A rocket's simple exterior can make you forget how many different systems lie underneath the surface, and how vital they all are to a successful launch. One thing people often forget about rockets is that while it must endure thousands of pounds of pressure and temperatures that match a small star's, it must also be brought back home (hopefully, in one piece). The avionics and recovery teams are dedicated to doing just this.
The last time RPL has had a successful launch and recovery combination was 3 years ago with Carbon Copy. If we want to get back whatever rocket eventually makes it to space (in one piece that is), we need to test out our avionics and recovery systems. Enter Déjà Vu – a reusable (hence the name) rocket serving as the test bed for our new, custom-made avionics system and dual-deployment recovery system. Juniors Roberto Lopez and Preston Fegley spearheaded the design and schedule of each subsystem. Through their leadership, many RPL members both old and new got first-hand experience in avionics, propulsion, recovery, and aerodynamics of the rocket.
Déjà Vu is a six-inch diameter vehicle standing at 7 feet tall. It's stubby compared to its older six-inch siblings such as SixyBack, DCX, and Tirebiter, but what it lacked in height, it gained in fins. Déjà Vu was designed with one more fin than its predecessors, bringing the total to four fins, like we've seen on larger vehicles such as Traveler. The switch from three to four fins was made to prevent the mid-flight "acrobatics” that Dutchman and Tirebiter experienced. Déjà Vu was equipped with an 18-inch solid propellant motor designed using a new and improved motor sim. This is significantly shorter than most of our other motors, but since we weren't aiming too high (relatively speaking), the motor was designed perfectly.
Of course, the team had to start the Déjà Vu build by diving into to it "nose" first. This nosecone is the traditional Von Karman Ogive nosecone, similar to Tirebiter’s, but made entirely of fiberglass. Twenty-two layers were cut and laid into a mold to get a sleek, sexy nosecone.
Check out those layers of reinforcement!
Next on the list was to make the fins. Déjà Vu's fins were made entirely of carbon fiber, leading edges and all. This was pretty unusual for the vehicles we've been making in the last few years. Usually, the leading edge is made of phenolic, an ablative material used for its thermal protection properties, and the carbon fiber is laid up onto them. Since Déjà Vu wasn't going to see extreme conditions such as going Mach 6 and higher, we decided the phenolic should be traded in favor for a more reusable material. Senior Arren Yedikian spent hours machining each leading and trailing edge on the mill. After a few days of constant work, the fins were complete and looking great.
Time came for the motorcase layup, a two day process involving getting up close and personal with 6-inch diameter aluminum mandrel. After laying down the rubber, hysol, carbon, and finishing it up with a day-long wind, RPL was gifted with a beautiful baby motor case. Déjà Vu’s motor case came off the mandrel with ease thanks to some help from our friendly neighborhood mold release products.
Déjà Vu awaits its fins
Once the motor case was completed, the machinists got to work. Bulkheads, retention rings, nozzle components, and G10 plates were coming hot off the lathe by our skillful machinists.
Feargus and Skye machining the fin alignment tool on the mill.
Turn Down for What: Sophomore Damian Balla turns down a 7 ½ aluminum block into a shiny nozzle carrier. (Not pictured: the hours of work in between these two photos)
Fins are tacked on and awaiting the warm embrace of the tip-to-tip carbon.
Avionics was also hard at work, having designed and printed out a circuit board for the new High Altitude Module for Sensing, Telemetry, and Electronic Recovery, or H.A.M.S.T.E.R. for short. Once it arrived, there was a lot of wiring and integrating to be done. With the help of some magnifying glasses, a soldering iron, and a toaster oven (which is definitely no longer rated for making food), each component found its place.
Adam adding the GPS unit to the circuit board
Carter assembling the avionics cartridge for flight
Déjà Vu was set to launch November 7th and, in usual RPL fashion, the fins were being tacked on the week of launch. Fast forward to November 6th, the day the team had to leave for the desert. Thanks to Murphy’s Law, the rocket wasn’t finished until 8 PM, the same time the lab made an unfortunate discovery. Upon finding the rocket’s center of gravity and re-running the simulations, the team discovered that the vehicle had a margin of stability of 1.1 calibers at take-off. Although this number still gives a stable flight, the rule of thumb for amateur rocketry is 1.5 calibers of stability. On top of this, there were some bugs in the avionics module that needed more time to troubleshoot. A decision had to be made and it wasn’t going to be an easy one.
