How big a telescope would you need to see the Apollo Landing Platform?

About 34 meters in diameter!

The landing platform is about 5 meters across. From a telescope near Earth, the platform would subtend an angle of 0.003 arcseconds of arc. You would need an orbiting optical telescope with an effective aperture of 34 meters. This comes from the formula 1.22 x 206265 x (wavelength/diameter) = angular resolution in arcseconds. where the wavelength is about 0.5 Angstroms and the angular size is 0.003 arcseconds.

At 5:32 p.m. EDT, June 18, 2009, an United Launch Alliance Atlas V rocket roared off the launch pad at Launch Complex 41 to begin the Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Satellite missions to the moon. The LRO instruments return global data, such as day-night temperature maps, a global geodetic grid, high resolution color imaging and the moon's UV albedo. However there is particular emphasis on the polar regions of the moon where continuous access to solar illumination may be possible and the prospect of water in the permanently shadowed regions at the poles may exist.

NASA's Lunar Reconnaissance Orbiter (LRO) has forever changed our view of the moon, literally bringing it into sharper focus and showing us the whole globe in unprecedented detail. This rich new portrait has been rendered by LRO's seven onboard instruments, which together have delivered more than 192 terabytes of data, images and maps -- the equivalent of nearly 41,000 typical DVDs.