|Mission type||Venus impact probe|
|Launch mass||6520 kg |
|Dry mass||948 kg|
(including an impact
probe of 285 kg) 
|Start of mission|
|Launch date||27 March 1964, 03:24:43 GMT|
|Launch site||Baikonur, Site 1/5|
|End of mission|
|Decay date||28 March 1964|
|Perigee altitude||167 km|
|Apogee altitude||198 km|
|Epoch||27 March 1964|
Kosmos 27 (Russian: Космос 27 meaning Cosmos 27), also known as Zond 3MV-1 No.3 was a space mission intended as a Venus impact probe. The spacecraft was launched by a Molniya 8K78 carrier rocket from Baikonur. The Blok L stage and probe reached Earth orbit successfully, but the attitude control system failed to operate.
Kosmos 27 was a "third-generation" deep space planetary probes of the 3MV series of the Soviet Union. The Soviet engineers planned four types of the 3MV, the 3MV-1 (for Venus impact), 3MV-2 (for Venus flyby), 3MV-3 (for Mars impact), and 3MV-4 (for Mars flyby). The primary difference over the second-generation was vastly improved (and in many cases doubled) orientation system elements as well as improved onboard propulsion systems. While these four versions were meant to study Mars and Venus.
The probe was the first dedicated 3MV spacecraft that the Soviets launched (earlier missions had been of the test "Object-Probe" versions as Kosmos 21). It was designed to accomplish atmospheric entry into Venus followed by descent and impact. On 27 March 1964, it had a perigee of 167 kilometres (104 mi) and an apogee of 198 kilometres (123 mi), with an inclination of 64.8° and an orbital period of 88.7 minutes. The spacecraft successfully reached Earth orbit but failed to leave for Venus when the Blok L upper stage malfunctioned. The upper stage lost stable attitude due to a failure in the circuit of the power supply circuit that powered the valves for the attitude control system; hence, the stage remained uncontrollable and not ready to initiate a burn to leave Earth orbit. The problem was traced to a design error, the examination of telemetry data found that the failure was due to a design flaw in the circuitry of the BOZ unit, which resulted in power not being transferred to the attitude control jets on the Blok L stage, rather than one related to quality control. The spacecraft burned up in Earth's atmosphere the following day, on 28 March 1964. If successful, this mission would have been given a "Venera" designation.