Lunar-A

Description

The Lunar-A mission is facing cancellation. JAXA has tentatively decided to scrap the mission due to cost considerations, a final decision is expected in February, 2007.

The scientific objectives of the Lunar-A mission to the Moon are to image the surface of the Moon, to monitor moonquakes, measure the near-surface thermal properties and heat flux, and to study the lunar core and interior structure. To achieve these objectives, Lunar-A will carry a mapping camera and two surface penetrators. The surface penetrators are equipped with seismometers and devices to measure heat flow. The seismometers will monitor moonquake activity over the course of a year and this information will be used to learn about the structure of the Moon's interior and the size of the core. The heat flow measurements will provide information on the thermal state and evolution of the Moon.

Mission Profile

The launch has been delayed a number of times for technical and financial reasons, it is now being re-evaluated. There is now no launch schedule for LUNAR-A, it will certainly launch no earlier than late 2007. After launch, Lunar A will go into Earth parking orbit. The spacecraft will then be injected into an orbit around the Earth and Moon. After four and a half of these orbits, Lunar-A will swing out into a wide single orbit with an apogee of 1,185,000 km. At the end of this orbit the spacecraft will re-encounter the Moon and be inserted into lunar orbit. This orbit will have an inclination of 30 degrees and bring Lunar-A within 40 km of the Moon's surface. The spacecraft will deploy two 13 kg penetrators over the course of a month. They will be individually released and impact the Moon at 250 to 300 m/s, burrowing 1 to 3 meters into the surface. One penetrator will be targeted at the equatorial area of the near side (in the vicinity of the Apollo 12 and 14 landing sites) and one at the equatorial far side. After deploying the penetrators, the orbiter will move up to a 200 to 300 km near circular mapping orbit. Data will be stored in memory in the penetrators and transmitted to the orbiter when it transits over each penetrator every 15 days.

The LUNAR-A Spacecraft

The main body of the orbiter is a 120 cm diameter cylinder which is 111 cm in height, excluding the engine nozzle which protrudes from the bottom of the craft. An orbit maneuvering system, S-band antenna, and UHF-band antenna are situated on an end of the cylinder, and a reaction control and another S-band antenna on the other end. Three solar arrays extend perpendicular to the cylinder axis, equally spaced around the body. A monochromatic mapping camera with a resolution of 30 m is attached to the side of the cylinder below one of the solar panels. It will be used to take images near the terminator, where the lighting will enhance subtle topographic features. The spacecraft is spin-stabilized. Attitude and spin rate are controlled by an N2H4 monopropellant reaction control system. Orbital maneuvering near the Moon is done using a bipropellant (N2O4 and N2H4) engine.

The Penetrators

The penetrators are missile-shaped cylinders, 75 cm in length and 14 cm in diameter, and are attached to the sides of the orbiter body between the solar arrays with their long axes oriented in the same direction as the cylinder axis. The penetrators have deorbit rocket engines which are fired after separation. During free fall descent side-jets are used to orient the penetrators. The deorbit motor and attitude controls are jettisoned before impact. Each penetrometer contains a two-component seismometer, a heat flow probe, a tiltmeter, an accelerometer, a radio transmitter and an antenna. The instruments are powered by Li-SOCL2 (super lithium) batteries with an expected lifetime of one year. The penetrators are designed to withstand an impact force of 10,000 G.

The Lunar-A project has an esimated cost of $135 million.