For Questions That Don't Merit Their Own Thread

[Kibble]

I heard that the Falcon 9's tanks/structure are so lightweight, thin, and fragile that the rocket cannot stand on the pad by itself (it would collapse) without the umbilical tower unless the tanks are pressurized enough to keep them firm and steady.

Is that true ? Where can i find a source ?

If so, How does the rocket hold itself together midflight, when the tanks are mostly empty, and thus mostly non-pressurized ?

The only in-production rocket stage like that (a stainless steel balloon) is Centaur, which is inflated and kept pressurized with nitrogen. Although other rocket stages would collapse without tank pressure during launch from thrust and aerodynamic loads. Falcon 9 is pressurized with heated helium.

Edited May 14, 2015 by Kibble

[Hcube]

The only in-production rocket stage like that (a stainless steel balloon) is Centaur, which is inflated and kept pressurized with nitrogen. Although other rocket stages would collapse without tank pressure during launch from thrust and aerodynamic loads. Falcon 9 is pressurized with heated helium.

So at launch the helium is cold and as the fuel/oxidizer deplete it is heated up to expand and maintain a constant pressure in the stage during launch (and in this case, re-entry and landing) ?

If so, what is the mass percentage of the helium that has to be stored in the rocket ?

Why helium anyway ? Does it have convenient density/temperature/pressure characteristics ?

[Frida Space]

Random question :

I heard that the Falcon 9's tanks/structure are so lightweight, thin, and fragile that the rocket cannot stand on the pad by itself (it would collapse) without the umbilical tower unless the tanks are pressurized enough to keep them firm and steady.

Is that true ? Where can i find a source ?

If so, How does the rocket hold itself together midflight, when the tanks are mostly empty, and thus mostly non-pressurized ?

Thanks !

'cause stuff happens

[Kibble]

So at launch the helium is cold and as the fuel/oxidizer deplete it is heated up to expand and maintain a constant pressure in the stage during launch (and in this case, re-entry and landing) ?

The helium is kept in separate high-pressure bottles, made as cold as possible (although helium doesn't liquefy) to keep it dense. Generally the bottles are positioned in the (very cold) liquid oxygen tank. When the valves open as propellant is depleted, the cold helium runs thru a heat exchanger and expanded into the tanks.

If so, what is the mass percentage of the helium that has to be stored in the rocket ?

Why helium anyway ? Does it have convenient density/temperature/pressure characteristics ?

The mass is fairly negligible, probably only a few kilograms. As a noble gas with a low atomic number, helium is inert and pretty undense.

[theend3r]

although helium doesn't liquefy

It does.

New question: What would happen if you, unbeknownst to any authority, launched a rocket into space. Would it get shot down? Would you be in trouble?

[peadar1987]

It does.

New question: What would happen if you, unbeknownst to any authority, launched a rocket into space. Would it get shot down? Would you be in trouble?

Depends where you launched it from. I can't see Somalia complaining, for instance. Or if you launched it from the high seas.

In any case, it would be almost impossible to shoot it down unless they knew you were launching it and had something on hand ready to go, which begs the question why they let you get to that stage in the first place

[shynung]

Would I be in trouble? Definitely.

Would my rocket be shot down? Depends on the quality of my country's strategic missile and aerial defense system, and what airplanes were airborne in my immediate location.

[K^2]

You are going to light up somebody's early warning systems. Response to that can vary all the way up to a full out nuclear war, but I doubt it'd be anything that severe over a single launch. As far as shooting it down, nobody's going to touch it on the lift to orbit, since there is simply not enough response time, and nothing that could intercept a rocket during launch is on high alert most of the time. US, China, and probably Russia can shoot down a rocket once it's in orbit. But again, it's unlikely they would bother. If they are expecting a nuclear strike, they'll probably be hoping to intercept it on re-entry. If your rocket does re-enter, it's very likely that it will get shot down if it's not identified by then. Nobody's going to take a chance with something like that. (Edit: That's assuming you re-enter over a country with capabilities to do so. If you re-enter over ocean, again, nobody's going to bother intercepting that.)

