CREATE TABLE table_20438 ("Engine type" CLOB, "Scenario" CLOB, "SFC in lb/ ( lbf\\u00b7h ) " CLOB, "SFC in g/ ( kN\\u00b7s ) " CLOB, "Specific impulse  ( s ) " FLOAT, "Effective exhaust velocity  ( m/s ) " FLOAT)

What is the effective exhaust velocity in a Space Shuttle Vacuum?
SELECT COUNT("Effective exhaust velocity (m/s)") FROM table_20438 WHERE "Scenario" = 'Space shuttle vacuum'
SELECT COUNT("Effective exhaust velocity (m/s)") FROM "table_20438" WHERE "Scenario" = 'Space shuttle vacuum'