The rabbit hole
P3 · INSIDE
Two ways to burn — and a printer that melts metal
3 engines, one trick: burn → push
01 CAR
Burns fuel in cylinders to spin wheels.
02 JET
Burns fuel + air scooped from the sky.
03 ROCKET
Carries its own oxygen — so it burns in space.
A rocket must bring its oxidiser along. How you carry it splits every rocket into two families.

The real showdown: solid vs liquid

Cutaway comparison: a liquid propellant rocket with separate fuel and oxidiser tanks feeding a combustion chamber, beside a solid propellant booster whose pre-mixed grain burns outward from a hollow core
LEFT: LIQUID — two tanks, pumps, plumbing.
RIGHT: SOLID — one cast block, hollow core.
Diagram after Wikimedia Commons
SOLID
LIQUID
What's inside
One rubbery block. Fuel and oxidiser pre-mixed and cast into the case.
Two tanks kept apart, pumped in and mixed only in the chamber.
Once you light it
It burns to the end. No throttle. No off switch.
Throttle, stop, relight. As many times as you need.
Thriftiness — specific impulse
≈ 250–280 s
≈ 300–450 s
Moving parts
Almost none. Sits ready for years.
Turbopumps, valves, kilometres of pipe.
Best at
Brute punch off the pad.
Precision — the exact orbit.
SPECIFIC IMPULSE = HOW LONG 1 KG OF PROPELLANT MAKES 1 KG OF THRUST. HIGHER = THRIFTIER.
Vikram-1
uses
both
Stages 1–3 · solid
Kalam-1200 / 250 / 100Raw shove. ~1,000 kN off the pad, no moving parts to fail.
Stage 4 · liquid
Raman-1 × 4Relights in vacuum to place each satellite exactly right.
Not the printer in your school lab

Now we print metal.

Close-up of a directed energy deposition print head: a laser melts metal powder blown onto a curved steel part, throwing sparks
A laser melting metal powder onto a part, sparks and all — this is the blown-powder (DED) method.

No plastic string. A laser melts metal powder — steel, titanium, nickel superalloy — into a layer 20–60 microns thick, thinner than your hair. Repeat a few thousand times and a solid part grows out of a tray of dust.

POWDER BED
Laser scans a flat bed of powder. Fine detail — injectors, cooling channels.
BLOWN POWDER · DED
Powder sprayed into the beam. Big shapes, and repairing worn parts.
Channels no drill reachesCooling passages curled inside the wall itself.
Hundreds → oneEvery joint deleted is a leak that can't happen.
Months → daysChange the file, print the new one tomorrow.
Skyroot's Raman-1 is India's first fully 3D-printed orbital engine — printing cut its build time by about 95%. That's the part that put four satellites in the right place.
This was the trailer. The full 3D-printing teardown is coming.
How a printer melts metal without warping it, why rocket firms bet everything on it, and what you can print yourself. Join the BB WhatsApp channel → so you don't miss the drop.
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Data: Skyroot Aerospace / ISRO / NASA / public sources · diagrams & photos for education P3 / 4