HWM Singapore – August 2019

these genes existed in diff erent cell types
and were almost all involved in DNA
repair and immune function. If humans
are to survive for long in space, these
genes will be crucial to protecting us from
radiation. Cells that cannot repair DNA
damage are prime fodder for mutations
to accumulate and give rise to cancer
and heritable diseases.

SHORTENED TELOMERES
Telomeres are the caps that protect
the ends of our chromosomes from
deterioration. They shorten as our cells
divide, and when they get short enough,
the cell simply stops dividing and dies,
which is what eventually leads to
aging and death.
Oddly enough, while Scott’s telomeres
lengthened onboard the ISS – likely the
result of the recommended exercise
regime – they rapidly shortened within
48 hours of returning to Earth, perhaps
a result of the stresses of reentering the
atmosphere and landing. Most of his
telomeres regained their baseline levels

eventually, but things were never quite

the same. Scott now has signi cantly

fewer telomeres overall and higher

numbers of critically short telomeres,

and telomere loss may eventually

make astronauts more susceptible to

cancer and other diseases associated

with old age.

VISUAL DEFICITS

Up to 40 percent of the astronauts who

have lived on the ISS have suff ered

some sort of damage to their eyes. NASA

isn’t completely sure how this happens,

terming it “space ight-associated

neuro-ocular syndrome”, or SANS. The

condition is characterized by optic disc

edema, globe  attening, choroidal folds,

and other structural changes. Some

astronauts also develop cotton wool

spots, which appear as  uff y white

patches on the retina.

The most common problem is

probably globe  attening, where what

we think of as the eyeball essentially

becomes less round at the rear-end.

It’s thought to be a result of  uid build

up and increased intracranial pressure,

which end up squishing the eyeballs

and  attening them.

POORER COGNITIVE

PERFORMANCE

Space also aff ected Scott Kelly’s

brain. He did worse on cognition tests

even six months after returning home,

responding more slowly and making

more mistakes. The  ndings were

slightly odd, since Scott’s performance

actually increased in space before

declining sharply upon return.

Obviously, the limitations of the

study – the sample size of 1, for instance

• make it diffi cult to attribute reasons
  to this decline.
  It’s entirely possible that Scott was
  simply less motivated once he was back
  on Earth, but there could also be more
  insidious mechanisms at work. Either
  way, it’s concerning, since any crew
  landing on Mars will need to be ready
  to tackle more challenges.

HOPPINGITSWAYTO SPACE

ButbeforeStarship

caneventhinkabout

liftingoff,testshaveto

beconducted.SpaceXis

usinga brandnewRaptor

engine,andthetoppriority

is toensurethatit works

and,well,doesn’texplode.

Todothat,theStarship

prototype,alsocolloquially

dubbedStarhopper,needs

tomakeseveral“hop”

tests,comprisingbothlow-

andhigh-altitudeflightsup

toheightsof16,400feet.

Eachhopis alsoperformed

ona tether,which

keepsStarhopperclose

tothegroundforsafety

purposes.

Thesetestsare

supposedtodemonstrate

thatStarhoppercan

hoverandlandsafely.In

addition,SpaceXis using

themtoexplorevarious

fuelmixtureratios,among

otherthings.Thecurrent

versionhasjustoneRaptor

engine,butlaterversions

willhaveuptothree,while

thefullyoperational

Starshipis expected

tohavesix.Fourofthese

willbespeciallyoptimized

toworkinthevacuum

ofspace.

Eventually,SpaceX

hopesforStarshipto

replacetheFalcon9 and

FalconHeavy,andeven

thecrewedandcargo

versionsoftheDragon

capsule.Starshipwill

handleallofSpaceX’s

loads,including,butnot

limitedto,thesettlingof

theMoonandMars.

AUGUST 2019 | HWM 43