Altitude Target Overshoot Analysis

1. Altitude Target Overshoot Analysis November 30th, 2010

2. Introduction On April 17th, 2010, the Madison West SLI2010 Senior Team exceeded SLI target altitude of 5,280ft by 34% (barometric altimeter recorded flight apogee of 7,070ft). Purpose of this investigation: • Re‐evaluate data and procedures that led to the overshoot • Determine the failure pointin data analysis • Devise safety measures that will prevent a repeat of such or similar incident

3. Vehicle

4. Investigation FOCUS - possible absence of red flags in apogee prediction • Rocket reassembled • All parts weighted and compared to records in PDR, CDR, and FRR • No significant discrepancies were found • Existing RockSIM model verified for accuracy • All calculations and data analysis of flight data verified

5. Scale Model Flight 1350ft Simulation Flight Data Cd = 0.49 Barometric altitude data compared with simulated altitude and velocity. Model fitting provided Cdof 0.49. The motor used was AT H250G.

6. Full Scale Low Flight - AT J800T Cd = 0.65 1110ft • The Simulated vs. Actual flight data. Cdof 0.65 was calculated by model fitting using flight data and RockSIM. Weather concerns (low visibility) forced the team to limit the flight to 1,200ft AGL.

7. Motor Selection Deadline At this point, motor selection for SLI launch had to finalized. Based on the measured Cd = 0.65, team selected AMW L1080BB motor, with apogee prediction being 5543ft. Because of AMW L1080BB and AT L850W shortage, the team ended up choosing AT 1390G motor. AMW L1088BB, predicted apogee 5,543ft AT L1390G, predicted apogee 5,843ft

8. Full Scale High Flight - AT L850W 6,100ft • Barometric altitude data from flight. Model fitting provided Cdof 0.48 (this value should have been carried over to further simulations) Cd = 0.48

9. Comparison: Cd = 0.48 vs. 0.65 Motor: AT L1390G Cd = 0.48 Cd = 0.65 At this moment, the inaccurate Cd = 0.65 prediction should have been replaced with the new value Cd = 0.48. Data and simulation indicate that the switch never occurred and the team continued using the incorrect Cd = 0.65 which resulted in 34% overshoot.

10. Full Scale SLI Flight – AT 1390G 7070ft Cd = 0.46 • Barometric altitude data from final flight at Braggs Farm, AL. Model fitting in RockSIM provided Cdof 0.46

11. Flight Tests

12. Conclusions • The multiphase apogee prediction procedure is reliable however: • SLI2010 senior team missed the indication of severe overshoot because they switched two data analysis results. • Cd from low (AT-J800T) full-scale test flight Cd = 0.65 • Cd from high (AT-L850W) full scale test flight Cd = 0.48 • Had the correct Cd been carried to further rounds of simulations, the indication of overshoot would have been clear (simulation predicts 6,900ft)

13. Incident Repeat Prevention • Better management of project files, data and documentation • More detailed labor division among team members • Closer initial estimates of flight apogee • Using the same motor for final test flight and SLI launch flight

14. Questions?