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[ Music ]

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>> ZBOT is a space experiment.

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It's a science experiment
performed

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in the International
Space Station in support

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of cryogenic fluid management
of propellant tanks in space.

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It's a science experiment

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because it studies fundamental
issues of phase change.

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Fluid flow.

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Heat transfer that
affects preserving

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and keeping fuels
in depots in space.

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ZBOT is important because it's a
step towards designing this zero

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boil-off tank control system
without which you won't be able

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to do the long-duration
expedition.

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For long-duration
missions you have

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to be able to fuel on orbit.

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Preserve these fuels.

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Which could be hydrogen.

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Methane. Oxygen.

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All of these liquids have
to be preserved in space

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under very low temperatures.

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Hydrogen, for example, has to be
preserved at 20 degrees Kelvin.

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That's very low temperature.

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So small heat leaks
from the environment,

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radiation on the tank surface
can penetrate the heavy

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insulation that's
installed on the tank.

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And once the heat goes in, it
starts evaporating the liquid.

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These tanks are also supported
by some support structure.

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Conduction through these support
structures also can cause

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localized heating of the tank.

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And that localized heating
can instigate boiling

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and evaporation in the tank.

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Which, again, means the
tanks would be pressurized.

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The physical phenomena
that happens

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in the storage tank
is very complicated.

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It requires solving the energy.

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The fluid flow.

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The species.

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And the mass equations in
the tank under conditions

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where the flow is very orderly,
which we call laminar flow.

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Or very chaotic, which
we call turbulent flow.

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This requires solving
these equations at many,

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many points in a
computational grid.

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So as a result, for simulating

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like a pressure control
situation, a mixing control

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in ZBOT, you might be solving 50
million simultaneous equations

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with 800 processes working.

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Some of the simulations take
over a month to perform.

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We had a few interesting
results for ZBOT.

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Let's start with
self-pressurization.

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Because those were
the first series

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of experiments that we made.

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When we self-pressurize the
tank, heat goes from the wall

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into the tank and causes
the temperatures to rise

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in the liquid and the vapor.

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And evaporation takes place.

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The pressure rises.

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Sometimes during
self-pressurization,

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boiling can occur at a
hot spot on the wall.

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This causes undesirable
pressure spikes in the tank.

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Because of microgravity
thermal stratification,

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boiling happens more easily
in space than on Earth.

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It was interesting to note
that the trend in microgravity,

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although a lot of things,
including the ullage shape,

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which is the bubble-shape
the vapor shape is different.

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And the amount of
convection is different.

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The trend followed the trend
that we observe on Earth.

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That's an important finding.

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Which, because it says that
we can use the Earth data

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as a conservative estimate

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of what pressurization
would be in space.

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And for the first
time ZBOTs was able

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to obtain this
self-pressurization data,

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in microgravity.

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And we were able to validate
our models against that data.

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During the pressure controlled
studies with the forced jets,

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we found out that actually
we can use the forced jet

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at very low velocities,
at very low speeds

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to position the liquid
where we want it to be.

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The follow-on experiment to
ZBOT-1 is called ZBOT-NC.

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It stands for ZBOT
non-condensible.

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What happens in a real tank
situation is, when you want

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to feed the engine, you want to
pressurize the tank very fast.

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So that's often done by
injecting a foreign gas.

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Like in a hydrogen tank,
you inject helium inside.

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Helium doesn't condense at
the temperatures of hydrogen.

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So it's referred to as
a non-condensible gas.

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Then you can feed your
engine the pressure drops.

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Now you have to store the
fluid, which is a mixture

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of hydrogen and helium.

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When the tank pressurizes
again because of heat leaks

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from the surroundings
and the pressure goes up.

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With the helium present
there, you will find

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out that you don't have the same
capability to bring the pressure

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of the tank down by
cooling the liquid.

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The non-condensible forms
a barrier to that process.

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ZBOT-NC is studying the
effect of non-condensible

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under the pressure
control strategy.