In movies about space, actors are always selected from that
rarefied group of spectacularly-attractive
people. And these gorgeous individuals continue to look beautiful whilst
floating across the screen and dealing with space crises (think Sandra Bullock
in Gravity, or Matt Damon and the
porcelain-faced Jessica Chastain in The
Martian). The selection criteria for astronauts is a little different than
for actors – crewmembers are picked for their STEM educational backgrounds, and their
technical skills and physical abilities. Appearance doesn’t really factor so
much in to crewmember selection. Now, I’m not saying they’re ugly. These are
nice looking folks (look up their pages on Wikipedia or profiles on your local
Space Agency website if you don’t believe me). But here’s the secret nobody
advertizes: ain’t nobody pretty in space.
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| Even extraordinarily attractive people - like the actors in Ridley Scott's The Martian would actually look a bit uglier in space. That's just how we roll in Microgravity (Source: IMDB) |
What do you think? Pretty, eh? How about posting that selfie
on Instagram?
You probably notice that your face is a bit redder than it
ought to be, that your cheeks and eyelids are a bit puffier – actually,
everything is a bit puffier. Also, maybe your head is a little uncomfortable. Did
you start to get a headache? Do you have a little ringing in your ears? That’s
what the astronauts on the Space Station have to deal with. Because of these
fluid shifts, crewmembers have puffy faces and another effect we in the
business professionally call “chicken legs” (This is something Hollywood may
want to look into reproducing if they want to go for an authentic look!)
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| Expedition 63 Crew currently on board the ISS (Source: NASA.gov) |
There are loads of different ways that researchers can look at pressure inside the head. Here are a few:
o
Blood
Pressure & Heart Rate
o
Vascular
Resistance. If blood vessels tighten or constrict, vascular resistance
increases, and the heart must work harder to push the blood forward. If blood
vessels dilate or relax, vascular decreases, reducing the amount of left
ventricular force needed to open the aortic valve.
o
Magnetic
resonance imaging (MRI) & Ultrasounds
can be used to to measure the shapes and sizes and thicknesses of tissue, the
veins and arteries, and the heart. Ultrasound measurements can be conducted on board
the ISS because the equipment is relatively small. MRI machines are made of
enormous magnets and are too big to go on the ISS. Therefore, all MRI
measurements have to take place before or after a crewmember’s mission (such as the ESA experiment Brain-DTI, which I mentioned in my last post).
o
Bioelectrical
impedance analysis (BIA). In this measurement, a weak electrical current is
passed through the body. Different types of tissue in the body will conduct or
impede this current, so BIA measurements are used to look at body composition.
Water in the body (typically stored in the muscles) is highly conductive, so higher
amounts of body water will lead to a lower impedance.
o
Cerebral
Cochlear Fluid Pressure (CCFP). This measures tiny displacements in the tympanic
membrane (your eardrum).
o
Distortion-Product
Otoacoustic Emission (DPOAE). Otoacoustic emmisions are sounds produced in
the cochlea (the inner ear). This happens when the small hairs (or cilia) in
the cochlea change their shape in order to amplify a sound and propagate it
forward. These emissions can happen spontaneously (for example, in the case of tinnitus),
or they can be evoked by an external sound. When the cochlea is stimulated
simultaneously by two sound frequencies (whose ratio is about 1.2), a
distortion-product optoacoustic emission is induced. This has to do with the
shape of the cochlea (It’s spiralled around in a sea-shell configuration). When
there is a large amount of intracranial pressure, this can affect the shape of
the cochlea, and this can reduce DPOAEs.
(The Italian Space Agency, ASI, has an experiment called Acoustic Diagnostics that measures OAEs. I just watched ESA
Astronaut Luca Parmitano and US Astronaut Andrew Morgan perform sessions for
this experiment during Increment 61/62).
o
Optical
Coherence Tomography (OCT) & MRI & Ultrasound. These are all
different ways to make ocular measurements (measure the structure of the eye). When
there is a lot of intracranial pressure, the eyeball can be flattened (called globe
flattening), and alternating light and dark bands can form on the retina
(called chorioretinal folds). The optic nerve can also be altered by this extra
pressure. OCT and MRI of the eyes can be conducted when crewmembers are on the
ground, but it’s possible to make structural measurements of crewmember’s eyes
using Ultrasound equipment on the ISS.
As an example, here are just a few of the experiments that ESA and our partners are doing to look at intracranial pressure:
NASA is currently conducting an experiment called Fluid Shifts – which is short for Fluid Shifts Before, During, and After Prolonged Space Flight and Their Association with Intracranial Pressure and Visual Impairment (Principal Investigators Michael B. Stenger, Scott A. Dulchavsky, and Alan R. Hargens). This experiment has been running since 2015 and will finish up this year. Researchers are looking at how microgravity induced changes in cranial pressure affects the eyes of crewmembers. Researchers hypothesize that this fluid shift to the head increases pressure on the brain, which may push on the back of the eye and cause it to change shape. This investigation measures how much fluid shifts from the lower body to the upper body, in or out of cells and blood vessels, and determines the impact these shifts have on fluid pressure in the head, changes in vision and eye structures.
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| ESA Astronaut Luca Parmitano conducting a session of NASA's Fluid Shifts Experiment (Source: NASA.gov) |
ESA’s experiment Space Headaches (Principal Investigator Alla Vein) started in 2011 during Increment 29/30 and finished in Increment 55/56 with US Astronaut Scott David Tingle and Japanese Astronaut Norishige Kanai as the 23rd and 24th subjects. ISS Crewmembers are tough and don’t complain much – so we don't have a way of knowing whether or not they're floating around with killer headaches. But this experiment had crewmembers filling out weekly questionnaires telling researchers how frequently they experienced headaches, and how intense these headaches were. This will give us a better understanding of how badly this intracranial pressure hurts.
The knowledge we gain from this research will be critically important as we expand human exploration through the solar system. I recently finished re-reading Andy Weir's book, The Martian (this is probably the reason I started thinking about this issue). If you're reading this blog, it means you're a space-nerd like me, so I don't need to tell you to read the book (but if you haven't, then give it a look. It's a lot of fun). When the crew members of the Ares III mission decide to go back to Mars for Mark Watney, they add more than another year onto their travel time - giving them more than 2 years in microgravity. With what we know about intracranial pressure, that's gotta hurt - and maybe cause some long-term damage.
Here's some real-world data for reference: To date, the longest number of consecutive days in space record holder is Russian cosmonaut Valery Polyakov who spent nearly 438 consecutive days aboard the Mir space station, from January 1994 to March 1995. Cosmonaut Gennady Padalka holds the record for most total days in space - with a little more than 878 days accrued over five spaceflights. That's almost two and a half years (2 years 4 months 3 weeks 5 days).
Of course the fictional spaceship in The Martian had some centripedal accelleration to simulate gravity - and this is probably something we'll need to consider if we want to have long spaceflight missions since this is the only effective countermeasure for the fluid shifts I describe here. However, this will present its own engineering challenges. Radial force due to centripedal motion is (mv^2)/r - so the speed of your rotating wheel will depend on how big your "r" is (for reference: the ISS is 109 meters [357 feet] end-to-end). If you have a spaceship built like a wheel - with a radius of 100 meters, you'd need to do about 3 revolutions per minute to simulate gravity. That's pretty darned fast.
