Earth's halo of rub­bish

DEMM Engineering & Manufacturing - - CASE STUDY -

LEO stands for low Earth or­bit and is the re­gion of space within 2,000 km of the Earth’s sur­face. It is the most con­cen­trated area for or­bital de­bris.

This com­puter gen­er­ated im­age (at right) shows ob­jects in Earth or­bit that are cur­rently be­ing tracked. Ap­prox­i­mately 95 per­cent of the ob­jects in this il­lus­tra­tion are or­bital de­bris, i.e., not func­tional satel­lites. The dots rep­re­sent the cur­rent lo­ca­tion of each item. The or­bital de­bris dots are scaled ac­cord­ing to the im­age size of the graphic to op­ti­mise their vis­i­bil­ity and are not scaled to Earth.

As if we’re not chuck­ing enough rub­bish across the earth, NASA es­ti­mates there are more than half a mil­lion bits of de­bris or ‘space junk’ or­bit­ting the Earth. Not all items are man- made but, of course, way too much is.

Space de­bris is made up of nat­u­ral (me­te­oroid) and man- made par­ti­cles but while the for­mer bits are or­bit­ing the sun, the lat­ter is or­bit­ing the Earth. This is Or­bital De­bris, the Space Junk, which in­cludes non­func­tional space­craft, aban­doned launch ve­hi­cle stages, mis­sion- re­lated de­bris and frag­men­ta­tion de­bris.

There are more than 20,000 pieces of de­bris larger than a softball or­bit­ing the Earth. They travel at speeds up to 17,500 mph, fast enough for a rel­a­tively small piece of or­bital de­bris to dam­age a satel­lite or a space­craft. There are 500,000 pieces of de­bris the size of a mar­ble or larger. There are many mil­lions of pieces of de­bris that are so small they can’t be tracked.

Even tiny paint f lecks can dam­age a space­craft when trav­el­ing at these ve­loc­i­ties. In fact a num­ber of space shut­tle win­dows have been re­placed be­cause of dam­age caused by ma­te­rial that was an­a­lyzed and shown to be paint f lecks.

With so much or­bital de­bris, there have been sur­pris­ingly few dis­as­trous col­li­sions.

In 1996, a French satel­lite was hit and dam­aged by de­bris from a French rocket that had ex­ploded a decade ear­lier.

On Feb. 10, 2009, a de­funct Rus­sian satel­lite col­lided with and de­stroyed a func­tion­ing U.S. Irid­ium com­mer­cial satel­lite. The col­li­sion added more than 2,000 pieces of track­able de­bris to the in­ven­tory of space junk.

China’s 2007 anti- satel­lite test, which used a mis­sile to de­stroy an old weather satel­lite, added more than 3,000 pieces to the de­bris prob­lem.

TRACK­ING DE­BRIS

The De­part­ment of De­fense main­tains a highly ac­cu­rate satel­lite cat­a­log on ob­jects in Earth or­bit that are larger than a softball.

NASA and the DoD co­op­er­ate and share re­spon­si­bil­i­ties for char­ac­ter­iz­ing the satel­lite (in­clud­ing or­bital de­bris) en­vi­ron­ment. DoD’s Space Sur­veil­lance Net­work tracks dis­crete ob­jects as small as five cen­time­tres in di­am­e­ter in low Earth or­bit and about one me­tre in geosyn­chronous or­bit. Cur­rently, about 15,000 of­fi­cially cat­a­loged ob­jects are still in or­bit. The to­tal num­ber of tracked ob­jects ex­ceeds 21,000. Us­ing spe­cial ground- based sen­sors and in­spec­tions of re­turned satel­lite sur­faces, NASA sta­tis­ti­cally de­ter­mines the ex­tent of the pop­u­la­tion for ob­jects less than ten cen­time­tres in di­am­e­ter.

Col­li­sion risks are di­vided into three cat­e­gories de­pend­ing upon size of threat. For ob­jects ten cen­time­tres and larger, con­junc­tion as­sess­ments and col­li­sion avoid­ance ma­noeu­vers are ef­fec­tive in coun­ter­ing ob­jects which can be tracked by the Space Sur­veil­lance Net­work. Ob­jects smaller than this usu­ally are too small to track and too large to shield against. De­bris shields can be ef­fec­tive in with­stand­ing im­pacts of par­ti­cles smaller than one cen­time­tre.

You can find out more about space junk HERE

ON 21 JAN­UARY 2001, A DELTA 2 THIRD STAGE, KNOWN AS A PAM-D (PAYLOAD AS­SIST MOD­ULE - DELTA), REENTERED THE AT­MOS­PHERE OVER THE MID­DLE EAST. THE TI­TA­NIUM MO­TOR CASING OF THE PAM-D, WEIGH­ING ABOUT 70 KG, LANDED IN SAUDI ARA­BIA ABOUT 240 KM FROM THE...

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