For Questions That Don't Merit Their Own Thread

[kerbiloid]

Because it's cheaper to make the whole satellite to be a gyroscope, and such "gyroscope" doesn't spend energy, it just keeps rotating for decades.

(Though, I'm not sure why the "planets" here?)

Primitive sats are stabilized this way, Pioneers are, too, warhead re-entry vehicles are, M93 Hornet anti-tank mine warhead also rotates fast even while it doesn't need to spiral around like SADARM warheads.

When you need just a single axis to be stabilized, it's the best option.

Edited March 14, 2021 by kerbiloid

[JoeSchmuckatelli]

2 hours ago, kerbiloid said:

Though, I'm not sure why the "planets" here?

Grin! Because after writing - I remembered that satellite does not exclusively mean man-made in English.  And I thought, "who here is most likely to add snark?"

 

(so it was a tongue in cheek preemptive counter snark! =D) 

 

Are there any recent sats they've done this with or is gyro the presumptive method these days? 

[kerbiloid]

8 hours ago, JoeSchmuckatelli said:

Are there any recent sats they've done this with or is gyro the presumptive method these days? 

It's a  https://en.wikipedia.org/wiki/Spin-stabilisation

 

Probably any looking like a cylinder covered with solar panels

https://en.wikipedia.org/wiki/Meteosat
(100 rpm)

Spoiler

https://en.wikipedia.org/wiki/Satélite_de_Coleta_de_Dados

Spoiler

 

And also

https://solarsystem.nasa.gov/basics/chapter11-2/

Quote

Spin: Stabilization can be accomplished by setting the vehicle spinning, like the Pioneer 10 and 11 spacecraft in the outer solar system, Lunar Prospector, and the Galileo Jupiter orbiter spacecraft, and its atmospheric probe.

and
https://space.skyrocket.de/doc_sdat/explorer_hessi.htm

Spoiler

and

https://space.stackexchange.com/questions/4441/does-a-satellite-naturally-turn-in-phase-with-its-orbit-always-facing-earth

Quote

Most communications satellites are dual spin satellites. The rotor (plastered with solar arrays) rotates rather quickly for stability while the communications platform rotates but once per day.

 

They can be rotating just around the main axis pointed at nowhere, just to keep predictable position and plane, or additionally around the perpendicluar axis to keep its main rotation axis poiting at the Sun or the Earth.

[Ziggy Kerman]

10 hours ago, kerbiloid said:

It's a  https://en.wikipedia.org/wiki/Spin-stabilisation

 

Probably any looking like a cylinder covered with solar panels

https://en.wikipedia.org/wiki/Meteosat
(100 rpm)

  Reveal hidden contents

https://en.wikipedia.org/wiki/Satélite_de_Coleta_de_Dados

  Reveal hidden contents

 

And also

https://solarsystem.nasa.gov/basics/chapter11-2/

and
https://space.skyrocket.de/doc_sdat/explorer_hessi.htm

  Reveal hidden contents

and

https://space.stackexchange.com/questions/4441/does-a-satellite-naturally-turn-in-phase-with-its-orbit-always-facing-earth

 

They can be rotating just around the main axis pointed at nowhere, just to keep predictable position and plane, or additionally around the perpendicluar axis to keep its main rotation axis poiting at the Sun or the Earth.

That's a lot of cylinders with panels

[JoeSchmuckatelli]

Is anyone developing an 'automated warehousing' robot for space stations?

 

Currently, it seems as if the only way to deliver stuff to a station is to have someone on the other end waiting to offload the stuff.  From what I understand, hanging out in space for long periods of time is hard on the body.

 

So after looking at the DragonXL stuff I had to wonder: if folks are serious about remote, moon orbiting stations shouldn't they have a robot that offloads the craft, warehouses the stuff and then when a crewed mission arrives they can just get whatever they want 'out of the closet'?

[StrandedonEarth]

29 minutes ago, JoeSchmuckatelli said:

Is anyone developing an 'automated warehousing' robot for space stations?

 

Currently, it seems as if the only way to deliver stuff to a station is to have someone on the other end waiting to offload the stuff.  From what I understand, hanging out in space for long periods of time is hard on the body.

