How fast does it have to move, though? This isn't anything you or I can really answer, because it requires a better understanding of the weather patterns and the capabilities of the materials which would be used. We know that it has to travel 100 KM vertical, in total, but its lateral movement means that it'll travel farther than that in the time period. How fast can it go from 50 KM to the surface? Can it do it in less than 15 minutes? I don't know. The faster you can get it down to the surface, though, the longer you have to get it back up to 50 KM. To go at a high rate of speed. XKCD says you could get off the ground at a running speed. Without having any idea of how long it'd take to get to the surface, its impossible to say what kind of speeds would be needed to get back to the 50 KM mark, other than it'd have to be traveling faster than 100 KM. Not mentioned in that XKCD piece is that there are near constant winds of a few KPH on the surface. These would push along any person standing on the surface of the planet. If they are blowing in the opposite direction of the high altitude winds, then they'd make it impossible to try sending a plane to the surface, since the plane would probably get ripped apart at the transition layer. True. On Mars, just to remain airborne, you'd have to have inflatable wings or travel at supersonic speeds. That's true with any planetary mission. The first time I heard about NASA's plans to use airbags, I thought it wouldn't work. Then there was the sky crane that put Curiosity on to Mars. Even just a few grams of surface material would be incredibly valuable. A plane on Venus also doesn't have to worry about AA fire or being intercepted by an enemy fighter. Oh, I'll be the first to admit that there's one helluva devil in the details of how this would work (assuming it could). Even if you had a craft which could cruise all day just above the surface and not be bothered by the heat or the acidic atmosphere, there's tremendous challenges involved in accomplishing it. Doesn't do you any good if the only materials which can protect it are more fragile than glass. Because of the complexities of what a lander would entail. You'll need to have some way of getting the material off the surface, and into the return rocket. This means either a robot arm or a rover equipped with a robot arm. I can't imagine either of those being very light mechanisms, since they're going to have to work in high heat, high pressure, and highly acidic conditions. Several of the Russian Venera probes failed to eject the lens covers on their cameras. Later probes, it turns out, were able to operate for 2 hours, so that opens the possibility of a longer flight time in the lower atmosphere with ill-effects. Depending upon how the "grabber" for the plane was designed, it should be possible to have it be a much simpler mechanism, which would lessen the chance of failure. Not seeing why you think it has to be a rocket. How would you design a drill to work on Venus? We've got a limited understanding of what the surface composition is like, and it'd be almost impossible to preselect a precise landing spot for a traditional sample and return lander because of how hard it is to study the surface. A sample from Venus, is better than no sample, even if its far from ideal. Remember NASA's Genesis mission that captured particles from the solar wind? Not only was the returned sample very small, but because the probe crashed, instead of being snatched out of the air by a helicopter, and they had to sift through the samplers inside to get usable material. Solar wind particles are pretty small, and if they can do a lot with those, then they could do the same with a small amount of Venusian material, I'd think. In the '80s, the Planetary Society hoped to gather Martian soil samples using a "snake" trailing from a balloon. Presumably a similar collection method could be designed to work on Venus. It may not be a trailing snake, of course, it might be an extendible section on the underbelly of the plane that is only deployed as it nears the surface. Hey, intellectual exercises are only fun if somebody starts hitting them with a stick. I'm sure most of us have learned something from this discussion. I know I have.
On my phone, so short response: The aircraft must be more like a rocket because of drag. Yes, you can takeoff at running speed but what's being missed is that in the much denser atmosphere, even running speed will be more difficult to attain. Need THRUST. Moreso to get back to 50km quickly.
You know, the flying grabber idea is not that great compared to using a lander that would do the following. 1) Does a soft landing on the surface. 2) Uses drill to take soil sample. 3) Deposits soil sample into container. 4) Uses balloon to carry soil sample to 50km. 5) Probe in upper atmosphere capture soil sample capsule. 6) Rocket launched soil sample to orbit from probe. 7) Sample returned to Earth. This would be easier than to try to guide a probe to the surface, grab samples without catching on something and causing a crash. The balloon could be smaller than one used on Earth since the atmosphere is denser, and as it rises the balloon would expand quicker giving a higher climb rate since the atmosphere density change is quicker. The balloon could be coated so it doesn't absorb heat as quickly, and also have some insulation. If you're trying to make a probe that can scan the surface, calculate altitude and speed needed to grab something off the surface, return it to a 50km altitude without human intervention. And do all this without knowing what the variable are for wind speed and direction, and how much mass its sample will be. And need to carry fuel and the rocket to launch back into space. It would be much easier to capture a balloon that it could track and capture. Once it has captured the balloon, the balloon itself can be released leaving only the sample container. Now you don't need to have a probe that can do all the above, just capture a balloon.
