# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/Dctc7ezgLYa
- **Gondola URL:** https://gondola.cc/posts/70003069-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/f899f04b85.jpg
- **Posted:** 2026-08-31T15:53:38.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A rocket test stand exists for one reason. To find out what the simulation got wrong.

Portal Space Systems fired its Flare thruster inside a vacuum chamber in Bothell, Washington, and the result reframes what liquid propellant actually means. Flare carries liquid ammonia. It never burns it.

A conventional liquid rocket is a chemistry problem. Fuel and oxidiser meet in a combustion chamber, release energy through exothermic reaction, and the resulting gas accelerates through a converging-diverging nozzle. Performance is capped by the energy stored in the molecular bonds you brought with you.

Solar thermal propulsion moves that ceiling. Concentrators focus sunlight onto an additively manufactured heat exchanger. Liquid ammonia flows through internal channels, absorbs the heat, expands to gas, and exits the nozzle. The energy source is the Sun. The propellant is only working fluid.

What the test demonstrated:
- Full-power operation of the heat exchanger thruster under vacuum
- Operating temperatures in the region of 1,500 degrees Celsius
- High-power electric heating standing in for concentrated solar input
- Measured thrust and specific impulse matching prediction
- A cold flow and calibration sequence before any high-temperature run

Vacuum matters because nozzle behaviour depends on ambient pressure. Fire an upper-stage nozzle at sea level and the plume separates from the wall, the flow destabilises, and the numbers mean nothing. Test in vacuum and the gas expands the way it will in orbit.

Ammonia earns its place through storability. It stays liquid without cryogenic tankage, and its low molecular mass raises exhaust velocity for a given temperature. No boil-off. No insulation penalty. No second tank of oxidiser.

Chemical propulsion gives thrust. Electric propulsion gives efficiency. Solar thermal is an argument that the choice was never fundamental.

#stemantics #rocketscience #propulsion #spacetechnology #aerospaceengineering

## Stats

- **Views:** 9,056
- **Likes:** 93
- **Shares:** 0
- **Comments:** 0

## Tags

spacetechnology, propulsion, rocketscience, aerospaceengineering, stemantics

---
Copyright (c) Gondola