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Topic Last Updated on 12-07-2024
Article about: Satellites.
Braking in Orbit
Let’s start with what’s most important — celestial mechanics. Star Wars and science fiction have taught us that you can do as you please in space — brake, accelerate, or even hover over any spot on a planet. Unfortunately, that’s far from reality. To enter Earth’s orbit, the orbital velocity required is 4.91 mi/s. Otherwise, a rocket with a payload will immediately start to fall back when the engines are turned off. You can imagine it like this — a satellite is like a stone thrown by a giant at great speed. This stone will fall to the Earth every time, as a stone should.
A spacecraft can “hover” over one point of the Earth in one case only — if it is in a geostationary orbit. There’s only one problem: geostationary orbit is at an altitude of 22,236 mi above sea level.
Geostationary orbit
Satellites in geostationary orbit are in the equatorial plane of the Earth and revolve around the center of the planet at the same speed as the Earth’s surface around its axis. This kind of satellite will always be located at one point in the sky for a ground observer. Satellites transmitting the signal of cable television work in this orbit — there’s no need to move the antenna.
Twenty-two thousand mi is very far, and it’s impossible to discern small details on Earth from such a distance. But what if you could reduce it? A satellite can be placed in a low Earth orbit — from 62 to 250 mi altitude (it will not go lower: there is a strong atmospheric effect, and the satellite will quickly lose altitude and fall). Here it will be as close to the Earth as possible to observe an object, but it cannot hang around over one point forever. A spacecraft can fly over the desired point for a few minutes and then must fly further before returning to this position after some time. Shooting a video will not work in this mode, so spy satellites operate with photographs only.
Low Earth orbit
Space stations and most of the Earth’s artificial satellites may be found in low Earth orbit. They rotate in different planes over the equator, so they cannot stay too long over any one point on Earth. For example, the trajectory of the International Space Station looks like a sine wave to a ground-based observer.
Can other countries see a satellite at this altitude? Of course. But since space is shared, you can’t just destroy a device simply because you don’t like it, even if it may be watching you.
As you can see, optical spy satellites that closely observe one desired object don’t exist. For constant observation, you’d need a large group of spacecraft that continuously replace one another.
What are near-Earth orbits?
The most popular orbits around the Earth are geostationary and low Earth orbits. These are used for a variety of spacecraft. There are many other kinds, such as polar, Sun-synchronous, circular, and Molniya (meaning “lightning” in Russian) orbits.
Polar orbit
Sun-synchronous orbit
Molniya orbit
Satellites | A Few Words on Resolution
So, if a spy satellite were to take a snapshot of your schoolyard, what level of detail could it capture? For the greatest detail, it would have to have been an orbiting satellite with the largest possible optical system mirror, in order to maximize the potential to zoom in on objects. This system is boasted by American spy satellites of the Keyhole series.
Of all spacecraft, the Keyhole satellites looked most like the Hubble Space Telescope — their mirrors, like in a space observatory, were 6.6–9.8 ft in diameter. If you think about it, they sort of worked as telescopes, but instead of following the stars, they did the opposite. Using the highest possible magnification, the satellites photographed secret military and civilian objects around the world.
Until the end of the 1980s, most of the spy satellites captured images on special film, which would then be placed into a return capsule headed for Earth. The rest of the journey was like with any crewed spacecraft: braking in the dense layers of the atmosphere, launching parachutes, landing, and throwing a special beacon overboard — a device sending the message “Your photos are ready — come and get them,” on a certain wave. Often, the capsule was disposed of at sea, away from prying eyes. Then, a special military vessel would find it via a beacon, and the film would be developed. In this way, the satellite transformed into a terribly expensive, secret, and high-tech piece of space debris.
Satellites | How the Images Came to Earth
From 1959–1972, the first series of American spy satellites were launched into orbit. After 12 unsuccessful attempts, the satellites eventually shot a total of 2.1 million feet of film in 39,000 canisters and obtained images of previously unknown Soviet airfields and missile locations.
