Venusian lander

[DDE]

26 minutes ago, lajoswinkler said:

Yes, a nuclear reactor powered refrigerator could do it. But just landing. Returning back to orbit is a nope.

Then leave the refrigerator behind.

If we built a drill for Venus, we should be able to manage a simple engine cycle. Tank pressurization can be made to keep up with atmospheric pressure to keep certain propellants liquid even at ambient temperatures.

Heck, the propellant could act as a heat sink even if the compensator valves let in atmospheric gas.

The souposphere should allow easy aerodynamic landing even for truly obscene payloads.

[kerbiloid]

3 hours ago, lajoswinkler said:

Yes, a nuclear reactor powered refrigerator could do it. But just landing. Returning back to orbit is a nope.

Though, jumping up as the first stage.

[StrandedonEarth]

4 hours ago, DDE said:

Then leave the refrigerator behind.

If we built a drill for Venus, we should be able to manage a simple engine cycle. Tank pressurization can be made to keep up with atmospheric pressure to keep certain propellants liquid even at ambient temperatures.

Heck, the propellant could act as a heat sink even if the compensator valves let in atmospheric gas.

The souposphere should allow easy aerodynamic landing even for truly obscene payloads.

Hmm, if the propellants are the heat sinks, perhaps propellants that are solid at STP should be used for Eve Venus ascent. I’m thinking the lighter alkali metals as fuel, and the heavier halogens as oxidizer. The ISP might not be great, but boiloff shouldn’t be a problem. 

As far as heat sinks go, I’ve often thought that a Venus surface probe should have an outer jacket of ice, with the steam released through a turbine to provide additional electrical power or to directly drive wheels/treads or drills 

Edited July 11, 2019 by StrandedonEarth

[lajoswinkler]

5 hours ago, DDE said:

Then leave the refrigerator behind.

If we built a drill for Venus, we should be able to manage a simple engine cycle. Tank pressurization can be made to keep up with atmospheric pressure to keep certain propellants liquid even at ambient temperatures.

Heck, the propellant could act as a heat sink even if the compensator valves let in atmospheric gas.

The souposphere should allow easy aerodynamic landing even for truly obscene payloads.

You're forgetting about the computer onboard. But it doesn't have to be cooling down to room temperature. Keeping stuff at 150 °C or a bit higher is also ok. We have such microprocessors. It could totally work.

[kerbiloid]

2 hours ago, StrandedonEarth said:

Hmm, if the propellants are the heat sinks, perhaps propellants that are solid at STP should be used for Eve Venus ascent.

No solid propellants. Liquids don't shrink, don't crack.
Look at the Piccard's submersible. A large tin can full of petrol. A (figurally) pressure equalizing piston.
And it happily survives ten times greater pressure than on Venus. Just the temperature is lower.

Venusian 90 atm ~= 900 m underwater.

Mariana Trench = 11 000 m ~= 1 100 atm ~= 12 Venuses

Spoiler

The only things to be strong in the Venusian landers are small (~4 m) titanium shells around two cabins (orbital and rover) and the vertical tunnel from one to another.
The rover stays on ground.
The tunnel falls down inside the 1st stage.
The titanium shroud around the orbital cabin gets jettisonned on ascent,  at 80 km or so, long before reaching the orbital speed.

Edited July 11, 2019 by kerbiloid

[StrandedonEarth]

6 minutes ago, kerbiloid said:

No solid propellants. Liquids don't shrink, don't crack.

I wasn’t clear enough. The “solids” I’m proposing, while solid at Earth’s Standard Temp and Pressure (273.15K, 100kPa) would be liquid at Venus surface temp and pressure, and would act as heat sinks as they warm and melt. 

[kerbiloid]

3 minutes ago, StrandedonEarth said:

The “solids” I’m proposing, while solid at Earth’s Standard Temp and Pressure (273.15K, 100kPa) would be liquid at Venus surface temp and pressure, and would act as heat sinks as they warm and melt.  

They start from the ship having "room" temperature of the ship, and heat up to 400°C while staying on Venus for ~12 hours.
So, if they are solid on the Earth, they will be melting in the tanks, so this should cause problems with the pressure equalizing.

[kerbiloid]

An illustration of the crewed part of the Venusian ascent stage.

