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2 hours ago, JoeSchmuckatelli said:

Odd question (perfect place for these!) about the COM of off-shaped things:

If you were to release a bowling pin (or a hand-axe, or anything really heavy on one side vs the other) in space adjacent to a free-falling ship... would it change its orientation relative to the observer?

  • i.e. you release it as stably as possible, imparting no other spin or residual motion... would the initial orientation change?
    • if it would move; would it settle heavy-end toward the Earth or in the direction of fall/motion?
    • if it would not move/reorient... is that because of a lack of drag?

This question arose b/c of @sevenperforce's comments on Shuttlecock behavior of a rocket during reentry.  I understand how atmospheric drag works - I'm just trying to figure out what would happen with a tail-heavy rocket in freefall, in vacuum... whether it would sling the butt around (eventually) and 'fall' or travel heavy end forward in the absence of drag.

If you are low enough in the thermosphere that drag is at all meaningful, then the random buffeting of particles it experiences will average out to cause it to orient with the heavy end forward (i.e., in the direction of travel).

At the same time, the tidal gradient of Earth's gravity well is going to try to pull the heavy end to point toward Earth. Gravity is stronger the closer you get to Earth, and so the "stable" position is to have the heavy end deeper in the gravitational field.

These two sets of perturbations will induce a rotation. In the absence of force, angular momentum is preserved, and so the bowling pin will eventually settle into a rotation equal to its orbital period:

tidal-lock.png

It may be weird to think about the bowling pin rotating as it orbits, but it will, just like a moon. Angular momentum is conserved even if something is small. The ISS, for example, always keeps the same orientation with respect to the Earth because it rotates every 90 minutes, the same as its orbital period. 

The amount of time that it takes to settle into a stable rotation, and the angle at which it will eventually settle, will ultimately depend on the sizes of those perturbing forces I noted above. At a very low altitude, where both thermospheric drag and tidal forces are higher, this will be faster and the angle will be more bent back. At very high altitudes it will take longer. 

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4 minutes ago, Rutabaga22 said:

What is the most use rocket engine?

Here's a good place to start:

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

I'm not sure what you mean by "most use[d]" but there are a few possibilities:

The oldest orbital-class rocket engines still in use

  • AJ10 (first flight in 1958, still flying today on the Orion spacecraft)
  • NK-33 (designed in the late 1960s, still flying today on the Soyuz-2-1v)
  • RD-107/8 (designed in 1957, still flying today on the Soyuz family)
  • RD-0110 (first flight in 1960, still flying today on the Soyuz family)
  • RD-253 (first flight in 1965, still flying today on Proton)
  • RL10 (first flight in 1962, still flying today on Atlas V, Delta IV, SLS, and Vulcan)

The engines that have launched the most total vehicles to orbit through history

  • RL10 (used on Atlas, Saturn I, Titan III, Atlas G, Titan IV, Atlas II, Atlas III, Atlas V, DC-X, and Delta IV)
  • RD-107/8 and RD-0110 (up to 1900 launches in the Soyuz family)
  • Merlin 1D (used on all Falcon 9 launches since 2013)

The engine that currently launches the most payload to orbit each year

  • Merlin 1D (Falcon 9 launches have made up approximately half of all mass to orbit so far this year)
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12 hours ago, Rutabaga22 said:

What is the most use rocket engine?

Not sure about most-used, but Sutton writes that 22 thousand of AGM-12 Bullpup missiles have been produced, all of them featuring a liquid-propellant rocket engine, and considers them the most widely-produced LRPE.

But this, of course, makes us then consider such things as the booster rocket on the RPG-7, or the various solid-propellant rockets slung about during WWII...

Edited by DDE
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21 hours ago, JoeSchmuckatelli said:

Figure that you would need not only the gun(s) and ammunition, but also the turret mechanism, framing and sensor arrays... And you've got a massive redesign & shift of weight. Good engineering can solve this - so it again goes to the threat: will the bomber have a sufficient threat of 'up the tailpipe missiles' coming at it to justify the effort and expense? (Tail defense turret may be utilized for incoming rear and maybe side threats - at the cost of constant 'here I am' pinging with the sole hope of overwhelming electronically/kinetically. )

I think here the balance has shifted somewhat, to the point where @SunlitZelkova's examples from B-52s may be invalidated. SAM operators and fighter pilots are both likely to attempt a shootdown from the longest possible range. This is going to cause the missile to come in from the side aspect rather than from below; in cases of extremely long-range missiles they have an actual ballistic arc and would come in from above. Furthermore, it seems a lot of the antimissile manuvers - certainly for the air raft big enough to mount a turret - amount to turning away from the missile and trying escape the engagement basket. Because of that, it would seem that a lot of missiles would end up coming in from the rear aspect - again, for an aircraft large enough to consider a turret, and thus not prone to flying within range of MANPADs and other "minor" AA.

