For Questions That Don't Merit Their Own Thread

[K^2]

9 hours ago, Codraroll said:

But if you didn't want your satellite to actually do anything, how cheap could you build something a launch provider would be willing to launch? If you just want your name written on a cubic strut somewhere in space, for instance. Would it be possible to just weld together something in a garage and take it to the launch provider for payload integration? In short, what's the absolute minimum cost of a satellite? Let's exclude cubesats since they are too small to be fun. We're talking something that would be launched on its own rocket.

There were some cheaper opportunities in the past. Right now, lowest I've seen quoted for 1U cube is ~$100k. However, you do still need to do some testing, including shake tests and outgassing in vacuum chamber, to demonstrate that your payload is safe to be included with all the other payloads. And they probably won't trust tests you do in the garage. So in practice, including paying some lab to do the tests for you, expect double that.

To me that says, "A little expensive," and my cost-perception is badly skewed by living in Silicon Valley. Anywhere else in US that's what, cost of a nice house? So upgrade that to "very expensive" if it's just a vanity project.

It's doable, though. We've knocked about an idea of crowd-funding a cubesat launch on this forum before. It quickly outpaced in cost and complexity what we were at all likely to put together, so that got abandoned. Interestingly, compared to cost of the certification and launch, it's actually not that hard to find quality parts to make it into a real mission. Nothing terribly complex, but an actual experiment that you can download data from is actually within realms of possible. The biggest challenge is the fact that to get rad-hard parts at reasonable cost, your CPU is basically 80s tech. You can, of course, throw a Pi Zero into the sat and have it handle absolutely everything, but the MTF is pretty short, and prior practice of various university projects shows that you might get lucky and have it last a month, or you can get unlucky and have it dead after a day. So anything you want to use to communicate with the sat should be wired through rad-hard CPU, and so the most budget thing was to get something like rad-hard 6502 for a few grand to handle stability and coms, with cameras and sensors handled by Arduino or Pi. You can also get solar panels that are just the right size to fit on a side of a 1U cube! Also in a range of a few hundred to a few thousand USD. Compared to launch costs, all very reasonable prices. Of course to make it all reliable in harsh environment of space would involve a lot of work to design, build and test the thing. If you were to outsource that to experts, it will easily surpass the cost of launch in labor.

That said, again, if it is just a vanity project, and you were just going to through $200k for a launch and lab tests, you might as well just bolt a Raspberry Pi to that thing with a radio and just hope it survives more than a day and you can download some neat pictures from it.

[magnemoe]

2 hours ago, DerekL1963 said:

No.  The payload provider is generally responsible for providing the required adapter and separation hardware (if any).  Even if it's just an adapter to support a inert payload, it's still precision machining.  Even if it's an inert adapter and payload, there's various certifications and proof testing required by the launch provider.  Even a cubesat, with everything but the payload proper provided by the integrator, is going to have certain minimum requirements - and proof (paperwork) that the payload meets those requirements.  Most providers and integrators have a user's guide online, so you can look up the requirements.

Then there's the cost of all the paperwork...  With the launch provider, potentially with the launch site, almost certainly with the responsible government agency.  After the Swarm Technologies fiasco in 2018, I suspect few launch providers will risk a launch without ensuring all the requisite paperwork is complete.

tl;dr  There's a certain minimum cost, and you're not going to pay it with change from your couch cushions.  Without detailed information, it's difficult to give a reasonable floor or range for the minimum cost.

Cube sats are secondary payloads, you want to be very sure that the secondary payload does not add any danger to the primary one who can be very expensive. 
And outguessing is likely to always be an issue unless you buy an electron launch or you get an starship launch of weird stuff. 
One point about starship is that you can get heavy stuff into space cheap. But I don't want to space qualify my new ion engine and deep space buss in an container with your inflatable troll head 

[ARS]

15 hours ago, Codraroll said:

But if you didn't want your satellite to actually do anything...

Well they DO contribute in cluttering the orbit with useless junk, and when it impacts another satellite and causing a Kessler syndrome, the "contribution" could be far greater than what you would think

To quote the Wikipedia: "In the context of spaceflight, a satellite is an object that has been intentionally placed into orbit" ...then technically EVERY JUNK IN ORBIT IS A SATELLITE (and they don't do anything)

[kerbiloid]

Why send scrap when you can send funny baloons.