As for trouble, at a minimum, you'll be in a violation of some air regulations. In US, that means you'll get fined by FAA and might lose some licenses, if you hold any. Rest of the world, I don't really know. Besides that, pretty much anyone who feels like you've ended up costing them money with your launch, say for expenses of shooting it down, can sue you for damages.

Finally, while I don't think there are any laws that would make it a crime, this is the sort of the situation where governments might not care. They can just throw you into a dark hole with no trial or lawyers involved.

All in all, high risk, absolutely no benefit. And it's not like it'd take a lot of effort to notify everyone that needs to be notified. In contrast to effort of actually making a launch, at least.

[Silver_Swift]

Do modern spacecraft contain a significant amount of iron/steel and, if so, would it be possible to make a spacecraft without any?

[K^2]

Absolutely. In the engines and pumps, primarily. And it'd be tricky, but there are materials that can be used for replacement if need arises.

[Hunting.Targ]

New question: What would happen if you, unbeknownst to any authority, launched a rocket into space. Would it get shot down? Would you be in trouble?

You are going to light up somebody's early warning systems. Response to that can vary all the way up to a full out nuclear war, but I doubt it'd be anything that severe over a single launch. As far as shooting it down, nobody's going to touch it on the lift to orbit, since there is simply not enough response time, and nothing that could intercept a rocket during launch is on high alert most of the time. US, China, and probably Russia can shoot down a rocket once it's in orbit. But again, it's unlikely they would bother. If they are expecting a nuclear strike, they'll probably be hoping to intercept it on re-entry. If your rocket does re-enter, it's very likely that it will get shot down if it's not identified by then. Nobody's going to take a chance with something like that. (Edit: That's assuming you re-enter over a country with capabilities to do so. If you re-enter over ocean, again, nobody's going to bother intercepting that.)

...

Finally, while I don't think there are any laws that would make it a crime, this is the sort of the situation where governments might not care. They can just throw you into a dark hole with no trial or lawyers involved.

All in all, high risk, absolutely no benefit. And it's not like it'd take a lot of effort to notify everyone that needs to be notified. In contrast to effort of actually making a launch, at least.

Aside from the 'dark hole' possibility, a ballistic unidentified launch could easily be assumed to be an ICBM, depending on the point of origin. Since it is unlikely to get intercepted on ascent, once the flight path was seen to be an orbital insertion, and not a ballistic free-fall, everyone watching (which would probably NOT include news media) would probably calm down somewhat and start looking for the party responsible. The U.S., Russian Republic, Chinese Republic, and Japan, all especially have an interest in know who put what up into space to do what.

As for trouble, at a minimum, you'll be in a violation of some air regulations. In US, that means you'll get fined by FAA and might lose some licenses, if you hold any. Rest of the world, I don't really know. Besides that, pretty much anyone who feels like you've ended up costing them money with your launch, say for expenses of shooting it down, can sue you for damages.

There's an interesting little factoid on Wikipedia about the Skylab mission; the end of the mission was a planned deorbit that was to send the module on a descent trajectory into the Great Australian Bight, but actually scattered debris up to 100 miles inland of the coast. NASA was, somewhat tounge-in-cheek, fined for littering. This fine was paid 30 years later by a radio show host who raised proceeds from his listeners.

Edited May 16, 2015 by Hunting.Targ
a little reformatting, and forgot an '-ing'.

[RainDreamer]

Do modern spacecraft contain a significant amount of iron/steel and, if so, would it be possible to make a spacecraft without any?

You can check this page out: https://howthingsfly.si.edu/structures-materials/materials

Although they are mostly for aircraft, it does have some relevance to spacecraft. Modern craft would likely have a lot of aluminum alloys, since that is cheap and lighter than steel, which somewhat comparable performance. It is all depending on what you plan to do with the craft and your budget, really. You can totally make a craft without steel anywhere using replacement material if you have the cash for it, like using titanium. The problem is not about whether we can or not making a craft without steel, but whether it is worth it.

