Colibrí Tech

Puebla | Let It Go (Without A Bang)

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High-Level Project Summary

In this challenge, an alternative solution has been developed, for the safe separation of two parts of an object, in space so that methods such as pyrotechnics or some known robust method are not used. Concentrated on the descent part of any space device, our cutter offers the safe opening of the parachute of this device since it cuts the cable that supports the suspension lines of the parachute without the need to use electricity or pyrotechnics. It is important to mention that the cut is totally mechanical and can serve as a basis for coupling it with the deployment of other space devices such as satellites or sounding.software and tools usedFreeCADCanvaFusion 360Filmora

Link to Project "Demo"

https://www.youtube.com/watch?v=N6qXazFkyiA

Link to Final Project

https://drive.google.com/drive/folders/1Klkgh8Atl5oSeMmwulCxmc7iazKh_mES?usp=sharing

Detailed Project Description

It is a mechanical device that solves the safe separation of two parts of an object in such a way that it does not use pyrotechnics or some other method already known or established. On the other side, it should be noted that THE FOCUS AREA of this solution is for the safe descent of space devices that descend on some surface. In this case, our test part will be the safe descent of a device on the planet Mars, gradually and safely opening the descent parachute. It is contemplated that this cutting device can be coupled, for the separation of other space objects depending on the conditions in the environment or, on parameters such as gravity, oscillations, etc.


The function of the cutter consists of a wedge to do the cut having limits on its sides so that it can slide within a cylindrical space. In addition, with the help of a pair of springs that are retracted by the action of a cable or rope, energy is obtained to drive the cutter or wedge so that the cable that holds the parachute can be cut by the action of the knife edge. The analogy is similar when an umbrella is opened; a button is operated so that the umbrella can come out completely and expand; in a way, the springs release the energy of the compression allowing to cut the cable that joins the retracted parachute and allows it to open or expand.


Some model ideas of the cutter are as follows:









Theoretical calculations 

In order to select the most optimal spring in this design, the following operations were performed.

First step, Hooke's Law was applied:  

                                                                       F=kx

Where: 




  • F (N) is the force.
  • x (m) the length of the extension or compression,according to the case.
  • k (N / m) is a constant of proportionality known as the spring constant.



For the objective of the project, the spring is in the compression state. The calculations performed to find the spring constant are shown below. The spring constant is the amount of force required to move the spring a fixed amount of distance.


Compression spring constant:


                                                                                k = Gd^4 / 8ND^3

Where:




  • d = Wire diameter (mm)
  • D = Average diameter (mm)
  • N = Number of active laps
  • D/d = Correction index 
  • G = Shear modulus 
  • k = Spring constant


Application of the formula for particular cases of the project:


k= (Gd^4)/8ND^3


The material that was chosen for the spring in FreeCAD is the following:



   k = (8 x 10 ^ 3 N/mm^2)(0.8 mm )^4 / 8(4)(6.8mm)^3

                                                                           k = 0.325 N/mm


Doing the corresponding conversion, the following was obtained:

                                                                          k = 0325.66 N/m


Then the spring constant for this particular case where the spring is in compression is:

                                                                            k = 325.66 N/m


The next thing was to calculate the compression distance necessary to be able to generate a force of 1.25N



Explanation of the choice of force for the following equations

To determine the force applied to the spring, it was carried out in a general way, that is, a random value was taken to be able to determine the process with which we could find the distance in which the spring must be compressed to generate a certain force.

                                                                                 F=ma

                                                                                F=(10.127kg)(9.81 m/s^2)

                                                                               F=1.25 N

For a practical case, the following value of F is taken into account:

                                                                               F=1.25 N

Hooke’s law:

                                                                                 F= kx 


Solving for x, the following is obtained:

                                                                                 x=F/k

                                                                                 x=(1,25 N)(325.66 N/m)


Theoretical result: 

                                                                                 x=3.838 x 10 ^ -3 m 


The theoretical result of the distance in m that the spring must be compressed in order to generate a force of 1.25 N is 3.838 mm.


Comparison between theoretical result and result obtained from FreeCAD simulation:


As can be seen in the table, when comparing the results we can see that the simulated results are reliable, since they have a low percentage of error.


Aerospace approach in mechanism simulations

Case 1 with atmosphere and earth acceleration

As a particular case, a CubeSat is taken which has 3U dimensions and a mass between 1kg and 1.3 kg. This will be supported by four strings to the parachute in this first case in the Earth's atmosphere.

Taking into account the spring constant calculated from the material and dimensions chosen for the spring previously explained, now only the force is calculated, this depending on the acceleration on Earth.


