Discover Satellites, Space Probes, and the Tools That Explore the Universe

When you look up at the night sky, you might not realize that hundreds of human-made objects are orbiting Earth right now. A satellite is any object that orbits a planet or other body in space. Satellites can be natural, like Earth's Moon, or artificial, meaning built and launched by humans.

A space probe is different from a satellite. While satellites typically orbit one body, space probes travel far into the solar system or beyond to explore distant worlds. Famous probes like Voyager 1, launched by NASA in 1977, have traveled so far that they have left our solar system entirely, making Voyager 1 the first human-made object to enter interstellar space.

You can connect what you know about Celestial Bodies, Planets, moons, asteroids to understand why scientists want to explore these objects up close using probes and satellites.

Not all satellites do the same job. You will find it helpful to know the four main types of satellites and what each one does.

• Weather satellites orbit Earth and use sensors to monitor clouds, storms, temperature, and atmospheric conditions to help forecasters predict weather.
• GPS (navigation) satellites send precise timed radio signals to receivers on the ground, allowing your phone or device to calculate its exact location.
• Communication satellites act like relay stations in space, bouncing phone calls, internet data, and television signals between locations around the world.
• Telescope satellites, like the Hubble Space Telescope, orbit above Earth's atmosphere to capture much clearer images of distant galaxies and nebulae than ground-based telescopes can.

Understanding how these satellites work connects to what you have learned about Light Properties, Reflection, refraction, color, since telescopes and sensors rely on collecting and analyzing light.

You might wonder why satellites do not fall back to Earth. Satellites move at very high speeds so that as gravity pulls them downward, Earth's curved surface falls away at the same rate, keeping them in a continuous orbit. An orbit is the curved path one object follows as it travels around another object due to gravity.

A special type of orbit is called a geostationary orbit. A geostationary satellite orbits at the same speed Earth rotates, so it appears to hover over the exact same spot on Earth's surface at all times. This makes geostationary satellites ideal for weather monitoring and communication. You can explore how gravity shapes these paths further in Gravity Effects, Gravitational forces in space and Planetary Motion, Orbits and rotations.

Space probes are robotic spacecraft sent far beyond Earth's orbit to explore planets, moons, asteroids, and other objects. Because they are uncrewed, probes can survive conditions that would be dangerous or deadly for human astronauts, and they cost far less than crewed missions.

Here are some important missions you should know:

• Voyager 1 and 2 Launched in 1977, these probes used a technique called gravity assist (also called a gravitational slingshot) to fly close to planets and use their gravity to gain speed and change direction, visiting multiple outer planets before heading into deep space.
• Curiosity rover A car-sized rover that landed in Gale Crater on Mars in 2012 and has been studying Martian rocks, soil, and climate ever since.
• Perseverance rover Launched in 2020, its main goal is to search for signs of ancient microbial life and collect rock samples from Mars.
• New Horizons Performed a flyby mission of Pluto in July 2015, capturing the first detailed close-up images of Pluto's surface.
• Cassini Explored Saturn and its moons, especially Titan, which has a thick atmosphere and lakes of liquid methane.
• James Webb Space Telescope (JWST) Launched in 2021, it detects infrared light to observe the earliest galaxies and stars formed after the Big Bang, seeing much older and more distant objects than Hubble can.

A flyby mission is one where a probe passes close to a planet or other body to collect data and images without slowing down to enter orbit or land. This is different from an orbital mission, where a probe circles a body, or a lander mission, where a probe touches down on the surface.

You can learn more about current discoveries in Space Research, Current space exploration.

Space probes carry special scientific instruments to gather data. You should know what each instrument does:

• A magnetometer detects and records the strength and direction of magnetic fields around planets and in space.
• A spectrometer splits light into its component wavelengths so scientists can identify the chemical makeup of a planet's atmosphere by analyzing which wavelengths are absorbed.

These instruments connect to your understanding of Energy Conversion, Transformations between forms, since probes convert solar energy into electrical power using solar panels to run their instruments. Some deep-space probes use nuclear power sources called RTGs when they travel too far from the Sun for solar panels to work effectively.

Scientists communicate with distant probes using radio waves transmitted through NASA's Deep Space Network, a system of giant dish antennas located around the world. Even at the speed of radio waves, signals can take hours to reach probes like Voyager.

Remote sensing lets scientists study Earth from above without landing on it. Remote sensing satellites use cameras and sensors to observe Earth's land, water, vegetation, ice, and atmosphere from space, helping scientists track environmental changes.

Deep space refers to the distant regions of space far beyond Earth and the Moon, typically beyond about 2,000 kilometers from Earth's surface. Probes like Voyager 1 and 2 now travel through deep space in interstellar space, the region between stars.

The International Space Station (ISS) is a large orbiting laboratory where astronauts from many countries conduct experiments in biology, physics, and medicine in the unique microgravity environment of space. International cooperation in space is essential because missions are so costly and complex that sharing resources and expertise helps everyone achieve goals no single nation could accomplish alone.

