My first exposure to satellites was in High School in October 1957 when the sound from Sputnik 1 (Wiki) was played overt he school loudspeakers. In late 1960 I applied for a summer job at Lockheed and it turns out it was for a photograph interpreter for spy satellite images, but when I told them I was going to college after the summer I didn't get that job.
While waiting for the fire fall at Yosemite National Park (Wiki) I saw what at first appeared to be a bright object very high going very fast, then I realized it was a satellite. When I pointed it out we all looked up to see a new thing. (See astronomy satellite watching)
When I was a microwave engineer working on Tunnel Diode Amplifiers where they had some very desirable attributes for use in space. The power consumption was very low and since the Tunnel Diodes (Wiki) are highly doped they are not effected be radiation. Because of that TRW (Wiki) ended up buying Aertech and we became a subsidiary of TRW called TRW Microwave.
Analysis of Sputnik led to the U.S. development of Transit (Wiki, Navy) which in turn lead to GPS (Wiki). GPS satellites have on board the Nuclear Detonation Detection System (Wiki:NDDS, NUDET) and that was a key element in the initial funding for the GPS system. (OSTI.gov: The GPS Burst Detector W-Sensor)
While a "satellite" is commonly thought to be a body that's orbiting the Earth, technically it's a body orbiting another body. So the Moon is an Earth satellite and the Earth is a satellite of the Sun.
In order to see a satellite with your eyes it's necessary for the satellite to be illuminated by the Sun and for the sky to be dark. When the satellite is in the Earth's shadow you can not see it. So the best time to see satellites is just after sunset or just before sunrise.
When you do see a satellite it will appear as a point of light. Even with powerful binoculars it still will be a point of light. In order to see a satellite that has any shape you been a high power telescope on a mount that can track the fast movement of the satellite, something that's very difficult to do.
Some satellites have flat surfaces that can act as mirrors, such as Solar Panels, and these can cause very bright flashes (Wiki: Satellite flare).
There's a patent for making a satellite invisible. It's done by having an inflatable balloon shaped like an ice cream cone with the pointed end aimed at the Earth. When an Earth bound observer looks in the direction of the satellite the gold plating on the balloon acts as a mirror for a broad spectrum of IR, light and microwave frequencies so all the observer sees is another part of space.
The cost to put something in orbit is very high. The higher the orbit the higher the cost. Because of this it's extremely important that whatever goes into orbit work and keep working. Some of the programs had a specified working lifetime plus a large bonus for every year that it continued to work after the specified life. This is a big incentive for the supplier to do their best in terms of reliability.
Most people, myself included when I first started working on satellite parts, think that it's a high technology business. But that's not the case. Pretty much all the technology used in satellites is old and that's because it takes years of testing to prove the reliability of a part. Reliability is spelled out in MIL-HDBK-217 (Wiki: MTBF).
When the Mean Time Between Failures (MTBF) is calculated for a complete system, say a military aircraft and that time is compared to the time required for a specific mission, if the mission time is greater than the MTBF they you can expect the mission to fail because there will be a failure of the aircraft. The more complex something is the more likely something will fail. I read that the Toyota Hilux (Wiki) is so reliable because the factory minimized the number of items on the Bill Of Materials (Wiki: BOM). This is one of the ways to add reliability to any product.
Redundancy (Wiki) is another way to add reliability. Note redundant parts do not increase the BOM line count.
Elimination of Single Point Failures (Wiki) is a system design way of making a product more reliable.
Rolls Royce entered and won many car races, not because they had a fast car, but rather because their cars finished races because they were reliable. Chevrolet torture tested the 265/283/327 cubic inch small block engine (Wiki) and kept improving the design of any part that failed. This resulted in a very reliable engine that went on to win many races.
I'd like to see high value products, like cars, to include MTBF on the sticker along with the gas mileage. This way consumers would have a way to trade off the higher initial cost of the more reliable products against the lower cost of products that will fail sooner.
Ideally all the parts in a car (or any product) would have the same MTBF. That's to say if a part has a much higher MTBF than the rest of the car it's over designed and a lower cost version can be made. Spending more money for a part with an MTBF higher than the final product is wasting money. For products made in high volumes there's money in the cost savings to pay an engineer to figure out how to lower the MTBF.
I knew an engineer Keith B. who worked for RCA. His job was to make the MTBF of the color picture tube be 366 days, i.e. one year plus one day. That way the dealer got paid by the customer to replace the picture tube and RCA got paid for the replacement tube.
AFAICR Gump's department store (Wiki) has a saying "The best costs no more". I'd rather spend more for something that will last, but know people who would rather spend as little as possible and keep buying another when the first one fails. Different strokes for different folks.
