You might think that we have a good idea of the planet Venus, because we are our next-door neighbor. You would be wrong. NASA hasn't visited the planet in more than 30 years, and there's so much we don't know about it, from its geological history to what kinds of rocks are on its surface.
Scientists think that Venus was the same as Earth, but the two different places they are today were at some point in their evolution. Venus is the hottest planet in the solar system because of its thick atmosphere. We know that its surface is covered in mountains, rifts, and volcanoes, but we don't know if these are still active.
Venus' thick atmosphere hides most of its terrain from view, and it is hard to peer through layers of clouds to see what is beneath. It is a chillingly inhospitable place. Nothing man-made has survived on its surface for more than a few minutes.
We need to visit this planet if we want to learn more about it. NASA plans to drop a probe through the atmosphere to take readings all the way down as it falls to the surface. The mission is scheduled to launch in 2029 and arrive at Venus in 2031.
To find out how you build a probe to survive this environment, and what we can learn from it, we spoke to two members of the DAVINCI team: Jim Garvin, principal investigator, and Mike Sekerak, systems project engineer.
Venus is a frontier in planetary science that very little is known about. What is happening in the upper cloud layer?
The atmosphere from the top of the clouds to the surface is almost unexplored.
In the 1960s and 1970s, probes were sent to Venus to gather data. Physical problems with previous probes and limited technology have made previous atmospheric measurements unreliable. Some of the readings don't make sense, according to Garvin.
The lower atmosphere is a mystery. It could be a supercritical fluid, in which the temperature and pressure is so great that it can move like a liquid. There is a question of how the rocks on the planet interact with the atmosphere.
One of the biggest questions we have about Venus is if it once had liquid water oceans on its surface.
Venus is twice as hot as an oven and has more pressure on the surface than being under a kilometer of ocean.
The technical challenges we have here are exciting. The surface temperatures on Venus can be as high as 900 degrees Fahrenheit, which is the most problematic issue for any potential mission. It is hot enough to melt lead and wreak havoc on electronics.
The environmental challenge is only one part of the problem. Engineering a probe for this kind of environment is like building a submarine because of the high pressure at the surface.
When it is dropped into the atmosphere, DAVINCI will be in a race against time to gather all the information it needs before the heat and pressure destroy its components. To keep the probe active for as long as possible, it is covered in a thick titanium shell and spherical. There is more insulation inside this shell made of special materials, such as Astroquartz, a type of fiber made from fused quartz.
To prevent heat from being transferred from the shell to the interior components, the interior is designed to keep components thermally isolated from the exterior. It is filled with carbon dioxide gas to protect the electronics from sparking and to stop Earth gases from leaking into the atmosphere.
The probe is about one meter across. The probe is so thick that it is like dropping it through water rather than through air.
It will take 63 minutes for the probe to reach the surface, and in that one hour it will gather as much data as it possibly can before it is destroyed by the brutal environment.
The descent sphere will be falling through the atmosphere and sampling all the way down, to build up a picture of the atmosphere from the top to the bottom.
Inside the sphere will be instruments similar to the instruments on the Mars rovers, which can measure the chemical composition of samples by looking at the wavelength of light that they absorb. Unlike the Mars rovers, which can take hours or days to collect and analyze a sample, DAVINCI will only have to do its sampling and analysis in a matter of minutes.
Ceramic covers break off to ingest gases at various points over the sphere. The gases have to be analyzed quickly so that more samples can be taken. This will allow the probe to get the most detailed look at the chemistry of the atmosphere.
Other sensors in the probe will be measuring factors like temperature and pressure to help understand the structure of the atmosphere. Before the probe hits the surface, all this data will be sent back to the orbiter.
The probe is designed to sample to the atmosphere. There is a chance that it will survive when it touches the surface. The thick atmosphere and parachute will help slow its descent, but it will hit at a slower rate than ideal for spaceflight hardware.
The probe might last up to 20 minutes of collecting data if it does survive the landing. There will be more data on the surface temperature and pressure, as well as the gases present.
The chemistry of the atmosphere is only one part of DAVINCI's goals. Taking photos of the mysterious Venusian surface might be the most exciting part.
In the mountains of Venus, the probe will come down in a terrain that has never been seen by humans before. The team wants to record the experience in both visual and chemical ways.
The descent sphere will have a camera that can take high-contrast images of the surface, which can be used to create 3D maps.
You need a window to operate a camera inside a metal sphere. Glass is not a great material for dealing with high-pressure environments. DAVINCI's window will be made of sapphires.
It is a very large piece of sapphire and it is clear. Engineers added phase change materials around the window assembly because a window that lets in light will also let in more heat. The excess heat from the window is absorbed by the material.
The camera will be able to take clear, sharp images during its descent. The terrain of Venus will be photographed from high up to the surface.
The final images will have a 10-centimeter resolution.
As well as offering a wealth of scientific data, Garvin hopes that capturing images at this scale will help the public feel like they can see Venus as a real place, not just a dot to be observed from afar.
He said that they want to bring human vision and perception to Venus.
The challenges we know about, like the temperature and the pressure, are not the most difficult part of a mission to Venus. We have so little information about the environment that we are trying to anticipate what challenges might arise.
Testing and preparation will be a big part of what the DAVINCI team does for the next seven years.
We do worst-case testing.
Researchers know that the clouds of Venus have drops of sulfuric acid in them. It is a concern for the lanyard that will attach the sphere to the parachute. Engineers coat the entire surface in acid to make sure the lanyard can survive in acidic environments.
To test hardware in environments that are different from Earth, you have to get creative. To see how long it would take for the metal sphere to heat up, the team took it to a metal foundry.
The idea is to build enough margin to allow for unknowns to be thrown at the sphere. A lot of engineering thought and risk reduction has been built into how we do this.
If we have a good day on Venus, we will probably get 500 descent images back. 35 is more than we need to do this kind of mapping. They will find out valuable information even in the worst conditions.
Visiting Venus is not easy, even by the high standards of big space missions. The payoff in terms of what we can learn is huge.
It will be fascinating to learn about Venus. It is also important for our understanding of exoplanets. We need a reference point for rocky planets like Earth, Mars, and Venus as we discover and investigate new planets outside our solar system.
Adding data from Venus will allow us to better understand distant planets.
Venus will become a calibration point for the kinds of big, rocky, atmosphere-bearing planets that we will be able to see and understand with the big telescopes which come beyond.
It is one of the reasons I love working on space exploration missions.
We have learned a lot about building for the environments of Earth and Mars, and now we can apply that knowledge to something different. Building for that environment will stretch our technology, and visiting it with a probe can start unraveling some of its mysteries. When visiting a new space environment, there is always something new to learn.
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