For Questions That Don't Merit Their Own Thread

[JoeSchmuckatelli]

23 minutes ago, DDE said:

A random musing at the intersection of so many topics.

Whenever I built a ship (a three-seat capsule and an SM) and a space station module or a standalone Salyut in KSP, despite the station being much larger in size (usually thanks to the Mobile Lab), even if I carefully trimmed the size of the SM's propellant tanks, the ship would usually end up heavier than the space station.

Why could that be? IRL, where does the additional mass of a station comes from to merit a Soyuz-Proton difference?

Empty space vs filled tanks? 

[DDE]

3 hours ago, JoeSchmuckatelli said:

Empty space vs filled tanks? 

IRL space stations aren't exactly propellant depots, yet the difference is manifold.

Edited August 15, 2021 by DDE
Deporting a typo

[Shpaget]

15 hours ago, DDE said:

difference is manifold.

Don't you think for one second that I haven't noticed the lack of "no pun intended" disclaimer.

[kerbiloid]

15 hours ago, DDE said:

IRL space stations aren't exactly propellant depots

That's what Nauka said.

[Dr. Kerbal]

Um. Does anyone know how many versions of ksp there been?

[Chemp]

8 minutes ago, Dr. Kerbal said:

Um. Does anyone know how many versions of ksp there been?

https://wiki.kerbalspaceprogram.com/wiki/Version_history

[AHHans]

On 8/15/2021 at 4:20 PM, DDE said:

Why could that be? IRL, where does the additional mass of a station comes from to merit a Soyuz-Proton difference?

The fuel tanks in KSP are made from armor-plating^(*), so if you add a fuel tank then it becomes unreasonably heavy.

A) In RL you have fuel tanks made from the thinnest material that you can manage, B) I believe most RL spacecraft have a lot less dV (and TWR) than what your usual KSP spacecraft has, and C) I think that while fuel tanks in KSP are heavier that their equivalent in RL the life-support systems in RL are heavier than in KSP.

P.S. (*) Well, plating as found on WW-I tanks. Not like the armor on WW-II tanks or battleships, but still.

Edited August 18, 2021 by AHHans
fixed typo

[Terwin]

30 minutes ago, AHHans said:

The fuel tanks in KSP are made from armor-plating^(*), so if you add a fuel tank then it becomes unreasonably heavy.

A) In RL you have fuel tanks made from the thinnest material that you can manage, B) I believe most RL spacecraft have a lot less dV (and TWR) than what your usual KSP spacecraft has, and C) I think that while fuel tanks in KSP are heavier that their equivalent in RL the life-support system in RL are heavier than in KSP.

The stock KSP solar system *requires* less dV than the real solar system.  

As a result, various components have been adjusted to provide a more reasonable challenge to players.

One of the methods chosen is to make fuel tanks much heavier so that the fuel fraction is lower and you can't accidentally make a SSTO  with a huge cargo margin as one of your first rockets.

 

Real vs KSP system Examples:

LKO is ~2km/s  

LEO is ~10km/s

 Pe of Eeloo is 66,687,927 km while the Ap of Mercury is 69,816,900 km, putting part of the orbit of the most distant KSP planet inside part of the orbit of mercury

The Moon orbits around 360-400 Mm(5.1% inclined), while The Mun orbits at 12Mm(0% inclined) with Minmus at 47Mm(6% inclined)

[magnemoe]

47 minutes ago, AHHans said:

The fuel tanks in KSP are made from armor-plating^(*), so if you add a fuel tank then it becomes unreasonably heavy.

A) In RL you have fuel tanks made from the thinnest material that you can manage, B) I believe most RL spacecraft have a lot less dV (and TWR) than what your usual KSP spacecraft has, and C) I think that while fuel tanks in KSP are heavier that their equivalent in RL the life-support system in RL are heavier than in KSP.

P.S. (*) Well, plating as found on WW-I tanks. Not like the armor on WW-II tanks or battleships, but still.

The round 3 man command module in KSP is also 2 ton, if you use an second as the orbital module its 4 ton, if you use the terrier engine its another half ton, so dry mass will be above 5 ton. 
An small station with the mobile processing lab and a hitchhiker module is 6 ton for these two parts add a ton for power and other stuff. 
So with fuel the Soyuz can easy be heavier. 
I say that station parts is lighter than RL while capsules, engines and fuel tanks are heavier. 

[JoeSchmuckatelli]

A little Fusion news to brighten your day... 

https://www.llnl.gov/news/national-ignition-facility-experiment-puts-researchers-threshold-fusion-ignition

In case you missed it 

Also -

"the fusion energy generated was about 5 times the energy absorbed by the capsule and about 70% of the laser energy shot at the target – these are the significant aspects."

https://www.google.com/amp/s/www.cnbc.com/amp/2021/08/17/lawrence-livermore-lab-makes-significant-achievement-in-fusion.html

 

Edited August 18, 2021 by JoeSchmuckatelli

[AHHans]

On 8/17/2021 at 3:59 PM, Terwin said:

The stock KSP solar system *requires* less dV than the real solar system.  

[...]

I know. I also agree with the reasoning why the differences between KSP and RL are there. But that won't keep me from making fun of them whenever I think I may get away with it.

