Orbits explained: It’s hard to get into space — but nifty once you’re there


As Richard Branson and Jeff Bezos quip about where space actually begins, let’s think about Isaac Newton and how we go about sending things moving around Earth.

SpaceX’s Crew Dragon Resilience swings sideways above Earth as it approaches the International Space Station first in 2020.

Space is closer than you think – about 62 miles up, San Francisco is only a little farther from you than San Jose. Heck, you can go up to half the space in a balloon.

The hardest part about space, it turns out, isn’t that much to live in. This is where the idea of ​​circumambulation comes from. Once you’ve done the hard work of putting a spacecraft into orbit, you can get years of use out of it as it moves more or less smoothly around the planet on its own invisible track. is.

Orbits are “roadways in space,” said Ajmal Yusuf, a professor at Drexel University who studies aerospace vehicles. “You put a vehicle in space, and it stays there.”

Scientists figured out how orbits work centuries before human spacecraft were launched, but there’s a lot more to learn about these looping tracks above Earth for the rest of us—and good reason to learn it. . With new government and private sector projects, space has become even more important than in the 1960s at the beginning of the space age.

Among other efforts, several companies are filling the skies with Internet-beaming satellites, new SpaceX rockets starting to send astronauts to the International Space Station, the US military establishing its new Space Force, and NASA Planning missions to the Moon and Mars.

Then there’s space tourists, let’s start with the crop of Billionaires and their rocket companies: Richard Branson and Virgin Galactic, Jeff Bezos and Blue Origin, and the even more ambitious Elon Musk and SpaceX. Branson walked to the edge of space on Sunday, while Bezos will move a little further on July 20, and Blue Origin has quipped over whether Branson actually flew high enough. Musk hopes to send a quartet of people around Earth by the end of this year – and to be freed from Earth orbit to walk around the Moon in 2023.

“It’s the new space age — and the new space race,” said Ben Lam, chief executive officer of software company Hypergiant. His company is working with the US Air Force on its Chameleon spacecraft, which is designed to be more adaptable, more independent and smarter than traditional spacecraft.

Let’s start with Isaac Newton

If you want to understand orbits, a great place to start is Isaac Newton, whose research paved the way for modern science with explanations of motion, light, and gravity. Newton’s treatise on the System of the World from 1685 elegantly explained how orbits work with a thought experiment that did not require any calculations.

This idea, sometimes called Newton’s cannonball, is as follows. Imagine shooting a stone horizontally from a high mountain, gradually increasing the speed at which it is shot.

Newton said, “The velocity with which it is launched is as far as it goes before it falls to the earth.” With increasing horizontal velocity, “it will describe an arc of 1, 2, 5, 10, 100, 1,000 miles before coming to Earth, until exceeding Earth’s boundary, without touching it.” Enough must pass.”

In other words, the stone will fall at the same rate as the Earth’s surface decreases due to the Earth’s curvature. In Newton’s experiment, a stone fired at the right speed would go round the earth and sink back into the mountain.

In 1685, Isaac Newton published a thought experiment showing how a projectile, shot slowly with high speed from the top of a mountain, would eventually orbit the Earth. Atmospheric drag makes this impossible on the real Earth, a point Newton acknowledged.

In the real world, friction with Earth’s atmosphere would slow down the projectile long before it would circle the Earth and return to the mountain. But a few miles up in space, where air is scarce, that projectile will continue to orbit and there will be almost nothing to stop it.

fast traveling sideways, not up

This brings us to the main difficulty of putting the satellite into orbit: achieving sufficient horizontal velocity.

Whether you’re looking at giant Saturn V rockets taking humans to the Moon or thin candlesticks launching small spacecraft, the rockets you see generate an enormous amount of thrust. The vast majority of rocket fuel, however, propels the spacecraft afterward, not up. When you watch a rocket launch, the tilt toward the horizontal begins almost immediately when the craft leaves the launchpad.

How fast are those spacecraft going? The first artificial satellite, Sputnik-1 that Russia launched in 1957, orbits the Earth’s surface at about 18,000 miles per hour, or about 8 kilometers per second. The International Space Station is whirring at 7.7 km/h, or about 17,000 mph.

In comparison, the supersonic Concorde passenger jet only accelerated at about 1,500 mph.

