Atlas G

Atlas G
	Launch of FLTSATCOM-7 on an Atlas G (AC-66).
Function	Expendable launch system
Manufacturer	Convair; General Dynamics
Country of origin	United States
Size
Height	43.90m (144.00 ft)
Diameter	3.05m (10 ft)
Mass	164,300kg (362,200 lb)
Stages	2.5
Capacity
Payload to 185 km (115 mi) LEO
Mass	5,900 kg (13,000 lb)
Payload to GTO
Mass	2,375 kg (5,236 lb)
Associated rockets
Family	Atlas
Launch history
Status	Retired
Launch sites	LC-36B, Cape Canaveral
Total launches	7
Success(es)	5
Failure(s)	2
First flight	9 June 1984
Last flight	25 September 1989
Boosters – MA-5
No. boosters	1
Powered by	2 LR-89-7
Maximum thrust	1,901.6 kN (427,500 lbf)
Specific impulse	293.4 s (2.877 km/s)
Burn time	155 seconds
Propellant	RP-1 / LOX
First stage
Powered by	1 LR-105-7
Maximum thrust	386.4 kN (86,900 lbf)
Specific impulse	316 s (3.10 km/s)
Burn time	266 seconds
Propellant	RP-1 / LOX
Second stage – Centaur
Powered by	2 RL-10A
Maximum thrust	147 kN (33,000 lbf)
Specific impulse	449 s (4.40 km/s)
Burn time	410 seconds
Propellant	LH2 / LOX
	[edit on Wikidata]

The Atlas G, also known as Atlas G Centaur-D1AR^[4]^[5] was an American expendable launch system derived from the Atlas-Centaur. It was a member of the Atlas family of rockets and was used to launch seven communication satellites during the mid to late 1980s. Atlas G consisted of an improved Atlas core with modernized avionics and stretched propellant tanks. The Centaur stage also had several updated components and other technical improvements. Atlas G flew 7 times, with all missions aiming to go to a geostationary transfer orbit. It was replaced by the near-identical Atlas I, which had an improved guidance system and offered a larger payload fairing.

Description

Atlas first stage

Atlas G was an evolution of the Atlas-Centaur, boasting numerous performance improvements. Compared to its predecessor, Atlas G featured an 81-inch stretch of its first-stage propellant tanks and a new MA-5 engine section on its first stage, increasing its thrust by 7,500 lbf (33,000 N).^[6]

The first stage MA-5 engine section consisted of 2 LR-89-7 booster engines and one LR-105-7 sustainer engine. 2 LR-101 vernier engines were mounted on the side of the vehicle for roll control. The structure of the first stage consisted of stainless steel balloon tanks, much like earlier Atlas rockets. The tanks featured extremely thin walls, saving a considerable amount of mass, but also requiring the stage to be constantly pressurized to not collapse. The sustainer and vernier engines were mounted onto this tank structure. The two booster engines, however, were mounted to their own cylindrical skirt structure which was attached to the bottom of the tanks. Each LR-89-7 had its own turbopump to feed propellants into the combustion chamber, but the two engines shared a single common gas generator.^[3]

The booster engines, along with their support structure and plumbing, would drop away around two and a half minutes into flight after the vehicle reached 5.3g of acceleration. As the sustainer engine was more efficient than the booster engines, dropping the booster engines increased the stage's performance.^[3] The LR-105-7 sustainer engine and LR-101 vernier engines shut down when all propellant in the first stage tanks was depleted, around four and a half minutes after liftoff. Toward the end of the first stage burn, the payload fairing was jettisoned.^[2]

Centaur upper stage

Atlas G's Centaur upper stage, known as Centaur D-1AR, featured several improvements over earlier Centaur variants. The hydrogen peroxide reaction control system (RCS) was replaced with a hydrazine RCS, a change that would persist up until the Centaur III flying on Atlas V. These controlled stage attitude during coasts between engine burns, as well as providing ullage thrust to settle propellants in the tanks. In addition, the hydrogen peroxide boost pumps on the RL-10 engines were removed, giving the improved engines the designation "RL-10A-3-3A". These engines also featured improved silver throat inserts.^[6]^[5]

To help slow the boiloff of liquid hydrogen in the tanks, Centaur featured fiberglass insulation panels that were jettisoned 25 seconds after the first-stage booster engines were jettisoned. The panels altogether had a mass of 553kg.^[5] This version of Centaur was one of the final variants to feature separating insulation panels.

Launches

The maiden voyage of Atlas G was the launch of Intelsat 5 on June 9, 1984. Atlas performance was normal as was Centaur orbital injection, but during the coasting phase prior to the second Centaur burn, the stage's LOX tank split open. Centaur and Intelsat tumbled end-over-end and were left in a useless orbit where they remained until reentering the atmosphere four months later.

