The Kármán line is defined as the boundary between Earth’s atmosphere and outer space. While the original definition refers to the altitude at which the atmosphere becomes too thin to contribute enough lift to support aeronautical flight, the Kármán line now is internationally recognized to be located at an altitude of 100 kilometers, or 328,084 feet, above Earth’s average sea level (AMSL). Beginning with the German V-2 rocket, the first rocket to cross that threshold, countries have been shooting for space for over half of the past century. Although private companies have been able to reach space and orbit for a few decades, a collegiate team has never independently designed, built and launched a rocket that went to space and was recovered intact. With that knowledge in mind, the USC Rocket Propulsion Lab was founded in 2005 with the goal of being the first student group to do exactly that. A space race arose from universities around the world, as many took incremental steps closer to reaching the Kármán line. Now, 14 years after RPL was created, the collegiate space race has ended; Traveler IV, the latest spaceshot vehicle from the USC Rocket Propulsion Lab, passed the Kármán line on April 21st, 2019.
Following the unsuccessful launch of Traveler III, the lab met to discuss the events of the launch weekend and the weeks leading up to it. After fully analyzing the successes and failures of Traveler III, a laundry list of action items emerged that accompanied the build of Traveler IV, a vehicle of almost entirely the same design as its predecessor. Some of these action items concerned the actual build and design of this spaceshot attempt, while others were directed towards the logistics of the launch weekend. Nevertheless, the engineers at RPL had to add onto their typical duties of building the rocket by figuring out how to successfully conduct launch operations for a vehicle intended for spaceflight.
As with all rocket builds in RPL, the motorcase layup was of primary importance as the lab set out on another year of building its most technically advanced vehicle yet. The goal with this layup was to not deviate from the case design seemingly perfected by Fathom II’s final static fire and flight, Graveler II, and Traveler III. However, as no new motorcases had been constructed in lab since spring of 2017, almost 18 months before, a practice case layup was necessary to perfect the layup procedures before scaling up to a nearly 10-foot final product. When the significantly shorter trial motorcase held up to the standard hydrostatic test, the composites team was ready to devote an entire weekend to the creation of Traveler IV’s case. The time spent constructing a practice case paid off, as a flight-worthy case was produced on the first attempt. This case passed a hydrostatic test, despite being slightly delayed by a concern during the pinning process that was quickly remedied, and was prepared for flight.
As the case hydrostatic test showed, and would be demonstrated in layups after, the goal of the Traveler IV build process was to avoid producing parts that would be denied by quality control reasons. Much of the time spent on Traveler III was due to improperly made parts, so the lab sought to learn from that lesson by choosing to delay layups, machining, or casting sessions to ensure that the right tooling, personnel, and equipment were present for every flight-critical process. The nosecone layup was a perfect example of this ideology: the correct epoxy had not been procured for the nosecone, so rather than continuing with the wrong chemical and hoping that it would work out, the engineers chose to wait to utilize the appropriate adhesive. This approach paid off as it produced a perfect nosecone on the first try, while Traveler III’s nosecone took several iterations until it passed the lab’s quality control standards. Likewise, the fin layups were set for a date where the appropriate composites team members would be available, thus ensuring the maximum chance of success. A manufacturing change for the fins was implemented to reduce quality control issues by switching from curing the fins in the lab’s oven and machining them entirely on the mill to utilizing a hot press for the cure and a water jet for the fin shape. Overall, this change ensured fin flatness and tolerances comparable to the lab’s previous processes at a fraction of the time. Altogether, the fins, nosecone, and case were essentially finished by the end of November, demonstrating much quicker processes for these significant components than for Traveler III while still maintaining the lab’s rigorous quality control standards.
Casting of the Traveler IV motor was also significantly smoother than that of its predecessor. The lessons learned from casting all of the 2017-2018 school year resulted in only two grains being denied, eliminating many Fridays of traveling to the lab’s offsite propulsion facility. Overall, the motor came out slightly higher in density than did Traveler III’s motor thanks to the improved processes developed over the course of the previous academic year. Thus, the lab returned to school in early January with nearly all of the work done for the structures of the vehicle and the motor, allowing the lab’s focus to shift to machining the final components, assembly and testing of the recovery and avionics systems, and addressing key action items that came out of the Traveler III after action review.
