During reentry, the base also served as a water-cooled heatshield. This was theoretically a good way to survive reentry, particularly for a lightweight reusable vehicle. However, using water as a coolant would require converting it into superheated steam, at high temperatures and pressures, and there were concerns about micrometeorite damage on orbit puncturing the pressure vessel, causing the reentry shield to fail. These concerns were resolved using a failure-resistant massively redundant flow system, created using thin metal sheets chemically etched with a pattern of micropores forming a channel system that was robust against failure and damage.