Btw. One sobering effect of that difference is that spaceplane-SSTOs are a lot less viable in RL than in KSP. The speed of sound on Kerbin and on Earth is about the same, so at Mach 5 - the typical speed that you can expect to reach with air-breathing engines - you are at about 1500 m/s. On Kerbin that's better than 2/3 of the orbital velocity, on Earth that's far less than 1/5 of the speed needed to get to orbit.

[magnemoe]

46 minutes ago, AHHans said:

I know. I also agree with the reasoning why the differences between KSP and RL are there. But that won't keep me from making fun of them whenever I think I may get away with it.

Btw. One sobering effect of that difference is that spaceplane-SSTOs are a lot less viable in RL than in KSP. The speed of sound on Kerbin and on Earth is about the same, so at Mach 5 - the typical speed that you can expect to reach with air-breathing engines - you are at about 1500 m/s. On Kerbin that's better than 2/3 of the orbital velocity, on Earth that's far less than 1/5 of the speed needed to get to orbit.

You sums it up well enough here. you only need oxidizer for 1/3 of the flight rater than 4/5 of it. 
Not that the 1/5 helps its an weak first stage after all, an suborbital plane releasing an payload at the edge of space would make a lot of sense, you could use rocket engines for higher velocity before dropping.
Problem is that designing and building an large hyper-sonic plane and its engines is very expensive compared to rockets. 

Another way to look at it is that and falcon 9 first stage would be able to reach orbit with the second stage and payload attached on Kerbin, you might even be able to recover first stage  

[JoeSchmuckatelli]

Wait - is the first stage the part that drops off into the ocean first, or the part that the payload is riding? 

[magnemoe]

49 minutes ago, JoeSchmuckatelli said:

Wait - is the first stage the part that drops off into the ocean first, or the part that the payload is riding? 

First stage is the stage who is dropped first, exception is then using boosters like all who uses SRB and Soyuz and falcon heavy. Then the boosters drop first, 
Then first stage and second in orbit however some has an 3rd stage. 

[DDE]

2 hours ago, magnemoe said:

First stage is the stage who is dropped first, exception is then using boosters like all who uses SRB and Soyuz and falcon heavy. Then the boosters drop first, 

In the US numbering tradition. The Soviet numbering tradition insists the four "carrots" on the Soyuz are the first stage.

@JoeSchmuckatelli

[mikegarrison]

There are so many different ways to do this that there really is no single comprehensive way to describe it.

The Shuttle, for instance, had "boosters", "main engines" (which were never dropped), and "orbital maneuvering engines" (which were also never dropped). Main engines were actually started before the boosters and burned continuously through the ascent. Final orbital insertion (and deorbit) was done with the OMS.

The original Atlas had a three-engine "first stage" that dropped two engines and kept burning on one, but they all used the same tank. This was sometimes called "stage and a half".

[DDE]

52 minutes ago, mikegarrison said:

This was sometimes called "stage and a half".

The term, as officially defined in GOST R 53802 2010, also applies to the Soyuz and Energia.

[JoeSchmuckatelli]

Why does my microwave have an all-metal interior (and heating coils) but it does not get exciting until I accidentally leave a fork, or some foil in it? 

[TheSaint]

1 hour ago, JoeSchmuckatelli said:

Why does my microwave have an all-metal interior (and heating coils) but it does not get exciting until I accidentally leave a fork, or some foil in it? 

Short version? Because a bunch of radar technicians (such as my uncle Victor, RIP) didn't want to be unemployed at the end of WWII.

Long version? Because the interior of the microwave is carefully engineered to match the wavelengths of the emissions from the magnetron such that they reflect around inside the heating chamber until they are absorbed by the target (i.e. the food). If you put another reflector inside, such as a spoon, or, say, an aluminum Jiffy-Pop popcorn container, (not that I have ever witnessed this, I'm just randomly selecting things for examples) then it disrupts that carefully engineered environment and starts reflecting the emissions of the magnetron back into the magnetron. Which is bad juju. And whatever day it is, it becomes the Fourth of July.

[kerbiloid]

Got it. They put radars around the sea area, and when a battleship gets in, it starts sparkling. That's how radars work.

[TheSaint]

23 minutes ago, kerbiloid said:

Got it. They put radars around the sea area, and when a battleship gets in, it starts sparkling. That's how radars work.

No, silly, only vampires sparkle.

(My uncle worked for Raytheon during WWII, and retired in the 1970s. I heard all the stories, including how they worked on the microwave oven. )

[kerbiloid]

As a radar was melting a foiled chocolate in a pocket, its primary objective was probably to prevent stealing small electric parts from the installation.

[TheSaint]

7 hours ago, kerbiloid said:

As a radar was melting a foiled chocolate in a pocket, its primary objective was probably to prevent stealing small electric parts from the installation.

No, that was my cousin who worked at Hasbro and stole toys incessantly. But, that's another show....

Edited August 20, 2021 by TheSaint
I could have worded that better

[cubinator]

Say you had invented a material strong enough for a space elevator, and could make a cable of it that's long enough. How would you get the cable up into space? Pulling it straight up from the ground doesn't seem terribly efficient, and going into orbit would just wrap it around the planet. Even the lightest cable would probably be very heavy. Would you have to build the cable in orbit and then push one end down to the ground to anchor it?

[DDE]

44 minutes ago, cubinator said:

Would you have to build the cable in orbit and then push one end down to the ground to anchor it?

I'd try this, after first investigating high-atmosphere momentum exchange tethers.