For Questions That Don't Merit Their Own Thread

[fredinno]

20 minutes ago, Veeltch said:

$600 per 1kg that's why. You could basically send a whole base or a lot of different satellites destined to a few planets at once. Also massive solar sails, lasers that could be put in low sun orbit and used to propel interstellar probes and missions, solar-powered plants beaming power back to earth, new research stations and many more.

Yeah, only problem is why would you want to launch those all at once? Satellites, especially in LEO, use a crazy number of different inclinations, and thus, you'd need to do numerous fuel-heavy inclination changes, negating any cost benefit. If you limit yourself to GEO, you'll have only a few launches a year due to the payload capacity, thus raising the cost.

 

Also, the massive engines are likely to be very expensive to develop.

[KerbonautInTraining]

15 minutes ago, Veeltch said:

You could ask the same question about any other rocket ever launched. What if Soyuz goes kablooey? What if Falcon goes kablooey? We could sit and think about all those rockets that could go kablooey and never really go anywhere.

My (admittedly weak) point was that you'd lose at least an order of magnitude more payload than you would with any modern rocket. 

[Wjolcz]

1 minute ago, fredinno said:

Yeah, only problem is why would you want to launch those all at once? Satellites, especially in LEO, use a crazy number of different inclinations, and thus, you'd need to do numerous fuel-heavy inclination changes, negating any cost benefit. If you limit yourself to GEO, you'll have only a few launches a year due to the payload capacity, thus raising the cost.

I was thinking about lots of satellites to different interplanetary destinations at once, but completely forgot about the fact that launch windows exist.

How about gas giant moons exploration packs? Wouldn't it be easier and cheaper to send a lot of satellites + surface landers and/or rovers in order to explore all (or rather majority) of the most interesting moons in the system?

[fredinno]

7 minutes ago, Veeltch said:

I was thinking about lots of satellites to different interplanetary destinations at once, but completely forgot about the fact that launch windows exist.

How about gas giant moons exploration packs? Wouldn't it be easier and cheaper to send a lot of satellites + surface landers and/or rovers in order to explore all (or rather majority) of the most interesting moons in the system?

You would never get that much money all at once...

[KerbonautInTraining]

Why don't modern mobile browsers (Mozilla, Chrome, etc) include some sort of flash player?

I've seen it done with some third party apps but they're all pretty terrible to use... not because they support flash, but because the author didn't put any effort into the browser itself.

[shynung]

How do we estimate a random animal's limb mass (limb defined as any body part that attaches to the abdomen at only one attachment point, and be movable by the animal) with a given physical structure and average density?

[Nibb31]

23 hours ago, KerbonautInTraining said:

Why don't modern mobile browsers (Mozilla, Chrome, etc) include some sort of flash player?

Because Flash is obsolete, buggy, and proprietary. Nowadays we have HTML5. Even Adobe has stopped supporting it. The question should be, why do some web designers still insist on using that old piece of crap.

[K^2]

8 hours ago, shynung said:

How do we estimate a random animal's limb mass (limb defined as any body part that attaches to the abdomen at only one attachment point, and be movable by the animal) with a given physical structure and average density?

For one-off measurement, assuming butchering isn't an option, your simplest method is going to be submerging limbs one at a time and measuring displacement and weight reduction. If you have access to an MRI machine, you can get very good estimates on local tissue density and simply integrate over the limbs numerically.

If you need to do this a lot for a given species, you are far better off constructing a model based on simple measurements you can quickly take. Of course, these will require a whole bunch of empirical measurements in advance. The advantage here is that you might be able to get your empirical data from carcasses, where difficulty of measuring a weight of a limb is determined by how good you are with a bone saw. Otherwise, you're back to the first two methods for constructing your empirical data.

[Wjolcz]

How do you determine the wing placement on a real life airplane? In KSP we have CoM and CoL indicators, but all that's possible to measure IRL is the CoM and the amount of lift the wings can create at different speeds.

[K^2]

Back in the day, trial and error. Mostly, with scale models in a wind tunnel. I mean, you have an estimate from empirical data and thin airfoil theory, but you always had to refine it with actual trials.

These days, computers are used to simulate CoL dynamics on a virtual model long before it goes into a wind tunnel.

[StrandedonEarth]

While model rockets are different than aircraft, there is a quick'n'dirty way to estimate Center of Pressure on rockets, for determining stability. Simply make a cardboard silhouette of the rocket and find the balance point, and that would be the center of pressure. It may be possible to use this method to estimate the center of lift, probably by replacing the cylindrical fuselage with the thinnest stick possible. This assumes consistent lift/area for the wings and tailplanes. This would at least give a starting point that can be refined in a wind tunnel. This method in side profile should also work fine for determining the size of vertical stabilizer needed.

But I really doubt that it was ever actually done that way.

[Guest]

Here's a question:

What movement type is more efficient, walking or serpentine movement?

As in, energy efficiency.

[max_creative]

Did anyone know that the first thing to be added to the iss in 5 years launches on Friday? Guys! Look here!

[fredinno]

2 hours ago, max_creative said:

Did anyone know that the first thing to be added to the iss in 5 years launches on Friday? Guys! Look here!

Yes, I knew. I've been following NASASpaceflight. Actually, this should be an entirely new thread; it's not a question.

[RainDreamer]

What is the absolute minimum size for a nuclear bomb? There are suitcases nukes, after all, so how small can they get? Ignoring whether it make sense or not to have a nuclear device of that size instead of conventional explosives, I just want to know how small a nuclear bomb can be, including all necessary component to trigger a nuclear explosion.