SpaceX needs a lot more power to take NASA astronauts to the ISS than it has for Blue Origin, the rocketry startup funded by Amazon chief executive Jeff Bezos, as its New Shepard rocket enters orbit. without having to pop up and down.

The fewer orbits a spacecraft makes, the faster it goes. This is why the Hubble Space Telescope, about 340 miles (547 km) above, orbits Earth every 95 minutes, but the Global Positioning System satellite for navigation services, 12,550 miles (20,200 km) above, orbits the Earth every 95 minutes. takes hours.

Getting Launch Boost from Earth

The rotation of the Earth gives the rocket a healthy flow to the east, and the closer a launch is to the equator, the larger it is.

This is why US launch sites are located towards the southern parts of the country and why European spacecraft are sometimes launched from the Guiana Space Center in South America only 5 degrees latitude away from the equator. NASA considered launching a Moon mission from an equatorial site – although the fling factor was secondary to considerations of fuel matching the Moon’s orbit.

When SpaceX launches a rocket, it reserves some fuel to return the rocket’s first stage to Earth when it’s done putting the spacecraft into orbit. For launch from Cape Canaveral in Florida, the rocket stage lands on a drone ship floating over the Atlantic hundreds of miles to the east.

Low Earth Orbit: Join the Party

Space begins about 62 miles (100 km) above us, although the range is somewhat arbitrary. (NASA and the Federal Aviation Administration put the limit for anyone reaching that far at just 50 miles.) Slightly more than that, reaching about 1,243 miles (2,000 km) above Earth’s surface, the most popular part. is. space, called Low Earth Orbit or LEO.

This is where you’ll find the International Space Station, along with satellites for weather forecasting, espionage, television, imaging, and increasingly satellite-based broadband. Every human who has been in space, except a few who made it around the Moon during NASA’s Apollo missions, has embraced Earth in LEO.

The SpaceX Starlink service, which is now in beta testing, has close to 1,000 satellites in its constellation, with more than 2,200 on the way. Amazon’s Project Kuiper plans to have 3,200 satellites. OneWeb envisioned 48,000 satellites, though its near-term plan ran into bankruptcy trouble this year. Companies based in Canada, Russia and China plan more.

Hawkeye 360 ​​chief executive John Serafini said that LEO is easier to access than ever before, and it has ushered in “a golden age of LEO innovation,” with the company helping government and military customers address topics such as smugglers or lost boats. Helps to track radio signal to locate.

NASA's Space Shuttle Endeavor orbits near the International Space Station in 2008.  The ISS orbits at an altitude of just over 200 miles above Earth's surface, roughly the distance from New York to Boston.

NASA’s Space Shuttle Endeavor orbits near the International Space Station in 2008. The ISS orbits at an altitude of just over 200 miles above Earth’s surface, roughly the distance from New York to Boston.

“10 years ago it would have been nearly impossible to build a constellation of satellites for Hawkeye 360,” but SpaceX’s reusable rockets and other improvements have reduced launch costs. “There are more opportunities to catch a ride in the classroom than ever before,” he said.

Because LEO is relatively accessible, however, it is also where most of Earth’s space junk orbits. Friction along the upper edges of the atmosphere moves a fraction of the detritus out of the way. Satellites must maneuver themselves to maintain proper orbit, often with gentle but easily solar-powered ion thrusters, even with atmospheric friction.

move to a higher level in geosynchronous orbit

Medium Earth orbit, which reaches about 22,233 miles (35,780 km) above Earth, is a desert compared to LEO. But the region has some notable inhabitants, particularly in navigation satellite constellations.

The larger Sat-Neo constellations, each containing about 24 satellites, are the United States’ GPS, Europe’s Galileo, Russia’s GLONASS, and China’s Beidou. GPS is handy for smartphone navigation, but military use is also a top justification for the expense of launching and maintaining these satellites.

Just above the upper limit of the MEO is the geosynchronous orbit, a sweet spot where the orbital period matches the Earth’s rotation. A satellite in geosynchronous orbit above the equator, called geostationary orbit, appears exactly in the sky as seen from Earth.

This is particularly useful for communications because you can point a fixed ground station antenna directly at the satellite. However, radio transmission delays and signal strength are worse than for spacecraft in lower orbits.

Not all parking lots are created equal in geosynchronous. Variations in Earth’s density push some of the satellites out of them…

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