wright goddard debris talk 6-2-10

8/4/2019 Wright Goddard Debris Talk 6-2-10

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First Annual Goddard Lecture

Goddard School of Science and Technology

Worcester, MA

David WrightCo-Director and Senior Scientist, Global Security Program

Union of Concerned Scientists

June 2, 2010

There are two main points I hope youll take away from this talk:

1) Space is extremely useful, and has become part of our daily lives to an extent that most

people dont realize. Robert Goddard was one of the first people to understand how useful spacecould be, and took some of the first steps toward making it a reality

2) Surprisingly, space is starting to get crowded, and to be able to continue to use it into the

future we need to take care of it

So let me try to explain these points.

When people think about outer space they may think of space exploration, and may picture the

moon landings or the International Space Station.


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But mainly outer space brings to mind vast, empty regions.

Earthrise over the moon

But today the area around the Earth is anything but emptyits getting crowded with satellites.

For one thing, there are nearly 1,000 active satellites currently in orbit around the earth. More

than half of these are owned by United States. In addition, there are more than 2,000 deadsatellites that have, for example, run out of fuel and are no longer active.

Satellites follow orbits around the Earth, and circle the Earth over and over. For satellites in

orbits near the Earth, it takes them about an hour and a half to go around once.

Because there is essentially no air in space to slow it down, once a satellite is in orbit it can

continue to circle the Earth for decades or centuries without needing an engine to keep it going.


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People are sometimes surprised to learn this. But keep in mind that the Moon is a type of satellite

that orbits the Earth, and it doesnt have a rocket engine to keep it going.

How Do We Use Satellites?

The first satellite was put into orbit just over 50 years ago by the Soviet Union. It was calledSputnik. It didnt do very much, but it showed that it was possible to launch something into orbit

around the Earth.

Since then, space has become incredibly useful and satellites have become part of our daily lives,

although people arent always aware of how we use them. Here are some examples:

(1) When you look at a weather map, those pictures came from a weather satellite. Because they

are so high above the Earth, satellites can see large areas of the Earth, which is what you need for

seeing weather patterns.


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The picture below shows a Chinese weather satellite, which operates about 500 miles above theEarth. You can see the main body of the satellite in the mddle with large solar panels on each

side. The solar panels collect sunlight to make the electricity the satellite needs to operate. This

picture shows the size of a medium-sized satellite, which weighs about one ton.

(2) From high up in space, satellites can also be used to take pictures of the Earth. This is whatsome spy satellites do. But there are a lot of other uses, too. I got on Google and was able to get

pictures of Worcester and of the school where we are today (see below), all of which were taken

by satellites.


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This picture was taken by a satellite called Geoeye-1 from a height of about 400 miles. Its

owned by a company in the United States that sells pictures from space. These satellites arebasically big orbiting telescopes that look at the ground rather than at the sky.

Pictures from satellites like these are also used for disaster monitoringto see flood damage, for

exampleand for managing forests and other natural resources.

(3) To drive here this morning I used a GPS navigating system in my car, which Im sure manyof your famililes have as well. The GPS system works by detecting navigation signals sent from

satellites that are more than 10,000 miles up in space.

One thing people dont always realize is that because GPS is a global system, it allows peoplearound the world to synchronize clocks with one another to very high accuracy. This was never

possible before. Having an international time standard turns out to be especially important forinternational businesses that uses computers to transfer money around the world.

(4) The main use of satellites is worldwide communications: nearly two-thirds of all satellites

are used for this purpose.

For example a lot of phone and internet communications are carried around the world by

satellites. Television signals are also sent around the world by satellite. If you watched a soccergame or a TV news broadcast from overseas, that broadcast was likely sent to the U.S. by

satellite. If you have a satellite TV dish at home, the TV signals are sent directly to your housefrom the satellite

You can send TV or phone signals around the world because satellites are so high above the

Earthmost of them orbit at an altitude of more than 20,000 miles. From that height they cansee large parts of the Earth, so they can relay signals from one side of the Earth back to someone

on the other side of the Earth, as shown below.


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These high-altitude communication satellites tend to be very largemuch larger than weathersatellites, as you can see in the picture on the left below. This satellite weighs about six tons.

On the other hand, people are also working to miniaturize satellites. The picture on the right

above shows a cubesat that weighs only a few pounds. A satellite this size cant do much

today, but that will change in the future. Making satellites as light as possible reduces the highcost of launching them into orbit.


