Chandra
Chandra does not orbit like anything else on this site. It swings out to 136,000 km — a third of the way to the Moon — and back in to 12,000 km, taking nearly three days to go round once. That extreme path is the entire design.
What makes Chandra different
An orbit built to escape the radiation belts
Earth is wrapped in belts of trapped charged particles that swamp an X-ray detector. Chandra’s long ellipse carries it clear of them for most of each circuit, and it observes only during that quiet stretch — roughly fifty-five hours out of every sixty-four.
Nearly three days for one orbit
Compare the ground track on this page with the ISS’s. Where a low satellite loops the planet in ninety minutes, Chandra takes 64 hours — which is why its map looks unlike any other satellite here.
X-rays cannot be focused normally
X-rays pass straight through an ordinary mirror. Chandra uses nested cylindrical mirrors that graze the incoming light at a very shallow angle, deflecting it a little at a time — which is why an X-ray telescope looks like a set of tubes rather than a dish.
The heaviest payload the Shuttle ever deployed
Columbia carried it up in July 1999, and an upper stage then pushed it out to its high orbit.
Chandra sees the universe at temperatures where matter emits X-rays: gas falling into black holes, the shockwaves of supernova remnants, the million-degree plasma filling galaxy clusters. None of that light reaches the ground, and none of it can be focused by a conventional mirror. The orbit is as unusual as the optics. Rather than sitting low like Hubble, Chandra flies a deep ellipse specifically to spend most of its time outside the Van Allen belts, where its detectors can work uninterrupted for more than two days at a stretch. It shares a scientific brief with AstroSat, which observes X-rays from a much lower and quieter equatorial orbit — two very different engineering answers to the same problem.
Frequently asked questions
Why does Chandra have such a strange orbit?
To get above Earth’s radiation belts. Trapped particles there would overwhelm its detectors, so it observes during the long stretch of each orbit spent far out.
How long is one Chandra orbit?
About 64 hours — nearly three days — against roughly 90 minutes for a satellite in low Earth orbit.
Is Chandra still operating?
Yes, well past its original five-year design life, though its future has been subject to budget uncertainty.
Can I see Chandra from the ground?
No. At apogee it is more than 136,000 km away, far beyond naked-eye visibility.