A160.-kilogram space vehicle is traveling along a
straight line at a constant speed of 800. meters
per second. the magnitude of the net force on
the space vehicle is
(1) 0 n (3) 8.00 × 10^2 n
(2) 1.60 × 10^2 n (4) 1.28 × 10^5 n

If the object is moving in a straight line at a constant speed, then that's
the definition of zero acceleration.  It can only happen when the sum of
all forces (the 'net' force) on the object is zero.

And it doesn't matter what the object's mass is.  That argument is true
for specks of dust, battleships, rocks, stars, rock-stars, planets, and
everything in between.