CHACHALACA: an L=6.6 field-line tracing experiment

CHACHALACA was an L = 6.6 field-line tracing experiment employing an explosive shaped charge barium payload injected at an altitude of 460 km over Poker Flats, Alaska at 12:58:01 UT (pre-dawn, local time), on 9 October 1972. Owing to less than nominal rocket performance, the detonation of the CHACHALACA payload took place below the planned altitude and hence within the Earth's U.V. shadow. Photoionization did not begin until the tip of the streak passed out of the U.V. shadow, a delay of 7 seconds. This delay in the onset of photoionization, coupled with a 10 degree misalignment of the payload axis with the local magnetic field, resulted in a broad diffuse ion streak 200 km wide 6 minutes after injection. The calculated number of ions in a particular velocity interval was significantly higher for CHACHALACA than for the earlier OOSIK experiment. The higher ion yield of the new skirted barium liner used in CHACHALACA compensated to some extent for the large crossfield spread, but it was still not possible to track the barium over the full length of the field line. Reliable triangulation was possible only for 11 minutes after injection