### Assignments:

Unfinished Assignment Study Questions for Lesson 65

### Lesson Objectives:

- Current spacecraft
- Challenges of interstellar travel
- Starship design

We have had five spacecraft leave our solar system. They are Pioneer 10, Pioneer 11, Voyager 1, Voyager 2 and New Horizons. Even though they are traveling through space at over 10,000 miles/hour, it would still take 100,000 years to reach the nearest star system - Alpha Centauri.

We would need to build starships that travel close to the speed of light to reach any other planet or star, but high speed interstellar travel would require vast amounts of energy. For example, a ship the size of Star Trek's Enterprise would require 2,000 times the amount of energy used by the entire Earth's population in a single year just to accelerate to half the speed of light.

We would also need to protect crew members from instant death because travel at such high speeds would cause ordinary atoms to hit the ship with the force of high-energy cosmic rays.

In addition, there is the time difference. According to Einstein's theory of relativity, time will run more slowly aboard a spaceship than on Earth. For example, if a space crew spent two years traveling close to the speed of light to the star Vega, 50 years would have passed on Earth. When the crew returned, life would be different; their skills would probably be obsolete and many of the people they knew would have passed away.

Building a starship that would be able to travel fast enough and survive the impacts of collisions is no easy task. Scientists and artists have been envisioning various ways to make this happen. One example is Project Orion, a concept for accelerating a starship with repeated detonations of hydrogen bombs. This would propel the starship forward and make it possible to reach Alpha Centuri within 50 years. However, this would be extremely expensive and currently, international treaties ban nuclear detonations in space.

Another idea is the interstellar ramjet, a massive spaceship that would collect interstellar hydrogen with a gigantic scoop using the collected gas as fuel for its nuclear engines. The problem is that since interstellar gas is so thin, it would take a scoop the size of a planet to collect enough hydrogen to make this idea work.

While high speed interstellar travel has not yet occurred and is beyond the capabilities of our current technology, there are people studying and experimenting with ways to make it possible some day.

In 1950, Nobel prize physicist Enrico Fermi asked, "So where is everybody?" in response to questions about alien life in the universe. He discussed the question further and proposed three possibilities, which came to be known as Fermi's paradox.

The 3 categories are:
- we are alone
- civilizations are common, but no one has colonized the galaxy
- there is a galactic civilization, but its existence has yet to be revealed

Each category has its own questions and concerns. Alien life has yet to be discovered or disproven.