Investigation into the failure found that a minor fatigue crack developed in the Centaur LOX tank during staging and orbital injection, which eventually led to complete tank failure and loss of the mission. The uprated Centaur flown on Atlas G, among other changes, deleted the propellant boost pumps in the interest of greater simplicity and weight-saving. To compensate for this, LOX tank pressure was increased by 25%. Although the tank had been designed to accommodate higher pressure, technicians at Convair inexplicably failed to test Centaur 5402 for leaks before shipping it to Cape Canaveral. In addition, engineers had not tested the Centaur G stages to verify if they could handle the shock from the explosive bolts on the booster firing during staging, but this test was performed later and the stage passed it.

Finally, the leak testing program and tools used at Convair were outdated and less reliable than newer methods and the tech personnel in charge of fabricating the Centaur's balloon tanks were badly inexperienced. Ultimately, this was a symptom of the entire US space program in the 1980s as plans to entirely replace expendable launch vehicles with the Space Shuttle had resulted in large-scale budget cutbacks and layoffs of experienced technicians.

All seven launches of Atlas G flew from Launch Complex 36B at Cape Canaveral.^[5]

Atlas G launches^[7]^[4]
Designation	Launch Date and Time	Mission	Outcome
AC-62	Sat Jun 09, 1984 23:03 UTC	Intelsat V F-9	Failure
AC-63	Fri Mar 22, 1985 23:55 UTC	Intelsat VA F-10	Success
AC-64	Sun Jun 30, 1985 00:44 UTC	Intelsat VA F-11	Success
AC-65	Sat Sep 28, 1985 23:17 UTC	Intelsat VA F-12	Success
AC-66	Fri Dec 05, 1986 02:30 UTC	FLTSATCOM-7	Success
AC-67	Thu Mar 26, 1987 21:22 UTC	FLTSATCOM-6	Failure
AC-68	Mon Sep 25, 1989 08:56 UTC	FLTSATCOM-8	Success

The first stage was derived from the SM-65 Atlas missile, and a Centaur was used as the second stage.^[8] The first stage was also flown without the Centaur, as the Atlas H.

References

^ Gunter D. Krebs. "Atlas-1 (Atlas I)". Gunter's Space Page. Retrieved 17 July 2022.
^ ^a ^b ^c ^d ^e General Dynamics (April 1992). "Atlas Mission Planner's Guide". Retrieved 17 July 2022.
^ ^a ^b ^c ^d ^e Norbert Brügge. "Variants of the "stage and a half" drive system (MA) of the Atlas rocket". Archived from the original on 20 January 2016. Retrieved 17 July 2022.
^ ^a ^b "Atlas-G Centaur-D1AR". Gunter's Space Page. Retrieved 2024-01-01.
^ ^a ^b ^c ^d Kyle, Ed. "Atlas Flown Variants". spacelaunchreport.com. Archived from the original on March 21, 2022.
^ ^a ^b John E. Pike. "Atlas variants". Retrieved 28 March 2023.
^ "Rocket Launch Manifest". nextspaceflight.com. Retrieved 2021-04-24.
^ Encyclopedia Astronautica - Atlas

[gunter-1] Gunter D. Krebs. "Atlas-1 (Atlas I)". Gunter's Space Page. Retrieved 17 July 2022.

[mpg-2] General Dynamics (April 1992). "Atlas Mission Planner's Guide". Retrieved 17 July 2022.

[ma5-3] Norbert Brügge. "Variants of the "stage and a half" drive system (MA) of the Atlas rocket". Archived from the original on 20 January 2016. Retrieved 17 July 2022.

[:0-4] "Atlas-G Centaur-D1AR". Gunter's Space Page. Retrieved 2024-01-01.

[slr-5] Kyle, Ed. "Atlas Flown Variants". spacelaunchreport.com. Archived from the original on March 21, 2022.

[global-6] John E. Pike. "Atlas variants". Retrieved 28 March 2023.

[7] "Rocket Launch Manifest". nextspaceflight.com. Retrieved 2021-04-24.

