The Recovery deployment sequence is "lines first," which has several advantages, noted by Wolf in his Parachute Seminar.
Lines First Deployment Example from Knacke (sourced from Wolf)
We will conduct research into the deployment sequence to mitigate possible failures, ensure a stable descent, and help inform our camera choices.
Chute Inflation
To inform our choice of camera, we need to gather information on chute deployment and inflation rates.
Drogue Parachute Inflation
The rate of drogue parachute inflation will depend on the airstream conditions and the parachute dimensions and its materials. To begin analysis, we examined the NASA TM X-1786 "Wind-Tunnel Investigation of Inflation of Disk-Gap-Band and Modified Ringsail Parachutes at Dynamic Pressures Between 0.24 and 7.07 Pounds Per Square Foot."
- Notably, the chute used in the study (~15 feet diameter) is much larger than our expected drogue parachute (~4 feet diameter)
- Study chute had geometric porosity ~12.5%
- Fabric: 2.0 oz/yd2 dacron
- Shroud lines: 550-lb coreless braided dacron, 15 ft long
- 5.52 lb mass
For the purpose of a simplified analysis, we examined a range of possible main-deployment dynamic pressures (using the chart featured in the Hermes Disk Gap Band Design page as a basis for our analysis). This analysis also made use of the atmosisa Matlab function.
First, we examined the range of possible dynamic pressures, which depends on both the deployment speed and air density (which depends on altitude). For a first-pass analysis, the following ranges of altitudes and Mach numbers were selected:
- Altitude: 90,000ft to 150,000ft
- Mach: 0.5 to 2
Terminology
geometric porosity: the percent of the nominal canopy surface area that is removed due to vents and gaps
Resources
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690014164.pdf