Fly Once, or Fly Again
Module 1 covered the physics every rocket obeys. This module is about the engineering and economic choices built on top of that physics — expendable vs. reusable, solid vs. liquid, and why a launch site's location is never arbitrary.
Expendable vs. Reusable
For most of the Space Age, every launch vehicle flew exactly once. That's no longer the only option.
Expendable (ELV)
Fly Once
Every stage is discarded after use — burned up, dropped in the ocean, or left in orbit. Simpler to design and doesn't need extra fuel margin for a landing, but a new vehicle has to be built for every single launch.
- No landing hardware or fuel margin needed
- Full manufacturing cost paid every flight
- The default for most of spaceflight history
Reusable
Fly Again
At least one stage — usually the booster — returns intact and flies again. Cuts the per-launch manufacturing cost, but the vehicle has to carry extra propellant and hardware for the return, which eats into how much payload it can lift.
- Reserves propellant and mass for landing
- Spreads manufacturing cost across many flights
- Proven at scale only in the last decade
Falcon 9
SpaceX's Falcon 9 is the reference case for reusability — not the only reusable vehicle, but the one that proved the economics at scale.
Powered Descent
After separating from the upper stage, the first-stage booster reignites its engines to slow itself, first for reentry and again just before touchdown — a propulsive landing rather than a parachute descent.
Grid Fins & Legs
Deployable grid fins steer the booster during descent through the atmosphere; deployable landing legs absorb the touchdown, whether on a ground pad or a droneship at sea.
Economics of Reuse
The first successful booster landing flew in December 2015; the first reflight of a recovered booster followed in 2017. Reflying hardware instead of rebuilding it from scratch is the whole cost argument for reusability.
Solid vs. Liquid
Module 1 covered specific impulse; this is the other half of the trade-off — how the propellant is handled, not just how efficiently it burns.
Solid
Simple, Committed
Fuel and oxidizer are pre-mixed into a solid grain inside the motor casing. Storable for years, mechanically simple, and ready on short notice — but once lit, it burns until it's gone. No throttling, no shutoff.
- Few moving parts, high reliability
- Cannot be throttled or stopped
- Common on boosters and strap-ons
Liquid
Complex, Controllable
Fuel and oxidizer are stored separately and pumped into a combustion chamber. Far more mechanically complex — pumps, valves, plumbing — but throttleable, and can be shut down and, in some designs, relit.
- Throttleable and restartable
- Required for propulsive landing (Falcon 9)
- More complex, more that can fail
Many vehicles use both: solid strap-on boosters for extra thrust at liftoff, paired with a liquid-fueled core that keeps running — and can be throttled — for the rest of the ascent.
Why Location Matters
Latitude
Earth's surface moves fastest near the equator due to its rotation. Launching eastward from a low latitude gives a "free" velocity boost toward orbit — which is why equatorial and near-equatorial sites are prized for high-inclination missions.
Safety Corridor
Rockets can fail. Launch trajectories are chosen so that spent stages and any debris from a failure fall over open ocean or unpopulated land, not over cities — which is why so many launch sites sit on an eastern coastline.
Range & Infrastructure
A launch site needs tracking radar, telemetry stations, and recovery assets along the flight path — plus roads, power, and a workforce. Existing government ranges accumulated this infrastructure over decades, which is a large part of why new commercial pads tend to cluster near them rather than starting from bare ground.
Cape Canaveral / Kennedy Space Center
USA — 28.5°N
East coast of Florida, launching out over the Atlantic. The busiest U.S. launch range, home to NASA and multiple commercial operators.
Baikonur Cosmodrome
Kazakhstan — 45.9°N
Russia's primary crewed launch site (leased from Kazakhstan), higher latitude than most — a legacy of Cold War-era geography and secrecy, not orbital efficiency.
Guiana Space Centre
Kourou, French Guiana — 5.2°N
ESA's spaceport, close to the equator — among the best-positioned major sites for the latitude boost described above.
Vandenberg Space Force Base
USA — 34.7°N
West coast of California, launching south over the Pacific — the preferred U.S. site for polar and sun-synchronous orbits, where the equatorial boost doesn't apply.
Tanegashima Space Center
Japan — 30.4°N
JAXA's primary launch site, on an island south of Kyushu, launching out over the Pacific. Home to the liquid-fueled H-IIA and H3 rockets — chosen partly for its relatively low latitude by Japanese standards.
Uchinoura Space Center
Japan — 31.25°N
JAXA's older, smaller site on the Kyushu coast, historically tied to Japan's solid-fuel rocket lineage — used for the solid-fueled Epsilon rocket and scientific/sounding-rocket launches rather than Tanegashima's larger liquid-fueled vehicles.
Key Terms
- Expendable Launch Vehicle (ELV)
- A rocket whose stages are used once and discarded — burned up, dropped in the ocean, or left in orbit.
- Reusable Launch Vehicle
- A rocket, usually its booster stage, designed to return intact and fly again — trading some payload capacity for lower cost per flight over time.
- Booster
- The first (largest, lowest) stage of a launch vehicle, responsible for the initial climb and the bulk of the vehicle's mass at liftoff.
- Grid Fins
- Deployable latticed steering surfaces used to control a returning booster's orientation during atmospheric descent.
- Solid Rocket Motor
- An engine burning a pre-mixed solid propellant grain — simple and storable, but not throttleable or stoppable once ignited.
- Liquid Rocket Engine
- An engine burning separately stored liquid fuel and oxidizer, pumped into a combustion chamber — mechanically complex but throttleable and, in some designs, restartable.
- Safety Corridor
- The planned flight path and surrounding exclusion zone chosen so that debris from a launch failure falls over unpopulated ocean or land rather than populated areas.
For This Module
SpaceX public technical fact sheets on Falcon 9 and booster recovery, NASA/FAA launch site and range safety documentation, ESA public materials on the Guiana Space Centre, and JAXA public materials on Tanegashima and Uchinoura Space Centers.
Continue the Sequence
Module 3 goes deeper into orbital mechanics and the space environment than SSA-01's preview.