For Questions That Don't Merit Their Own Thread

[Spaced Out]

Okay guys I got a new question. How about ideas for more bio-friendly rocket fuels? (Both solid and liquid)

EDIT: More environmentally friendly.

Edited September 16, 2017 by Spaced Out

[shynung]

1 hour ago, Spaced Out said:

Okay guys I got a new question. How about ideas for more bio-friendly rocket fuels? (Both solid ans liquid)

Did you mean less dangerous (=corrosive/poisonous) to the fuel handlers, or less damaging to the environment?

Edited September 16, 2017 by shynung

[Spaced Out]

1 minute ago, shynung said:

Wasn't this the same question as you asked before?

Last time I meant rocket fuels but I forgot to specify so I didn't really get any answers so I asked one abot just roclet fuels now.

[shynung]

Just now, Spaced Out said:

Last time I meant rocket fuels but I forgot to specify so I didn't really get any answers so I asked one abot just roclet fuels now.

Edited my response, misread.

[Spaced Out]

7 minutes ago, shynung said:

Did you mean less dangerous (=corrosive/poisonous) to the fuel handlers, or less damaging to the environment?

I meant environmentally. I will edit my question.

[shynung]

20 minutes ago, Spaced Out said:

I meant environmentally. I will edit my question.

Without sacrificing performance? LH2-LOX and kerosene-LOX are hard to beat in launch situations. In theory, a beamed-power thermal rocket with LH2 propellant can be much cleaner, but it needs to be fed power from the ground via lasers/microwaves.

A variation on this concept is the lightcraft, which are essentially beamed-power thermal ramjets. This design does not need propellant (LH2), but only works in an atmosphere. Unlike regular jet engines, it doesn't care about the atmosphere's composition - it'd work in oxygen-less atmospheres.

Edited September 16, 2017 by shynung

[Spaced Out]

That answer is good enough for me. Next question. Is it possible that any parts of the rocket equation are wrong?

[Steel]

29 minutes ago, Spaced Out said:

That answer is good enough for me. Next question. Is it possible that any parts of the rocket equation are wrong?

There aren't many "parts" to the rocket equation, it is very simple as far as rocket science goes and you can derive it directly from conservation of momentum. Unless we have the laws of physics completely wrong, it should be pretty correct!

Edited September 16, 2017 by Steel

[NSEP]

If a something explodes in a vacuum like a spaceship, could you still hear the gasses released from the explosion?

[Human Person]

17 minutes ago, NSEP said:

If a something explodes in a vacuum like a spaceship, could you still hear the gasses released from the explosion?

Why not? If you are close and the gasses hit your spacesuit, they might create a sound you can hear. Sounds like a dangerous experiment though. 

Edited September 17, 2017 by Physics Student

[Spaced Out]

Do spent boosters re-entering the atmosphere burn up completely?

[Kerbinchaser]

5 hours ago, NSEP said:

If a something explodes in a vacuum like a spaceship, could you still hear the gasses released from the explosion?

Ask the Apollo 13 astronauts. 

[Skylon]

2 minutes ago, Lo Var Lachland said:

Ask the Apollo 13 astronauts. 

I think he means through the vacuum; the vibrations probably passed through the apollo 13 spacecraft, not the vacuum

[Steel]

5 hours ago, NSEP said:

If a something explodes in a vacuum like a spaceship, could you still hear the gasses released from the explosion?

Unless the amount of gas is large enough that it can effectively transmit sound to you, then no.

21 minutes ago, Spaced Out said:

Do spent boosters re-entering the atmosphere burn up completely?

No. Depending on the amount of potentially explosive stuff onboard it may reduce into to very small pieces, but most stuff that boosters are made of do not combust, so there is no way that they can burn up completely. Most boosters will break up into small pieces.

Edited September 17, 2017 by Steel

[Spaced Out]

What are the equations for drag loss and gravity loss? Plus, does the weight of a rocket on wikipedia include the upper stages?

[Steel]

7 hours ago, Spaced Out said:

What are the equations for drag loss and gravity loss? Plus, does the weight of a rocket on wikipedia include the upper stages?

Unfortunately there aren't any nice analytical equations for those things. You end up with differential equations, which you (or a computer) would have to integrate at small intervals along your ascent trajectory in order to get the answer.

I'm assuming you're talking about the rocket equation? In that case there are two masses, the full mass (including any additional stages) and the empty mass (i.e the mass without propellant)

[peadar1987]

8 hours ago, Steel said:

Unfortunately there aren't any nice analytical equations for those things. You end up with differential equations, which you (or a computer) would have to integrate at small intervals along your ascent trajectory in order to get the answer.

