For Questions That Don't Merit Their Own Thread

[magnemoe]

3 hours ago, ARS said:

Thanks for the answer. It really helps me to define the changes of energy between cold and hot temperature.  I got the idea for the question when I stumbled upon a sentence:

"...coldness isn't energy, but rather lack of it (from the point of view of our environment's parameters)..."

Temperature is an thing in itself I say, you can measure the temperature even if all you can observe has the same temperature, the thermometer uses different expansion of different materials. 
Now cold is not an thing, neither is darkness as in you can not project cold or darkness, 
And spraying liquid nitrogen on something does not count even if very nice to cool down an room temperature coke, had to wait for the ice to melt and would prefer co2 here  

[JoeSchmuckatelli]

On 11/29/2020 at 9:18 AM, ARS said:

... 

Since Jupiter is already at the current ecliptic plane, it makes sense that any planets in the early age of solar system that's not at the ecliptic plane would be either thrown out or forced into the current ecliptic plane.... 

 

22 hours ago, K^2 said:

... .

So yeah, the disk is there because of the spin, but it's more that things remained as part of the disk because of the spin, rather than original shape getting flattened into the disk because of it. The flattening itself still happens primarily due to collisions.

Hmmmm. 

 

I'm still trying to get a handle on this.  So - presuming an active star forming region, there are eddies in the dust clouds with a net average spin.  Yet because it's a cloud - that net spin is just that - a net... Meaning there are clumps that are zipping around on their own program.  If I understand correctly, the objects that are in alignment with the net rotation of the system can form a stable orbit around the center... But the not aligned will be captured, reduced to zero AM (and eaten by the star), or flung out.  So what is the process to make the captured align?  

 

I get that the star is the heavyweight - but can't a Jupiter or the disk mass shape the non aligned into disk aligned orbits outside of a close interaction?  Or does it not work that way?  

[K^2]

4 minutes ago, JoeSchmuckatelli said:

I'm still trying to get a handle on this.  So - presuming an active star forming region, there are eddies in the dust clouds with a net average spin.  Yet because it's a cloud - that net spin is just that - a net... Meaning there are clumps that are zipping around on their own program.  If I understand correctly, the objects that are in alignment with the net rotation of the system can form a stable orbit around the center... But the not aligned will be captured, reduced to zero AM (and eaten by the star), or flung out.  So what is the process to make the captured align?  

Imagine that there are two rubble pile asteroids orbiting out of plane. They collide and produce a bunch of shrapnel. All that new shrapnel has alignment closer to the average of the two. Eventually that shrapnel becomes part of new rubble pile asteroids. Over enough collisions, everything converges to the plane of predominant angular momentum. A billion years is a lot of time.

[kerbiloid]

Temperature indicates your thermodynamic system uncertainty. At the absolute zero its particles are at certain positions.

Entropy indicates in how many ways your system can be built from same trashcan.

***

And of course, someone should mention the most important  pair of formulas in the Universe (no, not that "e=mc²", of course)

In the thermodynamic system delta of entropy is dS = dQ / T
(where dQ is delta of energy, and T is temperature)

In the information system S = k * ln(W)
(where k is a constant, W is the system statistical weight, i.e. in how many ways it can be composed from its particles).

It's the same entropy, so this is where the physical physics and the abstract mathematics get bound, i.e. the physical world and the abstract world.

***

The gas cloud shrinks spherically, the dust cloud becomes a disk due to collisions.

So, the star is spherical, the protoplanetary disc is flat.

Both keep rotating in same plane, ancested from the protostar cloud, because momentum can't disappear.

When the star is passing the phase of T (not tau, but T) Ceti (i.e. starts intensively burning), its electromagnetic forces force intensive ejection of the partially ionized gas, and it forms the gas giants , which brings chaos to the protoplanetary disk, but at the same time makes its survived particles be synchronized with the giants, and cause regular dust collisions bringing the planets.
At this point the angular momentum passes from the star to the exhausted gas and gets gathered in the largets giants of the system (Jup, Sat), and the star  rotation dramatically slows.
(By the electromagnetic interaction)
Then all survivors redistribute along safe orbits and we have what we have.

