Japan’s HTV-5 spacecraft “Kounotori 5” has launched en route to the International Space Station on Wednesday – lofted by a H-IIB rocket from the Tanegashima Space Center in Southern Japan at 11:50.49 GMT (07:50.49 EDT; 20:50.49 JST). HTV-5 is set to deliver a cargo of food, hygiene items, internal and external spare parts, and scientific experiments to the ISS and its crew.

HTV general overview:

The H-II Transfer Vehicles (HTVs), all named “Kounotori” (White Stork), are a fleet of uncrewed resupply vehicles for the Japan Aerospace eXploration Agency’s (JAXA’s) part of resupply contributions to the International Space Station (ISS).

Wednesday’s scheduled launch is the fifth flight of an HTV to the ISS, with four HTVs having flown to the Station to date – HTV-1 from September-November 2009, HTV-2 from January-March 2011, HTV-3 from July-September 2012, and HTV-4 August-September 2013.

Each HTV is comprised of four main components – a Pressurized Logistics Carrier (PLC), Unpressurized Logistics Carrier, an avionics module, and a propulsion module.

Generically, the HTVs’ PLCs are capable of holding eight International Standard Payload Racks (ISPRs) for ISS internal cargo requirements.

With the retirement of the U.S. Space Shuttle fleet in 2011, HTV became the only ISS resupply vehicle capable of carrying ISPRs to the Station – as Europe’s ATV, Russia’s Progress, and the U.S.’s commercial Dragon and Cygnus spacecrafts were not designed with such capability.

Likewise, HTV is one of only two resupply vehicles (the other being SpaceX’s Dragon) capable of delivering external supplies to the ISS via its Unpressurized Logistics Carrier (UPLC), inside which resides an Exposed Pallet (EP) onto which external cargo is mounted.

Once the EP is removed from the UPLC by the Station’s Canadian-built robotic arm, the external cargo is removed from the EP and installed onto the ISS.

Rounding out the HTV’s main components are the avionics module, which contains all of the vehicle’s power and command & control systems, and the propulsion module, which houses all of the vehicle’s propellant tanks and main orbital adjustment engines – which, for HTV-5 include both 500 N class HBT-5 thrusters and 120 N class HBT-1 thrusters.

Currently, JAXA plans to launch five more HTV missions to the ISS, including the HTV flight that began on Wednesday.

If that plan holds, a total of nine HTVs will have launched to ISS by the end of 2019 – as all five remaining flights are planned to take place roughly one year apart of each other.

However, those five remaining flights would put the total number of HTV missions to ISS at nine by 2020 – one less than originally planned when the ISS’s life was first extended to 2020.

Current ISS long-range flight schedules, through mid-2020, show HTV-9 as the last manifested HTV mission in 2019.

With ISS’s new life extension to 2024, it is currently unclear what JAXA and the Japanese government might contribute in terms of ISS resupply or why there are only nine scheduled HTV flights now instead of ten.

With the European Space Agency’s completion of its five contracted ATV resupply missions to ISS earlier this year, if new HTV resupply missions are not ordered by JAXA and the Japanese government, the two U.S. commercial resupply spacecraft and the Russian Progress vehicle would become the only resupply vehicles for ISS from 2020 through the end of the Station’s operational life.

However, the remaining five HTV missions (including Wednesday’s HTV-5) will likely take place through 2020 due to schedule slips.

HTV-5, itself, was originally set to launch in July 2014 before incurring numerous and multifaceted delays – none of which appear to involve HTV itself or the H-IIB launch vehicle – to its 19 August 2015 launch date.

HTV-6, likewise, had been set for a mid-August 2016 launch under previous ISS schedules. However, the most recent ISS Flight Planning Integration Panel document (available for download on L2) now shows HTV-6’s No Earlier Than arrival date to ISS at 6 December 2016.

Since it is highly unlikely that HTV-6 would launch in August 2016 and not arrive at ISS until December, this would represent a 3.5 month slip to HTV-6’s launch date – which would have a similar knock on effect to HTV-7 and so forth.

HTV-5 mission:

HTV-5, delayed most-recently from Sunday, 16 August due to inclement weather, launched atop a Japanese H-IIB booster – used specifically for the HTVs – from the Yoshinobu Launch Complex at the Tanegashima Space Center in Southern Japan at 11:50.49 GMT.

