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Why Satellites of the Future will be built to burn

There is no shortage of how a satellite in low ground path can fail during its mission. Even at best, the boat must survive the bombardment of cosmic rays and huge temperature variations. In order to even have a chance to survive the worst, such as a hardware failure or collision with a scanty space garbage, it must be designed with robust layoffs that can keep everything running with systemic damage. Of course, before any of it can happen, it will have to survive the wild ride to space; So add high G loads and intense vibrations to the list of things that can kill your expensive bird. After all the accurate technology and expense involved in putting a satellite into circulation, you might think it would be a hero welcome at the end of his mission. But it's actually quite the opposite. The great irony is that after all the time and effort it takes to develop a spacecraft that can survive the fighting in the space flight, the operators will even more likely go to destroy themselves by diving their orbit into the earth's atmosphere. The final act of a well-crafted satellite is likely to be committed to the same burning fate as it had spent years or even decades avoiding. You may be wondering how engineers design a spacecraft that is at the same time robust enough to survive years in space environment while remaining fragile enough that it completely burns up during reentry. Until quite recently,…

There is no shortage of how a satellite in low ground path can fail during its mission. Even at best, the boat must survive the bombardment of cosmic rays and huge temperature variations. In order to even have a chance to survive the worst, such as a hardware failure or collision with a scanty space garbage, it must be designed with robust layoffs that can keep everything running with systemic damage. Of course, before any of it can happen, it will have to survive the wild ride to space; So add high G loads and intense vibrations to the list of things that can kill your expensive bird.

After all the accurate technology and expense involved in putting a satellite into circulation, you might think it would be a hero welcome at the end of his mission. But it’s actually quite the opposite. The great irony is that after all the time and effort it takes to develop a spacecraft that can survive the fighting in the space flight, the operators will even more likely go to destroy themselves by diving their orbit into the earth’s atmosphere. The final act of a well-crafted satellite is likely to be committed to the same burning fate as it had spent years or even decades avoiding.

You may be wondering how engineers design a spacecraft that is at the same time robust enough to survive years in space environment while remaining fragile enough that it completely burns up during reentry. Until quite recently, the simple answer is that there was nothing that was taken into consideration. But with falling launch prices that promise to make the site much more lively over the next few years, the race is about to develop new technologies that will help a satellite to remain intact as long as it needs.

Sky falls

A piece of skylab that crashed in Australia

The possibility of debris surviving reentry and hitting the ground is nothing new, and there are documented cases that go back as long as we have shot things into space. Probably the most famous example was 1979, when the wreck from Skylab was strewn over Australia’s outback. The biggest pieces, such as tanks that kept oxygen aboard America’s most persnickety space station, tipped the scales into hundreds of pounds. Fortunately, these massive objects came down in one of the most scarcely populated areas on earth, but if they came down to a big city, the damage and the risk to human life could have been significant.

What has changed is how many objects we can expect to reintroduce the atmosphere in the near future. When only the world’s great powers had the ability to put something into space, it was relatively easy to keep track of when things returned. But increased competition has dramatically reduced the cost of putting satellites into circulation, and now companies are seeing space investments that would have been impossible just a decade ago. Companies like SpaceX, OneWeb and Samsung are eyeing satellite mega-constellations consisting of thousands of individual spacecraft, and each one will eventually nurture back through the atmosphere at the end of its nominal lifetime.

In a letter dated February 26, the Federal Communication Commission specifically announced SpaceX to detail its plans for deorbing the thousands of satellites in its proposed Starlink network. They wanted to know if SpaceX can ensure that the craft will return over the sea, and if not, to estimate the likelihood of falling debris causing material damage or human damage. The letter ends by stating that SpaceX’s Starlink Approval application could be dismissed if this information was not provided satisfactorily by the FCC.

Unacceptable Risk

Targeting a spacecraft to the tenant over the sea has always been the standard route to ensure that any debris that survives will not cause any problems on the ground. Because most of the plane’s surface is the sea anyway, it becomes a relatively simple matter to do if your spacecraft is operating normally and can maneuver itself. Although mistakes happen, Skylab was actually supposed to return south of Africa, a slight error in the calculations meant that it was significantly over-east.

Two prototype Starlink satellites before launch

But SpaceX’s proposed Starlink satellites (and others like it) are something of a special case. They utilize high-efficiency Hall-effect propulsion which is ideal for temporary orbital adjustment and stationary maintenance, but lacks the power required to put the ship on a targeted reindeer lane.

In other words, the satellites can lower their orbit sufficiently to ensure that they will burn up, but cannot indicate where it will be with sufficient accuracy to make any warranties. It can be an acceptable risk for just one satellite, but long-term Starlink plans require up to as many as twelve thousand. With so many games in play, the chance of one of them breaking up over a populated area could simply be too high.

In its official response to the FCC, SpaceX explained that while they could not guarantee that Starlink satellites would only reintroduce the atmosphere over the sea, they had come up with a solution that would make it unnecessary. After “extensive research and investment,” SpaceX says they have refined the design of their Starlink satellites to ensure they will completely burn up in the atmosphere.

Design for Demise

The idea of ​​designing satellites in such a way that they will burn up completely during a normal reentry has floated around for decades, but so far has struggled to catch on. Referred to as the “Design for Demise” or the D4D in the industry, its biggest advocate has probably been the European Space Agency, which has made it a central theme in its overall “Clean Space” initiative. As you can imagine it being a complex subject but at risk of overwriting things, there are essentially two main approaches: constructs that break into smaller pieces as they enter the atmosphere and the use of materials that cannot survive the intense heat of reentry . These two ideas are not mutually exclusive and would probably be used together for best results.

For example, instead of holding a satellite together with nuts and bolts, it can be glued together with epoxies formulated to break down at high temperatures. When the spacecraft hits the atmosphere and starts to heat up, the epoxy gives way and the structure simply falls apart. Not only does this technology reduce the number of large objects that may come through the atmosphere intact, but it also opens up the interior of the spaceship to the flow of hot atmospheric gases that will promote more complete firing.

A typical reaction wheel module.

Still, there are some components of the average satellite that are robust enough that they could survive. Probable candidates are titanium propellant tanks, silicon carbide mirrors (used in optical telescopes or laser communication systems), the iron cores of the Hall effect thruster, and the heavy duty stainless steel reactors used to provide spacecraft setting control. These components are a much more difficult problem, since the materials used in their construction were obviously chosen for one reason. As an example, replacement of a stainless steel reaction wheel with an aluminum of the same diameter would simply not work because of the differences in density. The entire system would need to be redesigned to take into account the material change.

According to its official response to the FCC, SpaceX says they have replaced these problem components with versions that they can guarantee not survive reentry. If true, it would be a great milestone for the D4D design, and probably the yardstick by which future large-scale satellite constellations will be measured. But not everyone is convinced that SpaceX has solved this complicated problem as nicely as they say. In a statement to IEEE Spectrum, professor of mechanical and space technology at the University of Buffalo John Crassidis said that he believes the requirements are a bit too bold: “Everything can come through the atmosphere if you hit the right angle. If they guarantee that it will not cause a problem, then I’ll call BS on it. “

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Faela