The problem with the balloon, however, is that it has to be capable of withstanding category 5 hurricane strength winds.
If you're trying to build a probe that can fly down and back up through such wind speeds, it's certainly a lot easier to use materials that can withstand the same wind speeds to build a balloon, perhaps a carbon fiber/kevlar material or something similar.
The problem's going to be with the amount of surface area a balloon has compared to something like a plane. The balloon and its gondola are going to be larger, which means that when you attempt to inflate them on the surface, before the balloon has even fully inflated, the winds are going to start dragging it along the ground, if its not very securely tied down. Which requires a release mechanism that has the potential for failure. (How do you keep the parts of the balloon and gondola from getting tangled up in the mechanism. Additionally, we don't know if there are any sandstorms on the surface of Venus. If there are, then that'd have to be an even tougher balloon envelope than it already is, because the sand would likely blast holes in the envelope. Note the comment from the actual NASA employee that I posted where a balloon is kept above 50 KM and drops a sampling "rope" down to the surface, rather than descending to land.
Using a pressurized canister, the balloon can be inflated almost immediately, and since at lower altitudes it doesn't need to fully expand to be buoyant the balloon wouldn't even touch the ground. When a weather balloon is released it isn't fully inflated. The canister can be supported by a single line from the balloon, and it can be released by having the probe use a cutter to physically cut the line. The balloon would be housed in a protective case that would open just before the balloon is inflated, and several of these could be placed on a probe that lands on the surface of Venus. And I would think that using a balloon to be captured would have less likely to go wrong than the idea of having a glider swoop down, grab material off the surface of the planet. Which would would require it to be accurate within 2-3 inches at the most. Any higher would miss any rocks or soil it could grab, any lower and the grabbing mechanism would hit and flip the glider.
You're talking about having a balloon inflate in an atmosphere that pushes down at 1260 PSI, you're not going to get a near instant inflation at those pressure levels, unless you inflate the balloon at a far higher pressure. Nope. That'd be way too heavy. You'd get a single shot at it. We've had "terrain hugging" radar since the '80s that have enabled planes to fly close to the tops of trees in order to evade enemy radar, by now, the technology has improved enough that we could trust it to fly a plane at that near ground level with few worries.
You seem awfully committed to the plane idea despite the fact that all the things you use to dismiss other ideas like balloons apply equally if not more so to an aircraft.
There's some rather large differences between a plane and a balloon, however. A plane has a smaller surface area, along with control surfaces, which means that its not necessarily a hapless puppet of the winds like a balloon would be. The plane could divert around a storm, while a balloon would have to ride through it. Then take ed629's redundant balloons for a lander. Can you name a single probe which had a redundant set up for the landing? I forget the costs for sending something to Mars, but they're considerably higher than what it takes to send things to LEO on the shuttle. If we give a lander with a triple redundant balloon set up, and we give each one of the balloons, and the deployment mechanisms the shockingly low weight of 10 lbs each, what's going to be raised in the engineering sessions about that is that this is very expensive and heavy. The ideal solution would be to have a more reliable system that didn't need the redundancies, and weighed less than 30 lbs. Because by adding the extra 20 lbs the redundant systems require is less propellant that can be carried, and cuts down on the number of instruments which can be brought on the mission. Then there's the engineering problems of how do you make sure that the functional balloon is connected to the cargo container and how do you sever the connections to the dead balloons reliably? The more complex a probe is, the more likely it is that something will go wrong. The plane is simpler than ed's proposed lander, but if you'd bothered to read the response I posted by the NASA employee, you'll see that its pretty clear neither idea will work.
