Japanese space agency JAXA conducted successful launch of their H-IIB rocket with HTV robotic cargo spacecraft. Mission destination is International Space Station and nadir docking port of Harmony module.

HTV-6 “Kounotori” mission was planned as first after 3 years of break and sixth mission of Japanese cargo vehicle in general. Its mission was important mainly because of payload – new batteries and spare parts for ISS electrical system, which requires general upgrade and overhaul  and supplies for crew members. Of course supplies would not be considered as very important part of the payload, but after disaster of Progress MS-04 cargo vehicle on December 1, 2016,  this aspect of mission became at least equally  important. HTV will deliver to International Space Station 5.8 t of cargo divided into pressurized and unpressurized sections. In pressurized compartment Kounotori will deliver 3.9 t of payload including: water (600 l), food, Carbon Dioxide Removal Assembly (CDRA Bed), HDTV cameras, experiments and hardware. Inside this section, HTV will also deliver new J-SSOD (small satellite deployer) and number of nanosatellites (AOBA-Velox III, TuPOD, Tancredo-1, OSNSAT, EGG, ITF-2, STARS-C, FREEDOM and WASEDA-SAT3). Inside unpressurized section six new Li-Ion batteries were packed – they will be used during planned EVA as upgrade for nickel-hydrogen batteries presently installed outside the Station. Weight of the payload stored in side unpressurized section is 1.9 t.

Already in the end of July 2016, HTV-6 was already after packing batteries and supplies; next it was installed on atop of upper stage of H-IIB. On July 31, H-IIB started its journey on boat from Mitsubishi Heavy Industries facility in Tobishima to Tanegashima Space Center. It seemed, that everything is fine and preparations are conducted according to plan, but on August 10, JAXA announced about spotting leakage in Kounotori pipe system. Launch was postponed from 30th September to the first half of December. After conducting additional leak tests and ensuring, that rocket and vehicle are in perfect condition, H-IIB F-6 was rolled out from assembling facility to Y-2 launch pad placed 400 m away on Thursday, 8th December.

Today since morning hours specialists and engineers from JAXA conducted fueling and last tests before launch planned for 22:26 JST (13:26 UTC). At T-10′ all systems were checked and ready, weather conditions were favorable with slight wind (4.3 m/s NW), clear sky and temperature at 15.5°C. Two minutes later countdown procedure started. AT T-1’30” fuel system was pressurized and ready for launch. At T+72″ water curtains were initialized; finally at 13:26:47 H-IIB with HTV started to rise over Y-2 launch pad. After 60 seconds of flight rocket passed sound barrier and already was on SE trajectory. SRB-A boosters were cut off at T+1’50”. Then they were released in pairs – first two were jettisoned at T+2’06”, third and fourth booster separated at T+2’09”. Payload fairing was jettisoned at T+3’42”, 2’16” before cutting off of the first stage on the altitude of 190 km. First and second stage separated at T+5’56” and 11 seconds later propulsion of the second stage started to work. At T+10′ upper stage and HTV were flying with speed of 23000 km/h on altitude of 290 km. Second stage was cut off finally at T+14’20” and HTV was deployed after short phase of ballistic flight at T+15’11”. It started its journey to ISS with planned contact with Canadarm2 robotic arm at 11:00 UTC on 13th December 2016.

H-IIB is strongest version of H-II based on H-IIA version. It is supported during launch by four SRB-A3 solid fueled with HTPB rocket boosters generating total thrust of 9220 kN. Each booster is long for 15 m with diameter of 2.5 m and weight at 306 t. First stage of the rocket is equipped with two LE-7A engines (fueled with LH2/LOX) providing thrust at 2196 kN. It is long for 38 m and its diameter is 5.2 m and weighs 202 t. Upper stage is powered with LE-5B engine with thrust at 137 kN. It is shorter and narrower than first stage, with length of 11 m and diameter at 4 m; it weighs 20 t. Total length of the rocket is 56.6 m and mass is  531 t with payload to LEO at 19 t. Payload (HTV) is covered with 5S-H fairing: 15 m long and with 5 m in diameter.

HTV (H-II transfer Vehicle) was developed by JAXA as unmanned automatic cargo vehicle without possibility of autonomous docking. Project started in the nineties with first planned mission in 2001. Unfortunately due the slower pace of progress of HTV vehicle, first mission was possible in 2009. Until now six HTV vehicles have been used for resupply missions to International Space Station.

HTV is cylindrical in shape with solar arrays placed around fuselage. It is long for 9.8 m with diameter at 4.4 m. It weighs 10.5 t (without payload) and is able to deliver to ISS up to 6 t of cargo (5200 kg in pressurized and 1500 kg in unpressurized conditions) in 14 cubic meters of cargo volume. HTV is able to perform 100 h flight and stay docked to ISS for around one month. It is controlled by 3 axis attitude control system (without any docking computer because vehicle is grabbed by Canadarm2 and not [performing docking). Propulsion is based on four 500 N thrusters (IHI HBT-5) as main propulsion and 28 maneuver thrusters (IHI HBT-1 with thrust at 120 N). They are fueled with 2400 kg of MMH/MON3 propellant stored in internal tanks.