21 hours ago, JoeSchmuckatelli said:

Adding a new thing at the back of the plane for the pilot to play with isn't going to improve his /her SA & effectiveness... And if everything was done right up front - the tail gun is looking back on smoking wreckage. 

Yeah, this is completely out of the question for single-seaters. However, aircraft as small as fighter-bombers (Su-34, certain Marks of F/A-18) tend to have a WO.

18 hours ago, JoeSchmuckatelli said:

My 'thought experiment' version of this was a tungsten-BB auto chaff shotgun that could be used to hard kill incoming missiles - but a pilot friend told me that you'd be losing more than you gain trying to build that into a jet 

When it comes to chaff, this has actually been attempted, with PRL-series rounds for 23 and 30 mm Soviet guns.

Hasn't heard much of the results, though.

21 hours ago, JoeSchmuckatelli said:

(Tail defense turret may be utilized for incoming rear and maybe side threats - at the cost of constant 'here I am' pinging with the sole hope of overwhelming electronically/kinetically. )

Maybe I misread this, but I know there's an issue with the turret gunnery radar inviting enemy and even friendly fire. However, there are still attempts to add dedicated rearward radars to aircraft (e.g. the Su-34M - apparently, contrary to all claims, it's not present on Su-34s) as well as significant advancement in infrared-based missile detection. Plus there's the fledging Tochmash school of passive-only AA systems (Palash/Pal'má and Sosna), so it may be possible to discard the targeting radar.

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20 hours ago, SunlitZelkova said:

I think this was what he meant, not using it against aircraft.

On a separate note, assuming a large portion of a nation’s air defences are knocked out by ICBMs and SLBMs, the small number of surviving fighters resorting to guns isn’t too far fetched.

Reading anecdotes from B-52 gunners, it seems like the existing detection arcs on their fire control radars (and presumably the Tu-95’s too) make an acquisition impossible against SAMs, and thus a missile fired from below by a fighter would not be trackable either.

Even if the radar was extensively redesigned to cover a wider arc all around, the existing gun mounts would require another redesign to have more depression, another factor mentioned by B-52 gunners is that the tail gun wouldn’t depress low enough to target a SAM.

Of course another option would be to reinstate belly and dorsal guns, which the Tu-95MS does not have and the B-52 never had. But then there would be another two CIWS mounts, with radars and all, with their weight.

If the aircraft is flying at low altitude, the radars may have a hard time picking up the small AAMs. If the aircraft fly high, they will probably get salvoed by the long range SAM that is targeting it, which a single CIWS alone might not be able to handle. I’m not sure what fighters would carry in an air defence role, but if they have their max load out of some 6x or so AAMs they could launch a large salvo too.

I would say no. 3x heavy CIWS mounts and a new constraint on the flight profile does not seem like a lot, when more ECM equipment and stand off cruise missiles could be fitted instead.

I think only deep penetration missions (like trying to strike in a continental sized nation’s territory in a nuclear war) would require such a system anyways. The sorts of missions flown by bombers under normal circumstances (launching conventional ALCMs) would be flown within friendly airspace.

It would not be worth it for a nuclear war scenario when ECM equipment and more room for ALCMs would be more useful in conventional scenarios. I have seen opinions that bombers aren’t even a key part of nuclear war strategy nowadays anyways, and exist for a pure psychological deterrence purposes (although of course they still have their aforementioned conventional role).

O. M. G.

I had to Google 'CIWS' to discover that I have a hidden bias / blind spot!

The acronym 'CIWS' in my mind was purely used for 'Commander's Independent Weapon System' - (an independent of the main weapon system used targeting pod to enhance offensive capabilities) but I discovered that it's presently used to mean 'Close In Weapon Systems' which are defensive (what I would have called AD 'air defense' - but the CIWS term (and targets /capabilities) has been been extended beyond merely 'A' threats to include boats, drones... Heck anything 'Close In' that a defensive 'Weapon System' might target.

In light of this - my prior response reads as incomprehensible babble! 

Sigh.  I'm out of date.  SMH. 

Edited by JoeSchmuckatelli
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7 minutes ago, JoeSchmuckatelli said:

The acronym 'CIWS' in my mind was purely used for 'Commander's Independent Weapon System' - (an independent of the main weapon system used targeting pod to enhance offensive capabilities) but I discovered that it's presently used to mean 'Close In Weapon Systems' which are defensive (what I would have called AD 'air defense' - but the CIWS term (and targets /capabilities) has been been extended beyond merely 'A' threats to include boats, drones... Heck anything 'Close In' that a defensive 'Weapon System' might target.

