|Mission type||ABM radar target|
|Mission duration||155 days|
|Launch mass||325 kg |
|Start of mission|
|Launch date||8 July 1966, 05:31:00 GMT|
|Launch site||Kapustin Yar, Site 86/1|
|End of mission|
|Decay date||10 December 1966|
|Reference system||Geocentric |
|Perigee altitude||256 km|
|Apogee altitude||512 km|
|Epoch||8 July 1966|
Kosmos 123 (Russian: Космос 123 meaning Cosmos 123), also known as DS-P1-Yu No.5 was a Soviet satellite which was used as a radar calibration target for tests of anti-ballistic missiles. It was built by the Yuzhnoye Design Bureau, and launched in 1966 as part of the Dnepropetrovsk Sputnik programme.
A Kosmos-2I 63S1 carrier rocket was used to launch Kosmos 123. The launch occurred from Site 86/1 at Kapustin Yar, at 05:31 GMT on 8 July 1966. and following its successful arrival in orbit the spacecraft received its Kosmos designation; along with the International Designator 1966-061A  and the Satellite Catalog Number 02295.
Kosmos 123 separated from the carrier rocket into a low Earth orbit with a perigee of 256 kilometres (159 mi), an apogee of 512 kilometres (318 mi), an inclination of 48.8°, and an orbital period of 92.2 minutes. It decayed from orbit on 10 December 1966. Kosmos 123 was the sixth of seventy-nine DS-P1-Yu satellites to be launched, and the fifth of seventy-two to successfully reach orbit.