Reefing Parachute Research

9/15/2024

Goals:

Develop a reefing parachute that successfully deploys and efficiently controls rocket flight/descent.

Purpose:

Condensing two parachutes (drogue + main) into a singular parachute that can perform the actions of both.

Skirt Reefing:

• controls canopy shape by routing a reefing line through reefing rings attached to the skirt of the canopy

Suspension-line reefing:

• controls the canopy shape by tying all the suspension lines together at some point between the canopy and the payload

Canopy reefing:

🦑: Not a fan of reefing the suspension lines as it seems there can be issues of it sliding down which could make the parachute expand slowly before the proper time.  I would be more interested in looking at skirt reefing primarily and then canopy reefing.  Canopy reefing could (negligibly) experience the same issues as suspension line reefing but the effects seem to be minimized by the parachute itself.

Line cutters:

https://www.apogeerockets.com/Building-Supplies/Recovery-Equipment/Tender-Descender/Piranha-Line-Cutters

          https://www.apogeerockets.com/Electronics_Payloads/Dual-Deployment

https://shop.fruitychutes.com/collections/recovery-tethers-line-cutters/products/td-2-recovery-tether-up-to-100lb-rockets

https://www.tinderrocketry.com/the-mako-para-cord-cutter

https://www.tinderrocketry.com/the-piranha-cutter

Line Material:

Open ended, nothing specific is used from what it seems.  Obviously needs to be cut-able by the line cutter used.

9/15/2024

Lines Diagram:

Assumes separation point is between the MPT and nosecone. Also assumes a skirt-reefing method where the line cutter is attached with lines/avionics wiring to the MPT. The reefing line remains attached to the parachute after the line is cut, so no components should fully separate from the rocket at any point.

10/3/2024

Parachute sizing was found using the drag force equation at the bottom left corner of figure 6.  Putting in average assumed values resulted into a previously made spreadsheet calculator resulted in a total diameter of roughly 9 feet and a reefed diameter of roughly 3 feet (updated on 10/25 to account for 80lb wet mass, not 70lb. This caused an increase in main parachute diameter from 8ft to 9ft, and minimal change in drogue diameter).

Figure 6 Spreadsheet calculator and values used

Using the values in the spreadsheet, the shock force was found on OSCalc as shown in figure 7.  For the drogue opening at 30000 ft, the upper bound of force is calculated to be 51.57 slugs*ft/s^2. For the main deploying at 2000 ft, the upper bound of force is calculated to be at 740.4 slug*ft/s^2 (values recalculated on 10/25 to account for 80lbs wet mass, not 70lbs).

(main parachute) 

(drogue parachute)

Figure 7 OSCalc results

10/06/2024

We developed a concept for the reefing skirt. 

Our concept is to stitch webbing onto the existing shroud line connections at the bottom edge of the parachute. Since there's already a connection point there for the lines we figured it would be a better place to stitch something else onto as compared to another point on the bottom edge of the parachute where the fabric is more fragile. The reefing line will be fed through all of these webbing loops and tied into a loop of the appropriate circumference to achieve our desired cross-sectional area.

We will have two line cutters at two points on the reefing line for redundancy and the wires to each cutter will be attached to the reefing line to hopefully prevent them from getting wrapped around as much. If a line cutter demonstration shows that they eject hot gas/flame on activation that would potentially damage the parachute material, we will make small covering bags for each line cutter to prevent the hot gases/flames from touching the parachute material.

The Parachute Systems Design Manual, Figure 5-76 indicates that the tension force on the reefing line is a very small fraction of the shock force (maximum 4%), we will use 4% of the shock force when sizing reefing lines. 