 

So after looking at the DragonXL stuff I had to wonder: if folks are serious about remote, moon orbiting stations shouldn't they have a robot that offloads the craft, warehouses the stuff and then when a crewed mission arrives they can just get whatever they want 'out of the closet'?

I assume that was one of the tasks envisioned for Robonaut 2 and Fedor

[kerbiloid]

All Soviet/Russian spacecrafts almost from the very beginning are equipped with radiotechnical automated docking system.
(First - Igla / Needle, later - several generations of Kurs / Course ).
If let alone numerous cases of its malfunction, it allows the crafts to dock automatically, manually, or telemanually, so normally it doesn't need a human assistance.

The US vessels since  Shuttle are equipped with the lidar TriDAR which uses laser scanning and is used for approaching and/or docking to an object like ISS or a Martian rock (if installed on a rover).
So, it's probably no problem with automatic docking, too.

***

Almaz-derived modules of Mir and ISS are equipped with the relocation manipulator Ляппа / Lyappa  
(idk what it means in Russian, let alone English, but maybe it's actually from eng→rus "lapper", who knows) 
to dock to the axial port and then self-re-berth to the radial port.

https://en.wikipedia.org/wiki/Lyappa_arm

(Photos inside).

So, the Almaz-derived modules (and if required - vessels) can self-relocate to any free port of the Mir-like sphere without manual canadarming, just extending and attaching a lever.

***

Almaz- and Spacelab-derived modules have some cargo transfer systems like rails or so, which allow to move heavy cargo of standard size from vessel to station.

The Common Berthing Mechanism standard is designed to transfer or temporarily extend equipment to space.
Every Spacelab-derived module is equipped with several of them perpendicularly

Spoiler

All of this is compatible with
https://en.wikipedia.org/wiki/International_Standard_Payload_Rack

and theoretically, with the APAS-95-derived IDSS docking system standard (Buran, Shuttle, Crew Dragon docking).

(If unscrew and unmount the soft-capture system of the IDSS docking port, they will get an empty tunnel 1.255 m in diameter, and the squared doors inside the CBM are 1.27 m wide exactly to match this size to transfer any 1.25 m-diametered cargo between any compartment of the station and the vessel).

Cygnus and Cargo Dragon get berthed to CBM by Canadarm.
So, they don't need the docking port unmounting, but need a Canadarm to attach.
Though, hypothetically they could use a simplified docking port to dock and some bigger Lyappa together with CBM to re-berth and transfer cargo, if they wanted so much.

So, if they actually wanted, they could make an internal railroad through all Spacelab-derived (i.e. non-Soviet/Russian ones) modules and the cargo ships.
And if they wanted more, probably it could be automated, too. Just why do it now when the crew is anyway bored. 

And Almaz had a mechanical system along the TKS and OPS to move the 350 kg heavy photocapsules and other cargos. 
The Soviet crewless industrial station project (partially derived from it) also had something like that, to move the cargo from the supply ship to the crystal workshop.

***

So, basically, anthropoid robots are not required, just better rails and motors, everything other is basically tested.

Edited March 15, 2021 by kerbiloid

[JcoolTheShipbuilder]

Hmmm... just wondering, what is the specific impulse of a water bottle rocket?

[K^2]

3 hours ago, JcoolTheShipbuilder said:

Hmmm... just wondering, what is the specific impulse of a water bottle rocket?

Not very high. Say, you have a 1L bottle that can take 5atm of pressure. (You might be able to go a bit higher, but not by much.) That's 1L of air compressed to 200mL and 800mL of water. If you were able to design the exhaust so as to uniformly accelerate all of the water, this is 4x10⁵Pa * 2x10^-4 m³ = 80J of energy applied to 0.8kg of water, giving you 14m/s exhaust, or I_SP of about 1.4s. And this is the upper limit. Realistically, it's going to perform a lot worse. You can play a bit with proportions to improve it a little, but you're still going to be in that ballpark.

Now, if instead of compressed air you used superheated steam, it is possible to do way better, because you can maintain high pressure throughout the work cycle. Still nowhere near what you'd want for an SRB, but getting into amateur rocketry territory. In fact, there was a guy by the name Mike Hughes who used to fly these to fairly impressive heights.

