XLR81

XLR81

Standard Agena D 108 being delivered to final assembly area. Would later become Gemini Agena target vehicle 5003.[1]
Country of origin	United States
Date	1957
First flight	1963-07-12[2]
Last flight	1984-04-17[2]
Manufacturer	Bell Aerosystems Company[3]
Application	upper stage engine[4]
Associated L/V	Thor, Thorad, Atlas and Titan
Predecessor	Bell 8081
Successor	Bell 8247
Status	Retired
Liquid-fuel engine
Propellant	RFNA[3] / UDMH[3]
Mixture ratio	2.55[5]
Cycle	Gas generator[3]
Configuration
Chamber	1[3]
Nozzle ratio	45[2]
Performance
Thrust (vac.)	71.2 kN (16,000 lbf)[2]
Chamber pressure	3.49 MPa (506 psi)[2]
Isp (vac.)	293 s[2]
Burn time	265 s[2]
Restarts	2[2]
Gimbal range	+/-2.5°[6][7]
Dimensions
Length	2.11 m (83.2 in)[7]
Diameter	0.90 m (35.5 in)[6]
Dry weight	134 kg (296 lb)[7]
Used in
RM-81 Agena[2]

Model 8048

The Bell Aerosystems Company XLR81 (Model 8096) was an American liquid-propellant rocket engine, which was used on the Agena upper stage. It burned UDMH and RFNA fed by a turbopump in a fuel rich gas generator cycle. The turbopump had a single turbine with a gearbox to transmit power to the oxidizer and fuel pumps. The thrust chamber was all-aluminum, and regeneratively cooled by oxidizer flowing through gun-drilled passages in the combustion chamber and throat walls. The nozzle was a titanium radiatively cooled extension. The engine was mounted on an hydraulic actuated gimbal which enabled it thrust vectoring to control pitch and yaw. Engine thrust and mixture ratio were controlled by cavitating flow venturis on the gas generator flow circuit. Engine start was achieved by solid propellant start cartridge.^[6]

Variants

Starting as an air-launched missile engine and finishing as a multi mission general propulsion for the space age, the basic design went through a series of iterations and versions that enabled it to have a long and productive career.

