Path Forward

Want to replicate deployment forces from Hermes I: 2018-07-21-serial-5102-flight-0002.eeprom

Need to write detailed test procedure, better logging of tests, and better understanding of COTS altimeters. 

Likely test will be to attach lines like in deploy, and drop onto lines in BC using a load cell (not just altimeter accelerations).

Structures Next Steps:

1. All nuts should be epoxied in on back side, or otherwise somehow fastened on better (maybe locking nuts). Almost all the bolts were loose after the three drops. 

2. Need the heat set inserts in the top 3D printed piece so we can appropriately fasten the structure to the payload bulkhead.

3. Rebuild structure. 

4. Make parts for at least 2 more AV towers, maybe 3. Consider adding more bolts to attach to payload bulkhead.

5. Figure out a way to fasten fireflies from the top, and keep SD cards in. 

Avionics Next Steps:

1. Learn to better get data from COTS altimeters, i.e. better control of turning them off and on. 

2. Attach screw switches so we can test these.

3. Check that COTS altimeters programming is correct, mostly unsure about Marsa main setting.

4. Finish cameras so we can test these. 

5. (Low priority) better connections for pyros connecting to Pyxida (NOT NEEDED FOR HERMES III)

Shake Test 1 

First attempt:

  • Dropped from around waist height 

  • Acceleration: 5 m/s^2

Second attempt:

  • dropped from around shoulder height

  • Acceleration: 18 m/s^2

  • Christmas light fell out

Third attempt:

  • Slammed the entire structure down
  • Whole AV tower broke
  • Measured 50 gs on Marsa, 70 m/s^2 on Telemega (Hermes I saw 140 m/s^2 max acceleration) 
  • These numbers seem fishy/not a great test

Notes overall:

  • All nuts were loose afterwards

  • SD card came out 

  • Firefly camera turned on

  • Used the 6061 non-optimized payload bulkhead

  • Used ground test MP tube (NOT flight)

  • Received telemetry the whole time 

  • Had continuity before and after test

Images of aftermath below:

side view:

SD card popped out of firefly:

broken piece of AV tower


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1 Comment

  1. Unknown User (astrocrg@mit.edu)

    Some thoughts:

    What was the shock load on the third test?

    Do we have graphs of acceleration during these tests?

    Using the 7075 bulkhead will add extra stress concentrators.

    Using nuts instead of heat set inserts significantly increases the stress concentrations on the end cap.

    SD cards flying out is bad, but not catastrophic. All the shock events happen after the coolest video (except for the parachute cameras). As long as the SD cards stay in the avionics bay we should be fine. Can we tape over them? Make 3d printed covers?

    Loose nuts is also not catastrophic, but still bad. This assembly should use nylock or similar locking nuts to help keep things together.