[ARS]

Does the radar on SPAAG (those spinning bits on top) works on area with a lot of overhead obstacle like those in the middle of a city where tall buildings are around it or in the forested area where there are a lot of large trees? Or is it only usable on large open areas?

[DDE]

2 hours ago, ARS said:

Does the radar on SPAAG (those spinning bits on top) works on area with a lot of overhead obstacle like those in the middle of a city where tall buildings are around it or in the forested area where there are a lot of large trees? Or is it only usable on large open areas?

It is impaired, yes. Heck, some of them are befuddled by large amounts of water droplets.

Hence one countermeasure, the 40V6.

Spoiler

Can fit most if not all S-300P/S-400-family radars:

And its lesser cousin with the S-350:

Spoiler

Never seen something like this on, or even for a SPAAG (there's usually a battery command vehicle camping out behind the Tunguskas).

[kerbiloid]

Also it can throw stones and logs.

[ARS]

8 hours ago, DDE said:

Never seen something like this on, or even for a SPAAG (there's usually a battery command vehicle camping out behind the Tunguskas).

Wait, so those SPAAG are not actually engaging the airborne target with their own targeting, but actually being 'directed' by other vehicle that provides targeting data?

[SOXBLOX]

20 minutes ago, ARS said:

Wait, so those SPAAG are not actually engaging the airborne target with their own targeting, but actually being 'directed' by other vehicle that provides targeting data?

Well, sometimes the radar and launchers are on the same vehicle, like Pantsir, I believe, but usually the radars are carried separately. This allows one set of radars to find targets for many launchers. It's cheaper and easier that way. And when you have multiple radars (one for scanning and one for targeting) it makes sense to separate them.

[JoeSchmuckatelli]

49 minutes ago, ARS said:

Wait, so those SPAAG are not actually engaging the airborne target with their own targeting, but actually being 'directed' by other vehicle that provides targeting data?

Typically you want the radar away from the payload delivery (and people you like). 

 

Radar is a great way to let 'the bad guys' know where you are.  It also provides them with a great way to guide missiles directly to the source of the radar, which is something we've been doing for decades.  

 

It literally is a light in the darkness saying 'here I am!' 

[Silavite]

This is something of an oddly-specific request, but here goes. Would anybody happen to have (and be willing to share) some thermodynamic tables? The substance in question is ideal gas combustion products of air and a hydrocarbon fuel (I believe that it would be something like jet A-1).

The tables which my propulsion professor provided are from another professor's old Romanian(?) textbook and are not of the greatest quality (and also use the European convention which swaps the roles of decimals and commas). Google has been surprisingly unhelpful in this regard...

 For illustration, this is what I'm currently working with:

Spoiler

The specific enthalpy, specific internal energy, and specific entropy are columns 6, 7, and 8 respectively. The entropy is calculated at a reference pressure of 1 bar (I think).

And this is more what I'm aiming for (with a different substance, of course). This is from Fundamentals of Engineering Thermodynamics by Moran, Shapiro, Boettner, and Bailey, though the table is cited as originating from J. H. Keenan and J. Kaye, Gas Tables, Wiley, New York, 1945:

Spoiler

Wherein s° is the contribution of R*ln(T2/T1) to the entropy change of an ideal gas and Pr2/Pr1 would correspond to P2/P1 for isentropic compression or expansion. Vr2/Vr1 similarly would similarly correspond to V2/V1 for an isentropic process.

Edit: Just to be perfectly clear, I'm looking for SI units

Edited March 24, 2021 by Silavite
SI units

[kerbiloid]

There are survey radars (can be on the firing vehicle or on a dedicated one) and aiming ones (on firing vehicles, watching a narrow sector in front of the turret).

[monophonic]

7 hours ago, JoeSchmuckatelli said:

Typically you want the radar away from the payload delivery (and people you like). 

 

Radar is a great way to let 'the bad guys' know where you are.  It also provides them with a great way to guide missiles directly to the source of the radar, which is something we've been doing for decades.  

 

It literally is a light in the darkness saying 'here I am!' 