• Bell Model 117: USAF designation XLR81.^[8] Also known as the Bell Hustler Rocket Engine. The engine was developed for the B-58 Hustler Powered Disposable Bomb Pod. It reached a maturity of development where its performance was confirmed through a Performance Flight Rating Test. However, the project was cancelled before it could be flight tested. It burned JP-4 aircraft kerosene as fuel and used RFNA as oxidant, to supply a thrust 67 kN (15,000 lbf).^[6]
• Bell Model 8001: USAF designation XLR81-BA-3.^[2] It was used on the Agena-A prototype. It was based on the Bell Model 117. In fact, it only needed a gimbal mount to provide thrust vectoring, relocating the gas generator exhaust port to enable the gimbal movement and addition of a nozzle closure as major modifications. As its predecessor, it burned RFNA and JP-4 propellant and had a thrust 67 kN (15,000 lbf) with an I_spof 265.5 seconds with its 15 expansion ratio. Its rated duration was 100 seconds and only launched twice. The first flight was on 28 February 1959.^[6][9][10]
• Bell Model 8048: Also known as the XLR81-BA-5.^[2] Used on the Agena-A, it switched propellants to the hypergolic RFNA and UDMH. Since the mixture self-ignites on contact, the engine could be greatly simplified. For example, the combustion chamber ignition system was eliminated. The most important system was the passive thrust regulating system. The use of a series of venturi holes in the gas generator allowed it to supply a 67 kN (15,000 lbf) with just a 1.6 kN (350 lbf) variability without moving parts. Also, the expansion ratio was increased to 20 which enabled it to achieve an I_sp of 276 seconds. First flew on January 21, 1959 and last flew on January 31, 1961. It was used for the first American experience on vacuum starting an engine, since it was believe at the time that engines would need atmospheric pressure for start up.^{[2][6][9][10]}
• Bell Model 8081: This version was the first designed to have two restart capability, by use of three ignition cartridges, and extensive validation of vacuum starting behaviour. Thrust was increased to 71 kN (16,000 lbf) and expansion ratio to 45 for an I_sp of 293 seconds. USAF designation XLR81-BA-7. Used on the Agena-B, it first flew on December 20, 1960 and last flight was on May 15, 1966.^[11]
• Bell Model 8096: USAF designation XLR81-BA-11 and later, YLR81-BA-11.^[3][6] Main production version, used on the Agena-D. It added to the 8081 a titanium with molybdenum reinforcements nozzle extension, which enabled it to reach an I_sp of 280s. It also added inducers to the turbopumps, reducing the pressurization requirements on the tanks. In 1968, restart capability was increased to three restarts.^[2][4][6][9]
• Bell Model 8096-39: This was a version that switched oxidizer to MIL-P-7254F Nitric Acid Type IV — known as HDA (High Density Acid) — mixture of 55% IRFNA and 44% N₂O₄ with some hydrogen fluoride as inhibitor.^[12] It achieved a thrust of 76 kN (17,000 lbf) with an I_sp of 300s.^[9]
• Bell Model 8096A: A proposed improvement over the 8096-39 that would increase the size of the nozzle extension at an expansion ratio of 75, achieving an I_sp of 312 seconds.^[9]
• Bell Model 8096B: Proposed version for use with an Agena based reusable upper stage for the Space Shuttle. It would switch propellant to MMH plus hexamethyldisilazone (HMZ) and N₂O₄ on a 1.78 mixture ratio and add a niobium nozzle with a 100:1 expansion ratio for an increase in I_sp to 327 seconds, or 330 seconds with a 150:1 nozzle. The propellant change would require modification of the gas generator venturi holes to achieve power balance with the new performance without redesigning the turbopump. The chamber pressure would be reduced to 3.35 MPa (486 psi). Within the same actuators, it enable to increase the gimbal angle to 3 degrees, change engine clocking to reduce oil leakage. It would decrease the coolant passage diameter, since the new oxidizer could stay within specification at a higher flow velocity. The injector would change from flat to a 5-legged baffle, the pump seals would be improved and the oxidizer valve would change to a torque motor design. It would also implement some material changes in the turbopump bearings that would eliminate the oxidized boiling that prevented a restart in the 15 minute to 3 hours period after an ignition. The multi start capabilities of the 8247 would have been ported. This would enable up to 200 starts. Also, single burn life was expanded to 1200 seconds.^[7][13]
• Bell Model 8096L: Since the 8096B would require expensive changes in propellant handling, a middle step was proposed. It would switch fuel to MMH plus hexamethyldisilazone (HMZ), while keeping the same oxidant as the 8096-39, and change the mixture ratio at 2.03. The rest of the changes were the same as the 8096B, except that it would keep the same cooling channel diameter as the 8096, the chamber pressure would be reduced to 3.34 MPa (484 psi), and the niobium nozzle would have a 150:1 expansion ratio. The restart capabilities would be 10 to 100 starts depending on certification effort.^[5][7][14]
• Bell Model 8247: USAF designation XLR81-BA-13. Used on the Agena target vehicle and as a pure upper stage in the form of the Ascent Agena. It added a new system that allowed multiple restarts. The system replaced the start up cartridges for two metallic bellows on the oxidizer and fuel tank, which could supply enough pressure for start up. Once the turbopump reached its peak power, the outlet pressure was used to refill those bellows, and thus it recharged itself. While it was rated at 15 restarts, in practice it never did more than 8, which were performed during the Gemini XI mission.^[6][9][15]
• Bell Model 8533: A program to develop an upgraded version of the 8247. It switched propellants to UDMH and N₂O₄ and had general performance improvements. The propellant switch not only enabled better performance, but also allowed it to stay fueled on the pad for periods of time longer than 15 days.^[6][16]

See also

• RM-81 Agena
• Thor-Agena
• Thorad-Agena
• Atlas-Agena
• Titan (rocket)
• Rocket engine using liquid fuel

References

External links

• B14643.de
• Nasaspaceflight.com thread on Agena Documentation.
• Nasaspaceflight.com thread on Agena Documentation.

