The Titan 23G, Titan II(23)G, Titan 2(23)G or Titan II SLV was an American expendable launch system derived from the LGM-25C Titan II intercontinental ballistic missile. Retired Titan II missiles were converted by Martin Marietta, into which the Glenn L. Martin Company, which built the original Titan II, had merged. It was used to carry payloads for the United States Air Force (USAF), NASA and National Oceanic and Atmospheric Administration (NOAA). Thirteen were launched from Space Launch Complex 4W (SLC-4W) at the Vandenberg Air Force Base between 1988 and 2003.^[1]

Titan 23G

The first Titan 23G prior to launch
Function	Expendable launch system
Manufacturer	Martin Marietta / Lockheed Martin
Country of origin	United States
Size
Height	31.4 m (103 ft)
Diameter	3.05 m (10.0 ft)
Mass	117,020 kg (257,980 lb)
Stages	Two or Three
Capacity
Payload to LEO
Mass	3,600 kg (7,900 lb)
Payload to Polar LEO
Mass	2,177 kg (4,799 lb)
Payload to HCO
Mass	227 kg (500 lb)
Associated rockets
Family	Titan
Launch history
Status	Retired
Launch sites	Vandenberg, SLC-4W
Total launches	13
Success(es)	12
Failure(s)	1
First flight	5 September 1988
Last flight	18 October 2003
Type of passengers/cargo	Clementine QuickSCAT
First stage
Powered by	LR-87 (one engine with two combustion chambers)
Maximum thrust	1,900 kN (430,000 lbf)
Specific impulse	258 seconds
Burn time	156 seconds
Propellant	N2O4 / Aerozine 50
Second stage
Powered by	1 LR-91
Maximum thrust	445 kN (100,000 lbf)
Specific impulse	316 seconds
Burn time	180 seconds
Propellant	N2O4 / Aerozine 50
Third stage (Optional) – Star-37XFP-ISS
Powered by	1 Solid
Maximum thrust	38.03 kN (8,550 lbf)
Specific impulse	290 seconds
Burn time	67 seconds
Propellant	Solid
Third stage (Optional) – Star-37S
Powered by	1 Solid
Specific impulse	287 seconds
Propellant	Solid
[edit on Wikidata]

Titan 23G rockets consisted of two stages burning liquid propellant. The first stage was powered by one Aerojet LR87 engine with two combustion chambers and nozzles, and the second stage was propelled by an LR91. On some flights, the spacecraft included a kick motor, usually the Star-37XFP-ISS; however, the Star-37S was also used.^[1]

A contract to refurbish fourteen Titan II missiles to the Titan 23G configuration was awarded to Martin Marietta in January 1986. The first launch occurred on 5 September 1988, carrying a classified payload for the U.S. National Reconnaissance Office. Thirteen were launched, with the fourteenth going to the Evergreen Aviation Museum.^[2] The final flight occurred on 17 October 2003, carrying a Defense Meteorological Satellite Program (DMSP) satellite.^[3]

During refurbishment, the forward structure of the second stage was modified with the addition of a payload attachment fitting to attach the payload to the rocket, and installing a payload fairing to protect it during launch. The engines were refurbished, and the rockets' guidance and control systems were upgraded by Delco Electronics.

The former Titan IIIB pad at Vandenberg, SLC-4W, was modified to accommodate the Titan 23G, and was used for all thirteen launches.