and SMS, and an API.
In red
- Its propagator is open to inspection and ships its own test against python-sgp4; we measured a worst error of 9.8e-11 km.orbit-engine.js 536–550
- No account and no server once loaded: the maths runs on your machine.orbit-engine.js 1–12
CelesTrak
celestrak.org · checked 27 September 2026, 20:19 UTC
The publisher of the GP element sets ORBIT uses, in TLE and the newer OMM formats. It checks for new data every two hours, and states that five-digit catalogue numbers ran out on 11 July 2026 and that TLE cannot carry objects above 99999.
In pencil
- Fresh elements several times a day, in OMM formats that can carry newly catalogued objects.
In red
- It turns raw element sets into a live globe and a pass table with nothing to install.orbit.js 1–8, 440–478
5Where it falls short
- Old input. The ISS elements were 31.7 days old at test time and the page does not refresh them; it shows the age rather than correcting for it.
- A format that has run out. CelesTrak says objects numbered above 99999 cannot be carried in TLE; ORBIT's highest catalogue number is 69998, so newly catalogued satellites cannot appear.
- 1.8 MB of elements must download before the globe fills.
- Near-earth only. GPS and geostationary satellites are excluded by design.
- No alerts, no star chart for a pass, no brightness prediction.
6The verdict
ORBIT's engine is as exact as its reference and admirably candid about its data; but that data is a month-old snapshot in a format that cannot carry new satellites, so read its pass times as a guide.
- In red ink
- Its own SGP4 engine, tested to 9.8e-11 km; 10,911 objects on one globe; visible passes marked honestly; data age printed.
- In pencil
- For ten-day predictions and sky charts, Heavens-Above; for alerts and breadth, N2YO.