1. The film is collected in one of two sealed, waterproof recovery capsules.
2. After each capsule is detached, they slow down when descending into the Earth’s atmosphere with the help of rockets.
3. A rescue plane detects a capsule using a radio signal and picks it up with a nylon rope.
Today, things are simpler — you can take pictures on a digital camera and transfer them using satellite data transmission. The first spy satellites to use an optoelectronic digital camera were the American Keyhole-11 (KH-11) satellites. A total of 16 such satellites were launched.
The first of the series went into orbit in 1976, and the latest were launched in 2013. These satellites have a complex elliptical orbit — they approach the Earth at a proximity of 168 mi in order to shoot the desired point at a minimal distance.
The Evolution of American Intelligence Systems
But if these satellites are so secret, then how do we know about them? Well, in 1978, a young CIA agent, William Kampiles, sold technical documentation for a secret satellite to the USSR, and he sold it quite cheaply — for $3,000 — not exactly a cosmic rate even in those days.
The intrigue doesn’t stop here. In 1984, Samuel Loring Morison, an analyst at the National Maritime Intelligence Center, sold three secret images from the KH-11 satellite to the reference book Jane’s Fighting Ships.
The publication had asked for beautiful illustrations for the book, and the analyst sold the latest images received from a secret satellite without so much as blinking an eye. The fantastic photos went to print, and specialists studied their resolution carefully.
The most recent leak from the Keyhole KH-11 satellite happened recently, when it was revealed by the US President Donald Trump, apparently to show off and get more likes. Without permission from the military, he tweeted a photograph of an Iranian spaceport after a rocket exploded on the launchpad. The photos confirm that the resolution of modern spy satellites is about 4–6 in per pixel.
Snapshot of an Iranian spaceport after a rocket explosion
Interestingly, one NASA study has confirmed the theoretical possibility of such a resolution. The minimum point that can be seen from orbit in ideal weather has a diameter of 4.7 in. Any smaller simply would not work, as the atmosphere and the laws of physics do not allow it. This, by the way, is in the presence of ideal conditions just under the satellite. If it moves even a little, the atmospheric layer can enlarge, and the image quality will suffer dramatically. Space satellites always have the same image quality. Due to atmospheric distortion, no matter how much the optical mirror is enlarged, the resolution will not improve.
EARTH’S SATELLITES
Is it legal to use spy satellites? The answer is simple — yes. Space is, well, a shared space, and any country, having informed the others, can send off almost any spacecraft (well, except for those with a powerful nuclear reactor or carrying nuclear weapons). And the fact that this spacecraft can photograph the territory of another country is well established and not prohibited in any way. Therefore, states can monitor others’ spacecraft and track their position in orbit — but they can’t knock them down, no matter how they feel about it. An attack on the spacecraft of another country will be regarded as justification for a conventional ground war.
Civil
Used for early warning, surveillance, reconnaissance, and technology development and belongs to the missile defense authorities
Civil
Used in university programs for research and technology development, for the study of space physics, and for amateur radio
Civil
Used for television broadcasts, Earth observation (Google Maps), SiriusXM satellite radio, and satellite phones, belongs to various companies
Civil
Owned by organizations like NASA and the European Space Agency, can be used for remote sensing, meteorology, space physics, astrophysics
Satellites | I See You, but Poorly
So, here’s the question: is 4–8 in per pixel a little or a lot? For example, a GMC Hummer will compose a dot of 30 × 10 pixels, and a Ford Focus will occupy a space of 20 × 10 pixels. That is, you’ll see the car, recognize that it is a car, but determining the make and model of the car is impossible. An image specialist may guess at the type of car body and suggest potential makes, but nothing more. Most likely, you’ll just get a general description — “a white passenger car.”
How about a person, can they be spotted by a satellite? The satellite takes photographs from above, so mostly heads, shoulders, shadows, or distorted silhouettes fall into frame. It’s certainly possible to make out figures, but you won’t be able to see who it might be or if that really is a person.