I never said the balloon would work, just that the arguments against it equally apply to an aircraft. I read that NASA employee response, I didn't realise you had accepted from his words that the plan isn't feasible, for mostly the same reasons that had already been stated in this thread.
Well, not exactly. "near ground level" for a low level bomber is considered from 200-500 feet in altitude IIRC. And even then, that kind of flying is EXTREMELY dangerous. At any rate, despite the term "terrain hugging radar" IIRC what radar systems on planes like the B-1B bomber do is scan the terrain ahead and compute the highest point within its range and then adds 200 feet (or more depending on the ride setting) as the aircrafts minimum altitude. Such a system would be woefully inadequate on Venus much less for "swooping close to the surface". And you would need to know the general composition of Venus's surface to get proper radar readings. A sandy surface gives you a different radar return than a rocky one.
Generally EGPWS will use GPS data, which means many of the ground avoidance technologies in use wouldn't be useful on Venus.
They don't, however. A balloon is flexible, a plane is rigid. A balloon has a larger surface area than a plane, this makes it far more susceptible impacts of being blown about than a plane (even ignoring the balloon's lack of control surfaces), and the key point in time is when you're trying to launch the balloon from the surface. As it inflates, and before it is capable of lifting the rocket from the ground, its going to be vulnerable to being whipped along by the winds. It doesn't matter if the plane gets pushed along by the wind, since that is what you want. The plane's not supposed to stop at all. I figured that was obvious from his comments. Nobody here stated, as he did, that it'd take an hour for something to fall to the surface of Venus. That's the killer. If you've got a 30 minute window, and can get down to the surface in 5 minutes, then it doesn't really matter if it takes you between 25 - 30 minutes to get back up to 50 KM, since as the plane is climbing, both the pressure and temperature start to drop, and as you get close to the 50 KM mark, you're effectively at Earth normal, so you've got a few minutes extra. A fall rate of 1 hour, however, means that even with a two hour window, you're pretty much screwed. And actually, I think his math is off, my back of the envelope, now that I think about it, is 2 hours. Which all-in-all, means I need to really rethink a few things, because it means that the window is larger than what I originally assumed, and the survivability is larger than either the two hours or even 30 minutes. Here's why: I was thinking of the lifespan of the Venera probes after they landed (which, if you'll recall, on the first mission was 30 minutes), and not thinking about the time that it took for them to get from the 50 KM level to the surface, which is considerably longer. If we take the NASA employee's number (his user name is Eye Zee, so I'm going to call him Zee from here on out) of one hour, and say that's how long it took a Venera probe to go from 50 KM to the surface. The actual lifespan of the Russian probes was longer than 30 minutes, since it took them an hour to go from 50 KM to the surface, and then once there, they survived for 30 minutes (or longer, if you're going for one of the later probes). So, you'd have, roughly speaking, an hour and thirty minutes for the probe to be below the 50 KM mark. Now, since the Soviet probes were designed to land on the surface, they had to start slowing themselves well before they touched the surface. They'd want to hit the ground at a speed of only a few KPH, but since a plane is going to be skimming the surface, and would never want to come to a complete halt, there's no need for it to try and slow down. Thus, it could reach the surface in less time than the Venera probe could, and don't forget that the Soviet probes were designed in a shape which would slow them down to a degree, even before a parachute was deployed. A plane isn't designed in such a manner, so it could dive faster than the Venera probes fell. Again, none of which means that this is a viable idea, but even if you say that the plane could only be at surface level for 30 minutes, it opens up a bit more time for the plane to be below the 50 KM mark. Is it enough? I don't know, but I'm going to bounce these ideas of off Zee and see what he has to say about it. You do know that the B-1B was built all the way back during the Carter Administration and that avionics have progressed much farther since then, don't you? Don't forget that while there's a chimp in the cockpit, he can freak out and grab the stick to pull himself out of a perceived danger, even though there isn't any, and that by putting him several hundred feet above the ground (at speeds far in excess of what something on Venus would travel), you lessen the chance that he's going to freak out and do something stupid. Which is why you'd send the probe with something that had been developed in the 21st Century, and not use 20th Century tech. Google's self-driving cars and the DARPA Grand Challenge both developed systems more akin to what would be needed than a 30+ year old bomber system. For fuck's sake, Google's talking about having drones drop off packages. If a civilian company can talk about doing such a thing, then surely the rocket scientists at NASA can figure out how to skim the surface with a plane. Even if it is another planet. Amazingly enough, we can figure out what a radar's bouncing off of. IIRC, they have a combination of systems available to them for terrain hugging use, and again, the systems in Google's self-driving cars and DARPA's Grand Challenge show that we can figure out how to work in such tight envelopes. I should also point out that 99% of the automatic doors you see in stores use radar to tell when someone's coming and that they need to open. The range at which the doors open is adjustable by service personnel with a screwdriver. How do I know this? Simple. My father sold automatic doors for 40 years, and I spent my school vacations working for him and installing the doors. If a radar unit can tell a door that it needs to open because a toddler is headed towards it, I think it can tell a plane it needs to adjust its course because a mountain is coming close.
