The fourth Japan Aerospace Exploration Agency (JAXA) H-II Transfer Vehicle, or HTV-4, launched aboard an H-IIB launch vehicle from the Tanegashima Space Center in southern Japan at 3:48 p.m. EDT Saturday (4:48 a.m. Sunday, Japan time) to begin a weeklong journey to the International Space Station. Also known as Kounotori, or “white stork,” because it is emblematic of an important delivery, HTV-4 is carrying more than 3.5 tons of supplies, food and experiment hardware for the station’s Expedition 36 crew. At the time of launch, the station was flying 260 statute miles over southwest Russia near the border of Kazakhstan.
On Friday, Aug. 9, the HTV-4 will approach the station from below and inch its way slowly toward a holding position about 40 feet from the complex. While Flight Engineer Luca Parmitano monitors the systems of the Japanese space freighter, Flight Engineers Karen Nyberg and Chris Cassidy of NASA will use Canadarm2, the station's Canadian Space Agency-provided robotic arm, to reach out and capture the vehicle at 7:29 a.m. With HTV-4 securely grappled, the robotics team at Houston’s Mission Control Center will command the arm to install the vehicle to its docking port on the Earth-facing side of the Harmony node beginning around 9:30 a.m.
HTV-4 is a 33-foot-long, 13-foot-diameter (10 meter by 4 meter) unmanned cargo transfer spacecraft with both pressurized and unpressurized sections to deliver supplies destined for inside and outside the station.
Among the items within Kounotori’s pressurized logistics carrier are test samples for research experiments inside the Kibo laboratory, a new freezer capable of preserving materials at temperatures below -90 F, four small CubeSat satellites to be deployed from Kibo’s airlock as well as food, water and other supplies for the station’s crew. The pressurized section also is delivering new hardware for the Robotic Refueling Mission to demonstrate robotic satellite-servicing tools, technologies and techniques.
The HTV-4’s unpressurized section is delivering two orbital replacement units (ORUs) – a spare Main Bus Switching Unit (MBSU) and a spare Utility Transfer Assembly (UTA) – to keep the space station’s electrical system operating smoothly. The UTA maintains electrical continuity through the Solar Alpha Rotary Joint, passing electrical power generated by the complex’s huge solar arrays to station elements and payloads, while the MBSU provides switching capabilities for the various power channels and sources. ORUs are modular station components designed to be replaced periodically.
Also inside HTV’s unpressurized cargo hold is the Space Test Program – Houston 4 (STP-H4) payload, which is a suite of seven experiments for investigating space communications, Earth monitoring and materials science. Its predecessor, STP-H3, which was delivered to the station during the final flight of space shuttle Endeavour in May 2011, will be placed inside Kounotori’s unpressurized section for disposal when the cargo craft departs in September and descends to a destructive re-entry over the Pacific Ocean.