More info on contacting the astronauts on the ISS via ham radio.
The following frequencies are currently used for Amateur Radio ISS contacts (QSOs):
Voice and SSTV Downlink: 145.80 (Worldwide)
Voice Uplink: 144.49 for ITU Regions 2 and 3 (The Americas, and the Pacific and Southern Asia)
Voice Uplink: 145.20 for ITU Region 1 (Europe, Russia and Africa)
VHF Packet Uplink and Downlink: 145.825 (Worldwide)
UHF Packet Uplink and Downlink: 437.550
VHF/UHF Repeater Uplink: 145.99 (PL 67 Hz)
VHF/UHF Repeater Downlink: 437.80