Danger: Orbital Debris

It is the most iconic piece of space debris: that famous little screwdriver that slipped through an astronaut’s grasp and has been circling low Earth orbit at up to 21,600 mph for, like, what now—35 years?
Space Debris Basics

That seemingly innocuous little screwdriver litters space, along with gloves, cameras, lens caps, an astronaut blankie, garbage bags, paint flecks, solid fuel, wrenches, nuts, bolts, a tool bag, a pair of pliers, and a toothbrush (don't ask).

The problem is, the above space debris items are nothing compared to what’s also out there: obsolete spacecraft, chunks of satellites and rockets, momentum flywheels, nuclear reactor cores, and fragments of rockets that have broken up or collided with other objects.

Simply put—space debris is anything man-made that isn’t in active use.

Sizes of space debris range from microscopic particles to obsolete spacecraft and rocket bodies that stand several stories tall. Considering that a tiny paint fleck in space can crack a space shuttle window, can you imagine the damage caused by a giant rocket fragment crashing into a U.S. national security satellite at 21,600 mph? Such a collision would create stupendous problems back on Earth, endangering our warfighters and civilians alike.

Space Debris Basics
Artist's rendition of a satellite taking a hit from space debris.

The Risks of Space Debris

Orbital debris moves very fast.

In low Earth orbit (altitudes lower than 2,000 km), with an average impact velocity of 21,600 mph, even tiny particles can wreak havoc. NASA often had to replace space shuttle orbiter windows because they were significantly damaged by these minuscule "speckles". To further illustrate this damage potential, consider that an aluminum sphere 1.3 mm in diameter can inflict damage similar to a .22-caliber long rifle bullet, the energy of an aluminum sphere 1 cm in diameter hits a target like a 400-lb safe traveling at 60 mph, and a fragment just 10cm long impacts like 25 sticks of dynamite!

What’s more, it’s unlikely you’d be able to see this debris coming at you. Space debris moves about 10 times faster than a bullet—and no one can see a bullet coming. Although debris smaller than 1 mm in size does not generally pose a hazard to spacecraft, it can still damage optics and solar arrays. So while a spacecraft may survive being hit by tiny debris, such hits can still result in catastrophe and mission failure.

The Causes of Space Debris

A major contributor to orbital debris has been object breakup. As of August 2007, there have been 194 breakups and 51 events in which debris was shed from an object. Since that data compilation, many more are believed to have occurred. Breakups can be caused by explosions and collisions. Explosions can result from residual propellant, overheated batteries, collisions, or in some cases, deliberate destruction of the satellite. The cause of approximately 22% of observed breakups is unknown.

Two events in recent years have greatly increased the amount of debris on orbit. In 2009, the active U.S. Iridium 33 satellite collided with the defunct Russian Kosmos 2251 satellite, creating about 2,000 tracked objects. In 2007, the Chinese deliberately destroyed their own FY-1C satellite in a test of an antisatellite weapon, creating more than 3,000 tracked objects. (The tracked objects represent only a small fraction of the debris objects created by that event.)

Approximately 70,000 objects about 2 cm in size have been observed in the 850 to 1,000-km altitude band above Earth. NASA has hypothesized that these objects are frozen bits of nuclear reactor coolant leaking from several Russian RORSATs (Radar Ocean Reconnaissance Satellite).

Space Debris Basics
Artistic rendition of the space debris surrounding Earth. Illustration courtesy ESA.

How Aerospace Handles Space Junk

Until we have futuristic, space-faring scrap dealers from salvaging companies scouring low Earth orbit for space junk, The Aerospace Corporation is needed to help rocket and satellite designers and operators address space debris problems.

Aerospace works with the government to design satellite architectures that consider debris risk. Orbit choices take into account both on-orbit risk and post-mission disposal to minimize future debris. Aerospace works with the government and with contractors to design spacecraft that can maneuver to avoid collisions, withstand small debris strikes, and move to disposal orbits or reenter the Earth’s atmosphere at end of life. If a spacecraft is intended for reentry, Aerospace considers design changes that will minimize the risk to life on the ground from falling debris.

Aerospace screens launch trajectories to avoid collisions with any tracked objects and compares all potential launch trajectories at all possible launch times to calculate the positions of all tracked space debris. Aerospace aggressively seeks new ways of computing close calls with space debris, and of developing better processes to ensure smooth operations.

If a collision does occur, there is an immediate risk to operational satellites from the resulting debris cloud. Aerospace formed the Debris Analysis Response Team (DART) to pioneer new tools and techniques to compute that risk. The DART is on call to help the government determine the immediate risk to critical national assets.