Australian Sky & Telescope - June 2018

NASA OFFICIALS HAVEannounced

thatthelaunchoftheJamesWebb

Space Telescope will be delayed until

approximately May 2020, slipping

morethanayearfromitspreviousgoal

betweenMarchandJune2019.

Todate,theagencyhasspent$7.

billiononWebb’sdevelopment.Ifthe

mission’sdevelopmentcostsgooverthe

$8 billion maximum that Congress set

in2011,Congresswillneedtoreautho-

risetheproject.Anindependentreview

will nail down the changes in cost and

schedule, and NASA will report its

assessment to Congress in late June.

ThepiecesofWebbareallcomplete;

what’scostingtimeandmoneyisthe

often unpredictable “integration and

testing” phase. NASA officials admit

that the initial schedule for this phase

was optimistic.

JamesWebbSpaceTelescopedelayeduntil

Some of the technical challenges
facedwereinstructive.Forexample,
thecomplexsunshieldwastornduring
testing, so engineers made changes to
itsstorageanddeployment.Preventing
damage is crucial, as the shield protects
the telescope’s sensitivity at near-infra-
red wavelengths.
Therewerealsoavoidableerrors:A
transducer was incorrectly powered and
hadtobereplaced,resultinginathree-
monthdelay,andanincorrectsolvent
was run through the propulsion system,
damaging valves and seals and neces-
sitatingtheirreplacement.Toavoid
future mistakes, NASA officials outlined
plans to monitor contractor Northrop
Grumman more closely.
Webb is a top priority within the
astronomical community and repre-
sents NASA’s largest international space
science project. Once it launches, the
6.5-metrenear-infraredtelescopewill
orbittheSunattheLagrangianpoint
L 2 ,1.5millionkmfartheroutthan
Earth.Thetelescopewillpeerfarther
back in cosmic time than Hubble to see
the universe’s first stars and galax-
ies.AstronomerswillalsouseWebbto
characterise nearby exoplanets.
The delay will have a broad impact
ontheastronomicalcommunity,notes
associate administrator Thomas Zurbu-
chen,bothintermsofperceptionand
actual cost. Nevertheless, he insists, he
doesn’t want the agency to shy away
from large, complex projects: “I want us
NORTHROP GRUMMAN CORPORATION to have ambition.”■MONICA YOUNG

S This 2017 image shows all ive tennis-court-

size, membranous layers of Webb’s sunshield,

displayed in Northrop Grumman’s clean room

in Redondo Beach, California. These will have

to fold into the Ariane 5 rocket fairing.

ton’s team concludes could be anything

from a cigar to a fat pancake. For the

moment, either shape is equally likely.

‘Oumuamua’s overall spectrum and

apparent lack of outgassing imply that

it’s rocky, which could mean that it

was ejected from the inner region of

its host solar system. Yet Sean Ray-

mond (University of Bordeaux, France)

and others argue that too few aster-

oidal fragments would be ejected to

Update on the aurora

named STEVE

For years amateur astronomers have

seen and photographed a thin, faintly

pink- or purple-coloured ribbon that runs

east-to-west southward of the northern

lights. (To read about the discovery, visit

https://is.gd/aurorasteve.) Eventually

dubbed ‘Steve,’ neither amateurs nor

researchers knew what the phenomenon

was. Analysing data from the European

Space Agency’s Swarm A satellite, which

lew directly through a Steve ribbon

in 2016, Elizabeth MacDonald (NASA

Goddard) and colleagues suggest that

the amateurs had spotted the subauroral

ion drift (SAID), a rapid low of charged

particles through Earth’s atmosphere

that’s associated with brightening aurora.

However, scientists had never known

of visible emission from SAIDs, and the

radiation mechanism remains unclear. In

the meantime, the visual phenomenon

gets to keep its name: STEVE, short

for Strong Thermal Emission Velocity

Enhancement.

■ MONICA YOUNG

Tiangong 1’s remote

re-entry

China’s irst space station, Tiangong 1

(Chinese for “celestial palace”), re-entered

Earth’s atmosphere over the South Paciic

on April 2 after almost seven years in

space. No humans reported witnessing

the re-entry, but NASA and the European

Space Agency mounted a campaign to

remotely monitor the space station in an

effort to better model future reentries. The

re-entry location was largely unknown

beforehand, complicated by the vehicle’s

uncertain mass: While the media often

cited it as 8.5 metric tonnes, that number

assumed a tonne of fuel still onboard.

Tracking the re-entry impressed upon

scientists the sensitivity of predictions

to solar activity, the state of Earth’s

thermosphere and atmospheric drag.

■ DAVID DICKINSON

make it statistically likely for one to

reach us, unless it was ejected from a

two-star system.

‘Oumuamua may keep its secrets,

but chances are we’ll find another inter-

loper soon: Calculations by Aaron Do

(University of Hawai‘i) and colleagues

suggest that there are likely several of

these objects in the inner Solar System

at any given time.

■ J. KELLY BEATTY

IN BRIEF

http://www.skyandtelescope.com.au 7