Sorry but you can't drain the fuel of your probe for the challenge, it has to be sent full.
Your launcher is a good basis, but it weighs only 230 tons, you can add some fuel. I would add at least 15 tons of fuel to the last stage, and you still have some margin to add fuel to the first stage.
Also, don't forget that you can now go up to 265 tons (see
Voyager quest challenge rebalanced).