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Changing Plans

Changing Plans

If you look at our BOM (Bill of Materials, keep up!) you’ll catch us in the middle of a very important decision. How are we going to test our rocket?

The Purpose:

To be sure our design works, we need to have data on-record from a simulated run. This includes measuring the lifting force generated from combustion, the temperature of the engine chamber, and the fluid pressure at a few key points along the plumbing.

It’s also an excellent chance to test our dump, abort and kill sequences in case of emergency down the line.

Plan A:

From Day One, it’s been clear we would need to test the full stack. Otherwise, how could we be convinced it would work before launch? Since our propulsion system is pressure-fed, the tanks need to be tested vertically. (If the rocket were horizontal, our high-pressure helium would be able to flow right through the tanks when they’re half full, rendering the test futile.)

Proof that a horizontal test is no good. We would lose pressurant before we were halfway done.

This means we have to test vertically. Right-side up. Which, with rockets, is also the direction you point them if you want them to leave the ground. Not as much the plan, with a static fire test.

To get around this pesky bit of physics, the team designed, modeled, and specified the materials in our BOM for a full-height, vertical test stand. Essentially, we designed a cylindrical sheath (for containing the rocket) inside a rectangular frame (to provide structure) weighed down with water, sand, and concrete (so it didn’t fly away).

A full CAD render of our initial vertical test stand, complete with counterweight barrels.

The Problem:

Upon igniting the engine, the nose of the rocket would be forced upwards into the integrated force sensor. This is unrealistic launch behavior, since it puts the entire rocket in compression. Alternatively, the rocket pushing upward into the stand can be viewed as the stand forcing the rocket down

Plan B:

Back to the drawing board. We needed to come up with a test mechanism that would better simulate launch by placing the rocket in tension, rather than compression. As it turns out, the best place to turn for inspiration is still the Internet.

The verdict? “Tie it down.” Plain and simple. All that’s needed is a rocket, something tall to hang it from, and a few (very strong!) wires to secure it to the ground. It may sound silly, but there are plenty of videos detailing the process and showing positive results.

A quick sketch of our new vertical testing plan.

It requires less logistically, too, as it no longer requires us to maneuver an expensive rocket inside a bulky steel cage. Sold.

What Now?

Now we continue the process of finding a place to launch. We have yet to nail down an official location, but we’re zeroing in pretty quickly. (A few amazing spots have jumped out at us this week and we’re following up.)

And after that? We build, we go, we test.