On November 7th, 2:00 AM, after a lot of discussion, energy drinks, and re-re-re-running the sims, among dozens loyal lab members ready and eager to leave for the desert made the decision to postpone the launch until we had adequate time to solve these issues. As difficult a decision it was to make, we thought it was the responsible engineering decision - one where everyone set aside their emotions to consider the numbers and facts, rather than rushing through a process only to make a small but critical mistake.
To fix the stability profile of the rocket, more mass needed to be added near the top. After some truly impressive brainstorming and math, it was determined that the nosetip would be remachined with added weight attached to it, to nudge the center of gravity. A stainless steel ballast was machined within a day and bonded into the nose cone. Like magic, the stability margin changed to a cozy 1.5 calibers off the pad!
Thanks to the two week delay, the avionics team had enough time to debug and re-program H.A.M.S.T.E.R. With a fully functional avionics unit, and a by-the-book stability profile, the team was confident in flying Déjà Vu.
Jack and Carter celebrate fixing Hamster with an obligatory high five!
Also thanks to the delay, some of our members got to flex their artistic talents and give the rocket an amazing paint job. The theme for the paint job is summed up in the words of Jake Hunter, “Rebel scum!” Déjà Vu wore imperial-like orange and white stripes on a light gray background. On the fins were dark gray hexagons that gave the rocket an even more space-age look.
Jake giving the rocket a PJ
On November 20th, the team was ready to leave for Mojave (Déjà vu, am I right?) but this time at the more functional hour of 7 PM. When the clock struck midnight, the gang was already in Mojave and being greeted by the trailer team, who had departed even earlier.
Mojave-bound!
November 21st was launch day! The team woke up at a shockingly early 8 AM to get everything set up. Miraculously, erecting the launch rail, readying the avionics, and integrating the GoPro only took a few hours. Because everything went so smoothly, Déjà Vu was ready to go to the launch rail a little after noon. Meanwhile, a few brave members made the journey to a remote ground station, a few miles away.
RPL’s strongest raise the rail in an Iwo Jima like manner.
View of the Mojave Test Area and Friends of Amateur Rocketry site from the remote ground station.
The time to light this candle has finally come. At 1:52 PM, November 21st, Déjà Vu took to the skies.
Déjà Vu flew off the rail like butter thanks to the wonderful work of the tower crew. Off the rail, Déjà continued to fly perfectly straight thanks to the stability fix done by the Aerodynamics team. In an instant, the roar of the motor quickly hushed and left the ground team in an anticipatory silence. Carter’s read outs of the altitude data from the rocket were the only words to break the silence. “10,000 feet…15,000 feet…20,000 feet...25,000 feet…we’ve reached apogee!”
The desert came to life with the cheers and happiness of dozens of rocket scientists. The rocket survived to apogee, and avionics was still getting a signal. But that was only half the mission - the drogue and parachute needed to deploy to prevent Déjà Vu from digging itself into the ground like SixyBack. Everyone awaited the next stage.
“The vehicle is decelerating…the chutes are deployed!”
Cue more cheering and hugging as the rocket gracefully floated down to Earth. H.A.M.S.T.E.R. performed beautifully, providing GPS coordinates of the rockets while transmitting altitude and velocity data. Once the rocket touched down, the recovery team set off to retrieve it. Journeying across lake beds, shrubs, and mountains, the rocket was located at the exact GPS coordinates avionics had received. Déjà Vu was laying on ground, nosecone popped and chute out, looking as pristine as when it left the launch rail.
One rocket ready to be taken home!
Watch the in-flight footage from the GoPro!
Finally we had a successful launch thanks to the hard work of every lab member. All the long hours of sanding in the hot sun, drilling hole after hole, and machining pass by pass was worth it. Many lessons were learned by members old and new. These lessons will be remembered to build flight vehicles even better than Déjà Vu.
The story does not end here. Stay tuned for updates on future flights of Déjà Vu and as always…
