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Engine hot fire: 10 MPa!

Published on:
May 18th 2021

9.8 seconds firing. Reached chamber pressure goal - 10 MPa. Two times the pressure of Rocketlab or any competitor in our rocket class (<500kg to LEO). Achieved +90% of theoretic thrust level!

But not without scars...

Mid-January Asterex hot-fired for the first time. Increasing pressure and propellant to focus the flame was next. We ended that update:

"We'll keep raising the bar in a series of tests to see how far Asterex can go before blowing up."

Well, we didn't have to wait long.

Wild with triumph, and a number of promising full-pressure water tests behind us, only one month later we decided to skip the incremental part.

Our second hot firing went full pressure on almost triple the amount of propellant going out all at once, and yes, the engine blew up. Only the pintle was still barely hanging on to the test stand. The rest laid scattered around our feet. We had redlined it and the gods of Olympus Mons decided to teach us a lesson.

Bummed, we returned to the drawing board to design for mass flow control. We also immediately ordered not one, but three Asterex to be printed in Germany.

Turned out, adjustable valves for our high pressure- and control demands were nowhere to be found so again we had to build from scratch, software and all. It took 100 water tests, and another 3 hot tests of the new system (using a makeshift engine we'd machined at the shop) to get back to the starting line. Out of sheer want for revenge, we bumped up one of the provisional hot firings to a restart, which worked out (30 sec between firings).

And then the replacement Asterex engines arrived. We mounted one to the test stand and hardly slept that night.

We named the hot firing Tsiolkovsky Rematch. Before leaving the shop at 8 am, I gave a small speech for the fast-growing Pythom crew: “Tsiolkovsky because it’s thanks to this modest, hard-of-hearing, math teacher from Kaluga we can do what we are doing today. Only now we will do something that has never been done before, and last time we tried it the engine blew up,” I pointed to the shrapnels behind me.

“Today we’ll try again, and that’s why it’s called a rematch.”

This time we won the game.

We fired the engine at 10 MPa. It sounded like a tornado and kicked up a storm of sand. A beautiful, slender jet shot out, diamonds and all. The afterburn was spectacular. With one last puff (I swear there was a smoke ring) Asterex sat back like nothing had happened at all. As we had guessed, controlling the propellant flow made all the difference.

To our knowledge, 10 MPa of pressure has never been demonstrated for an engine in our class (Rocketlab has 5 MPa). Several records were broken but that’s not what’s important.

What’s important is that now we have what we need to go to Space.

Key take-aways:

1. We reached target pressure and 90% of the target total thrust (had hoped for 60-70%). This means we can leave Earth with a cluster of Asterex.

2. To our knowledge, this is also the first time a rocket engine demonstrates 10MPa chamber pressure on a storable propellant for travel in space (Apollo Lunar Lander had 1 MPa, SpaceX SuperDraco has 6.9 MPa). This means less rocket weight and up to 200% more payload.

Black Magic is the last unknown. Most else - our abort system, fairing, orbital calculations, etc - are sourced, detailed, and were also vetted by FAA subject matter experts in our time with the DARPA challenge.

Parts for Black Magic are arriving at the shop already this week. We are rolling up our sleeves for the finish line - and the beginning of a whole new race.

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Tina Sjogren
Tina Sjogren

Split-second after ignition. April 26 test sequence. Demonstrated restart capacity: Fire - shutdown 30 seconds - fire.

The Theoretical Max Thrust is the max thrust that can be achieved by a perfect propellant mix and combustion. 100% is not possible, but a great propulsion system will produce above 95%. At this stage we would have been happy with a 60% reading - we got 90.1%!!

Shrapnel from March explosion. Too much propellant going out way too fast. Performed 100 water tests and 3 hot-tests in April to reach the correct mass flow. Skeleton not related to the event.