BT-4 (rocket engine)

BT-4

Orbital Maneuvering Engine of the SELENE lunar orbiter
Country of origin	Japan
Designer	IHI Aerospace
Associated LV	HTV, Cygnus
Status	In production
Liquid-fuel engine
Propellant	N2O4 / Hydrazine
Cycle	Pressure fed
Configuration
Chamber	1
Performance
Thrust, vacuum	500 N (110 lbf)
Dimensions
Length	80 cm (31 in)
Dry mass	4 kg (8.8 lb)

The BT-4 is a pressure-fed liquid rocket engine designed and manufactured by IHI Aerospace of Japan. It was originally developed for the LUNAR-A project, but it has been used as a liquid apogee engine in some geostationary communications satellite based on the Lockheed Martin A2100 and GEOStar-2 satellite buses. It has also been used on the HTV and Cygnus automated cargo spacecraft.

History

During the 1970s, Ishikawajima-Harima Heavy Industries had built under license the Rocketdyne MB-3 for the N-I rocket, for which it had also developed the second stage attitude control system. ^{[1] [2]} In the 1980s it also developed the thrusters for ETS-4 (Kiku-3), the first to be built in Japan. In 2000 it acquired and merged with the aerospace division of Nissan and became IHI Aerospace. ^[2]

IHI Aerospace started developing the BT-4 for the later cancelled LUNAR-A mission to the moon. While the mission was cancelled, the thruster has seen success as a liquid apogee engine on the Lockheed Martin A2100 and Orbital ATK GEOStar-2 platforms. ^[3] Two other Orbital ATK products that use the BT-4 due to their leverage of the GEOStar-2 platform are the Cygnus spacecraft and the Antares Bi-propellant Third Stage (BTS). ^{[4] [5] [6] [7] [8] [9]}

The use on the A2100 platform has allowed IHI to export the BT-4 even to American military programs such programs as the MUOS and AEHF. ^{[10] [11] [12] [13] [14]}

On March 9, 2006, IHI Aerospace announced that the AEHF-2 BT-4 engine had successfully performed its mission, unlike AEHF-1's. ^{[14] [15] [16]} On November 29, 2010, IHI Aerospace announced that it had received and order from Lockheed Martin of four BT-4 engines for AEHF-4, MUOS-4, MUOS-5 and Vinasat-2. With this order, it achieved its 100th-unit foreign engine export since it started selling abroad in 1999. ^{[17] [18]}

For the HTV project, IHI developed a new version, the HBT-5, which enabled them to replace the American R-4D from the third flight onward. ^{[19] [20]}

On October 3, 2013, with the successful berthing of the Cygnus Orb-D1 mission, IHI announced that the propulsion was based on their 500N Delta-Velocity Engines. ^[21]

In January 2018, a BT-4 kick motor was used on the GovSat-1 geosynchronous commsat flight. ^[22]

Versions

The BT-4 is a family that has been used as liquid apogee engine, orbital maneuvering engine and as a thruster. Known variations:

• BT-4 (Cygnus): Used mainly as thruster, it burns MMH/N₂O₄ with a thrust of 450 N (100 lb_f). It weighs 4 kg (8.8 lb) and is 65 cm (26 in) tall. ^{[9] [10]}
• BT-4 (450N): Used mainly as LAE, it burns Hydrazine/N₂O₄ in a 1.69 O/F ratio. It has a thrust of 450 N (100 lb_f), a specific impulse of 329 s (3.23 km/s) and an input pressure of 1.62 MPa (235 psi). As of 2014, it had a demonstrated life of 32,850 seconds. ^[18]
• BT-4 (500N): Used mainly as LAE, it burns Hydrazine/N₂O₄ with a thrust of 500 N (110 lb_f), a specific impulse of 329 s (3.23 km/s). It weighs 4 kg (8.8 lb) and is 80 cm (31 in) tall. ^[14]
• 490N MON Thruster: Burns MMH/MON-3 with a 478 N (107 lb_f) nominal thrust, a specific impulse of 316 s (3.10 km/s) and an inlet pressure of 1.72 MPa (249 psi). As of 2014, it had a demonstrated life of 15,000 seconds. ^[18]
• HBT-5: Developed for the HTV to crew-rated standards, it burns MMH/MON-3, and has a thrust of 500 N (110 lb_f). Used in HTV-3 and since HTV-5 onward. ^{[19] [23]} The specific impulse is 316s ^[24]
• SELENE OME: Based on the DRTS Liquid apogee engine, the SELENE Orbital Maneuvering Engine burned a Hydrazine/MON-3 mixture. It had a thrust of 547 ± 54 N (123 ± 12 lb_f) and a specific impulse of 319.8 ± 5.1 s (3.136 ± 0.050 km/s) with an input pressure of 1.77 MPa (257 psi). ^{[25] [26]}

