TOUGH­EST RO­BOT EVER

To build a rover that can sur­vive in the crush­ing pres­sure and tem­per­a­ture of Venus, we need to re­think ev­ery­thing...

Science Illustrated - - CONTENTS -

Crash. The Soviet probe Ven­era 7 speeds down through Venus' thick at­mos­phere, land­ing hard on the sur­face, when the para­chute does not func­tion prop­erly. For 23 min­utes, it sends data back to Earth, be­fore fall­ing silent. The scanty mea­sure­ments tell a story of an ex­tremely hos­tile en­vi­ron­ment. Sur­face tem­per­a­tures are close to 475 °C – enough to melt lead – and the pres­sure, which is more than 90 times that of Earth’s sur­face, would crush most sub­marines. Venus is more ex­treme than any­one had ever imag­ined, so no won­der the probe quickly suc­cumbs to the dev­as­tat­ing con­di­tions.

Ven­era 7 was the first probe to land on Venus on 15 De­cem­ber 1970, and for the next 15 years, only nine other Rus­sian and one Amer­i­can probes man­aged to fol­low suit. Since the space race calmed down in the 1980s, Venus has only been vis­ited by or­biters, but NASA still dreams of ex­plor­ing our neigh­bour­ing planet’s sur­face once again. So, engi­neers have de­signed the ro­bust AREE rover, which can re­sist the in­tense pres­sure and the high tem­per­a­tures.

The rover will study the planet’s sur­face and de­ter­mine what caused the run­away green­house ef­fect on Venus. How­ever, the stud­ies can­not be car­ried out us­ing in­stru­ments like those on the Mar­tian rovers. In­stead, AREE must carry out its pi­o­neer work by means of springs, gears, and Morse-like code.

Rover to ex­plain dis­as­ter course

In spite of its hard land­ing, the Ven­era 7 mis­sion was suc­cess­ful. It was the first time that a probe sent a sig­nal to Earth from the sur­face of an­other planet, and al­though sub­se­quent Venus probes lived longer, none of them kept up a sig­nal to Earth for more than two hours and seven min­utes. The brief lives of the probes are a ma­jor part of the rea­son why our clos­est neigh­bour has been vis­ited so rarely since 1985. When equip­ment is to be brought to the sur­face of Venus, it must first pass through clouds con­sist­ing of sul­phuric acid droplets, and at lower al­ti­tudes, other highly cor­ro­sive chem­i­cal com­pounds such as hy­drochlo­ric acid and hy­dro­gen flu­o­ride ex­ist. On the planet's sur­face, the pres­sure could eas­ily de­stroy sen­si­tive in­stru­ments.

How­ever, the high tem­per­a­tures are the ma­jor prob­lem, as they will melt some met­als and over­heat all elec­tric systems. The elec­tric re­sis­tance of the cir­cuits will in­crease with tem­per­a­ture, mean­ing it will be more dif­fi­cult for a cur­rent to flow through the elec­tron­ics. But what is worse, the tran­sis­tors of mod­ern mi­crochips are based on sil­i­con, which loses its semi­con­duc­tor prop­er­ties in the heat, mak­ing com­puter units break down.

The mere iden­ti­fi­ca­tion of a heat-de­fy­ing ma­te­rial that can pro­tect in­di­vid­ual mi­crochips cause prob­lems for engi­neers.

Old in­ven­tions in­spire rover

To over­come the planet’s harsh con­di­tions, as­tronomers and engi­neers from NASA’s Jet Propul­sion Lab­o­ra­tory have de­signed a rover that would be able to func­tion on Venus for months. Known as the Au­toma­ton Rover for Ex­treme En­vi­ron­ments, AREE, the project has been on the draw­ing board since 2015.

In­spired by re­li­able clock­works and me­chan­i­cal ma­chines of the past, sci­en­tists imag­ine a me­chan­i­cal rover con­trolled by gears and en­er­gized by springs, that are pow­ered by the wind. All parts are to be made of spe­cial metal al­loys and syn­thetic fi­bre ma­te­ri­als that can re­sist the high tem­per­a­tures. The de­sign of the rover is in­spired by the World War I tanks, which were built to climb steep ob­sta­cles such as bomb craters and trenches. Due to vol­canic ac­tiv­ity on Venus, a crawler would also have to be able to han­dle dif­fer­ent types of ter­rain.

At the cen­tre of the rover, there is a sim­ple wind tur­bine, that can gen­er­ate wind en­ergy 24/7. The low sur­face wind speed of av­er­agely 0.6 m/sec­ond is suf­fi­cient to make the wind tur­bine ro­tate in the thick at­mos­phere. By mak­ing the rover be sta­tion­ary for seven hours, en­er­giz­ing a spring by means of wind power, the rover can drive 100 m in one hour, as the spring is au­to­mat­i­cally re­leased. Dur­ing the planned 116 Earth days of the mis­sion – cor­re­spond­ing to one Venus day – the rover can drive 35 km in the Sek­met Mons lava field, which has a ver­sa­tile ge­o­log­i­cal his­tory.

