Answer:
- Bigger mass of planet B
- orbiting closer to planet B
Explanation:
The orbital velocity of the vessel around the planet can be found by equalizing the force of gravity between the vessel and the planet and the centripetal force:

where
G is the gravitational constant
m is the mass of the vessel
M is the mass of the planet
r is the distance between the vessel and the centre of the planet
v is the orbital velocity of the vessel
Re-arranging the formula, we find an expression for v:

We see that:
- the bigger the mass of the planet, M, the bigger the velocity
- the bigger the distance between the vessel and the planet, r, the smaller the velocity
So, the correct choices that increase the orbital velocity are:
- Bigger mass of planet B
- orbiting closer to planet B