Daily forecast of when NASA’s Neil Gehrels Swift Observatory will re-enter the atmosphere, for the NASA Swift re-entry challenge. The forecast takes in SWORD Track 1’s 1 to 30 day forecasts of the F10.7 solar radio flux and the Ap geomagnetic index, which set how fast drag lowers Swift’s orbit.
Re-entry prediction
Our estimate of when Swift will drop to 80 km, the altitude
counted here as re-entry, is updated daily. The calculation starts
from Swift’s latest orbit from
Space-Track
and steps it forward with NASA’s GMAT orbit software and the
NRLMSISE-00 model of air density. How strongly drag acts on Swift,
and a correction to F10.7, are fitted from the recent orbits of
Swift and about 80 other satellites. Future F10.7 and Ap come from
the SWORD Track 1 forecasts below. For comparison, the same calculation is
also run with every pair of the F10.7 and Ap forecasts in the grid
beside the plot.
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Air density along the path
Predicted date from each daily update
Swift’s predicted altitude, averaged over each orbit, down to
80 km, and the air density it meets along the way, for the pair of
F10.7 and Ap forecasts picked in the grid; the faint grey lines are the
other pairs. With SWORD Track 1 for both, the red line is the middle of a few
hundred runs, each with the errors of one past SWORD Track 1 forecast and its
own drag value, and the shading shows their 50% and 90% ranges. Every
other pair is one run, drawn in blue, with SWORD Track 1 kept in red. A pair
runs only as far as the shorter of its two forecasts: if Swift is still
above 80 km when one ends, the grid shows “after” that
time and the lines stop there. The lowest plot shows the predicted date
from each daily update for the same pair; the updates of 5 to 7 October
were recalculated on 7 October with a corrected drag value.
The forecasts: SWORD Track 1 (below); NOAA SWPC’s 27-day outlook (issued on
Mondays); NJIT’s 60-day
F10.7; ADAPT-SIFT’s 7-day F10.7; SWORD Track 3’s 7-day F10.7 and
3-day ap; ESA’s short-term forecast (daily); the Schatten forecast
(monthly); and the last observed day held flat.
SWORD Track 3’s, ESA’s and the Schatten forecasts come from the
CCMC challenge page,
which posts SWORD Track 3’s a day or two late. Each run uses the newest
issue of each forecast.
Swift’s ballistic coefficient from each daily update
Swift’s ballistic coefficient, its mass divided by its drag
coefficient times its area, fitted in each daily update from the recent
orbits of Swift and about 80 other satellites, with the 50% and 90%
ranges of the drag values used in the runs.
F10.7 prediction
F10.7 tracks the solar ultraviolet output that heats the upper
atmosphere, so it sets how fast low satellites lose altitude to drag.
The forecast uses one gradient-boosted tree model per lead day, fed
with the last 60 days of F10.7, sunspot number,
NOAA SWPC solar region reports,
and far-side active-region detections from
GONG and
SDO/HMI.
On 2024–2026 test data its error is 11% lower than the
SWPC 27-day outlook.
↔ Drag to pan
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Black: observed daily F10.7 from the Penticton observatory. Red:
the newest forecast, issued once a day from the last full day of
data. The shaded bands are the ranges that held the observed value
50% and 90% of the time, refitted for each forecast on the
model’s earlier forecast errors at the same level of solar
activity. Show forecast
from draws the forecast the same model gives from any day since
January 2024, a period it was never trained or tuned on, so it can
be checked against what happened. These past forecasts use
today’s data archive, not the data available on that day.
The other lines are the other groups’ newest F10.7 forecasts,
each labelled with the day it was issued: from
NOAA SWPC,
the 45-day forecast, the 27-day outlook (issued on Mondays) and the
3-day forecast (from the daily report of solar and geophysical
activity); the 60-day forecast from
NJIT;
the 7-day forecast from
ADAPT-SIFT;
SWORD Track 3’s 7-day forecast; and ESA’s short-term forecast and
the Schatten forecast (monthly), both from the CCMC challenge page. For a past date each is the issue that was
out on that date; most have been saved only since early or mid-October
2026. Click a name in the legend to hide or show its line. Drag the plot
to pan back through the last six months (back to late 2023 for a past
date); double-click snaps back.
1 sfu = 10−22 W m−2 Hz−1.
Ap prediction
Ap is a daily index of geomagnetic activity from a worldwide network
of magnetic observatories. In a geomagnetic storm the upper
atmosphere heats and expands, and drag rises. The forecast uses one
gradient-boosted tree model per lead day, fed with the last 60 days
of 3-hourly ap, sunspot number and F10.7 from
GFZ Potsdam. On 2024–2026
test data its error for the next day is 18% lower than always
forecasting the long-term average. From the second day on it is
only 1–4% lower: nothing in its inputs says when the next storm
will arrive, so it does not forecast storms more than a day ahead.
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Black: observed daily Ap from GFZ Potsdam (the most recent weeks are
GFZ’s preliminary values). Red: the newest forecast, issued
once a day from the last full day of data. The red line is the
expected Ap; because a few storm days pull that average up, a typical
day falls below it. The shaded bands are the ranges that held the
observed value 50% and 90% of the time, refitted for each forecast
on the forecast errors of the previous 11 years. About 70% of storm
days (Ap 30 or more) fall above the 90% band. Show forecast
from draws the forecast the same model gives from any day since
January 2024, a period it was never trained or tuned on, so it can
be checked against what happened. These past forecasts use
today’s data archive, not the data available on that day.
The other lines are the other groups’ newest Ap forecasts, each
labelled with the day it was issued: the NOAA SWPC 27-day outlook
(issued on Mondays), SWORD Track 3’s 3-day forecast, ESA’s
short-term forecast and the Schatten forecast (monthly). For a past date each is the issue that was out on that date;
all but SWPC’s have been saved only since mid-October 2026. Click a
name in the legend to hide or show its line. Drag the plot to pan back through the last six months (back to late
2023 for a past date); double-click snaps back. Ap is in units of
2 nT.
Forecast performance
Each forecast against what then happened; before 1 October 2026 the
SWORD Track 1 values are hindcasts. SWPC issues its 27-day outlook once a week,
so the tables score both on those days only. Swift’s measured
altitude is a one-orbit average from each new Space-Track orbit. The
runs of 5 to 7 October were recalculated on 7 October with a
corrected drag value.
