Interstellar travel facts for kids

Interstellar space travel is all about traveling between different stars. It's a huge challenge, much harder than traveling within our own Solar System. Even though starships are common in science fiction stories, we don't have the right technology for real interstellar travel yet. However, scientists are studying ideas like using a special probe with an ion engine, powered by a laser from a base station.

With enough time and smart engineering, both unmanned (robot) probes and sleeper ships (where people sleep for a long time) might be possible for interstellar travel. But these ideas come with big technology and money problems. Space agencies like NASA and the ESA have been looking into these topics for years, coming up with some theoretical plans.

It seems that "generation ships" (where many generations live and die on the ship) would need too much energy. But heavily shielded sleeper ships might be more practical.

Challenges of Traveling to Other Stars

The biggest problem for interstellar travel is the incredibly long distances. This means we need either super-fast speeds or journeys that take a very, very long time. With most realistic ways to power a spacecraft, a trip could take anywhere from decades to thousands of years.

Because of these long trips, an interstellar ship would face many dangers. These include the empty vacuum of space, harmful radiation, weightlessness, and tiny bits of space dust called micrometeoroids. If a vehicle travels very fast, even tiny particles could cause damage unless the ship is heavily protected. But adding a lot of shielding makes the ship much heavier, which makes it even harder to move.

Space Radiation

Cosmic rays are a big concern because there's no protection from them outside of Earth's atmosphere and magnetic field. Some of these rays are incredibly powerful, much stronger than anything we can create on Earth. Even though most cosmic rays aren't that strong, they still pose a risk to spacecraft and any living things inside.

Power Needed for Star Travel

A major challenge is finding enough energy to travel at a reasonable speed. To get a ship moving, you need a lot of kinetic energy. If the ship also needs to slow down when it arrives at its destination, it will need at least double the energy.

To send a manned ship on a round trip to the nearest star in just a few decades, it would need to go thousands of times faster than today's spacecraft. Because the energy needed goes up with the square of the speed, this means millions of times more energy is required. For example, accelerating one ton to one-tenth the speed of light would need a huge amount of energy – more than 125 billion kilowatt-hours!

This energy source would have to be carried on the ship, because solar panels don't work far from the Sun or other stars. The sheer amount of energy needed might make interstellar travel impossible. One engineer even said that a trip to Alpha Centauri would need "At least 100 times the total energy output of the entire world [in a given year]".

Space Dust and Gas

The space between stars, called the interstellar medium, contains tiny bits of interstellar dust and gas. At very high speeds, these small particles could cause a lot of damage to a spacecraft. Larger objects are rare, but they would be even more destructive.

How Long Would it Take?

The very long travel times make it hard to plan missions with people on board. The basic rules of space-time also create challenges. Plus, it would be hard to explain why we should spend so much money on such long trips.

Some people argue that if an interstellar mission can't be finished within 50 years, we shouldn't start it. Instead, we should use our resources to design a much better way to travel. This is because a slow spacecraft would likely be passed by a newer mission sent later with more advanced engines.

On the other hand, some believe we should start a mission now. They think that the problems not related to propulsion (like keeping people alive) might be harder to solve than building faster engines.

Traveling between galaxies (called Intergalactic travel) is even harder. The distances are about a million times greater than between stars!

Waiting for Better Tech

Scientists have looked at how waiting for new technology could affect travel times. They found that there's a best time to leave for a destination. If you leave too early, a later mission with better technology might pass you. If you leave too late, you'll never catch up to those who left at the best time.

For example, a journey to Barnard's star, which is six light years away, might take 1,110 years from 2007, even with improvements in travel speed.

Distances to Other Stars

Astronomical distances are often measured by how long it takes a beam of light to travel between two points. This is called a light-year. Light in empty space travels super fast – about 300,000 kilometers (186,000 miles) every second.

The Earth to the Moon is 1.3 light-seconds away. Our current spacecraft can cover this distance in about eight hours. This means light travels about thirty thousand times faster than our fastest ships! The distance to other planets in our Solar System can range from a few light-minutes to about four light-hours. For a typical robot spacecraft, these trips take from a few months to over ten years.

The distance to other stars is much, much greater. If the distance from Earth to the Sun was shrunk down to just one meter, then the distance to Alpha Centauri A would still be 271 kilometers (about 169 miles)!

The closest known star to our Sun is Proxima Centauri, which is 4.23 light-years away. Our fastest outward-bound spacecraft, Voyager 1, has only covered 1/600th of a light-year in 30 years. It's moving at 1/18,000th the speed of light. At this speed, a trip to Proxima Centauri would take 72,000 years! Of course, Voyager 1 wasn't built to be a fast starship. Newer technology could do much better. We might reduce travel time to a few thousand years using solar sails, or even a century or less using nuclear pulse propulsion.

Special relativity suggests a way to make the trip feel shorter for the travelers. If a starship could go almost as fast as light, time dilation would make the journey seem much shorter for those on board. However, many years would still pass for the people back on Earth. When the travelers returned, they would find that much more time had passed on Earth than for them (this is called the twin paradox).

Many problems would be solved if "wormholes" existed. These are theoretical shortcuts through space-time. General relativity doesn't say they are impossible, but we don't know if they really exist.

Talking Across Space

The "round-trip delay time" is how long it takes for a signal from a probe to reach Earth, and then for Earth's instructions to reach the probe. Since information can't travel faster than the speed of light, for Voyager 1, this delay is about 32 hours. Near Proxima Centauri, it would be 8 years! This means that faster actions would have to be programmed into the ship to happen automatically. If there are people on board, they can react right away to what they see. But the long delay still makes them very far away and very isolated from Earth in terms of communication. Another challenge is having enough energy to send signals reliably over such vast distances. Gas and particles in space can also weaken signals.

Missions with People

Any spacecraft carrying humans would need to be much bigger than a robot probe. The incredibly long travel times would also require a complex life support system to keep people alive. Because of these difficulties, the first missions to other stars will probably not carry any living things.

Best Stars to Visit

There are 59 known star systems within 20 light-years of our Sun, with 81 visible stars. Some of these could be good targets for interstellar missions. However, the dangers of radiation would likely prevent any living beings from going on an expedition to a star like Sirius. It's hard to imagine any manned expeditions at all, given how long the journeys would take.

Perhaps the most likely time for interstellar travel would be when another star passes through our Oort cloud (a distant cloud of icy objects around our Solar System). We would get about 10,000 years' warning, which would give us time to plan a mission in detail. Scholz's star was the last one to come through.

Today's astronomy tools, and those coming soon, can find planets around these stars. This makes them even more interesting to explore!

Images for kids

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  A Bussard ramjet, one idea for how to power a spacecraft.

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  This chart shows how far a ship could go if it could accelerate like Earth's gravity.

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  This drawing shows how a light-sail might slow down when it reaches a star system.

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  An artist's idea of a "Wormhole Induction Propelled Spacecraft."

See also

In Spanish: Viaje interestelar para niños