Synchronous Earth Orbits
This graphic from Boeing illustrates about 300 communication satellites were in geosynchronous orbit in 2012. They include Echostar and DirectTV, as well as those for Canada, Central and South America, Europe, Asia, Africa, and Australia. The ones colored blue are Boeing satellites. This graphic does not include the GOES weather satellites. They are parked in the same orbit as these shown. Click to enlarge for much more detail.
The detailed view shows the satellites spaced apart by small angular amounts directly above the equator. Over densely populated regions, where there are more satellites in orbit, they are 0.5˚ apart in the sky, the same as the width of a full moon. In less populated regions, as over the Pacific, satellites are 1˚, 2˚, up to 3˚ apart. All satellites are to remain in their assigned location and not drift east or west into the zone occupied by a neighboring satellite. Low-power rocket thrusters work periodically to keep them on-station.
Click enlarges for detail in a new tab.
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Discussion in a previous post centered on getting to space and into an orbit near Earth. This post is about how spacecraft return from orbit. Some returns are under control and some are not.
Launch to orbit requires giving a spacecraft a large amount of kinetic energy of motion (KE) and a large amount of gravitational energy (PE) due to its altitude. The large amount of work done to gain those energies comes from the potential energy released by an engine(s) as fuel burns. Once in orbit with engine(s) off, the total of those two energies (KE+PE) stays constant except for the small decrease due to the small atmospheric drag at high altitudes. If the orbit is a circle the two energy quantities are unchanging.
If the orbit is an eccentric ellipse, the quantities do change but not their total. The next graphic shows an eccentric orbit of an Earth satellite. When it passes closest to Earth (perigee), the KE is at its maximum value and the PE is at its minimum. Font size was changed to illustrate their inequality. When at its farthest point in orbit (apogee), it is going slowest with minimum KE and is at its highest altitude with maximum PE.
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Take a time-out from the news of the day or your busy routine. Tour some of the interesting features of our Moon as presented by the NASA Goddard Space Flight Center/David Ladd. Best viewed in HD by using the gear button at the bottom right of the video window.
Earth has been moving closer to Mars this spring as we orbit the Sun. We reach inferior conjunction, our closest to the planet, in late July 2018. Mars will appear larger in telescope views until then. No, it will not appear as large as a full moon contrary to an internet meme that has gone around for years.
Saturn is in the distant backround when viewed early in the mornings. Because Mars is closer to the Sun than Saturn, it passed by the slower moving Saturn. This short animation illustrates the passage. Watch Saturn slowly move across the frame. Also, watch for the Moon to pass by at the end of the animation. That happened on 7 April 2018.
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The concepts are simple to place a satellite or a manned space capsule into orbit near the Earth. But, they are very difficult to achieve.
- Engines must exert a lot more upward force than the downward force of the weight of the fueled rocket.
- After lift-off, gradually point the rocket more horizontally as it moves faster.
- Jettison the empty 1st stage. The 2nd stage engine(s) continues to speed up the payload horizontally.
- Shut down the engine(s) to allow the payload to coast in circular orbit when at altitude of about 120 miles (~200 km) and speed of about 17,500 mph (~ 28,200 kph).
The orbit drawn here to scale in yellow allows the spacecraft to coast for some time above most of the atmosphere. But it will not coast forever. The thin atmosphere will gradually bring it down.
Earth image from NASA
The U.S. started launching rockets from Cape Canaveral Florida in 1950. The European Space Agency launches from Guiana Space Centre northwest of Kourou in French Guiana. France established that space port in 1964. Each site has open water to the east avoiding the danger to populated areas. Each site uses the speed boost from the eastward rotation of the Earth to assist launch speeds. Guiana is near the equator and moves east about 1000 mph. Cape Canaveral moves east over 900 mph. With the better technologies today, rockets can be launched to orbit from about anywhere and in non-east directions such as for polar orbits.
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The Twins Study
How does an extended mission in space lasting as long as a year affect the human body? Answers to that question are being investigated by ten research teams from around the country. They used astronaut twins Mike Kelly and Scott Kelly as subjects. Scott spent 340 days aboard the Space Station from 27 March 2015 to 1 March 2016. Mike remained on Earth. Each was tested in a variety of ways by the research teams in order to compare results of long duration space flight.
Scott Kelly (left) and Mike Kelly (right) | NASA
Scott Kelly wrote the book Endurance about his experience. It is an excellent account of the lives of Mark and Scott, how they became astronauts, and behind the scenes events in the space program. My previous posts about this Twins Study mission can be found here and here.
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