Research in microgravity (low-gravity) combustion promises innovations and improvements in fire prevention and response for human-crew spacecraft. Findings indicate that material flammability and fire spread in microgravity are significantly affected by atmospheric flow rate, oxygen concentration, and diluent composition. This information can lead to modifications and correlations to standard material-assessment tests for prediction of fire resistance in space. Research on smoke-particle changes in microgravity promises future improvements and increased sensitivity of smoke detectors in spacecraft. Research on fire suppression by extinguishing agents and venting can yield new information on effective control of the rare, but serious fire events in spacecraft.
Abstract The near-zero (microgravity) environment of orbitingspacecraft minimizes buoyant flows, greatly simplifyingcombustion processes and isolating important phenomenaordinarily concealed by the overwhelming gravity-drivenforces and flows. Fundamental combustion understanding-the focus to date of the NASA microgravity-combustionprogram-has greatly benefited from analyses and experi-meats conduaed in the microgravity environment. Becauseof the economic and commercial importance of combustionin practice, there is strong motivation to seek wider applica-tions for the microgravity-combustion findings. This paperreviews selected technology developments to illustrate someemerging applications. Topics cover improved fire-safetytechnology in spacecraft and terrestrial systems, innovativecombustor designs for aerospace and ground propulsion,applied sensors and controls for combustion processes, andself-sustaining synthesis techniques for advanced materials. Introduction Combustion reactions are the dominant mode of energyproduction for transportation, electric power generation,industrial fiL,'nac,_, and habitat heating. Combustion is theprincipal reaction in the creation of many commodities,such as the refining of metals _ the synthesis of plastics andceramics. Combustion is also essential to a wide range ofindustrial operations, including process heating, pollutioncontrol waste incineration, cutting, brazing, and welding.Access to the non-convective, microgravity eaviron-meat in cxbitmg and ballistic spacecraft or in ground-based,free-fall facilities has proven to be highly advantageous forcnmbustion research.' In microgravity, buoyancy-inducedflows are nearly eliminated, permitting the isolation of nor-really obscured forces and flows, the creation of simplifiedsymmetries (isolated fuel particles, for example), and theexpansion of experimental time and length scales withoutthe development of disturbances3The application of fundamental knowledge in com-bustion science offers great benefits to combustion-derivedtechnology. An immediate advantage of microgravityresearch is in spacecraft designs and operations, namely, theimprovement of fire-safety procedures based on the under-standing of the nature of fires in space) Because of theimportance of combustion in practice, a wide range of ter-restrial uses for the microgravity-combusfion-science datais also foreseen. The exploitation of these applications isnow the responsibility of a new Center for CommercialApplications of Combustion in Space (CCACS). TheCCACS is ajointly funded NASA/university/industry con-stxfium located at the Colorado School of Mines. The Cen-ter has already identified several technology areas withrecognized potential for commercialization, namely: 1) f'aresafety, 2) combustors, 3) sensors and controls, and4) advanced materials.This paper reviews the status of practical applicationsofctxnbustion and fire research in space through a summaryof combustion-science results in selected fields of solid-sur-face combustion, droplet combustion, and soot formation,and through descriptions of emerging technology in theidentified areas of commercialization.
Fire extinguishment agents range from water and foam in early-design spacecraft (Halon 1301 in the present Shuttle) to carbon dioxide proposed for the Space Station Freedom. The major challenge to spacecraft fire extinguishment design and operations is from the micro-gravity environment, which minimizes natural convection and profoundly influences combustion and extinguishing agent effectiveness, dispersal, and post-fire cleanup. Discussed here are extinguishment in microgravity, fire-suppression problems anticipated in future spacecraft, and research needs and opportunities.
