Thread by @Andercot

How to Get to Orbit Cheaper than SpaceX's Starship

Ian Brooke has developed a new kind of jet engine that can act as the first stage of a rocket.

I get brunch with him every Sunday and have grilled him for hours on how it works.

Adaptive Cycle Jet Engines, the primer 🧵

Two facts about rockets:
- They have to carry a lot of fuel
- Structurally they are quite weak

The miracle of the Falcon 9 and Starship is they can be re-used, 10, maybe even 20 times.

But even a Falcon 9 that lasts forever has to consume massive amounts of fuel

On the other hand, commercial airplanes are designed for 30,000 cycles. They don't carry as much fuel for an important reason:

Jets use the atmosphere as a ladder

Air is mixed with fuel, combusted, and used as reaction mass. Rockets have to carry their own liquid air

"But jets can't go to orbit because they need air, and there's no air in space"

Space is an altitude. Orbit is a velocity

Using the atmosphere for reaction mass up to Mach 6 is like a free booster.

( Falcon Heavy boosters detach at Mach 10 )

This is the beauty of the adaptive cycle jet engine for orbit - a far more reusable first stage with tiny fuel requirements.

A second stage rocket takes you from Mach 6 to Mach 25, orbital velocity.

You skip using rockets when they suck - at low speeds with variable pressure

More re-usability, far less fuel, means cheaper, easier, more frequent launches.

To appreciate how it works, we need to look at the pinnacle of air-breathing engine design, the SR-71 Blackbird.

The fastest plane ever flown.

The SR-71 uses the J58 Pratt and Whitney engine, capable of two modes of operation:

Normal Turbojet, for speeds up to Mach 2.

"Turbo Ramjet," for speeds up to Mach 3.3

Ramjet mode is by far more fuel efficient, and can go up to Mach 6 in principle.

Ian's engine? Three modes

Three modes are what make this jet engine adaptive - maintaining high efficiency at different velocities.

Turbofan for low speeds, then Turbojet, then Ramjet.

What enables this is using a second turbine which is always running at its ideal RPM to drive the fan

Normal commercial jet turbofans are optimized to be efficient at cruising speeds, and so burn massive amounts of fuel at lower velocities.

Ian uses a second turbine that drives the main turbofan with a cryogen-cooled AC motors, like an electrical transmission.

This all sounds obvious - why now?

Electric motors are finally getting good enough in performance. Before, losses in the motor windings and weight would've killed the efficiency gains from having a second turbine drive an adaptive cycle jet engine.

Now it makes sense.

The net-net of all this is that @k2pilot developed a platform that traverses this entire chart to stay maximally efficient.

See how badly rockets perform at low velocities? Ian waits until ramjet speeds to use rockets. Smart.

But orbital launches are just the beginning

While the Space Launch market is projected to reach $30 billion in a few years, the commercial aircraft market is 15x larger.

Boeing and Airbus are the only two players. Both have become sprawling bureaucracies that don't innovate. 737MAX was a tragedy

The problem with trying to build a new commercial aircraft is that its absurdly expensive to certify and operate.

This means your jets have to be absurdly expensive too, or else just assume you can raise unlimited venture capital.

Boom goes your business model.

This is why people love @k2pilot's startup so much.

Like his engine, the company has three modes:
- Generate massive free cash flow through high-margin space launches
- Use this money and flight data to certify a new airframe
- Use this airframe to make the world 3x smaller

That's the win - Commercial flights anywhere in the world 3x faster than anything today, same price.

@k2pilot isn't competing with SpaceX.

Rather, he's building the Tesla of airplanes, to take on 110-year old Boeing.

Space planes just happen to be how you get there