Spoiler

The animal - the orbital craft. A weak, thin alumium cabin of the arbitrary, non-aerodynamic shape.
Its eyes - kinda windows, jaws - kinda the crew hatch and the sample hatch.

Orange egg - the strong titanium capsule, about 4 m in size.
The upper part (in the lander - rounded conical and larger than here) gets jettisonned at 80 km.
The lower part (in the lander - smaller and more shallow, a spherical segment) stays till the orbit as the fairing.

The orange egg is filled with gas (air or hydrogen), 1 atm = cabin pressure.
So, the cabin doesn't withstand any high pressure.

In the lander there is an apogee rocket stage below the orange egg, inside the chocolate egg.

The chocolate egg - thin and lightweight aluminium covered with carbon+resin heat protection. ~6 m wide.
It's filled with hydrogen under 90 atm pressure, so the chocolate egg has 90 atm both in and out, and doesn't struggle against the pressure at all.
The hydrogen has great heat capacity, so it slows the titanium (orange egg) shell warming for 12 hours. If required, it's pumped through, if not then stays still.

So, the second stage lifts this whole thing up to 60 km (pressure ~1 atm), permanently venting out the hydrogen from inside to match the external pressure.

At 60 km the chocolate egg gets jettisonned.
A little later the second stage separates, too.

The 3rd stage lifts the orange egg to 80 km.
The upper part of the orange egg gets jettisonned.

The 3rd stage with the lower part of the orange egg and the orbital craft reaches the orbit.

The orbital craft (the animal) leaves the fairing and orbits the Venus awaiting the Orion.

***

The rover cabin looks similar, but the shells get not jettisonned, they are nailed.
And between the chocolate and the orange eggs the hydrogen is pumped at 90 atm pressure, from hydrolox tank, to the turbine, and back into the tank.

Rover cabin inner diameter ~= 2.5 m, outer diameter ~3 m.
The rover consists of the rover itself (Lunokhod-like, 4-wheeled, 4x4 m, 3 m wide and 2 m high vertical cylinder of the cabin, hydrolox tank behind)
and the trail (4-wheeled, engine, turbine, drill, arm, vertical exhaust pipe, active cooling system).
The trail is attached hardly, so originally the whole rover thing looks  like a 4x8 m, 8 wheels single rover.

As unlike the Apollo rovers it doesn't stay waiting for the crew walking around, it has only two modes: moving and digging.
So, the turbine+engine constantly rotate either wheels or drills.

After making a circle around the lander, 1-2 km far from it, 6 hours road time, the rover returns to the lander.
Near the lander they shutdown the engine and detach the trail.

Then they switch the cooling system into the evaporation mode.
The cabin gets cooled by the hydrolox remains passive evaporation around the cabin, between the shells.
This should give 1.5-2 hours before the cabin temperature raises from 25°C to 50°C.

The lightweight rover (cabin on 4 wheels, batteries, and hydrolox tanks with remains of hydrolox) gets to the docking ramp and docks to the tunnel with the hatch on top.

They spend about 30 min lifting the buckets with samples and putting them into the orbital cabin.

So, they spend  ~1 h for docking, loading, and taking seats, and have ~0.5-1 hour in reserve.

Then they start.

***

Sample buckets.

The grabbed ground sample gets actively cooled down to the cabin temperature in the trail-mounted cooler.
Then it gets into the pressurized volume of the cabin through a pipe.

The crew puts an empty plastic bag onto the inner end of the pipe, so the next portion of ground falls into the buckets separately from others.

The vertical tunnel between the cabins is eqipped with a winch, 200 kg of payload, 15 m tether.

The bags with samples are collected into 200 kg buckets (a thin, open from top, aluminium cyliinder, 1 m high, 25 cm in diameter).

Six such buckets are installed in a rotating drum in the rover cabin. Like a revolver drum with 6 cells, with empty buckets instead of rounds.
The drum is 1 m wide and high. its total loaded mass ~1.3 t (6 x 200 kg buckets of stones).

The crew rotates the drum setting the next empty bucket below the sample dispenser.

When they return to the lander, the geologist stays in cabin, while the engineer gets into the tunnel and up to the cabin (using the winch).

The orbital cabin looks somewhat like this.

Spoiler

(But the holes are 30 cm wide).

It's equipped with similar 6-cell rotating drum, but inside like a torpedo tube sticking out below the crew hatch.
The tube with the drum inside is closed from both ends with hatches.

