Challenges of Space Travel (SQA National 5 Physics): Revision Note

Challenges of space travel

• Space travel poses several challenges, including:

  • travelling large distances by using as little fuel as possible

  • manoeuvring a spacecraft in a zero-friction environment

  • maintaining sufficient energy to operate life support systems

Ion propulsion

• Ion drives are an advanced propulsion method that uses electric fields to accelerate charged particles (ions)

• This produces a small, unbalanced force (thrust) that acts over an extended period of time

• How it works:

  • Ions are produced by bombarding a gas or plasma with electrons

  • The ions are accelerated between positively and negatively charged metal grids

  • The ions are ejected backwards at very high speed, creating forward thrust (from Newton’s third law)

  • Electrons are released to neutralise the exhaust, preventing a build-up of charge

• Benefits:

  • Very high fuel efficiency, as only a small mass of propellant is required

  • Enables spacecraft to travel very long distances

• Limitations:

  • Can only be used in the vacuum of space, as it is not powerful enough for launching from Earth

An ion drive used for space travel

Gravitational slingshot

• A gravitational slingshot, or gravity assist, is a manoeuvre where a spacecraft uses the gravitational pull of a fast-moving planet, moon, or asteroid to change its speed or direction

• How it works:

  • As the spacecraft approaches the planet’s gravitational field, it accelerates towards it

  • As it passes the planet (in the direction of its orbit), the spacecraft is flung forward, gaining kinetic energy and changing direction

  • The planet loses the same amount of kinetic energy, but due to its massive size, this has no noticeable effect on its speed

• Benefits:

  • Saves fuel and time, reducing the need for on-board propulsion

  • Enables missions to reach the outer planets of the solar system

Using gravity assist to reach the outer solar system

Manoeuvring in space

• In space, there is no air resistance or friction, which means:

  • spacecraft will travel at constant velocity (Newton’s first law), even when the engines are switched off

  • an unbalanced force must be applied to change the spacecraft's speed or direction

• This makes manoeuvring in space very difficult

• For example, if a spacecraft wants to dock with the ISS

  • It must slow down or change direction very carefully

  • This requires using an ion drive to produce small forces in the opposite direction to its motion

• Astronauts are also fitted with propulsion devices for manoeuvring during spacewalks

Photo credit: NASA (opens in a new tab)

Supplying energy in space

• Spacecraft require a continuous supply of energy to power:

  • life support systems

  • instruments that collect information in space

  • communication systems to send information back to Earth

• This energy can be obtained using solar cells, which use energy from the Sun to generate electricity

• The light available to a solar cell depends on

  • the distance from the Sun

  • the area of the solar cell

• Individual solar cells can be combined to create solar panels and arrays, increasing the total area which can receive light

  • The further a spacecraft moves from the Sun, the greater the area of cells required to generate the same power

• Benefits:

  • Solar cells can generate electricity continuously in space

  • For spacecraft which are close to the Sun (e.g. satellites orbiting the Earth), the power generated by solar cells is sufficient for powering life support systems

• Limitations:

  • Solar arrays with very large areas are required to travel to distant parts of the solar system

  • The furthest a solar-powered spacecraft has gotten today is the orbit of Jupiter (NASA's Juno spacecraft (opens in a new tab))

  • It may not be feasible for solar-powered spacecraft to travel beyond Jupiter without further developments in solar technology

Variation of solar cell area with distance from the Sun