For Questions That Don't Merit Their Own Thread

[kerbiloid]

19 hours ago, DDE said:

The question: why the inverted faux-glacis of ERA blocks?

Probably because they are overturned.

[monophonic]

  

On 4/16/2023 at 4:28 AM, JoeSchmuckatelli said:

Certainly an odd design choice ‐ I'd think you would want anything that might ricochet to be directed up and away from the hull!

Cool looking turret,tho.

Not really an issue with reactive armor as anything with low enough energy to ricochet off the cover plate won't have anywhere near the energy to penetrate even the thinner hull roof armor. The logic behind this arrangement could be to get the back ERA plate to move in the same direction as the penetrator. The resulting lower relative velocity would give the plate more time to feed more material into the penetrator's path and/or increase the plates ability to wear down the penetrator (thanks to it being in effect a lower velocity impact than on the opposing velocities situation).

Notice the newer arrangements seen are in effect a combination of this and the original, with two plates affixed on the turret (low and high) from one end and each other on the other forming a protruding wedge shape not dissimilar in appearance to the Leopard 2A5+ NERA elements. This in my opinion indicates it doesn't actually matter which way the plate is angled, but a steeper angle is apparently desirable.

[SunlitZelkova]

If object 2021 QM1 actually was on a path to hit Earth in 2052, would we have been able to change it's course in time to prevent an impact? Or would it have been too close?

It's not a planet killer and even "only" half the size of the Tunguska object, but 6 megatons worth of explosive power is still dangerous. I'm curious about whether this object would make a good candidate to include in a story where an asteroid redirection mission needs to be launched in the 2030s.

[mikegarrison]

On 3/27/2023 at 8:55 AM, TheSaint said:

At the USAF museum in Dayton you can just walk right up to the damn thing.

Best aviation museum in the world.

[mikegarrison]

The US National Air And Space Museum is a pretty good example of the two kinds of aviation museums. One kind has lots of displays, interactive exhibits, movies, etc. etc. This is the one on the Mall. The other kind just has lots and lots of airplanes. This is the Udvar-Hazy. I much prefer the second kind.

The National Museum Of The USAF is one of those second kind of museums.

[sevenperforce]

On 4/17/2023 at 6:51 PM, SunlitZelkova said:

If object 2021 QM1 actually was on a path to hit Earth in 2052, would we have been able to change it's course in time to prevent an impact? Or would it have been too close?

It's not a planet killer and even "only" half the size of the Tunguska object, but 6 megatons worth of explosive power is still dangerous. I'm curious about whether this object would make a good candidate to include in a story where an asteroid redirection mission needs to be launched in the 2030s.

It's definitely big enough to be a city-killer, so it would absolutely be a worthy candidate for deflection if it was anywhere near dangerous to Earth. 

It takes 691 days to orbit the sun and goes from a perihelion of 0.5 AU (nearly as close to the sun as Mercury) all the way up to an aphelion of approximately 2.6 AU (well beyond Mars and inching into the asteroid belt). Its inclination, ascending node longitude, and argument of periapsis nearly matches that of Earth, although with enough variation that close passes are rare.

From a ▲v perspective, it's not significantly more difficult to reach than, say, Ceres. Dawn took 7 years to reach Ceres, but that was with a flyby of Mars and a fourteen-month orbital vacation around Vesta, and it used ions which obviously are slow. We could reach 2021 QM1 quickly enough in a pinch. Because Earth's orbit has so little eccentricity, it doesn't matter where in our orbit we launch from. Leaving Earth orbit and going from 1 AU to 2.6 AU will cost around 4 km/s of ▲v BLEO and require a coast period of around 14 months, but that's if we want to do a minimum-energy Hohmann transfer and actually match velocity to 2021 QM1 to use some sort of gravity tractor. On the other hand, if we are hitting it with a simple impactor or a nuke, we can do a much faster transfer. It may or may not cost more ▲v for the fast transfer since 2021QM1's orbit is so eccentric. 

[sevenperforce]

Assuming 3-4 years to set up and launch the mission and a pure impactor mechanism, we could reach 2021QM1 in under 5 years. The asteroid is smaller than Dimorphos, the target of the Dart mission, and so we could expect a fairly significant amount of deflection from a simple impactor. Another impactor like DART would change 2021QM1's orbital velocity enough that its path would diverge by half the diameter of Earth over a 10-year period. So we would have plenty of time.

I suspect that in a real-world situation, we would use dramatic overkill and launch multiple megatonne-class nukes to make absolutely sure that it was deflected well out of Earth's path.

Makes me think of a fictional setting where someone alters the detonation times of the nukes such that it is nudged into a collision course with a specific point on Earth....

