The thread for space cadets!

[Winner]

Well see, that's why I was actually asking... Sinister alien space station (OR INVASION FLEET) monitoring us wouldn't be noticeable over there, and it would have the ability to sustain its position.

I think that with their level of technology, station keeping wouldn't be that much of a problem (and why wait anyway, it's not like we could do anything about them even if they approached in plain sight )

 

[gozpel]

Don't spoil my Star Trek: Next Generation!

I'm going through the whole box again, the whole series.

So! Not another word, please.

I think the next planned mission to Mars is 2030 btw, not sure if I can hang on that long.

But I'll try, for for sake of all of us.

 

[hobbsyoyo]

A small change would work in an earth orbit, but the effect would not be worth the time. More energy is needed to make the change more significant in a shorter period of time.

Define 'work'. Lots of energy is needed to do an inclination change, whether in orbit about the sun or about the Earth. To move an asteroid, you aren't actually changing the inclination much (if you decided to change the inclination instead of the apoapsis/periapsis), it's just that the orbit is so large that changing the inclination by a fraction of degree means a move of thousands of kilometers, but the angle change is still tiny.

One would think that if the LG points were a serious thing - like the old SciFi writers made of it - that it would be like that location in the Pacific ocean where garbage collects. The LaGrange points should be full of loose debris.

Hobbs, get on this....

None of the lagrangian points are stable in the long run. As Winner points out, 3 of them are completely unstable, including the L3 point on the other side of the sun (which we can't see because the sun is in the way). The other 2 are somewhat stable, but over geological time, perturbations from the other planets will clear them of much debris.

Well, define "something". We've sent probes around the solar system, and if there was a planet or anything larger than a ~few km we'd have known by now.

The thing is, it is not really dynamically stable in the long term. The only two Lagrange points which are semi-stable are the "Trojan" ones. The other three are not - you still require fuel for station keeping.

BTW, when we say "we've put a telescope in a Lagrange point", what we really mean is that we've put it on an "orbit" around that Lagrange point...

I don't think we've ever been to the L3 point because we can't communicate with satellites placed there. But as you said, I'm sure we'd have spotted anything large at L3 since other probes we've dispatched around the solar system would have had a line-of-sight with the L3 spot. I'm sure we took a look out of curiosity, but I don't know that for sure.

Well see, that's why I was actually asking... Sinister alien space station (OR INVASION FLEET) monitoring us wouldn't be noticeable over there, and it would have the ability to sustain its position.

Yeah, pretty much. L3 would be one of the best places to hide in the inner solar system. Then again, any alien INVASION FLEET that could cross interstellar space could just as easily hide behind and asteroid or something. We'd be screwed either way!

 

[peter grimes]

Swinging a pendulum and perturbing that arc isn't really comparable as the scale of energy required to move its arc is teeny tiny compared to that of an orbit. However, I suspect that if you measured the energy needed to perturb a pendulum a good deal relative to the amount of the energy you put into the initial swing, you'd find that they probably of similar magnitude in relation to each other. It may seem like you only need a tiny amount to perturb the arc, but then you only needed a small amount to get it swinging in the first place. Also, to change that arc a great deal then you are going to need more force than if you just change it a tiny bit.

Ok, this is making more sense to me. I wasn't considering the relatively small energy required to start a pendulum.

I was wondering about that when I saw this thread (and regaining an interest in aircraft after getting some 1/200 scale model airliners). Though I'm afraid that mines would get drowned out by space .

A guy I know (ex boyfriend of a former coworker) is a ME at an aerospace design firm that does a lot of work on control surface systems for Boeing and EADS. he occasionally sends me email forwards that are making the rounds among his colleagues.

I find them fascinating, as it's a probing look into aspects of design, engineering, fabrication, system integration, and human behavior.

A recent one detailed the chain of events that resulted in a runway fire upon landing and the complete loss of the aircraft. All because of a single washer left out of an assembly by a maintenance tech!

I'll try to dig up the email later today..

 

[timtofly]

Define 'work'. Lots of energy is needed to do an inclination change, whether in orbit about the sun or about the Earth. To move an asteroid, you aren't actually changing the inclination much (if you decided to change the inclination instead of the apoapsis/periapsis), it's just that the orbit is so large that changing the inclination by a fraction of degree means a move of thousands of kilometers, but the angle change is still tiny.

The earth orbit is smaller and a slight change would take a lot longer to accomplish (many times around the earth) the desired result. There needs to be a greater inclination change (lots of energy) to accomplish the desired results.

A slight change will work, but it would take some time, and may not be the exact result one was looking for.

 

[hobbsyoyo]

The earth orbit is smaller and a slight change would take a lot longer to accomplish (many times around the earth) the desired result. There needs to be a greater inclination change (lots of energy) to accomplish the desired results.

A slight change will work, but it would take some time, and may not be the exact result one was looking for.

The change in orbit happens once; no matter how many times you go around the planet, it won't change beyond that unless outside forces (drag from dipping into the atmosphere, thrusters firing, etc) are acting on it.

 

[GenMarshall]

What's on your mind about airplanes?

I have a couple of handful of DC-9 family planes in 1/200 scale (including an MD-80 & 90) and I notice something common across all of the planes that's really bugging my mind: What's the purpose of the hole at the base of the tail in this family of planes (DC-9, MD-80, MD-90, & 717)?

