First Results of the Goldstone High-Resolution Chirp Radar
Imaging System: Application to Near-Earth Asteroid 2010 AL30
We report the first results of a new delay-Doppler radar chirp waveform system at Goldstone
that improves the range resolution by a factor of five from 18.75 m to 3.75 m. We successfully
tested the new system on diminutive near-Earth asteroid (NEA) 2010 AL30 in January, 2010. 2010 AL30
has an absolute magnitude of 27.2, suggesting a diameter of ~10 meters, and was a target
of opportunity observed only three days after its discovery by LINEAR on January 10. During
2.3 hours of observations, 2010 AL30 moved between 1.0 to 0.8 lunar distances from Earth en route
to a close approach at only 0.34 lunar distances. Due to the extremely short round-trip light-travel time,
the observations were bistatic with transmissions at the 70-m DSS-14 antenna and reception at the
34-m DSS-13 antenna. We imaged 2010 AL30 at resolutions as high as 3.75 m, which reveal a somewhat
elongated and optically dark object roughly 30 m in diameter, making 2010 AL30 one of the smallest NEAs spatially
resolved with radar to date. The new 3.75-m resolution capability at Goldstone offers
significant scientific potential to reveal much more detailed surface features than previously
possible, to yield more detailed 3D shapes, and to substantially improve long-term NEA orbit prediction.
Fig. 1. OC echo power spectra obtained with solution 14 (top) and 16 (bottom). Echo power in arbitrary
units is plotted as a function of Doppler frequency. The frequency resolution is 0.5 Hz.
Fig. 2. Goldstone 40 MHz (0.0375 microsecond) images of 2010 AL30. In each panel, range increases
from top to bottom and Doppler frequency increases from left to right, so rotation is counterclockwise.
Time increases from left to right. The echo bandwidths and visible range extents indicate that 2010 AL30
is a rapid rotator, which is consistent with results from lightcurves obtained by Bill Ryan that
yield a period of ~9 minutes. The entire sequence spans about one rotation by the asteroid.
The images were double sampled, so each row corresponds to 1.875 meters.
Additional information on 2010 AL30's close flyby is available from the NASA Near-Earth
Object Program Office website
Last update: 2011 October 4