Mission Shakti: What is Low-Earth orbit? What use is it to space-faring nations like India?

On Wednesday, 27 March 2019, Prime Minister Narendra Modi made an announcement in a television address to the nation. He said India would only be the fourth country to have used such an anti-satellite weapon after the United States, Russia, and China.

Capabilities like these have raised eyebrows, questions and importantly, fear that space is being weaponised.

"Some time ago, our scientists, shot down a live satellite 300 km away in space, in low-earth orbit," Modi said, calling it a historic feat for the country. "India has made an unprecedented achievement today...India registered its name as a space power."

What is the Low-Earth Orbit?

Low-Earth orbit — the messy home to hundreds and thousands of active satellites, a grave of hundreds of dead ones, and an undoubtedly hostile place for people to be (and for some satellites, too, apparently.)

This massive, Earth-centered orbit, the low-Earth Orbit (LEO), makes up most of the planet's lower atmosphere, starting at an altitude of 160 to 2,000 km from the surface.

By and large, the vast majority of missions to space over the years – manned or unmanned – have been to the low-Earth Orbit (LEO). It is here that you'll find much of Earth's communication, navigation and military satellite arsenal that feeds signals down to men and machines on Earth. The LEO is also where the International Space Station (ISS) orbits the Earth and carries out its operations.

 Mission Shakti: What is Low-Earth orbit? What use is it to space-faring nations like India?

Three CubeSats being deployed from the space station into low-Earth Orbit. image: NASA

Why are we so intent on sending things to the Low Earth Orbit?

Most rockets may launch satellites into LEO, but whatever these objects may be, and of whatever size, they won't stay there forever. Any object that orbits the Earth interacts with the blanket of gases and particles that make up the atmosphere.

The air up there, being really thin, exerts just a tiny force on objects. This gives LEO objects a tiny drag (a resistance/opposing) force that acts on all the objects orbiting or in motion up there. While this demands that satellite missions factor in the marginal energy needs to oppose this 'drag force', there are definitely benefits to have an LEO satellite.

For one, LEO is the simplest, cheapest and safest location to deploy a satellite, a space station or a crewed space mission. It also offers high signal bandwidth and low time lag for communications, navigation satellites and space missions.

An image of Mount Dukono located in northern Indonesia captured by a Dove satellite. Since they orbit in 'flocks', it's possible to make daily or even hourly image updates of the earth's surface. Image courtesy: Wikimedia Commons

An image of Mount Dukono located in northern Indonesia captured by a Dove satellite.
Since they orbit in 'flocks', it's possible to make daily or even hourly image updates of the earth's surface. Image courtesy: Wikimedia Commons

Whether you're one of the hundreds of tiny Dove satellites, a huge HySIS keeping an eye on Earth's surface or the soon-to-launch EMISAT satellite that can intercept ground communication networks, LEO is where you want to be. It is just low enough to get a good view of Earth's surface, be it for images, surveys or monitoring the weather. Satellites that rapidly orbit the Earth in this region (one hour to two hours for a single orbit) can also fly over the same area on the surface multiple times a day.

And if all that isn't enough, objects in the LEO are also spared from a lot of the intense radiation that is an unavoidable part of missions in space.

LEO isn't all sunshine and rainbows, though

On 2 July 2018, the European Space Agency's (ESA) CryoSat-2 spacecraft was orbiting just fine and where it should be: at an altitude of 700 km. But mission controllers at the ESA were woken up to alarm bells that day — a piece of space debris was hurtling uncontrollably towards the €140 million (Rs 11,000 million) satellite that did a Grade-A job of monitoring ice cover and density on the planet.

Chances of a collision were very high, and the ESA was forced to take action. On 9 July, mission controllers fired CryoSat-2's thrusters and boosted it up into a higher orbit. 50 minutes passed before the debris zipped past CryoSat-2 at ~4 kilometres per second.

This is only one of many incidents that are growing increasingly common in LEO because of how congested it is. Commercial companies, military organisations, and amateurs sent more than 400 satellites into orbit in 2017 alone. That was 4 times more than the average per year between 2000–2010.

Space Debris = Space Danger

With more private space companies entering the fold, along with affordable rideshares and liberalisation of technology, this is an enormous problem waiting to explode.

Another collection of commercial satellites — the Iridium constellation — smashed into Cosmos-2251, an inactive Russian communications satellite in 2009. The thousands of shards and shrapnel from this accident are waiting threats for satellites, rockets and astronauts that visit or pass through low Earth orbit. This risky zone, stretching ~2,000 kilometres in altitude, is now under constant watch for potentially killer debris.

These pieces don't pose any significant threat to people on Earth because most of them would simply burn up in the atmosphere on re-entry. They are a guaranteed risk to astronauts and objects that go up to space.

Travelling at speeds of up to 8 kilometres per second, even the tiniest piece of debris could be lethal if it collides with a functional satellite, the Space Station, space shuttles, or any other type of spacecraft.

"A 1-centimetre object can have energy on collision that is comparable to an exploding hand grenade," Tim Flohrer, a space debris expert at the European Space Agency told EuroNews.

Updated Date: Mar 27, 2019 15:43:03 IST