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Satellites Why do objects move in a circle? • http://www.youtube.com/watch?v=h3fH84fE 0eo&feature=related Why doesn’t the moon fall down? • It does. • http://www.youtube.com/watch?v=RsFf9gl6lL 8&feature=related What is a satellite? • Technically, anything that is in orbit around Earth is technically a satellite, but the term "satellite" is typically used to describe a useful object placed in orbit purposely to perform some specific mission or task. We commonly hear about weather satellites, communication satellites and scientific satellites. Whose Satellite Was the First to Orbit Earth? • The Soviet Sputnik satellite was the first to orbit Earth, launched on October 4, 1957. • It weighed 184 pounds and was 23” in diameter. What happened to it? • After 92 days, gravity took over and Sputnik burned in Earth's atmosphere. Thirty days after the Sputnik launch, the dog Laika orbited in a half-ton Sputnik satellite with an air supply for the dog. It burned in the atmosphere in April 1958. Progress since then… • ISS Video • http://www.theblaze.com/stories/one-of-thebest-time-lapsed-videos-of-earth-from-spaceyet/ How Do You Put Something In Orbit? • If the Earth were flat like some people used to believe, no matter how fast you threw something out horizontally, it would hit the ground. The faster you threw it, the farther away along the ground it would hit. Plus - all of the balls will hit the ground at the same time. But the Earth is not flat! • As something falls "straight" toward the center of the Earth, it has to curve around with the Earth. • Throw an object fast enough that its “fall” matches the curvature of the Earth. • The Earth’s curvature is such that it “drops” about 5 meters every 8,000 m. • So what speed would it have to go to orbit the Earth at the surface? 8 km/s! The only force on a satellite is the force of gravity. That’s the force pulling it in to the center. Launch • Space shuttle Atlantis final launch: NASA video of last take-off • http://www.youtube.com/watch?v=2EFuLap5 Pgg • Mars exploration rover Let’s use equations to check how fast an object near the Earth’s surface is orbiting? • Fg = Fc • Fg = mv2 / r • m g = m v2 / r • g = v2 / r • v2 = g r • If r = 6.38 x 106 m, what is v? The orbital velocity is • v2 = ( 9.8 m/s ) ( 6.38 x 106 m ) = 6.25 x 107 (m/s)2 • v = 7.9 x 103 m/s • That’s 17 000 mi/h! What about the period? How long does it take to make one orbit? • v=d/T • T=d/v • T = 2π r / v • T = 2 ( 3.14 ) ( 6.38 x 106 m ) / ( 7.9 x 103 m/s ) • T = 5074 s [ 1 min/60 s ] = 84 min The Space Shuttle is an excellent example of a satellite in a low-Earth orbit. • The Space Shuttle orbits about 100 km to 200 km above Earth's surface. Earth's radius is about 6 000 km so this is an increase of only about 2% or 3%. That means the force of gravity is only about 4% to 6% less than at Earth's surface. Low Earth Orbit • Imagine yourself in an elevator when the cable breaks! The only force on you is gravity! The Physical Aspect • Bodily fluids are redistributed, with less in the lower extremities, and more in the upper body. Without the pulls of normal gravity, blood doesn't flow downhill, but pools in the extremities including the face, hands and feet, causing a puffy appearance. And without that downward pressure, height increases. Body mass often decreases with a loss of muscular tissue from nitrogen depletion; the veins and arteries of the legs become weaker, anemia occurs, accompanied by a reduction in blood count. Astronauts report an overall feeling of weakness and loss of balance upon return to Earth, though recovery is nearly complete after a week. Types of Satellites • http://www.windows.ucar.edu/spaceweather/effects1.html Types of Orbits • Polar Orbits This orbit allows the satellite to observe the entire