Launch Vehicles

Prerequisites: Orbital Mechanics, Rocket Propulsion Feeds problems: cost to orbit, rapid and total reuse

Practitioner

Anatomy first. A typical launcher is a stack: a first stage (or booster) with the big engines and most of the propellant; an upper stage that finishes the job in vacuum; a fairing, the nose shell protecting the payload from wind and heating; and the payload on its adapter at the top. Two stages is the modern sweet spot — each stage exists because of the rocket equation, and each piece of this stack gets dropped the moment it stops earning its mass.

Now the flight, minute by minute, because the choreography is the subject:

1. Liftoff. Thrust must exceed weight — typically by 20–40%. Too little margin and you waste propellant hovering; too much and you’ve built engine you didn’t need.
2. The turn begins almost at once. Within seconds the vehicle tips over and starts trading vertical for horizontal — remember, orbit is sideways speed, and altitude is just the errand you run to get above the air. From here the rocket flies a gravity turn, letting gravity swing the nose over gradually so it never fights its own velocity.
3. Max-q, ~1 minute in. Maximum aerodynamic pressure: the vehicle is fast but the air is still thick. Engines throttle down briefly to keep the structure inside its limits, then back up as the air thins.
4. MECO and staging, ~2–3 minutes. Main engine cutoff; the empty first stage separates and the upper stage lights. On a reusable vehicle the booster now begins its own mission — flip, braking burns, landing — covered in Reentry & Reusability.
5. Fairing jettison, ~3–4 minutes. Above ~110 km the air can no longer hurt the payload, so the shell is dead weight — off it comes.
6. Orbital insertion, ~8–10 minutes. The upper stage burns until the target velocity is hit, often coasting and relighting to shape the final orbit before releasing the payload.

The whole climb costs about 9.4 km/s of delta-v to deliver 7.8 km/s of orbital speed — the difference is the ~1.5 km/s tax of fighting gravity during ascent plus a few hundred m/s of drag. Trajectory design is the art of minimizing that tax.

Geography is destiny. A launch site’s latitude sets the minimum inclination you can reach directly, and launching eastward collects the Earth’s rotation as a free tip (~460 m/s at the equator) — which is why pads cluster on east-facing coasts, and why equatorial sites are prized for GEO missions. Launch windows follow from the same geometry: your target orbital plane sweeps over the pad only briefly, so rendezvous missions (to the ISS, say) get windows measured in seconds.

The market, briefly. Heavy and medium rockets move most of the mass. Small launchers sell schedule control and orbit choice to single payloads — and struggle, because rideshare (dozens of smallsats splitting one big rocket) undercuts them several-fold on price per kilogram. The going rate decision: if your smallsat can tolerate the bus schedule and the bus destination, ride the bus; pay for a dedicated launcher only when your orbit or your calendar can’t compromise. Between them sits a growing tier of orbital tugs — last-mile delivery vehicles that carry rideshare payloads from the drop-off orbit to the one actually wanted.

When you compare vehicles, read performance tables the way practitioners do: capacity is always quoted to a specific orbit (LEO numbers flatter; GTO numbers are the honest test of an upper stage), and price per kilogram only matters if you can fill the rocket.

Expert pointers

The frontier questions: whether full reusability (both stages) collapses cost per kilogram again; whether launch cadence — flights per year, now in the hundreds for the market leader — matters more than per-flight price; and whether small launchers survive rideshare at all. Air-launch and spaceplanes, perennial contenders, remain perennially marginal: the physics savings are small and the operational complexity is not.

Misconceptions

• “Rockets fly straight up.” Only for seconds. Nearly all the work is sideways; a rocket still climbing vertically at altitude is a rocket wasting its propellant.
• “Bigger rocket, better rocket.” Payloads are limited by fairing volume as often as by mass, schedules slip, and inclinations differ — customers routinely pick the smaller or costlier vehicle that flies when and where they need.
• “Launches either succeed or explode.” The quiet failure mode is the wrong orbit — an underperforming stage that leaves the payload spending its own station-keeping propellant, and therefore its lifespan, to limp to the right one.

Check yourself

1. Two minutes into a webcast the engines throttle down, then back up thirty seconds later. What’s happening, and why is it necessary?
2. Why does launching due east from the equator outperform launching east from 45° latitude — and what does that imply about launching into a polar orbit?
3. Your 200 kg imaging satellite needs a sun-synchronous orbit within six months. Rideshare or dedicated small launcher — and what two questions decide it?
4. Why does a rocket need ~9.4 km/s of delta-v to reach an orbit whose speed is only 7.8 km/s, and what design choices shrink the gap?

Apply it

Watch a launch webcast — any provider, live or archived — with a timer and this topic open. Log each event (throttle bucket, max-q, MECO, staging, fairing jettison, SECO, deploy) and write one line on why it happens at that moment. If the booster lands, log its events too; they’ll make full sense after the next topic. Your annotated timeline is raw material for a capstone review of a real vehicle. (~45 minutes)