NASA Scientific and Technical Aerospace Reports

20040120944 NASA Langley Research Center, Hampton, VA, USA
Preliminary Convective-Radiative Heating Environments for a Neptune Aerocapture Mission
Hollis, Brian R.; Wright, Michael J.; Olejniczak, Joseph; Takashima, Naruhisa; Sutton, Kenneth; Prabhu, Dinesh; [2004];
12 pp.; In English; AIAA Atmospheric Flight Mechanics Conference and Exhibit, 16-19 Aug. 2004, Providence, RI, USA
Contract(s)/Grant(s): NAS2-99092; NAS1-00135; NCC1-02043; 320-10-00
Report No.(s): AIAA Paper 2004-5177; No Copyright; Avail: CASI; A03, Hardcopy
Convective and radiative heating environments have been computed for a three-dimensional ellipsled configuration which
would perform an aerocapture maneuver at Neptune. This work was performed as part of a one-year Neptune aerocapture
spacecraft systems study that also included analyses of trajectories, atmospheric modeling, aerodynamics, structural design,
and other disciplines. Complementary heating analyses were conducted by separate teams using independent sets of
aerothermodynamic modeling tools (i.e. Navier-Stokes and radiation transport codes). Environments were generated for a
large 5.50 m length ellipsled and a small 2.88 m length ellipsled. Radiative heating was found to contribute up to 80% of the
total heating rate at the ellipsled nose depending on the trajectory point. Good agreement between convective heating
predictions from the two Navier-Stokes solvers was obtained. However, the radiation analysis revealed several uncertainties
in the computational models employed in both sets of codes, as well as large differences between the predicted radiative
heating rates.
Author
Aerocapture; Convective Heat Transfer; Radiative Heat Transfer; Neptune Atmosphere; Aerothermodynamics
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GROUND SUPPORT SYSTEMS AND FACILITIES (SPACE)
Includes launch complexes, research and production facilities; ground support equipment, e.g., mobile transporters; and test chambers
and simulators. Also includes extraterrestrial bases and supporting equipment. For related information see also 09 Research and
Support Facilities (Air).
20040111057 Jet Propulsion Lab., California Inst. of Tech., Pasadena, CA, USA
Comparison of Classical and Charge Storage Methods for Determining Conductivity of Thin Film Insulators
Swaminathan, Prasanna; Dennison, J. R.; Sim, Alec; Brunson, Jerilyn; Crapo, Eric; Frederickson, A. R.; 8th Spacecraft
Charging Technology Conference; March 2004; 20 pp.; In English; See also 20040111031; No Copyright; Avail: CASI; A03,
Hardcopy
Conductivity of insulating materials is a key parameter to determine how accumulated charge will distribute across the
spacecraft and how rapidly charge imbalance will dissipate. Classical ASTM and IEC methods to measure thin film insulator
conductivity apply a constant voltage to two electrodes around the sample and measure the resulting current for tens of
minutes. However, conductivity is more appropriately measured for spacecraft charging applications as the ‘decay’ of charge
deposited on the surface of an insulator. Charge decay methods expose one side of the insulator in vacuum to sequences of
charged particles, light, and plasma, with a metal electrode attached to the other side of the insulator. Data are obtained by
capacitive coupling to measure both the resulting voltage on the open surface and emission of electrons from the exposed
surface, as well monitoring currents to the electrode. Instrumentation for both classical and charge storage decay methods has
been developed and tested at Jet Propulsion Laboratory (JPL) and at Utah State University (USU). Details of the apparatus,
test methods and data analysis are given here. The JPL charge storage decay chamber is a first-generation instrument, designed
to make detailed measurements on only three to five samples at a time. Because samples must typically be tested for over a
month, a second-generation high sample throughput charge storage decay chamber was developed at USU with the capability
of testing up to 32 samples simultaneously. Details are provided about the instrumentation to measure surface charge and
current; for charge deposition apparatus and control; the sample holders to properly isolate the mounted samples; the sample
carousel to rotate samples into place; the control of the sample environment including sample vacuum, ambient gas, and
sample temperature; and the computer control and data acquisition systems. Measurements are compared here for a number
of thin film insulators using both methods at both facilities. We have found that conductivity determined from charge storage
decay methods is 102 to 104 larger than values obtained from classical methods. Another Spacecraft Charging Conference
presentation describes more extensive measurements made with these apparatus. This work is supported through funding from
the NASA Space Environments and Effects Program and the USU Space Dynamics Laboratory Enabling Technologies
Program.
Author
Spacecraft Charging; Electric Charge; Capacitance
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