Rocket engines and solid motors for orbital launch vehicles
See also: Comparison of orbital rocket engines
Liquid fuel	Cryogenic (LH2 / LOX) China YF-73 YF-75 YF-75D YF-77 Europe HM7B Vinci Vulcain India CE-7.5 CE-20 Japan LE-5 LE-7 Russia KVD-1 (RD-56) RD-0120 USA BE-3U J-2 RL10 RS-25 (SSME) RS-68 Cryogenic (CH4 / LOX) USA BE-4 Raptor Semi-cryogenic (RP-1 / LOX) China YF-100 YF-115 India SCE-200 New Zealand Rutherford Russia NK-33 RD-58 RD-0105, 0109 RD-0107, 0108, 0110 RD-0110R RD-0124 RD-107, 108, 117, 118 RD-120 RD-170, 171 RD-180 RD-191, 151, 181 RD-193 S1.5400 Ukraine RD-8 RD-801 RD-810 USA F-1 H-1 Kestrel LR-79 LR-89 LR-105 Merlin 1 RS-27 RS-27A RS-56 S-3D XLR50 Hypergolic (UDMH, UH 25, Aerozine or MMH reacting with N2O4) China YF-1, 2, 3 YF-20, 21, 22, 24, 25 YF-23 YF-40 YF-50D Europe Aestus Astris Vexin Viking India PS4 Vikas Israel LK-4 Russia 17D61 RD-0202 to 0206, 0208 to 0213 RD-0207, 0214 RD-0216, 0217, 0235 RD-0233, 0234 RD-0236 RD-0237 RD-0243, 0244, 0245 RD-0255, 0256, 0257 RD-250, 251, 252, 261, 262 RD-253, 275 RD-263, 268, 273 RD-270 RD-854, 861 RD-855 RD-856 RD-864, 869 S5.92 S5.98M Ukraine RD-843 USA AJ10 LR-87 LR-91 TR-201 Hypergolic (other oxidizers) Europe Gamma Russia RD-119 RD-214 USA XLR81
Solid fuel	China FG-02 FG-36 FG-46 FG-47 SpaB-65 SpaB-140C Europe Mage 1 P-4 P-6 PAP P80 P230 Topaze Waxwing Zefiro 9 Zefiro 23 India S7 S9 S12 S139 S200 Israel LK-1 RSA-3 Japan KM-V1 KM-V2b M-14 M-24 M-34 M-34c SRB-A USA AJ-60A Algol Castor 30 GEM Orbus-6 Orbus-21 Orion Space Shuttle SRB Star 27 Star 37 Star 48 UA120 USRM X-248 X-254
Engines under development are in italics.

Orbital spacecraft rocket engines and motors that have flown
Liquid fuel engines	17D12 11D426 17D61 AJ10 BT-4 Draco KTDU-426 LEROS LMAE LMDE R-4D RS-25 S400 S5.4 S5.60 S5.79 S5.80 S5.92 SuperDraco TR-201 XLR81
Solid propellant motors	Star 37 Star 48 FG-15 FG-36 SpaB-65 SpaB-140C
Related articles	Spacecraft propulsion Spacecraft Satellite

