This document is separated into two sections, the test specification and the test procedure.
The test specification section defines the purpose of the test, the test approach, the item under test, test sequence, test facility, pass/fail criteria, required documentation, participants and test schedule.
The test report section gives directions for conducting a test activity in terms of description, resources, constraints and provides detailed step‐by‐step instructions for conducting test activities with the selected test facility and set‐up.
This document aims to confirm the structural integrity of the coupler under cryogenic conditions by performing thermal cycling, monitoring deformation, checking for cracks, and verifying that bolted joints do not loosen.
It provides the guidelines to the person performing such tests.
It covers the testing protocol as well as the different points of analysis.
It does not cover the actual analysis of the results, neither the test report.
There are 3 main types of documents which relate to testing activities.
Test specification section explains:
Document should be prepared after the baseline AI&T and ~1 month before the actual test.
Test procedure serves as a detailed plan for each individual test, it contains (among other things):
Document should be prepared after the test specification and at least ~1 week before the actual test.
The requirement verified by this TSP is:
No other requirements are covered by this cryogenic test. All other requirements are verified through separate inspections, mechanical tests or analyses.
The main issue with this test procedure is access to temperatures cold enough to suit the requirement.
A cryogenic chamber is not accessible, therefore the test has to be achieved using the flow of cold liquid oxygen in the cap couplers during VSFT.
- The main constraint that arises is therefore that this test must be accomplished during VSFT of the Firehorn launch vehicle.
Testing Objectives:
To verify that the Firehorn standard coupler can withstand thermal stresses and avoid unscrewing phenomena when exposed to temperatures as low as –180°C, fulfilling REQ_04.
Testing Methods:
All of the couplers will be assembled on the vehicle and fastened according to 2024 Coupler DDF standards. The test will occur during the VSFT, and will be accomplished by letting liquid oxygen, which has a boiling point of 183°C, flow through the Caps iteration of the couplers, inside the tank.
This allows for seamless integration of the test inside of the VSFT event.
After the event, visual inspection and torque measurements will verify that no cracks, deformations, or loosening occur.
Test Environment:
The test will be conducted at the ERT testing facility (TF). The facility must be accomodated for complete VSFT of the Firehorn I vehicle.
Once again, this test must not only be conducted at the TF, but also during the VSFT of the Firehorn I vehicle.
Test Data and Scenarios:
Temperature vs. time profiles will be logged inside the TF. Torque readings before and after the cycle will be recorded. Any deformation or cracks will be documented with pictures. An additional 3D printed PETG mould could be considered to better estimate eventual coupler deformation.
Configuration of Item Under Test:
The test item is a flight-ready coupler assembly manufactured and inspected according to 2024_C_ST_COUPLERS_DDF and 2025_C_ST_COUPLER_IR.
Main Tools Needed:
The main test requirement is to maintain measurement accuracy for temperature (±1°C) and torque (±0.1 Nm).
Personnel must follow all TF safety procedures.
Test Pass :
No visible cracks or permanent deformations.
No loss of bolt preload (torque) or unscrewing.
No material failure or damage beyond acceptable surface marks.
Test Fail :
Visible cracks or permanent deformations.
Loss of bolt preload (torque) or unscrewing.
Material failure or damage beyond acceptable surface marks.
Teams and Roles:
Schedule:
The test is expected to take place on VSFT day. The couplers must be fully inspected before test. Any delays in Firehorn vehicle assembly could affect VSFT scheduling, and thus this test.
| Sub-System | Part Name/ID | Type of Part | Version ID |
|---|---|---|---|
| Structure | 214201_Coupler_Female | Flight hardware | All iterations |
| Structure | 214202_Coupler_Male | Flight hardware | All iterations |
Test setup, apart from coupler fastening to the LV according to DDF standards by structures members, is handled by TF staff. It involves complete setup of the LV for VSFT procedure inside the TF.
| Packed ? | Equipment |
|---|---|
| ☐ | FHI LV |
| ☐ | TF Thermocouples |
| ☐ | Torque Wrench |
| ☐ | Data Logger |
| ☐ | Camera |
| ☐ | Gloves and protection glasses |
| ☐ | 3D printed moulds |
The test will be conducted at the EPFL Rocket Team testing facility (TF), during the Firehorn I VSFT event.
Specific event conditions are ensured by TF staff.
| Safety Concern | Probability | Impact | Severity | Mitigation | Post-Mitigation Probability | Post-Mitigation Impact | Post-Mitigation Severity |
|---|---|---|---|---|---|---|---|
| Test item damage during handling | Low | High | High | Use proper procedures and handle all test items with care. | Low | Low | Low |
| Data logger / thermocouple malfunction | Low | Medium | Medium | Data evidence useful but not necessary; LOx presence proves sub -180°C temperatures solely by its existence | Low | Low | Low |
| Safety Concern | Probability | Impact | Severity | Mitigation | Post-Mitigation Probability | Post-Mitigation Impact | Post-Mitigation Severity |
|---|---|---|---|---|---|---|---|
| Exposure to LOx and cold burns, or to fire from engine exhaust | Low | Low | Very High | Wear PPE (cryo gloves, goggles); strictly follow TF procedures and staff instructions. | Very Low | Low | Very High |
| Done ? | Step | Tool |
|---|---|---|
| ☐ | Perform visual inspection; note any pre-existing defects | Camera / Inspection Form |
| ☐ | Tighten bolts to nominal torque; record values | Calibrated Torque Wrench |
| ☐ | If necessary, attach thermocouples at specified points | Thermocouples, Tape |
| ☐ | Check thermocouple connectivity (if applicable) and logger status | Data Logger |
| ☐ | Conduct TF safety briefing with all participants | - |
| Done ? | Step | Tool |
|---|---|---|
| ☐ | Record VSFT event with a clear view on couplers | Camera |
| ☐ | Confirm data logger is recording without faults | Data Logger |
| Done ? | Step | Tool |
|---|---|---|
| ☐ | Remove thermocouples carefully (if applicable) | - |
| ☐ | Inspect for deformation or damage on all couplers, record all findings | Camera |
| ☐ | Measure bolt torques and compare to pre-test readings | Calibrated Torque Wrench |
| ☐ | Archive all logged temperature and torque data | Data Logger, PC |
| ☐ | Complete checklist and help TF staff for post-VSFT procedures | - |