[peadar1987]

9 minutes ago, RainDreamer said:

What is the absolute minimum size for a nuclear bomb? There are suitcases nukes, after all, so how small can they get? Ignoring whether it make sense or not to have a nuclear device of that size instead of conventional explosives, I just want to know how small a nuclear bomb can be, including all necessary component to trigger a nuclear explosion.

The smallest nuclear warhead we know about is the W54, used in the "Davy Crockett" battlefield mortar. It had a mass of 23kg and a yield of about 10-20 tonnes. I assume it used plutonium for the core, as this would give a smaller critical mass than Uranium.

You are limited in the size of your nuclear warhead by the critical mass of your nuclear material. Too small a mass, and too many neutrons will escape from the surface to maintain a chain reaction.

Plutonium has a critical mass of about 10kg. In theory you could reduce the size of the warhead by using different materials. Californium-252 has a critical mass of just 2.5kg, and this is the lowest listed in the wikipedia article.

However, Californium-252 has a half-life of 2.6 years, and is a strong alpha and fast neutron emitter. It also produces 39W of thermal energy per g (source), or almost 1kW for a 2.5kg critical mass. You probably could make a small tactical nuclear warhead using it, but you'd need to use it extremely soon after production, keep it actively cooled right up until it was pretty much ready to be deployed, and it would cost you approximately $67 billion at today's production prices!

[shynung]

17 hours ago, Aperture Science said:

Here's a question:

What movement type is more efficient, walking or serpentine movement?

As in, energy efficiency.

I think walking is more efficient. Less muscles to move, and less contact points on the ground (less friction).

Not an expert, though, so don't take it as face value. I might be wrong.

Edited April 6, 2016 by shynung

[Nibb31]

I'd also say walking is more efficient. Walking is a kind of "controlled fall". Much of the work is helped by gravity and inertia.

[Wjolcz]

I saw the ISS flying about 3 hours ago (21:06 CET to be exact) and I think I saw two dots of light instead of one. Is something going on there? Is Cygnus undocking or something, or was it just my eyes playing tricks on me?

[adsii1970]

On 4/3/2016 at 7:53 PM, Veeltch said:

How do you determine the wing placement on a real life airplane? In KSP we have CoM and CoL indicators, but all that's possible to measure IRL is the CoM and the amount of lift the wings can create at different speeds.

Back in the mid 1980s, in a high school physics class, we asked our teacher this same question. He worked for North American Aviation until the mid 1970s, retired, and started teaching high school history in the late 1970s. Anyway, we always bombarded him with such questions...

First, there are some stages that get completed before the demonstrator aircraft is built. After the drafting stage, a scale model is built, which includes scale weighted model. It is at this stage where it is tested in the wind tunnel - and if the aircraft is off, the design can be redone with minimal cost and effort (compared to actually building the demonstrator and discovering the COL/CM is off... Once the desired performance is met in wind tunnel model trials, the first demonstrator - usually unpowered - is built and glide-flighted to check aerodynamics. IF you are old enough to remember the glide tests of the STS Enterprise, this is precisely what NASA was doing in the 1970s. IF this series of tests went well, the powered demonstrator was built, and in the case of the shuttle program, the STS Columbia was built.

Modern aircraft design now relies of sophisticated computer design software (CAD) long before the first scale model for wind tunnel testing is even completed (if at all). This allows the designer to have immediate feedback on aerodynamics, power requirements, and weight distribution using a sophisticated algorithm to compute the impact of the design (think KSP on steroids and less user friendly graphics). Boeing still, as of the mid 1990s, still used wind tunnel models before pre-production demonstrator models were even built...

Edited April 7, 2016 by adsii1970

[Hcube]

On 2/4/2016 at 4:23 PM, shynung said:

How do we estimate a random animal's limb mass (limb defined as any body part that attaches to the abdomen at only one attachment point, and be movable by the animal) with a given physical structure and average density?

Just put it in water to measure its volume, and then, if there is enough muscle on it, it's usually safe to assume that the density is 1.

[RainDreamer]

Is there any difference between micro-gravity (constant free fall inside a gravity well by going to orbit) and actual zero gravity (imagine a magical zone where the force of gravity simply go poof inside)?

[KerbonautInTraining]

13 minutes ago, RainDreamer said:

Is there any difference between micro-gravity and actual zero gravity?

If you were a single point in space, they would be identical in every way.

Since you aren't a single point, while in a low orbit you will notice the effects of gravity gradients. If you held a ball and let it go a few feet north of you it would drift back towards you, go south of you, and start over every 90 minutes. 

I've done it in orbiter, it looks really cool.

[shynung]

19 minutes ago, RainDreamer said:

Is there any difference between micro-gravity (constant free fall inside a gravity well by going to orbit) and actual zero gravity (imagine a magical zone where the force of gravity simply go poof inside)?

Expanding @KerbonautInTraining's response.

In an area where the force of gravity is magically eliminated, for any two non-thrusting objects, there won't be any relative movement between them. If an astronaut in a space station released a ball while floating in the station, he would observe the ball either perfectly still, or moving at a very constant velocity.

In micro-G environments, such as when in low orbit, each individual objects of the previous scenario are instead at slightly different orbits around the celestial body. Due to this difference in orbit, from one object's perspective, the other would move relative to the observing object, producing the effects described in the post above.

[fredinno]

How does the gravity of the Earth change as you go down into the planet? I heard that you'd be weightless in the core, but how about everywhere else? The mantle? The outer core?