Below, Trisha Muro shares five key insights from her new book, It’s (Just) Rocket Science: Exploring Physics Through Spaceflight Missions.
Trisha is a former high school physics teacher. Her passion for getting people excited about physics led her to write for Science News Explores, OpenMind Magazine, and NSF NOIRLab.
What’s the big idea?
Physics becomes most powerful and exciting when we stop treating it like a list of equations and start seeing it as a story about how humans explore the universe. Through spaceflight missions, we can understand abstract ideas like gravity, energy, waves, and motion in ways that feel personal, surprising, and full of wonder.
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1. Gravity.
There are only four fundamental forces in all of physics. Gravity is one of them. But get this: Gravity is the weakest of all the forces, and there is nowhere in the universe we can go to escape it—its reach is infinite. Gravity determines that the true shape of an orbit is an ellipse (not a circle!), and astronomers can use that basic geometric concept as the underpinning of our most successful technique to find exoplanets. (Exoplanets are planets that orbit stars other than our Sun.)
Isaac Newton took descriptions of gravity to the next level by quantifying how it does what it does. He put numbers and relationships into a relatively straightforward equation. Newton’s law of universal gravitation is extremely powerful, and it can explain almost everything we see—almost.
For extreme situations, and really for a more complete explanation of how gravity works, we need relativity and Albert Einstein. General relativity gives us a beautiful, elegant framework for how to see gravity’s hand in places like black holes and gravitational lenses. But relativity also offers a cogent answer to the “why?” behind Newton’s equations.
2. How a rocket beats gravity to get into orbit.
A rocket is not really “beating” gravity and it’s certainly not “escaping” gravity—those are two common misunderstandings. Instead, a rocket harnesses the incredible power of combustion to outmatch gravity by just enough that the rocket can get itself out of the most powerful part of a gravity well.
The key takeaway here is to see how Newton’s laws fit together with his mathematical description of gravity to explain orbits. An orbit really starts as a balance. If you think about throwing a ball, and throwing it harder and harder so that it flies farther and farther away from you, you can imagine taking that simple idea to an extreme and asking what Newton did: what if you could throw that ball so fast that its path of falling actually matches the curvature of Earth itself?
“An orbit really starts as a balance.”
Fun fact: astronauts in orbit are not weightless because there’s no gravity in space. Gravity is everywhere. The reason astronauts experience weightlessness is because they’re constantly falling, just like the ball that you try to throw harder and harder. But they’re falling around Earth. Being in orbit around Earth is an exquisite balance between the forces at play and the motion energy of your spacecraft.
3. Energy, momentum, and rotation.
If you study physics, you’ll often see examples of applying clever techniques to solve problems, and that’s how I see the unifying principles here. Our summary here is that energy, momentum, and rotation (or angular momentum) offer us jaw-droppingly cool ways to see the physics of spaceflight more clearly.
Momentum comes into play especially with collisions, and it’s the key to one of my favorite space missions of all time: DART. The DART mission was just a few years ago, when we intentionally smashed a small spacecraft into an asteroid as we attempted to change its orbit.
Rotation (and angular momentum) is a tricky piece of the puzzle to add, but it’s essential. Everything we launch from Earth carries with it the natural rotation of our planet, but that includes not only Earth’s rotation around its axis, but also its orbital revolution around the Sun. This adds up to a crazy amount of spinning motion! And if you’ve ever heard the term “gravitational slingshot,” whether in descriptions of real spaceflight missions or in science fiction stories, this is where it’s at. Sending something on a gravitational slingshot around another planet gives your spacecraft an enormous boost in speed and usually an essential pivot in direction for no additional engine power. As a timely bonus, this concept was key to Artemis II’s free-return trajectory around the Moon.
4. Waves.
Why are sound waves so different from light waves? Why does it take so long for radio transmissions to go back and forth from a spacecraft to controllers on Earth, when those transmissions are traveling at the speed of light? Humans are only able to perceive a tiny fraction of the electromagnetic spectrum. Beyond visible light, there are ultraviolet, X-rays, and gamma rays on the more energetic side of things, and infrared, microwaves, and radio waves on the less energetic side. Waves can interact with one another and with physical objects, too.
“Humans are only able to perceive a tiny fraction of the electromagnetic spectrum.”
Astronomers have learned to build telescopes that can collect and focus distant light from stars and galaxies, building them bigger and bigger to see celestial objects that are fainter and farther away. But we’ve also built telescopes that can collect and focus every other type of light, from radio waves to gamma rays. Some of those telescopes operate just fine here on Earth, while others have to be in space. And from each different kind of telescope, we learn different facets of information about the celestial bodies we look at.
5. Frontiers.
Bigger and bigger rockets need more and more fuel, which makes it harder and harder to launch. How might we learn to travel in space in different ways?
One idea is solar sails, which are designed to harness the momentum of photons to propel a spacecraft. Yes, you heard that right: photons, which have no mass, still have momentum. Solar sails are no longer science fiction. In recent years, two highly successful missions have begun demonstrating the possibilities.
In a different strategy, what about using a very, very small engine over a very, very long time, like when a long-distance spacecraft is in its cruise phase to one of the outer planets? Would you believe that a force that’s equivalent to the feel of a slice of bread in your hand can actually propel a spacecraft? Just like the power of compound interest on a bank account, a tiny force over a very long time can yield a truly significant difference.
And, finally, we can’t talk about spaceflight without addressing the issue of radiation. This last mission takes us literally to the Sun itself, with an incredibly innovative spacecraft that sums it all up: elliptical orbits, gravitational slingshots, energy and forces, and gravity, and the cherry on top is how to effectively and efficiently protect a spacecraft from the intense radiation of the Sun. Wow. Talk about turning assumptions upside-down and inside-out to get creative!
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