Earth's surface as it rotates beneath it. Most desired orbits are between 700 and 800 km altitude with orbit periods between 98 and 102 minutes. Uses of Polar Orbiting Satellites • This orbit provides global daily coverage of the Earth with higher resolution than geostationary orbit. Even though satellites do not pass directly over the poles they come close enough that their instruments can scan over the polar region, providing truly global coverage. • Geosynchronous Satellites Orbit around the Earth at the same speed that the Earth rotates. • What’s its period? • 24 hours • If they stay over the same place, they are called geostationary. Where do they orbit? • Over the equator. Because of this, it appears to remain over a fixed point on the Earth's surface. Uses of Geosynchronous Satellites • Perfect for communications satellites because always in view of the ground station providing continuous TV and telecommunications services to customers. Also ideal for making uninterrupted observations of the weather or environmental conditions in a given area. Definitions: • Geosynchronous- same period as Earth • Geostationary – orbits over the same location on Earth • Asynchronous – not once a day, like the space station. What is the orbital radius of a geosynchronous satellite? • Fg = Fc • Fg = mv2 / r • GMEMS/r2 = MS v2 / r • GME/r2 = (2πr/T)2 / r • GME/r2 = (2πr)2 / T2r • GME/r2 = 4π2r2 / T2r • GME/r2 = 4π2r2 / T2r • Move r2 to top • GME = 4π2r2r2 / T2r • GME = 4π2r3 / T2 • Solving for r: • r3 = GME T2 / 4π2 • This means that for a fixed period – like 24 hr – there is only ONE radius that will work!! • r3= (6.67 x 10-11)(6 x 1024kg)(86,400s)2 /4 π2 • r3 = 7.54 x 1022 m3 • r = 4.2 x 107 m • If we subtract off the radius of the Earth, which is 6.38 x 106 m (or 6380 km), then • The orbital radius is 36,000 km above earth, or 6 rE (6 times Earth’s radius). What’s the velocity of a geosynchronous satellite? • Fg = Fc • Fg = mv2 / r • GMEMS/r2 = MS v2 / r • GME/r2 = v2 / r • GME/r = v2 • v= square root of (GME/r) • V = 3070 m/s So all the geosynchronous satellites orbit at this radius! Geosynchronous orbits are 1/10 the distance to the moon! Space Junk at Tipping Point • http://www.youtube.com/watch?v=2gTkoFJ2yI Q&feature=fvsr • Debris – green dots • http://www.youtube.com/watch?v=L915JJMcu 4s What happens when satellites plunge back toward Earth? • This happened on Sept. 22, 2011. • Watch Out! NASA UARS satellite to hit Earth... Anywhere! • (Upper Atmosphere Research Satellite) • http://www.youtube.com/watch?v=vwnNTllrA dM • http://www.youtube.com/watch?v=GCd4Vw mNATU&feature=related Comparing velocity, radius and period: Radius r Period T Velocity v 6.38 x 106m 83 min. 8 km/s Geostationary 4.23 x 107m 24 hr. 3 km/s Moon 27.3 days 1 km/s Surface/ LEO 3.84 x 108m Does this make sense? • • • • • • • Doesn’t v = 2πr/T? Then doesn’t that mean that as r ↑, v ↑? But v depends on T, so to eliminate v: Fc = Fg⇒ mSv2/r = GmSmE/ r2⇒ v = √GmE/r v2 = GmE/r = 4π2r2/T2 r3/T2 = Gm/4π2= constant • r3 ∝ T2 • So as r increases, T increases. Summary - 2 ways to find velocity: • V = 2πr / T • V = √ (GME/r) (This means square root!) • Where r is the orbital radius, not the height above the surface. Problem Solving • What is the speed of a space shuttle in a circular orbit 1000km above Earth’s surface? • The mass of Earth is 6 x 1024 kg and the radius of Earth is 6.38 x 106 m. G = 6.67 x 10-11. Solution • • • • R = 7.38 x 106 m Fc = Fg V2 = GMe/R V = 7.35 x 103 m/s or 16,500 mph NASA GOES - P Mission Overview • http://www.youtube.com/watch?v=QpBSwwC PC94&feature=related • Cup of coffee • http://www.youtube.com/watch?v=pk7LcugO 3zg&feature=related • Going to the bathroom • http://www.youtube.com/watch?v=HUe2HcF UPSo&feature=related Space Junk Video • 4 min. • http://videos.howstuffworks.com/hsw/19197satellite-technology-orbit-and-orbital-debrisvideo.htm