They step on the outer hatch when getting in/out of the crw hatch, so when the engineer stays aside, he sees the crew hatch at hands and the drum hatch at feet.

After getting on top, the engineer opens the outer hatch of the torpedo tube and sees the orbital cabin samples drum.

The geologist attaches the next bucket to the tether.
The engineer lifts it with the winch.
The geologist rotates the rover drum with next loaded cell to under the tunnel.
The engineer grabs the lifted 200 kg bucket with a simple mechanical arm, pushes it to the cabin and lowers into the cabin drum.
Then releases the tether, lowers it down to the rover, and rotates the cabin drum with the next empty cell next to the tunnel.

They repeat this 6 times, spending 5 minutes for every bucket. So, it takes 30 min to upload 1.2 tonnes of samples.

Then the engineer closes the torpedo tube hatch, while the geologist gets up from the rover.

Both take seats, close the crew hatch, and detach the tunnel.

In orbit, after getting captured by Orion, they open the inner hatch of the torpedo tube, take all six buckets one by one, and transfer it into Orion.

Then all four spacemen and 1.2 tonnes of stones return to the interplanetary ship.

Edited July 11, 2019 by kerbiloid

[DDE]

5 hours ago, lajoswinkler said:

You're forgetting about the computer onboard. But it doesn't have to be cooling down to room temperature. Keeping stuff at 150 °C or a bit higher is also ok. We have such microprocessors. It could totally work.

Not yet we don't... but it's the next stop for Venus probe design. Venera-D uses a Soviet-style pressurized hull but it's also supposed to plant an unpressurized science package with nearly unlimited longevity.

[lajoswinkler]

25 minutes ago, DDE said:

Not yet we don't... but it's the next stop for Venus probe design. Venera-D uses a Soviet-style pressurized hull but it's also supposed to plant an unpressurized science package with nearly unlimited longevity.

Yes we do and it's nothing new. Example:

https://www.datarespons.com/processors-high-temperature-applications/

[Space Nerd]

A manned venus flyby/orbit mission should come after manned mars orbit mission .

A manned venus atmospheric mission (like HAVOC) should come after manned mars landing and return.

A surface return mission is definitely possible, but I think we should do a lot of interplanetary missions before doing that.

@kerbiloid

Your mission plan looks very promising!

 

 

[kerbiloid]

I now guess, not just mission is possible, but a ground base or a settlement, too.
No volatile balloon cities, right on solid ground.

Venusian conditions are hostile, but not as deadly as they look like, mostly blackmailed.

The 90 atm pressure is like underwater 1 km. Not for outdoors walking, but there is a lot of things withstanding that pressure. Say, pressure accumulators in planes (a steel spherical balloon, ~70 atm insde).
It's far from the metals strength limit.

The 450°C temperature is hot, but it's far from 1000+, many construction materials consider it as something usual.

***

Say, we have a stationary cylindric habitat on Venusian ground. Diameter ~= height to keep it close to sphere with its surface/volume ratio.

Its average density inside the hull is same as the average density of matter inside a building, a spaceship, a submarine.
Because it consists of same rooms for same humans. So, ~250 kg/m³ or so. It's constant and doesn't depend on the habitat size.

Its human capacity is propoprtional to volume.
Resources, power plant, life support systems, are proportional to the amount of humans, so also propoprtional to volume.

So, the interior mass is proportional to the habitat volume, i.e. to size³.

***

Say, for simplicity, the hull is a simple, single-layered tank.

The external temperature is constant, 450°C.
The external temperature is kept constant, 20+°C.
So, the temperature difference is constant, ~430 K.

The heat income per surface area throw a thin envelope, W/m² = Delta-Temperature,K * ThermalConductivity,W/(m*K) / Thickness,m.

As dT = const, and ThermalConductivity = const given for a material, so the only variable here is the hull thickness, and the heat income ~ thickness^-1.

***

The hull should withstand 90 atm pressure.
It is a thin envelope, so its strength condition in first approximation is defined as:
for a cylinder: stress / strength_limit = thickness / radius of curvature
for a sphere: stress / strength_limit = thickness / (2 * radius of curvature)

As the hull shape proportions are same, the thickness/size ratio = const (for same pressure and same material)

So, the hull thickness ~ size¹.

***

As heat income per surface area, W/m² ~ thickness^-1 ~ size^-1..