You do know that the B-1B was built all the way back during the Carter Administration and that avionics have progressed much farther since then, don't you? .[/quote] The B-1A was built in the mid 1970s. The B-1B was built in the mid to late 80s and has been continually updated ever since. And I'm pretty sure that cruising at low level over central Iraq is an order of magnitude less difficult than an unexplored planetary surface.
Regarding the google car tech, it is an example of something that would not work on Venus. They have to do a very precise survey of any road before certifying it for use by the robot car, and the reason for this is that the data available from remote sensing is inadequate to the car's requirements. Instead it needs a high precision map created specifically for the route(s) it will take.
Yes, but navigating around the surface of Venus would be like doing the same thing in some large empty area of Earth. There's no competing traffic, only ground features to avoid. There's no "road" you need to follow, just a safe flight path.
Who on Venus is going to be shooting back at a plane? As we found out in Gulf War 1.0, you get too close to the ground, and even small arms fire can screw up your day. Let's look at some other differences between the B1-B and a plane flying on Venus, shall we? A B1-B is equipped with jet engines, AKA "vacuum cleaners," meaning that you get too close to the ground, and they're going to suck up any loose material which happens to be on the ground. If you'll recall, the Soviets installed grates in front of the inlets of their fighters, because they figured that they'd have to be taking off from debris littered runways in the event of an all out war between the US and the USSR. This limits how low you dare fly the B1, since it doesn't have the same kind of protection against debris that a Soviet plane would. A B1-B also travels anywhere between a few hundred miles an hour and faster than the speed of sound, these things, along with the processing speed of the computers onboard the B1-B impact how close it can go to the ground. The kind of plane I'm talking about would trundle along on Venus at less than the stall speed of a B1-B, in all likelihood, which means that the onboard systems have far longer to react than the systems on a B1-B would. Finally, the exact performance capabilities of a B1 are a matter of national security, and thus and publicly available performance figures for them must be considered suspect. If the exact figures are known, then it is easy to develop countermeasures against them. Perhaps they can do better than the public figures, perhaps they can do worse. We don't really know. However, it seems unlikely to me that they'd be worse than what is known. And here is what Zee had to say in response to my query about if his figures for a descent time were correct: Superficially, I will admit that this makes it look like you can stick a fork in my idea and call it done. However, without precise data from the Venera probes regarding descent times and drag coefficients, I don't think that we can say for certain, as there are a few other potential issues which haven't been addressed, and that I don't have time to work out all the details, or even approximate them, right now. With luck, I might be able to do it around the 4th of July or so.
