"A white stork carries an image of conveying an important thing (a baby, happiness, and other joyful things),
therefore it precisely expresses the HTV's mission to transport essential materials to the ISS"
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This past month, the 9th and final H-II Transfer Vehicle (HTV) departed the International Space Station, marking the end of 11 years of successful deliveries by the Japanese autonomous spacecraft!  Nicknamed Kounotori (こうのとり), the Japanese word for the Oriental stork, the HTV is manufactured by Mitsubishi (yes, the same corporate family as the car manufacturer) and designed to be launched by the HII-B rocket, grappled by the Canadarm on the ISS, and berthed to the station's Harmony module. And like its 8 predecessors, after having delivered its 6,200 kgs of cargo to the astronauts living onboard, Kounotori-9 safely reentered Earth's atmosphere and burned up.

The manned spacecraft that send crews to the ISS tend to get all the fanfare (Space Shuttle, Crew Dragon, Soyuz), but the various robotic vessels that resupply the space station are just as essential to its continued operation: 

• Progress, active (RKK Energia / Russia)
• Dragon, active (SpaceX / United States)
• Cygnus, active (Northrop Grumman / United States)
• HTV, retired 2020 (Mitsubishi Heavy Industries / Japan)
• Automated Transfer Vehicle, retired 2015 (EADS Astrium + Thales Alenia / Europe)

HTV (left), Progress (top center), Dragon (bottom center), Cygnus (top right), ATV (bottom right)

Because we humans are flimsy, high-maintenance creatures in constant need of life support and other essentials, that translates to an ISS resupply vehicle getting launched every few months. For example, here are some of the items Kounotori-9 carried, in addition to food and other basic crew commodities:

• Water storage system tank
• High pressure nitrogen tank for the Nitrogen Oxygen Recharge System
• Six lithium-ion batteries needed to replace the aging nickel-hydrogen batteries on the ISS
• A huge variety of scientific experiments 

Furthermore, these resupply vehicles are essential not just for what they replenish, but also for what they dispose of. Given the limited storage on the space station, waste management is an important consideration for mission planners, since it's not as simple as just blowing trash out the airlock (think of all the space debris that would generate!). Any garbage that the astronauts generate, be it disposable food packaging, worn out clothes, or the leftovers of their scientific experiments, has to be stored until the next resupply mission, then carefully loaded into the spacecraft so that it can be jettisoned into the atmosphere

Astronauts Sunita Williams and Joe Acaba carefully unloading HTV-3's cargo in 2012

Now here's the thing: resupply spacecraft need to launch on rockets, and rockets sometimes... explode. While this most recent flight of the HTV went off without at hitch, it was arguably the 5th flight of the Kounotori back in 2015 that proved to be the most crucial. Here's the background of that mission (I'll share some excerpts from astronaut Scott Kelly's book Endurance, since he was completing his famous year in space during at the time and provides some fantastic insight)

Beginning in the fall of 2014, a string of launch failures occurred in quick succession over the next several months. First off was the Cygnus' 4th flight, which lifted off on October 28, 2014. Just 15 seconds after ignition, one of the liquid oxygen turbopumps in the Antares rocket carrying Cygnus exploded, resulting in an absolutely gnarly fireball that lit up the night sky and obliterated over 2,000 kgs of supplies and experiments in the inferno (watch the full video here, it's intense!). The next few ISS resupply missions were successful, but then in April 2015, a Russian Progress spacecraft botched its planned rendezvous with the ISS due to a malfunction in the Soyuz's upper stage. Flight controllers in Moscow tried in vain to reestablish contact with the crippled spacecraft, and the mission was soon deemed a total loss as Progress helplessly fell back into the atmosphere and burned up, taking another 2,000 kgs of cargo with it

"Up here, we talk about what it will mean for us if Progress is lost... the Russians will low on food and clothing, which means we will share ours with them and eventually run low ourselves...

We don't normally worry about shortages, but losing Progress suddenly makes us think about how much we depend on a steady stream of successful resupply missions. We can afford one or two failures, but then we will have to start rationing"

Here's the Antares rocket and Cygnus spacecraft blowing up; think that bird in the middle of the picture made it out alright?

SpaceX was up next - two months after the loss of Progress, a Falcon 9 and Dragon capsule lifted off from Cape Canaveral, but 137 seconds into what seemed like a routine flight, a strut securing a high pressure helium bottle failed, rupturing a liquid oxygen tank that caused the vehicle to disintegrate. Now the supplies on the ISS are getting precarious; Kelly described his reaction to the failure quite succinctly:

"You've got to be fucking kidding me...

It starts to sink in that we have lost three resupply vehicles in the last nine months, the last two in a row. Our consumables are now down to about three months' worth, and the Russians are much worse off than that"

Cargo destroyed by Dragon's loss included a $100M docking adapter and a gorilla suit from Scott Kelly's brother

The Russians figured out the issue with their Progress spacecraft and successfully launched one soon after, but the ISS was still way low on supplies. All eyes are on Kounotori-5 now, set to launch on August 19, 2015. Lifting off on an HII-B from Tanegashima Space Center, this HTV was loaded to the brim, hoisting over 6,000 kgs of cargo into low Earth orbit (including 200 kgs of last minute additions following the SpaceX failure). After a five day orbit-raising journey, the HTV successfully rendezvoused with the ISS, drifting to a point 30 meters below the space station before killing its thrusters so that astronauts on board could capture the spacecraft with the Canadarm and secure it to the station's Harmony module. There it remained for nearly 35 days, a much needed delivery for the crew onboard. My favorite part of the cargo manifest - a small sample of whiskey, tequila, and Midori, sent up as part of an experiment to see how zero gravity affects the mellowness of alcohol!

Capture of HTV-5, as posted by Japanese astronaut Kimiya Yui who was onboard the station at the time

Now that HTV is retired, the ISS will be serviced by just the Progress, Dragon, and Cygnus spacecraft for the time being. But in case you're missing the white space stork already, the Japanese space agency is working on an upgraded version, the HTV-X, that will make its first ISS delivery in 2022 and will one day be capable of delivering cargo to NASA's planned lunar Gateway space station! 

Before we know it, we'll be sending Kounotori on its way to the moon