If calculate the momentum of the planets (m * v * Rorbit), we can easily see that almost total angular momentum of the Solar System which is not in the Sun, belongs to Jupiter.  Others just gather remains under table.
So, the Solar System consists of the Jupiter, its lesser sibling Saturn (the two oldest ones), and everything other is just an aftermath of their forming.

So, basically Ancient Greeks and Romans were not that wrong about Jupiter.

Edited November 30, 2020 by kerbiloid

[JoeSchmuckatelli]

9 hours ago, K^2 said:

Imagine that there are two rubble pile asteroids orbiting out of plane. They collide and produce a bunch of shrapnel. All that new shrapnel has alignment closer to the average of the two. Eventually that shrapnel becomes part of new rubble pile asteroids. Over enough collisions, everything converges to the plane of predominant angular momentum. A billion years is a lot of time.

That's interesting - and makes sense.  So the collisions and near-misses all get averaged out over time.

 

I don't know why - but I also presumed that distant object 'nudging' was involved - hence my expectation that the angle between the non-aligned and a Jupiter (or just the net mass) would play a part - even if the two never got close.

 

So what effect can a gas giant have over the evolution of a planetary system once orbits stabilize?  What has been explained above makes sense if you follow the wandering Jupiter/Saturn - where they get close enough to fling stuff about... but some of my past reading suggests that Jupiter has an outsize impact on the other planets.  Should I start to doubt that it still does (now that everything is stable)?

Edited December 1, 2020 by JoeSchmuckatelli

[JoeSchmuckatelli]

Would a higher metallicity star imply that it's planets would be higher in metals as well? 

Edited December 5, 2020 by JoeSchmuckatelli

[kerbiloid]

Low metallicity stars would not provide significant solid planets.

So, not no.

[ARS]

Is there any reason or backstory why prototype model is almost always referred as "mark" (like mark.1, mark.2, mark.3, etc.) or "object" for Soviet/Russian-made ones (object 279, object 195, object 252, etc.)?

[kerbiloid]

It's an object made for project.

[DDE]

1 hour ago, ARS said:

why prototype model

OK, hold on. The "object" name is given to all models, at least over in the tank department (aviation is more inclined towards the equally bland Izdeliye), you just have to dig it out from under the other designations.

[kerbiloid]

And "izdeliye" means literally "something manufactured", i.e. "artifact".

***

That's because "We aren't sure what we have made, but that's it. The object. The artifact. Number 291 if I recall this right."

And correspondingly, "Well... It looks.... er... creative...  Whatever it is, let's mark this... thing... as 3. Because marks 1 and 2 are already stored in that shed."

Edited December 6, 2020 by kerbiloid

[ARS]

The An-225 Mriya has twintail design to mitigate the lack of airflow when Buran is loaded on top the fuselage by moving the rudders on the sides. If for example, on aircraft with large propellers on wings placed directly on the way of rear twintail with short fuselage length, (think V-22 Osprey design) does the fast-moving airflow from behind the propellers hitting on twintail rudders actually improves rudder performance compared with regular airflow without propellers in front of the twintails?

[magnemoe]

1 hour ago, ARS said:

The An-225 Mriya has twintail design to mitigate the lack of airflow when Buran is loaded on top the fuselage by moving the rudders on the sides. If for example, on aircraft with large propellers on wings placed directly on the way of rear twintail with short fuselage length, (think V-22 Osprey design) does the fast-moving airflow from behind the propellers hitting on twintail rudders actually improves rudder performance compared with regular airflow without propellers in front of the twintails?

I will think so, however its rarely worthwhile to make the twin tail outside some settings, the V-22 tail is not very wide but is still inside the area of the propellers. 
The B-24 twin tail is behind the inner engines, but the B-29, B-17 and B-36 did not follow this design.

Now on the V-22 the twin tail might make the folded down size of it smaller but overall an single larger tail fin is lighter. 

[JoeSchmuckatelli]

1. Absent some form of aerobraking - does capture at a planet require the same d/v regardless of altitude (pe)?

2. Could you use aerobraking on a gas giant - not for entry, but to adjust ap to some lower altitude - with any hope of having a useable ship afterwards?

3.  Is there enough 'atmosphere' around the sun to slow a ship into an orbit with Mercury, or is the definition of having sufficient atmosphere to slow a ship the same as 'flying into the sun'?

