# Presentation: 335952

## Section 25

_***Section 25***_
***Pulse Plasma Thruster***

*** ******. . . Charles Zakrzwski***
*EO-1 Pulse Plasma Thruster Systems Lead*

## PPT Key Team Members and Reviews

***PPT Key Team Members and Reviews***

***Team Member***
***Andy Hoskins – PRIMEX Aerospace Co.,  PPT Product Lead***
***Scott Benson – NASA/GRC, GRC EO-1 PPT Lead***
***Chuck Zakrzwski- NASA/GSFC, EO-1 PPT Technology Lead***
***Paul Sanneman- Swales, EO-1 ACS Lead***
***Mitch Davis- NASA/GSFC, EMI Investigation Lead***
***PPT Unique Reviews***
***CDR, 7/97, at PRIMEX, Peer Review***
***Quality Assurance Review, 5/98 at PRIMEX, System Review***
***Pre-Ship Review, 7/98 at NASA/GRC, Peer Review***
***Acceptance Review, 11/99 at Swales, System Review***
***Problem Review, 9/99 at GSFC, System Review***

## PPT Design

- ACE IO

- PSE OPMI

- Main Cap & Plug Charge/Discharge
- Cap and Electronics Temp
- Main Cap & Plug Voltages
- Fuel Gauges

- +28 V Power

**Technology Principle**

**S/C Interface**

## Performance Required

***Performance Required***

***PPT hardware performance is driven by requirements to perform pitch axis attitude control***
***The primary performance requirement of the PPT is deliver the expected impulse bit as a function of command charge level.***
***Impulse bit versus charge time defined by graph in ICD***
***Impulse bit can only be measured at unit level in a specialized vacuum thrust stand facility.***
***Functionality of PPT at the spacecraft level is verified by assuring main and spark plug capacitors charge and discharge appropriately when commanded.***
***PPT temperature and fuel bar measurements are also monitored to assure PPT health.***

## PPT Verification Approach

***PPT Verification Approach***

***Unit Qualification/Acceptance Tests***
***Bench Top Functional***
***Vacuum Functional***
***Random Vibration to Proto-Qualification Levels***
***Impulse Bit Performance***
***Thermal Vacuum (Four Cycles)***
***EMI Measurements***
***Life/Contamination (100,000 cycles per side)***
***Spacecraft Level Tests***
***Bell Jar Vacuum Integration Test with Spacecraft***
***Integration Functional Testing with Load Box and Breakout Box (Pre-Environmental Testing) ***
***Post-Environmental Testing with Load Box (and EMI Shield)***

## PPT Residual Risk

***PPT Residual Risk***

***PPT contributes negligible residual risk to EO-1 Minimal Mission***
***Category III experiment which will not be operated until after completion of minimum science instrument mission***
***Residual Risk to PPT Experiment***
***Inherent to Design***
*PPT single-string device – acceptable for technology demonstration*
***Flight Hardware Development and Test Processes***
*S/C level end-to-end vacuum firing not performed*
*Considered to pose too much risk to ALI*
***Problem Solving***
*Not applicable:  All PPT test anomalies identified and resolved*
***Waivers ( Highlighted in following Test Matrix chart)***

## PPT Test Matrix

## PPT Test Matrix (continued)

## S/C Test Results

***S/C Test Results***

***PPT functioned nominally during all Pre-Environmental Testing***
***No functional testing of PPT during Environmental Testing because of EMI concern***
***PPT powered on and off ***
***Static telemetry was verified during environmental testing***

***Post-Environmental Testing***
***All S/C level anomalies resolved with addition of second S/C test:***
*GSE malfunction*
*Misunderstanding of telemetry formatting*
***PPT is functionally nominal after environments***

## S/C Test Results (continued)

***S/C Test Results ****(continued)*

***Deviations from Expected Values***
***Pre-Environmental Testing: None***
***Environmental Testing:***
*PPT Safehold mode temperatures lower than predicted and previously tested at component level (-35 C versus –28 C)*
*PPT design for non-operating temperature of (-55 C)*
*Lower than expected temperature of no consequence*
***Post Environmental Testing: None***
*Additional testing verified no PPT anomalies*

## Configuration Changes

***Configuration Changes***

***PPT Not Tested During S/C CPTs (with trigger unit and load box)***
***Radiated EMI Concern (See Special Topic Below)***
***PPT Not Fired in Thermal Vac***
***Radiated EMI Concern (See Special Topic Below)***
***Positive independent verification of PPT firing polarity not possible due to implementation of EMI shielding***

## Action Item Status

***Action Item Status***

***High Degree of confidence that PPT flight unit is functionally nominal and will be able to successfully complete flight validation experiment***
***On-orbit check out procedure will allow for software adjustment in polarity***

***Readiness &Residual Risk***

***PRs***
***All open PR’s resolved***
***Waivers***
***All waivers submitted ***

## Special Topic:

***PPT Emissions***

## PPT Emissions

***PPT Emissions***

***PPT Flight Unit exceeds component level radiated emissions by as much as 60-80 db over broad range of frequencies as tested per Mil-461C RE02***
***PPT was successfully tested in Bell Jar while connected to S/C (without instruments) to confirm benign interaction***
***Prior to S/C Environmental Tests the Advanced Land Imager (ALI) team raised concern that PPT emissions could damage ALI focal plane***
***Thin IC layers potentially very sensitive to EMI***
***No Susceptibility data available on ALI or focal plane***
***Ambient discharge of PPT using trigger unit and load box still activated spark plugs which where determined to be the largest source of radiated emissions***
***Effort lead by Code 565 to quantify risk through analysis and test concluded that to obtain conclusive proof that PPT emissions posed no risk to ALI was beyond time and cost constraints***
***Unique design of ALI requires testing with a spare ALI unit with functioning focal plane array which does not exist***

## PPT Emissions (continued)

***PPT Emissions ****(continued)*

***To allow verification of PPT functionality after environmental tests a method of shielding the PPT emissions from the S/C was developed***
***A shield for the PPT which could be attached to flight unit without de-integrating PPT from S/C was developed and tested with PPT breadboard unit to verify its effectiveness***
***A shield box for PPT GSE was also utilized***

- Verification of Shield boxes Utilizing PPT Breadboard

## PPT Emissions (continued)

***Testing of shield boxes with Breadboard PPT verified reduction in emissions to an acceptable level***

## Shield boxes utilized during PPT post-environmental testing
ALI instrument operated nominally after PPT testing
Because risk to ALI from PPT nominal on-orbit operation (without shield box) could not be quantified,  PPT experiment is planned to occur at the end of the baseline science mission as originally proposed

***Shield boxes utilized during PPT post-environmental testing***
***ALI instrument operated nominally after PPT testing***
***Because risk to ALI from PPT nominal on-orbit operation (without shield box) could not be quantified,  PPT experiment is planned to occur at the end of the baseline science mission as originally proposed***

***PPT Emissions ****(continued)*