If you were to not-quite-spend all the fuel, you could use https://en.wikipedia.org/wiki/Nuclear_thermal_rocket https://en.wikipedia.org/wiki/Nuclear_thermal_ro

If you were to not-quite-spend all the fuel, you could use https://en.wikipedia.org/wiki/Nuclear_thermal_rocket https://en.wikipedia.org/wiki/Nuclear_thermal_rocket, which coincidentally would be your best chance at getting to the Sun.