The most significant delay of the Traveler IV build process came from outside of the lab’s control. The government shutdown, which began in December of 2018, meant that no launch paperwork could be processed or approved, leaving the launch in limbo for nearly two months. As the days stretched on without FAA clearance, the lab remained optimistic and focused on finishing Traveler IV, with the knowledge that roughly 45 days would be necessary from the end of the shutdown until the approval of the launch paperwork. In addition, another delay arose from needed repairs to the lab’s lathe, which prevented much of the machining work for the vehicle during the early stages of the build. Although the lathe was unusable for around a month following the Traveler III launch, the lab persevered by focusing its attention on finishing work on the composite structures and other lab projects. Overall, these delays did not present a significant risk to the vehicle, as the extra build time allowed each team to work on perfecting their subsystems. This also gave the lab the opportunity to pursue other projects, such as upgrades to the avionics system, development of a new propellant formulation, and the static fire of the future Poise vehicle (the latter two items will be discussed more in-depth in a write-up of their own in the coming days, but are featured on the lab’s Facebook and YouTube pages).
The return to school in the spring semester was followed by the final manufacturing of the vehicle, assembly and testing of the recovery and avionics systems, and working with Spaceport America on the logistics of launching by the end of the semester. The item of paramount importance was the nozzle, as the lead time on this part would drive much of the schedule for launch. The nozzle design, tested on Graveler II and flown on Traveler III, was known to be reliable, but would require dozens of hours of machining to produce a final product. During the initial build of the nozzle, a simple manufacturing error set back the machining timeline by a couple of weeks in late January but posed no risk for flight as the part in question was swapped out and the build was resumed. While machining was ongoing, other teams got their first look at how their systems would stack up during flight.
The overhaul of the avionics system was by far the most crucial development of this launch, and what made it possible to retrieve as much data as this lab did. From the onset of the academic year, especially after the Traveler III launch, the largest avionics team in lab’s history, made up of over 20 engineers, had the determination to root out every software, hardware, and structural flaw in their unit. This enormous endeavor required complete redesigns of many portions and significant hours spent meeting, reviewing, and working towards resolving the issues that had plagued lab for its entire lifespan. Even bugs in the old drivers and problems with the custom PCB designs that plagued Fathom II’s flight were remedied. This tireless work was taken up by willing lab members, and everyone from freshmen to seniors actively created a significantly different system. Altogether, the overhaul of the avionics system would represent Traveler IV as a new era for the RPL avionics team as an integrated team within lab, as opposed to a black box subsystem expected to perform nominally at all points. Significant effort was therefore dedicated to bridge the gap between electronics and mechanics such that this system would be understood by all lab members, making the lab stronger as a whole and able to reach space with confidence on all pieces of flight hardware and software alike. When the avionics unit was finally assembled and sitting on the desk in lab, a round of congratulations were certainly in order. Afterwards, the team went straight to work testing the unit to root out any software or hardware bugs, accounting for as many edge cases as possible to ensure that issues wouldn’t occur during launch that would prevent data retrieval. Meanwhile, a team closely tied to the avionics system, the recovery subsystem, set about testing their deployment method to ensure a successful recovery of the vehicle from the vacuum of space.
The recovery team used the time between the Traveler III and Traveler IV launches to perform more extensive testing of the nosecone deployment system. The recovery system changed from a dual-parachute deployment system to single deployment between Fathom II and Traveler III, but the new configuration had yet to be proven in flight. With concerns of the nosecone failing to eject in the vacuum of space, the recovery team conducted experiments to ensure that the system would function at apogee. A test schedule was devised with various levels of pressure ranging from atmospheric pressure at sea level to near vacuum and recorded the ability of the system to puncture empty gas canisters and simulate ejection. This joined the recovery team’s normal suite of ground tests, which ensured that RPL would not only be able to send a rocket to space, but recover it.
While most of the teams in lab were working on testing their units, the propulsion group wanted to tie up the loose end of the motor integration to be able to work on other projects while ensuring that no issues like the original Traveler III integration would occur. The team drove out to its offsite propulsion facility in late January to integrate the motor cartridge, a task undertaken 3 times now in the past year and a half for spaceshot motors. This integration went smoothly, as the abundance of hands and experience in the lab produced a motor cartridge that was ready for integration into the flight vehicle and, most importantly, for flight. At the same time, the composites team placed their final touches on the vehicle.
Of course, a rocket is not complete without fins! While the fins had been machined to final dimension before the winter break, they still had to be attached onto the body. Luckily, the composites team was able to work quickly, passing down knowledge to freshmen and sophomores about these crucial layups, and the flight vehicle had its final structures complete. Now all that remained was final testing, integration, and a flight permit from the FAA. As the lab waited, work was done on addressing key launch day items from the Traveler III after action review. Most notably, creating a launch day script and planning the launch and its preparations were of paramount importance to the team, hoping to root out the issues that occurred in the Traveler III launch. Additionally, the work of the new quartermaster team, created in October to improve lab’s internal organizational methods and trip logistics, made the process of packing and inventory before and after trips of these scales as smooth as possible. This work eliminated the need for last minute Home Depot runs before the launch for tools, improving the lab’s state of preparedness. Overall, the main issues seen in the lead-up and launch of Traveler III were addressed throughout the 2018-2019 academic year, spawning new teams within lab and conversations regarding the best way to prepare for future high-altitude launches. Meanwhile, the final component machining was still underway as the lab pushed to finish the vehicle.
