Targeting Halley's comet which had been predicted to reappear in 1985 after 76 years, ISAS started to develop the fourth generation Mu launch system, M-3SII, in 1981. It used the first stage of M-3S, and the rest of the stages were replaced by new ones to enhance its payload capability. The M-3SII-1 and -2, with an optional fourth kick stage, sent the first and second Japanese interplanetary probes, SAKIGAKE and SUISEI, into orbit in 1985 to encounter Halley's comet. Seven M-3SII launches out of eight were successful. It could send a 770 kg satellite into low earth orbit.
Mission by M-3SII Launch Vehicle
| Launch Date | Mission |
|---|---|
| 1993.2.20 | X-ray Astronomy ASCA |
| 1991.8.30 | Solar Observation YOHKOH |
| 1990.1.24 | Lunar Swing-by HITEN |
| 1989.2.22 | Aurora Observation AKEBONO |
| 1987.2.5 | X-ray Astronomy GINGA |
| 1985.8.19 | Halley’s Comet Explorer SUISEI |
| 1985.1.8 | Halley’s Comet Test Explorer SAKIGAKE |