[EA-8] Encyclopedia Astronautica - Atlas

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v t e Orbital launch systems
List of orbital launch systems Comparison of orbital launch systems
Current	Angara 1.2 A5 Ariane 6 Atlas V Ceres 1 1S Chollima-1 Electron Falcon 9 Block 5 Falcon Heavy Firefly Alpha Gravity-1 GSLV H-IIA H3 Hyperbola-1 Jielong 1 3 KAIROS^† Kaituozhe 2 Kinetica 1 Kuaizhou 1 1A 11 Long March 2C 2D 2F 3A 3B/E 3C 4B 4C 5 5B 6 6A 7 7A 8 11 11H LVM3 Minotaur I IV V C Nuri OS-M1^† Pegasus XL Proton-M PSLV Qaem 100 Qased RS1^† Shavit 2 Simorgh SLS Block 1 Soyuz-2 2.1a / STA 2.1b / STB 2-1v SSLV Starship Tianlong-2 Unha Vega C Vulcan Centaur Zhuque 2
In development	Antares 330 Bloostar Cyclone-4M Deca Epsilon S Eris Gravity-2 Hyperbola-2 Irtysh Kuaizhou 21 31 Long March 9 10 12 Miura 5 MLV Neutron New Glenn New Line 1 NGLV Nova OS-M 2 4 Orbex Prime Pallas-1 Red Dwarf SLS Block 1B Block 2 Soyuz-7 Terran R Tianlong-3 VLM Vega E Zero Zhuque 3 Zuljanah
Retired	Antares 110 120 130^† 230 230+ Ariane 1 2 3 4 5 ASLV Athena I II Atlas B D E/F G H I II III LV-3B SLV-3 Able^† Agena Centaur Black Arrow Conestoga^† Delta A B C D E G J L M N 0100 1000 2000 3000 4000 5000 II III IV IV Heavy Diamant Dnepr Energia Epsilon Europa I^† II^† Falcon 1 Falcon 9 v1.0 v1.1 v1.2 "Full Thrust" Feng Bao 1 GSLV Mk I H-I H-II H-IIB Juno I Juno II Kaituozhe-1 Kosmos original 1 2/2I 3 3M Lambda 4S LauncherOne Long March 1 1D^† 2A 2E 3 3B 4A Mu 4S 3C 3H 3S 3SII V N1^† N-I N-II Naro-1 Paektusan^† Pilot-2^† R-7 Luna Molniya M L Polyot Soyuz original FG L M U U2 Soyuz/Vostok Sputnik Voskhod Vostok L K 2 2M R-29 Shtil' Volna^† Rocket 3 Safir 1 1A 1B Saturn I IB V Scout X-1 Blue Scout II^† X-2^† X-2M X-3 X-3M X-4 X-2B^† B A B-1 D-1 A-1 E-1 F-1 G-1 Shavit original 1 SLV Space Shuttle SPARK^† Sparta SS-520 Start-1 Terran 1^† Thor Able Ablestar 1 2 Agena A B D Burner 1 2 Delta DSV-2U Thorad-Agena SLV-2G SLV-2H Titan II GLV IIIA IIIB IIIC IIID IIIE 34D 23G CT-3 IV Tsyklon R-36-O original 2 3 Universal Rocket UR-500 Proton Proton-K Rokot Strela Vanguard Vega original VLS-1^† Zenit 2 2M 2FG 3SL 3SLB 3F Zhuque 1^†
Classes	Sounding rocket Small-lift launch vehicle Medium-lift launch vehicle Heavy-lift launch vehicle Super heavy-lift launch vehicle
This Template lists historical, current, and future space rockets that at least once attempted (but not necessarily succeeded in) an orbital launch or that are planned to attempt such a launch in the future Symbol ^† indicates past or current rockets that attempted orbital launches but never succeeded (never did or has yet to perform a successful orbital launch)

v t e Orbital launch systems developed in the United States
Active	Atlas V**^†† Electron Falcon 9 Block 5 Falcon Heavy Firefly Alpha Minotaur I IV V C Pegasus XL RS1^† SLS Block 1 Vulcan Centaur
In development	Antares 330 Daytona I MLV New Glenn Neutron Nova Red Dwarf SLS Block 1B Block 2 Starship Terran R
Retired	Antares 110/120/130/230/230+^††† Athena I II Atlas B D E/F G H I II III LV-3B SLV-3 Able Agena Centaur Conestoga Delta A B C D E G J L M N 0100 1000 2000 3000 4000 5000 II III IV IV Heavy Falcon 1 Falcon 9 v1.0 v1.1 v1.2 "Full Thrust" H-I* Juno I Juno II LauncherOne N-I* N-II* Pilot Rocket 3 Saturn I IB V Scout Space Shuttle SPARK Sparta Terran 1 Thor Able Ablestar Agena Burner Delta DSV-2U Thorad-Agena Titan II GLV IIIA IIIB IIIC IIID IIIE 34D 23G CT-3 IV Vanguard
* - Japanese projects using US rockets or stages ** - uses Russian engines ^† - never succeeded ^†† - no new orders accepted ^††† - used Ukrainian first stage