Following the delay caused by a small manufacturing concern in January, the nozzle continued to be machined in lab throughout February and March. At the end of March, the final product was finished and ready for the final motor integration into the flight vehicle. However, when the lab went out to the offsite propulsion facility to integrate the Traveler IV motor and the Poise static fire motor, a concern was raised about the nozzle again. Rather than push through and produce a motor that was inferior to the lab’s quality standards, the integration was delayed a week to analyze the problem further. The team used that week to finish up sanding of the outside of the vehicle, producing a smoother outer contour, and to repair the nozzle to the best of the lab’s abilities in order to make it flight worthy. When the team came back out to do the final motor integration, the tooling developed in August for the second integration for the Traveler III motor continued to prove useful, as this integration went incredibly smoothly, and the motor was ready for flight. At the same time, recovery had finished their final testing, including a test powered by the avionics unit to simulate an apogee deployment. The avionics team continued to test their system and implement solutions to the bugs that they encountered throughout late March and early April. Altogether, the lab was teeming with excitement as the launch window of April 20th and 21st crept closer.
The lead-up to launch in RPL is always an exciting time, and this launch was no different. Continuing to act on the lessons learned from the Traveler III launch, the lab leadership had committed to a hard launch deadline for each day that would avoid the high winds that would arise afterwards. Additionally, sticking to that tight window would avoid rushing to the launch, as occurred with its predecessor; if the lab didn’t meet its goal time on Saturday, the group would come back, solve any issues, and launch on Sunday morning, rather than trying to launch in between random gusts of wind. In that same light, the trailer that has an issue every time the lab goes to Blackrock or Spaceport was taken to a repair shop a week before the launch; although the drive out to the launch roughed up the outside of one of the trailer’s tires, a quick stop in Tucson ended up solving that issue easily and more severe issues were avoided. With these preparations in order, the lab left on Wednesday and Thursday to drive out to Truth or Consequences, eager to launch and see years of hard work fly to space.
Apart from the aforementioned tire concern near Tucson, the lab had a smooth drive out to New Mexico, and arrived at the campsite just outside of Truth or Consequences just after sunset on Thursday. Friday morning brought an early wake-up in order to drive to the Vertical Launch Area at Spaceport America, where the lab quickly unpacked and started to prepare their respective stations and the vehicle for launch. The plan was to do a full launch rehearsal for Friday afternoon, ideally finishing before dark to allow for as much sleep as possible. Although the vehicle itself, the launch tower, and the ignition system were ready for this rehearsal shortly after lunch, some small complications with the avionics and recovery systems led to schedule delays, for which the early rehearsal time provided plenty of leeway. By the time these issues were rectified, it was well past sunset, and two items had to be addressed: preparation of the lab and the vehicle by completing a full launch rehearsal, and plenty of sleep, especially for the launch operations team that would have to make key decisions in the final hours before launch. The launch day script provided the solution for the first of these, as a large amount of work could be done while vital engineers got sleep until their presence was necessitated by the script. The latter issue was rectified by a great solution that the avionics team in particular implemented, by having a “night shift” and a “day shift” of engineers, where the “night shift” would solve any issues or bugs with their system, while the “day shift” was responsible for the launch events. This seamless system provided valuable sleep while still allowing work to be done, and the rehearsal was completed early enough to allow for a Saturday morning launch.
The sun rose on Saturday morning and lab members could be seen across the Vertical Launch Area, prepping the tower, the vehicle, and each subsystem for the launch. After a brief setback with the final integration of the vehicle, everyone was set for launch, Traveler IV was set into the tower, and the ignition system was prepared for insertion. The checklist called for a check of the avionics unit’s preparedness and appropriate calls to ensure a cleared airspace before insertion of the igniter. While the avionics check came back in the clear, the airspace was deemed to be unsuitable for launch on Saturday, and the launch had to be scrubbed until Sunday morning. Determined to make the most out of the day, the lab still ran through the rest of the launch script, excluding the ignition system, to ensure that all teams were appropriately prepared for Sunday’s launch attempt. At this point, the lab had run through a full launch rehearsal twice in less than 12 hours and was faced with high winds at the campsite. Many people went to their tents to sleep, while others went back to Truth or Consequences to get a shower or went to tour the facilities at Spaceport America. The lab regrouped shortly before sunset for a well-deserved dinner and early bedtime before the early wakeup calls of Sunday morning.
