Question

An astronaut on board a spacecraft is in orbit around the earth in uniform circular motion.
Is her velocity speed and acceleration constant?

Answer 1

Both velocity and acceleration are vectors. Vectors have magnitude and DIRECTION.
Their magnitudes may stay the same, speed may be constant tangential to orbit path and acceleration magnitude toward earth.
HOWEVER
The velocity and acceleration DIRECTIONS change constantly, so the vectors are NOT constant.
Speed is a magnitude.
Velocity is a VECTOR.

Answer 2

Remember:
In a car you can measure speed with a speedometer.
but
for velocity you need both a speedometer and a compass.

Speed is the magnitude of the velocity vector, a scalar.