No abstract available

[en] Large transient pressure pulses, referred to as a helium hammer, which occurred in the transfer line of the main cryogenic tank during the development tests of the Infrared Astronomical Satellite, launched on January 25, 1983, are analyzed, and the measures taken to prevent a failure described. The modifications include an installation of a 2.3-liter surge tank upstream, and a back-up relief valve downstream, of a burst disk. The surge tank is designed to attenuate a 0.33-MPa pressure pulse at the inlet down to 0.092 MPa at the outlet. A mechanism of the pulse generation is suggested, which involves flashing and rapid recondensation of the small amount of liquid entering the warm section of a transition to room temperature

[en] NASA plans to use superfluid cryostats for a number of missions requiring temperatures in the superfluid regime, below 2.172K. The work reported here provides an operational demonstration of the usefulness of porous plugs for liquid-vapor separators and associated temperature control in a zero-gravity environment. Previously reported work on superfluid filters is expanded to find useful materials to match a range of requirements for cooling power, temperature range, and conditions for venting to space. (author)

[en] The behaviour of nearly-saturated superfluid helium films, several hundred Angstroms thick was investigated under zero gravity conditions in a small cryostat carried on a 0.3 m diameter, 3 m long sounding rocket, using a quartz microbalance technique. The flight provided 30 s of high acceleration, about 5 min. of zero gravity, and 90 s of mg acceleration. The temperature of the experiment ranged from 1.67 to 2.15 K. In contrast to ground test results, thick films uniformly distributed on all surfaces were observed in zero gravity. (author)

[en] Atkin's theory of third sound in thick films of superfluid helium-4 has been extended to include a heat source for excitation. Calculations based on the resulting equations reveal the physical structure of third sound, and it is shown that this structure is not consistent with the standard description, which is based largely on qualitative analysis. Calculations also predict the existence of solitary waves, a new type of third-sound signal excited by very short heat pulses. They have not yet been observed experimentally. Additional calculations show in detail how such waves are generated at a localized heater. Results of various observations of third sound reported in the literature during the past 30 years are studied with the aid of the more complete theory. This study indicates a number of factors that complicated interpretation of the observations and suggests that large discrepancies between theoretical and experimental results that have been reported may be largely due to inappropriate comparisons. Conditions favorable for observing individual normal modes of third sound, where interpretation of the results should be particularly transparent, are investigated and could serve as a useful basis for new experiments. A direct method for accurately measuring the vaporization coefficient utilizing results in this article is described. This coefficient is of central importance in accounting for third-sound attenuation. Failure to account for that attenuation was believed to be a major deficiency of the theory in the past. Also, an energy conservation law is derived and then used to help explain the physical nature of third-sound attenuation

[en] An experiment to investigate the properties of superfluid helium in a microgravity environment flew on the Shuttle on the Spacelab 2 mission in July and August of 1985. This paper summarizes the flight experiment and describes some preliminary results. The experiment comprised an investigation of long-wavelength third-sound waves in micron-thick films, a study of the motions of superfluid helium under milli-g and micro-g accelerations, and measurements of the fluctuations in temperature associated with the small motions of the bulk helium. An additional objective was to qualify and characterize a reflyable, space-compatible cryostat