Thor and Delta rockets
PGM-17 Thor Thor family Delta family
Rockets	Thor Thor Thor-Able Thor-Ablestar Thor-Agena Thor-Burner Thor-Delta Thor DSV-2 Thor DSV-2U Thorad-Agena Delta Alphabetical Delta A Delta B Delta C Delta D Delta E Delta F Delta G Delta J Delta L Delta M Delta N Numerical Delta 0100 Delta 1000 Delta 2000 Delta 3000 Delta 4000 Delta 5000 Delta 6000 Delta 7000 Delta 8000 Delta 9000 Modern Delta II Delta III Delta IV Export N-I N-II H-I
Launch sites	Canaveral (S)LC-17 LC-18B SLC-37B Johnston LE-1 LE-2 Tanegashima Osaki Vandenberg SLC-1 SLC-2 SLC-3 SLC-6 SLC-10 Bases Bardney Breighton Caistor Carnaby Catfoss Coleby Grange Driffield Feltwell Folkingham Full Sutton Harrington Hemswell Ludford Magna Melton Mowbray Mepal North Luffenham North Pickenham Polebrook Shepherds Grove Tuddenham
Components	Boosters Castor-1 Castor-1 Castor-4 Castor-4A CBC GEM-40 GEM-46 GEM-60 First stages Common Booster Core Upper Stages Delta Delta-A Delta-D Delta-E Delta-F Delta-K Delta-P DCSS Other Able Ablestar Agena Altair Burner FW-4D IABS PAM-D Star UM-129 Engines AJ10 B-8048 B-8081 B-8096 LE-5 LR-79 R-4D RL10 RS-27 RS-68 TR-201
Manufacturers	Rocket Douglas McDonnell Douglas Boeing United Launch Alliance Engines Aerojet Alliant Rocketdyne Thiokol TRW
Launches	1957–1959 1960–1969 1970–1979 1980–1989 1990–1999 2000–2009 2010–2019

Atlas rockets
Main articles	Atlas family SM-65 Atlas
Rockets	Prototypes MX-774 Atlas A Atlas B Atlas C Missiles Atlas D Atlas E Atlas F Launch systems Alphabetical Atlas B Atlas D Atlas E/F Atlas G Atlas H Upper stages Atlas-Able Atlas-Agena Atlas-Centaur Numerical Atlas I Atlas II Atlas III Atlas V Other Atlas LV-3B Atlas SLV-3 GX
Launch sites	Cape Canaveral LC-11 LC-12 LC-13 LC-14 (S)LC-36 SLC-41 Vandenberg LC-576 SLC-3 SLC-4 Bases Altus Dyess Fairchild Forbes Francis E. Warren Lincoln Offutt Plattsburgh Schilling Walker
Components	Boosters AJ-60A Castor 4A MA First stages Common Core Booster Upper stages Able Agena Altair Burner Centaur IABS MSD OIS PTS SGS Star SVS Trident Engines AJ-10 B-8048 B-8081 B-8096 LR-89 LR-105 R-4D RD-180 RL10 RS-56
Corporations	Manufacturers Rocket Convair General Dynamics Martin Marietta Lockheed Martin Engines Aerojet NPO Energomash Pratt & Whitney Rocketdyne Thiokol LSPs International Launch Services United Launch Alliance
Launches	1957-1959 1960-1969 1970-1979 1980-1989 1990-1999 2000-2009 2010-2019

Titan rockets
Main articles	Titan family SM-68 Titan Launches
Rockets	Missiles HGM-25A Titan I LGM-25C Titan II Launch Systems Titan II GLV Titan IIIA Titan IIIB Titan IIIC Titan IIID Titan IIIE Titan 34D Titan 23G Commercial Titan III Titan IV Unbuilt Ares Titan-Vanguard Titan-C Titan IIB Titan IIL Titan IIS Soltan Titan IIIL Titan IIIM Titan V
Launch sites	Cape Canaveral LC-15 LC-16 LC-19 LC-20 (S)LC-40 (S)LC-41 Vandenberg OSTF SLTF LC-395 SLC-4 SLC-6 Bases Larson Mountain Home Beale Ellsworth Lowry Davis-Monthan McConnell Little Rock
Components	Boosters UA1205 UA1206 UA1207 USRM Upper stages Agena Centaur IUS Star-37 TOS Transtage Engines AJ-10 B-8096 Orbus 6 Orbus 21 LR-87 LR-91 RL10
Manufacturers	Rocket Martin Lockheed Martin Engines Aerojet Pratt & Whitney Thiokol