I can see it working as a multistage mission. 1 - Several vehicles go from Earth to Venus. One is an Earth-return booster to get from Venus orbit to Earth orbit. One is the probe carrying the lander/airplane vehicle. The airplane includes a Pegasus-style booster for getting from Venus' upper atmosphere into orbit. 2 - The Earth-return booster enters Venus orbit and sits there waiting. 3 - The lander/airplane vehicle makes the actual descent from Venus orbit to the surface, or at least to flying just over the surface. It must of course be able to withstand the heat and acidic conditions long enough to do something useful. I'm thinking some kind of ceramic skin? 4 - Given conditions on Venus, the airplane doesn't have to be able to go very fast - you could probably get away with a propeller-driven thing vice a "jet" (however you expect that to work on Venus) or rocket powered deal. It just has to be able to survive entry into Venus' atmosphere on the way down. 5 - Airplane flies low and slow, dangles some sort of sample retriever and gets some soil and rocks - probably a fairly small sample. It also takes pictures and other sensor data. The swing-wing arrangement I mentioned upthread means that once it has its samples, it can adjust its wings to maximize aerodynamic lift as it then climbs slowly up and out of the dense lower atmosphere. Perhaps it goes from small stubby wings where the air is thick into a sailplane-like configuration at high altitude. Either way, it's using aerodynamic lift to gain altitude, not brute-force rocket thrust. I suspect a large slow-turning prop would work quite well in Venus' dense lower atmosphere. As it climbed it could simply rev up the RPMs. 6 - Once at maximum altitude, the Pegasus lights off and carries the sample canister up to the waiting Earth return booster vehicle in orbit. The airplane can then either continue to fly around Venus doing science or simply be allowed to fall back to the surface and be destroyed. 7 - The Earth return booster lights off and pushes out of Venus orbit into a transfer orbit back to Earth, carrying the sample cannister. 8 - Earth orbit - the return vehicle either enters Earth orbit or perhaps actually reenters and splashes down somewhere. 9 - Ymir emerges and destroys civilization. Designing an airplane that can operate on Venus long enough to accomplish its mission is simply engineering - dealing with heat, pressure, and nasty chemicals. I don't think it would require too much in the way of new science.
Yup. That's pretty much it. There's devils in the details, and some of them could kill the idea altogether, but I'm not seeing anything obvious (such as trying to use a jet engine on Venus) that would completely kill the concept. I think that there'd have to be lots of work to custom design a prop that would work effectively at both high, and low altitudes on Venus, since the differences are so dramatic. You'd also have to make sure that all the interior spaces inside the plane were sealed off from the atmosphere (unlike an Earthbound plane), which might make it difficult for it to get down to the surface, since it would make such a craft "lighter than air" on Venus, if you kept the interior at Earth normal pressure. So, you'd ideally have to figure out a way to add ballast after you got the plane to Venus, rather than sending the ballast all the way from Earth.
I wouldn't do a propeller -- far too vulnerable. The plane should essentially be a glider with rocket engines that occasionally fire for control and for powering the ascent. Given the thickness of atmosphere, a glider could almost function in perpetuity. The only real need for propulsion is the ascent (and maybe for speeding the descent).
Props are far less vulnerable than jet engines, and NASA has pioneered all kinds of weird designs, tailoring them for things like fuel economy, or operating a high altitudes, or abnormally high speeds, so they ought to be able to come up with something that'd work well on Venus. The beauty of using the stirling engine over a rocket engine is that with the stirling engine, you'd not need to bring fuel for it from Earth, since it'd operate off of temperature differentials between an interior portion of the plane and the exterior of the plane.
Have you calculated how much energy you could get from a stirling engine? It seems to be that using a stirling engine to give power for ascent could be difficult. The energy required would need quite a large mass at cold temperature, but the more mass you include the more energy you need to lift it, which means you need more mass, and so on. Without having done any calculations I can imagine that you would swiftly reach a level of required mass that would make it easier to just use that mass in the shape of batteries or a RTG.
I reckon you'd find this link really interesting, and relevant to this topic: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120013601.pdf It's a report on the idea of a theoretical airship designed to operate at low altitudes in the Venusian atmosphere. I'm only a few pages in but it already has covered several things we've wondered in this thread such as wind speeds at various altitudes and even a graph showing the speed of sound in the atmosphere of Venus. edit: They propose using a stirling engine as well, however their proposed idea works the other way, with a radioisotope energy source being used to produce heat that is transferred out into the atmosphere, rather than the other way around.
With Venus, I'd actually go the other direction. Would be simpler. Send a space vehicle full of genetically hardened Bacillus Infernus. Drop it. See what happens. As for we don't have surface samples of Mercury... well, to be honest, for me that's the most boring of all planets. It's just a rock with nothing interesting on it I'd rather see the money go towards a mission to one of the great moons of Jupiter or Saturn to try and drill beneath the ice. I have a feeling we could find interesting things there.
I'd rather we had a space program that had a budget large enough so we could afford to all that and more.