Total surface area ~ size².

So, total heat income ~ size² * size^-1 ~ size¹.

***

The incoming heat warms the interior of the habitat.
The interior total mass (as we see above) is ~ size³.

The interior is made of materials, and has some average thermal capacity, J/(kg*K) of these materials (metal, plastic, air, water, etc). It is constant, given for those materials.
So, the interior total thermal capacity (as we see above), kg * J/(kg*K) = J/K, is ~ size³.

The heat income raises the interior temperature as: HeatIncome,W_{i.e. J/s} / TotalThermalCapacity,J/K = TemperatureRate, K/s.

So, TemperatureRate, K/s. = HeatIncome,W_{i.e. J/s} / TotalThermalCapacity,J/K = size¹ / size³ = size^-2.

Sic!
The warming rate of the habitat interior slows down as a square of the habitat size!

So, in a passive mode (when no active cooling is provided), the habitat warming rate is ~ size^-2.

Make a habitat 10 times larger, it will warm up 100 times slower.

***

But we are interested in the active cooling mode, as we want the habitat to last infinitely.

So, total heat income ~ size¹.
We should get this energy income with an active cooling system and throw away as a hot carbon dioxide torch.
So, the active cooling system energy consumption ~ size¹.

Total energy consumption rate of the habitat, excluding the hull cooling = power of life support and workplaces equipment ~ human amount ~ habitat volume ~ size³.

So, the ratio of (active cooling system consumption / total consumption) ~ size¹ / size³ = size^-2.

Sic!
The part of the powerplant energy production required for the habitat cooling lowers propoprtionally to the habitat squared size, too.

So, for a large habitat the active cooling requires almost nothing, compared to the total lifesupport and productive energy consumption.

***

The powerplant itself doesn't require such intensive cooling, as 450°C outside is anyway much cooler than 1000+°C inside.
Only control devices and other weak parts should be pressurized and actively cooled.

***

I.e. a 100 m large Venusian habitat is 100 times more effective and coolable than a 10 m size habitat, in both active (daily) and passive (emergency) modes.

Size matters!

***

What should this hull look like.

I see 3 layers, 3 cylindric hulls inside each other. All three are pressurized. Between them a layer of gaseous coolant is flowing.

The outer hull. Not strong (it doesn't withstand pressure), but with as low thermal conductivity as possible.
Probably, a thin aluminium tank covered with thick layer of (silicium carbide + carbon) composite ouside with (carbon matrix + resin) next to the aluminium.

It slows down the heat income rate.

Inside there is gas (maybe, nitrogen or cooled carbon dioxide) pressure 90 atm, so the outer hull stays thin.

The intermediate hull is strong, made of thick steel. (Such amount of titanium would be too expensive, it's not a tiny lander)
It withstands 90 atm pressure.

Inside there is gas (Probably nitrogen) pressure 1 atm, temperature ~20°C.

The inner hull is a thin aluminium, just to keep the coolant out of cabin. It's thin and weak, it just keeps the cabin air composition.

***

There is a lot of carbon around (CO₂).

There is sulfic acid in clouds, and some amount of water below them.
So, the airships are useful, but not with humans, but as acid/water and scattered hydrogen collectors.
They should extract hydrogen and nitrogen, store them as, say ammonium hydrosulfide (NH₄)₂S and deliver it down to the surface base.
(No need to carry O and C, it's a lot of them everywhere.)

So, the base collects C and O itself, gets H and N from the cloud catchers, and provides the dwellers with life support and fuel resources.

***

The best place for the base are maybe Maxwell Mountains, as:
1) they are high and closer to the sky;
2) they have interesting various rocks here and there, as they are mountains;
3) they are not worse than anywhere else.

Edited August 4, 2019 by kerbiloid

[DDE]

4 hours ago, Space Nerd said:

A manned venus flyby/orbit mission should come after manned mars orbit mission .

Flybys are in themselves a pointless mission type. There were attempts to make them more valid by including unmanned landers, but that was back when those probes were primitive.

Also, for many mission plans a Venus flyby is a necessary component of a trip to and from Mars.

