Feb 13, 2025 09:34 PM
https://www.bbc.com/future/article/20250...rth-orbits
EXCERPTS: . . . "When you start describing it to people, it starts to sound like a perpetual motion machine," says Spence Wise, senior vice-president at Redwire, an aerospace firm in Florida. A perpetual motion machine is not meant to be possible. But it almost is, in this instance.
A handful of pioneering companies have begun work on designs for satellites that may be able to orbit the planet at these unusually low altitudes while simultaneously harvesting air and using it to make propellant – literally on the fly. This new generation of orbiters could enable ultra-high-definition surveillance of activities on the ground, or superfast satellite-based communications.
If you want to send something into orbit, you have to decide how high your satellite is going to fly. Earth orbits are generally described in terms of altitude and are categorised into different sections. In high orbits, 22,000 miles (36,000km) above Earth, satellites enter a geostationary position, meaning they are always above the same location on Earth below. This is useful for telecommunications and weather monitoring, for example. Next is Medium Earth orbit, which spans from roughly 22,000 miles (36,000km) down to 1,200 miles (2,000km) above the planet's surface. Below this is Low Earth orbit, which stretches down to altitudes of 250 miles (400km), where the International Space Station (ISS) is found.
[...] Even further below this lies VLEO, loosely defined as anything below the ISS and down to an altitude of about 60 miles (100km). Operating here is difficult because of the influence of Earth's atmosphere. "The atmosphere will increase exponentially as you come down," says Hugh Lewis, a professor of astronautics and a space debris expert at the University of Southampton in the UK.
That creates more drag on your satellite, which can spell doom. As molecules in the atmosphere smash into the satellite, they rob the vehicle of its momentum, causing the tug of our planet's gravity to drag it towards the ground.
[...] All satellites pass through VLEO on their way up or down, but not many have purposefully tried to stay there. One such spacecraft, however, was the European Space Agency's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite. Launched in 2009, it orbited at an altitude of around 155 miles (250km), using an ion propulsion system to fire out charged particles behind the spacecraft. This gave it a constant level of thrust that could counteract the drag of the atmosphere. ... GOCE ultimately ran out of fuel and burned up in the atmosphere on re-entry in 2013.
Several companies are now trying to do something even more impressive. They are developing technology to harvest molecules from the thin layer of air that is present in VLEO in order to actually propel satellites here. Such a system, called Air-Breathing Electric Propulsion (ABEP), has been made possible by advancements in electric and ion propulsion in recent years. In essence, it involves fixing a large bucket or opening to the front of the satellite, into which gas molecules from the atmosphere flow before they are ionised to create plasma that generates thrust.
"The idea is to use the same air slowing down your satellite as a propellant," says Francesco Romano, a scientist at the Swiss Plasma Center in Lausanne, Switzerland, who has previously studied this technology. Using electric and magnetic fields, the engine would ionise gas from the atmosphere, taking away one electron from each molecule, to produce a free electron and an ion. Then, using magnets, the electrons and ions are pushed out the back of the spacecraft, producing thrust. "Theoretically, if you can generate a thrust that is the same as your drag, you stay at this altitude for an infinite amount of time," says Romano.
To date, an assortment of experimental ABEP systems have been able to produce relatively small amounts of thrust at ground level.. (MORE - missing details)
EXCERPTS: . . . "When you start describing it to people, it starts to sound like a perpetual motion machine," says Spence Wise, senior vice-president at Redwire, an aerospace firm in Florida. A perpetual motion machine is not meant to be possible. But it almost is, in this instance.
A handful of pioneering companies have begun work on designs for satellites that may be able to orbit the planet at these unusually low altitudes while simultaneously harvesting air and using it to make propellant – literally on the fly. This new generation of orbiters could enable ultra-high-definition surveillance of activities on the ground, or superfast satellite-based communications.
If you want to send something into orbit, you have to decide how high your satellite is going to fly. Earth orbits are generally described in terms of altitude and are categorised into different sections. In high orbits, 22,000 miles (36,000km) above Earth, satellites enter a geostationary position, meaning they are always above the same location on Earth below. This is useful for telecommunications and weather monitoring, for example. Next is Medium Earth orbit, which spans from roughly 22,000 miles (36,000km) down to 1,200 miles (2,000km) above the planet's surface. Below this is Low Earth orbit, which stretches down to altitudes of 250 miles (400km), where the International Space Station (ISS) is found.
[...] Even further below this lies VLEO, loosely defined as anything below the ISS and down to an altitude of about 60 miles (100km). Operating here is difficult because of the influence of Earth's atmosphere. "The atmosphere will increase exponentially as you come down," says Hugh Lewis, a professor of astronautics and a space debris expert at the University of Southampton in the UK.
That creates more drag on your satellite, which can spell doom. As molecules in the atmosphere smash into the satellite, they rob the vehicle of its momentum, causing the tug of our planet's gravity to drag it towards the ground.
[...] All satellites pass through VLEO on their way up or down, but not many have purposefully tried to stay there. One such spacecraft, however, was the European Space Agency's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite. Launched in 2009, it orbited at an altitude of around 155 miles (250km), using an ion propulsion system to fire out charged particles behind the spacecraft. This gave it a constant level of thrust that could counteract the drag of the atmosphere. ... GOCE ultimately ran out of fuel and burned up in the atmosphere on re-entry in 2013.
Several companies are now trying to do something even more impressive. They are developing technology to harvest molecules from the thin layer of air that is present in VLEO in order to actually propel satellites here. Such a system, called Air-Breathing Electric Propulsion (ABEP), has been made possible by advancements in electric and ion propulsion in recent years. In essence, it involves fixing a large bucket or opening to the front of the satellite, into which gas molecules from the atmosphere flow before they are ionised to create plasma that generates thrust.
"The idea is to use the same air slowing down your satellite as a propellant," says Francesco Romano, a scientist at the Swiss Plasma Center in Lausanne, Switzerland, who has previously studied this technology. Using electric and magnetic fields, the engine would ionise gas from the atmosphere, taking away one electron from each molecule, to produce a free electron and an ion. Then, using magnets, the electrons and ions are pushed out the back of the spacecraft, producing thrust. "Theoretically, if you can generate a thrust that is the same as your drag, you stay at this altitude for an infinite amount of time," says Romano.
To date, an assortment of experimental ABEP systems have been able to produce relatively small amounts of thrust at ground level.. (MORE - missing details)
