Space debris is getting SSPICY

Posted: October 21, 2024

In 2016, European Space Agency astronaut Tim Peake shared a photo of a 7mm (0.3-inch) chip on the outside of the fused silica and borosilicate glass window of the International Space Station (ISS). The chip was likely created by a collision with a tiny piece of debris just a few thousandths of a millimeter across, such as a paint chip or metal shard from a defunct satellite.

“[…] this is the chip in one of our Cupola windows, glad it is quadruple glazed!” was Peake’s understandable reaction.

Objects orbiting Earth at the distance of the ISS generally travel about 7.8 km (4.9 mi.) per second. At those speeds, even very tiny pieces of debris impart enough force to cause serious damage. The European Space Agency estimates a piece of debris more than 1 cm across could penetrate the shields of the ISS. Particles even smaller than that could disable a satellite.

Destructive collisions with space debris are becoming more unavoidable as the quantity of spacecraft—and space debris—continues to grow. It’s a problem we all have a stake in solving as we rely more and more on the communications and data that orbiting spacecraft provide.

How much debris is there in space?

There are currently over 7700 satellites in low Earth orbit, within a few hundred miles of the Earth’s surface. Many of them relay communications or GPS signals, or monitor climate, agriculture and geomorphology. Their numbers could grow nearly 10-fold by 2027.

The Harvard astrophysicist and astronomer, Jonathan McDowell, told Space.com that with the expansion of commercial space programs:

"It's going to be like an interstate highway, at rush hour in a snowstorm with everyone driving much too fast, except that there are multiple interstate highways crossing each other with no stoplights."

In total, zooming out to include objects farther out than several hundred miles, NASA tracks about 27,000 objects larger than 10 centimeters orbiting the Earth as of February of 2023. About 75% of those objects are non-functional debris: defunct spacecraft, parts of rockets, or fragments of spacecraft from explosions or collisions.

But in addition to these trackable objects, there are an estimated 100 million pieces of small debris—less than 10 cm—that NASA doesn’t track. These include tiny shards of paint and metal of the sort that may have cracked the window of the ISS. NASA pegs such debris as posing more risk than anything else to spacecraft travelling through Earth orbit.

Over the long term, we risk a situation in which more space debris leads to more collisions, which leads to more space debris, and so on—in a vicious cycle called the “Kessler Syndrome,” after a 1978 paper describing the problem by NASA researcher Donald Kessler.

The Otter gathering data on space debris

To gather data on space debris in low earth orbit, NASA is employing a SSPICY Otter. The Otter in question is not a snarky aquatic mammal, but a spacecraft about the size of an oven designed by the five-year-old commercial startup, Starfish Space. NASA awarded a contract to Starfish to use the Otter to execute what it calls a “small spacecraft propulsion and inspection capability” (SSPICY) mission.

The Otter will use its electric propulsion system to visit and inspect several defunct satellites. Though the Otter is capable of docking with, servicing and even piloting decommissioned satellites out of orbit, its NASA mission is purely to gather information. It will stay several hundred meters away from the satellites and gather information about their spin rate, spin axes and the condition of their materials. The data it gathers will help NASA understand how to reduce space debris and extend the operational life of satellites.

The technical lead for in-space servicing, manufacturing and assembly at NASA’s Space Technology Mission Directorate said the mission

“[...] helps us characterize the physical state of a satellite, gather data on what may leave spacecraft stranded, and improve our understanding of fragmentations and collisions, a difficult but critical factor in a sustainable space operating environment.”

The SSPICY Otter mission will also help hone the Otter’s electric propulsion system, which has not yet been deployed extensively in rendezvous missions, and develop capabilities for additional commercial servicing of satellites.

Detecting micro-debris in space

While the data from the SSPICY Otter mission will help researchers understand and remediate future collisions, scientists are also developing better ways to track all the tiny bits of debris less than 10 cm that continue to accumulate. This debris is too small to be tracked with radar or optical sensors.

The Intelligence Advanced Research Projects Activity’s Space Debris Identification and Tracking Program (SINTRA) is working on a number of projects to “ detect, track, and characterize lethal non-trackable orbital space debris.” One of the first projects being developed will attempt to detect the brief electric signals produced when debris fragments pass close to one another. Many details remain to be worked out, and the team is using computer simulations to refine the technique.

What’s clear is that all solutions to the space debris problem start with gathering and analyzing data. Understanding where debris is and how it’s moving will not only help satellites avoid it, but could also help us avoid creating it in the first place, leading to a (hopefully) less spicy future in low-orbit space.