southwest research institute nsf conference on small satellites plasma instrument miniaturization...

Southwest Research InstituteSouthwest Research Institute

Plasma InstrumentMiniaturization and Integration:

Approaches and Limitations

C.J. Pollock, R. Torbert, and D.T. Young


Plasma Instrument Miniaturization and Integration: Approaches and Limitations

- Functional Guidelines- Measurement Focus- Sensor vs Electronics- System Integration

-Examples of Low Resource Flight or Prototype Instruments- PEPE

- IES- TECHS- MOSS

-Limitations and Pitfalls:- It takes an aperture- It often takes high voltage


Functional Guidelines

Measurement Focus• Disciplined approach that focuses narrowly on priority science• Sensor technologies for disparate plasma regimes:

• Langmuir Probe – Temperature and density of thermal plasma• Segmented Faraday Cup/RPA: High Mach # flowing plasma• Curved Plate ESA: Low mach number, structured plasma distributions

Sensor vs Electronics• In some cases there are limitations to sensor size reduction (aperture size dictates signal)

( X ~ A1A2/L2)

• Other times, the electronics may be irreducible (high voltage circuits)

System Integration vs Modularity(?)• A high degree of functional integration is helpful to minimize resource consumption and unintended functional redundancy;• Still, developmental modularity allows parallel development, often critical for small budget/short time scale flight development


Particle Experiment for Planetary Exploration (PEPE) on Deep Space-I

• Developed as outgrowth of Dave Young’s Internal Research project at SwRI, entitled: Miniaturized, Optimized Smart Spectrometer (MOSS)

• Designed as a low resource, high performance electron and ion composition spectrometer

• Design principals include:• Innovative use of materials to reduce mass (ESAs are plated plastic)• Tight integration of electronics and sensor• Ions and electrons share entrance aperture

• ~5 kg, 5W dual spectrometer with LEF TOF measurement included


Miniature -15kV Power Supply


Flight Model – Ready for Cal


Thermal Electron Capped Hemisphere Spectrometer(TECHS)

• Developed to target thermal electron fluxes in Earth’s ionosphere;

• Extreme miniaturization of tophat ESA necessary to measure low energy electrons in Earth’s ~0.4G field;

• Prime target electron energy from 0.1 to 100 eV

• Radius of curvature of ESA plates ~5mm.

• ESA Analyzer gap < 1 mm

• With analyzer ratio of ~7, application of 1kV ESA voltage would allow viewing of 7 keV electrons;

• Sensor the size of 35 mm film can;

• pre-amp boom and electronics box presently occupies more macroscopic scale.


A Very Small & Very Black Inner Tophat Electrode


TECHS Sensor Elements


E-box and Boom Not So Small (room for improvement)


Ion an Electron Sensor (IES) on Rosetta

• This was an exercise in extreme resourse conservation, patterned on the PEPE development.

• Dual, shared aperture ion and electron tophats with FOV deflection

• No time of flight (read: no ion composition)

• Tightly integrated but no modularity (difficult to troubleshoot and repair)

• Good performance obtained;

• Flight resource requirements: 1.25 kg; 1.8 Watts

• Severe compromises sometimes required. In IES, for example, to save power, the 1st HV step on the z-style MCP stack is 2.5 kV (for both electron and ion stacks), and the stacks are enabled and commanded in common;

• This is scary (perhaps less so for those with rocket background); It has worked well on orbit.


IES Sensor Design


Rosetta Ion and Electron Sensor Parameters.Parameter ValueEnergy

Range 1 eV/e to 30 keV/eResolution (DE/E) 0.04Scan Mode-dependent

AngleRange (FOV) 90 x 360º (2.8p sr)Resolution (e-) 5 x 22.5º (16 azimuthal x 16 polar)Resolution (ions) 5 x 45º (16 azimuthal x 7 polar)

Temporal resolution 3D distribution 3 sGeometric factor

Total (ions) 5 x 10-4 cm2-sr-eV/eV count/ionPer 45º sector (ions) 6 x 10-5 cm2 sr eV/eV count/ion

Total (e-) 5 x 10-4 cm2 sr eV/eV count/electronPer 22.5º sector (e-) 3 x 10-5 cm2 sr eV/eV count/electron

Mass 1040 gVolume 1297 cm3

DimensionsSensor: 73 mm dia x 101 mmElectronics box: 139 x 121 x 64 mm

Power 1850 mWDownlink data rate 5 - 250 bit s-1


A MagCon System Concept

• Magnetometer, e and i+ plasma spectrometer, energetic particles

• A 3-instrument suite, integrated with a single central c&dh

• Instruments are sensors with bare bones co-located support circuitry;

• C&DH system that holds all possible command functions;

• C&DH system holds all possible signal processing functions;


Micro-Satellite Architectural Diagram


Final Draco Bench-Top Configuration

CDPU

Mag Sensor

Mag Electronics

IES Elec.

EPSElectronics


Conclusions

• Significant miniaturization in capable plasma instrumentation is possible;

• Limitations exist, however:

• Aperture size sets limits on sensor miniaturization

• HV requirements set limits on certain electronics miniaturization

• Minimum resource plasma instruments and instrument suites can be focused on limited science goals

• Minimum resource/limited capability instrument suites can also be fielded for constellation-class payloads

• Continual investment in instrument & advanced technology development is a must!

southwest research institute nsf conference on small satellites plasma instrument miniaturization...

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