Australian Sky & Telescope - April 2018

34 AUSTRALIAN SKY & TELESCOPE April 2018

NASA / BILL RODMAN

qualityimages)fromthestratosphere?Advancesinballoon

andcontroltechnologymakethisarealpossibility.Among

the major recent developments aresuper-pressure balloons,

whichwillenablelongerandhigherflights.

Conventional balloons maintain what’s calledzero pressure:

They vent helium as they fly in order to keep the pressure inside

theballoonequaltotheatmosphericpressureoutside.Butat

nighttheseballoonssinkastheheliumcools,sotheymust

dropballast.Thenextday,theballoononceagainascendsin

thewarmthofthesunlight,ventingheliumtostabilisealtitude.

And the next night, it will cool again and drop more ballast —

andsoon.Thiscyclemakeslongflightsimpossible.

Super-pressure balloons, however, are closed systems

madeofstrongmaterialthatcanmaintainpositivepressure

(thatis,higherpressureinsidetheballoonthanoutside).

Assuch,theyflyatnearlyconstantaltitudes,evenwhenthe

Sunsets.Theseballoonscanbelaunchedfromanywhereon

Earthandstayafloatformonths,tracingawanderingpath

around the planet.

NASA’s super-pressure balloon program has only been

availabletoscienceexperimentsforafewyears,butalready

therecordforoneoftheseflightsatmid-latitudesis46

days—muchlongerthanpreviouslypossible.Thegoalisto

routinelyhaveflightsofupto100days.

Anothermajordevelopmenthasbeenintelescopecontrol.

It remains a challenge to take deep visible light images

withoutsmearingthem,asthetelescopemustdriftless

thanafractionofanarcsecondwhenpointingatatarget

—that’slikethreadinganeedlefromakilometreaway.The

Stratoscope II telescope, which operated about 50 years ago,

achievedaremarkable0.2-arcsecondresolutionforimages

with5to20secondsofexposuretime.Toimagefaintobjects,

though,we’dneedsimilarstabilityforatleastafewminutes.

TheSuper-pressureBalloon-borneImagingTelescope

(SuperBIT)hasmadehugeadvancesinthisarea.Itusesmotors

topointtheballoongondola;thetelescope,whichismounted

to an inner frame, can then be positioned to compensate for

anyrockingmotion.Motorscanalsoadjustamirrorinside the

camera to keep the image centre from drifting.

SuperBITshouldhaveitsfirstfullscienceflightonasuper-

pressureballooninaboutayear.LaunchingfromWanaka,

NewZealand,itwillmakedeep,high-resolutionmapsof

hundredsofgalaxyclusters.Astronomerscanthenusestrong

andweakgravitationallensingtomapdarkmatteraround

andbetweenthegalaxies.

This next-gen technology will make balloon-borne

telescopesanexcellentoptionforlongviewsofthesky

in visible light as well as ultraviolet and near-infrared

wavelengths, all of which require the dark-sky conditions

ofmiddlelatitudes(asopposedtothemidnightSunof

Antarctica). Soon we may have balloon telescopes mapping

distantgalaxieswithimageclaritysimilartotheHubble

Space Telescope or searching for planets around other stars.

For balloon astronomers, the sky is no longer the limit!

„LAURA FISSELis a postdoctoral research fellow at the US

National Radio Astronomy Observatory and a member of the

BLAST team.

• Watchballoonslaunchathttps://is.gd/balloonastroandfollowtheBLASTteam’sprogressonTwitter:@BLAST_TNG.

THE NEXT GENERATION A super-pressure balloon is readied for launch from Wanaka, New Zealand. The May 16, 2016, take-off

marked the first time a super-pressure balloon carried a scientific payload, called the Compton Spectrometer and Imager.

BALLOON ASTRONOMY