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As you can see from these examples, satellites are useful largely because they are so high that

they have a global view of the Earth.

Just how high are satellites? Jets fly at an altitude of 7 to 8 miles. Thats also about the height of

the peak of Mt. Everest. The International Space Station, which is a fairly low-altitude satellite,

is about 25 times higher than thisabout 200 miles up. Most satellites that take pictures of theEarthincluding spy satellitesare 500 to 600 miles up. These are still considered low-

altitude satellites.

Thats because most other satellites are 20 to 40 times higher than this. GPS navigational

satellites are 12,000 miles up, and most communication and TV broadcast satellites orbit some20,000 miles above the Earth. Thats about one-tenth of the way to the moon.

Keeping Space Useful

The point of these examples of how we use space is to show you that satellites have become part

of our daily lives, whether people realize it or not. There are things you can do from space thatyou cant do anywhere else.

So its important to protect the space environment to make sure we can continue to use it in the

future. Because people think of space as big, empty, and far away, this isnt something people

thought much about in the pasteven those people who were launching the satellites.


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But today that part of space around the Earth is starting to get crowded. People are starting to

think more and more about how to keep space as useful as possible.

One important idea is developing international rules on managing traffic in space.

Imagine if there were no air traffic control for airplanes, so that every plane made its owndecision about when and where it was going to take off and land, and what route it was going to

fly. If there were only a few airports, and only a few planes took off and landed every day, thelack of air traffic control probably wouldnt matter. But thats different once you have a lot of

airplanes and busy airports like in Boston. Without rules that all the planes follow and a control

tower that coordinates all the traffic, it would be very dangerous and you would have collisions.

Well, today there is nothing like air traffic control for satellites. Since satellites orbit in many

different directions, as shown in the picture below, their orbits can cross each other. Without

rules and coordination, they can run into each other. With the number of satellites increasing,that is becoming a bigger and bigger problem.

This actually happened for the first time in February 2009 when two satellites collided at very

high speed and destroyed each other. The collision was between a U.S. communication satelliteand a Russian weather satellite that was no longer working. Collisions like this can become more

common in the future as the number of satellites continues to rise.

What this shows is that all the countries that use space need to sit down and agree on a system of

space traffic management and coordination to help avoid problems like this in the future. I hope

this will begin to happen in the near future.


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The Problem of Space Junk

Another important thing countries have to do is stop littering in space. As space becomes more

crowded, space junk is becoming a bigger and bigger problem.

The picture of the Earth to the left above is a NASA drawing that shows all the know

objects in space larger than a couple inches in size. The image on the right is a view from

much farther away. It shows the Earth surrounded by debris in the center, surrounded by

a ring of objects in the GEO belt, and other objects orbiting in between.


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What is space junk, or space debris as it is usually called? Its any object in space that doesnt

have a useful purpose. This includes:

dead satellites that have run out of fuel and dont operate any more old rocket stages that are still drifting in orbit screws, springs, paint chips and other things that have come off of satellites gloves and tools dropped by astronauts on space walks pieces of satellites that have exploded

For a long time, people thought space was so big and empty that you didnt need to worry about

littering space with junk. As a result, today there nearly a million pieces of junk in orbit largerthan a marble.

To understand why space junk is such a problem you have to understand something about thescience behind satellite orbits.

One of the main things I want you to remember from this talk is that to stay in orbit satelliteshave to go very fast. If they dont travel fast enough, gravity will pull them back down to Earth.

To see this, imagine standing on the Earth and throwing a ball (see the pictures below). After you

throw the ball, gravity pulls it down to Earth. If you throw it harder and faster, it goes fartherbefore it gets pulled down to Earth. But what you can see from the pictures is that because the

Earth is curved, if you could throw it fast enough the ball would travel all the way around the

world. And if there wasnt any air to slow it downlike in spaceit would just keep goingaround and around. Thats what a satellite does.


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How fast does a satellite need to travel to do this and stay in orbit? Unbelievably fast. A satellite

needs to go nearly 20,000 miles per hourthats 20 times faster than a bullet! At that speed you

could get from Worcester to Fenway Park in downtown Boston in about 7 seconds.

The fact that satellites travel that fast is important for two reasons:

First, it explains why it is so difficult and expensive to build a rocket to put a satellite in orbit.The rocket not only has to lift the satellite hundreds of miles above the Earth, but it has to

accelerate it so that it is traveling 20 times faster than a bullet.