In or­der to make sure that the rover does not drive in a cir­cle, but rather ex­plores a long cross sec­tion of Venus, a me­chan­i­cal sys­tem must con­tin­u­ously count the num­ber of rev­o­lu­tions of each tread of the ve­hi­cle. If one tread is ahead of the oth­ers, the rover must have turned, and so, the de­vice makes sure to get it back on track again. A sim­i­lar sys­tem en­sures that the rover con­tin­ues in the same di­rec­tion if it en­coun­ters an ob­sta­cle and has to re­verse to take a slightly dif­fer­ent route.

Data sent as flash­ing code

How­ever, the Venus rover can­not han­dle all tasks with me­chan­ics. Par­tic­u­larly the more de­tailed ge­o­log­i­cal mea­sure­ments re­quire elec­tronic sen­sors. The in­ven­tors trust physi­cists and engi­neers from NASA’s Glenn Re­search Cen­tre to de­velop new elec­tron­ics, which can func­tion at tem­per­a­tures of about 500 °C. In 2016, sci­en­tists man­aged to make sim­ple cir­cuits based on the ex­tremely durable sil­i­con car­bide ma­te­rial func­tion un­der con­di­tions like those on Venus for 21 days. How­ever, the sim­ple cir­cuits can­not make up a real com­puter, and more­over, sci­en­tists would like to get data that spans a longer pe­riod of time.

Apart from the elec­tric com­po­nents, the rover will be as­sisted by a satel­lite or­bit­ing Venus, which is not ex­posed to the harsh con­di­tions of the rover. The satel­lite is to aim an ul­tra-strong ra­dio sig­nal at four radar tar­gets on the top side of the rover. Sci­en­tists ex­plain that the tar­gets func­tion as in­verted stealth planes that be­come in­vis­i­ble by bend­ing radar waves. In­stead, the radar tar­gets con­cen­trate the radar sig­nal back to the satel­lite. By means of gears, the rover’s mea­sure­ments are trans­ferred to four ro­tat­ing discs with holes in them, that al­ter­nately hide and show the radar tar­gets. So, the re­flected radar sig­nal is in­ter­rupted in a rhythm that re­flects the col­lected data and sent back as a type of flash­ing Morse code in the same way as the sig­nal lamps of ships. Fi­nally, the satel­lite sends the about 1,000 bits of data col­lected per day to Earth.

Me­chan­ics al­low visit to Mercury

Venus is highly in­flu­enced by vol­canic erup­tions, and the sur­face is cov­ered in lava fields. NASA’s sci­en­tists hope that a new mis­sion can teach them more about how pe­ri­ods of vol­canic ac­tiv­ity have shaped the sur­face over bil­lions of years and per­haps spot min­eral ev­i­dence of a time, when the planet was a much more friendly place to be. Al­though the con­di­tions sound over­whelm­ing, pro­longed me­te­o­ro­log­i­cal and ge­o­log­i­cal stud­ies of the bar­ren desert sur­face are im­por­tant in or­der to un­der­stand why the planet’s green­house ef­fect went berserk. More than 2.5 bil­lion years ago, Venus was not just like Earth in size, it also in­cluded oceans and per­haps even life. So, Venus is also known as Earth’s twin. Data from the me­chan­i­cal rover is to help sci­en­tists solve the mystey of why Venus was trans­formed. This is not only im­por­tant to Earth’s fu­ture, rather also to the pos­si­bil­ity of ex­plor­ing the prospects of life on other plan­ets or­bit­ing re­mote stars.

A mis­sion to the sur­face of Venus has not yet been planned, but with AREE, it might be done. The re­spon­si­ble sci­en­tists em­pha­sise that a me­chan­i­cal rover could also ex­plore Mercury, whose sur­face has not yet been vis­ited. On Earth, it can be used to ob­serve ac­tive vol­ca­noes. No mat­ter what, the ro­bust ve­hi­cle is in for a hot fu­ture.

96.5 % of Venus' at­mos­phere is car­bon diox­ide, whereas ni­tro­gen makes up 3.5%.

THESIZE VENUSIS BIL­LION AND2.5 EARTH, OF HAVE ITMIGHT YEARSAGO, LE. HABITAB BEEN

In the GEER pres­sure cham­ber, NASA engi­neers can sim­u­late Venus. They have made sim­ple cir­cuits func­tion for 21 days at a tem­per­a­ture of 425 de­grees.

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