A tiny unmanned probe could deliver a soil sample from Mars, but even that can lead to problems in one launch. If we mean manned travel with a single launch, this is almost impossible.
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To launch a substantial spacecraft from Earth into interplanetary space, we need something about the same size as the Saturn V. This eventually got us to the Moon and back, and to fly to Mars, the spacecraft needs to be able to carry a reasonable payload as well.
So what about the return? Well, we’ll have to take the second rocket with us.
Mars has about 40% of Earth’s gravity and a thin atmosphere, so we need about 1/3 the size of Saturn V to get home.
To return to Earth, there will be a need for a rocket about the size of a Falcon Heavy fully fueled when taking off from Mars.
So, a larger rocket would be needed than Saturn V. In fact, more than anything previously invented, not based on nuclear weapons or science fiction.
Mars has an atmosphere. The atmosphere is convenient for slowing down spaceships, but unfortunately, it is not dense enough for the parachutes to work properly.
Thus, we will need even more rocket power for a braked landing, and this fuel will have a serious volume, which further increases the launch mass. We will also need a heat shield, which for such a large ship needs to be commensurately massive, further reducing the payload.
It would probably be a little easier if Mars had no atmosphere at all. At least then the landing could be more precisely controlled.
Part of the reason that any space agency has such a low success rate on Mars is that the density of its atmosphere changes quite dramatically. This means that sometimes the atmosphere is dense and stops the ship (or burns it), while other times it is too diffuse and barely slows down the ship.
This is why engine landing is the preferred method at the moment. However, such a landing should be fully automated due to a time delay (there is a huge distance between Mars and Earth, and the speed of light is not infinite). Landing anything on Mars is still a huge technical achievement, no matter how many times it is done.
That is why it is difficult to return to Earth from Mars, and a direct return flight is impossible. The only two real options are nuclear-powered spacecraft (hypothetical), or fueling on Mars and traveling with multiple launches (also hypothetical).
This will include sending a small refinery forward, sending an empty rocket (optional), filling it or some tank with Martian fuel, sending a disposable rocket with astronauts, landing your astronauts in a nice light spacecraft, completing astronaut tasks, refueling the first rocket, and finally flight home.
[…] Why Is It Absolutely Impossible To Return From Mars To Earth? […]
You need to learn the difference between “hypothetical” and “absolutely impossible.”
NASA is never going to return mars samples then