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Muses A (Hiten)

Muses A (Hiten) with Hagoromo on top [ISAS]

Hiten (originally called Muses-A) was an ISAS (Japanese Space Agency) Earth orbiting satellite designed primarily to test and verify technologies for future lunar and planetary missions. The spacecraft carried a small satellite named Hagoromo which was released into orbit around the Moon. Hiten itself was put into a highly elliptical Earth orbit which passed by the Moon ten times during the mission, which ended when Hiten was intentionally crashed into the Moon on 10 April 1993. The primary objectives of the mission were to:

  • test trajectory control utilizing gravity assist double lunar swingbys;
  • insert a sub-satellite into lunar orbit;
  • conduct optical navigation experiments on a spin-stabilized spacecraft;
  • test fault tolerant onboard computer and packet telemetry;
  • conduct cis-lunar aerobraking experiments; and
  • detect and measure mass and velocity of micro-meteorite particles.

Three follow-on objectives were also added: excursion to the L4 and L5 Lagrangian points of the Earth-Moon system, orbit of the Hiten spacecraft around the Moon, and hard landing on the lunar surface. Hiten was named after a flying, music-playing Buddhist angel. Hagoromo was named for the veil worn by Hiten. This mission included Japan's first-ever lunar flyby, lunar orbiter, and lunar surface impact.

Hiten was a cylindrically shaped spacecraft, 1.4 m in diameter and 0.8 m high. The small polyhedral-shaped Hagoromo lunar orbiter was mounted on top of the spacecraft. The fully fueled mass of Hiten was 197 kg, this included 42 kg of hydrazine fuel and the 12 kg Hagoromo orbiter. Solar cells on the cylindrical surface of the spacecraft supplied the power requirement of 110 W, backed up by a small onboard battery. The spacecraft was spin-stabilized at 10 - 20.5 rpm.

Spacecraft propulsion and attitude control was provided by eight 23-N and four 3-N hydrazine thrusters, two spin-type Sun aspect sensors, a star scanner, a steerable horizon crossing indicator, three accelerometers, a nutation damper, and control electronics including an onboard processor. An optical navigation subsystem, consisting of two CCD image detectors to detect the Moon and bright stars was also tested.

Communications were accomplished through a medium gain collinear array antenna in both X-band and S-band protruding from the bottom surface of the spacecraft and two cross dipole omni-directional low gain antennas in S-band only, one mounted on the top and one on the bottom. Downlink is via onboard X-band and S-band transmitters, each with two power levels. Two receivers are used for S-band uplink, one connected to the low-gain antennas and the other to the medium gain antenna. Commands were sent from ground stations at 1 kbps. The onboard command computer consists of three independent processor cells with a total of 2 Mbits ROM and 512 Kbits RAM.

Hiten was launched into highly elliptical Earth orbit on a M-3S-2 [KM-M] rocket from Kagoshima Space Center in Japan at 11:46:00 UT on 24 January 1990. Injection velocity was 50 m/s less than the nominal value, resulting in an apogee of only 290,000 km compared to the expected 476,000 km. A number of trajectory correction maneuvers were performed and Hiten was put back in a nominal orbit. At 19:37 UT on 18 March 1990 as Hiten approached its first lunar flyby, the small Hagoromo spacecraft was released into lunar orbit, making Japan the third nation to orbit the Moon. Although the S-band transmitter aboard Hagoromo had failed on 21 February 1990, the ignition of the Hagoromo deceleration rocket was confirmed by ground observation at 20:04:03 UT, the estimated orbit was 7,400 × 20,000 km with a period of 2.01 days. Six seconds later, at 20:04:09 UT Hiten reached its closest flyby distance to the Moon of 16,472.4 km.

Further manuevers were made to have Hiten simulate the planned trajectory of the future Geotail spacecraft. Hiten completed seven more lunar swingbys by 4 March 1991 and then started the aerobraking portion of its mission. On 19 March at 00:43 UT Hiten flew into the Earth's upper atmosphere at an altitude of 125.5 km over the Pacific at 11.0 km/s. Atmospheric drag lowered the velocity by 1.712 m/s and the apogee altitude by 8665 km. This was the first time aerobraking was used to modify a spacecraft orbit at close to escape velocity. Another aerobraking maneuver was done at 11:36 UT on 30 March at 120 km altitude, reducing velocity by 2.8 m/s and apogee by 14,000 km. This concludied the primary mission and a follow-on mission was started. A ninth lunar swingby was used to increase the apogee to 1,532,000 km and a tenth on 2 October 1991 put Hiten into a looping orbit which passed through the L4 and L5 stable libration points to look for trapped dust particles. No obvious increase was found. On 15 February 1992 at 13:33 UT at a closest approach of 422 km most of Hiten's remaining fuel was used to put it into lunar orbit. The very last fuel was used to have the spacecraft, whose orbit was decaying after almost two months in lunar orbit, crash into the lunar surface on 10 April 1993 at 18:03:25.7 UT at 55.3 E, 34.0 S.

Nation: Japan
Type / Application: Technology, lunar orbiter
Operator: ISAS
Configuration: Cylinder, 1.4m in diameter and 79cm high
Power: Solar cells, batteries
Lifetime: 4.6 years
Mass: 197 kg (incl. Hagoromo)
Orbit: 262 km × 28600 km, 31 (initial orbit)
Satellite COSPAR Date LS Launch Vehicle Remarks
Muses A (Hiten) 1990-007A 24.01.1990 Ka LP-M M-3S-2 [KM-M] with Muses A Subsatellite (Hagoromo)