A series of 0.2‐ to 3‐gm HNS charges were detonated in vacuums of 10−3
Torr. The resultant freely expanding, detonation product, gas blast achieves terminal velocities of 8 to 12 km∕sec within 3 to 5 μsec after the detonation wave arrives at the free surface. Measured pressure profiles display rise times to maximum stagnation (``reflected shock'') pressure varying from ∼30 μsec, 20‐cm away from a 2.6‐gm charge, to ∼185 μsec, 127‐cm away from 0.2‐gm charge at 10−5
Torr. Rise times were generally shorter at 10−3
Torr; the 10−5
Torr values agree with numerical calculations. Using cube root scaling of charge mass, the observed peak reflected pressure as a function of range may be represented by
the ratio of the range to the equivalent charge radius.