Venus return practical with propellers?

[Pds314]

Venus return is normally considered highly impractical due to the relatively enormous amount of air that is in-between Venus's surface and space. Indeed, Venus's atmosphere is 100 times thicker than that of Earth.

For an example of what I mean when I say highly impractical:

But what if we used fuel cells to power a helicopter-like propeller? Surely it wouldn't take much to get off the ground on Venus.

Then once we get to high altitude, we ditch the heat/acid-shielding and the propeller and burn to orbit just like we would on Earth. We'd only need like 7 km/s or so. That's well within the realm of practicality.

Is there anything obviously wrong with this idea? I realize it obviously requires beefy acid-resistant heat shielding, good insulation, and the mother of all AC units to land on Venus, but besides that, is there anything I'm overlooking with the whole "use props to fly back to cloudtop" idea?

Edited May 1, 2015 by Pds314

[xenomorph555]

No just stop, the manned Venus landing dream is impossible and any idea, including this one, is full of flaws. Two examples would be that the pressure instantly break your helicopter, the lander would have to be super reinforced and ultra heavy, basically impossible to fly. There are too many flaws to go over.

[YNM]

TWR problem, I guess. On higher altitude, thinner air means less thrust by the same rotation, faster rotation might broke things. Not to mention lubrication in such hot place...

Helicopter and rocket ? Stop you're asking everyone to work and spend for it to be ever accomplished (i guess)

[Pds314]

No just stop, the manned Venus landing dream is impossible and any idea, including this one, is full of flaws. Two examples would be that the pressure instantly break your helicopter, the lander would have to be super reinforced and ultra heavy, basically impossible to fly. There are too many flaws to go over.

I never said it had to be manned, but pressure-wise, it is more than doable.

Remember, there are diving suits meant to withstand 800 meters. That's 90% of the pressure on Venus.

Additionally, the lander doesn't have to fly using rocket thrust. All it need do is get thrown at Venus along with an orbital module, deorbit, etc.

Titanium has a Yield Strength of 800,000,000 N/m^2. If we imagine a Titanium sphere 1 meter in radius, and 6 centimeters thick, it has a cross-sectional area of 0.1885 m^2. That means it should be capable of withstanding a force of slightly greater than that it would experience on the surface of Venus.

Granted, there are probably much better material choices. Aerogels, etc would probably be better, considering their low weight and high yield strength. Furthermore, a latticework of cross-beams could probably further strengthen the structure.

As for the prop blades, they aren't hollow, so the dynamic pressure when they aren't moving is zero. I.e. They would not be even slightly problematic.

As for the structure, it would have a not insignificant mass of about 3.34 tonnes. While this may sound like a lot, let's not forget that the contents of such a vehicle probably weigh in at 4 tonnes anyway.

So basically, we have to double the mass of our vehicle if we use Titanium for crush-resistance. That isn't actually very problematic.

Let's say we sent down a 100-tonne rocket. All we need is an extra 100 tonnes of hull-strengthening in order to protect it from the pressure. Bonus: That much hull strengthening allows for heat resistance and acid resistance to be trivial matters.

And again, we don't need to put the armoring back in orbit from Venus. Just send it up from Earth and ditch it on Venus. It would only double the cost of landing compared to if Venus had an atmosphere or 2 worth of pressure, as far as I see.

[cryogen]

You could use balloons instead! They're much simpler and probably lighter. One JPL study proposes a teflon-coated Zylon balloon to lift a sample-return probe, and a three-stage solid rocket, from the surface to high altitude:

Mission overview

A single launch with a medium-to-large expendable launch vehicle (in the Delta IV M+ class) suffices to launch the spacecraft on a ballistic transfer to Venus, where it will spend a year before beginning the return journey to Earth. After aerocapture at Venus, the mission adopts a strategy reminiscent of the Apollo manned missions to the Moon. A propulsive plane change and aerobraking put the spacecraft into a circular equatorial orbit. A lander separates from the orbiter and descends to the surface to collect a sample, which is placed in a sample carrier at the tip of a three-stage Venus ascent vehicle (VAV). A variety of passive thermal and pressure protection techniques are used to protect the landed hardware and the VAV during a rapid descent and 90-minute stay on the surface. The lander inflates a balloon which carries the VAV with the sample to a high altitude (60 km - 70 km) in a few hours, from whence the VAV puts the sample carrier into orbit around Venus. Then the orbiter which brought the lander to Venus uses a beacon on the sample carrier and its own telescopes to rendezvous with the sample carrier. After transferring the sample into an Earth entry vehicle (EEV) on board, the orbiter deploys solar arrays to power a solar electric propulsion (SEP) system which is used to spiral out from Venus and travel back to Earth, taking two and a half years in total for the return.