[Space Nerd]

Yeah, I was thinking about manned venus flyby from 1970s, but we should still do it(if it will have a point 20 years later)

[Guest]

It should be noted that moving heat from 20 degrees to 450 is not trivial. For one, a Carnot-cycle refrigerator running at those parameters will have a coefficient of performance of only about 0.5. Which means that for every watt of heat you produce, you need, at least, two watts of electricity. You can't do better, and given that such a pump would not have 100% efficiency, you'll do worse. At 50%, you need four watts input per watt of heat removed. High external temperature will also reduce efficiency of any nuclear reactors you bring (again, because they're most likely going to be heat engines).

This is one thing a large habitat would not change, nor would it ever make life support and useful equipment power outweigh total cooling. Why? Because of conservation of energy. It's a closed environment, so all energy you put into it will, in the end, be deposited as heat inside the colony. If the equipment inside consumes 1MW, it will produce 1MW of heat (which would require about 4MW of electricity to remove, which would produce further 4MW of waste heat...) unless it's charging a battery or conducting an endothermic chemical reaction. Anything you can put outside would be exempt, but given the environment we're talking about, you'll be lucky if you can do that with the powerplant and the cooling system. The latter is particularly critical, because the heat pump would be unable, at this parameters, to remove its own waste heat if placed inside.

This also means the emergency passive mode is suddenly a lot less workable. Heat will not only be seeping in from outside, but most importantly of all, it would not be removed from the inside. It might allow running off stored power long enough for the colony to evacuate, but likely little else.

[kerbiloid]

31 minutes ago, Dragon01 said:

It should be noted that moving heat from 20 degrees to 450 is not trivial.

1. Why heat something from 20 to 450? Here we heat 450 up to 1000 and cool 20 downto -250.
2. Any chemical plant heats and cools fluids between supercool and superhot states many times. Just an expansion turbine and its counterparts.

31 minutes ago, Dragon01 said:

Which means that for every watt of heat you produce, you need, at least, two watts of electricity. You can't do better, and given that such a pump would not have 100% efficiency, you'll do worse. At 50%, you need four watts input per watt of heat removed. 

And the bigger it gets, the cheaper it... gets. Because ~1/size².

31 minutes ago, Dragon01 said:

High external temperature will also reduce efficiency of any nuclear reactors you bring (again, because they're most likely going to be heat engines).

It's just a working temperature of reactors cooled with liquid bismuth, used since 1950s or so. In 450°C the life just begins.

31 minutes ago, Dragon01 said:

This is one thing a large habitat would not change, nor would it ever make life support and useful equipment power outweigh total cooling. Why? Because of conservation of energy. It's a closed environment, so all energy you put into it will, in the end, be deposited as heat inside the colony.

If you read the post, that's exactly why I speccially notice that the powerplant is not put inside a habitat.
Why? Its parts hotter than the Venusian "air", it is like fresh wind for them.

So, all energy waste is exhausted from a reactor module, separated from the habitat.
To prevent the habitat warming by the powerplant cooling system, I by default always suppose they are separated by a thick barrier, like a hill or a crater wall.

So, no additional waste heat in the habitat.
So, it may produce even 100 MW of heat per 1 MW of cooler, this plays any role only in terms of efficiency, not of the energy balance.

31 minutes ago, Dragon01 said:

but given the environment we're talking about, you'll be lucky if you can do that with the powerplant and the cooling system.

What's wrong with the environment? 450°C? Phew... Chemical and metallurgical equipment works in much higher temperatures.

31 minutes ago, Dragon01 said:

The latter is particularly critical, because the heat pump would be unable, at this parameters, to remove its own waste heat if placed inside.

The pump extracts "+25" °C coolant long before it gets +450°С.
Your conditioner doesn't wait until the air in the room gets +40°C, the same here.

31 minutes ago, Dragon01 said:

This also means the emergency passive mode is suddenly a lot less workable.

I believe you, but as Venera and Pioneer-Venus landers worked for ~1 h just with several fans and a pipe, and they were ~1 m in diameter,
a 100 m wide habitat, at 1/100² = 1/10000 warming rate would warm to that temperature after ~10 000 hours ~= 416 days.

So, the emergency passive mode looks enough sufficient to survive for several weeks without active cooling until they repair the equipment or evacuate from the base.

