"Annenberg Media" "¶" "CAPTIONING IS MADE POSSIBLE BY THE ANNENBERG/CPB PROJECT" "VOYAGESTOOTHERPLANETS REQUIREENORMOUSENERGY." "THE AMOUNT OF ENERGY EXPENDED CANBEMINIMIZED" "BYUSINGTHESAMEFORCE" "THATMOVESTHEPLANETS THROUGHTHESOLARSYSTEM." "THEFORCEOF THESUN 'S GRAVITATIONALFIELD" "ISUSED TONAVIGATEIN SPACE." "A FEW YEARS AGO," "THE ONLY CONCEIVABLE PURPOSE FOR THE CELESTIAL MECHANICS" "WE'VE BEEN TEACHING YOU" "WOULD HAVE BEEN TO PLOT THE COURSES OF THE PLANETS." "TODAY, MANY OF THE OBJECTS UP THERE" "WERE PUT UP THERE," "EITHER BY US OR BY OUR FRIENDS" "ON THE OTHER SIDE OF THIS TINY PLANET." "IN A FEW YEARS, THERE ARE SURE TO BE MANY MORE." "THE ROUTES FOLLOWED BY SPACECRAFT" "AND ARTIFICIAL SATELLITES" "ARE GOVERNED BY THE SAME RULES" "THAT GOVERN THE ORBITS OF THE PLANETS." "IF SOMEDAY, SOMEBODY OPENS THE WINDOW OF HIS SPACECRAFT" "AND SAYS, "HOW DO I GET TO VENUS FROM HERE?"" "YOU SAY, "I'LL DRAW YOU A MAP."" "MARINER10.1973." "TO VENUS AND MERCURY." "AN EXQUISITE VESSEL," "A SCIENTIFIC EXPLORER LAUNCHED ACROSS THE SOLAR SEA." "VIKING.1975." "TO MARS." "ANOTHER MECHANICAL MARVEL LAUNCHED IN SEARCH OF ANSWERS" "ANSWERS THAT MAY RETURN TO HAUNT LONG-HELD THEORIES," "ANSWERS TO SUCH QUESTIONS AS" "WHAT WAS THE BIOLOGICAL SPARK THAT IGNITED THE HUMAN SPECIES?" "VOYAGER.1977." "TO JUPITER AND TO SATURN" "TO URANUS AND TO NEPTUNE." "MARINER," "VIKING," "AND VOYAGER..." "THIS CENTURY'S FRANCIS DRAKE, FERDINAND MAGELLAN," "ERIC THE RED" "LAUNCHED TO DISCOVER HOW THE PLANETS WERE CREATED." "FIRSTHAND ANSWERS MAY TURN CURRENT MATTERS OF FACT" "INTO HISTORICAL CHAPTERS OF SCIENCE FICTION," "OR THEY MAY DO THE OPPOSITE." "WHATEVER THE ANSWERS FROM OUTER SPACE," "FIRST COME THE QUESTIONS ON EARTH" "QUESTIONS BEGINNING WITH, "IN SEARCH OF THE UNKNOWN," "HOW DO THEY REACH BEYOND THE KNOWN?"" "WITHOUT EVEN THE AID OF A LIGHTHOUSE," "HOW CAN A MODERN MARINER OR ANY OTHER SPACE-AGE VESSEL" "SAIL FROM HERE TO THERE?" "AND, ONCE LAUNCHED INTO THE COSMIC SEAS," "WHO NAVIGATES?" "CAL TECH'S JET PROPULSION LABORATORY--JPL" "PASADENA, CALIFORNIA." "NERVE CENTER FOR EXPLORATION" "INTO THE ENDLESS FRONTIER OF SPACE." "THE CEREBRAL CORTEX" "OF NASA'S UNMANNED PLANETARY PROGRAM," "THE DEEP SPACE NETWORK OPERATIONS CENTER." "ONLY A FEW PROBLEM SOLVERS" "ARE QUALIFIED TO SOLVE PROBLEMS IN OUTER SPACE