Then the spring constant for this particular case where the spring is in compression is:

                                                                            k = 325.66 N/m

                                                                               F=ma

                                                                                F=(1kg)(9.81 m/s^2)

                                                                               F=10 N


Taking into account that the force of the divide between four strings then the force of a single string is:

                                                                               F=2.5 N


Hooke’s law:

                                                                                 F= kx 


Solving for x, the following is obtained:

                                                                                 x=F/k

                                                                                 x=(2.5 N)/(325.66 N/m)


Theoretical result: 

                                                                                 x=7.67 x 10 ^ -3 m


The theoretical result of the distance in m that the spring must be compressed in order to generate a force of 1.25 N is 3.838 mm.


Comparison between theoretical result and result obtained from FreeCAD simulation:

As can be seen in the table, when comparing the results we can see that the simulated results are reliable, since they have a low percentage of error.


Aerospace approach in mechanism simulations

Case 1 with atmosphere and Martian acceleration

As a particular case, a CubeSat is taken which has 3U dimensions and a mass between 1kg and 1.3 kg. This will be supported by four strings to the parachute in this first case in the Earth's atmosphere.

Taking into account the spring constant calculated from the material and dimensions chosen for the spring previously explained, now only the force is calculated, this depending on the acceleration on Mars.


Then the spring constant for this particular case where the spring is in compression is:

                                                                            k = 325.66 N/m

                                                                               F=ma

                                                                                F=(1kg)(3.62 m/s^2)

                                                                               F=3.62N


Taking into account that the force of the divide between four strings then the force of a single string is:

                                                                               F=0.905 N


Hooke’s law:

                                                                                 F= kx 


Solving for x, the following is obtained:

                                                                                 x=F/k

                                                                                 x=(0.905 N)/(325.66 N/m)


Theoretical result: 

                                                                                 x=2.77 x 10 ^ -3 m

The theoretical result of the distance in m that the spring must be compressed in order to generate a force of 1.25 N is 3.838 mm.


Comparison between theoretical result and result obtained from FreeCAD simulation:



As can be seen in the table, when comparing the results we can see that the simulated results are reliable, since they have a low percentage of error.



A Free CAD design software was used, which is FREECAD to be able to make the solids and assemblies. Also, Fusion 360 was used to make exploded views. So that the following model was chosen:


The benefits of the model are as follows:






  •  Low maintenance cost (no need to replace parts).
  • No use of pyrotechnics or robust methods.
  • Ideal size for attaching to other separation and descent objects.
  • Reusable for ground tests.
  • No use of electricity unless conditions require.



We hope to achieve that this cutter can be coupled in different ways to other space devices either for descent or recovery for both ground tests and space tests.


On the other side, we are expected that this type of cutter will also be improved in the future so that it has electronic parts such as timers, actuators or the use of controllers that perform the function of retracting and ejecting the cutter by means of the springs.

Space Agency Data

The model to follow for the development of the CAD file is based on the following image from the resource files:


The cutter that appears in the information serves as a basis to be able to replace the pyrotechnics taking into account the cable that supports the suspension lines will be released if it is cut with our device. It would be as if, instead of using the electric shock, it would only be to cut it mechanically.


Documentation on the descent of a subsystem, showing reefing line cutter.

CSM12_Earth_Landing_Subsystem_pp93-98.pdf (nasa.gov)


Short video with an explanation about the challenge and how they apply it in a separation of parts.

Let It Go (Without a Bang) | NASA Space Apps Challenge - YouTube


Page about the problem regarding the parachute.

NASA - The Root of the Problem: What Caused the Ares I-X Parachute to Fail?

Hackathon Journey

It is a great experience for everyone, where we can develop our knowledge and skills, being engineers, solving problems. We all chose this challenge, since it is of interest to make a small mechanism which fulfills a function, an aerospace approach, having limitations such as dimensions, weight and environment. With this we are contributing great innovation in design to obtain this purpose. Being a great challenge, because many factors intervene, which is a complex mechanism and this in turn can be reused in other projects. Without leaving behind that we are all working online, coordinating to successfully develop the solution.


We thank the organizers of the event for this opportunity in Puebla, giving the support with their mentors and staff. They help us a lot with their feedback and advice. Also to our mentor Dr. Jorge Ferrer-Pérez for the time dedicated to our team, clarifying and guiding us in our ideas.

References







Tags

#ColibriTech #ReefingLineCutters #Engineering #ProjectSimulation

Global Judging

This project has been submitted for consideration during the Judging process.

Let It Go (Without A Bang)

Letting things go in space, or separating spacecraft parts, is often a violent, high-shock event. Your challenge is to design a mechanical separation device that can cut a parachute reefing line, a bolt for an adapter ring, or a cable, or release two parts from each other smoothly in space without pyrotechnics.