Spoiler

Spoiler

 

P.S.
Don't tell SpaceX.

[ARS]

Okay, so let's assume these 2 situations:

1. Imagine you are at the maximum range of field artillery (let's pick 150mm caliber as an example). You cannot see the artillery, but you know it's pointed at you. The artillery fires a single shell at your position (and you know about it). Assume the shell landed dead center at your position (Target is stationary)

2. Imagine you are flying at supersonic speed. A missile is fired at you from the front beyond your visual range. The missile is supersonic too. Assume the missile hit your aircraft directly dead-on while in-flight (Target is moving directly for collision)

In these 2 situation, before the explosion happened, does human eyes has enough sensitivity to catch the glimpse of incoming shell and missile, process the image in the brain so you recognize it as such?

[kerbiloid]

Artillery shells are subsonic and visible at long range, it's an empirical fact.

 

Depending on the rocket albedo and sunlight, its brightness (so, the visibility range) may vary.

If its albedo is low, you can see it only shading other objects (clouds).

You unlikely can distinguish it from other details when its angular size is less than 1 angular minute.

The rocket diameter is ~0.1..0.15 m.

So, max visibility range ~= 0.15 / (pi/180/60) ~= 500 m.

The rocket max speed is ~2.5 M ~= 850 m/s,

So, max visibility time ~= 500 / 850 ~= 0.6 s.

Human recognition and reaction time ~0.1..0.2 s.
Max frequency of human finger tapping ~10 tap/s.

So, (0.6-0.2 / 0.1) ~= 4

So, if you exactly know where the rocket is coming from, you can quickly tap a 3-5 beat rhythm by fngers before it hits.
Or press the flare/chaff button, though it anyway won't help.
But don't press F5 !

Edited August 20, 2020 by kerbiloid

[coyotesfrontier]

Small question: What was the TWR of the Saturn V's second stage, the S-II? I can't seem to find this information anywhere for some reason.

[GuessingEveryDay]

Well, you can figure it out by taking the total weight of the Saturn V, minus the first stage, and then divided by the thrust of the 5 J-2 engines. From what I can see.

[ARS]

Is it feasible to put an air filter on jet engine's intake to make it (at least when disregarding performance loss) capable of flight operation in airspace saturated with volcanic-ash. On a side note, why we can't put a wire mesh on jet engine's intake (like on F-117) to prevent it from ingesting debris (or people)?

[kerbiloid]

I guess, the volcanic ash is known to be very thin, so an effectively filtering mesh would stop the air flow at all.

[AngrybobH]

4 hours ago, ARS said:

Is it feasible to put an air filter on jet engine's intake

It is feasible, But look at it this way, how long can the engine operate in those conditions without a filter? what is the likelihood of failure? Now with a filter, how long can it operate before the filter is clogged and gets sucked into the engine and 100% causes a failure? Then you look at the performance hit to see if it is really worth it. I would guess it is not worth it.

 

[DDE]

17 hours ago, ARS said:

Is it feasible to put an air filter on jet engine's intake to make it (at least when disregarding performance loss) capable of flight operation in airspace saturated with volcanic-ash. On a side note, why we can't put a wire mesh on jet engine's intake (like on F-117) to prevent it from ingesting debris (or people)?

You end up needing an almost solid shield, and an additional intake atop the wing.

[K^2]

At some point, it ought to make more sense to just have an auxiliary ox tank.

[JoeSchmuckatelli]

Okay - new question:  

Does the ability to use Ray Tracing in the new / next generation of video cards give First Person Shooters (etc.) the ability to utilize the ray tracing part of the card to more effectively model physics of bullets, ricochets, and so on as they interact with the virtual environment - or are they strictly limited to lighting / shadow effects and reflections?

[DDE]

Let's say I insist on having power armor with current technology.

Can an internal combustion engine provide the right amount and kind of electricity or pressure?

[Spacescifi]

54 minutes ago, DDE said:

Let's say I insist on having power armor with current technology.

Can an internal combustion engine provide the right amount and kind of electricity or pressure?

 

Yes... but consider that a rolling wheel is an easier feat than powered humanoid armor because inertia helps it.

