Logistics in ISS
Since November 2, 2000, the International Space Station has been
continuously crewed meaning humanity has had a permanent presence in space. The importance of this station cannot
be overestimated — NASA literally filled out a book with all the ways that the
ISS has benefited humans on earth. It has helped develop new treatments for
cancer, enhanced technology for robotic surgery, improved techniques for data
processing, and its benefits stretch far and wide. It is quite possibly humanity's
most significant scientific experiment ever undertaken. It is also the most expensive single item humanity has ever built at an
overall cost, of about $160 billion. Breaking that down, every astronaut spends
around $7.5 million on the ISS.
The ISS is a joint project between Russia’s Roscosmos agency,
Japan’s JAXA, Europe’s ESA, Canada’s CSA, and the US’ NASA. However,
physically, it is split into the Russian segment and the US segment, these two
countries more or less take responsibility for managing and supplying their
side. The station is longer than 747 at more than 350 feet or 110 metres in
length and has more interior space than the average six-bedroom house. However,
as science experiments and equipment take up most of the room, space is still
at a premium, so normally there is only a maximum of six onboard crew members
at any given time. But there are thousands of people back on earth working to
support the activities of those six.
Now that the international space station is
built and operating, the whole mission is basically a big logistics problem—it
involves getting people, food, water, supplies, and experiments up and down
from the station in a consistent, cost-effective, and safe manner. Food is one
of the only non-renewable resources onboard the ISS, as an example. It is
possible to recycle water, to generate oxygen, to reuse supplies, but the food is
one and done. That means consistent shipments have to be made from earth to
station. The Russians provide about half of the food, and the Americans supply
the other half. There are a few constraints to space food—it has to be shelf-stable as there are no refrigerators on board, it has to last about two years as
resupplies only happen a few times a year, it has to be light as weight is
precious on the resupply rockets, and it has to be easy to prepare as
astronauts’ time is valuable. Within those parameters, the Russians use a
system of canned food while the Americans use a system of flexible pouches
which have the advantage of being lighter weight than the cans.
The NASA food is processed at the Johnson Space
Center in Houston, Texas. The astronauts do a taste test long before they
launch to determine which foods they like the most and they express those
preferences. Based on those, NASA will produce and load more of the best-liked
foods. The astronauts can choose from hundreds of items. There’s no special
sourcing or special ingredients, although they do inspect the ingredients
carefully after buying to be extra sure that they’re safe. No astronaut has
gotten food poisoning in space and NASA wants to keep it that way. The food is
then prepared fairly conventionally until the last step. Food is made shelf-stable and lightweight by these methods—thermostabilization or freeze-drying.
With thermostabilization, heat is used to destroy microorganisms and enzymes
that would cause food to spoil. With freeze-drying, the food is frozen and all
moisture is removed. With this technique, there is no water left in the food,
which is normally the bulk of its weight.
The space station has a water recycling system
that recovers about 80% of the water onboard which means that they occasionally
have to resupply water from the earth, it’s more efficient to ship food up without
water in it since the water onboard can be reused for multiple meals and helps
to keep it shelf-stable. Overall, freeze-drying reduces total food weight.
NASA
currently pays $29,000 per pound for shipment to the Space Station. Each gallon
of water they bring therefore costs them about a quarter of a million dollars.
They’ll also typically include a few pieces of fresh fruit anytime a rocket
goes up and, with these shipment costs, each apple is worth almost $10,000.
This is why so much focus is put on minimizing weight. In addition to the food
they make, some foods are just shipped up as it is. For example, if a crew
member has a particular type of granola bar they like, the food preparation
team will go out and buy some of those as a sample and perform some tests in their
lab to figure out if it is “flight compatible”. They make sure that it’s not
too crumbly or too liquid as they don’t want crumbs and liquids floating around
into all the nooks and crannies of the station. Assuming it passes these tests,
astronauts can pretty much bring what they want for snacks. It will be
repackaged into NASA’s pouches. Once the food is produced and packaged, it is
shipped to one of four launch sites—either the Mid-Atlantic Regional Spaceport
in Virginia where Northrop Grumman Cygnus resupply spacecraft is launched
from; Cape Canaveral, Florida where SpaceX Dragon spacecraft are launched from;
Baikonur Cosmodrome in Kazakstan where Russian Progress resupply and Soyuz
crewed spacecraft are launched from; or Tanegashima Space Center in Japan where
Japanese Kounotori spacecraft are launched.
Similar to all, the food will be carefully
prepared for the journey providing optimal nutrition for the spacecraft. Thanks
to both of these weight-saving methods, crew materials, including food,
constitute just a small part of the total weight of each rocket. The rest of
the launch capability is geared towards equipment and experiments. Now, the
difficulty of this supply chain is that launch dates often change. Even just
getting a launch or landing date in the first place is difficult enough. Each
site has its own set of constraints potentially preventing use. Even the angle
of the sun relative to the ISS constrains when a spacecraft can dock. The other
factor that can affect the supply chain is that rockets are imperfect. 5 of 117
resupply missions to date to the International Space Station didn’t make it for
one reason or another, meaning there’s a failure rate of 4.3%. There was a
nine-month period from 2014 until 2015, during which three resupply flights
crashed. In times like these, having plenty of food, water, and supplies to
back up is very critical for the ISS.
Sometimes, to stretch the food supply, NASA will
have to extend the certified shelf life of food onboard. For this they keep a
sample of each batch of food they make on earth, packaged and stored in the
exact same conditions as on the ISS. Assuming a rocket doesn’t have any issues,
it will typically make it to the ISS in about two to three days. Once the
spacecraft is near the ISS, the crew will spend almost a whole working day
dealing with the docking process. Once that’s completed, either the same day or
the next morning, they will open the hatch where the crew care package is. This
includes fresh fruits and vegetables and some items sent up by the crew’s families.
One time, the crew care package even included real ice cream. While there isn’t
normally a freezer on board, a portable freezer was sent up in order to
transport samples from an experiment back to earth but, since it was empty on
the trip up, the crew got this treat.
For the next few months, astronauts go through
their food one container at a time scanning a barcode each time they open one
to let mission control know what their inventory level is like. That way, if
the food is going quicker or more slowly than expected NASA can adjust future
shipments. Onboard, dehydrated food is heated up and hydrated using a food
rehydrator. The point of putting so much effort into food on the ISS is for
the psychological well-being of the astronauts. With long working hours bottled
up in a small space for up to a year, the mental stress of the job is enormous
so any effort that can help reduce it is worth doing.
NASA puts a good amount of work into a movie
night. They have a large projector screen and, in addition to their onboard
digital library of 500 movies, the crew can download new movies. The ISS does
have an internet connection to get some movies. That same internet connection
lets astronauts browse the web quite freely, even if it’s not quick. While the
station does have 300 megabits per second of downlink capacity, the vast
majority of it is dedicated to experimenting and other data and astronauts can
regularly video call their families. The unloading process of resupply vessels
is quite a slow process, partially because there isn’t much storage space
onboard. Once a resupply vessel is unloaded, the crew starts loading it again
with trash.
The Northrop Grumman Cygnus, Russian Progress,
and Japanese Kounotori spacecraft is unable to return to earth so they
actually, burn up like all the debris in the atmosphere. The SpaceX Dragon and
space craftsmanship crewed Russian Soyuz return to earth so they can bring back
samples and tests. The spacecraft will then undock and slowly drift away from
the ISS until it disappears from view, the ISS is then ready for another
delivery of humans or cargo—one of the most unique regular deliveries in our
universe.
