How to make artificial gravity?

    How to make artificial gravity? 

Above is the artist's impression of a giant O'Neill cylinder. The hypothetical megastructure or "artificial Earth" can make it possible to travel between stars. But the fact is that smaller cylinder-shaped capsules can make similar things like anchor saucers on the table. That means the rotation speed must not be as high as people think. Making a gravitational field that is 1/1 with Earth is not possible. 

But the thing is that when this artificial world travels between planets or stars the system can make gravitation weaker in the space journey. And when that giant cylinder reaches the target, that cylinder increases its rotational speed. And that makes the gravitational field stronger. 

But gravitational cylinders are not necessarily big. They might be a group of rotating cylinders. That connected to the spacecraft's outer shell, like in the imaginational Mars craft in the second image. 

Gravitation is one of the biggest problems in long-term spaceflights. Many fungi and vegetables require artificial gravitation. And one solution could be rotating spacecraft, where centrifugal force creates synthetic gravitation. The problem is that those spacecraft should rotate quite fast. That they can create similar gravity as is on Earth. But the purpose of that gravitation is to keep the crew in good condition and avoid osteoporosis. Also, gravitation is required to anchor vegetables to tables. 

But the thing is that artificial gravity doesn't necessarily need to be in the entire craft. There could be smaller cylinders outside the main body of the craft that can rotate quite fast. Astronauts can use those cylinders as training houses. There they do their physical exercises. 

Above is the concept of futuristic Mars craft. The system can create artificial gravitation by using multiple, independently rotating cylinders outside the craft's main body. Those cylinders can involve "gardens" and gyms where those astronauts can maintain their health. In the case of damage those "miniature versions of O'Neill cylinders" would act as rescue capsules. 

And there is no gravitation in the main body and cabins in the spacecraft. So artificial gravitation doesn't mean that the craft is fully equipped with artificial gravity. The smaller fast-rotating cylinders are tools where astronauts can keep their physical health. 

And that thing means that those miniature versions of the "O'Neill cylinders" can make interstellar travel possible and at least in the solar system travel those modular structures seem more realistic than giant kilometers-long cylinders. The modular structure means that in the case of the microasteroid impacts those separated modules can act as rescue ships. The crew can evacuate in those cylinders if the craft is damaged. 

https://en.wikipedia.org/wiki/O%27Neill_cylinder