Last month I had posted about Steel Eagle, a modern-day counterpart to the Igloo White acoustic/seismic sensors dropped on the Ho Chi Minh Trail during the Vietnam War. The use of such remote-sensing pods that embedded themselves in the ground after being dropped by an aircraft weren't just limited to tactical use- a similar program was under taken in the 1960s called Tabasco (the unclassfied project name was Purple Flash) to drop sensor pods from Lockheed U-2 spyplanes flying some of the longest range flights in the aircraft's history over the Chinese nuclear tests sites at Lop Nor, deep in the desert basins of northwest China.
Corona satellite imagery detailed the Lop Nor installation ever since the first Chinese nuclear detonation in 1964 caught Western scientists off guard. The Department of Energy's Sandia Labs in Albuquerque had been working on adapting US seismic equipment used to analyze nuclear tests in Nevada to fit into the air-dropped pods that weighed 285 lbs. The pods were carried under the U-2 wing and a parachute deployed after the drop to slow the pod just enough to not damage the sensors but allow the spike-shaped pod to embed itself in the ground. Once on the ground, a 10-foot telescopic antenna deployed to transmit data to listening posts on the periphery of the People's Republic of China.
On 29 April 1966 the first prototype pod was dropped over the White Sands Missile Range from a U-2 and landed only 800 feet from the target but the sensors were damaged. While the design was being reworked by Sandia, Lockheed and the CIA embarked on a series of long-range flights to see just how much range they could get out of the U-2 to demonstrate the Lop Nor site could be reached from Takhili AB in Thailand.
By 1967 Taiwanese pilots with the RoCAF were training in the United States for the Tabasco flights. On 7 May 1967 the first operational Tabasco mission successfully dropped two sensor pods at Lop Nor, but for whatever reason, no signal was received from them. Another Chinese nuclear test took place that June while the CIA was still trying to interrogate the sensor pods in the desert. Needless to say, it was frustrating for intelligence officials. It was concluded the only way to know for sure was to send another U-2 flight to Lop Nor carrying interrogation equipment to try and activate the pods. On 31 August 1967 another RoCAF pilot took a U-2 to Lop Nor and was nearly ambushed by a salvo of SAMs but no signal was received from the pods.
After two high-risk flights, a second set of Tabasco pods were dropped at Lop Nor, this time by a Lockheed C-130 flown by Taiwanese pilots flying at low level. The outcome of that mission remains classified. After the second Lop Nor mission, the six year program of overflights of the People's Republic of China by the Taiwanese pilots of the "Black Cat" squadron came to an end as improved defenses made further flights too risky.
Source: 50 Years of the U-2: The Complete Illustrated History of the "Dragon Lady" by Chris Pocock. Schiffer Publishing, 2005, p246-252.