3D Systems Injector Earns the Nickname “Old Reliable”

Pictures: https://imgur.com/a/ExpjtEA

5, 4, 3, 2, 1!” Members of the Student Space Initiative huddle in silence and trepidation, peering out at a bundle of tubes, pipes, and electrical connectors set up in the distance. For about a year, the engine test stand had been collecting dust and the test site had been silent. The team had stood down from firing their first liquid rocket and over the course of a year, developed a new prototype to eliminate the problems of the old. Multiple attempts at firing up this new engine had been thwarted by faulty pyrotechnics and electrical snafus. Now they watch and wait as the engine startup sequence unfolds, hoping for ignition. The engine roars to life, spewing flames, rocking the test stand, and sending out a rolling thunder across campus.

Video of Hotfire: https://www.youtube.com/watch?v=9osoALNrB40

This was the first engine test witnessed by a couple of the observers, an awe-inspiring experience. The team was ecstatic – at last all of that hard work had been rewarded. However, the high spirits were quickly taken down a notch by a discovery of damage to the engine. The injector, the heart of the engine, was melted and scorched by the flames. The team had developed a new prototype, 3D printed from stainless steel. The very flames that power the engine, reaching about 4000°F, had consumed the outer wall of the injector itself, exposing the internal manifolds. This new design, created in partnership with Protolabs, a prototype manufacturing company, had pushed the limits of the hardware, cutting away unnecessary material and riding the edge of what was possible to print. The design would need further iteration. 

With a few weeks left in the year, it looked like any hope of certifying the engine for flight was lost. However, one shot remained for the team. Buried in a box of old hardware was the green Inconel injector from the previous year, the “3D Systems injector,” named after the company that printed it. The chief designer of this part, James Kolano, had since graduated and went to work at SpaceX. Little did he know that his old part was about to be put to use again. 

The part was a marvel of engineering for a student project. The students had worked with engineers at 3D Systems and their Design for Additive Manufacturing (DfAM) tools to craft a printable injector that, to a casual observer, resembled a circus tent. The structure resembled that of a cathedral, with sloped ceilings rising up from the injector face. A complicated pattern of colliding orifices shoots the propellant into the fires of the combustion chamber, releasing an incredible amount of power – about 1.5 MW or equivalent to the P-51 Mustang fighter plane – all within a 4” combustion chamber.  

A key DfAM capability the team took advantage of with its 3D Systems fuel injector was parts count reduction: going from a product that would traditionally require multiple assembled components to a monolithic structure that requires no assembly. The student designer, James Kolano, says removing fasteners from the design not only helped the team lower final weight, but also helped remove known points of failure. In a non-3D printed design, the team would have had to make several parts and fasten them together with O-rings and bolts. Not only is this assembly typically difficult, but it is not always reliable. “O-rings notoriously have leaks,” says Kolano. “By using 3D printing we had a single part with no failure points.” 

Beyond eliminating the need for fasteners, the team requested 3D Systems’ assistance in removing additional weight from a few internal cavities. 3D Systems’ application engineers incorporated internal lattice structures within the designated areas using 3DXpert®, an all-in-one software that covers the entire metal additive manufacturing process. In addition to this weight reduction, 3D Systems performed pre-printing operations to facilitate powder removal in post-processing, as well as a printability check using 3DXpert to ensure the part would build without complication. 
The final part was printed on a 3D Systems ProX® DMP 320 metal printer in LaserForm® Ni718 (A), an oxidation and corrosion-resistant Inconel alloy. Once printed, 3D Systems’ team removed unused material from the part’s interior, heat-treated the part for stress relief, and removed the part from the build plate using wire Electrical Discharge Machining (EDM). The final part weighed 1.16 pounds (0.53 kg), quite a small amount in comparison to the 350 pounds of thrust it produced.

The part had performed fantastically the year prior, leading to the first successful firing of a student liquid rocket engine at Stanford University. But as the team’s second prototype firing revealed shortcomings in their new prototype injector’s design, all attention was turned yet again to “Old Reliable,” the 3D Systems injector. 

On June 14th, 2019, the students of SSI pulled together one final effort to re-test their engine. Attempting a full-duration burn, all stakes were riding on this final test. Deep within the engine lie the 3D Systems injector, freshly oxygen-cleaned. When the engine fired up this second time, reports came in from across campus that SSI was “at it again” with their rocket testing. The engine eclipsed all previous power records of the team, coming in at an average sustained thrust of 310 pounds for a whopping ten seconds, enough to send SSI’s rocket past the student amateur altitude record. The 3D Systems injector, “Old Reliable,” endured the test completely unscathed. 

“3D Systems’ guidance and design reviews were very helpful to the students, and I think the benefits worked both ways,” says Greg Zilliac, NASA Research Scientist and consulting professor in Stanford’s Department of Aeronautics and Astronautics. “I believe 3D Systems added to its knowledge of the concerns involved in manufacturing high temperature parts for aerospace applications, which are different from other applications. This project was a definite win-win on both ends.”

-Nick Gloria

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IREC 2018

Pictured: IREC 2018 team poses with fully-assembled rocket before launch

The IREC 2018 team launched the final version of their rocket on Thursday, June 21 at the Intercollegiate Rocket Engineering Competition in Spaceport America, New Mexico. Flying to an altitude of 28,448 feet, the rocket reached an apogee close to the team’s target altitude of 30,000 feet. It successfully recovered under drogue, and remained completely intact throughout the flight. All of these factors went into the team’s flight altitude and performance scores, winning the team second place in their category.

