Slush hydrogen is a combination of liquid hydrogen and solid hydrogen at the triple point with a lower temperature and a higher density than liquid hydrogen. It is formed by bringing liquid hydrogen down to nearly the melting point (14.01 K or −259.14 °C) that increases density by 16–20% as compared to liquid hydrogen. It is proposed as a rocket fuel in place of liquid hydrogen in order to improve tankage and thus reduce the dry weight of the vehicle.
The continuous freeze technique used for slush hydrogen involves pulling a continuous vacuum over triple point liquid and using a solid hydrogen mechanical ice-breaker to disrupt the surface of the freezing hydrogen.
- Christopher P. McKeehan, Terry L. Hardy, Margaret V. Whalen, Maureen T. Kudlac, Matthew E. Moran, Thomas M. Tomsik and Mark S. Haberbusch (April 1995). A summary of Slush hydrogen. NASA
- Density Archived 2008-07-06 at the Wayback Machine.. Astronautix.com. Retrieved on 2012-12-29.
- Mark S. Haberbusch and Nancy B. McNelis (1996). Comparison of the continuous freeze slush hydrogen production. NASA Technical Memorandum 107324. Retrieved on 2012-12-29.
- R. O. Voth (February 1978). Producing Liquid-Solid Mixtures of Hydrogen Using an Auger. Cryogenics Division. Institute for Basic Standards National Bureau of Standards, Boulder, Colorado (report for NASA). Retrieved on 2012-12-29.
- A.S. Rapial and D.E. Daney (May 1969). 1966 – Preparation and characterization of slush hydrogen and nitrogen gels. Cryogenics Division. Institute for Basic Standards National Bureau of Standards, Boulder, Colorado (report for NASA). Retrieved on 2012-12-29.