HTV-6 completes death plunge swansong

by Chris Bergin

Japan’s HTV-6 cargo vehicle has completed its destructive re-entry on Monday, February 6, following its departure the International Space Station (ISS) over a week ago. The spacecraft performed without issue as it delivered vital supplies both for the crew and the Station itself during its mission, with its final role involving a cargo of ISS trash – and replaced Station batteries – being disposed of during its fiery EOM (End Of Mission).


The latest JAXA resupply vehicle delivered 2,566.25 kg (5,657.6 lb) of internal cargo when it was berthed with the Station back in December.

Among these pressurized cargo items included 156 kg (344 lb) of computer resources, 35 kg (77 lb) of EVA (Extra-Vehicular Activity) supplies and 663 kg (1,461 lb) of vehicle hardware and spare parts (including a new Carbon Dioxide Removal Assembly – CDRA – bed).

Additionally, 420 kg (926 lb) of utilization and science experiment/hardware – including a Two-Phase Flow experiment unit, a Position-Sensitive Tissue Equivalent Proportional Chamber radiation measurement instrument, the Exposed Experiment Handrail Attachment Mechanism, an HDTV-EF2 hi-def and 4K camera, a new JEM Small Satellite Orbital Deployer – were also aboard HTV-6.

The Japanese vehicle also provided a 28.25 kg (62.28 lb) supply of hardware for the Russian segment of the Station, along with 1,264 kg (2,786.6 lb) of food, water (600 liters), clothing, and various other items for crew health and daily activity.

The external cargo warranted additional focus for the future longevity of the Station, with 1,367 kg (3,014 lb) of external cargo including Lithium Ion batteries and adapter plates.

The six new batteries replaced 12 aging Ni-H (nickel-hydrogen) batteries via two highly successful EVAs in January.

“Lithium Ion Channel 1A Installation: Crew successfully completed US EVA 39 for the installation of Lithium Ion Batteries for Channel 1A on the S4 Integrated Electronics Assembly (IEA),” L2 ISS Status information outlined.

“Adapter Plates (AP) E, F, and D were released from the Exposed Pallet (EP) and installed on the S4 IEA. The remaining NiH2 battery was transferred to Adapter Plate F. Following installation of the Adapter Plates, each Battery Charge Discharge Unit (BCDU) was activated successfully. ”

Several of the old batteries were placed into the HTV ahead of meeting their end when the vehicle conducts a destructive re-entry.

“Battery Installation onto the External Pallet: Ground teams successfully installed the NiH2 batteries from the Special Purpose Dexterous Manipulator (SPDM) into the HTV External Pallet (EP) slots D and E and from the Enhanced ORU Transform Platform (EOTP) in the EP slot F,” added L2 ISS Status information. “This completed the robotics cleanup following the LiON battery installations.”

Work ahead of departure for the HTV-6 involved the Mobile Transporter (MT) being translated from Work Site (WS) 2 to WS5.

On January 22, the ground controllers using Space Station Remote Manipulator System (SSRMS) successfully grappled HTV6’s EP from the Mobile Base System (MBS) Payload ORU Accommodation (POA) and installed on its Unpressurized Logistics Carrier (ULC).  The SSRMS was then maneuvered and successfully grappled HTV6’s Flight Releasable Grapple Fixture (FRGF) in preparation for release.

Ahead of the end for HTV-6, trash items were loaded into its place and the Common Berthing Mechanism (CBM) hatches between the vehicle and the ISS were closed.

Following CBM vestibule depressurization and removal of all 16 CBM bolts (in four stages of four bolts), marked the unattaching of the vehicle, whilst under the firm grip of the SSRMS.

Over the following few hours, the SSRMS manuvered HTV-6 to the release position around 30 feet below the ISS, following which, with both ISS and HTV-6 thrusters inhibited.

HTV-6 was then ready to be released under the stewardship of European Space Agency astronaut Thomas Pesquet and Commander Shane Kimbrough at the Robotic Work Station (RWS) in the Cupola module.

The SSRMS ungrappling of HTV-6 was next, to signify its release from the ISS.

After a period of 90 seconds, the ISS crew sent the retreat command to HTV-6, which initiates the departure sequence burns.

A few hours after its release, the cargo ship will fire its engines to begin the path towards a controlled deorbit and entry through Earth’s atmosphere, where it will burn up over the Pacific Ocean.

In total – per the timeline – four departure burns were called for, known as ISS Departure Maneuver (IDM) -1 and -2, followed by Descending Maneuver (DSM) -1 and -2, following which ISS and HTV-6 integrated operations officially ended.

HTV-6 remained in orbit for several days before conducting a series of de-orbit burns for a destructive re-entry over the Pacific Ocean on February 5.

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As with previous HTVs, this vehicle’s scientific utility continued even before its destruction however, since two re-entry payloads were stowed inside HTV-6 to gather data to compare to computer models, in order to improve knowledge of re-entry characteristics.

She also conducted the KITE (Kounotori Integrated Tether Experiment), which involved the release of a 700-meter long Electrodynamic Tether with a 20-Kilogram end mass. This will allow for the study into the feasibility of using such tethers for in-space propulsion and space debris removal.

Initial reports claim the deployment of the tether suffere issues, although the electron generator was successfully tested.

This was the six mission of an HTV to the ISS, following in the footsteps of four HTVs having flown to the Station previously – HTV-1 from September-November 2009, HTV-2 from January-March 2011, HTV-3 from July-September 2012, HTV-4 August-September 2013 and HTV-6 in 2015.

(Images via JAXA and NASA).

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