The rocket featured many student researched and designed components, including an avionics bay with a long-distance radio system, a reduced-diameter recovery system, a tip-to-tip carbon fiber fin lay-up, a powered decoupling mechanism, and a software-defined GPS payload.

The team is excited to return next year, with new designs and a continued enthusiasm for engineering excellence. Forwards and upwards!

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Rockets 1st Place in Category at IREC

 This last week, SSI Rockets embarked on a long journey to New Mexico to compete in the first inaugural Spaceport America Cup, one of the world's largest rocketry competitions, with over a hundred teams from five continents.
Our official mission patch!

After a long car trip to Spaceport America in New Mexico, we set about preparing for launch in the blistering 118F heat and occasional 25mph winds. And although everything we owned was soon covered in a light layer of dust, we managed to be one of the first teams to launch!

The IREC team at the launch site, taking a break just before launch!

Our rocket, Heart of Steel, officially became SSI's fastest and highest launch, getting within 1.5% of our altitude target of 30,000 feet, reaching a final maximum velocity of 1.8 times the speed of sound and enduring, at one point during recovery, over a hundred gravities of acceleration! Although we suffered an imperfect recovery and our payload - a novel telemetry system which does not require a ground station - failed to deploy, our launch overall was one of the most successful in the competition.

In fact, when the (literal and figurative) dust had settled, we were first place in our altitude and motor category, with a score nearly 50% higher than the second place team!

Heart of Steel taking off - PC Benno Kolland

We are immensely grateful to everybody who made this success possible - our team, the university, our sponsors, our friends in the amateur rocketry community, and of course Spaceport America and the Experimental Sounding Rocket Association, for making all of this possible. IREC 2017 was a wonderful experience, full of growth and progress for our team - we gained invaluable experience managing what was by far our largest project yet, becoming even more professional and efficient, forming relationships in the collegiate rocketry community and building the expertise we need to make even greater leaps in the future!

We are impossibly excited for this coming year and are already busy cooking up something even cooler - onwards and upwards!

Heart of Steel, heading skywards - PC Benno Kolland

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IREC Test Launch at FAR

This past Saturday, April 16th, the IREC team on Rockets made a journey down to the launch site owned and operated by the Friends of Amateur Rocketry (FAR) near Mojave, CA. It was a long car ride there and back, but it was well worth getting a chance to test the rocket design that we will ultimately take with us to New Mexico for the Spaceport America Cup in June.

From left to right: Saylor Brisson, Marie Johnson, John Dean, Rushal Rege, Logan Herrera, Ian Gomez, James Kolano, William Alvero-Koski, Derek Phillips, Christopher May, Thomas White, Rebecca Wong, Shi Tuck, Ruqayya Toorawa

Although we only managed to get one flight of our rocket in, we were very pleased with the opportunity to test all of our basic systems, from the deployment mechanism for our payload, to our motor retention system, to our SRAD avionics and beacon + GPS tracking. All of our sub-teams learned a lot from the journey and were excited that we got to return home with all of our components in-tact and recovered! We're looking forward to our next test launch when we return with various tweaks and improvements.

Some additional bonuses to the trip were getting to meet the Cal Poly team and watch their rocket have a beautiful flight, and getting a chance to chat with some local middle school students about our project! Lastly I'd like to make a large shout-out to Eric Melville for his continuous support as we progress through our project. He's been a wealth of guidance and information both on and off the launch site. Thank you, Eric!Lift Off!

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Vibration test at Quanta Labs

On Tuesday, March 7th, members of our rockets Intercollegiate Rocket Engineering Competition (IREC) team visited Quanta Labs to perform a vibration test of our avionics system. Our unit passed the test. No major problems were detected, but we did gain insight into how to make our avionics system even more vibration and shock tolerant.

The Avionics System:
The avionics system in our rocket for IREC has been designed for high-reliability using redundant commercial altimeters and a custom student researched and developed flight computer. Its main function is to trigger deployment of the payload and recovery parachutes. In addition, the unit provides an RF beacon for locating the rocket after landing and a telemetry stream of live flight data using an RF link. Thanks to our recent sponsorship from Harwin, our avionics system features high-reliability connectors in important, safety critical connections.

The Test:
The unit that we tested included the parachute deployment assembly and avionics. This full assembly sat inside a sample section of our in-house custom fiberglass and carbon fiber airframe. To fixture our airframe section to the shake table, a CNC’ed delrin clamp was bolted into the shake table.
Integration of the system on the shake table

Using a shaker table at Quanta Labs, we performed the following tests of the system 
  1. 30G 6ms positive direction per axis, 3 axes
  2. 30G 6ms negative direction per axis, 3 axes
  3. 10Grms thrust axis 20Hz - 2kHz 20 seconds
  4. 7.6Grms lateral axes 20Hz - 2kHz 20 seconds each

The test specifications came from two sources. For shock, we used real values that we had recorded on previous flights. For vibration, we used the specs from the NASA Sounding Rockets User Handbook - Vehicle Level 1. These vibration specs are used to qualify payloads for going to space on NASA sounding rockets.

Here is a plot of the spectral content of the vibration applied for one of the tests:

To measure the continuity of the ignition lines from the avionics bay during the vibration and shock tests, we used one of our Keysight oscilloscopes, and recorded a 30 second session of the voltage across all of the lines.Our Keysight Oscilloscope used for recording ignition line continuity during the test

Here are some other pictures from our testing:Overhead view of the shake table
Connections for the test

We owe a huge thanks to Quanta Labs for providing their facilities and time to allow us to perform this test. Vibration and shock testing is critical for safety and reliability, and would not be possible without our sponsors.

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