Thats why a rocket is almost entirely made of rocket fuel. If you look at a picture of a rocket

like the one below, only the very tip is the satellite. The rest of the rocket is the fuel. For

example, to put a one-ton satellite into orbit, a rocket needs about 100 tons of fuel.


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Delta IV rocket launching a satellite

Second, the high speed of objects in orbit explains why junk in space is very dangerous and is

becoming a big problem.

Since they travel 20 times faster than a bullet, even small pieces of debris can damage or destroy

satellites if they smash into them. For example, a few years back a small paint fleck hit the

windshield of the Space Shuttle when it was in space and put a crack in it. This is shown in the

picture below. If it had been a marble-size piece of debris rather than a paint fleck, it would havepunched a hole in the Shuttle, which could have been a disaster.

A marble in orbit around the Earth at 20,000 miles per hour would have as much energy as abowling ball traveling 500 miles per hour. Imagine how much damage that could do if it hit

something.


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There are seven known cases in the past 20 years in which satellites have been hit by debris,

causing various levels of damage. As the number of satellites and the amount of debris increase,this will become more and more of a problem.

If a big enough piece of junk hits a satellite, or if two large pieces of junk hit each other, they

break up and make many more pieces of space junk. The junk then spreads out in a shell aroundthe Earth, making it a global problem that affects everyones satellites.

These pictures show what happens to the space junk created when two satellite collide. Shortly

after the collision, the top picture shows that there will be two small clouds of junk that continue

to orbit. After a few days, these clouds spread out into rings of junk orbiting the Earth. And after

a few years, the debris will spread out in a shell around the Earth.

Remember I told you earlier that once satellites are in orbit, they dont need to be powered to

stay in orbit. For the same reason, space junk can stay in orbit for decades or centuries. So it

accumulates as more is made, and the total amount keeps increasing.

Once junk is in space it is very hard to get it out. So the only real solution is for the countries

using space not to make more, or at least to make as little as possible.


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Over the past 15 years, countries have developed international guidelines to reduce the amount

of space junk that is being made. Thats a step in the right direction, but its not enough. Theinternational community needs to work to make sure everyone obeys those guidelines.

And countries should agree not to develop weapons that destroy each others satellites, since

destroying a single large satellite in orbit can add hundreds of thousands of pieces of junk inorbit.

All these things are doable. The biggest barrier at this point, in my opinion, is getting people to

realize this is a problem that needs to be solved.

Learning about space like you have been here at the Goddard School is absolutely critical in

getting that to happen.

The Role of Robert Goddard

Since Robert Goddard is the reason we are all here today, I wanted to end with what we can learnfrom Goddards life. And in particular about the role individual people can play in changing the

world.

Goddard graduated from high school in 1904, around the same year as the Wright Brothers' first

airplane flights. At a time when most people werent even thinking about airplanes, Goddard was

thinking about rockets and getting into space.

Only 5 years later (1909), he wrote about the possibility of liquid-fueled rockets and began to

think about multi-stage rockets. Both of these are key concepts that are still used today in

rockets.

Goddard not only had a vision of the future and big ideas, but he then turned to the hard work of

taking the first steps to make that vision a reality. And he stuck to it, year after year, even whenhe was ridiculed because people thought his vision was impossible.


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It took nearly 50 years from his 1909 paper to the launch of the worlds first satellite in 1957.

And it took 60 years to land the first person on the moon. But the Saturn rocket the United States

used to get to the moon was a direct outgrowth of the principles Goddard developed.

To see how far the things he put into motion have come, lets compare Goddards early rocketsand the Saturn moon rocket.


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Notice the red rectangle Ive drawn around a part of the Saturn rocket near the bottom of the

picture above. Lets zoom in and look just at that part and compare it to the size of Goddard andhis early rocket.

In 1904, few people could have imagined landing on the moon, or the role that Goddards first

steps would play in bringing about a different future.

I dont know what the world will look like in 20 years. But I know that it will look different in

ways we cant imagine now. And I know that some of you in this room will be part of making

that happen.

So keep in mind that individual people can change the world, and that doing so takes both avision, and a lot of hard work.

Thank you.

A video of this talk is online at http://www.wccatv.com/node/14920

wright goddard debris talk 6-2-10

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