After more than 20 years of neglect, the planet Venus is once more drawing NASA's eye for ambitious new missions.
A Venusian dream expedition for some scientists would include nothing short of an exploration flotilla — a ground robot, planetary airplane and orbiting manned spacecraft. The potential mission to Venus could investigate its surface from up-close for the first time in several decades, a NASA scientist said.
"Recently there has been a renaissance in looking at proposals to study Venus," researcher Geoffrey A. Landis at NASA's John Glenn Research Center in Ohio told SPACE.com. "One very good reason is that there has been a renewed interest in study of the atmospheres and climates of planets, and — being the planet that is most like the Earth in size — learning more about the atmosphere of Venus may help us learn more about the atmosphere (and climate) of the Earth."
NASA is expected to hold its first meeting to discuss potential new Venus missions in early August, Landis said.
There hasn't been a dedicated U.S. mission sent to Venus since the Magellan probe in 1989, but that doesn't mean the planet has not seen its share of visitors.
The European Space Agency currently has an orbiter called Venus Express circling Venus, and Japan launched its spacecraft Akatsuki (Japanese for "Dawn") toward the planet in May. Several NASA probes have flown by Venus in the last 20 years, but only as a pit stop on the way to other planets in the solar system.
Venus also saw visiting probe from the United States and Russia the 1960s, '70s and '80s, even some landings on the Venusian surface. But those probes were extremely short-lived because of the crushing pressure and extreme heat of Venus' atmosphere.
Bring humans to Venus
And after two decades of technological advancements, an extended robotic landing on Venus is now possible, Landis said. Today's high-temperature electronics, power and cooling systems could allow a ground probe to explore for longer than two hours.
The last spacecraft to land on Venus was Russia's Venera 14, which touched down on Venus in March 1982 and survived for 57 minutes — nearly twice its expected design lifetime, according to NASA records.
But humans from Earth will still likely not step foot on the hellish Venus surface, where the temperature is hotter than most ovens — about 870 degrees Fahrenheit (465 degrees Celsius) — and the atmospheric pressure is about 90 times that of the Earth.
"Venus is so hostile that we're not likely to land humans on it anytime in the foreseeable future," Landis said.
But scientists still have a technique up their sleeves that could allow humans to explore Venus virtually via "teleoperation" of a remote-controlled probe from inside an orbiting spaceship.
By connecting astronauts to real-time visual and tactile data streamed by the robot, the system can allow astronauts to interact with the Venusian environment without the time-lag of controlling a robot from Earth, Landis said.
There are still some challenges for astronauts even if they don't set foot on Venus.
Venus explorers orbiting the planet would still need radiation and heat protection from the effects of orbiting a little closer to the sun. In addition, a source of artificial gravity may be necessary to counteract the loss of bone mass expected for astronauts living for long periods in weightlessness.
"Fortunately, we are learning a lot about long-duration habitation in space from the International Space Station, and by the time we're ready to send this mission, most of the difficult questions will be better understood, and many of the technologies chosen," Landis said.
Dusting off a solar plane
Another possible component of the mission may involve resurrecting a solar-powered airplane concept to traverse the planet's thick and "tremendously exciting" atmosphere, Landis said.
Since Venus resembles the surface of Earth when it first formed, the thick carbon dioxide covering Venus could tell us a lot about our own planet's evolution, he added. A compact plane that could unfold during entry could be a vital probe to record conditions from inside Venus' atmosphere.
The project was cancelled years ago, but not before engineers completed enough work to be confident it would work in the atmosphere of another world.
Initially conceived for Mars aerial exploration, the solar-powered planetary airplane would work especially well for Venus because the planet takes 243 Earth days to complete a single Venusian day.
"Venus rotates so slowly that we could essentially fly forever because the airplane can fly faster than the speed it rotates and then stay in sunlight all the time. It never runs out of fuel, or energy," Landis said.
Venus' long days do come with a price: high winds that would challenge the plane's flight limits.
In theory, the plane's speed would be a mere 10 mph (16 kph). But once immersed in the atmosphere of Venus, the aircraft would have to battle wind speeds of around 200 mph (321 kph) in order to keep in the sun.
So the speed required to compensate would be pretty high for solar airplanes but slower than a typical airliner, Landis said.
There's an aerodynamic challenge, too. In the earlier studies, engineers had to work hard to pack as many solar panels as possible onto wings yet still minimize drag.
"Turns out the interesting thing about the solar plane is that the bigger you make the wing the more power you get," Landis said.