Following a 14-minute ride to orbit, the H-IIB booster placed HTV-5 into an initial orbit of 200 x 300km, inclined at 51.6 degrees to the equator.

HTV-5’s controllers will then spend the next six days conducting a series of rendezvous burns designed to raise HTV-5’s altitude to around 410km, the height of the ISS, in order to put the craft in the correct position to rendezvous with the Station.

After those six days of free flight, HTV-5 will then fly itself to a point 30 feet below the ISS, whereupon the Station’s crew will use the Space Station Remote Manipulator System (SSRMS) arm to reach out and “capture” the vehicle.

The crew will then maneuver HTV-5 to the Common Berthing Mechanism port on the Nadir side of the Node 2 “Harmony” module.

Rendezvous and capture of HTV-5 should occur, assuming a 19 August launch, on 24 August at 06:55am EDT (10:55 GMT).

Once there, HTV-5 will be berthed to the station, with hatch opening following within a day.

Current ISS schedules (available for download on L2) show HTV-5 performing a 37-day docked mission to the ISS, during which internal and external cargo operations will proceed.

If HTV-5 launches on 19 August, the craft will most likely be un-berthed from ISS on 29 September for a destructive reentry into Earth’s atmosphere on 1 October.

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HTV-5 Payload Complement

In all, HTV-5 is carrying 5.7 tons of cargo to the ISS, 4.7 tons of pressurized cargo and 1 ton of unpressurized cargo, including 600 liters of potable water as well as food, crew commodities, system components, and science experiments.

Included in the systems payloads are a galley rack for the Node 1 “Unity” module, a new Fluids Control and Pump Assembly for the Urine Processor Assembly, Water Processing Assembly Multifiltration Beds, and a new SAFER (Simplified Aid For EVA Rescue) unit.

Additionally, HTV-5 is carrying 14 Dove satellites for NanoRacks CubeSat Deployer investigations as well as the GomSpace GOMX-3 satellite, a three-unit CubeSat mission to demonstrate aircraft Automatic Dependent Surveillance-Broadcast signal reception and geostationary telecommunication satellite spot beam signal quality for global aircraft tracking to, in part, help identify and locate vessels to support collision avoidance and search and rescue efforts.

HTV-5 will also deliver the NanoRacks External Platform (NREP) which will be able to handle multiple, diverse investigations on the JAXA Japanese External Facility (JEM-EF).

Moreover, HTV-5 will also bring to ISS a compilation of 10 investigations for the Twins Study.

These investigations will help scientists better understand biomolecular responses to the physical, physiological, and environmental stressors associated with spaceflight through the collection of biological specimens like urine and blood from one twin in orbit and the other on Earth.

Finally, for HTV-5, the primary external piece of equipment for this mission is the CALorimetric Electron Telescope (CALET).

CALET will search for signatures of dark matter and provide the highest energy direct measurements of the cosmic ray electron spectrum to help scientists answer questions about the origin of cosmic rays, how cosmic rays accelerate and travel across the galaxy, and whether dark matter and nearby cosmic ray sources exist.

Additionally, CALET might help characterize the radiation environment and the risks it may pose to humans in space as well as yield evidence of rare interactions between matter and dark matter.

In all, this represents the 5.5 tons of cargo that was the original cargo manifest for HTV-5 as of early June 2015.

However, HTV-5’s total cargo load was increased to 5.7 tons in July due to the addition of several last minute supplies that were lost in the launch failure of the SpaceX CRS-7 resupply mission in late June.

This ability to add last minute items to HTV-5 demonstrates the ongoing cooperation between the ISS partner agencies and nations to rearrange and accommodate last-minute cargo needs – regardless of the reason for that need.

Once all of the equipment and supplies are removed from HTV-5, the craft will be filled with thousands of pounds of disposal material from ISS, including among other things the Multi-mission Consolidated Equipment, Space Test Program Houston 4, and the Superconducting Submillimeter-Wave-Limb-Emission Sounder experiments.

This equipment, along with all the other disposal material, will be destroyed when HTV-5 performs its mission-ending destructive plunge into Earth’s atmosphere in early October.

(Images via L2 artist Nathan Koga, L2 HTV, JAXA and NASA).

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