Japan is planning to launch its most ambitious space mission Thursday, a flight that will not only usher in a new era for the country's domestic space program but also inaugurate an important new capability for the International Space Station.

Credit: JAXA

The long-awaited launch from the seashores of southern Japan will be a monumental moment for the Asian power's growing space industry.

"We consider this as a huge chance and a significant stepping stone for the Japanese space industry to take a lead in some areas of manned space activities," said Hiro Uematsu, a senior engineer on the H-2 Transfer Vehicle for the Japan Aerospace Exploration Agency.

Liftoff is scheduled for 1701:46 GMT Thursday (1:01 p.m. EDT; 2:01 a.m. JST) from Launch Pad No. 2 of the Yoshinobu launch complex at the Tanegashima space center.

The pad is nestled along the Pacific Ocean among hills and rocky outcrops jutting into the sea.

The ship's H-2B launcher is undergoing final checks inside the spaceport's Vehicle Assembly Building. Rollout of the rocket to the launch pad should occur around 0200 GMT Thursday.

The rocket will have until Sept. 30 to get off the ground or else wait until next February. Japan must schedule launches around the peak times for the country's powerful fishing industry, and the next opportunity will not come until early 2010.

The HTV will mark Japan's first foray into major orbital rendezvous and the nation's first launch to a manned space station.

JAXA tested key autonomous navigation and rendezvous procedures on the Engineering Test Satellite 7 mission in 1998, but officials say the HTV is a much more complicated vehicle.

Japan also built the three-part Kibo laboratory facility, the station's largest scientific section.

Under development since 1997, the HTV program has cost JAXA about $700 million so far. The unit cost for the first HTV spacecraft is about $200 million, not including the launch vehicle, according to JAXA.

Stretching 33 feet long and spanning 14 feet across, the HTV is about the size of a tour bus. The cylindrical spacecraft will weigh about 35,000 pounds at launch.

But just as important as its history-making storyline will be the new capability the futuristic freighter will bring to the International Space Station.

"It's the first unmanned vehicle that brings with it both pressurized and unpressurized cargo," said Dana Weigel, NASA's lead flight director for the HTV's first mission.

If successful, the HTV would be the only unpiloted spacecraft currently able to deliver large scientific payloads and equipment for operations on the U.S. segment of the complex.

"We are so proud to take this new responbility to provide cargo transportation capability to the ISS program," said Masazumi Miyake, deputy director of JAXA's offices in Houston.

Progress vessels and Europe's Automated Transfer Vehicle dock with the Russian segment, which has smaller hatches than U.S., European and Japanese modules. The wider doors opening into those modules allow larger cargo to moved into the station.

After the space shuttle retires, the HTV will probably be the only ship of any kind then flying to carry payload racks and large spare components to the outpost.

"It's very critical," said Mike Suffredini, NASA's space station program manager. "First of all, it's unique. It brings external (spares and payloads) to orbit, something we won't be able to do after shuttle leaves."

NASA has contracts with two U.S. companies, SpaceX and Orbital Sciences, to develop commercial resupply spacecraft to fill a gap in cargo capacity after the shuttle is retired.

The HTV will also demonstrate rendezvous techniques to be employed by the new American vehicles. The ships will fly within about 30 feet of the station and stop, waiting for the complex's robotic arm to reach out and grapple the spacecraft. All three vehicles will then be berthed to the station with the crane-like arm.

Artist's concept showing the HTV awaiting capture by the station's robot arm. Credit: JAXA

"This is a unique method to not only make the vehicle simple but also to provide standard rack delivery capability," Miyake said.

"All of those are techniques we're going to need for other vehicles that are going to come. So not only are we going to have a new system, we're going to test techniques that we need for future systems," Suffredini said.

But both commercial spacecraft will are not slated to enter operational service until after the shuttle is phased out. If the new ships, named Dragon and Cygnus, are delayed or run into problems, NASA will have to rely on the HTV for heavy logistics work on the U.S. segment.

Of the U.S. Commercial Resupply Services participants, only Orbital Sciences' Cygnus spacecraft will be able to carry external hardware.

"What's unique about HTV is it's capable of transferring unpressurized cargo," Uematsu said. "This capability is, at this point, unique to only the space shuttle and the HTV."

Seven HTV flights are on the books, flying at a pace of about one per year through the middle of the next decade. Suffredini said JAXA and its industrial team, led by Mitsubishi Heavy Industries, could build two HTVs per year with enough money.

NASA would have to pay for much of the bill, and funding is not currently appropriated to support the increased production rate, if it is needed.

Future HTV missions will carry up to 13,000 pounds of supplies to the station, but the first spacecraft is loaded with extra batteries and propellant, limiting its cargo cache to about 7,500 pounds.

Inside the pressurized compartment, the HTV is filled with food, computers, experiments, crew provisions and other maintenance components. The internal logistics totals about 5,600 pounds.

The pressurized supplies are in transfer bags loaded inside eight filing cabinet-sized racks attached to the walls of the HTV.

Although the station does not need the cargo immediately, much of the equipment and food is necessary in long-term planning.

"This (carries) logistics that's required, and if for some reason this vehicle doesn't make it, we'll have to make it up on future flights," Suffredini said.

About 2,000 pounds of equipment will ride to the station inside an unpressurized section in the middle of the spacecraft.

The external hardware comprises Earth science experiments for NASA and JAXA to be mounted on Kibo's exposed science facility.

The 840-pound NASA payload, called HREP, holds two experiments to study the oceans and atmosphere. HREP's ocean sensor will focus on coastal features, and the atmospheric ultraviolet and visible instrument will look at the ionosphere and thermosphere.