Edited August 4, 2019 by kerbiloid

[Guest]

1 minute ago, kerbiloid said:

1. Why heat something from 20 to 450? Here we heat 450 up to 1000 and cool 20 downto -250.

You are misunderstanding the problem. Heating something to 450 degrees is easy. Moving heat from 20 to 450 degrees is hard. The only way to get rid of heat from somewhere is to put it somewhere else. This is a fundamental law of physics. Air conditioning only works because somewhere outside, there is a cooling tower to which all that heat goes to. The temperature of the cooling tower is a crucial factor affecting efficiency of the entire process. There are many ways to heat something, but only one way to cool it.

5 minutes ago, kerbiloid said:

And the bigger it gets, the cheaper it... gets. Because ~1/size².

Wrong. Size doesn't matter here. You have a box that produces 1W of heat, you have to remove 1W of heat. It doesn't matter if the box is 1 or 1000 cubic meters, or how big the space you put the box into is. It would matter if you were storing it, but you aren't, you're trying to get an equilibrium system. Again, fundamental thermodynamics. 

11 minutes ago, kerbiloid said:

The pump extracts "+25" °C coolant long before it gets +450°С.
Your conditioner doesn't wait until the air in the room gets +40°C, the same here.

My point was that you need to build heat pump machinery that would operate at 450 degrees, because it cannot cool itself to 25 degrees. It is probably possible to build one, just hard. However, currently used pumps do not work in such conditions.

Just now, kerbiloid said:

So, all energy waste is exhausted from a reactor module, separated from the habitat.

And all non-waste energy from the powerplant module? It goes into habitat. And there, it gets converted into heat by equipment. The electrical energy you put into the habitat does not just go away. If you use it to move something, it creates heat. If you use it to run a computer, it creates heat. If you use it to create light, the light hits something, and it is converted into heat. All electrical energy becomes heat that you need to somehow remove. Everything produces waste heat. And in a closed system, all energy will eventually become heat. Again, there is no way around laws of thermodynamics.

28 minutes ago, kerbiloid said:

It's just a working temperature of reactors cooled with liquid bismuth, used since 1950s or so. In 450°C the life just begins.

Yes. And how much efficiency do you get out of a heat engine with the hot end at 450 degrees and cold end at 450 degrees? Zero. This problem is not engineering, but physics. You will not be able to extract as much energy as on Earth. What matters for a heat engine is the difference between hot and cold ends. If you raise the temperature of the cold end (say, by putting it on Venus), thermal efficiency plummets. The nuclear plant will have to be much bigger than for an equivalent colony on Earth or Mars.

Also, unless you can mine uranium on Venus, or build a fusion plant that can survive those conditions, energy efficiency is very much important, because the end result is, for every gram of uranium or plutonium, you get much less electricity on Venus than you do on Earth. Which means more nuclear fuel needs to take an interplanetary trip.

[Lisias]

6 minutes ago, Dragon01 said:

Yes. And how much efficiency do you get out of a heat engine with the hot end at 450 degrees and cold end at 450 degrees? Zero. This problem is not engineering, but physics. You will not be able to extract as much energy as on Earth. What matters for a heat engine is the difference between hot and cold ends. If you raise the temperature of the cold end (say, by putting it on Venus), thermal efficiency plummets. The nuclear plant will have to be much bigger than for an equivalent colony on Earth or Mars.

I think I have a "solution" for this problem.   Space Elevators.

Making a floating nuclear reactor to exploit cooler environment high in the Venus skies is unfeasible (and you would need to transmit the electricity anyway, somewhat hard to accomplish when the energy source is moving around).

But a space elevator would provide anchorage for such a stunt. I doubt it would be cost effective to move the whole shebang to the high atmosphere of Venus, but heat pipes would do. And the Space Elevator would then transmit the energy to the consumers, probably floating cities in the high atmosphere of Venus, where the temperature and pressure are pleasant for humans (saving costs on housing and EVA suits.

[kerbiloid]

1 minute ago, Dragon01 said:

Moving heat from 20 to 450 degrees is hard.

Moving mechanical one is easy. One turbine expands 20, cooling it down to -200..250. Another part compresses 450 heating it up to 1000. No heat exchange, two adiabatic processes and mechanical job.

4 minutes ago, Dragon01 said:

Wrong. Size doesn't matter here. You have a box that produces 1W of heat, you have to remove 1W of heat. It doesn't matter if the box is 1 or 1000 cubic meters, or how big the space you put the box into is. It would matter if you were storing it, but you aren't, you're trying to get an equilibrium system. Again, fundamental thermodynamics. 

