For almost two decades, humanity has followed NASA's lead with a mantra of "Moon, Mars, and Beyond" as the widely accepted formula for expanding our species' presence into the cosmos. However, we can now see that VENUS presents a compelling path that we can pursue IN PARALLEL to those worthy efforts.
MOON, MARS, AND BEYOND
Despite valid counter-arguments from proponents of the "Mars Direct" approach, the rationale for the stair-step approach underlying the "Moon, Mars, and Beyond" plan certainly makes sense. After all, we can build technologies, skills, and experiences by learning to live and work first in Earth's orbit and then in our lunar backyard before taking the huge leap to the far-off surface of Mars.
However, the "Moon, Mars, and Beyond" paradigm does not take into account the possibility that Venus may present an equally feasible (and some might argue even more feasible) alternative destination for humanity's next home. [That is, of course, unless we consider Venus within the category of "Beyond", namely, somewhere we might consider AFTER we establish a human presence on the Moon and on Mars.]
More importantly, the stair-step approach that forms the foundational rationale for the "Moon, Mars, and Beyond" plan does not necessarily apply to getting to Venus.
Source: NASA/JPL-Caltech/ESA
BUILDING TOWARD VENUS
Much has been written and spoken about the many reasons that the Venusian atmosphere may be the most viable place in the solar system for humans to exist away from Earth. Therefore, let's consider the six general categories of capabilities that we would have to develop in order to survive in that extreme environment.
Scientific Data. First and foremost, we do not have nearly as complete an understanding of the Venusian atmosphere as we do about the lunar and Martian surfaces. Before any meaningful development effort can be undertaken, we need to collect more data, conduct more experiments, and analyze more models.
Interplanetary Travel. Perhaps obviously, we cannot live and work in the Venusian atmosphere if we do not have the ability to get to Venus. No human has ever traveled beyond the gravitational pull of the Earth-Moon system, so we are not certain how to do it and how to best protect our crews during the long journeys.
Stratospheric Operations. We have not yet properly explored our own planet's stratosphere, so we certainly do not yet have the capabilities to bring crews into the Venusian atmosphere, house them in floating structures, and then return them back into space for journeys elsewhere in the solar system.
Making Air Out of CO2. The Venusian atmosphere is almost entirely CO2, which makes it unbreathable for human beings. Although we currently have existing technologies that can convert CO2 into breathable air, we do not yet have the capability to do so at scale, permanently, or in the Venusian atmosphere.
Making Acid-Resistant Structures. The Venusian atmosphere is covered in clouds made of sulfuric acid, which is toxic for human beings. We currently have materials (e.g., Teflon) that are resistant and can provide protection, but we do not have the capability to use those materials to create liveable structures floating in the Venusian atmosphere.
Making Water out of Sulfuric Acid. Humans cannot survive without liquid water, so we will have to develop the capability to create water out of the available elements. Fortunately, it is theoretically possible to extract liquid water from the sulfuric acid found in the Venusian clouds.
NOT GOOD TEST BEDS
As we can see above, any effort to create a human presence in the Venusian atmosphere does not truly benefit from the lessons learned in the stair-step approach of the "Moon, Mars, and Beyond" plan.
By definition, (1) can be done only in the Venusian atmosphere.
While sending humans to Mars can certainly support (2), the reality is that Venus is much closer to Earth and has a much more similar orbit, which makes it much more accessible than Mars (lower cost, more frequent flight windows, shorter transit times, higher safety, etc.). Also, we don't have to worry about conducting successful landings on the planet's surface, which is one of the biggest challenges awaiting us on Mars. If anything, one could argue that sending humans to Venus BEFORE sending them to Mars might be a better way to safely develop the capabilities to create a Martian community.
Finally, while we could certainly gain some near-term experience with (3), (4), (5), and (6) practicing in our own atmosphere, the ultimate test will be in the Venusian atmosphere. Since neither the Moon nor Mars has a stratosphere, a CO2 atmosphere, or sulfuric acid clouds, they do not present relevant "testing grounds" for the capabilities we will require for Venus.
WHY WAIT?
There is no reason to wait decades for the "Beyond" part of the current plan. We could embark on our Venusian journey TODAY ... and do it safely and cost-effectively.
There is also no reason to derail all of the valuable hard-won momentum building up within the global effort following the "Moon, Mars, and Beyond" approach. We certainly will benefit in the long-term by having a human presence all across the solar system.
The best path for humanity is to embrace both efforts IN PARALLEL: "Venus" AND "Moon, Mars, and Beyond".
As a global community, we have the human and financial resources to pull off this parallel undertaking. All we have to do is get started.