Empirical Earth · Space, Satellites & the Edges of the Map

Lunar retroreflectors & Apache Point

The claim

“We never went to the Moon, and it is just a nearby disc with nothing solid to hit.”

What is true

Nobody can go and look. The reflectors are 384,000 km away and cannot be inspected by anyone who doubts them.

What is measured

Lasers bounce off five Moon-based reflector arrays, timing the ~2.5 s round trip to ~1 mm and clocking the Moon receding 3.8 cm/yr.

What would show this is wrong

a timed laser echo from the Moon returning far from ~2.5 s; or no measurable recession over years; or a demonstration that a passive corner-cube array can return a timed pulse from somewhere other than the coordinates an orbiting camera independently photographed it at.

Sources

  1. Lunar laser ranging (APOLLO, Apache Point). Retroreflectors left by Apollo 11/14/15 and the Soviet Lunokhod 1/2 rovers return laser pulses; the 3.5-m Apache Point telescope times the ~2.5 s link
  2. Lunar recession. Laser ranging shows the Moon receding ~3.8 cm/yr from tidal friction, gradually lengthening Earth’s day. NASA GSFC — measuring the Moon’s distance . link
  3. Lunar laser ranging by observatories worldwide. Stations in the US (McDonald, Apache Point, Haleakala), France (Grasse), Italy (Matera), Germany (Wettzell), China (Yunnan) and the former USS link
  4. The lost Lunokhod 1 reflector, found in 2010. Lunokhod 1 was delivered to Mare Imbrium by the Soviet Luna 17 mission on 17 November 1970 and drove about 10.5 km before contact was lost in 19 link
  5. Murphy et al., “Laser ranging to the lost Lunokhod 1 reflector,” Icarus (2010). The peer-reviewed account. The rover’s previous best-estimate position was almost 5 km from its true location. link
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