JAXA's SMILES experiment will detect trace gases in the ozone layer using a submillimeter sounder. The 1,047-pound instrument will help determine the extent of human activity's affects on ozone.

HREP and SMILES are the station's first significant science payloads devoted to Earth science.

"It's good to be able to finally start having this kind of research on board the ISS," Suffredini said.

A propulsion and service module at the aft end of the ship houses a network of computers, electronics, propellant tanks, plumbing and engines to keep the spacecraft working.

Four main engines and 28 maneuvering jets will fine-tune the HTV's approach to the station. The thrusters are wired to two redundant primary control strings.

More than 5,000 pounds of fuel and oxidizer are on the automated vehicle, enough for the ship to get to the space station and then de-orbit itself back into Earth's atmosphere at the end of the mission.

Fifty-seven solar panels are affixed to the HTV's exterior to provide electricity for the craft.

The first leg of the HTV's journey will be up to a brand new heavy-duty rocket specifically built to send cargo to the space station.

The 186-foot-tall H-2B booster traces most of its pedigree to the H-2A launcher, a rocket with a successful track record since it entered service in 2001.

The new rocket, the largest ever developed by Japan, uses a new first stage tank and two LE-7A hydrogen-fueled first stage engines.

Each producing about 200,000 pounds of thrust, the LE-7A engine was originally developed for the H-2A rocket, which uses a single engine.

For the H-2B, engineers added a second engine and doubled the number of large solid rocket boosters strapped to the first stage.

The second stage uses an LE-5B engine identical to the power plant flying on the H-2A rocket.

JAXA spent more than $400 million designing, building and testing the new rocket.

Because of its design heritage and an exhaustive test campaign, NASA officials say they have a "high degree of confidence" the H-2B's first launch will be successful.

Artist's concept of the H-2B rocket's payload shroud separating. Credit: JAXA

The rocket's second stage should release the HTV around 15 minutes after liftoff in an orbit ranging between 124 miles and 186 miles in altitude.

Over the first six days of its flight, the spacecraft will refine its approach to the space statiion through a series of maneuvers to adjust its trajectory.

If the HTV launches on time, the ship will spend Saturday conducting a series of key demonstrations to prove it can safely fly away from the station in case something goes wrong.

The abort maneuvers can be triggered automatically, by ground controllers, or by the station's crew during final approach.

Engineers will evaluate the HTV's performance during the tests before officials convene a Mission Management Team meeting next Tuesday. Station managers will then give a "go" to proceed with the rendezvous if everything is working as planned.

"There's quite a bit of choreography associated with flying these vehicles, especially the first-time vehicle because of the checkout we do as we approach the ISS to ensure that all of the systems on board are working as we had planned," Suffredini said.

Meanwhile, astronauts aboard the space station will be readying the complex to receive the new arrival. The crew will complete proficiency training by the fifth day of the HTV's mission.

Final rendezvous activities will begin early Sept. 17 as the HTV flies to an approach initiation point about five kilometers, or 3.1 miles, directly behind the space station.

See our detailed mission timeline here.

More than 800,000 parts in the freighter's avionics and propulsion systems will have to work in perfect cadence during the rendezvous, according to JAXA.

Next, the HTV will fly itself to a location about 1,600 feet below the station, called the rendezvous insertion point. From there, the craft will gradually approach the complex using a laser-guided navigation system.

The ship will pause twice at a range of approximately 1,000 feet and 100 feet to give the crew and ground controllers an opportunity to double-check the vehicle's systems.

More than 800,000 parts in the freigher's avionics and propulsion systems will have to work in perfect cadence during the rendezvous, according to JAXA.

"On the actual rendezvous and capture day, there are a handful of additional demonstrations that we'll be doing, and we have very specific success criteria associated with those. So that will be evaluated in real time," Weigel said.

The vehicle will automatically stop at those hold points and unless the ground gives a 'go' to the HTV, it will never start from those hold points," Uematsu said.

Because the HTV must be manually captured by the robot arm, astronauts will take a hands-on approach in the final minutes of the rendezvous.

The crew has a control panel with buttons to send instructions for the HTV to halt, retreat, or abort the rendezvous. The astronauts will test the unit's ability to command the spacecraft as it flies within about 1,000 feet of the outpost.

Astronauts must also send a "free drift" command to the HTV once it flies inside a capture box about 30 feet below the Kibo laboratory module.

"When the vehicle arrives at the capture point, it's controlling with its thrusters. Then the crew takes it to free drift, which means we shut off all of its thruster systems and it's just drifting," Weigel said.

This will disable the ship's propulsion system long enough for Nicole Stott to move the robot arm into place and pluck the floating vehicle from space.

Canadian astronaut Bob Thirsk will take over arm operations to berth the HTV on the downward-facing port of the station's Harmony module.

The crew will open hatches and ingress the pressurized portion of the vehicle the day after it arrives.

Thirsk will again use the station's robot arm on the fourth day of combined operations to retrieve the HTV's exposed pallet and place the HREP and SMILES experiments in their respective science bays outside the station.

The empty carrier will be put back into the HTV's unpressurized section a few days later.

The rest of the mission will be spent removing supplies from the HTV and loading some of the station's waste into the spacecraft.

Current plans call for the HTV to remain at the station for about 45 days before being released in early November. Two days after departure, the ship will be guided into the atmosphere for a destructive grand finale over the far southern Pacific Ocean, disposing of the garbage-filled freighter.