Unlike home-cut phonograph records, which can accommodate only a few minutes of audio on each side, the steel wire can be repeatedly rerecorded and allowed much longer uninterrupted recordings to be made. The earliest magnetic tape recorders, not commercially available in the U.S. until 1948, were too expensive, complicated, and bulky to compete with these consumer-level wire recorders. During the first half of the 1950s, however, tape recorders which were sufficiently affordable, simple, and compact to be suitable for home and office use started appearing and they rapidly drove wire recorders from the market. Exceptionally, the use of wire for sound recording continued into the 1960s in Protona's Minifon miniature recorders, in which the importance of maximizing recording time in a minimum of space outweighed other considerations. For any given level of audio quality, the nearly hair-thin wire had the advantage that it was a much more compact storage medium than tape. The Minifon wire recorder was designed for stealth use and its accessories included a microphone disguised as a wristwatch. Wire recording was also used in some aircraft flight recorders beginning in the early 1940s, mainly for recording radio conversations between crewmen or with ground stations. Because steel wire was more compact, robust, and heat-resistant than magnetic tape (which is plastic-based), wire recorders continued to be manufactured for this purpose through the 1950s and remained in use somewhat later than that. There were also wire recorders made to record data in satellites and other unmanned spacecraft of the 1950s to perhaps the 1970s. Poulsen's original telegraphone and other very early recorders placed the two poles of the record/replay head on opposite sides of the wire. The wire is thus magnetised transversely to the direction of travel. This method of magnetization was quickly found to have the limitation that as the wire twisted during playback, there were times when the magnetization of the wire was at right angles to the position of the two poles of the head and the output from the head fell to almost zero. The development was to place the two poles on the same side of the wire so that the wire was magnetised along its length or longitudinally. Additionally, the poles were shaped into a "V" so that the head wrapped around the wire to some extent. This increased the magnetising effect and also increased the sensitivity of the head on replay because it collected more of the magnetic flux from the wire. This system was not entirely immune to twisting but the effects were far less marked.