Static Testing Hybrid Rockets For A Flight To Space

A team of rocketry enthusiasts at Boston University have been working on a small hybrid rocket motor that serves as a test bed for a larger, yet-to-be-designed power plant that will hopefully launch a rocket into space.

The static tests of the BURT Mk. II began last April with a series of tests using HTPB solid fuel and Nitrous Oxide as the oxidizer. The team had a series of failures – mostly due to the JB Weld seal on the igniter leads blowing out – but managed a 10 second burn on April 21st.

For later tests, a vector drive system built by a complimentary Boston University engineering group was used to control the direction of the thrust up to 12 degrees away from the axis of the engine. That’s an impressive bit of kit, especially considering the exhaust from the rocket reaches over 5000 degrees Fahrenheit.

Even though it’s summer now and the Boston University team is on a much deserved break, we can’t wait to see what the BURT team comes up with next year. Hopefully we’ll see a flight test that reaches the team’s goal of the Karman line.


7 thoughts on “Static Testing Hybrid Rockets For A Flight To Space

    1. Yeah, JB Weld. It came down to crunch and since we knew it’d at least be a relatively manageable failure point, we didn’t spend the time to make a proper engineering decision with respect to what epoxy or sealing solution to use. Surprisingly, JB Weld actually works almost-well-enough without any additional help.

      Originally, we had larger holes drilled in the ignitors for leads – something like 3/16″. Those failed sometimes even in tests, although the mode was usually the heavier insulation melting on the stranded wires we used – once the insulation was gone, there was a nice big void for blow-by between the conductors and epoxy.

      We switched to thinner lead wires – wire wrap wire, in fact. It’s not nearly large enough to handle the current, but then we’re TRYING to burn something anyway, so as long as it holds until the pyros ignite, that’s fine. And it does. We packed new ignitors with the thinner wires, but we still had a bunch of bolts drilled with 3/16″ lead holes, and when those were fired live, they blew out pretty quickly.

      We adapted the hole size to 1/16″ for the tinner leads, so that there was less surface area (and therefore less distributed pressure) on the plug of epoxy sealing the hole. That worked alright, but the ignitors still blew out, just usually much later in a test (we had maybe one or two blowouts, one of which caused an abort 400ms before the test otherwise would have ceased).

      In our most recent test, we actually had no blowouts, but the chamber combustion was actually unstable and didn’t achieve the design spec of 500psi, it was more around low 400s. So it turns out, we’re probably using the JB Weld JUST on the edge of its capabilities in this application.

      For that reason, I think that the ignitors would actually survive just fine with a little mechanical backing to distribute the load off of just the one plug over the open lead hole. For example, if we pressed a dime into the unset epoxy and ran the leads out at a 90 degree angle through the gap, I think that would fix our ignitors completely. But the overall construction, even besides this one issue, is super unreliable, so they’re being completely redesigned for the next motor as it is.

  1. I think a more interesting thing than reaching Karman line may be launching a small rocket from high altitude balloon and try to find out what maximum horizontal speed it can achieve in thin atmosphere.

    Btw. I don’t understand what’s so magic about Karman line. More interesting is a speed mark 7.2km/s ;)

    1. There are a lot of interesting goals to reach and which one you choose depends on personal preference, interest and funding. The Karman line is I think a rather respectable goal, since the eventual goal seems to be a rocket to deliver a payload and the Karman line is just one mark on the road to space payload delivery.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.