Questions about how Space Debris can Threaten the ISS?

Our Space Debris Expert is back to answer questions about protecting the International Space Station, the consequences of a debris cloud, and how we track space debris.

The International Space Station. Photo courtesy NASA.

How small and how large is space debris?

Space debris can be as big as a large rocket body (over 10 meters or 33 feet long) down to microscopic particles that are barely visible. The ones that we are most worried about are those larger than 3 mm (BB sized), although even impacts of very small debris can gradually degrade a solar panel or ruin a scientific instrument.

Why is small debris a problem?

Anything that is in orbit is moving very fast, typically 7.5 km/sec, or more than 17,000 mph in low Earth orbit (LEO). This is ten to twenty times faster than a bullet. If you are in orbit, you are also moving that fast, and the debris may be coming at you from the other direction, so the relative speed could be twice that. The result is that even tiny particles can be extremely deadly, and an object the size of a pinhead can pack a huge wallop.

What is an on-orbit breakup, how do they happen and what can be done about it?

Known orbit planes of Fengyun-1C debris one month after its disintegration by a Chinese interceptor missile in 2007. The white orbit represents the International Space Station

Are chain-reaction collisions or cascades real?

Unfortunately, yes. Mathematical modeling has repeatedly shown that the number of objects in low Earth orbit will likely grow from collisions. However, these cascades take place over decades and centuries, with a large collision happening currently only about once every five to ten years.

What does an on-orbit collision look like?

A hypervelocity collision, like those at orbital speed, doesn’t behave like collisions on Earth. The objects are moving so fast that they travel through each other faster than the shock waves can travel so it appears more like an explosion of each object — as if they passed through each other and exploded on the other side. The shock waves in the structures of each object then shatter them into fragments of varying sizes and, in the process, give each fragment a boost in a different direction. Each one of these fragments is then in a different orbit than the original object and will move away according to the laws of orbital motion. With thousands of fragments, each moving in slightly different directions, it looks a lot like an explosion.

Hypervelocity impact test to a cylinder by a 3.17mm aluminum projectile traveling at 7.03 km/sec. Video courtesy NASA WSTF

What are debris clouds?

When an object in space breaks up or blows up, each of the pieces will fly in its own, independent orbit. These orbits are mathematically related to one another, and we analyze them collectively as a “cloud.” Since there is no air or other medium in which the cloud is suspended, the cloud grows and changes shape based solely on the laws of orbital motion. In models, you can see the cloud grow and change shape as the cloud forms into a ring around the Earth. But in real life, on a human scale, the pieces are too small and much too far apart to actually see debris as a coherent cloud.

Can we protect the ISS and other satellites?

Impact on Whipple shields. Image courtesy NASA.

Are some orbits more dangerous than others?

Certain orbit altitudes are more crowded with space debris than others. Orbits between 800 and 1100 km in altitude are the most crowded and contain 40 percent of the tracked space debris. Orbits going near the Earth’s poles, for example, are more dangerous because they cross other orbits more frequently. Because space debris comes from human activity, the most useful orbits will also have the most space debris.

Who is responsible for creating and controlling space debris?

The nations that launch and operate satellites are responsible for the space debris from their satellites and rocket bodies. There is no one responsible for tracking it internationally, but the United States does track space debris to protect our own satellites and those of other nations, sharing orbit information with the rest of the world. Other nations also have tracking capabilities and perform similar services for their satellites. Satellite operators try to reduce space debris from recently launched satellites and rocket bodies by carefully designing them to prevent explosions, reentering them, or moving them to disposal orbits when their mission is over. Space debris from older objects, explosions, and collisions is not controlled at all.

Can you see space debris coming?

It is very unlikely you would see space debris. Relative to a person in orbit, space debris is moving about ten times faster than a bullet. The vast majority of debris is on that scale or smaller. Just as you can’t see a bullet coming, an object moving 10x faster would be impossible to see with the naked eye.How do we track space debris?

The Space Surveillance Network of radar and sensors.

Is there an “air traffic control” equivalent for space?

The closest agency to an air traffic control system is the US Space Force’s Combined Space Operations Center. The CSpOC operates the Space Surveillance Network and maintains the most complete catalog of objects on orbit. If they predict a collision between a cataloged object and a known operational satellite, they usually attempt to notify the owner/operator. The CSpOC monitors the ISS and other NASA satellites for collisions in coordination with NASA. Other nations use CSpOC data as well as their own tracking data to protect their satellites. To date, there is no internationally recognized “Space Traffic Control” agency.

If most debris is too small to be seen, how do we know it exists?

Some radar installations can see small objects pass through their beams but can’t track them for enough time to determine their orbit. We can determine the approximate amount of small space debris by counting these radar returns over a short period of time and then estimating the total. There are also special sensors that can be flown in space to measure small debris impacts or detect debris that passes nearby using lasers.

LeoLabs tracks current satellites in Low Earth Orbit with their visualization tool. Image Courtesy LeoLabs

How far in advance can you predict a collision or a reentry?

We can reasonably predict close approaches in space beginning a week prior to the event. Predicting where space debris will reenter and land is much harder to do because we don’t know when the object will actually enter the denser atmosphere and begin its final dive. Reliably predicting a reentry location more than a day ahead of the event is difficult, and even then our margin of error could be several hours, which is equivalent to multiple orbits.

If we know about it in advance, can space debris be identified and moved to avoid a collision?

The debris can’t be moved with other technology, but if the other object is a maneuverable satellite, it may be able to move out of the way in time to avoid a collision. Most satellite operators require hours or days to plan and execute a collision avoidance maneuver.

Will the space debris problem take care of itself?

In low Earth orbit (below 600 km or 370 miles), the little atmosphere that is there will, over weeks, months, and years, drag the space debris low enough to reenter. Between 600 km and 1000 km (620 mi) it may take tens to hundreds of years for the debris to reenter. For orbits from 1000 km to 2500 km (620 to 1550 miles) re-entry may eventually occur, but it may take thousands of years. Above 2500 km, lifetimes can be much longer.

How much debris is there? How many objects are in orbit?

The Space Age began in October of 1957, with the launch of Sputnik 1. In the last 56 years there have been over five thousand launches. Each launch typically has several separate objects associated with it that may remain in orbit. In addition, there have been explosions and other violent breakups of vehicles that have resulted in thousands to hundreds of thousands of fragments.

Can space debris be cleaned up?

There is no easy or cheap solution to space debris. Cleaning it up will be very expensive and time-consuming. Big debris, like used rockets, is most likely to create more debris and is heavy and difficult to move. Small debris that can still damage a satellite is very hard to find and track and there are very large quantities of it. Both types of debris are difficult to remove for their own reasons. There are on-going efforts by both governmental organizations and commercial companies to develop the technologies needed to remove debris.

Will space debris eventually make it impossible to fly or operate in space?

No, this is very unlikely. Over many decades, the growth in space debris will make orbit operations more hazardous, and more costly. The growth of debris will make tracking and avoiding the debris more complicated, costly, and operationally difficult. It might be tough to perform a mission if frequent maneuvers are required to avoid debris. A satellite would have to carry extra fuel for these extra maneuvers and would likely need to shield critical areas from collisions with small debris. Space debris can make space missions more costly and difficult, but it won’t make them impossible.

We operate the only federally funded research and development center (FFRDC) committed exclusively to the space enterprise.

We operate the only federally funded research and development center (FFRDC) committed exclusively to the space enterprise.