Real Time Satellite Tracking • Click and drag applet • http://www.n2yo.com/ Tracking ISS • Another ISS tracking site. • http://spaceflight.nasa.gov/realdata/tracking/ index.html Satellite Tracking • Position of ISS and other satellites • http://science.nasa.gov/Realtime/jtrack/3d/JT rack3d.html History of ISS • http://www.nasa.gov/worldbook/intspacestat ion_worldbook.html Attitudes of ISS • Adjusting the angle for solar panels. • http://spaceflight.nasa.gov/station/flash/iss_a ttitude.html Interactive Reference Guide • Videos of how the crew eats, sleeps and exercises. • http://www.nasa.gov/externalflash/ISSRG/ Upcoming Launches • http://www.nasa.gov/missions/highlights/sch edule.html NASA in motion • Link to NASA Drawing Video Cup of Joe • Link to Cup of Joe Video Atlantis leaves ISS • Link to Undocking Video Takeoff and Landing of Discovery • http://www.youtube.com/watch?v=5B9ff2bDb4 Apollo Guys – Co Ops http://www.youtube.com/watch?v=sItKDSf0xl8 • Link Apollo Guys (Apologize) Watching on the screen Saturn V lifts off the ground After many sims, Flight control has got it down You say that its not easy, but Astronauts are all moonbound and wait Were watching them on TV Walking on the lunar ground and say We did it Apollo Guys! How GPS Works •The dashed lines show the actual intersection point, and the gray bands indicate the area of uncertainty. The solid lines indicate where the GPS receiver "thinks" the spheres are located. Because of errors in the receiver's internal clock, these spheres do not intersect at one point. Three spheres are necessary to find position in two dimensions, four are needed in three dimensions. Problem Solving #1 • A satellite over Jupiter is placed 6 x 105m above surface, given mass of Jupiter, find v. • Mass of Jupiter = 2 x 1027 kg, • Radius of Jupiter = 71,492 kilometers • • • • • So r = radius of Jupiter + height over surface r = 7.2 x 107 m V2 = GMJ/r v2 = 1.76 x 109 m/s v = 4.195 x 104 m/s Problem Solving #2 • A satellite wishes to orbit the earth at a height of 100 km (approximately 60 miles) above the surface of the earth. Determine the speed, acceleration and orbital period of the satellite. (Given: Mearth = 5.98 x 1024 kg, Rearth = 6.37 x 106 m) • Speed = = 7.85 x 103m/s • Acceleration = a = 9.53 m/s2 • Orbital period = T = 5176 s = 1.44 hrs #3 • One of Saturn's moons is named Mimas. The mean orbital distance of Mimas is 1.87 x 108 m. The mean orbital period of Mimas is approximately 23 hours (8.28x104 s). Use this information to estimate a mass for the planet Saturn. • Using the T and R values given, the T2/ R3ratio is 1.05 x 10-15. This ratio is equal to 4*pi2/ G * Mcentral. • Mass of Saturn can be found to be 5.64 x 1026kg. #4 • Satellites circling unknown planet. Sat1 has v1 = 1.7 x 104 m/s, and r = 5.25 x 106 m. Sat2 has r = 8.6 x 106 m. Find v for Sat2. • • • • V2 = GMPLANET/r So MPLANETG = constant = v2r V12r1 = v22r2 V2 = 1.33 x 104 m/s Which of following statements is accurate regarding man-made satellites? • A. It is possible to have a satellite traveling at either a high speed or at a low speed in a given circular orbit. • B. Only circular orbits (and not elliptical ones) are possible for artificial satellites. • C. A satellite in a large diameter circular orbit will always have a longer period of revolution about the earth than will a satellite in a smaller circular orbit. • D. The velocity required to keep a satellite in a given orbit depends on the mass of the satellite. Next Genertion Car Navigation • http://my.clarion.com/en-ca/html/products Practice Questions Giancoli • http://cwx.prenhall.com/giancoli/chapter5/m ultiple1/deluxe-content.html Satellites orbiting earth • http://www.youtube.com/watch?v=gEOAp6k7 2gc Launching Satellites • http://www.youtube.com/watch?v=W4PE8LK 2Ga0