[magnemoe]

1 hour ago, sevenperforce said:

Assuming 3-4 years to set up and launch the mission and a pure impactor mechanism, we could reach 2021QM1 in under 5 years. The asteroid is smaller than Dimorphos, the target of the Dart mission, and so we could expect a fairly significant amount of deflection from a simple impactor. Another impactor like DART would change 2021QM1's orbital velocity enough that its path would diverge by half the diameter of Earth over a 10-year period. So we would have plenty of time.

I suspect that in a real-world situation, we would use dramatic overkill and launch multiple megatonne-class nukes to make absolutely sure that it was deflected well out of Earth's path.

Makes me think of a fictional setting where someone alters the detonation times of the nukes such that it is nudged into a collision course with a specific point on Earth....

Assuming Starship as an lunar landing and orbital refueling works out you have an 50 ton or more impactor moving well above solar escape velocity. 
Against something much larger we would use nukes, yes they might still be used as an way to cheat the ban on nuclear test ban   its for all humanity after all so who can complain. 

[TheSaint]

5 hours ago, mikegarrison said:

The US National Air And Space Museum is a pretty good example of the two kinds of aviation museums. One kind has lots of displays, interactive exhibits, movies, etc. etc. This is the one on the Mall. The other kind just has lots and lots of airplanes. This is the Udvar-Hazy. I much prefer the second kind.

The National Museum Of The USAF is one of those second kind of museums.

Have you ever been to Pima?

[DDE]

A bit of an orphaned piece of junk here. According to Ukrainian authorities, NASA's RHESSI has reentered over Kiev tonight, right as Russian drone attacks pick up after a lull.

https://www.thesun.co.uk/news/22096665/meteor-explodes-kyiv-air-raid-nasa-satellite-crash-fears/

Apparently this is physically impossible due to orbit's inclination (off by 12⁰), but this is an explanation multiple official sources are by now citing. And it looks like a legit reentry. Basically I see no reason why they would forego Occam's Razor and just say it was a Kinzhal - they had no trouble claiming half a dozen Kinzhals used on March 9 - but the variable flashes don't seem to be an indicator of a robust, man-made reentry vehicle.

At the very least, we're looking at an amusing case of information contagion.

[mikegarrison]

3 hours ago, TheSaint said:

Have you ever been to Pima?

No.

[sevenperforce]

6 hours ago, magnemoe said:

Assuming Starship as an lunar landing and orbital refueling works out you have an 50 ton or more impactor moving well above solar escape velocity. 
Against something much larger we would use nukes, yes they might still be used as an way to cheat the ban on nuclear test ban   its for all humanity after all so who can complain. 

Well, there’s some question as to whether more mass or more speed does a better job. DART seems to suggest that energy is the primary driver, given the tremendous multiplier over the pure momentum exchange.

The nuclear test ban treaty only forbids nuclear TESTING in space; it doesn’t prohibit the USE of nukes. If we were deflecting an asteroid, the use of nukes wouldn’t even be a technical violation of the treaty. 

[kerbiloid]

6 hours ago, DDE said:

Apparently this is physically impossible due to orbit's inclination (off by 12⁰)

Also because NASA said that it's still in orbit.

https://www.rbc.ru/politics/20/04/2023/644077739a79476a7d3e76b2?from=from_main_6

6 hours ago, DDE said:

and just say it was a Kinzhal

An anti-aircraft S-300, like always when it fails and falls down.

Of course, "used by R as tactical missile", not "dropped by handy U rocketeers".

[TheSaint]

5 hours ago, mikegarrison said:

No.

If you like NMUSAF, and you have the opportunity, I would recommend you visit Pima. It's not as focused or organized, but it is just as fascinating if you like looking at aircraft.

[monophonic]

8 hours ago, sevenperforce said:

The nuclear test ban treaty only forbids nuclear TESTING in space; it doesn’t prohibit the USE of nukes. If we were deflecting an asteroid, the use of nukes wouldn’t even be a technical violation of the treaty. 

I could be argued that using a device of a novel design with the explicit secondary purpose of obtaining data on the designs performance would constitute a technical violation of the treaty. Personally, I would consider the risk of primary mission failure due to nonperforming device a much, much more grievous offence. An asteroid redirect mission is important enough that one should always choose a design that can be trusted to give full yield.

[SunlitZelkova]

On 4/19/2023 at 4:06 PM, sevenperforce said:

Well, there’s some question as to whether more mass or more speed does a better job. DART seems to suggest that energy is the primary driver, given the tremendous multiplier over the pure momentum exchange.

The nuclear test ban treaty only forbids nuclear TESTING in space; it doesn’t prohibit the USE of nukes. If we were deflecting an asteroid, the use of nukes wouldn’t even be a technical violation of the treaty. 

The Outer Space Treaty prohibits placing of nuclear weapons in space though.

I'm not a law expert, but I would guess that in an emergency, so long as there was international agreement we could find a cheap work around of the treaty. Like saying "the nuclear weapon is not in space, it is in a spaceship" and therefore doesn't violate the treaty.