ITSELF." "ONE AGE-OLD PROBLEM OF OUTER SPACE" "CONCERNS GETTING THERE." "YOU COULD FLY A SPACECRAFT ON A STRAIGHT LINE" "FROM ONE POINT TO ANOTHER IN THE SOLAR SYSTEM." "IT WOULD REQUIRE AN EXORBITANT AMOUNT" "OF PROPULSIVE CAPABILITY." "WE USE ONE OF KEPLER'S LAWS," "WHICH TELLS US THAT THE PLANETS MOVE" "AROUND THE SUN ON ELLIPSES," "AND THE SPACECRAFT WILL FOLLOW EXACTLY THESE SAME LAWS." "OBVIOUSLY, TO AIM TOWARD THE PLANETS" "WITH BRUTE FORCE ALONE IS TO MISS THE POINT ENTIRELY." "SPACE NAVIGATORS LOOK TO THE FUTURE" "BY WAY OF THE PAST." "KEPLER'S THREE LAWS STATED HOW THE PLANETS ORBIT THE SUN." "NEWTON EXPLAINED WHY KEPLER'S LAWS WORK." "NO MATTER HOW FUTURISTIC THE PROBLEMS," "SPACE NAVIGATORS USE NEWTON'S AND KEPLER'S LAWS" "AS OPERATING PRINCIPLES." "THE WAY WE GET A SPACECRAFT FROM EARTH TO MARS" "IS TO PUT THE SPACECRAFT IN AN INDEPENDENT ORBIT" "AROUND THE SUN" "THAT INTERSECTS EARTH'S ORBIT AND MARS' ORBIT." "THE LAUNCH VEHICLE HAS TO IMPART ENOUGH SPEED" "TO THAT SPACECRAFT RIGHT AFTER LAUNCH" "SO IT WILL COAST FROM EARTH TO MARS" "ONCE THE LAUNCH VEHICLE BURNS OUT 30 MINUTES AFTER LIFTOFF." "TO TRAVEL BETWEEN TWO POINTS IN SPACE," "A CRAFT COASTS TO ITS DESTINATION" "IN ORBIT AROUND THE SUN" "AS IF IT WERE AN ORBITING PLANET." "THE PATH OF A SPACECRAFT FROM ONE PLANET TO ANOTHER" "IS CALLED A TRANSFER ORBIT." "FOR THE VIKING MISSION, WE WERE LIMITED" "IN SELECTING THE TRANSFER ORBIT" "BECAUSE VIKING WAS THE MOST MASSIVE" "INTERPLANETARY SPACECRAFT EVER LAUNCHED." "THE THEN MOST POWERFUL LAUNCH VEHICLE" "COULD JUST BARELY GET US TO MARS." "THE CLASSICAL TRANSFER BETWEEN TWO PLANETS" "IS REFERRED TO AS THE HOHMANN TRANSFER." "WE FOLLOWED A TRANSFER CLOSE TO THIS." "WE LAUNCH FROM EARTH, TANGENTIALLY," "AT THE LOWEST POINT IN THE ORBIT," "THE POINT CLOSEST TO THE SUN," "AND ARRIVE AT MARS AT THE HIGHEST POINT," "THE MOST DISTANT POINT FROM THE SUN." "THIS ORBIT JUST MANAGES TO CONNECT" "FROM THE EARTH'S ORBIT TO MARS' ORBIT." "THE SPACECRAFT DOES 1/2 A REVOLUTION" "IN THIS ORBIT TO MAKE THE TRANSFER." "[NARRATOR] THE TRIP CAN'T JUST START ANY OLD TIME." "THE CREW MUST WAIT UNTIL IT'S TIME FOR LAUNCH." "GETTING THE SPACECRAFT TO ANOTHER POINT" "IS LIKE SHOOTING AT A MOVING TARGET." "THE TARGET MUST BE WITHIN RANGE." "YOU MUST ESTABLISH THE AMOUNT" "BY WHICH YOU'LL