Gat3way has recently posted on his blog an article showing how he was able to receive a signal from the Lunar Reconnaissance Orbiter (LRO) using only an RTL-SDR, WiFi grid antenna and a low noise block (LNB). The LRO is a NASA spacecraft which is currently orbiting and being used to create maps of the moon.
The LRO transmits a tracking, telemetry and control (TT&C) signal at 2271.125 MHz which is in the S band (2 to 4 GHz). Since the S band frequencies are commonly used for Indovision satellite TV, gat3way was able to find a cheap LNB which could downconvert the GHz level S band frequencies down into a frequency receivable by the RTL-SDR. For the antenna he used a high 22dBi gain motor controlled WiFi mesh parabolic grid antenna.
After aiming the antenna at the moon, gat3way was able to clearly see the LRO carrier signal in the RTL-SDR waterfall as shown in the image below.