Japan’s HTV-6 resupply vehicle arrives at the ISS

by Chris Gebhardt

Following what was the fifth orbital launch of December, the Japanese Aerospace Exploration Agency (JAXA) HTV-6 resupply vehicle completed a four day journey to the International Space Station on Tuesday, via capture by the SSRMS. The cargo vehicle was launched on December 9 from the Tanegashima Space Center, via the use of a H-IIB rocket.

HTV-6 overview:

HTV-6 (H-II Transfer Vehicle 6) is the sixth craft in a fleet of one-time use uncrewed resupply vehicles that serve JAXA’s commitments to the International Space Station (ISS).

screen-shot-2016-12-06-at-15-11-29Unlike Orbital ATK’s Cygnus and ESA’s ATV (Automated Transfer Vehicle) resupply vehicles which receive (or received, in ATV’s case) individualized names for each mission, every HTV carries the same name: Kounotori, meaning white stork.

As with its HTV predecessors, HTV-6 is comprised of four main components – a Pressurized Logistics Carrier (PLC); Unpressurized Logistics Carrier (UPLC), inside of which is an Exposed Pallet (EP) onto which external cargo is mounted; an Avionics Module; and a Propulsion Module.

Generically, the PLCs can accommodate up to eight International Standard Payload Racks (ISPRs) for ISS internal cargo while the large UPLC makes HTV one of only two resupply vehicles (the other being SpaceX’s Dragon) capable of delivering external supplies to the ISS.

The Avionics Module contains all of the power and command & control systems while the Propulsion Module houses all of the propellant tanks and main orbital adjustment engines – including both 500 N class HBT-5 thrusters and 120 N class HBT-1 thrusters.

Moreover, HTV-6 will debut five new updates and upgrades from its immediate predecessor, HTV-5.

The major alterations for HTV-6 include the removal of one solar cell panel, bringing the total to 48; the elimination of one primary battery, bringing the total to 6; the removal of navigation/position lights that face Earth during ISS approach operations; the introduction of a strengthened EP to hold a maximum of 1.9 t, up from 1.6 t; and the inclusion of built-in payloads for technology demonstrations.

Specifically, HTV-6 will carry two technology demonstrations, SFINKS (Solar Cell Film Array Sheet for Next Generation on Kounotori Six) and KITE (Kounotori Integrated Tether Experiment).

SFINKS will test thin film solar cells while KITE will test an experimental electrodynamic tether – which will eventually aid space debris removal efforts.

HTV-6 mission:

HTV-6, delayed from September 2016 due to leaking pipes, launched atop the Japanese H-IIB rocket – developed exclusively for HTV – from the Yoshinobu Launch Complex at the Tanegashima Space Center in Southern Japan at 22:26:47 local time (13:26:47 GMT – 08:26:47 EST) on Friday, 9 December 2016.

screen-shot-2016-12-06-at-15-17-14Just prior to liftoff, the H-IIB core stage’s two LE-7A engines ignited and ramped up to full thrust – a combined 494,000 lbf.

At liftoff, the four strap-on A3 Solid Rocket Boosters (SRBs) ignited, providing a combined 2,070,000 lbf of thrust for a total liftoff thrust of 2.564 million lbf.

Each of the four A3 SRBs weighed 76,500 kg (168,654 lb) and carried a total of 65,950 kg (145,395 lb) of HTPB propellant.

The four A3 SRBs burned for a total of 114 seconds (1 minute 54 seconds) before they burned out and separated.

The first stage, which thrusts continuously through SRB flight, burned a mixture of LH2 and LOX, carried a total of 177,800 kg (391,982 lb) of propellant and burned for 352 seconds (5 minutes 52 seconds).

screen-shot-2016-12-06-at-15-22-50After first stage shutdown and separation, the second stage’s single LE-5B engine ignited, producing 31,000 lbf of thrust – from 16,600 kg (36,597 lb) of LOX and LH2 – for 499 seconds (8 minutes 19 seconds).

Following a 14 minute 11 second ride to orbit, the H-IIB booster placed HTV-6 into an initial orbit of 200 x 300 km, inclined at 51.6 degrees to the equator.

HTV-6 controllers then spent the next four days conducting a series of rendezvous burns to raise HTV-6’s altitude to around 405 km, the height of the ISS, in order to put the craft in the correct position to rendezvous with the Station on Tuesday, 13 December.

HTV-6 Payload Complement:

While upcoming resupply missions in January and February 2017 might see their payload complement adjusted following last week’s loss of the Progress MS-04/65P vehicle, HTV-6’s payload is unaffected, with NASA public affairs noting to NASASpaceflight.com that “There were no items added to the HTV-6 manifest following the anomaly with ISS Progress 65.”

screen-shot-2016-12-06-at-15-27-41In total, HTV-6 is packed with 2,566.25 kg (5,657.6 lb) of internal cargo – with an additional 186 kg (410 lb) of packaging for that payload.

Among these pressurized cargo items include 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 – is also riding to orbit aboard HTV-6.

Moreover, the craft is carrying 28.25 kg (62.28 lb) of hardware for the Russian segment of the Station.

screen-shot-2016-12-06-at-15-35-15Importantly for the Expedition 50 crew, HTV-6 is carrying 1,264 kg (2,786.6 lb) of food, water (600 liters), clothing, and various other items for crew health and daily activity.

Additionally, HTV-6 is also tasked with delivering 1,367 kg (3,014 lb) of external cargo – Lithium Ion batteries and adapter plates – in the UPLC.

The six new batteries will replace 12 aging Ni-H (nickel-hydrogen) batteries.

At the end of its planned 60-day mission at ISS, HTV-6 will be packed with nine of the 12 Ni-H batteries and will dispose of them during its destructive End Of Mission plunge into the atmosphere.

The three remaining Ni-H batteries will remain on ISS for the time being.

The six new Li-ion batteries will be installed via a series of robotic operations followed by two planned EVAs (with two back-up EVAs as contingencies) in January 2017.

All told, HTV-6 is set to deliver 3,933.25 kg (8,671.3 lb) of supplies and hardware to ISS.

HTV future manifest:

Currently, JAXA plans to launch three more HTVs to the ISS, not including HTV-6.

screen-shot-2016-12-06-at-15-06-50Under the current plan, a total of nine HTVs will launch by the beginning of 2020 – with HTV-7 currently slated to launch in February 2018 for a 60-day stay on the Station.  This will be followed in February 2019 by HTV-8 (60-day stay) and then in February 2020 by HTV-9 (60 day stay).

With this, HTV-9 will be the last of the current series of HTV vehicles, which will be replaced by HTV-X beginning in 2021.

With the Station’s life extension to 2024, the Strategic Headquarters for Space Policy of the Cabinet Office in Japan’s government officially approved a plan to develop the HTV-X in December 2015.

The overall aim of the HTV-X project is to reuse the design of the PLC while adding a side hatch for late cargo stow and access while at the same time replacing the UPLC, Avionics Module, and Propulsion Module with a new Service Module that will cut the cost of HTV in half while extending its capability and increasing the amount of payload the craft is capable of carrying to the Station.

Under the current plan for HTV-X, the total weight of the craft will decrease by 1 t (from 16.5 t to 15.5 t), while 1.2 t of added upmass capability will be introduced into the system.

(Images: JAXA, NASA)

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