Tutorials specific to the Recovery Subteam
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Deciding which parachutes to use: where to buy them from, how big, and other things to consider
For parachute purchasing, Recovery typically sources from FruityChutes. They also provide us with a 10% discount if you mention that you are with STAR. Their chutes have a coefficient of drag (CD) of 2.2 for large iris or 1.9 for smaller iris parachutes used for drogues which is ideal, we would not want that to significantly decrease.
This is the order of recovery. Note the order of deployment and location.
The purpose of the drogue parachute is to slow down the rocket such that once at terminal velocity we can safely deploy the main parachute. It is deployed at apogee. The drogue parachute should be significantly smaller than the main parachute so as not to exacerbate wind drift. With respect to mounting in the rocket, the drogue is typically attached the the lower portion of the rocket (nose cone side).
The purpose of the main parachute is to significantly slow down the rocket to allow it to land safely and softly. This is to preserve the rocket and materials within it. The main parachute is deployed after the rocket with the drogue parachute has reached terminal velocity. Recently, deployment has been within a range of 700-800 feet of elevation. It should be significantly larger than the drogue parachute. With respect to mounting in the rocket, the main parachute is typically attached to the upper portion of the rocket (booster side).
Our goal in parachute sizing is to reasonably minimize ground hit velocity, the kinetic energy at landing, and drift of the rocket.
We use Open Rocket as our main calculator for kinetic energy, drift, and ground hit velocity. You should also be sure that there is not an issue with the jerk moment, which would occur if there is too much of a difference in size between the drogue and main chutes. If there is an issue, it will be easily identified in Open Rocket.
We typically try to minimize the ground hit velocity. According to IREC regulations: ground impact speed should be no more than 30 ft/s or 9 m/s.
We typically try to minimize the kinetic energy of sections. According to our STAR regulations: maximum section Kinetic Energy should be no more than 100 Joules . This is for the purpose of safety and to ensure delicate components are not broken upon landing .
The upper section, avionics bay, and lower section should all meet this requirement.
where m is the mass per section, v is the terminal velocity post main chute deployment.
We typically try to minimize the wind drift. According to IREC regulations: main deployment should not exacerbate wind drift (eg 75 - 150 ft/s or 23-46 m/s). Furthermore, we have additional STAR specific regulations: drift should be within the confines of launch site, drift should be less than ⅖ of apogee.
Wind drift should be calculated for 10 mph wind = 4.47 m/s
Open Rocket will give results of expected drift based on inputs of weight of the rocket, apogee height, parachute sizes, and wind conditions. Or calculations can be made from the expected flight time.
Where v is wind speed (4.47 m/s) and t is expected flight time.
Tutorial on how to safely and efficiently manage wires.
IREC has some requirements for safety critical wires. This is defined as wiring associated with drogue (or other drag device) deployment, main parachute deployment, and any air-start rocket motors. These requirements are summarized as follows:
“Individual wires should be bundled together to make a harness”
Twisted together
Zip Ties every 5 cm
Mesh sleeving ( should allow for inspection of wiring inside)
Harness supported by plastic P-clamps
All connected items by the harness should be rigidly fixed and cannot move
Allow some slack in the wire
Wires should allow for some slack but avoid excess length when possible. Dedicated wire support can be mounted on the walls so wires can be run-through them conserving space. Wires can also be labeled so that they can easily be distinguished in a timely manner.
IREC wiring requirements and suggestions can be referenced starting at page 23 here:
Updates to the avionics sled to improve ease-of-use during launch.
The avionics sled fits into the avionics bay tube of the rocket. The sled must hold two altimeters and two 9V batteries. On the day of launch, altimeters need to be wired twice - first for ground test and then for the main flight. In order to be time-efficient, it is important that the altimeters can be easily accessed.
The AirBears avionics sled was the same as that used for Arktos. It fit into a 4" rocket and was used for the test launch on Nov 16, 2019. Overall, the design was effective as all components were housed and both parachutes successfully deployed. However, there was difficulty in wiring the altimeters due to their placement along the raised edges where the sled slides into the avionics bay.
The goals of the redesign of the avionics sled for the IREC 2020 rocket were the following:
Optimize the avionics bay for a 6" rocket
Address wiring concerns from AirBears to improve ease-of-use during launch
The new chosen design was an I-beam model, in which the batteries were placed in a center section of the sled and one altimeter was mounted to each side, as shown below. This design somewhat improved the space usage in the vertical direction, but there was significant unused horizontal space. The Recovery subteam selected this design because they felt it was more important to be able to wire the altimeters efficiently at launch than to use the least possible space.
The goals for the avionics bay designs for the 2022 Stage Separation vehicle were as follows:
Integrate sufficient room in at least one avionics bay to accommodate the Common Avionics Stack (CAS).
Integrate sufficient room to accommodate off-the-shelf altimeters in addition to CAS, to allow for flights without CAS integration and also ensure failsafes for early CAS test launches.
Include multiple avionics bays, as the two-stage nature of the SSEP vehicle requires at least one for each stage.
In the end, the SSEP vehicle incorporated three different avionics bay designs:
An upper stage avionics sled used to manage recovery of the upper stage. Its overall structure similar to the IREC 2020 design, but with an additional hole to accommodate CAS. This design placed CAS in its own "hole" in the bottom while the altimeters and batteries were secured to a central "wall".
An interstage avionics bay used to ignite the upper stage motor after stage separation. Its structure is different compared to the other ones; because of the limited space available in the interstage, it is not CAS-compatible. It has similar top and bottom pieces that neatly slide into each other, and are held closed by the bulkheads and spacers.
A lower stage avionics bay used to manage recovery of the lower stage. It is somewhat different from the IREC 2020 design but maintains the same basic structure, with a sled sliding out of two rings, which in this case are connected with an overall housing. Similar to the upper stage avionics bay, it places CAS in its own "level" while the other altimeters are kept on the second level.
Commercial off-shelf altimeters are often required and just nice to have for redundancy. We use the 2 perfectflite stratologger in the avionics bay for main and drogue parachute deployment.
For the most part, the altimeters do not need to be programmed once bought. It can be reprogrammed for different modes including ignoring the first X seconds of flight. Refer to the manual linked at the bottom of this page but the reprogramming wires are purchased and housed in the Etcheverry locker.
Positive and negative does not matter for main and drogue as both sides go to an E-match. Same with switch, both sides are the same. However, make sure that the positive and negative sides of the battery is connected properly and listen to beeps for accuracy.
Manual: http://www.perfectflite.com/Downloads/StratoLoggerCF%20manual.pdf