LEAD THE TARGET" "SO IT DOESN'T PASS YOU BEFORE YOU GET THERE." "JUST AS KEPLER'S THIRD LAW" "FIXES THE LENGTH OF AN EARTH YEAR..." "AND THE LENGTH OF A MARS YEAR..." "IT ALSO DICTATES HOW LONG A SPACECRAFT," "COASTING IN ITS OWN ORBIT," "WILL TAKE TO GET FROM THE EARTH" "TO THE POSITION OF THE ORBIT OF MA." "IT TAKES ABOUT 8.5 MONTHS." "IN ORDER FOR MARS TO BE WAITING" "WHEN THE CRAFT ARRIVES," "IT HAS TO BE LAUNCHED WHEN MARS IS JUST 44 DEGREES" "AHEAD OF THE EARTH." "THAT ALIGNMENT IS CALLED AN OPPORTUNITY." "IN A PLANETARY PROBLEM," "WE HAVE TO WAIT TO GET THE PLANETARY ALIGNMENT" "TO BE JUST RIGHT." "WHEN THE ALIGNMENT IS CORRECT," "WE HAVE WHAT IS CALLED AN OPPORTUNITY." "THESE OPPORTUNITIES HAVE A DURATION" "OF ONE TO TWO WEEKS." "SPACE NAVIGATORS MUST WAIT FOR THE RIGHT MOMENT," "WHEN A COASTING ORBIT WILL TAKE THE SPACECRAFT" "FROM THE POSITION OF THE EARTH TO THE TARGET PLANET'S ORBIT" "JUST WHEN THE TARGET PLANET ARRIVES THERE." "THAT MOMENT IS CALLED AN OPPORTUNITY." "OPPORTUNITY DOESN'T KNOCK" "AT THE SAME TIME" "FOR ALL PLANETS." "PROSPECTS LOOK GOOD FOR MARS ABOUT EVERY TWO YEARS." "AN OPPORTUNITY TO VISIT VENUS" "PRESENTS ITSELF EVERY 19 MONTHS..." "AND FOR JUPITER, EACH 13 MONTHS." "WHEN THESE TIMES COME," "SPACE NAVIGATORS MUST BE READY TO MOVE QUICKLY" "THROUGH A LAUNCH WINDOW" "A FEW FLEETING MOMENTS EACH DAY WHEN THE ROCKETS MUST BE FIRED." "EACH DAY THERE IS A RESTRICTED TIME" "WITHIN WHICH WE COULD LAUNCH." "THIS PROBLEM IS LIKE RIDING ON A CAROUSEL" "AND PLAYING CATCH WITH A FRIEND STANDING OFF TO THE SIDE." "FOR EACH REVOLUTION OF THE CAROUSEL," "YOU'D HAVE A SHORT RANGE OF TIME" "WHERE YOU COULD THROW THE BALL TO YOUR FRIEND." "EACH TIME THE EARTH COMES AROUND," "WE HAVE AN ALIGNMENT BETWEEN THE LAUNCH SITE" "AND THE DIRECTION IN WHICH WE NEED TO DEPART." "WHEN WE GET THIS ALIGNMENT, WE LAUNCH." "THE CAROUSEL CALLED EARTH" "IS IN A NEARLY CIRCULAR ORBIT AROUND THE SUN." "ANY INCREASE OR BOOST IN SPEED" "CREATES A BIGGER, MORE ECCENTRIC ORBIT." "TO GO FROM AN EARTH ORBIT INTO A MARS TRANSFER ORBIT" "REQUIRES A BOOST" "OF EXACTLY 2.9 KILOMETERS PER SECOND." "THE FIRST TASK IS TO ESCAPE" "FROM THE PARKING ORBIT" "AROUND THE EARTH." "A ROCKET THRUST" "WILL BOOST THE CRAFT" "INTO A HYPERBOLA" "THAT DRIFTS TO INFINITY" "AT JUST THE RIGHT SPEED" "OF 2.9 