6 minutes ago, Dragon01 said:

My point was that you need to build heat pump machinery that would operate at 450 degrees, because it cannot cool itself to 25 degrees.

We don't need to cool the reactor don't to +20°. It stays +500°C hot. The habitat is just a parasite power consumer. The larger is the habitat, the lesser is the heat flow into the habitat, the lesser is the part of the reactor power required for the habitat cooling.

7 minutes ago, Dragon01 said:

And all non-waste energy from the powerplant module? It goes into habitat.

Once again. The reactor is outside the habitat. No reason to put it inside.
By no means its waste heat can reach the habitat. It's exhausted from the reactor module far away from the habitat, heating the atmosphere.

9 minutes ago, Dragon01 said:

And all non-waste energy from the powerplant module?

It is electric power required for the habitat module.
Your computer consumes electricity, it produces heat, and you conditioner easily pumps the warm air out and cools it. You don't include a 1000 MW powerplant with 2000 MW waste heat in your room heat balance.
Same here.

12 minutes ago, Dragon01 said:

And how much efficiency do you get out of a heat engine with the hot end at 450 degrees and cold end at 450 degrees?

The hot end is 1000°C. The cold end is 450°C. Looks nice, Carnot is happy.

You take the inner gas energy from the 20°C gas by adiabatically expanding and cooling it down to -200° in one turbine, then move its mechanical energy to another turbine which compresses the outside 450°C cold CO₂ up to hot 1000°C, then exhaust it. The 1000°C CO₂ dissipates in the infinite 450°C pool of the atmosphere warming it a little. No heat passing, only mechanical energy.

Just now, Lisias said:

Space Elevators.

On Venus - not an elevator, but a 60 km high tower would be great.
But a 100 m habitat looks more realistic for the very beginning.

[Guest]

42 minutes ago, kerbiloid said:

It is electric power required for the habitat module.

Which turns into heat. Which needs to be removed. On Earth, it is exactly the same. If you have a computer running in a room with AC, your AC will use more energy to cool the room, and you will not only pay for electricity used to power the computer, but also for electricity to remove the heat generated by the computer. Nothing is free in physics.

42 minutes ago, kerbiloid said:

We don't need to cool the reactor don't to +20°. It stays +500°C hot. The habitat is just a parasite power consumer. The larger is the habitat, the lesser is the heat flow into the habitat, the lesser is the part of the reactor power required for the habitat cooling.

Heat flowing into the habitat is, with proper insulation, always be negligible compared to the heat produced inside habitat. The latter will be equal, or nearly equal, to electrical energy flowing into habitat from the reactor. It's like on a spaceship, where you need radiators to cool the crew section. Only now, they cannot operate at low temperatures, and you need to work against heat gradient. This is also the reason why reactor's waste heat is irrelevant. What you are persistently trying to ignore is habitat waste heat.

42 minutes ago, kerbiloid said:

Moving mechanical one is easy. One turbine expands 20, cooling it down to -200..250. Another part compresses 450 heating it up to 1000. No heat exchange, two adiabatic processes and mechanical job.

Except that you still can't exceed Carnot cycle efficiency with this. Your Rube Goldberg heat pump is still a heat pump. It will not work any better than a regular one. In fact, a pair of Brayton cycle turbines will be much worse than a single Carnot cycle cooler. Converting heat to mechanical work can only be done with an efficiency equal to Carnot cycle maximum, and when you're doing it a second time, it multiplies (and since efficiency is always a fraction, this sends it to the bottom). Not to mention you would somehow need to generate a low pressure area in your first turbine... additional mechanical work, which needs to come from somewhere. 

Better thinkers than you have tried to cheat thermodynamics. None succeeded. 

Edited August 4, 2019 by Guest

[Flying dutchman]

I do wonder if Venus is 450c consistantly. Perhaps it's a bit cooler on a mountain. Maybe not by that much but even if the temp is slightly lower it matters a lot.

 

The highest mountain on venus is 11km or 7mi. It seems this would make a difference of about 20 degrees c.

 

Edited August 4, 2019 by Flying dutchman

[kerbiloid]

27 minutes ago, Dragon01 said:

Which turns into heat.

Your computer also produces, say, 200 W of heat. Do you include 2000 MW of powerplant waste into your room heat balance?
Our you consider your conditioner as a weak external parasite attached to the powerplant with its own cooling system far away?
Do you cool the powerplant reactor/boiler down to your room temperature?
Our you consider it as two separated cooling system, one of which is powered by another one, and increasing it total cooling balance?

