The trouble with prior radar mapping missions, was that only single radar transmitters and receivers were used during any one mission. 3-D images had to be created from data taken during separate orbits, and even separate missions. The widely diverging tracks leads to lower resolution, reduced accuracy in elevation profiles, and of course, uneven coverage of the Earth's surface. The SRTM was to solve all these problems by using a single radar transmitter and two receivers simultaneously, to obtain all data in a single pass using a technique called radar interferometry. Use of this technology is just being trialled on Earth based telescopes in the infrared and optical wavebands.
Space borne optical interferometry is still for the future.
An artists impression of the shuttle with the SRTM mast partially extended. Since 60 metres is a lot larger than the length of the shuttle payload bay, a lightweight, extendable and retractable, but rigid mast was necessary. The whole design of SRTM was very original, both mechanically, electronically, and in terms of signal processing requirements, and pushed the state of the art considerably in many respects. It operated throughout the whole 11 day mission whenever the shuttle was over land. Robert demonstrated many aspects of visual perception that demonstrate that the eye lies.