KILOMETERS PER SECOND." "THE THRUST MUST COME" "AT JUST THE RIGHT MOMENT." "THAT MOMENT IS 7:56 P.M.," "LOCAL TIME." "THE SUN DOES THE REST OF THE JOB," "BENDING THE TRAJECTORY INTO A MARS TRANSFER ORBIT." "IF THE DESTINATION IS VENUS RATHER THAN MARS," "THE BASIC IDEA IS THE SAME..." "BUT NOW THE JOURNEY IS INWARD TOWARD THE SUN." "BLASTING OFF IN THE MORNING AT 7:40 A.M.," "THE CRAFT ESCAPES FROM THE EARTH," "BUT THIS TIME, IT'S GOING BACKWARD," "RELATIVE TO THE EARTH'S ORBIT," "LOSING SPEED AND FALLING INWARD TOWARD VENUS." "SO IF SOMEDAY" "SOMEONE DOES OPEN HIS SPACECRAFT WINDOW" "AND ASKS YOU," ""HOW DO I GET TO VENUS FROM HERE?"" "YOU KNOW WHAT TO TELL THEM." "GETTING THE CRAFT INTO THE PLANET'S VICINITY," "MAKING THE ORBITS INTERSECT," "IS ONLY PART OF THE SPACE NAVIGATOR'S CHALLENGE." "THE OBJECT IS TO LAND THE CRAFT." "IN PREPARATION TO LAND VIKING," "AN EARLIER MISSION, MARINER9 ," "TOOK PHOTOGRAPHS TO STAKE A VISUAL CLAIM ON MARS." "WITH PREPARATIONS COMPLETED," "VIKINGISREADYTOLAND ." "VIKING'SCAMERASREVEALASITE  THAT'S SURPRISINGLY" "AND DANGEROUSLY LADEN WITH BOULDERS." "FORTUNATELY, VIKINGHASTHEABILITY" "TO SCOUT ANOTHER LANDING SITE." "BUT FINDING A SAFE SITE IS ONE THING," "ACTUALLY LANDING SAFELY, QUITE ANOTHER." "ONE FALSE CALCULATION, WHICH IS EASY TO IMAGINE" "AT A DISTANCE OF 200 MILLION KILOMETERS," "COULD MEAN THE DESTRUCTION OF VIKING." "BUT THE PREPROGRAMMED COMPUTER ONBOARD VIKING" "SAVES THE DAY AND THE CRAFT." "FOR THE FIRST TIME, THE PLANET MARS" "IS PHOTOGRAPHED FROM ITS OWN SURFACE." "NEWTON AND KEPLER MIGHT HAVE FANTASIZED" "ABOUT SETTING A SCIENTIFIC GADGET" "ATOP A DISTANT PLANET," "BUT IT TOOK JPL's SCIENTISTS TO DO IT." "SCIENTISTS AND ENGINEERS" "DON'T TEND TO REST ON THEIR ACCOMPLISHMENTS." "THE SPACE NAVIGATORS SET THEIR SIGHTS" "NOT ONLY ON MARS," "BUT ON THE ENORMOUS JOURNEY TO THE FOUR OUTER GIANTS" "OF THE SOLAR SYSTEM" "JUPITER, SATURN, URANUS, AND NEPTUNE." "IN THIS CASE, TIMING IS EVERYTHING" "BECAUSE THESE PLANETS LINE UP RIGHT" "FOR ONE SPACECRAFT" "TO VISIT ALL FOUR IN THE SAME TRIP," "JUST ONCE EVERY 175 YEARS." "THAT 175-YEAR CYCLE CAME AROUND IN 1977." "IN THAT YEAR, NOT ONE, BUT TWO FRAGILE VESSELS" "SET FORTH ON A JOURNEY" "THAT WOULD TAKE THEM TO THE GIANT PLANET JUPITER..." "THEN THROUGH THE RINGS OF SATURN." "ONE OF THEM WOULD