References

1. Wade, Mark. "MB-3-3". Astronautix.com. Archived from the original on September 15, 2016. Retrieved 2016-08-29.
2. IHI Aerospace. "IHI Corporate Profile" (PDF). pp. 6–7. Archived (PDF) from the original on 2022-04-17. Retrieved 2016-08-29.
3. Krebs, Gunter Dirk (2016-04-17). "Lunar A". Gunter's Space Page. Retrieved 2016-08-29.
4. Krebs, Gunter Dirk (2016-04-17). "Cygnus-PCM". Gunter's Space Page. Retrieved 2016-08-29.
5. Krebs, Gunter Dirk (2016-08-19). "Cygnus-PCM (enhanced)". Gunter's Space Page. Retrieved 2016-08-29.
6. Krebs, Gunter Dirk (2016-08-12). "Antares (Taurus-2)". Gunter's Space Page. Retrieved 2016-08-29.
7. Brügge, Norbert. "Antares, Propulsion". b14643.eu. Archived from the original on September 17, 2016. Retrieved 2015-08-29.
8. "Antares Fact Sheet" (PDF). Orbital ATK . Retrieved 2016-08-29.
9. "ISS Utilization: Cygnus". eoPortal Directory. Archived from the original on 2016-08-29. Retrieved 2016-08-29.
10. DeSantis, Dylan. "Satellite Thruster Propulsion-H₂O₂ Bipropellant Comparison with Existing Alternatives" (PDF). The Ohio State University. Retrieved 2016-08-29.
11. Wade, Mark. "AS 2100". Astronautix.com. Archived from the original on September 15, 2016. Retrieved 2016-08-29.
12. Krebs, Gunter Dirk (2016-06-24). "MUOS 1, 2, 3, 4, 5". Gunter's Space Page. Retrieved 2016-08-29.
13. Krebs, Gunter Dirk (2016-06-24). "AEHF 1, 2, 3, 4, 5, 6". Gunter's Space Page. Retrieved 2016-08-29.
14. "ロッキード・マーチン社向け衛星用エンジンがフライトに成功〜独自開発の世界最高性能のエンジンで２回連続のフライトに成功〜" [Success in two successive flights for the engine with world's best performance] (in Japanese). IHI Aerospace. March 9, 2006. Archived from the original on 2010-09-24. Retrieved 2016-08-29.
15. Krebs, Gunter Dirk (2016-08-05). "OSC → Orbital ATK: StarBus → Star-2 → GeoStar-2". Gunter's Space Page. Retrieved 2016-08-29.
16. Krebs, Gunter Dirk (2016-04-17). "Telkom 2". Gunter's Space Page. Retrieved 2016-08-29.
17. "IHI Aerospace Manufactured Engines Selected for AEHF-4, MUOS-4, MUOS-5, and Vinasat-2 Satellites by Lockheed Martin Space Systems Company". IHI Aerospace. November 29, 2010. Archived from the original on 2016-08-29. Retrieved 2016-08-29.
18. "IHI Aerospace Bipropellant Thrusters" (PDF). IHI Aerospace. December 2014. Archived from the original (PDF) on 2016-08-29. Retrieved 2016-08-29.
19. IHI Aerospace. "IHI Corporate Profile" (PDF). pp. 15–16. Archived (PDF) from the original on 2022-04-17. Retrieved 2016-08-29.
20. Krebs, Gunter Dirk (2016-08-24). "HTV 1, ..., 9 (Kounotori 1, ..., 9)". Gunter's Space Page. Retrieved 2016-08-29.
21. "Orbital Sciences developed CygnusTM Spacecraft which uses IHI Aerospace's Delta-Velocity Engine as its main engine successfully berthed to the International Space Station". IHI Aerospace. October 3, 2013. Archived from the original on 2016-08-29. Retrieved 2016-08-29.
22. Graham, William (January 31, 2018). "Falcon 9 launches GovSat-1 from SLC-40 – Booster survives water landing". nasaspaceflight.com. Retrieved September 29, 2025.
23. "HTV4 (KOUNOTORI 4) Mission Press Kit" (PDF). JAXA. August 2, 2013. Archived from the original (PDF) on 2016-08-29. Retrieved 2016-08-29.
24. "Spacecraft Thrusters - IHI Aerospace". satnow.com. Retrieved September 29, 2025.
25. "On-orbit operation result of "KAGUYA" Lunar Explorer propulsion subsystem" (PDF). JAXA. 2008. Retrieved 2016-08-29.
26. Ideo Masuda (JAXA); Hideshi Kagawa (JAXA); Daisuke Goto (JAXA); Hiroyuki Minamino (JAXA); Kenichi Kajiwara (JAXA); Yoshihiro Kishino (IHI Aerospace); Masayuki Tamura (IHI Aerospace); Mamoru Takahashi (IHI Aerospace); Yosuke Iwayama (NEC Toshiba Space Systems); Shingo Ikegami (NEC Corporation); Makoto Miyata (NEC Corporation). "Final Operations of Kaguya" (PDF). Archived from the original (PDF) on 2016-12-21. Retrieved 2016-08-29.