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NASA spacecraft

STEREO-A

Also stereo · stereo a · stereo ahead

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Active — "The STEREO-A spacecraft remains active" (science.nasa.gov, page updated 2025-12-12); JPL's trajectory is fitted to tracking through 2026-10-29 (Horizons, read 2026-11-04). It circles the Sun near the Earth's orbit, watching the Sun. Its twin, STEREO-B, went silent in 2014.

Measured

Agency
NASA
Launched
2006-10-26
From the Earth today
1.15 AU (172 million km)
Across its solar arrays
6.47 m

How far, from the Earth

1.15 AU. To cross it:

  • Light9 minutes 34 seconds
  • Voyager 1's speed3.88 months
  • Driving at 100 km/h196 years

Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.

Facts

  • JPL Horizons trajectory round the Sun: worst miss 69 km on the dates it was checked against (median 56 km); between those dates as much as about 206 km. Dates after the data was fetched are Horizons' predictions, which it revises as a mission flies.

Where this comes from

  • NASA/GSFC/JHUAPL
  • Spacecraft trajectories: JPL Horizons, NASA/JPL-Caltech; each mission's agency credited on its card.
  • 3D model: STEREO model: NASA 3D Resources

Every catalogue Ouranos draws is credited on the credits page.