[monophonic]

41 minutes ago, SunlitZelkova said:

The Outer Space Treaty prohibits placing of nuclear weapons in space though.

I'm not a law expert, but I would guess that in an emergency, so long as there was international agreement we could find a cheap work around of the treaty. Like saying "the nuclear weapon is not in space, it is in a spaceship" and therefore doesn't violate the treaty.

Probably more in the lines of "it's an industrial explosive for a civil engineering project, not a weapon." Also I believe the treaty does not prohibit use of nukes as weapons in space, just pre-placing them in orbit for use at an indeterminate later time. Haven't done myself the reading on that one to be sure though.

[DDE]

25 minutes ago, monophonic said:

Probably more in the lines of "it's an industrial explosive for a civil engineering project, not a weapon." Also I believe the treaty does not prohibit use of nukes as weapons in space, just pre-placing them in orbit for use at an indeterminate later time. Haven't done myself the reading on that one to be sure though.

This was definitely the rationale cited within the US when the decision was made not to raise a ruckus over the Soviet FOBS.

[kerbiloid]

FOBS was military, but it wasn't orbiting the Earth at least once, so it wasn't placed.

[mikegarrison]

There can be as many laws against nuclear weapons as  grains of sand on the beach, and it still wouldn't change that if someone used a nuclear weapon to successfully intercede between the Earth and a space rock that was going to hit it, they would not get into any trouble.

[Terwin]

1 hour ago, mikegarrison said:

There can be as many laws against nuclear weapons as  grains of sand on the beach, and it still wouldn't change that if someone used a nuclear weapon to successfully intercede between the Earth and a space rock that was going to hit it, they would not get into any trouble.

I think you overestimate the rationality of the average activist or dictator.

They may not actually be able to do anything(depending on the organization that uses the nuke), but they will still raise a ruckus.

[kerbiloid]

1 hour ago, mikegarrison said:

There can be as many laws against nuclear weapons as  grains of sand on the beach, and it still wouldn't change that if someone used a nuclear weapon to successfully intercede between the Earth and a space rock that was going to hit it, they would not get into any trouble.

Unless some parts of the destroyed rock (or the declined entire one) is considered heading another one's territory.

[SunlitZelkova]

So now that North Korea is reliably building a large number of heavy lift liquid fueled ICBMs, what do you guys think the prospects are for a North Korean man in space? Does Hwasong-17 have the performance to put a man into orbit?

I suppose the hardest part would be returning one from orbit, but that would be a good way to test reentry vehicle technology without doing a scandalous normal trajectory ICBM test.

Images released by KCNA a couple days ago revealed they are working on a new medium lift launch vehicle.

[kerbiloid]

With its up to 2.5 t payload it probably can put in orbit a one-day-long craft like Mercury (< 2 t) if they need. And their tech is definitely not worse than the American one of late 1950s.

Mercury (as well as its foreign counterparts) is a normal recon/spotter craft to recon the aim, spot it, check the hit results, and return.
(What the very first flights of Mercury have demonstrated).

A 1-2 revolution interceptor as well (same flight experiments), but there are much more sats in orbit, so it's unlikely important now.

As NK unlikely has enough developed spysats, it can be a thing for their purposes.

Spoiler

Though, according to their test trajectories, they believe that the Earth is flat, and are trying to launch it up enough high to reach the solid sky dome.

 

As we know, if launch a thing at 11.2 km/s up (without the air drag, of course), it won't return.

So, the sky dome is ~6 400 km high.

This, int its turn, raises a question.
Is the sky dome closer to the ground near the Earth rim, so you can reach it by pogo.

Edited April 22, 2023 by kerbiloid

[K^2]

On 4/22/2023 at 12:09 AM, SunlitZelkova said:

Does Hwasong-17 have the performance to put a man into orbit?

With a reported range of 15,000km and upper estimate on warhead at 3.5T? No. You still need a pretty significant kick from that trajectory to orbit and then de-orbit the payload, and if you squeeze another stage into this ICBM's payload, what's left for orbital mass is tiny. They might be able to put a small satellite into space with it, but not a human. Especially not with any chance of returning back.

Hwasong-17 has very similar performance to early R-7. That one had a touch shorter range with a heavier payload. And indeed, the Sputnik rocket was effectively a modification of R-7, whereas the Vostok rocket that carried the first human flight mission was a significant upgrade. On top of that, R-7 was built from the start to be upgradable to heavier payloads, in part, helped by the four booster design. I don't think Hwasong-17 would be easy to upgrade to a human flight capable rocket without attaching boosters to it. SRBs might be a cheap option to achieve that, though. These weren't as viable of an option in the 60s as they are today. It would still be a huge project, and a very unsafe one under the best circumstance. The safety margin on something like this would be hair thin with basically no spare mass for any safety features.