Table 1.

Comparison of NASA-Approved Methods for Bioburden Assessment of Spacecraft Surfaces

Methods	NASA implemented	Analysis targets	Microbial diversitya	Quantification	Turnaround time	Cost	Background contamination risk
NSA	Since 1970s	Culturable bacterial endospores	No	Absolute	72–96 h	$b	Low
ATP assay	Since 2010c	Metabolizing cells	No	Absolute	∼30 min	$$	Medium
LAL assay	Since 2010c	Endotoxin producing cells	No	Absolute	∼30 min	$$	Medium

^a Microbial diversity assessment capability.

^b Labor cost is not included and when labor is considered, NSA is more expensive than ATP and LAL assays.

^c Since 2010 during and after Mars Science Laboratory.

ATP = adenosine triphosphate; LAL = Limulus Amoebocyte Lysate; NSA = NASA Standard Assay.