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The explorers' rocket engine: Ready for steel

Published on:
July 9th 2018

6 months of intense work, finalized in one push of a button.

"A long time ago, people who sacrificed their sleep, family, food, laughter and other pleasures of life were called Saints. Now, they are called engineers."

This makers' meme pretty much sums up our existence lately.

Our world celebrates summer. There are barbecues, fireworks, hanging with family and friends, vacation trips, swimming in lakes. Meanwhile, we've been in a dark forest, wrestling math, code and design challenges the size of Olympus Mons. No joy, no rest.

But three days ago, we finally arrived at our "real" MAV engine design. The one that will take our butts of Mars surface back to the Mothership. The one that ultimately our lives will depend on.

6 months of intense work, one last push of a button. Time to face the world.

Or rather, a vetting process including senior engineers from the traditional Space industry, as well as young talent from the fairly new world of additive manufacturing.

Learning from our polar expeditions, we knew that you can plan and calculate to the world's end; ultimately you'll have to run your setup with experienced folks and be prepared to face criticism if you really want to succeed.

You know; check with the Eskimos.

The verdict

We started with the Space engineers. On a scorching Saturday, out in the legendary Mojave desert, we showed them our design with trembling hands.

What they said:

“Oh, wow.”

Seriously. They did say that. Twice.

And then:

1. Regen cooling: Fix manifold, uneven flow, recalculate!

2. Thicken around joints.

3. Seals/O-rings - remember the SpaceX rocket that blew? - check they all come in materials compatible with our propellant.

Print maybe transparent first to check mechanics. Start crude, add complexity (print pintle in several version - one fixed/one movable - test, test), add body only when pintle proves to work.

Shuffling our feet into the desert, we went flying out of Mojave.

To the printers

Amundsen, Cook, Columbus and other successful explorers watched for and made use of new tech available at their time and so do we.

Rapid prototyping (CAD/CAM, additive manufacturing/3D print) brings possibilities to Space that weren't there only years ago.

Problem is now you must design not only for Space requirements but also for tool and material restrictions. Will the materials available for print hold up in required vacuum/heat/pressure? What is the print tolerance (how smooth will the surface get and how will it affect fluid and heat exchange)? How do you avoid support structures (design with angle restrictions) and keep costs down (printing within the standard printer box sizes)?

The printing specialists came back with a hefty price tag, but only a few small changes, all related to printer capacity.

Next up

Someone said that Mathematics is not about numbers, equations, computations, or algorithms: it is about understanding.

To understand the challenges of Space, we had to build the first engine ourselves. Now, so close to summit, we feel the fever. Will we survive, or will we burn. We're talking at least ten thousand USD blowing up in a puff of smoke if we don't get it right.

The final adjustments actually mean starting from scratch (version 7) but should be done in a week. Simultaneously we'll finish the plumbing architecture and decide on tanks. Give a few weeks for that.

A final piece of good news by the way: We have got a source for furfuryl. So won’t have to cook mountains of corncobs. Phew.

Tina Sjogren
Tina Sjogren
CEO & Founder
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Oxidizer (nitric acid we made in the previous report) will be injected at the top. Fuel (furfuryl alcohol) at the bottom inlet. Controlled remotely, the (black) servo adjusts the fuel and oxidizer injector openings providing for throttability.

The combustion temp of 2700 C is almost twice the melting temp of stainless steel (1500 C). Front image shows the engine without outer wall, exposing ridges dividing the inner shell into channels. These will guide fuel around the walls before combusting, thus cooling the structure.

Component side view of cooling ridges (engine outer wall not showing) and injector package. The "wings" will hold the the engine together with plumbing, tanks and later the body of the Mars ascent vehicle.

The pintle arrangement is robust and allows for high throttability, both important parameters for a Mars mission. A similar design was used by the Apollo moon lander in the 60's.

The pintle, support and round pintle casing 3D printed in stainless steel. The threaded inlet to the left will be welded to the pintle casing.

Pintle peeking out of the movable sleeve. As our fuel and oxidizer are hypergolic, exact gaps and sealing solutions are critical. Any minor leak would result in "spontaneous reaction" (big explosion).