How Rockets and Orbits Work
These modules cover the engineering layer of spaceflight: what the space environment does to hardware, how rockets get a payload up, how orbits work and how satellites do their jobs once they are there.
Modules On This Topic
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Physical Environment and Astrodynamics
Vacuum, radiation, thermal extremes, why orbits don't fall, and the reference frames — LEO, MEO, GEO, Lagrange points. Module 2 of SSA-01.
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Launch Vehicles and Spacecraft
The difference between a launch vehicle and a spacecraft, the three systems every spacecraft needs, and how both vary by mission type. Module 3 of SSA-01.
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Rocket Propulsion Basics
Newton's third law, the rocket equation conceptually, specific impulse, and why staging exists — traced from early rocketry forward. Module 1 of SSA-02.
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How Do Reusable Rockets Work?
How reusable rockets work: Falcon 9's powered landing, the payload trade-off, solid vs. liquid propellant, and why launch site location matters.
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How Do Orbits Work? Kepler's Laws Explained
How orbits work: Kepler's three laws, the three numbers that describe an orbit, the Hohmann transfer between orbits, and how space shapes spacecraft design.
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Applied Satellite Systems
How GPS/GNSS, weather satellites, and telecom satellites actually work end to end — the segments and signal chains behind the everyday uses. Module 4 of SSA-02.
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Frequently Asked Questions
What is the difference between a launch vehicle and a spacecraft?
A launch vehicle's only job is delivering a payload to the right altitude, speed and trajectory, and most of its own mass is discarded or burned along the way. The spacecraft is the payload that does the actual mission after the launch vehicle has separated.
Are orbits circles?
No. Every orbit is an ellipse with the central body at one focus. A circular orbit is the special case where eccentricity is 0.
What is the difference between an expendable and a reusable rocket?
On an expendable launch vehicle every stage is discarded after use, so a new vehicle is built for each launch. A reusable vehicle brings at least one stage back intact to fly again, spreading manufacturing cost across many flights but giving up some payload capacity for landing propellant and hardware.
Is it free, and do I need an account?
Yes. The lessons are free and open to read without an account. There is no accreditation or certificate attached: it is a self-directed curriculum built from primary sources.
How long does it take?
Each module is sized for one sitting, and the module pages estimate 25 to 35 minutes each. All of the modules on this page add up to about 3.1 hours of reading.