Although in reality many a SPAAG/SPAD do carry some sort of radar on them. You don't have to turn your flashlight on just because you have it, but when the bad guys shoot out the streetlights (surveillance radars) you are blind without one (to keep with the analogy; LLTV and IR imagers do exist and are used on SPADs too for night operations).

Many SPADs (e.g. ZSU-23-4, Gepard, Roland, Tunguska) specifically were also meant to protect armored forces on attack, so they had to move at high speeds over rough terrain (to keep up with the attacking MBTs and IFVs) while being capable of engaging rapidly appearing targets at a moments notice. So they could not count on communications to and coverage of higher eschelon surveillance radars to be there for them.

They fell out of fashion in the west after the Cold War ended but Russia has kept building on the Soviet legacy systems after the 90s slump. Even they seem to have put more emphasis on lighter systems like the truck mounted Pantsir over tracked and armoured types like Tunguska, but those do still have radars. The export and news coverage of Pantsirs in Syria and elsewhere may have made that shift seem stronger than it really is though. Their effectiveness against the much improved missiles of today can be legitimately challenged, and that is part of what is driving current developments towards lasers and other direct energy weapons in air defence. (Drone swarms being the other big driver but that is another discussion.)

All in all the balance of weapon versus counter-weapon keeps swinging from side to side, and the only constant is that they all keep getting more and more expensive.

[DDE]

13 hours ago, ARS said:

Wait, so those SPAAG are not actually engaging the airborne target with their own targeting, but actually being 'directed' by other vehicle that provides targeting data?

This is where we get to the topic of networked air defense, which hapenned a lot earlier than you think. For SPAAGs and some short-ranged SAMs, it's common to have a gunnery radar but not a wide-angle radar. The two things are really visible on Tunguska, for example:

Whereas the prior Shilka has only the narrow-field non-spinning gunnery radar:

And as systems get bigger, the launching vehicle typically ends up with no radar at all. There's also a trend towards going fully electrooptical for short-range systems, e.g. Sosna and Derivatsya-PVO.

Individual SPAAGs usually come with a battery control vehicle. In case with Tunguska as well as Tor and other Soviet divisional maneuver AA and below, that would be 9S737 Ranzhir, which doesn't have a radar of its own but would network them with the army-level Buk SAM radars and distribute targets between SPAAGs. And that's in the 1980s; today this sort of layers upon layers of Integrated Air Defense Systems are the hot stuff. You never know for sure how many shooters are usuing that one active radar.

Edited March 24, 2021 by DDE

[kerbiloid]

4 minutes ago, DDE said:

networked air defense, which hapenned a lot earlier than you think

Spoiler

 

Edited March 24, 2021 by kerbiloid

[kerbiloid]

https://www.nature.com/articles/s41561-021-00706-3

Quote

A pole-to-equator ocean overturning circulation on Enceladus

Even there...

[JoeSchmuckatelli]

File this under: Things that make you go Hmmmm...  

 

They say the universe is 13.8 billion years old. 

 

Yet we've spotted a star that is older yet https://www.google.com/amp/s/www.space.com/amp/how-can-a-star-be-older-than-the-universe.html. *

And they also say that there is a galaxy we can see that is 13. 7 blya* 

https://www.google.com/amp/s/www.space.com/amp/oldest-most-distant-galaxy-discovery

 

So - I'm good with the 'age of the star is within the margin of error' argument... But how long does it take to get a whole galaxy of stars? 

 

 

 

 

 

*yes I had fun reading what I wrote as something other than 'billion light years away' 

Edited March 27, 2021 by JoeSchmuckatelli

[DDE]

5 minutes ago, JoeSchmuckatelli said:

*yes I had fun reading what I wrote as something other than 'billion light years away' 

Spoiler

 

[Gargamel]

The stuff about a boat wedged in a lake somewhere  has been split off.   Congratulations thread, it’s a little baby thread!  

 

Edited March 29, 2021 by Gargamel

[SunlitZelkova]

Would a 1 megaton ground burst at the Waste Isolation Pilot Plant cause enough extra fallout to be worth targeting an ICBM at? Assuming the winds are coincidentally optimal enough to blow towards the direction of the Great Plains/farming states.

I apologize if this doesn't count as a science related question.