For Questions That Don't Merit Their Own Thread

[tater]

Saw this image and needed to post it:

 

[StrandedonEarth]

42 minutes ago, tater said:

Saw this image and needed to post it:

It is a pretty sweet pic.

It's also quite the wedge of a vertical stabilizer. 

[darthgently]

15 minutes ago, StrandedonEarth said:

It is a pretty sweet pic.

It's also quite the wedge of a vertical stabilizer. 

I think it is merging into conning tower territory

[tater]

It's the X-15 at the Air and Space Museum in DC, but taken from an angle regular people don't get to see (higher than the second floor balcony).

[JoeSchmuckatelli]

Rivets? 

[TheSaint]

On 3/25/2023 at 9:23 AM, tater said:

It's the X-15 at the Air and Space Museum in DC, but taken from an angle regular people don't get to see (higher than the second floor balcony).

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

2 minutes ago, JoeSchmuckatelli said:

Rivets? 

Most aircraft are held together with rivets. it's just not as noticeable on other aircraft because they're painted. The skin on the X-15 is mostly bare Inconel.

[tater]

^^^ 2 epic aircraft in that image.

[TheSaint]

That whole gallery is cray-cray.

(Please excuse the potato phone camera.)

If you have the opportunity to visit the USAF Museum, take it.

 

[razark]

1 hour ago, TheSaint said:

If you have the opportunity to visit the USAF Museum, take it.

And if you do, make sure you have plenty of time.  The place is huge.

[TheSaint]

39 minutes ago, razark said:

And if you do, make sure you have plenty of time.  The place is huge.

This. We did it in one day, open to close, and I felt like I was jogging the whole time.

[razark]

10 minutes ago, TheSaint said:

This. We did it in one day, open to close, and I felt like I was jogging the whole time.

I went in 2017, and I think we spent a day and a half.  Could have spent more, too.

[sevenperforce]

17 hours ago, razark said:

18 hours ago, TheSaint said:

If you have the opportunity to visit the USAF Museum, take it.

And if you do, make sure you have plenty of time.  The place is huge.

And if you come to Air and Space, let me know since I live in DC; we'll get a beer beverage.

[JoeSchmuckatelli]

22 hours ago, sevenperforce said:

And if you come to Air and Space, let me know since I live in DC; we'll get a beer beverage.

Is it reopened?  I took my son to DC last May and it was under renovation 

[burn n crash]

Does anyone know where ESA usually livestreams their launches? Do they have a youtube channel?

[Chemp]

1 hour ago, burn n crash said:

Does anyone know where ESA usually livestreams their launches? Do they have a youtube channel?

https://youtube.com/@arianespace

[sevenperforce]

On 3/29/2023 at 8:20 AM, JoeSchmuckatelli said:

Is it reopened?  I took my son to DC last May and it was under renovation 

The one in DC proper is open but under renovation so not all of the exhibits are available. But there's also one at the Udvar-Hazy Center in northern Virginia; it's much much bigger. That's where all the planes are (SR-71, Discovery, the Enola Gay, a Concorde, and an F-14).

Not to say that there AREN'T planes at the DC location, but it pales in comparison.

[king of nowhere]

space probes use hydrazine fuel because it can be stored. cryogenics will eventually boil off, so they have to use hydrazine even though it's got half the Isp compared to LH2/LOx.
couldn't they use some kind of refrigeration system instead to keep the cryogenics cold? the hydrogen tanks on the apollo missions would have taken years to boil off, so if those tanks are well insulated, it should really take very little energy to keep the fuel at their ideal temperature. yes, you'd need to add some kind of cooling system, and you'd need to add insulation to the tanks, but you get to double your specific impulse; you should still get more deltaV for the same mass

[magnemoe]

1 hour ago, king of nowhere said:

space probes use hydrazine fuel because it can be stored. cryogenics will eventually boil off, so they have to use hydrazine even though it's got half the Isp compared to LH2/LOx.
couldn't they use some kind of refrigeration system instead to keep the cryogenics cold? the hydrogen tanks on the apollo missions would have taken years to boil off, so if those tanks are well insulated, it should really take very little energy to keep the fuel at their ideal temperature. yes, you'd need to add some kind of cooling system, and you'd need to add insulation to the tanks, but you get to double your specific impulse; you should still get more deltaV for the same mass

Apollo was an week long mission space probes tend to be multi year ones. Size also matter its easier to insulate something large like the service module rather than an small probe. 
Starship who is even larger will use cryogenic for moon landings. 
You are add that the insulation is dead mass while extra fuel get used up leaving you with an lighter probe. 

