Calacorm

Learn to use a Delta-v map with kerbal engineer mod to design rockets that make it there and back again. Otherwise it's trial and error.

I just do these missions in 2 steps. 1 plane flight to grab low altitude measurements or landed measurement. Then a small orbiting probe for the high altitude. Remember the planet is rotating when you align the orbit. keep em cheap and profit. An epic space plane would be great but if it's proving hard, do it in 2 steps! I had to do this on hard mode due to tech limitations.