Would it be possible to go beyond Jupiter without making any slingshot?

Question

It is said that we do not have such advanced technology in order to send a spacecraft out of the solar system. (Source: Everyone around)

When a spacecraft is launched from Earth and aims to leave the solar system, it would get slowed down due to the Sun's gravitational pull. And at some point, it will have a speed of 0 and would start falling into the Sun (if it only uses fuel to propel itself).

But if an object is traveling faster than the escape velocity at that certain location, then it would end up escaping from the gravitational pull at some point, but its speed would get slowed down. $v_\infty=\sqrt{V^2-v_e^2}$

The orbital velocities of planets in the solar system are used to gain speed in interstellar trips. The voyagers are good examples, they both used Jupiter for a slingshot so they could boost their speed in order to overcome escape velocity at that certain location and be able to leave the solar system. (Source: NASA)

Most interstellar ships (so far) use Jupiter for gravitational slingshots. Would humans be able to launch a spacecraft and make it go beyond Jupiter or if possible leave the solar system without making any gravitational assist?

Such spacecraft has an IMPORTANT launch mass, it is not like the New Horizons which was about 500kg. A big rocket such as the Apollo 11 has a launch mass of 45,000kg. (Source: Apollo11)

How far would it go beyond Jupiter, could it reach Saturn or go even farther?

Answer 1

It is absolutely possible, just not advised. New Horizons was launched at Solar System Escape Velocity, meaning it could have visited anywhere beyond Earth without stopping. It did visit Jupiter, however, that was to allow it to leave even faster, the Jupiter stop was purely optional.

As for the issue of human capable spacecraft, again, it could be done, if one is willing to use a large enough rocket. The proposed BFR could certainly launch a satellite in to Earth orbit that could leave the solar system without a gravity assist required. The Delta V requirements for such can be see at the Delta-V Budget Wikipedia stage. It requires 8.8 km/s from Earth orbit to flyby Jupiter. It requires 12.3 km/s to escape the Sun's gravity. So it saves quite a bit of delta-V, which allows for more payload and/or quicker times, but overall it can be done. But it hardly makes sense to talk about outer solar system manned spacecraft when we haven't even sent a manned mission to Mars.

Answer 2

With a light enough spacecraft and large enough rockets, it is possible to achieve solar escape velocity directly. Currently this has only been done with the New Horizons probe. So it's possible - just very hard to do.

Hence the slingshot orbit, which gives you "free" acceleration without needing extra rocket fuel. It's not that it's 100% required, simply that it's the most practical way of doing it. An analogy would be whether you choose to walk along a smooth path around the outside of a mountain, or whether you go over the top - both will get you to the same place, and the smooth path covers a longer distance, but doing it the hard way is slower and takes a lot more effort.

On the surface of the Earth, the gravitational attraction of the Sun is 0.0006 times Earth's gravity. G=9.8N/kg, so this gives a gravitational attraction of approximately 6mN/kg. An unpowered spacecraft which does not have solar escape velocity would eventually be pulled back towards the Sun unless there were other factors controlling its trajectory. It would not necessarily fall "into" the Sun, but it would most likely end up on an elliptical orbit around the Sun.

However gravity is not the only game in town here. The Sun produces a radiation pressure which allows solar sails to propel a spacecraft. Although this radiation pressure decreases with distance from the Sun, it decreases with an inverse-square characteristic, the same as gravity does. A solar sail which can exceed gravity in Earth's orbit will therefore also exceed gravity for the remainder of its journey out of the solar system, and the spacecraft will always be accelerating away from the Sun. Currently we have one successful solar sail craft demonstrating that this theory does actually work in practise, but we have not yet had a serious spacecraft using this as a primary means of propulsion. It's still worth mentioning though.