BBC Focus

THE PEOPLE PROBLEM

ELEC TRO-

MAG NETIC DRIVE

How aboutathruster that uses nofuelat all?Most

physicists say theelectromagnetic(EM)drive is a

fantasy –but to itsproponents, it is a game-changer.

When we launch a craft, most of its mass is the fuel.

The Space Shuttle was 16 times heavier with its fuel

than without. Mostphysicistssaythereisnowayto

get aroundthis,because as therocketfuelisburnt

andexpelledathighspeedin onedirection, itpropels

therocketintheopposite direction. This is

encapsulatedin Newton’s ThirdLaw, whichstates

thatallforceshaveanequal and opposite reaction.

Without requiring fuel, the EM drive violates a

basic law ofphysics and therefore cannot work. The

trouble is, whenpeopple test it in the lab, it seems to

work. Also known assthe radio frequency (RF)

resonant cavitythruster, the EM drive was conceived

byBritishaerospaceengineer Roger Shawyer. Despite

profound theoreticallobjections, a number of

independent groupshave built their own versions

andtestedthem.Thesee includeateam from

Northwestern Polyteechnical Universityin Xi’an,

China, and one fromDresden Universityof

Te c h nology.Nonehaave been able to rule out that the

engine wasproducinngthrust,andin2015,NASA’s

Eagleworks researchgroupreported seemingly

positive results fromprototypes its built.

Critics are unconvinced. Theysayit is as

impossible as liftingyourselfoffthegroundby

tuggingatyour shoellaces, and attribute the results to

experimental error.IIthasbeensuggestedthattheEM

drive works through interaction with the vacuum ofdriveworksthrough

space, which somephysicists believe will turn out to

be a seething mass ofquantumparticles rather than

the nothing of traditionalphysics. But one thing is

certain,itisoddthatsuchasimple experimental

setupcancauseresultsthataresohardtoexplain.

“In science, new data must takeprecedence over

old theory. There is always the risk of experimental

error, but the fastest progress has always come from

paying attention to interesting anomalies,” says Mike

McCulloch,a lecturer in the school of Marine Science

and Engineering, Universityof Plymouth. “If the EM

drive is confirmed, then new physics is needed.”

If the EM drive holds up to scrutiny, then it

could change space propulsion forever.

The biggest problem with

spaceflightisalways mass. Robotic

spaceprobes can be fairlycompact

and lightweight, but when you add

humans, thingsget more complex.

Peopleneedto space tolive and

work, as well as complicated life

support systems, water andfood

stores. Put this alltogether andthe

mass ofaspacecraftskyrockets.

But what ifyou could send

humansascargoandrevive them

whenthecraftreachesits

destination? NASA has been

investigatinga‘torpor-inducing

transfer habitat’ in conjunction

with an American company called

SpaceWorksEnterprises. The

inspiration comes from the care of

heart attack victims. For years,

doctorshavebeen inducinga

sleep-state, or torpor, in such

patients by lowering their body

temperature. This slows the

metabolism andgives a chance for

their bodyto recover. Thepatient

staysthatwayfor afew days.

Now NASAisinvestigating

whether astronauts could bekept

inatorpor statefor weeks or

months. Theirbody temperature

would be lowered by a few degrees

by inhaling a coolant through a

fluid linefed throughthenose.

Nutrientswould administered

intravenously, and their vital signs

would be monitored remotely.

NASA is alreadylooking

seriouslyatusingthistosend

peopletoMars,butajourney to an

exoplanet would be a far more

difficultproposition. Unless we

make some kind ofspectacular

breakthrough, voyages couldtake

decades or centuries,and that’s a

long time to be a sleep.

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Dr Stuart Clarkis an astronomy writer with a PhD in astrophysics.

His latest book isThe Search For Earth’s Twin(£20, Quercus).

Don’tmissTheSkyAtNight,on BBC Four everymonth.

CheckRadio Timessformoredetails.

u

Were we contacted byaliens in 1977? Read BBC iWonder’s

online guide to the Wow! signal, the Drake Equation, and more.

bbc.co.uk/guides/zqdbgk 7

DISCOVER MORE

Microwaves

areproduced in a

traditional

magnetron by the

interactionof

electronswitha

mmagnetic field

Theconical

shape of the cavity

was shownbyNASA

tobeessential:

without it,no thrust

wasmeasured

Some physicists

thinkthemicrowaves

areinteractinginan

as yet unknown way

with space itself to

produce thethrust

Themicrowaves

arefedinto a

resonating cavity

where theybounce

back and forth,

exerting pressure onexerting pressure on

thewalls

Ait
experiments that have
been conducted,the
thrustonthelargeend
is larger than on the
smallend

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