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Harcke, L. J.

Publications and source records attributed to Harcke, L. J..

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Radar Observations of the Icy Galilean Satellites During 2000 Opposition

We report results of radar observation campaigns of Europa, Ganymede, and Callisto carried out during the November/December 2000 Jovian opposition using the Arecibo 12.6 cm, Goldstone 3.5 cm, and Goldstone/VLA 3.5 cm bistatic radars. Additional information is contained in the original extended abstract.

Harcke, L. J.↗
NASA NTRS2001

Radar Imaging of Mercury's North and South Poles at 3.5 cm Wavelength

The Goldstone Solar System Radar has been used to image the north and south poles of Mercury during the inferior conjunctions of February 2001 and June 2001. The sub-Earth latitude was -10.7 degrees in February during observations of the southern hemisphere, and +8.4 degrees in June during observations of the northern hemisphere. These excellent viewing angles provided an opportunity to resolve the radar bright material in polar craters at 6 km range resolution. Fine-scale (1.5 km) resolution images of the northern craters have previously been obtained at 13 cm wavelengths during the July 1999 inferior conjunction. However, due to geometric constraints, the Arecibo radar cannot observe the southern polar region of Mercury until 2004. Our new Goldstone 6 km data are a factor of two higher resolution than Arecibo data collected in March 1992 at 15 km range resolution, and will remain the most highly resolved images of the south polar region for the next few years. Additional information is contained in the original extended abstract.

Harcke, L. J.↗
NASA NTRS1997

Comparative Study of Optical and Radio-Frequency Communication Systems for a Deep-Space Mission

We have performed a study on telecommunication systems for a hypothetical mission to Mars. The objective of the study was to evaluate and compare the benefits that microwave-X-band (8.4 GHz) and Ka-band (32 GHz) - and optical communications technologies a afford to future missions. The telecommunication systems were required to return data after launch and in orbit at 2.7 AU with daily data volumes of 0.1, 1.0, or 10.0 Gbits (Gb). Spacecraft terminals capable of delivering each of the three data volumes were proposed and characterized in terms of mass, power consumption, size, and cost. The estimated parameters for X-band, Ka-band, and optical frequencies are compared and presented here. For all cases, the optical light terminal exhibits about 60 percent of the mass of the corresponding radio frequency (RF) subsystem. Power consumption is comparable for all three technologies at a 0.1 Gb/day data volume, but the power required at either Ka-band or optical is less than half of the X-band requirement at 10 Gb/day. These benefits can be obtained only with a suitable investment in reception facilities for Ka-band or optical frequencies.

Hemmati, H.↗