[Hcube]

New question :

When a rocket crashes and the payload is destroyed, is the customer get refunds for his satellite ? or does he have to deal with it ?

I guess that it very much depends on the contract, but how does it go in general ?

[Kryten]

Commercial satellite operators typically purchase from a separate insurance company, while government launches are usually self-insured. Some launch companies have options to include a reflight clause in the contract; i.e. 'if the launch fails we'll build another one and put it up'; with a few exceptions, this is mostly restricted to the Chinese commercial launch group, China Great Wall.

[Hunting.Targ]

Commercial satellite operators typically purchase from a separate insurance company, while government launches are usually self-insured. Some launch companies have options to include a reflight clause in the contract; i.e. 'if the launch fails we'll build another one and put it up'; with a few exceptions, this is mostly restricted to the Chinese commercial launch group, China Great Wall.

(emphasis by quoter)

Self-insured => taxpayer-insured.

Also of note; after the Challenger incident, the United States Air Force backed away from using the Shuttle Orbiter as a launch vehicle for its surveillance satellites and other classified operations; they went with the Atlas/Centaur program instead, which was operated completely in-house. I still have a copy of a Shuttle operations manual with a mission profile for self-contained satellite insertion that would, hypothetically, be used to insert a payload into orbit that would then self-transfer into a new orbit meeting the mission profile. (The Shuttle Orbiter was trackable from ground telescopes and radar; a stealth satellite using an ejectable booster motor would be much more difficult to track to a new orbit.)

[Hcube]

(emphasis by quoter)

Self-insured => taxpayer-insured.

Also of note; after the Challenger incident, the United States Air Force backed away from using the Shuttle Orbiter as a launch vehicle for its surveillance satellites and other classified operations; they went with the Atlas/Centaur program instead, which was operated completely in-house. I still have a copy of a Shuttle operations manual with a mission profile for self-contained satellite insertion that would, hypothetically, be used to insert a payload into orbit that would then self-transfer into a new orbit meeting the mission profile. (The Shuttle Orbiter was trackable from ground telescopes and radar; a stealth satellite using an ejectable booster motor would be much more difficult to track to a new orbit.)

Very interesting. Thanks !

[WinkAllKerb'']

MACS1149-JD isn't that far at all.

... question(s) ?

EDIT: btw if not by pass bypass may be "by past" could fit better to this sentence ... just a "quick" though anyway.

Edited May 21, 2015 by WinkAllKerb''
adjustement

[hugix]

While browsing this thread on Moon images I've decided to upload my own... While browsing my pictures I found this one.

It is not the best image, but it has something peculiar that I've seen once before through a telescope. That weird blue hue on top and orange on the bottom. What is it? Sometimes when I look at the moon through a camera or telescope the Moon gives this weird dual colored glow.

[AngelLestat]

Maybe because the bottom of the moon needs to overpass more atmosphere than the top... not sure.

[Kryten]

Chromatic aberration?

[K^2]

Chromatic aberration?

Yeah. Means lenses are just a tiniest bit out of alignment.

[Robotengineer]

Yeah. Means lenses are just a tiniest bit out of alignment.

Or the different wavelengths of light focus at different points.

[hugix]

I suspect it is in the lensing since blue / orange hues are a very common (and pretty) color scheme

http://www.slashfilm.com/orangeblue-contrast-in-movie-posters/

[K^2]

Or the different wavelengths of light focus at different points.

There is an asymmetry, which requires misalignment. With perfectly aligned optics, the only breaks in symmetry are related to optical axis. E.g. lens flares. Image posted has broken symmetry which implies that either lenses aren't perfectly parallel to each other, or not perfectly parallel to the sensor.

This is also very common for amateur astronomy telescopes. If mirrors/lenses aren't absolutely perfectly aligned, you'll have blue/red aberrations on stars/planets that are always angled the same way.

[shynung]

Is it possible to devise a solid-state thermoelectric generator? As in, one that does not require mechanical parts or circulating fluids to generate electricity from temperature gradients?