Japan's new H-2B rocket rolled to its oceanfront launch pad this week and briefly fired its two main engines Thursday, concluding the heavy-lift booster's first practice countdown after a six-day delay due to faulty ground equipment.

Credit: JAXA

The orange and white rocket, stripped of its payload shroud and four solid rocket boosters, was driven atop a mobile platform overnight Tuesday to Launch Pad No. 2 at Tanegashima space center's Yoshinobu launch complex.

It was the second trip to the pad for the H-2B. Two previous attempted countdowns ended with scrubs on March 27 and again Wednesday.

Engineers began loading cryogenic liquid hydrogen and liquid oxygen into the rocket Thursday morning.

Clocks counted down to zero at 2 p.m. local time, or 0500 GMT Thursday, when the first stage's two LE-7A main engines ignited for a 10-second burn.

Early results indicate the engines performed well during the test, according to the Japan Aerospace Exploration Agency, or JAXA.

Thursday's exercise included the real first and second stages that will be used on the rocket's maiden flight later this year. The test was designed to validate the H-2B rocket's first stage propulsion system and the launcher's connections with the newly renovated launch pad, according to JAXA.

The "captive firing test" was first delayed from March 27 when launch pad's water system failed to activate moments before engine start. The water helps cushion the launch platform and ground facilities from the shock of ignition.

A second attempt on Wednesday was cancelled after officials detected a water leak in ground fire suppression equipment, according to Mitsubishi Heavy Industries Ltd., the rocket's prime contractor.

Both delays were caused by problems in ground infrastructure. The H-2B launch pad was originally built to handle flights of the smaller H-2A rocket, but the facility has never been used for a launch.

Although the complex was built prior to JAXA's approval of the H-2B program, the pad was designed to support launches of larger rockets.

Another test is slated for April 16 or 17 to give the launch team more practice in countdown procedures. That rehearsal will culminate with a much longer 150-second engine firing to collect data on the vibrations experienced by the rocket during a simulated first stage burn.

Components of the H-2B arrived at Tanegashima on Feb. 18, and technicians integrated the first and second stages inside the spaceport's Vehicle Assembly Building. Four large solid rocket boosters will be added later.

Japanese designers devised the H-2B to take advantage of parts proven by the less powerful H-2A, which has successfully launched 14 times since debuting in 2001. One H-2A rocket failed to orbit a pair of spy satellites during a 2003 flight.

The H-2B rocket uses a larger "widebody" first stage with a diameter of about 17 feet. The H-2A's first stage measures 13 feet wide.

The widebody stage houses larger propellant tanks that feed dual hydrogen-fueled LE-7A main engines. The H-2A first stage is powered by an identical single main engine.

The H-2B's second stage and solid rocket boosters are unchanged from the designs used by the H-2A rocket.

The new rocket's streamlined development has allowed officials keep development costs to an estimated $444 million. The funding is being split between JAXA and Mitsubishi.

Japanese officials have penciled in the H-2B's first launch for early September. The mission will carry a new cargo delivery ship for the international space station.

The first H-2 Transfer Vehicle is undergoing final checks at JAXA's Tsukuba space center near Tokyo. The HTV is scheduled to be shipped to Tanegashima later this month to begin launch processing.

The HTV will carry experiments, spare parts and crew supplies to the station. The craft will be grappled by the complex's robot arm and attached to the station's Harmony module for about one month.

After departing the station, the HTV will plunge into the Pacific Ocean, destroying the spacecraft and a load of garbage loaded aboard the ship by the outpost's crew.

JAXA has agreed to launch at least seven HTV's to the station over the next decade.

Officials say they also hope to put the H-2B rocket on the commercial market. Engineers predict the launcher will be able to deliver more than 17,000 pounds to geosynchronous transfer orbit, a number that closely matches other leading commercial launch providers.