Satellite: A satellite is any object that orbits a planet or other body in space. You can find both natural satellites, like Earth's Moon, and artificial satellites built by humans, like weather or GPS satellites.

Space Probe: A space probe is a robotic spacecraft sent far beyond Earth's orbit to explore distant planets, moons, asteroids, and other regions of the solar system and beyond. Probes are uncrewed, meaning no astronauts travel on them.

Orbit: An orbit is the curved path one object follows as it travels around another larger object due to the force of gravity. For example, Earth orbits the Sun, and the Moon orbits Earth.

Remote Sensing: Remote sensing is the method of collecting data and studying Earth's surface, oceans, and environment from space without physically landing on it. Remote sensing satellites use cameras and sensors to observe changes on Earth from above.

Deep Space: Deep space refers to the distant regions of space far beyond Earth and the Moon. Probes like Voyager 1 and 2 explore deep space and have even traveled into interstellar space beyond our solar system.

Geostationary Orbit: A geostationary orbit is a special orbit where a satellite moves at the same speed Earth rotates, so it appears to stay over the same spot on Earth's surface at all times. This is useful for weather monitoring and communication satellites.

Gravity Assist: Gravity assist, also called a gravitational slingshot, is a technique where a spacecraft flies close to a planet and uses its gravitational pull to gain speed and change direction, saving fuel and travel time. The Voyager probes used this technique to visit multiple outer planets.

Flyby Mission: A flyby mission is a space mission where a probe passes close to a planet or other body to collect data and images without slowing down to enter orbit or land on the surface.

Magnetometer: A magnetometer is a scientific instrument on a space probe that detects and records the strength and direction of magnetic fields around planets and in space.

Spectrometer: A spectrometer is an instrument that splits light into its component wavelengths. Scientists use spectrometers to identify the chemical makeup of a planet's atmosphere by analyzing which wavelengths of light are absorbed by different gases.

Natural Satellite: A natural satellite is an object that formed naturally and orbits a larger body in space without being built by humans. Earth's Moon is the best example of a natural satellite.

Artificial Satellite: An artificial satellite is a human-made object launched into orbit around Earth or another body. Examples include weather satellites, GPS satellites, and the Hubble Space Telescope.

Microgravity: Microgravity is the condition in space where objects and people experience very little gravitational force, making them appear to float. The ISS uses this environment for scientific experiments.

You can strengthen your understanding of Space Technology, Exploration and observation tools by thinking about how each type of satellite serves a different purpose and how space probes are designed for specific missions.

Try these thinking challenges:

• Can you explain why scientists send robotic probes to Mars instead of astronauts right now?
• Can you describe the difference between a flyby mission and an orbital mission?
• Can you explain how a geostationary satellite is different from other satellites?
• Can you name at least three types of satellites and describe what each one does?

Connecting your knowledge of Data Collection, Quantitative and qualitative data will help you understand how probes gather and send scientific measurements back to Earth. You can also apply Scientific Models, Creating and using models to understand how scientists use data from probes to build models of distant planets.

Before exploring this topic, you should be comfortable with several foundational ideas. Your knowledge of Celestial Bodies, Planets, moons, asteroids and Orbital Patterns, Planet and moon movements gives you the foundation to understand why probes are sent to specific destinations and how satellites maintain their orbits.

Understanding Systems Thinking, Interconnected components helps you see how satellites, ground stations, and receivers all work together as a system. Your knowledge of Design Cycle, Problem-solving methodology connects to how engineers design and test spacecraft for specific missions.

This topic connects to many other important areas of science and engineering. Here is how each related topic links to what you are learning:

• Space Research, Current space exploration You will discover the latest missions and discoveries that build directly on the tools and probes you have studied here.
• Gravity Effects, Gravitational forces in space You will understand how gravity keeps satellites in orbit and how probes use gravity assist to travel faster through the solar system.
• Planetary Motion, Orbits and rotations You will see how the orbital paths of planets relate to the paths satellites and probes follow.
• Scientific Models, Creating and testing predictive models You will learn how data collected by probes and satellites is used to build and test scientific models of space.
• Design Process, Engineering methodology You will explore how engineers use a structured design process to plan and build satellites and space probes.
• Data Collection, Precision and accuracy in measurements You will understand why precise measurements from satellite sensors and probe instruments are critical for accurate scientific conclusions.
• Testing and Evaluation, Performance assessment You will see how scientists test and evaluate the performance of satellites and probes before and during missions.
• Energy Conversion, Transformation between forms You will connect how solar panels on satellites convert sunlight into electrical energy to power instruments and systems.
• Universe Structure, Galaxies and solar systems This is where your learning leads next, as you use what you know about exploration tools to understand the larger structure of the universe.
• Space Technology, Satellites and exploration You will continue building your knowledge of how satellites and exploration technology are developed and used in advanced missions.