EVEN PASS BY MYSTERIOUS URANUS..." "EVEN BEYOND DISTANT NEPTUNE..." "AND FINALLY, BOTH WOULD COAST" "INTO THE ENDLESS REACHES OF INTERSTELLAR SPACE." "TO MAKE THE TRIP MEANT, FIRST OF ALL, OVERCOMING GRAVITY" "JUST TO ESCAPE FROM THE PLANET EARTH." "BUT EVEN GIVEN THE GRAND ONCE-IN-175-YEAR OPPORTUNITY," "IT STILL COULDN'T HAVE BEEN DONE" "WITHOUT THE HELP OF GRAVITY ITSELF." "GRAVITY ASSIST USES THE GRAVITY OF A PLANET" "TO CHANGE THE SPEED AND DIRECTION" "OF A SPACECRAFT AS IT GOES PAST THE PLANET." "THAT CHANGE IS WITH REFERENCE TO THE SUN." "FROM THE PLANET'S POINT OF VIEW, NOTHING MUCH HAPPENS." "THE SPACECRAFT IS HERE." "IT SPEEDS UP, WHIPS AROUND, AND LEAVES," "SAME SPEED LEAVING AS COMING IN." "FROM THE SUN'S VIEWPOINT, IT'S QUITE DIFFERENT." "BOTH VOYAGER MISSIONS GOT THEIR FIRST GRAVITY ASSISTS" "FROM THE PLANET JUPITER," "PROPELLING THEM ONWARD TOWARD SATURN." "TO APPRECIATE THE CONCEPT," "IT'S NOT NECESSARY TO GO QUITE THAT FAR." "SUPPOSE WE IMAGINE A BASEBALL GAME." "HERE'S A BATTER, AND HE'S GOING TO BUNT." "HE HOLDS THE BAT ABSOLUTELY STILL." "THE PITCH COMES IN, BOUNCES OFF THE BAT." "THE BAT JUST CHANGES" "THE DIRECTION OF THE BASEBALL'S FLIGHT." "IT HASN'T ADDED ANY ENERGY TO IT." "IF THE BATTER'S SWINGING, THE BAT HAS ENERGY." "WHEN THE BAT HITS THE BALL NOW, IT ADDS ENERGY TO IT." "THE COMBINATION OF THE ENERGY THE PITCHER GAVE TO THE BALL" "AND THE ENERGY THE BALL GOT FROM THE SWINGING BAT" "CARRIES IT OVER THE CENTERFIELD WALL." "OF COURSE, A SPACECRAFT DOESN'T BOUNCE OFF A PLANET." "THE SPACECRAFT APPROACHES THE PLANET." "THE GRAVITATIONAL PULL OF THE PLANET" "CAUSES THIS INTERACTION." "IF JUPITER REALLY DID HIT VOYAGER," "THAT WOULD BE THE BALL GAME." "WHILE THERE'S NO PHYSICAL CONTACT," "THERE IS A STRIKING CONNECTION BETWEEN BASEBALL AND PHYSICS." "JUPITER DOESN'T STAND STILL." "IT MOVES." "LIKE A SWINGING BAT," "IT GIVES UP SOME OF ITS ENERGY" "TO THE BALL OF VOYAGER AS IT FLIES BY." "PLAYING ON THE LARGEST FIELD AROUND" "THE UNIVERSE ITSELF" "SPACE NAVIGATORS HURLED VOYAGER PAST SATURN" "AND HER FABLED RINGS." "AND THERE, LIKE MIGHTY CASEY AT THE BAT," "THEY CAME UP AGAINST THE UNEXPECTED." "THE RINGS ARE SMALL BODIES IN ORBIT AROUND SATURN." "WE FOUND" "THAT THE TWO BRIGHTEST RINGS" "THE A" " AND B-RING," "WHICH LOOK HOMOGENEOUS FROM EARTH," "WHEN