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MIT Rocket Team > Hermes Webbing Lengths > Complete Hermes Unlabeled Webbing.jpg

MIT Rocket Team > Hermes Webbing Lengths > Complete Hermes Labeled Webbing.jpg

For the Hermes Pathfinder vehicle, the relevant dimensions are:

Variable	Length (in inches)	Description
h_mp	57.4	Height of the mission package from nose cone tip to the end of the airframe
l_mp	14.5	Depth into the cup
l_fc	7.6	Depth of booster coupling section
h_fc	86.23	Total height of booster including coupling section.
R_B	7.5	Height of the main deployment bag, not including flaps (should make sure there is enough margin on relevant constraint(s)).
D_M	114 (9.5 ft)	Diameter of the main parachute
R_M	80.6	Height of the main parachute (found using 0.707 aspect ratio): R_M = D_M*0.707
S_M	126	Length of shroud lines on the main parachute (may change when we update the main)
R_D	31	Height of the drogue parachute (measured 2/15/2018)
S_D	100	Vertical length (accounts for confluence angle) of the drogue shroud lines. Taken from the DGB parameters spreadsheet.

These calculations and constraints are only a preliminary estimation, with the following assumptions:

Neglect drogue deployment bag as of right now, we will take this into account on calculations further down the line.
Vehicle dimensions are subject to change
Main parachute shroud line length are subject to change–I also don't think this value accounts for the confluence angle, so it will actually be a little lower than advertised.

Constraint	Description
W_C,D > R_B	The line connecting the top of the main chute canopy to the inside of the deployment bag must be long enough such that the main parachute is not stuck inside the deployment bag upon full line extension.
W_A,H > W_A,E,F,G + R_D + S_D + l_fc	When lines between the mission package and fin can are fully extended, the drogue parachute must be within the airstream.
W_A,H > l_mp + h_mp + l_fc	Assuming full line extension, the mission package and booster section should not hit one another during descent. This neglects the effect of drag on these sections and their respective masses.
W_A,E,F,G - l_mp > 9h_mp -	This constraint reduces the impact of forebody wake on the drogue parachute during drogue descent. The same definition of forebody is chosen as in the previous constraint for the same reason. We subtract the vertical height of the shroud lines to reach a total canopy distance of ~9 forebody diameters. Unknown User (jcoray@mit.edu) add source?