Space Debris FAQs

Inquiring Minds

Experts will answer your space debris questions HERE.

Additional information can be found on Space Debris FAQs – Part II.

Q1. Are the astronauts at risk? What can NASA do about it?

Astronauts are at risk in the International Space Station and during extra-vehicular activities (spacewalks). Their suits can protect them from extremely small particles and most of the ISS has shields to protect them from objects with sizes up to one cm in diameter. To protect them from larger objects, the Space Station must navigate out of the way or the astronauts can use the auxiliary Soyuz spacecraft as a “lifeboat.”

Photo: courtesy of NASA

Photo: courtesy of NASA

Q2. Can we protect the ISS and other satellites?

Whipple shields are used on the ISS. Most of the ISS shielding protect against particles up to about 3 mm in size. A Whipple shield is a multi-layered shield designed so that the first layer breaks up the impacting object; the second layer breaks those fragments into smaller objects, and so on until the fragments are too small to penetrate the last layer. The difficulty is that to shield against bigger objects, the shields must be bigger and eventually they become too heavy to launch and must be spaced too far apart. That is one of the reasons that the shields on the ISS do not protect it from everything that cannot be tracked.


Q3. What is the risk to people on the ground?

The overall risk to an individual from reentering debris is extremely small compared to the other hazards we face daily. It is estimated to be less than a one in one trillion chance that a particular person will be injured by falling space debris. By comparison, the risk of being hit by lightning is one in 1.4 million and the risk that someone in the U.S. will be killed in a hurricane is about one in six million.



Q4.  “Zero” gravity – are the astronauts constantly spinning in space if they are not tethered or how do they control their direction?

Something would need to cause the astronaut to spin in the first place. After which, an untethered astronaut will continue to spin at the rate they started with until acted upon by an external torque— such as a tether, jet pack, grabbing onto something or even throwing or getting hit by something. An astronaut will be unable to change course, but similar to an ice skater, will be able to  slow down or speed up the spin by sticking out or pulling in arms or legs. The astronauts would not be able to stop the spin on their own, though.

Q5. Is there a sunrise and sunset in space?

The sun will rise and set whenever your orbit takes you behind the Earth opposite the sun.  There will be a sunrise on every orbit unless you are in one of the few orbits that are in full sun all or most of the time. These orbits are generally high orbits or some polar orbits.  A sunrise or sunset in low orbit happens much quicker than on the ground, because you are moving much faster, and there are no clouds around you to reflect the sun.

Q6. 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 can analyze them collectively as a “cloud.” Space debris clouds are not at all like clouds in the sky, or a cloud of ink in a beaker of water. 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 computer graphics, 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.

Q7. Can you see space debris coming at you?

It is very unlikely that you would see space debris.  Relative to a person in orbit, space debris is moving about ten times faster than a bullet, and the vast majority of debris is as small as or smaller than a bullet. No one can see a bullet coming, let alone an object moving ten times faster.

Q8. What is an on-orbit collision like?

It looks more like an explosion of each object, as if they passed through each other and exploded on the other side.  A hyper-velocity collision like those at orbital speed doesn’t behave like collisions that we are used to seeing. The objects are moving so fast that they travel through each other faster than the shock waves can travel. 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.

Q9. Do breakups look like the movies?

For dramatic purposes, movies, TV, and commercials tend to show space breakups at a much slower speed than they would happen at in real life. A breakup in space, especially a collision, can involve a lot of energy, and the pieces are flung away at extremely high speeds. Since there is no air to slow the pieces down the fragments would all fly away from one another and rapidly disappear from view. For many breakups, a softball-sized fragment would fly the length of the space station (a little less than a football field) in less than half a second. If you were watching it from nearby, you would see a flash, and the object that broke up would just disappear and be gone. It would be very unlikely for you to see pieces drifting away. Similarly, a low orbit space collision is unlikely to look much like a car crash — the speeds are much too high. The collisions would look like explosions to a nearby observer.

Q10. 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, whether or not we launch more space missions.  However, these cascades take place over decades and centuries, with a large collision happening currently only about once every five to ten years. So while the “Kessler Syndrome” — a scenario where space debris collisions cause a domino-effect resulting in an overwhelming amount of debris — is quite real mathematically, it is a slow-motion disaster that we have time to affect. If we start limiting the growth of space debris right now, we can prevent it from being an unmanageable problem.

Q11. Will space debris 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. And 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.

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