VIEWED UP CLOSE, APPEAR TO BE STRUCTURED." "PERHAPS THE MOST INTRIGUING SURPRISE" "WAS THAT ASSOCIATED" "WITH THE NARROW F-RING." "IT WAS DISCOVERED IN 1979 BY PIONEER 11." "WE DISCOVERED WITH VOYAGER 1 AN ESSENTIAL KEY" "TO UNDERSTANDING THE DYNAMICS OF SUCH A NARROW RING." "WE FOUND TWO SATELLITES," "ONE JUST INSIDE THE F-RING AND ONE JUST OUTSIDE." "THE KEY TO THE MYSTERIOUS F-RING" "IS THE SAME PRINCIPLE" "THAT HAD GOTTEN VOYAGER THERE TO SEE IT" "THE PRINCIPLE OF GRAVITY ASSIST." "THE F-RING AND ITS SHEPHERDING MOONS" "ARE ALL IN ORBIT AROUND SATURN." "OBEYING KEPLER'S THIRD LAW, THE INNER MOON MOVES FASTEST," "THE RING MATERIAL, SLOWER, THE OUTER MOON, SLOWER STILL." "WHEN A RING PARTICLE ENCOUNTERS THE FASTER-MOVING INNER MOON," "THE MOON PULLS IT ALONG, SPEEDING THE PARTICLE UP" "AND FLINGING IT INTO A HIGHER ORBIT." "WHEN A RING PARTICLE ENCOUNTERS THE SLOWER-MOVING OUTER MOON," "THE PARTICLE GETS HELD BACK, SLOWS DOWN," "AND FALLS INTO A LOWER ORBIT." "THESE EFFECTS, TOGETHER WITH COLLISIONS" "AMONG THE RING PARTICLES THEMSELVES," "SHEPHERD THE MATERIAL BETWEEN THE MOONS" "INTO A NARROW RING." "WHILE THIS KIND OF MOTION WAS SOMEWHAT UNEXPECTED," "ITS DISCOVERY WASN'T A TOTAL SURPRISE." "SHEPHERDING WAS OFFERED AS A THEORY" "BEFORE VOYAGER ENCOUNTERED SATURN" "TO EXPLAIN ANOTHER PLANET'S RINGS." "WHEN THE SHEPHERDING THEORY WAS FIRST PROPOSED" "TO EXPLAIN NARROW RINGS AROUND URANUS," "IT WASN'T UNIVERSALLY ACCLAIMED." "IT REQUIRED THE PRESENCE OF TWO UNSEEN OBJECTS" "TWO SMALL MOONS" "TO EXPLAIN THE PRESENCE" "OF ONE OBSERVED OBJECT-- THE NARROW RING." "THE FIRST DIRECT EVIDENCE OF THIS SHEPHERDING EFFECT" "WAS WITH VOYAGER." "IT WASN'T A SURPRISE TO THOSE WHO BELIEVED IN THE THEORY." "TODAY, SHEPHERDING AND GRAVITY ASSIST" "COMBINE TO ILLUSTRATE" "THAT 300 YEARS AFTER THE DISCOVERY" "OF CLASSICAL MECHANICS," "THERE ARE STILL NEW DISCOVERIES TO BE MADE." "CELESTIAL SCIENTISTS FROM JOHANNES KEPLER ONWARD" "COULD CALCULATE THE MOTIONS OF THE SOLAR SYSTEM." "ANY SCIENTIST WHO UNDERSTOOD THE PLANETS' ORBITS" "HELD WITHIN HIS GRASP" "A PROFOUND AND TRULY HEAVENLY KNOWLEDGE." "BUT FOR 300 YEARS, EVEN TO THE GREATEST MINDS," "THE HEAVENS REMAINED WITHIN REACH" "OF THE INTELLECT ALONE." "THREE CENTURIES WOULD PASS BEFORE THE FIRST HESITANT STEPS" "BEYOND THE BARRIER OF EARTH'S