China’s Long March 5B rocket fell out of orbit last weekend in an uncontrolled re-entry back to Earth. It landed in the ocean without incident, where most experts thought it would. However, that ocean destination was the product of chance not purpose. As the world watched with anticipation, valid questions were being asked. What are the odds it would fall over land? And would pieces hit the ground? How big would they be? Finally, why the confusion and uncertainty about when and where the rocket would fall?
NASA officials, on two occasions, as have others, criticized China’s handling of the descent of their spent rockets as being irresponsible. International standards for managing end-of-life space assets have been in place for decades. When a space asset is launched, it needs to return to Earth in a controlled way at the end of its mission. While this is certainly the goal, it does not always happen.
On March 26, a SpaceX Falcon 9 booster rocket suffered a similar fate. The Falcon 9 rocket’s Merlin engine failed to relight at the appropriate time, leaving the re-entry of second stage uncontrolled. There was no media lead up, no anticipation, no warning and no condemnation. The second stage re-entered with a firework show showering debris over the Northwest. Four 200-pound fuel tanks impacted the ground as the first video posts hit Twitter. One tank landed 20 feet away from a home. The debris from the Falcon 9 booster fell over farmland, orchards and rural communities. The odds always favor scarcely populated areas. Had the booster rocket entered 30 seconds earlier though, the debris would have fallen near a major coastal city.
Following the event, a 300km long linear cloud appeared over Oregon. Mirroring the rocket’s reentry trajectory, it lingered in the air and slowly precipitated out for more than three hours. While big objects obviously get headlines, all sizes and types of debris materials enter the atmosphere and slowly fall reaching the ground and potentially come in contact with humans and nature. Could these finer space debris particles pose a health risk?
The odds of a person being struck with space debris of any size are slim. Simply given that 71 percent of the globe is water and urban areas encompass 3 percent of the land. Agriculture fields take up 40 percent and the remaining is open wilderness. Further, most rockets and space assets descend in a managed and controlled way. A non-controlled rocket entry has a 29 percent chance of hitting land. If that happens, there is then a 3 percent chance of hitting a populated area.
Using these numbers, the Chinese Long March 5B had a .87 percent chance of hitting an urban area. These are small odds, but not impossible. The question is not if space debris will hit a home and/or in a populated area, because it already has, more than once. The question is, given the rapid race for the commercialization of space, how often this will happen and what can we do — if anything — about it. Do we have the systems in place to finely monitor space and identify reentry events that may impact land and populated areas?
The commercial space race reminds most of us of the 1960s, the Apollo missions and the first satellites. These Cold War developments created the aerospace industry we have today. While historic and amazing, the Cold War space race pales in comparison to what is happening now.
For perspective, this chart plots annual satellites launched according to the Union of Concerned Scientists Satellite database.
Since 1957, more than 6,000 rocket launches have occurred, deploying 11,370 satellites into space. Roughly 6,900 of these are still there. Currently, 1,500 Starlink satellites are in space with 12,000 planned and 30,000 more reserved. SpaceX leads the race in launches and the delivery of satellites into service, but they are one of many space flight service companies, domestically and internationally.
As the exploitation of space increases, the more likely debris will come down, some of it uncontrolled, and some reaching the ground. An increasingly larger concern is interspace collision between satellites and satellites with space debris.
This too has already happened. In 2009 an Iridium satellite and an old defunct Russian military satellite collided. Pulverizing each other at 26,000mph, the impact created 1000s of smaller objects. Accidental and purposeful incidents have contributed to an estimated 129 million human-made fragments larger than 1mm currently in orbit. Over 900,000 are fragments 1 to 10cm with over 34,000 objects greater than 10cm. However, only 28,000 of those objects are tracked by military and civilian entities to varying degrees.
A NASA scientist, Donald Kessler, in 1978 described the potential of a cascading impact scenario. He stated that if or when space becomes too crowded, one collision incident could lead to a chain of impacts. This domino effect would produce so much debris, space would become unusable for any purpose. Space debris would potentially rain into the Earth’s atmosphere for decades.
As the density of objects increases so do the chances of realizing this effect. The onset of this new commercial space race demands we be more responsible, not less. To raise the standard, not lower it.
International collaboration and communication are critical to address space debris. Automated avoidance systems are needed in newer satellites as are open location trackers and protocols. Further, enhanced observational infrastructure could better monitor space debris and its re-entry no matter the destination. Space commercialization has and will continue to provide incredible opportunity for humankind. However, it must progress with the greatest of caution, ingenuity, collaboration and transparency.
Mike Hankey is an entrepreneur, software developer and operations manager for the American Meteor Society. In 2010, Hankey and his company rebuilt the AMS online fireball tracking tool and since that time they have collected over 200,000 witness reports about bright lights and fireballs in the sky. Occasionally these systems receive and track space debris reentry events.