Artist’s impression of HTV approaching ISS (Image:JAXA) Runners and riders in the space cargo race (Image: New Scientist)

Update: Japan’s HTV cargo ship launched successfully on 10 September at 1701 GMT


If the first launch of Japan’s new heavy-lifting rocket passes without incident this month, the residents of the International Space Station will soon be taking delivery of food, water, some spanking new laptops, a robot arm and a couple of Earth-observing experiments. Business as usual, you might think, except that the way this particular cargo gets to its destination is subtly different to its predecessors.

The reason? The cargo is being carried by the latest uncrewed spacecraft to vie for a place in the emerging market to supply the ISS. The driving force behind this latest space race is the impending retirement of NASA’s space shuttle fleet, sometime in 2010. This latest vehicle is the work of the Japan Aerospace Exploration Agency. JAXA’s H-II Transfer Vehicle, or HTV, offers the space station a range of new capabilities.

See a graphic showing the runners and riders in the race to supply the ISS.

Docking ports

Unlike previous uncrewed cargo-carrying craft, which dock automatically or under human control, the HTV stops dead alongside the ISS when its retro rockets fire and it is grabbed by the space station’s giant robot arm. Then the arm pulls the HTV slowly but surely into the docking port on the US Harmony module.

“This will be our first free-flier capture from the space station,” says Dana Weigel, lead flight director for the ISS at the Johnson Space Center in Houston, Texas.

The advantage of this, says JAXA mission spokesman Masazumi Miyake, is that the HTV does not need an elaborate approach and docking guidance system. And that in turn frees up space for yet more payload. “Without a complicated rendezvous, attitude and range-control system, the whole spacecraft is far simpler than other cargo supply craft,” Miyake says.

In addition, the HTV has separate compartments for both pressurised and unpressurised cargo, allowing astronauts to unload the likes of food, water and laptops from the pressurised section in just their shirtsleeves.

Supply fleet

An unpressurised cargo module can hold racks for experiments and equipment designed to sit outside the ISS. Such gear can be removed from the HTV by the robot arm and installed on the “porch” platform on Kibo, the Japanese ISS lab module. Two of the outdoor experiments on the HTV’s first flight are a NASA ionospheric and thermospheric mapping device, and a JAXA system for monitoring the ozone layer’s chemistry.

“The HTV is just an amazing vehicle and it’s a pleasure to have it in the supply fleet,” says Mike Suffredini, NASA’s ISS programme manager.

But just what vehicles have the space agencies recruited for this fleet? Until now, uncrewed missions to space stations like the now defunct Mir, and the ISS, have been carried out by the veteran Russian craft, Progress. This is effectively an uncrewed version of a Soyuz capsule. Then just last year, another option arrived when the European Space Agency successfully flew its own uncrewed cargo carrier, the Automated Transfer Vehicle, to the ISS – carrying three times the cargo of a Progress vehicle. Both Progress and ATV dock with the Russian Zvezda module of the ISS.

Now JAXA is adding a third option with the HTV. This craft, however, docks with the American Harmony module.

Cosmic trashcans

The usual mode of operation for these cargo beasts is to deliver their payloads and then morph into a cosmic trashcan, remaining at the station until the vessel is brimming with ISS waste – whereupon it is jettisoned, deorbited and burned up.

But a fourth, less wasteful, cargo option beckons. SpaceX, the civilian spaceflight firm backed by PayPal founder Elon Musk, has won a NASA contract to ship cargo to the ISS, running 12 resupply flights between 2012 and 2015. And the upper capsule of SpaceX’s new Dragon vessel, which resembles an Apollo spacecraft, is recoverable – via a parachute splashdown in the Pacific ocean. It too can dock via the robot arm.

SpaceX’s programme is at an advanced stage. Last week, it supplied NASA with the UHF radio system that will enable the Dragon to dock with the ISS: it will be taken up on the next flight of the shuttle Atlantis. “This radio unit had to pass NASA’s strict

ISS safety standards and reviews, demonstrating our progress and laying the groundwork for Dragon flights,” says SpaceX president Gwynne Shotwell.

JAXA is also investigating capsule reuse. “One of our upgrade plans is to make HTV recoverable. It’s something we’re studying right now,” Miyake says.

First flight nerves

HTV is scheduled for lift-off sometime between 10 September and the end of the month, on board the HII-B launch vehicle, which has never flown before – and the record of successful first rocket launches is poor. For instance, the giant Ariane 5, which carries ESA’s ATV, failed to launch several times before the glitches in the technology were finally ironed out.

A variant of JAXA’s workhorse HII-A rocket, the HII-B has four solid rocket boosters instead of the HII-A’s two – and has two main liquid-fuelled engines instead of the HII-A’s one.

“This is indeed the HII-B’s first launch. But many of the components are already working well on the HII-A,” says Miyake. “We have great confidence in it.”