Orbits can be described using Two Line Element sets (Wiki). These are based on Newtonian mechanics that take into account the gravity of the Earth, Moon and Sun as well as atmospheric drag. They are not adequate to describe the path a satellite takes when it falls back to Earth or to determine the quantum mechanical effects of things like light or radio waves pushing the satellite.
Satellites are characterized by the height of their orbits.
Low Earth Orbiting (Wiki: LEO)
Orbital period less than 128 minutes (11.25 orbits per day) or less than 1,200 miles altitude.
Medium Earth Orbiting (Wiki: MEO)
Between 1,243 and 22,236 miles above sea level.
Geosynchronous orbit (Wiki)
High Earth Orbiting (Wiki: HEO)
Higher than 22,236 miles above sea level.
Is directly related to orbit. Short periods correspond to low orbits and longer periods correspond to higher orbits. A geosynchronous orbit has a period of 24 Hours. The GPS satellites have a period very near 12 sidereal hours (Wiki) which means each satellite has a repeatable ground track.
The military is very interested in knowing about all the satellites in orbit (Wiki: Space Surveillance). There are a number of ways to discover a new satellite and to determine is orbital parameters, Optical and RADAR are the key methods.
An early optical system was the Baker-Nunn camera (Wiki). This telescope has a very low f/number (f/0.75) which translates to high resolution which is needed to separate the faint point of light of a satellite from the surrounding star field.
The AN/FPS-133 was a bi-static RADAR system (Wiki, China Lake/Space Fence) operating at 216 MHz. In 2013 it was shut down and replaced by a new system that operates in S-band. I'm guessing that the technology has progressed in being able to generate more power in S-band so that it's practical to use a shorter wavelength where the antenna can be more directive for a given size thus improving the overall operation of the system.
The lower the orbit the more atmospheric drag there is and so the sooner the satellite will slow and fall back to Earth. The email server "SeeSat" has a group of people who came up with a computational procedure to make predictions for satellite reentry. This happened around January 2014. The idea was to let people know when and where to look in order to observe a reentry event.
But it was realized that this analysis could also be applied to past reentry events and this was done for large satellites, like the shell of booster rockets and the results have a high correlation with mass UFO sightings (New UFO Info Jan 2014).
An early example of telemetry is the Radiosonde (Wiki) where weather instruments lofted by a balloon transmit back pressure (altitude), temperature, humidity &Etc. When rockets were being developed the Inter-Range Instrumentation Group (Wiki:IRIG) came up with standards to lower the cost of telemetry. The data format of time stations like WWV are in IRIG format.
By having real time data during a test when something goes wrong it's possible to replay the tapes (Wiki) and figure out what when wrong.
Most satellites today have telemetry to let the people controlling the satellite that status of key parameters like battery state of charge, temperatures of key components, the status of things that can change such as the routing of signals and power, &Etc.
It turns out that when I first went to work at Aertech one of the first projects I worked on were the unified S-band (Wiki, YouTube) ground station Tunnel Diode Amplifiers. Because of the low noise figure (Wiki) of the TD amplifiers compared to the mixer the signal to noise ratio (Wiki) was improved allowing the ground stations to clearly hear satellites that were further away or satellites that had a problem and the telemetry signal was weaker than usual.
Rockets data back to the 13th century (Wiki). During W.W. II there as a lot of development of rockets, like the Bazooka, and Missiles (Wiki). Early in the history of rocketry there were famous people who said putting something into Earth orbit would be impossible because the weight of the rocket needed to be a huge multiplier on the weight of the satellite. In the U.S. that was the end of the story, but in the USSR they just said OK we need to build a huge rocket. It was a wake-up moment for the world when Sputnik (Wiki) went into orbit. That's because theoretically it meant that the USSR had the capability to send a weapon anywhere in the world.It turns out that the rockets used to launch satellites are the same rockets that might launch weapons (Ref 1, Ref 2, Ref 3). The first generation strategic rocket based weapon systems were termed ICBMs (Wiki). As the Wiki page says "Early ICBMs had limited precision, which made them suitable for use only against the largest targets, such as cities."
Ref 1. Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance, MacKenzie, 1993 - makes claims of percision based on the quality improvements of gyroscopes. Note that none of the non submarine launched ICBMs were ever tested. The accuracy of dumb bombs is very poor, see Norden Bombsight.
Ref 2.Meeting the Challenge: The Hexagon KH-9 Reconnaissance Satellite, Phil Pressel, 2013 -
Ref 3. Minuteman: A Technical History of the Missile thatDefined American Nuclear Warfare, David Stumpf, 2020
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