Also consider that no one has done it even though it is possible.

Why? It's slow... slower than wheels, and a few more mobile soldiers with rifles could wreck it.

By the time it was armored enough to deflect bullets, it's still slow, and the IC engine is going to have issues with overheating unless you go big, and tanks tend to win out against mechs for mobility and traction.

 

[DDE]

13 minutes ago, Spacescifi said:

Yes... but consider that a rolling wheel is an easier feat than powered humanoid armor because inertia helps it.

They see me rolling,

they hating!

[Spacescifi]

1 hour ago, DDE said:

They see me rolling,

they hating!

 

Wow.

I guess the US and Russia are officially tied for outlandlish ideas.

US for orion pulse propulsion project. Russia for so many smaller scale projects I would literally have to write a long list 

[razark]

1 hour ago, Spacescifi said:

I guess the US and Russia are officially tied for outlandlish ideas.

I'd suggest you look into Blue Peacock, if you want outlandish.

 

Also known as the Chicken Powered Nuclear Bomb.

[kerbiloid]

6 hours ago, DDE said:

Let's say I insist on having power armor with current technology.

Can an internal combustion engine provide the right amount and kind of electricity or pressure?

You'd be more specific. Is the PwA an exoskeleton to assist the muscles, a deflector shield against bullets, or what.

[DDE]

6 hours ago, Spacescifi said:

Wow.

I guess the US and Russia are officially tied for outlandlish ideas.

US for orion pulse propulsion project. Russia for so many smaller scale projects I would literally have to write a long list 

Some people have a head start

"Stalin's Steel Balls" is the source for the illustration above

Spoiler

 

Also, don't forget this beauty:

And this one:

World of Tanks just have the author of the book above mining the Red Army's 'rejected popular suggestions' archive.

And this one, this time from actual tank designers of the late Cold War:

Spoiler

Which is, I guess, the same as this one:

 

Edited August 28, 2020 by DDE

[DDE]

Oh, crazy suggestions, you say. They can't hurt you, they aren't real, you say.

Spoiler

BMPT prototype be like:

Note the three turrets (there's a fourth in the back) and the additional machine gun on the left.

 

[magnemoe]

3 hours ago, DDE said:

Some people have a head start

"Stalin's Steel Balls" is the source for the illustration above

  Reveal hidden contents

 

Also, don't forget this beauty:

And this one:

World of Tanks just have the author of the book above mining the Red Army's 'rejected popular suggestions' archive.

And this one, this time from actual tank designers of the late Cold War:

  Hide contents

Which is, I guess, the same as this one:

 

Top one looks like an joke Mitch and match job. 

Second one looks a bit like something real back in the early 1930 the idea of tanks with many turrets but then usually machine gun turrets was common 

Last one looks pretty cool and something who might well work. 

2 hours ago, DDE said:

Oh, crazy suggestions, you say. They can't hurt you, they aren't real, you say.

  Reveal hidden contents

BMPT prototype be like:

Note the three turrets (there's a fourth in the back) and the additional machine gun on the left.

 

Now why would you want two independent AAA guns on it? 
Much better to have one turret, with an radar and IR sensors and then mount 2-3 of these guns together. 
And the remote weapon station on top of the track looks weirs and kind of pointless as you have machine cannons. 
Now that thing would be nice other places like on an normal tank or an APC. 

[K^2]

12 hours ago, DDE said:

Let's say I insist on having power armor with current technology.

Can an internal combustion engine provide the right amount and kind of electricity or pressure?

Power is the easy part. The problem is turning it into linear motion. There are three ways people have tried. Mechanical, electrical, and hydraulic. None of them work well for power armor.

Lets get the easy one out of the way. Mechanical transmission of power to limbs is a nightmare. You can do it with clutches and linkages, but you're either burning your clutches or aren't getting fidelity you need. It's extremely inefficient and extremely unreliable. It might work for some very narrow range of motions, like if you need to be running in a straight line at fixed pace, but that's about it. It's not impossible in theory to build a power armor where nearly all of the power is delivered through mechanical systems with almost no losses, but that would be the most complex mechanical system ever built by a very wide margin. I don't see it happening.

