Recent comments in /f/askscience

graebot t1_j5yj1aq wrote

Reply to comment by [deleted] in How hot is the steam coming out of nuclear power plants? by ivy-claw

Clouds are water vapour, but I wouldn't refer to them as steam. Technically, steam is invisible, and exists above 100 C at 1 atmosphere. Only once it drops below the vapour point (100C @ 1 Atm) does it start condensing into water vapour. Water vapour is not steam, it's just liquid water droplets suspended in air.
When steam is used to do work, it starts as high pressure, high temperature, and as it does work, the pressure reduces, and the temperature with it, and after doing work you're usually left with water vapor as the spent product.

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cjameshuff t1_j5ygqwh wrote

Reply to comment by ninthtale in Why do sample return missions such as OSIRIS-REx use their own reentry vehicles instead of just going to the space station for pickup and return with ISS equipment? by PromptCritical725

A landing on an airless Earth, launched from the moon? It would be a bit more efficient than the moon landing, because the spacecraft would be at its heaviest (with a full stack of stages fully loaded with propellant) in low lunar gravity and would be doing its final braking in Earth's heavy gravity after burning most of its propellant and discarding most of its stages, but gravity losses are fairly small in comparison to the overall acceleration/deceleration requirements. You'd need something of similar size, just with fewer first stage engines to get it off the moon.

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cjameshuff t1_j5yfrbi wrote

Reply to comment by CountingMyDick in Why do sample return missions such as OSIRIS-REx use their own reentry vehicles instead of just going to the space station for pickup and return with ISS equipment? by PromptCritical725

> they would presumably cheaply adjust their incoming trajectory to be as close to the ISS orbit as possible

That's a pretty major presumption. It can be hard enough just intercepting Earth, requiring that interception to also occur with the probe trajectory aligned with the orbital plane of the ISS would greatly restrict the set of targets we could retrieve samples from.

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123frogman246 t1_j5yf6h8 wrote

Reply to Is it possible for me to develop a cold from a virus i was exposed to before qnd fought off and/or been gone latent in my body without being exposed to other sick people? How long can cold viruses be latent in the body with the ability to reactivate? by sewcrazy4cats

Not sure about developing a cold but if you look at CMV (cytomegalovirus) and EBV (Epstein Barr virus), those are both prevalent in most people as latent infections. If you get another infection, are immune suppressed, or pregnant, then those viruses can flare up and cause their relevant symptoms.

Probably the most well known is glandular fever which is caused by EBV. You can have it, then recover, bit still have dormant/latent virus in your system that flares up again in the future. Same goes for TB

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AboveTheCarmanLine t1_j5yak2w wrote

Reply to Why do sample return missions such as OSIRIS-REx use their own reentry vehicles instead of just going to the space station for pickup and return with ISS equipment? by PromptCritical725

Relative velocity at earth is extremely high. The minimum velocity from LEO to escape is ~3350 m/s, which you would need to burn off on the trip back. That‘s a lot of fuel you‘d need to burn off that delta v, so immediate reentry from escape trajectory is the way to go

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KnoWanUKnow2 t1_j5ya81i wrote

Reply to comment by Limos42 in Where do bears go when they hibernate? Cartoons convinced me they all lived in caves, but I'm not so sure. by Forge_craft4000

She doesn't pee. Apparently her kidneys shut down and other processes are used to remove toxins from the blood without wasting water.

She doesn't sweat.

The only water she loses is from respiration. This quickly forms ice on the surface of her den, which solidifies and creates a physical barrier that hinders further moisture from leaving.

She's using her fat reserves, she'll emerge having lost 30% of her weight. Part of the biological process of breaking down fat into energy releases water. For instance, the equation for breaking down triglycerides is:

C^(55)H^(104)O^(6) + 78 O^(2) --> 55 CO^(2) + 52 H^(2)O + energy

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