Why the orbit is falling

Hubble does not “run out of fuel.” It has no station-keeping thrusters. The orbit decays because the upper atmosphere, thin as it is at ~500 km, still drags on a bus the size of a school bus. That drag tracks solar extreme ultraviolet and the 10.7 cm radio flux: when the Sun is loud, the thermosphere swells, density at Hubble’s height goes up, and the telescope comes down faster.

Solar Cycle 25 has been stronger and longer than a lot of the forecasts used when people still talked about Hubble lasting comfortably into the 2030s. The graph above is measured apogee and perigee from published element sets, not a decay model. A straight line from today’s yearly rate puts 400 km about — years out. That is a ruler, not a prediction: drag increases as altitude falls, and the next cycle will not copy this one.

If nobody reboosts it, Hubble will reenter uncontrolled sometime this next decade. This site started as a quick test. It will stay up until the altitude does not.

How to read the graph

White is apogee (highest point in the orbit). Grey is perigee (lowest). They have been closing for years; Hubble is in a nearly circular orbit now. Toggle F10.7 to see the Penticton 20:00 UTC observed flux on the right axis — the same number that shows up in the metric strip.

Dashed horizontals at 400 km and 200 km are operational bookmarks, not physics cliffs. Around 400 km, remaining useful life is likely a year or less and a reboost becomes a scramble. Around 200 km, reentry is imminent. Vertical marks are servicing missions. “Reentry view” stretches the time axis toward 2040 and drops the altitude floor to 150 km so the remaining air is visible.

Reboost

Hubble has been raised three times, always by a Space Shuttle:

• SM-1 (Dec 1993) — COSTAR, first reboost.
• SM-2 (Feb 1997) — STIS and NICMOS, reboost.
• SM-3A (Dec 1999) — emergency gyros. No reboost.
• SM-3B (Mar 2002) — ACS, reboost. Last time the orbit was raised.
• SM-4 (May 2009) — WFC3 and COS. Last visit. No reboost.

NASA has not approved another raise, including after Jared Isaacman’s offer to use a Crew Dragon. Gyros already steal observing time. The air will only get thicker.

This site is not affiliated with NASA. It is somewhat disappointed that NASA is not more open to a reboost. More on that later.

Uncontrolled reentry

Hubble was never designed to steer itself down. A controlled deorbit needs either a visiting vehicle that can dock or grapple and fire, or a dedicated disposal craft. Without that, the telescope will tumble in, and surviving hardware can reach the surface. That is the usual argument for doing something while there is still altitude to work with.

This page does not forecast a footprint or a date. Dates require an atmosphere model, a solar forecast, and a choice about whether anyone flies. What you can watch here is the only number that is not an argument: how high it is today.

Data

History is Space-Track gp_history for NORAD 20580, downloaded once and stored here. Daily updates use Space-Track gp (current element set only — that class is allowed hourly) and fall back to Celestrak if login fails. Mean altitude is (apogee + perigee) / 2. Yearly decay is a linear fit on recent points, not SGP4 and not NRLMSISE.

Solar flux is Natural Resources Canada’s Penticton 10.7 cm series, 20:00 UTC observed, from spaceweather.gc.ca. Pre-2004 values come from the same observatory’s earlier tables.