 

[Spacescifi]

1 hour ago, JoeSchmuckatelli said:

1. Absent some form of aerobraking - does capture at a planet require the same d/v regardless of altitude (pe)?

2. Could you use aerobraking on a gas giant - not for entry, but to adjust ap to some lower altitude - with any hope of having a useable ship afterwards?

3.  Is there enough 'atmosphere' around the sun to slow a ship into an orbit with Mercury, or is the definition of having sufficient atmosphere to slow a ship the same as 'flying into the sun'?

 

What? You write scifi?

I am no expert, but I do have a grasp of these subjects.

1. I want to say yes...unless you're using gravity flyby assist, which can either slow or speed you up depending on how you do it. Someone can correct me if needed to clarify, but I do not think I am wrong.

2. Yes. The more surface area hitting the air the better you brake. No matter what you will need either ablative or cooling systems in play.

3. Magnetic fields interacting with solarwind at a distance is the safest way..it would take a while though, and by a while I mean longer than your average space opera trip. Flying anywhere near the sun is suicide...it's just too much heat. Unless you were traveling near lightspeed so you spent little time,  but then braking would also be impossible. The magnetic field pushed by solar wind is a concept researchers have at least wrote about on paper. As a propulsion system it is not high thrust like a rocket, but if you don't mind waiting...for a looong time...it will push you. Works a lot better and faster on low mass probes obviously.

Edited December 16, 2020 by Spacescifi

[Terwin]

5 hours ago, JoeSchmuckatelli said:

1. Absent some form of aerobraking - does capture at a planet require the same d/v regardless of altitude (pe)?

Any time you have a gravity well, you can take advantage of the Oberth effect to improve the effects of your burn.

5 hours ago, JoeSchmuckatelli said:

2. Could you use aerobraking on a gas giant - not for entry, but to adjust ap to some lower altitude - with any hope of having a useable ship afterwards?

I think most of our gas giants have some radiation issues if you get too close, but other than that, you can always do a little bit of aero-breaking if you plan for it.

I suspect it has not been done much due to both radiation concerns as well as uncertainty with regards to the atmospheric density at various altitudes, making it just safer to take along the extra fuel instead of risking an aero-braking maneuver.

[kerbiloid]

5 hours ago, JoeSchmuckatelli said:

1. Absent some form of aerobraking - does capture at a planet require the same d/v regardless of altitude (pe)?

You have to burn more when you need to go deeper.

Lower (lesser semiaxis) orbit needs more fuel, otherwise geostationary sats would require same dV as LEO ones.

Oberth is not about the aerobraking and capture, he's about the passing-by.

5 hours ago, JoeSchmuckatelli said:

2. Could you use aerobraking on a gas giant - not for entry, but to adjust ap to some lower altitude - with any hope of having a useable ship afterwards?

Theoretically - yes. Practically - they have too hard gradient of density and high (re)entry speed.

So, unless the ship and the crew can withstand many g's, no.

(Like jumping from the Golden Gate Bridge).

5 hours ago, JoeSchmuckatelli said:

3.  Is there enough 'atmosphere' around the sun to slow a ship into an orbit with Mercury, or is the definition of having sufficient atmosphere to slow a ship the same as 'flying into the sun'?

Gasbraking at 50 km/s (the Mercury orbital speed) looks not healthy at all, and the Sun is mostly the atmosphere.

Let alone the planet-sized atmospheric turbulences.

Edited December 16, 2020 by kerbiloid

[JoeSchmuckatelli]

25 minutes ago, Terwin said:

Any time you have a gravity well, you can take advantage of the Oberth effect to improve the effects of your burn.

 

3 minutes ago, kerbiloid said:

You have to burn more when you need to go deeper

 

 

Confused.  

 

Do these statements not contradict one another?

 

 

4 hours ago, Spacescifi said:

What? You write scifi?

Don't we all?

(I write: I have not attempted to publish)

[kerbiloid]

1 minute ago, JoeSchmuckatelli said:

Do these statements not contradict one another?

Do you ask about a capture or about a passing-by?

[JoeSchmuckatelli]

Capture.

I'm thin on the details, and don't mind admitting it. 