GRAVITY WERE TAKEN" "TO FINALLY ALLOW SCIENTISTS" "TO TAKE PART IN THE WORLDS BEYOND THE PLANET EARTH." "NAVIGATING AS WELL AS CALCULATING," "MAKING HEAVEN PASSABLE AS WELL AS POSSIBLE" "THATISTHEMIRACLE OF THE SPACE AGE." "THAT'S WHAT THE FATHER OF CLASSICAL MECHANICS" "MIGHT HAVE DREAMED OF." "BUT THAT IS WHAT THE SPACE NAVIGATORS" "MADE REALITY." "OF ALL THE MAGNIFICENT DISCOVERIES" "OF THE VOYAGER MISSION," "ONE OF THE MOST UNEXPECTED AND SPECTACULAR" "WAS THE COMPLEXITY OF THE RINGS OF SATURN." "WHEN THIS DISCOVERY WAS MADE," "SCIENTISTS WENT SCRAMBLING AROUND" "TRYING TO FIND AN EXPLANATION." "SO FAR AS I KNOW, NO ONE HAS SUCCEEDED." "I HAVE A THEORY." "YOU CAN CALL THIS THE GOODSTEIN THEORY." "I HAVEN'T PUBLISHED IT YET IN A SCIENTIFIC JOURNAL." "THE VOYAGER SPACECRAFT, LIKE THE PIONEER 10 BEFORE IT," "IS GOING TO ESCAPE FROM THE SOLAR SYSTEM" "AND DRIFT FOREVER IN THE ENDLESS REACHES OF SPACE." "THERE'S THE TINIEST CHANCE THAT SOMEDAY," "SOMEONE OR SOMETHING FROM AN ALIEN CIVILIZATION" "WILL COME ACROSS ONE OF THOSE CRAFT." "JUST IN CASE THAT HAPPENS," "WE'VE PUT ON EACH CRAFT A MESSAGE." "ON THE VOYAGER CRAFT, AMONG OTHER THINGS," "THE MESSAGE HAS A PHONOGRAPH RECORD." "IT HAS MUSIC AND SAMPLES FROM VARIOUS LANGUAGES" "AND A GREETING FROM PRESIDENT CARTER" "AND OTHER THINGS AN ALIEN CIVILIZATION" "JUST COULDN'T DO WITHOUT." "WE ASSUME THAT IF AN INTELLIGENT BEING" "FINDS A FLAT DISC WITH GROOVES IN IT," "THEY'LL KNOW WHAT TO DO WITH IT." "WELL, THE RINGS OF SATURN" "ARE A FLAT DISC WITH GROOVES IN IT." "BOO!" "HISS!" "BOO!" "ON SECOND THOUGHT," "I THINK I'LL KEEP MY THEORY TO MYSELF." "TO NAVIGATE FROM THE EARTH TOANOTHERPLANET," "ASPACECRAFTIS LAUNCHED INTOA TRANSFERORBIT." "THELAUNCHMUSTOCCUR INA BRIEFWINDOW" "DURING A SPECIAL OPPORTUNITY FOREACHPLANET." "NAVIGATORSALSOUSE GRAVITYASSISTS" "FROM THE PLANETS THEMSELVES" "TO PROVIDE ADDITIONAL BOOSTS." "CAPTIONING PERFORMED BY THE NATIONAL CAPTIONING INSTITUTE, INC." "CAPTIONS COPYRIGHT 1985 CALIFORNIA INSTITUTE OF TECHNOLOGY" "THE CORPORATION FOR COMMUNITY COLLEGE TELEVISION, AND THE ANNENBERG/CPB PROJECT" "PUBLIC PERFORMANCE OF CAPTIONS PROHIBITED WITHOUT PERMISSION OF NATIONAL CAPTIONING INSTITUTE" "Annenberg Media" "¶" "For information about this and other Annenberg Media programs call 1-800-LEARNER and visit us at"