Parachute Prototype List:

 - Parachute

 - Nylon webbing (loops)

 - Nylon cord (reefing line)

 - Line cutters x2

 - Black powder and associated safety things

 - E-matches

 - 9-volt battery and wires

 - sewing thread

 - epoxy and qtips

 - wire cutter

 - small lightweight hammer

 - needlenose pliers

 - 7/32 drill bit

11/10/24 - Post Tow Testing Discussion

Reefing Sizing + Shape

https://ntrs.nasa.gov/api/citations/20130011075/downloads/20130011075.pdf

FSI modeling of the reefed stages and disreefing of the Orion spacecraft parachutes | Computational Mechanics

• Current design
• Not mathematically possible to get 3 ft drogue from 9 ft main
• Tried to hold 8’ parachute closed with 0’ reefed diameter and max diameter is too big
• Currently reefed at bottom
• Need to find another method

• Orion parachute goes from 40 ft to 11 ft and reefs at the bottom once, with more of a “lightbulb” shape (potentially using less material or an extra line?)

Need to find a way to get more vertical “lightbulb” shape

• Reefing higher up
• Venting (how Orion does it? We are going to email people (Jared Daum jared.daum@nasa.gov) to ask)
• Orion has a top section (reefed max diameter) that does not expand much after disreefing. Stays similar and becomes the top of the parachute. Area under that is very narrow before disreefing and then expands drastically

1. Use a 3 ft drogue and attach extra material to create the 9 ft main when disreefed

• Potentially connecting shroud lines to the bottom of the parachute rather than to a specific point
• Reefing line will still likely be at the bottom of the parachute

1. Have multiple reefing sections

• To create the lightbulb shape
• Material might bulge in between reefed sections 

Wires

• Making sure ematch to long wire attachment is more secure (soldering, HEAT SHRINK)
• Need to determine why wire experienced force
• Make sure wire is long enough
• Make sure enough of wire comes out of bag so there isnt pulling before bag opens

Reefing Line Attachment

• Attach a longer wire to the reefing line which ties onto one of the loops (this should prevent cinching of the parachute when reefed)
• Do wind tunnel testing to make sure the loops can withstand force from reefing

Nov 17: Prototype 2 Ideas 

Problem: Can’t reef the parachute as small as we were hoping

1. Maintain one reefing line at the bottom, accept that the diameter will be bigger than we hoped
1. Accept up to 5.5 ft drogue
2. Multiple horizontal reefing lines, stacked up the parachute, potentially connected
3. One reefing line, pleating the sides of the parachute before running the reefing line through

Problem: Pyro wires are unprotected and snapped during tow test

1. Secure wires better: solder connections and use heat shrink tubing, run wire and some rope through the heat shrink
1. Move rope up to where the line cutters are attached to reefing line
1. Braided kevlar (bc that’s what we’re using for the parachute lines and it’s what we have in lab)
2. Solder and heat shrink the line cutter wires to the ignition wires
2. Use more wire, ensure there’s extra length 
1. 1.5x length we’re expecting
1. 25.5 ft (1.5 times MPT riser)

Problem: Parachute was singed where the line cutter was

1. Make a bag of the fire-retardant nylon fabric to cover the line cutter

11/17/2024 - Redesign of Reefing Prototype

Problem: Can’t reef the parachute as small as we were hoping

1. Maintain one reefing line at the bottom, accept that the diameter will be bigger than we hoped
   1. We can accept up to a 5.5 ft drogue and stay within the 65-165 fps descent rate specified by Spaceport
   2. This assumes the C_D stays at 2.2 (which is doubtful)
2. Multiple horizontal reefing lines, stacked up the parachute, potentially connected
   1. 
3. One reefing line, pleating the sides of the parachute before running the reefing line through
   1. 

Problem: Pyro wires are unprotected and snapped during tow test

1. 1. Secure wires better: solder connections and use heat shrink tubing, run wire and some rope through the heat shrink
      1. Move rope up to where the line cutters are attached to reefing line
         1. Braided kevlar (bc that’s what we’re using for the parachute lines and it’s what we have in lab)
      2. Solder and heat shrink the line cutter wires to the ignition wires
   2. Use more wire, ensure there’s extra length 
      1. 1.5x length we’re expecting
         1. 25.5 ft (1.5 times MPT riser)

Problem: Parachute was singed where the line cutter was

1. 1. Make a bag of the fire-retardant nylon fabric to cover the line cutter