Waking up to a cold, dark desert on Sunday morning did not deter the engineers of RPL, as everyone prepared to finally launch the rocket that had been the focus of the lab for nearly 7 months. In order to avoid a more severe wind forecast than the previous day, the lab pushed to be ready for the earliest launch that the launch window could provide for. Again, integration of the vehicle brought no significant issues, Traveler IV was brought to the pad and inserted into the tower, the avionics system was confirmed operational, and the airspace was confirmed clear for launch. Now, the igniter could be inserted and put in a safe state, the tower raised to the final launch angle, and the very few trained personnel who were still at the pad returned to camp.
The countdown over the loudspeaker in camp brought a hush over the crowd at Spaceport. Generations of lab members were gathered to witness history in the making. The final few seconds slowed until the rocket was ignited and propelled forward to space. Traveler IV finally flew, clearing the tower, burning out its motor, and continued to the final frontier. The avionics team, in a departure from the previous launch, was in communication with the vehicle for the entire motor burn, and was able to reestablish communication at apogee with the unit in order to announce the declaration that the lab had been anxiously waiting for since September: the drogue parachute had deployed, and Traveler IV would come back to lab intact. While the rest of the camp celebrated a decade and a half of work bringing RPL to space, the avionics team confirmed touchdown as the GPS unit reported a final landing location.
A small team drove out with Spaceport personnel to recover the rocket, having to traverse about 2 miles each way of shrubbery, cacti and dirt from the point where the cars could no longer keep traveling before finally seeing the vehicle. The nosecone and a fully intact airframe, a far departure from its predecessors, stood out against the New Mexico background. Charring on the nosecone and a lack of white paint remaining on the vehicle, as the design had predicted, confirmed that the vehicle had indeed gone fast, presumably faster than Fathom II, but only careful analysis of the data recorded on the avionics unit would yield a final apogee number. Additionally, the fins appeared to have suffered some damage to their leading edges during flight, which are thought to have caused increased drag and decreased overall flight performance. The nozzle, which was repaired before the final motor integration, had sustained damage during flight as well; although unconfirmed as of now, this is considered a possible explanation for the strong oscillation of the vehicle seen during the early seconds of flight. After the data from the avionics unit was downloaded and pictures of the state of the vehicle when it was found were taken, the long walk back to the cars with Traveler IV was done, bringing the vehicle back to camp and an excited group of Trojans. The return to campus was largely uneventful as the lab returned to USC for a well-earned rest.
Since the GPS unit did not maintain a lock throughout the flight due to the rocket’s high altitude and speed, rigorous analysis had to be performed on the data collected by multiple other instruments on the avionics unit. As a result of Traveler IV, significant effort is being driven towards the formation of a data analytics team, in the pursuit of progress for future rocket development and test firings. After the past 3 weeks, this analysis (which can be found here) produced a conservative apogee altitude estimate of 339,800 ft AMSL with an uncertainty of +/- 16,500 ft, producing a confidence of 90% that the vehicle crossed the Kármán line at 328,084 ft (100 km) AMSL. This altitude makes Traveler IV RPL’s highest-performing rocket to-date, as well as the highest performing fully student-designed and student-built rocket of all time. It is also the first student designed and built rocket to reach space and be recovered. This conclusion has been reached by taking all possible care to validate all collected data, tabulate and quantify all sources of error and uncertainty, and, when necessary, err on the side of underestimating the final apogee number. Data points which pushed the final estimate higher, yet were not validated by other live readings, were rejected from the analysis. Overall, the aforementioned confidence interval of 90% reflects a highly conservative approach to determining the vehicle’s apogee, and as such has the full support of the RPL team. USCRPL has competed in the collegiate space race with a variety of other teams since the lab’s founding in 2005, including established teams from Princeton, MIT, Boston University, UCSD, Berkeley, and Portland State, as well as top international contenders such as Delft University (Netherlands), the University of Stuttgart (Germany) and TU Vien (Austria). This active competition and inspiration from teams around the world has, without a doubt, spurred this lab forward and made this achievement a reality.
The immense amount of work done over the past 14 years by every generation of RPL members has led to this moment; while the lab has reached its original goal, it now seeks to go forth and tackle new problems, creating new vehicles to reach new heights. Every current member of this lab wishes to thank the alumni, faculty, department staff, the university, and all others who have supported this dream for so many years. This outrageous goal that a few teenagers had almost a decade and a half ago has finally been achieved, and every second that someone has spent working or making something in lab since then has led to this accomplishment. There are truly no words to describe how incredible this achievement is for the lab and the university, but rather it should stand as an example of how perseverance and tenacity are the core components of every rocketeer’s character. It is truly fitting, after all of this, to sign off in typical fashion, as this group continues to seek new, even more ambitious goals: Flight On!