Scientific American May 2020 pp74 “Satellite Surge”. “Low-orbit instruments are taking over the skies” by Mark Fischetti. Source of information JOHNATHAN McDOWELL’S SPACE REPORT, 2019 https://PLANET4589.ORG
Since the 2010s most satellites have been launched into low-earth orbit that being less than 1231 miles above earth. Most notable have been the Tiny Cube Satellites weighing just 3 pounds and having the mission of surveillance of the planet on a daily basis. They have enough resolution to know how many people are moving around in Wuhan China and even how many new cars hit the street. SpaceX’s Starlink satellites with the mission to enable global broad band internet now number 240 with 12,000 authorized (that’s six times the current number of satellites aloft), weighing in at 572 pounds.
In the 1980s and 1990s most satellites were launch into geosynchronous orbit at more than 22,000 miles above earth. Most of these vehicles weigh in at one to eleven tons. Of the 2244 satellites as of July 2019; 22% are Geosynchronus, 9.4% are Medium Earth (1,231-22,026 miles), 29% are Upper Low Earth (338-1230 miles), 39% are Lower Low Earth (<338 miles). Satellites below 338 suffer more atmospheric friction and if not corrected will drag down to earth in a decade while those higher could come down in centuries.
Notable Vehicles
Hubble Space Telescope Launched April 24, 1990 from Space Shuttle Discovery, 43.5 ft. long, maximum diameter 14 ft., 24,000 pounds, Low Earth Orbit at 340 miles, Orbits Earth 95 minutes, travels at 17,000 mph, 150 gigabits of data/week, energy from Sun by two 25-foot solar panels, generates 5,500 watts and uses 2,100 watts on average. (Source NASA.GOV)
International Space Station (spottthestation.nasa.gov). Launched November 20, 1998, 925,335 pounds, 239 ft. long, 358 ft. wide, pressurized to 1 atm 21% oxygen and 79% nitrogen, orbits at 253.5 miles (205-255), Orbits earth in 92.68 minutes, travels at 17,100 mph, orbital decay 6,500 ft./month or 14.8 miles per year. Orbital boosting is done by engines taking two-three orbits using 7.5 tons of chemical fuel at an annual cost of $210M. It is the largest satellite in low Earth orbit, regularly visible to the naked eye from Earth’s surface. Purpose; laboratory, observatory, factory and a low Earth staging base for possible future missions to the Moon, Mars and asteroids. As of 2010, the ISS also serves commercial, diplomatic and educational purposes. (Source Wikipedia.org)
Cube Satellites or CubeSat or nanosatellites a class of research spacecraft. Standard dimensions 10cmX10cmX10cm=1 unit they can be 1U, 2U, 3U or 6U with each U less than 3 lbs. and four inches long with a volume of 1 quart. Research includes remote sensing and communication but now mostly interplanetary. Low Earth Orbit. Low weight, easy to launch but last weeks, months or years before ceasing operations and as in low Earth orbit fall back to Earth. Use many off-the-shelf components. (Source NASA.gov and Space.com)
SpaceX Starlink. 338 miles above Earth, 572 pounds and the size of a table. Launched from SpaceX’s Falcon 9 rocket. First Launch February 22, 2018 with 417 active currently. Equipped with Ku and Ka band phased array antennas will deliver internet speeds of 1 gigabit per second. Can sometime be seen in the dusk and dawn skies and reportedly sometimes as a “trail of lights”.