[king of nowhere]

1 minute ago, magnemoe said:

You are add that the insulation is dead mass while extra fuel get used up leaving you with an lighter probe. 

I made some calculations there. on a probe with 50% of its mass as fuel (a common case, by what I see for some notable missions), replacing hydrazine (Isp 230 s) with LH2/LOx (Isp 440 s) while keeping the same wet mass would increase deltaV as long as the extra mass for refrigeration and insulation is below 35% of the dry mass (or 17% of the mass of the whole probe).

So, for a probe with 1 ton to orbit and 500 kg of propellant, using cryogenics would be convenient as long as the extra mass for insulation and refrigeration would be no greater than 170 kg. I doubt a small refrigerator and a stirrofoam suitcase could be that massive. so I'd think the issue not the extra mass, but something else.

possible advantage of hydrazine would be reduced complexity and single point of failures, reliability of cryogenics engines over long missions, and total probe volume. none of them look insurmontable as far as I know, but I'm not enough of an expert to judge.

[kerbiloid]

The hypergolic engines don't need ignition system and can be restarted thousands times.

[Terwin]

1 hour ago, king of nowhere said:

I made some calculations there. on a probe with 50% of its mass as fuel (a common case, by what I see for some notable missions), replacing hydrazine (Isp 230 s) with LH2/LOx (Isp 440 s) while keeping the same wet mass would increase deltaV as long as the extra mass for refrigeration and insulation is below 35% of the dry mass (or 17% of the mass of the whole probe).

So, for a probe with 1 ton to orbit and 500 kg of propellant, using cryogenics would be convenient as long as the extra mass for insulation and refrigeration would be no greater than 170 kg. I doubt a small refrigerator and a stirrofoam suitcase could be that massive. so I'd think the issue not the extra mass, but something else.

possible advantage of hydrazine would be reduced complexity and single point of failures, reliability of cryogenics engines over long missions, and total probe volume. none of them look insurmontable as far as I know, but I'm not enough of an expert to judge.

To keep things cryogenic you would need larger radiators and a lot more power.  Radiators are more efficient the hotter they are, and it takes more power to move heat from lower temps to higher temps.

It is not just Styrofoam and a mini-fridge.  

It also means that any temporary power loss could let your fuel boil off.

Also, long-term storage of hydrogen is not really a thing as far as I know, between embrittlement and and just seeping through solid materials, hydrogen just does not like to stay in place.

It might be easier to take up water and just use electrolysis(adding a delay before any burns as the fuel is produced). 

Hypergolics are also much easier to ignite as they are hypergolic, greatly simplifying the engine, and reducing points of failure.

[DDE]

A quickie. "Burlak" was an abortive early 2000s Russian project for a new common T-72/T-80/T-90 turret. As you can see, it looked rather distinctive.

Spoiler

(This sort of casual leaks started in 2011 when a "T-90 Ya-2" was hauled off to Kubinka for storage)

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

[SunlitZelkova]

8 hours ago, DDE said:

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

Probably for similar reasons to the Leo 2A5. From Reddit-

“2.    ⁠While not necessarily optimised against shaped charges, the detonation of a shaped charge upon the add-on wedge likely causes non-optimal stand-off distance for maximum penetration. Furthermore, once the shaped charge jet contacts the wedge, it is likely to spend some of its energy overcoming the sloped metal, resulting in possible earlier particulation and thus ineffectiveness once it enters the hollow portion.”

Assuming, of course, normal ERA is at times ineffective against HEAT thus requiring the slope. It could also be intended to help counter tandem charge ATGMs, although a lot of those modern ones are top down attack, so maybe RPGs?

Does the normal ERA cause damage to the turret when it detonates? If so, this design could be intended to prevent damage from the ERA itself rather than a particular projectile.

Or perhaps the tank designers were unfamiliar with giving it a flat turret face akin to the Leo 2A4, but didn’t have ERA blocks that fit the new turret height and so had to angle it. They chose to angle it facing down instead of up to make space for the driver’s hatch to open.

I just realized it reminds me of an inverted T-80U of sorts.

[DDE]

5 hours ago, SunlitZelkova said:

Or perhaps the tank designers were unfamiliar with giving it a flat turret face akin to the Leo 2A4

T-90's turret is slab-sided with an ERA wedge. While Burlak was criticized for being a bone thrown to the increasingly hapless plant at Omsk instead to the one actual factory at Nizhniy Tagil, I don't think they'd go completely off-kilter and ignore the design of the tank they're trying to improve.

[JoeSchmuckatelli]

15 hours ago, DDE said:

inverted

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.