Hydraulic transmission has a lot of good qualities if you aren't interested in speed. It's pretty efficient and will deliver the power where you need it. With the right pump design you won't have a lot of power overhead and can still deliver fine precision in motion. Unfortunately, the moment you need to start moving fast it breaks down. To deliver significant forces at anything like acceptable pressure of the working fluid, pistons need to be chunky. That's a lot of extra weight by itself, but then you start factoring in how much fluid you have to move to fill these pistons. And when you have to move it fast, you are suddenly wasting all your power accelerating hydraulic fluid, and any time you need to start or stop rapidly you have to deal with hydraulic hammer which risks rupturing your already overstressed hydraulic lines.

Due to the above limitations, the go-to for military uses has to be electric. And it's an absolutely perfect way to transfer power. In theory. The problem is that there are only two forces that can convert electric power into mechanical. That's electrostatic and magnetic forces. Electrostatic forces would be ideal, but the voltages required increase with the size of moving parts. Unless you have nano-motors pulling countless fibers to actuate your limbs (hm, sounds familiar), in order to generate required forces you need voltages that break down any insulation you might reasonably have on hand. So while this is a great contender for future tech, if we figure out practical nanomachines, with modern tech, it's a non-starter.

Which leaves magnetic forces, and these have a tiny little flaw. Efficiency of electromagnets in converting electric power into mechanical is directly proportional to the movement speed of the magnets and/or coils. This is not a problem for rotational motion - just up the RPMs, but it's a problem for linear motion. Linear magnetic drives would be the best solution, but you just can't get the forces necessary for armor to support its own weight, let alone do anything useful. So people go with servos. Take fast spinning motion, convert it into slow spinning motion with a gearbox, then use linkages to get the linear motion you actually want. Yay! It's efficient, it is precise, it can be fast, and it can apply a lot of force. Problem is with trying to get these last two at the same time. Specific power of servo motors sucks, because not only do you need chunky magnets to get good torque, but also a massive gearbox to convert this into even more torque. And all of this adds to inertia of the system, so you need even more torque to get things going... You'll end up with more weight in motors than armor and will probably still be unsatisfied with performance.

At the end of the day, servos and hydraulics are still the best we've got. And yeah, there are plenty of projects that use a combustion engine with either one of these. Boston Dynamics does a lot of their testing with batteries, but pretty much everything they build with military in mind is designed to work with a motor and generator. We're already doing more with this tech than seemed possible a couple of decades ago, but in terms of using it for power armor, it's still entirely impractical.

[wumpus]

17 hours ago, JoeSchmuckatelli said:

Okay - new question:  

Does the ability to use Ray Tracing in the new / next generation of video cards give First Person Shooters (etc.) the ability to utilize the ray tracing part of the card to more effectively model physics of bullets, ricochets, and so on as they interact with the virtual environment - or are they strictly limited to lighting / shadow effects and reflections?

The Ray Tracing (at least as used in the current line of nvidia Turing processors) is almost certainly limited to lighting/shadow effects and reflections.  It is hardwired in, presumably for maximum efficiency of reflections.  Furthermore, using such a system would affect the "ingame world", meaning that in multiplayer you'd almost certainly have to have it either on for everybody or off for everybody.  With the possible exception of some future "Fallout 5" (and Bethesda corporate seems only interested in multiplayer and it's whales), I don't expect games written about single players, especially bothering to pioneer interactive virtual environments.

On the other hand, next gen consoles will have a sufficiently large "leveling effect" such that next-gen consoles could play together and be assumed to have sufficiently similar ray tracing hardware.  Once AMD (or Sony and/or Microsoft) spills the beans on how their ray tracing works (whether hard wired or using the shading/compute units to calculate the rays) we might get a better guess as whether this is possible or not.

One thing that nvidia relies on to make ray tracing works is large neural nets interpolating the results from the ray casters.  This was also shown separately as DLSS (deep learning super sampling) and really didn't work at all well.  DLSS2 appears to work better, and I'm guessing they are feeding the "AI" at least the mathematical bits of edge detection (similar to nvidia's previous work with FXAA anti-aliasing).  Assuming the player isn't using all the available neural net hardware to upscale the video, it might be useful to let these bits assist the NPC "AI" algorithms (hopefully not just making so-called "allies" even more annoying).