I thought Oberth depended upon proximity to the body.  So closer should (maybe?) require less d/v.  Except - if you have a given velocity from your escape from the last body... then (maybe?) to capture you merely need to slow down enough - which may not be altitude / distance determinative?

(Again - failed Calc many times; struggling to figure this out on my own + w/ help from ally'all)

[kerbiloid]

The Oberth maneuver doesn't require delta-V.
It effectively adds additional delta-V from engines to the local fly-by speed and turns the velocity vector in desired direction.
It's a fly-by technics.

You can use it to get the ship captured by another celestial body, after the Oberth velocity vector correction at the previous one, but for that latter one this is a fly-by, not a capture, while the former one doesn not care what maneuvers have been performed previously.

[JoeSchmuckatelli]

4 hours ago, kerbiloid said:

The Oberth maneuver doesn't require delta-V.
It effectively adds additional delta-V from engines to the local fly-by speed and turns the velocity vector in desired direction.
It's a fly-by technics.

You can use it to get the ship captured by another celestial body, after the Oberth velocity vector correction at the previous one, but for that latter one this is a fly-by, not a capture, while the former one doesn not care what maneuvers have been performed previously.

So - I can use Oberth and my rockets to get from one space rock to another more efficiently, but once there I can use Oberth for a flyby enroute to a third rock - but not capture at the second? 

[kerbiloid]

Yes. You can redirect your ship by additional impulse on an intermediate rock fly-by to get to the final rock at proper angle and relative speed.

[AHHans]

12 hours ago, JoeSchmuckatelli said:

3.  Is there enough 'atmosphere' around the sun to slow a ship into an orbit with Mercury, or is the definition of having sufficient atmosphere to slow a ship the same as 'flying into the sun'?

At Mercury's orbit there is not enough "solar atmosphere" to lead to significant aerobraking. (Not really surprising.) Once you get close enough to the sun to have significant aerobraking you also face massive heating, not only from the radiation, but also from the sun's atmosphere itself. So for practical purposes it is the "same" as flying into the sun.

12 hours ago, JoeSchmuckatelli said:

2. Could you use aerobraking on a gas giant - not for entry, but to adjust ap to some lower altitude - with any hope of having a useable ship afterwards?

If you bring enough of a heat-shield, then yes. (Wasn't there a probe recently that was something like two thirds heat-shield and burned away most of that while entering Jupiter's atmosphere?) But unless you are aiming for a really low orbit you probably save mass by doing a propulsive capture instead of lugging a heavy heat shield around with you.

12 hours ago, JoeSchmuckatelli said:

1. Absent some form of aerobraking - does capture at a planet require the same d/v regardless of altitude (pe)?

No. With a single capture burn the capture into a lower orbit requires more dV than capture into a higher orbit. (You need to get rid of more energy.) But clever use of the Oberth effect can save significant dV. A propulsive capture maneuver is the same as a transfer maneuver, except in the other direction. So once you figured out what the best maneuver for a transfer burn is, you also know what the best maneuver for the capture burn is.

And in nearly all cases the best maneuver is to capture into a circular orbit is to enter the SOI with a low PE, do most of the capture burn at that low PE until your AP is where you want the target orbit to be, and then circularize at that new AP. That way you make maximum use of the Oberth effect. The exception is when you come into the SOI with little extra velocity so that the additional cost of the circularization burn is higher than the savings from the Oberth effect.

 

7 hours ago, kerbiloid said:

Oberth is not about the aerobraking and capture, he's about the passing-by.

I don't really understand what you want to say about the Oberth effect, but I have the impression that you didn't really understand it. The Oberth effect says that using your engines is more efficient when you do that at high speeds than when doing that at lower speeds - all relative to the system in which you want to change your orbit. Because of orbital mechanics that means doing a burn at lower altitude is more efficient than doing it at a larger altitude.

[kerbiloid]

9 minutes ago, AHHans said:

I don't really understand what you want to say about the Oberth effect, but I have the impression that you didn't really understand it. The Oberth effect says that using your engines is more efficient when you do that at high speeds than when doing that at lower speeds - all relative to the system in which you want to change your orbit. Because of orbital mechanics that means doing a burn at lower altitude is more efficient than doing it at a larger altitude.

Oops, you're partially right.

Confused the "Oberth effect" and the "Oberth maneuver".