You may have seen in the headlines this week that a Japanese company, Star-ALE, plans to create an artificial meteor shower for the opening ceremony of the 2020 summer Olympics in Tokyo. I think this is a really neat idea, so I thought I’d make a quick video about the engineering behind it. Star-ALE hasn’t released many details about this project, but there are some fundamental aerospace concepts that don’t require wild speculation on my part to associate with these synthetic cygnids. In fact, we’ve been creating artificial meteors for a long time, just not for the purpose of entertainment. This is something new I'm trying: Practical Engineering shorts, where we just dip our toes in the pool of technical details behind current events.
Satellites don’t last forever, so their disposal is as crucial a part of their mission as anything else. Before a satellite even sees the glow of the rocket engine that will carry it into orbit, mission planners already know what they’ll do when the end of its usable life is reached. For a low-earth satellite, decommissioning usually means turning off the instruments and letting its orbit slowly decay until it burns up in earth’s atmosphere. Predicting when and where a satellite will re-enter is a challenge. Factors like solar activity causing variations in the density of earth’s upper atmosphere make it almost impossible to know for sure when re-entry will occur. And orbiting objects are moving so quickly that even a 10% error on the final time of re-entry can mean a difference of 7,000 kilometers on the ground. Even with this challenge, members of the amateur satellite observation group SeeSat-L have tallied over 250 natural re-entries of Earth satellites which have been visually observed.
But these are just the natural re-entries, where a satellite was simply turned off and left to fend for itself. But every so often a satellite is big enough or important enough that mission planners deem it necessary to perform a controlled re-entry. In these cases, the decommissioned satellite is piloted through reentry to the ocean or a sparsely populated area to make sure that any debris which reaches the surface of the earth doesn’t endanger people or property. And it’s not just decommissioned satellites that get piloted through the upper atmosphere. Don’t forget that we routinely put humans into low earth orbit to carry out scientific and technical endeavors aboard the international space station. To get satellite debris and astronauts back to earth safely and accurately, we need to have a way to control the time and place where reentry occurs.
Design of a re-entry trajectory is a complex balancing act between deceleration, heating, and accuracy. Some scientists and engineers spend their entire careers studying ballistic coefficients and free molecular gases and hypersonic shock waves, etc. And just like bringing astronauts back from the ISS or safely decommissioning a large satellite that’s reached the end of its mission, creating an artificial meteor shower will require the dutiful application of the exact same body of engineering theory. Aerospace engineers will have to carefully plan and execute how the meteors are released from the Star-ALE satellite in order to for them to re-enter the atmosphere at the just the time and location for the opening ceremonies. I guess we’re lucky that each nation that hosts the Olympics tries to one-up the festivities that came before, and I have to say that an artificial meteor shower is certainly one the most innovative ideas for outdoor entertainment I’ve heard of in quite some time. Let’s just hope none of those artificial meteors turn into artificial meteorites.