I'm assuming you're talking about the rocket equation? In that case there are two masses, the full mass (including any additional stages) and the empty mass (i.e the mass without propellant)

Drag losses are given by  where \rho\ is the density of the fluid, u is the velocity, c_d is the drag coefficient and A is the cross-sectional area. 

Getting the coefficient of drag is the hard part, as it depends on the shape of the projectile and the mach number (as well as some impact from the viscosity of the fluid and other factors). The c_d for a Saturn V is calculated here: 

So basically what you'd have to do to find out drag losses is run a simulation of the whole launch, calculating the drag force at every time step, taking into account the fact that c_d is changing with velocity and density is changing with altitude. It's not actually that difficult if you have some processing power available, but a bit of a mission to do it by hand, and probably next to impossible to give a general solution.

[kerbiloid]

Martian rover.

Spoiler

Terrestrial rover.

Spoiler

Because Mars doesn't have kangaroo?

Edited September 20, 2017 by kerbiloid

[kerbiloid]

(Not a question, but unlikely merits its own thread. )

Science now got a solid base.
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3039505

[ChrisSpace]

In Isaac Arthur's "Dead Aliens" video, he described a scenario in which multiple alien individuals intentionally froze themselves in a crater of permanent darkness so their bodies could be brought back to life in the distant future. In the scenario, humans showed up 2-4 million years later, but given the circumstances described in the video, what's the longest the bodies could've stayed sufficiently intact?

 

Also, I once heard that one possible solution to the Fermi Paradox is that aliens could be contacting Earth, but their thoughts and actions are so slow that it takes months for them to say a single word, and as such it's indistinguishable from background noise. While I highly doubt this is common enough to be relevant to the FP, or that it would take MONTHS to hold a single conversation, I'm still wondering: What's the slowest speed at which thoughts and actions can occur in a complex biological organism? One-quarter of a human's? One-tenth? One-thousandth?

[Steel]

1 hour ago, ChrisSpace said:

In Isaac Arthur's "Dead Aliens" video, he described a scenario in which multiple alien individuals intentionally froze themselves in a crater of permanent darkness so their bodies could be brought back to life in the distant future. In the scenario, humans showed up 2-4 million years later, but given the circumstances described in the video, what's the longest the bodies could've stayed sufficiently intact?

 

Also, I once heard that one possible solution to the Fermi Paradox is that aliens could be contacting Earth, but their thoughts and actions are so slow that it takes months for them to say a single word, and as such it's indistinguishable from background noise. While I highly doubt this is common enough to be relevant to the FP, or that it would take MONTHS to hold a single conversation, I'm still wondering: What's the slowest speed at which thoughts and actions can occur in a complex biological organism? One-quarter of a human's? One-tenth? One-thousandth?

1) Hard to say, since these are alien bodies (and thus could/will work completely differently to our bodies). If they are very close to humans then they're stuffed (for want of a better phrase), since we currently have no way of re-animating frozen human bodies unless they have been incredibly carefully looked after with life-support. If they're nothing like humans then ther'es no way to answer the question, since we've never seen any advanced beings that are not like humans.

 

2) There's no biological limit that we're aware of. The sort of life you're talking about here is so unlike anything we've ever encountered that we simply have no data to answer that question I'm afraid.

[shynung]

Would altering a human's body metabolism rate affect their perception of time? If so, by how much?

[Green Baron]

36 minutes ago, shynung said:

Would altering a human's body metabolism rate affect their perception of time? If so, by how much?

No data available to answer that, since metabolism is a set of autonomous body functions and difficult to alter without killing the organism and perception of time happens in the mind. Also the term "perception of time" might need some clarification ?

Activity or occupation change my perception of time. If the mind is occupied, time flies ...

Edit: do other vertebrates have a perception of time ? If so, is it connected to their mental abilities or the metabolism ? idk

Edited September 22, 2017 by Green Baron

[shynung]

@Green Baron Well, that's going to be tricky...

What I'm going towards is this: space is vast, and traveling through it takes a lot of time. The travelers are going to be stuck in their pods without much to do. Is it possible to alleviate their boredom by altering their perception of time so that, to their minds, 1000 seconds felt like 1 second?

[Green Baron]

Well, that leads to the discussion about suspended animation through cooling, deep freeze, drugs, ... that all are less than impractical.

How are people doing in all the south pole research stations during the long winter months ? I know that they go through a selection process that especially looks at their mental abilities to cope with stress and solitude. It is lonelier than on the ISS where one at least has a constant link down and a view to the outside.