This text was initially printed at The Dialog. The publication contributed the article to House.com’s Professional Voices: Op-Ed & Insights.
There are about 15,000 satellites orbiting the Earth. Most of them, just like the Worldwide House Station and the Hubble Telescope, reside in low Earth orbit, or LEO, which tops out at about 1,200 miles (2,000 kilometers) above the Earth’s floor.
However as increasingly more satellites are launched into LEO – SpaceX’s Starlink web constellation alone will ultimately ship many 1000’s extra there – the area’s getting a bit crowded.
Which is why it is lucky there’s one other orbit, even nearer to Earth, that guarantees to assist alleviate the crowding. It is referred to as VLEO, or very low Earth orbit, and is simply 60 to 250 miles (100 to 400 kilometers) above the Earth’s floor.
As an engineer and professor who’s creating applied sciences to increase the human presence past Earth, I can inform you that satellites in very low Earth orbit, or VLEO, supply benefits over larger altitude satellites. Amongst different advantages, VLEO satellites can present higher-resolution pictures, sooner communications and higher atmospheric science. Full disclosure: I am additionally a co-founder and co-owner of Victoria Protection, which seeks to commercialize VLEO and different house directed-energy applied sciences.
Benefits of VLEO
The photographs from very low Earth orbit satellites are sharper as a result of they merely see Earth extra clearly than satellites which might be larger up, form of like how getting nearer to a portray helps you see it higher. This interprets to larger decision footage for agriculture, local weather science, catastrophe response and navy surveillance functions.
Finish-to-end communication is quicker, which is right for real-time communications, like cellphone and web service. Though the indicators nonetheless journey the identical velocity, they do not have as far to go, so latency decreases and conversations occur extra easily.
A lot climate forecasting depends on pictures of clouds above the Earth, so taking these footage nearer means larger decision and extra knowledge to forecast with.
Due to these advantages, authorities businesses and trade are working to develop very low Earth orbit satellites.
The holdup: Atmospheric drag
It’s possible you’ll be questioning why this area of house, thus far, has been averted for sustained satellite tv for pc operations. It is for one main motive: atmospheric drag.
House is commonly regarded as a vacuum. So the place precisely does house truly begin? Though about 62 miles up (100 kilometers) – often known as the the von Kármán line – is extensively thought of the start line, there isn’t any arduous transition the place house immediately begins. As an alternative, as you progress away from Earth, the ambiance thins out.
In and under very low Earth orbit, the Earth’s ambiance remains to be thick sufficient to decelerate satellites, inflicting these on the lowest altitudes to deorbit in weeks and even days, basically burning up as they fall again to Earth. To counteract this atmospheric drag and to remain in orbit, the satellite tv for pc should continuously propel itself ahead – like how using a motorcycle into the wind requires steady pedaling.
For in-space propulsion, satellites use numerous sorts of thrusters, which offer the push wanted to maintain from slowing down. However in VLEO, thrusters should be on all, or almost all, of the time. As such, typical thrusters would rapidly run out of gasoline.
Thankfully, the Earth’s ambiance in VLEO remains to be thick sufficient that ambiance itself can be utilized as a gasoline.
Modern thruster applied sciences
That is the place my analysis is available in. At Penn State, in collaboration with Georgia Tech and funded by the U.S. Division of Protection, our group is creating a brand new propulsion system designed to work at 43 to 55 miles up (70 to 90 kilometers). Technically, these altitudes are even under very low Earth orbit – making the problem to beat drag much more tough.
Our strategy collects the ambiance utilizing a scoop, like opening your mouth extensive as you pedal a motorcycle, then makes use of high-power microwaves to warmth the collected ambiance. The heated gasoline is then expelled by a nozzle, which pushes the satellite tv for pc ahead. Our group calls this idea the air-breathing microwave plasma thruster. We have been capable of exhibit a prototype thruster within the lab inside a vacuum chamber that simulates the atmospheric stress discovered at 50 miles (80 km) excessive.
This strategy is comparatively easy, however it holds potential, particularly at decrease altitudes the place the ambiance is thicker. Increased up, the place the ambiance is thinner, spacecraft may use various kinds of VLEO thrusters that others are creating to cowl giant altitude ranges.
Our group is not the one one engaged on thruster know-how. Only one instance: The U.S. Division of Protection has partnered with protection contractor Pink Wire to develop Otter, a VLEO satellite tv for pc with its model of atmosphere-breathing thruster know-how.
One other choice to maintain a satellite tv for pc in VLEO, which leverages a know-how I’ve labored on all through my profession, is to tie a lower-orbiting satellite tv for pc to a higher-orbiting satellite tv for pc with an extended tether. Though NASA has by no means flown such a system, the proposed follow-on mission to the tether satellite tv for pc system missions flown within the Nineties was to drop a satellite tv for pc into a lot decrease orbit from the house shuttle, linked with a really lengthy tether. We’re presently revisiting that system to see whether or not it may work for VLEO in a modified type.
Different problems
Overcoming drag, although probably the most tough, just isn’t the one problem. Very low Earth orbit satellites are uncovered to very excessive ranges of atomic oxygen, which is a extremely reactive type of oxygen that rapidly corrodes most substances, even plastics.
The satellite tv for pc’s supplies additionally should face up to extraordinarily excessive temperatures, above 2,732 levels Fahrenheit (1,500 levels Celsius), as a result of friction heats it up because it strikes by the ambiance, a phenomenon that happens when all spacecraft reenter the ambiance from orbit.
The potential of those satellites is driving analysis and funding, and proposed missions have turn out to be actuality. Juniper analysis estimates that $220 billion will probably be invested in simply the following three years. Quickly, your web, climate forecasts and safety could possibly be even higher, fed by VLEO satellites.