"Venus Surface Sample Return: A Weighty High-Pressure Challenge"

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010003946.pdf

There's another concept somewhere that proposes a balloon-carried probe thats "hops" across the surface. Which gives you new options for thermal management, since you're at the surface for only minutes at a time, and can cool off at higher altitude.

Edited May 1, 2015 by cryogen

[Pds314]

As for the prop....

If our lander (shield-included) has a diameter of 6 meters (and masses 200 tonnes) and our folding prop is 10 meters in radius after deployment, we have a disk loading of about 637 kg/m^2. On Venus, this means we need the exhaust velocity of the prop to be around 10 m/s for takeoff. In order to go to an altitude of 50 km, where the pressure is 1 Bar, the atmosphere density is about 1.9 kg/m^3 and the temperature is 75 C, it would need to reach an exhaust velocity of about 55 m/s. While it may indeed be difficult to reach such altitudes, let's not forget that the disk loading of such things as the F-35B, which works at 10% higher gravity at 5000 kg/m^2.

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You could use balloons instead! They're much simpler and probably lighter.

Maybe. The main thing I'd worry about is how to make a balloon that can resist the conditions on the surface and higher up.

[AngelLestat]

There is nothing wrong with your idea.. is possible.

If your vehicle is manned then the amount of time you can stay in the surface is lower, also you can not descend from the vehicle to ground so is pointless.

I dont see any problem with the unmanned case.

Also you dont spent any energy to land because you use autorotation.

As someone else point.. A lighter than air vehicle may be a better idea, because the helicopter would consume more energy to reach 50km altitude to launch your rocket from there.

But the vehicle needs to have variable bouyancy and able to resist a higher difference of pressure and temperature..

It will be easier to use 2 lighter than air vehicle, for example one for 30km to 50 km, and another one to 0km - 30 km. The land vehicle needs to wait until the upper vehicle do a whole turn over the planet (4 days)

Edited May 1, 2015 by AngelLestat

[Fel]

For an example of what I mean when I say highly impractical:

Can I please make a small point here, KSP is 100% invalid as engineering simulation software. Note ENGINEERING simulation. The stuff we'd have to go through just to get the blades to turn; let alone the structural integrity to worry about. Not saying it is impossible, just saying that KSP ignores many issues and makes things seem deceptively simple.

But what if we used fuel cells to power a helicopter-like propeller? Surely it wouldn't take much to get off the ground on Venus.

It is easier to think of this like swimming. The same helicopter that works so well in the air has a harder time underwater (aka a denser atmosphere). Air density goes two ways, and again, the engineering isn't something to make lightly of.

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For an example of what I mean when I say highly impractical:

Can I please make a small point here, KSP is 100% invalid as engineering simulation software. Note ENGINEERING simulation. The stuff we'd have to go through just to get the blades to turn; let alone the structural integrity to worry about. Not saying it is impossible, just saying that KSP ignores many issues and makes things seem deceptively simple.

But what if we used fuel cells to power a helicopter-like propeller? Surely it wouldn't take much to get off the ground on Venus.

It is easier to think of this like swimming. The same helicopter that works so well in the air has a harder time underwater (aka a denser atmosphere). Air density goes two ways, and again, the engineering isn't something to make lightly of.

[AngelLestat]

It is easier to think of this like swimming. The same helicopter that works so well in the air has a harder time underwater (aka a denser atmosphere). Air density goes two ways, and again, the engineering isn't something to make lightly of.

Is still a gas, any liquid comparison will confuse much more than help.

I dont understand what is his plan to reach the ground, with the rocket+helicopter, or is a 2 atmosphere stage vehicles and only the helicopter down..

You will have to have into account this table to calculate the bouyancy at each altitude..