It's offensive, too.
(Not only in terms of social relations).

The fact that you are a cargo plane doesn't mean that you are not an attacker.

Spoiler

 

 

 

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On 9/24/2022 at 11:59 PM, kerbiloid said:

It's offensive, too.
(Not only in terms of social relations).

The fact that you are a cargo plane doesn't mean that you are not an attacker.

  Reveal hidden contents

 

 

 

Months ago the PLA used the Y-20s to do the humanitarian aid in Afghanistan. When I watch something about IL-76, I always thinking would there had something happened like this in Afghanistan airport: an elder ground staff who was already served the planes from the Soviet and the US, and a rookie. One morning, the rookie: wake up, master! Looks like the American is back! The elder: shut up rookie, must be the Russian! I don’t even need to see it, just hear the sound of engines!

Few minutes later, when the plane finally touched down, both of them: ???

Edited by steve9728
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4 hours ago, JoeSchmuckatelli said:

O. M. G.

I had to Google 'CIWS' to discover that I have a hidden bias / blind spot!

The acronym 'CIWS' in my mind was purely used for 'Commander's Independent Weapon System' - (an independent of the main weapon system used targeting pod to enhance offensive capabilities) but I discovered that it's presently used to mean 'Close In Weapon Systems' which are defensive (what I would have called AD 'air defense' - but the CIWS term (and targets /capabilities) has been been extended beyond merely 'A' threats to include boats, drones... Heck anything 'Close In' that a defensive 'Weapon System' might target.

In light of this - my prior response reads as incomprehensible babble! 

Sigh.  I'm out of date.  SMH. 

Just say 'R2D2'. For clarity.

phalanx.jpg&f=1&nofb=1&ipt=e5de3f40a489f

As far as putting some sort of active defense on large bombers: Here's the thing. Those bombers are 50+ year old weapon systems. The last time they were considered front-line aircraft, The Beatles were still together. I can't really speak for it's Russian counterparts, but the B-52 is specifically not used in any sort of contested airspace anymore. It either carries standoff weapons, or it flies in totally uncontested, asymmetrical warfare environments. So, installing an active defense system on it would be a waste of payload weight.

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1 hour ago, TheSaint said:

R2D2

We had those in my time - and we referred to them as R2D2 or AD (air defense) exclusively.  Be interested to see the etymology of CIWS being the used term for those and the other systems - but I literally never heard CIWS from any of my Navy brethren 

Edited by JoeSchmuckatelli
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2 hours ago, TheSaint said:

I can't really speak for it's Russian counterparts, but the B-52 is specifically not used in any sort of contested airspace anymore. It either carries standoff weapons, or it flies in totally uncontested, asymmetrical warfare environments.

Word is, the Tu-22M has been barred from contested environments, and the Tu-95MS can't carry anything besides cruise missiles in the first place. Tu-160... hasn't seen anything on their use since Syria.

That said, the Tu-22M3M is the ideal case study for my question... and it doesn't come out in my favor. Back when designing the Tu-22M Tupolev offered the military either a tail gun or more ECM. Back then they went with what the rivet counters today deride as the "holy twin-mount". However, as of the most recent mod, they're removing it... to put in more ECM.

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1 hour ago, JoeSchmuckatelli said:

We had those in my time - and we referred to them as R2D2 or AD (air defense) exclusively.  Be interested to see the etymology of CIWS being the used term for those and the other systems - but I literally never heard CIWS from any of my Navy brethren 

As far as I know, the system is called "Phalanx".  Supposedly the term means the whole system from the  RADAR to weapons control, but the media typically just refers to the gun itself as "Phalanx".   This sounds like what I was working on in the 1990s, where they were trying to tie all the communications of the ship together, some long alphanumeric string lost to time like AN/Q80, which tied together a bunch of systems including "Phalanx".  All our company did was build trainer RADAR consoles, computer-monitor map tables (no idea if anyone set up the projection system to show any big football games), and submarine monitor relays (a monitor that  let you choose from various video inputs).

The whole notion of "Commander's" probably doesn't make any sense to the Navy.  Presumably everything is fed to the captain anyway.  Having the weapons system controlled by anyone not onboard ship doesn't sound like something they'd be happy about, although I suspect they beam E2C/D/F RADAR information from the "eyes in the sky" to various surface ships.