27 minutes ago, Dragon01 said:

Heat flowing into the habitat is, with proper insulation, always be negligible compared to the heat produced inside habitat.

Just playing with words. Let's add the heat producing when they open doors or knocking.
Heat flowing into the habitat by wires is negligible, and its much less than heat extracted from inside, so can be considered insignificant.

27 minutes ago, Dragon01 said:

The latter will be equal, or nearly equal, to electrical energy flowing into habitat from the reactor.

And the larger is the habitat, the lesser amout of heat is added to this heat produced inside, due to the 1/size² proportion.
So, the larger is the habitat, the lesser is difference between the Earth and the Venus, exactly what we should achieve.
Ideally, the external powerplant should extract only the heat produced inside from electricity.

27 minutes ago, Dragon01 said:

It's like on a spaceship, where you need radiators to cool the crew section.

It has nothing at all common to a spaceship where I need radiators to cool the crew section.

Because the Venusian base is not in a vacuum, and its powerplant:
is separated from the habitat by an infinite heat protection barrier and doesn't return the waste heat back to the common structure;
is surrounded by a infinte cold fluuid pool to drop the waste heat;
does not use ineffective radiator panels, but uses gasodynamics for cooling;

27 minutes ago, Dragon01 said:

What you are persistently trying to ignore is habitat waste heat.

The only thing I am persistently trying to keep is the habitat waste heat.

27 minutes ago, Dragon01 said:

Except that you still can't exceed Carnot cycle efficiency with this. Your Rube Goldberg heat pump is still a heat pump. It will not work any better than a regular one. In fact, a pair of Brayton cycle turbines will be much worse than a single Carnot cycle cooler. Converting to mechanical work can only be done with an efficiency equal to Carnot cycle maximum, and when you're doing it a second time, it multiplies (and since efficiency is always a fraction, this sends it to the bottom). Not to mention you would somehow need to generate a low pressure area in your first turbine... additional mechanical work. 

The reactor is an external source of energy, it has 1000..1200° hot active zone, and gets cooled by heating the 450° cold agent up to 1000°C. Then it drops the heated agent outside  into infinite 450°cold pool,
That's how all in the world coolers basically do.

Of course, the turbine is powered from the reactor, this is included.

The habitat heat production just adds more heat to make the powerplant cooling system exhaust not just 800°C, but 1000°C.

27 minutes ago, Dragon01 said:

Better thinkers than you have tried to cheat thermodynamics. None succeeded. 

I hope, I'll get a little farther than you did.

Btw, how do your fridge and conditioner work?

 

7 minutes ago, Flying dutchman said:

I do wonder if Venus is 450c consistantly. Perhaps it's a bit cooler on a mountain. Maybe not by that much but even if the temp is slightly lower it matters a lot.

 

The highest mountain on venus is 11km or 7mi. It seems this would make a difference of about 20 degrees c.

Skadi Mons is in Maxwell Mountains, Ishtar Land.

Edited August 4, 2019 by kerbiloid

[Flying dutchman]

This may sound a bit far fetched. But what if we were able to lift a platform with baloons to an altitude of 40 to 50 km. (30 to 40 from skadi mons)

Ancor it with 4 cables so it stays put.

Then we use this platform as an heatsink. Insulate hoses that run some sort of gas from sea level up to the heatsink and back again.

 

 

I don't know if this would be feasable, but if it could possibly be it would be a great way to cool a surface base.

[kerbiloid]

13 minutes ago, Flying dutchman said:

But what if we were able to lift a platform with baloons to an altitude of 40 to 50 km. (30 to 40 from skadi mons)

Ancor it with 4 cables so it stays put.

Then we use this platform as an heatsink. Insulate hoses that run some sort of gas from sea level up to the heatsink and back again.

For titanium or steel the stress is ~= 8.89 * 30 000 * 4500..7800 ~= 1200..2100 MPa, while strength limit is 2000 MPa maximum.

Also such narrow pipe would have very high inner drag force, so the flow speed would decrease significantly.
And while the gas would be moving, it probably should get cooled down to that 450°C, so the local exhaust is just a lesser trouble.

[Flying dutchman]

The gas would never exceed 450c.