About 3% of Starlinks have failed so far

Spacex has received much praise and criticism with the creation of Starlink, a constellation that will one day provide broadband Internet access to everyone. To date, the company has launched more than 800 satellites and (as of this summer) is producing them at a rate of about 120 per month. There are even plans to have a constellation of 42,000 satellites in orbit before the decade is out.

However, there have also been some problems along the way. Aside from the usual concerns about light pollution and radio frequency interference (RFI), there is also the failure rate these satellites have experienced. Specifically, about 3% of its satellites have proven to be unresponsive and are no longer maneuvering in orbit, which could prove dangerous to other orbiting satellites and spacecraft.

To avoid collisions in orbit, SpaceX equips its satellites with krypton Hall-effect thrusters (ion engines) to elevate their orbit, maneuver in space, and deorbit at the end of their lives. However, according to two recent notices SpaceX sent to the Federal Communications Commission (FCC) during the summer (mid-May and late June), several of its satellites have lost maneuverability since they were deployed.

Unfortunately, the company did not provide enough information to indicate which of its satellites were affected. For this reason, astrophysicist Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics (CfA) and the Chandra X-ray Center presented his own analysis of the orbital behavior of satellites to suggest which satellites have failed.

The analysis was published on McDowell’s website (Jonathon’s Space Report), where he combined SpaceX’s own data with US government sources. From this, he determined that about 3% of the satellites in the constellation they have failed because they no longer respond to commands. Naturally, some level of wear is unavoidable and 3% is relatively low as failure rates progress.

But each satellite that is unable to maneuver (due to problems with its communications or its propulsion system) creates a collision hazard for other satellites and spacecraft. As McDowell told Business Insider:

“I would say that their failure rate is not atrocious. It is no worse than anyone else’s failure rates. The concern is that even a normal failure rate in such a large constellation will end up with a lot of bad space junk. “

SpaceX began to implement its Starlink constellation on May 23, 2019, with the launch of its first batch of 60 satellites. Its last launch took place today (Saturday, October 24), effectively bringing its constellation to 835. Thus, a 3% failure rate means that approximately 25 satellites will fail and become part of the growing problem of ” space junk “.

Kessler syndrome

Named after NASA scientists Donald J. Kessler, who first proposed it in 1978, Kessler syndrome refers to the threat posed by collisions in orbit. These lead to catastrophic ruptures creating more debris that will lead to more collisions and ruptures, and so on. When failure rates and SpaceX’s long-term plans for a “mega-constellation” are taken into account, this syndrome naturally rears its ugly head.

Not long ago, SpaceX obtained permission from the Federal Communications Commission (FCC) to deploy around 12,000 Starlink satellites to orbits ranging from 328 km to 580 km (200 to 360 mi). However, more recent filings with the International Telecommunications Union (ITU) show that the company expects to create a mega-constellation of up to 42,000 satellites.

In this case, a 3% failure rate equals 360 and 1,260 (respectively) 250 kg (550 pound) satellites that will die out over time. As of February 2020, according to ESA’s Space Debris Office (SDO), there are currently 5,500 satellites in orbit of the Earth, of which around 2,300 are still operational. That means (using naked math) that a Starlink Mega constellation would increase the number of satellites not operating in orbit by between 11% and 40%.

The debris and collision problem seems even more threatening when you consider the amount of debris in orbit. Beyond the satellites that are not working, the SDO also estimates that there are currently 34,000 objects in orbit that measure more than 10 cm (~ 4 inches) in diameter, 900,000 objects between 1 cm and 10 cm (0.4 to 4 inches) and 128 million objects between 1 mm and 1 cm.

Mitigation strategies

Naturally, SpaceX has emphasized that the risk of collision is very small. In its filings with the FCC in April 2017, SpaceX addressed the possibility of collision risks by assuming rates of “satellite failures resulting in the inability to perform collision avoidance procedures of 10, 5 and 1 percent.” In response, the company indicated that even a 1% risk was unlikely, given the following specifications and guidelines:

• Design the Starlink constellation to exceed NASA’s debris mitigation guidelines and an “aggressive monitoring program” to detect potential problems and deorbit affected satellites
• An incremental deployment program over a long period of time (which they are doing by deploying a batch of 60 satellites per launch)
• An iterative design process that takes advantage of new technologies and updates, avoiding the launch of more satellites identified as problematic and exorbitant those identified as a risk

Last but not least, SpaceX emphasized that it conducts simulations, which it corroborates with information from the USAF’s Joint Space Operations Center (JSpOC) and NASA’s Orbital Debris Engineering Model. From this, they claimed that based on a 1% satellite failure rate and no corrective maneuvers, there was “about a 1 percent chance per decade that any failed SpaceX satellite would collide with a tracked piece of debris.”