Credit: JAXA

Heralded as the most advanced lunar exploration mission in more than 30 years, a sophisticated Japanese spacecraft is on the cusp of launching the first wave of a scientific assault on the moon to probe its history and prepare for future human voyages to Earth's celestial companion.

The pickup truck-sized spacecraft will be rolled to the launch pad early Thursday atop Japan's flagship H-2A rocket. After workers make connections between the booster and its oceanfront launch pad, officials will begin final testing of the rocket's systems before pumping thousands of gallons of chilled liquid hydrogen and liquid oxygen propellants into fuel tanks aboard the launcher.

Preparations for the launch continue to proceed as planned, according to a spokesperson with the Japanese Aerospace Exploration Agency, or JAXA.

Clocks at the control center on Tanegashima Island are counting down to the scheduled launch time at 0131:01 GMT Friday (9:31:01 p.m. EDT Thursday). Blastoff will be in the late morning hours Friday in Japan.

Improperly installed parts aboard the Kaguya probe postponed the launch by a month as technicians replaced the suspect components. Bad weather earlier this week forced Japanese officials delay the flight an additional day because it interfered with work to prepare for the launch, according to JAXA.

The 174-foot-tall rocket will roar to life with the ignition of its LE-7A main engine in the final seconds of the countdown. Twin 50-foot-long solid rocket boosters will fire when the countdown clocks reach zero. Two smaller solid-fueled motors will ignite moments after the H-2A rocket vaults into the sky.

The H-2A will roll onto a path flying east of Tanegashima just seconds after liftoff, and the four solid rocket boosters will complete their job in the first two minutes of flight. The first stage will be shut down and jettisoned nearly seven minutes after launch, followed by ignition of the upper stage's LE-5B engine, which will power the rocket and payload into a preliminary parking orbit about 12 minutes into the mission.

After a speedy trip across the Pacific Ocean, the upper stage engine will fire again for about three-and-a-half minutes to extend the high point of its orbit to nearly 145,000 miles from Earth, or about three-fifths of the way to the moon. Deployment of the 6,360-pound satellite should occur off the west coast of South America about 45 minutes after liftoff.

Kaguya will deploy its solar panel and high gain antenna in the hours after the craft is released from the H-2A's upper stage. Next for the robotic explorer will be two burns to gradually raise its orbit over the next two weeks.

The science team will also check the $480 million mission's suite of 15 science instruments, which include two 110-pound daughter satellites and the first high-definition television camera to travel beyond Earth orbit.

After two-and-a-half high-altitude orbits around Earth, Kaguya will fire its largest maneuvering thruster to nudge itself toward the moon. The trip will take five days to complete, and Kaguya will slide into an egg-shaped lunar orbit circling the moon's poles about 20 days after launch.

At least six further engine firings will slowly circularize the orbit at an altitude of about 60 miles. Along the way, Kaguya will deploy two sub-satellites in different orbits to study the lunar gravity field on the moon's far side and detect the moon's feeble ionosphere.

Once it arrives in its operational orbit, the probe will begin a one-year observation campaign that will center on studies of the moon's origin and evolution. The mission will be the first to globally map the moon in three-dimensional stereo imagery, according to JAXA.

A high-definition television camera will record brief video clips of the moon and Earthrise during the mission. The 36-pound camera will capture wide-angle and telephoto videos and downlink the imagery back to ground stations.

The camera was provided by Japanese broadcasting giant NHK, according to JAXA.

A laser altimeter will measure the moon's topography and a radar sounding instrument will beam radio waves into the lunar subsurface to map the moon's interior to a depth of several miles.

Spectral imagers will measure the composition of the lunar surface at high resolutions, providing scientific clues about the origin of the moon. The leading theory for the moon's origin among scientists today is that a Mars-sized object crashed into the primordial Earth about 4.5 billion years ago and material ejected from the collision came together to form the moon.

A magnetometer on a 39-foot-long boom will also study the moon's faint magnetic field.

The instruments will also be valuable in the search for evidence of water ice on the moon. Kaguya's spectrometers will be able to detect the presence of hydrogen at the lunar surface, which is often a telling sign of water.

Two U.S. lunar orbiters in the 1990s returned high readings of hydrogen in the moon's polar regions. Scientists hypothesize that water ice is frozen in the bottoms of craters near the lunar poles, where sunlight is permanently blocked by the crater walls.

The launch of Kaguya will soon be followed by the beginning of China's first planetary science mission. Called Chang'e 1, the probe is expected to launch before the end of this year.

India's Chandrayaan 1 spacecraft and NASA's Lunar Reconnaissance Orbiter will launch to the moon next year.

If all goes according to plan, the four missions will be operating simultaneously in lunar orbit by late next year. Just four scientific probes have visited the moon in the past 31 years.