KTDU-425 explained

KTDU-425 (11D425)
Country Of Origin:	Soviet Union
Manufacturer:	Isayev Design Bureau
Status:	Retired Propellent: UDMH/N2O4
Designer:	Aleksei Isaev
Thrust(Vac):	18.85 kN (KTDU-425) 18.89 kN (KTDU-425A)
Used In:	Mars 2-7, Venera 9-16 Vega 1,2 Astron, Granat Phobos 1,2
Mixture Ratio:	1.9

The KTDU-425 was a former Soviet liquid fuelled engine designed Aleksei Isaev of the Isayev Design Bureau. It was mainly used on the 4MV bus, which employed it as its main propulsion system. The first version which was the KTDU-425 (11D425), which had a thrust of 18.85kN was first used in 1971 for Mars-2, Mars-3 as well as the failed M-71C (Kosmos 419) probe.^[1] This was soon replaced by the KTDU-425A, which had a thrust of 18.89kN. This version was employed on the remaining 4MV and 5VK probes built, as well as Phobos 1 and 2.^[2]

Variants

• KTDU-425 (11D425) - First version of the KTDU-425. Employed in 1971 on M-71 Probes. Thrust: 18.85Kn, Specific Impulse: 312s, Burn time: 520s.^[3]
• KTDU-425A (11D425A) - Improved version of KTDU-425. Employed between 1973 and 1989. Thrust 18.89Kn, Specific Impulse: 315s, Burn time: 560s.

References

1. Web site: KTDU-425 . https://web.archive.org/web/20161228034718/http://astronautix.com/k/ktdu-425.html . dead . December 28, 2016 . 2022-04-17 . www.astronautix.com.
2. Web site: KTDU-425A . https://web.archive.org/web/20160819190952/http://www.astronautix.com/k/ktdu-425a.html . dead . August 19, 2016 . 2022-04-17 . www.astronautix.com.
3. Web site: Spacecraft-propulsion blocks from Isayev Design bureau (Khimmash) . 2022-04-17 . www.b14643.de.