Although there are many different methods for recovering a rocket (i.e SpaceX and their landing systems), PTR used a single separation dual deployment system (the body separates between the nose cone and top of the body) This recovery system was also tested on SR-1 and validated during its recent launch.

Creating a single separation dual deployment system is fairly complex, but reliable for the scope of the project. When the rocket reaches apogee, the Avionics Flight Sensor (AFS: an in–house telemetry sensor that controls logging and ejection) ignites the black powder in the ejection chamber to separate the nose cone (tip of the rocket) and release the drogue to stabilize the rocket as it descends. At a certain height (700 feet for SR–1), the main parachute deploys and the rocket is ‘recovered’ upon touchdown.

The ejection system separates the nose cone from the main body of the rocket. The main reason for testing the redesigned ejection system with SR–1 is to determine the possibility of reducing  the amount of black powder residue (similar to gunpowder) that is ejected. The decrease in high temperature particles would minimize the risk of damaging the recovery harness and chutes.

3D printed ejection chamber

Through testing, the LV team qualified their newly designed black powder chamber with a filter (experimental) and one without filter (control). By placing a piece of paper nearby to collect all of the emitted black powder particles, the LV team’s new ejection chamber (ejection canister) with the inclusion of a filter left the least amount of residue. 

Though the ejection system improved through successive ground tests, the rest of the recovery system behaved differently. When SR–1 reached apogee (1,400 feet), only the drogue should have been deployed. While the ejection system performed as intended, there was an issue with the main parachute’s deployment. Because the flap of the deployment bag was not secured, the ejection charge pushed the parachute out prematurely, resulting in the main parachute being deployed at apogee. 

“Although the vehicle recovered safely under both parachutes, this result was not what we planned for. Our competition guidelines state that the main chute must deploy at a target altitude (less than or equal to 1000 ft above ground level).”

This is an issue that the Launch Vehicle team will need to address in the next solid test rocket, SR–2. Resolving the early deployment of the main chute will be essential for recovering the team’s competition liquid rocket.

The recovery harness is a series of tough, lightweight straps that are mounted within the rocket’s body to secure and connect components during the intense forces of ejection, including both the main parachute and drogue. For SR–1, the LV team designed the harness with a Kevlar shock cord (Kevlar is prominent for being bulletproof and its fire resistant properties).

The harness also incorporates a tender descender (a temporary linkage device that separates at a set altitude, allowing the main parachute to deploy). The Kevlar shock cord dramatically minimizes the risk of recovery harness failure from the  ejection system’s residue and immense shock forces generated during parachute deployment. 

The LV team also implemented a new parachute selection process for SR–1. Last spring with PTR, the team was unfamiliar with how the recovery shock force (an abrupt stretching force generated from the influx of air during the parachute’s inflation, resulting in the rapid deceleration of the vehicle and the ‘shocks’ directed at the airframe) would impact the parachute, and selected a drogue parachute whose canopy profile and material were unsuited for high velocity deployments. 

By design, rockets also have a natural tendency to fly into the direction of the airstream. On a windy day without proper stabilization, the rocket will pitch over (fly at an angle), decreasing the vertical altitude and increasing the horizontal velocity. Although PTR reached a maximum speed of 523 mph (Mach 0.7), the vehicle’s liftoff speed was relatively low. As a result, the vehicle’s initial velocity was more sensitive to the higher velocity wind gusts that led to the aforementioned pitching motion. Ultimately, the horizontal velocity, alongside inadequate parachute profile and material strength, caused the drogue to tear.

The LV team’s previous process for selecting the drogue parachute overemphasized the idea of slowing down the rocket as it descended. While this process reduces the shock forces generated from the main parachute’s deployment at a lower altitude, an oversized drogue presents the risk of higher shock forces at apogee deployment. This dilemma is one of the biggest challenges for recovering a rocket because a successful recovery requires the optimization of harness integrity and functionality. For future rockets, the LV team has decided on a drogue parachute made of Kevlar and intends to scale up the recovery harness for the next liquid rocket competition. 

Moving forward, the team plans to experiment with new methods of accurately estimating and reducing shock forces. Learning from the outcomes of both PTR and SR–1, the LV team will pivot focus towards launching SR-2, a solid-fueled rocket equipped with a revised recovery harness and new shock force data acquisition system, in the upcoming Spring Quarter (Q2 2024). 

TLTR:

The Launch Vehicle team of UCI Rocket Project – Liquids successfully launched and recovered SR-1 (Solid Rocket–1) to an altitude of 1,400 feet. This test flight validated improvements made to the recovery system after initially losing PTR (Preliminary Test Rocket) in the Mojave Desert. For SR-1, the LV team tested a new ejection system to reduce residue, a Kevlar shock cord harness to withstand forces during parachute deployment, and a more appropriately sized drogue parachute (that did not tear this time!). While the ejection system performed as intended, an unexpected issue arose when the main parachute deployed early at apogee. Luckily, SR-1 landed safely and the lessons learned from its flight will be applied to future rockets. The team plans to launch SR-2 in the Spring quarter of 2024, with a revised recovery harness and shock force data acquisition system.