Scope
Overview
This document will analyze the flight of Hermes 1 at Friends of Amateur Rocketry in July of 2018. The document will outline the flight performance of the vehicle, calling specific attention to any deviances. These flight events will be discussed in roughly chronological order, by subsystem. Under-characterized or poorly understood behaviors will be noted for future efforts. A section at the end of this document will discuss lessons learned.
Methodologies
Times are indicated as T+ or T- from the first vertical motion on the rail (liftoff). Times are indexed off of the Telemetrum data.
Timeline
| Time [s] | Flight Event |
|---|---|
| T-3.83 | Ignition |
| T+0.00 | Liftoff |
| 0.27 | Tower Cleared |
| Pierced Cloud Ceiling | |
| 6.75 | Burnout |
| 43.79 | Apogee |
| 48.60 | Drogue Inflation |
| 298.20 | Main Release |
| 300.5 | Main Inflation |
| 363.00 | Touchdown |
Flight Statistics
| Parameter | Metric | Imperial | Other Units |
|---|---|---|---|
| Apogee | 10,187 m | 32,406 ft | 6.14 mi |
| Max Velocity | 557.7 m/s | 1830 fps | Mach 1.6 |
| Max Acceleration | 116.6 m/s^2 | 383 ft/s^2 | 11.9 G |
| Ground Impact Velocity | 9.6 m/s | 32 fps | 21.8 mph |
| Flight Duration | 363.0 s | - | - |
Avionics
Payload
Propulsion
Thrust Curve
Long startup time
The motor took significantly longer to light than previous tests, including the second P motor test that used an identical igniter with twice the propellant. In the P motor test, the igniter lit the motor in less than a second because it was held in the core by gravity until the motor had built up enough pressure to push it out. The smaller flight motor was almost certainly slower to light because the igniter fell out of the motor within a second of firing and thus was only able to light a small portion of the propellant. This theory is supported by the video as you see a bright spot hit the ground shortly after the ematch is heard popping. To prevent this from happening, make sure the igniter includes some faster-burning substance like pyrogen, uses more propellant dust , or is held to the stick with extra wire or something that won't burn like the tape did. Though just a minor inconvenience on a single stage flight, ignition time becomes much more critical on a multistage flight. Care must be taken to not overpressurize the motor, though, so unless it is determined to be essential to a flight, a relatively slow igniter is not a problem and is the safer solution.
Recovery
Piston Deployment
Firing Force
Comparison with Ground Test
Parachute Velocities
Parachute Drag Coefficients (Effective)
It is not possible to do perfect analysis of the Parachute Drag coefficients because we cannot back out the drag on the mission package and booster sections. However, we can determine the effective coefficients (including the drag on these bodies).
Drogue
We trimmed the data so that it didn't include opening shock loads or main opening. We then performed analysis at two different altitudes (~30k ft, ~20k ft, and ~10k ft) in order to see the difference between different altitudes.
Main
Parachute Shock Loads
Drogue
Main
Structures
Integration
Integration began at roughly 1:30 pm PST and the rocket arrived on the pad at roughly 3:00 pm PST.
Lessons Learned
- Having a good checklist would have been beneficial, even though we likely wouldn't have been able to integrate the rocket in the amount of time that we were given before the end of the launch window if we had been following a strict checklist.
- Regular batteries are NOT enough to fire 2 e-matches in parallel. We ran into this problem during the ground test, as well as a previous static fire.
Times are indicated as T+ or T- from the first vertical motion on the rail (liftoff). Times are indexed off of the nadir (aft) facing Mobius camera. The zenith camera timestamps lag by 4.076s. Values are taken from either Pyxida or TeleMetrum data. Most StratoLogger data was unavailable to the author of this document.