Checked against NASA
MARGEN's numbers come from NASA's laser-measured lunar terrain and JPL's planetary ephemerides. Before computing any result, we wrote down what agreeing with NASA would mean. This is how it went.
Pass marks, set before measuring
| Check | Pass mark | Result |
|---|
Sunlight, 2008–2026
Earth in view, 2008–2026
Each dot is one of 160 random spots between 85°S and the south pole, averaged from 2008 to 2026, a full 18.6-year cycle of the Moon's orbit. Across: NASA's long-term maps (LOLA AVGVISIB, PGDA). Up: MARGEN, with the same terrain and JPL DE440. On the diagonal, the two agree. NASA counts Earth in view when any part of Earth shows; MARGEN does the same here, and in the navigator it asks for Earth's center, which is stricter. A few spots differ by more than 10 points, likely on steep slopes and rims where small terrain details decide whether the Sun or Earth clears the horizon. Download the 160 points.
The Athena landing, March 6, 2025
How it works
- Terrain. For every 20 m spot in a 2 × 2 km site, MARGEN traces the horizon in 360 directions across NASA LRO LOLA terrain: 20 m detail nearby, 80 m out to 250 km, with the Moon's curvature.
- Sky. JPL DE440 ephemerides (NAIF SPICE) give the Sun and Earth every hour from January to mid-April 2027. Sunlight counts the visible part of the Sun's disc; Earth in view needs Earth's center above the terrain. Solar panels and antenna sit 2 m above the ground.
- Landings. 1,000 landing points scatter around the aim with a 100 m typical miss. A landing works if, for its first 14 days, sunlight reaches it at least 50% of the time and Earth is in view at least 30% of the time. With 1,000 landings the chance is accurate to ±3.1 points or better (95%).
What it doesn't model
- Rocks, small craters and slopes smaller than the 20 m map spots. Athena's crater is one of them.
- Lander tilt, dust, temperature and batteries.
- Radio links. Earth in view is a clear line to Earth; it does not check antennas or ground stations.
- Light during the descent.
- Real landing errors are not the same in every direction. MARGEN uses a 100 m typical miss.
- Terrain more than 250 km away.
Data and references
- NASA LRO LOLA south pole elevation models, 20 m and 80 m (PGDA, NASA GSFC): pgda.gsfc.nasa.gov/products/90
- NASA LOLA average illumination and Earth visibility maps, AVGVISIB (PGDA): pgda.gsfc.nasa.gov/products/69
- JPL DE440 ephemerides and lunar frame kernels via NAIF SPICE: naif.jpl.nasa.gov
- JPL Horizons API: ssd.jpl.nasa.gov/horizons
- Mazarico, E. et al. (2011). Illumination conditions of the lunar polar regions using LOLA topography. Icarus 211, 1066–1081.
- Barker, M. K. et al. (2021). Improved LOLA elevation maps for south pole landing sites: error estimates and their impact on illumination conditions. Planetary and Space Science 203, 105119.
- Software: NumPy, SciPy, SpiceyPy, tifffile, fsspec, Vite, TypeScript. Font: Geist (SIL Open Font License).