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9 minutes ago, wumpus said:

As far as I know, the system is called "Phalanx".  Supposedly the term means the whole system from the  RADAR to weapons control, but the media typically just refers to the gun itself as "Phalanx".   This sounds like what I was working on in the 1990s, where they were trying to tie all the communications of the ship together, some long alphanumeric string lost to time like AN/Q80, which tied together a bunch of systems including "Phalanx".  All our company did was build trainer RADAR consoles, computer-monitor map tables (no idea if anyone set up the projection system to show any big football games), and submarine monitor relays (a monitor that  let you choose from various video inputs).

The whole notion of "Commander's" probably doesn't make any sense to the Navy.  Presumably everything is fed to the captain anyway.  Having the weapons system controlled by anyone not onboard ship doesn't sound like something they'd be happy about, although I suspect they beam E2C/D/F RADAR information from the "eyes in the sky" to various surface ships.

Honestly, from my observations, the CIWS refers to a concept, and then that concept gets rather nebulous. For example, Phalanx's contemporary counterpart the AK-630 has a separate fire director/radar unit (that's shared with other AA gun systems, if present) and so doesn't seem that drastically different from a WWII AA gun with centralized fire control. Basically, at this point in common parlance a CIWS is any shipborn, anti-air, light and rapid-fire autocannon (up to circa 40 mm), which just happens to be only really practical against enemy missiles.

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5 hours ago, Rutabaga22 said:

Why don't private companies have their rockets sponsored? That would be a good source of funding.

Rocket launches are one of the few places where advertising budgets pale.

If you’re charging $70-200 MILLION for a single launch, the amount of money an advertiser can pony up is negligible. 

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14 hours ago, DDE said:

I think here the balance has shifted somewhat, to the point where @SunlitZelkova's examples from B-52s may be invalidated. SAM operators and fighter pilots are both likely to attempt a shootdown from the longest possible range. This is going to cause the missile to come in from the side aspect rather than from below; in cases of extremely long-range missiles they have an actual ballistic arc and would come in from above. Furthermore, it seems a lot of the antimissile manuvers - certainly for the air raft big enough to mount a turret - amount to turning away from the missile and trying escape the engagement basket. Because of that, it would seem that a lot of missiles would end up coming in from the rear aspect - again, for an aircraft large enough to consider a turret, and thus not prone to flying within range of MANPADs and other "minor" AA.

It sounds like this could be countered in certain situations. If a PL-15/R-37/AIM-260 is being fired at max range against a bomber doing conventional strike stuff in protected airspace, it would work. But in a deep penetration mission likely to be undertaken in a nuclear war, there isn’t much stopping the fighters from getting up close and personal and flying and firing outside of the gun arcs.

5 hours ago, Rutabaga22 said:

Why don't private companies have their rockets sponsored? That would be a good source of funding.

What @sevenperforce said, but also a company can only charge so much for ad space as people will watch. The profitability of the Olympics is primarily driven by ad revenue because millions watch it, but if only a few thousand people watch a launch being live streamed and maybe a couple important executive people, the ad space isn’t worth anything.

They may barely break even as a result of the extra work involved in painting the rocket, combined with the low viewership.

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9 hours ago, Rutabaga22 said:

Why don't private companies have their rockets sponsored? That would be a good source of funding.

Well:

But honestly this kind of thing actually does happen. And it probably depends on how strict your definition of a private space company is:

The orange word "DouYu"(斗鱼) is a live streaming platform like Twitch. And you think there are not enough sponsors for rockets? Try this one:

The blue words “长安欧尚” is a car brand. They sell cars and SUVs for under 200,000 RMB (personally I don't like this brand). The small logos on top are the banks and venture capital companies.

In fact, even if you are not a private company, it isn't impossible to do such things:

640.png

The little blue words “安溪铁观音” is a tea brand. I tried it these days when I finally got back home from the UK and it's not bad at all!

Edited by steve9728
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First, a message to @intelliCom continued from the DART thread where we were told to stay on topic.

You can learn about the presence of alien life on exoplanets on the KSP forum. The entire forum is dedicated to alien spaceflight!

https://forum.kerbalspaceprogram.com/index.php?/forum/3-kerbal-space-program/

Second, a question not really related to DART so I put it here.

I have seen a lot of comments in jest making fun of the terrestrial dinosaurs for not having a space program. But how logical are these statements?

Based on human technological standards circa the 2020s, would the dinosaurs even have been able to detect the asteroid that hit Earth? Even if they had the means to stop it?

Not much* is known about the origin of the asteroid that caused the K-Pg extinction event, for all we know it came from the Kuiper Belt and could not have been stopped.

*I feel like I may have seen an article about this a year ago or so but I didn’t see anything in my saved links. I still could be wrong though

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