Inside view of the Pressurised Logistics Carrier section of HTV-1.
Canadarm2 removing unpressurised payload from HTV-2.
The HTV is about 9.8 m long (including maneuvering thrusters at one end) and 4.4 m in diameter. Total mass is 10.5 tonnes, with a 6,000 kilograms (13,000 lb) payload. The HTV are comparable in function to the RussianProgress, EuropeanATV, commercial Dragon, and commercial Cygnus spacecraft, all of which bring or are planned to bring supplies to the ISS. Like the ATV, the HTV carries more than twice the payload of the Progress, but is launched less than half as often. Unlike Progress capsules and ATVs, which dock automatically, HTVs and American commercial crafts approach the ISS in stages, and are signaled by ISS crew or ground control to continue from one holding point to the next. Once they reach their closest parking orbit to the ISS, crew grapple them using the robotic arm Canadarm2 and berth them to an open berthing port on the Harmony module.
The four main thrusters. Smaller attitude control thrusters can be seen at the right side of this view of HTV-1.
The baseline configuration, known as the "Mixed Logistics Carrier", uses one pressurized and one unpressurized segment and can carry 7,600 kg of cargo in total and is 9.2 m long. When two pressurized units are used together the cargo decreases slightly to about 7,000 kg, and the overall length is reduced to 7.4 m.
As of March 2015[update], five subsequent missions are planned—one each year for 2015–2019 —one fewer total mission than had been planned in August 2013 at the time the fourth HTV mission was underway.
As of 2010[update], JAXA is planning to add a return capsule option. HTV's Pressurized Cargo is replaced by a reentry module capable of returning 1.6 tonne cargo from ISS to Earth. It is expected to be launched by 2018.[not in citation given]
Further, it is expected to be followed on by 2022 by capsules which accommodate a crew of three and carry up to 880 pounds (400 kilograms) of cargo.
As of 2014[update], both JAXA and Mitsubishi have conducted studies of a next generation HTV as a possible Japanese contribution to the proposed international manned outpost at Earth-Moon L2. This variant of HTV is to be launched by H-X Heavy and can carry 1.8 tons of supplies to EML2. Modifications from the current HTV includes the addition of solar electric paddles and extension of the propellant tank.