 

[hobbsyoyo]

Probably an exhaust pipe for the secondary power generator(s). Most airlines have a small internal combustion engine in the tail to power systems in event that the engines fail, they place a hole in the tail for the exhaust. Well, modern jetliners do; not sure about the older planes.

 

[Thorgalaeg]

As hobbsyoyo said it is the APU (Auxiliary power unit) intake which is usually under the tail or APU exahust which is at the extreme end of the tail. The APU is a relatively small engine usually located at the tail section which can be started with battery power, and its main purpose is to provide energy to plane systems while the main engines are off and there are no ground power lines available, and to start the very main engines.

 

[PlutonianEmpire]

None of the lagrangian points are stable in the long run. As Winner points out, 3 of them are completely unstable, including the L3 point on the other side of the sun (which we can't see because the sun is in the way). The other 2 are somewhat stable, but over geological time, perturbations from the other planets will clear them of much debris.

Does that include the Trojan points around Jovians and SuperJovians?

 

[hobbsyoyo]

I have no idea but I gather that would depend on how many other planets are in extrasolar systems and how big they are.

For the Earth Lagrangian points, it's typically Jupiter that really yanks objects around. I went to a graduate student thesis defense on halo orbits about Lagrangian points and you have to expend a bit of propellant to keep your station thanks to Jupiter according to that guy. If anything, the PhD's in the room attacked him for underestimating Jupiter's effect.

 

[Winner]

Also, the size of Jupiter explains why it has little problem keeping its Trojan (yes, I know the ones on the other side are called differently, but I am lazy) asteroids in place.

For a planet the size of Earth, it's much more difficult. Actually, it's been theorized that the body which collided with Earth and created the Moon in the process formed in one of the semi-stable L-points.

 

[Winner]

BTW, I have a semi-sci-fi question for discussion.

Do you think that in the (far, far away) future, there will be armed, military spaceships used by major powers in the Solar System? What prerequisites are there in terms of technology to make this anything more than a fantasy?

(I am developing my own sci-fi setting, and I am trying to establish an ultra-hard baseline ideas of how space combat might look like, before I deviate from it and introduce magic tech )

 

[PlutonianEmpire]

I know on the CosmoQuest forums (Formerly Universe Today), there was a huge thread entitled "The logistics of space marines", debating that very subject.

http://cosmoquest.org/forum/showthread.php?138467-The-logistics-of-Space-Marines

I have no idea but I gather that would depend on how many other planets are in extrasolar systems and how big they are.

For the Earth Lagrangian points, it's typically Jupiter that really yanks objects around. I went to a graduate student thesis defense on halo orbits about Lagrangian points and you have to expend a bit of propellant to keep your station thanks to Jupiter according to that guy. If anything, the PhD's in the room attacked him for underestimating Jupiter's effect.

Also, the size of Jupiter explains why it has little problem keeping its Trojan (yes, I know the ones on the other side are called differently, but I am lazy) asteroids in place.

For a planet the size of Earth, it's much more difficult. Actually, it's been theorized that the body which collided with Earth and created the Moon in the process formed in one of the semi-stable L-points.

Ah, ok. I asked because I was considering penning a short story where, after many years meticulously combing through Kepler data, they found a truly Earthlike planet (aka, an Earth analog or Earth 2.0, etc) in a jovian or superjovian's trailing Trojan point. Still trying to decide whether to give it its own large moon.

 

[Symphony D.]

What prerequisites are there in terms of technology to make this anything more than a fantasy?

(I am developing my own sci-fi setting, and I am trying to establish an ultra-hard baseline ideas of how space combat might look like, before I deviate from it and introduce magic tech )

This is basically your one-stop shop.

 

[GenMarshall]

Well, I found something in relation to a series of early Jet Age airlines that I like, the DC-8. In 1961, A DC-8-43 in a controlled dive broke the sound barrier at Mach 1.012 at 41,088ft. Source.

I find them fascinating, as it's a probing look into aspects of design, engineering, fabrication, system integration, and human behavior.

I'm interested on the design, performance, features, and the history of the aircraft and it's family line. The interest in history has also bleed into learning about the airliner's history. Likely carried over from my other transportation interest, railroads.

 

[Ajidica]

BTW, I have a semi-sci-fi question for discussion.

Do you think that in the (far, far away) future, there will be armed, military spaceships used by major powers in the Solar System? What prerequisites are there in terms of technology to make this anything more than a fantasy?

(I am developing my own sci-fi setting, and I am trying to establish an ultra-hard baseline ideas of how space combat might look like, before I deviate from it and introduce magic tech )

You might want to look at some of the early Larry Niven stuff. He had some pretty interesting concepts on space battles with physics in them. IIRC, the two best books for that were A World of Ptavs and Protector.

My personal opinion is that technology won't be the determining factor in the creation of armed spaceships (after all, the Soviets stuck a cannon on Almaz), but rather incentives. You would need a situation where there is a compelling reason to engage in space combat that creates results superior to sending a cruise missile at the enemy's spaceport here on Earth. Spaceships are very expensive things, and would presumably only be launched by relatively wealthy powers, not rogue states or space pirates.

 

[Cutlass]

BTW, I have a semi-sci-fi question for discussion.

Do you think that in the (far, far away) future, there will be armed, military spaceships used by major powers in the Solar System? What prerequisites are there in terms of technology to make this anything more than a fantasy?

(I am developing my own sci-fi setting, and I am trying to establish an ultra-hard baseline ideas of how space combat might look like, before I deviate from it and introduce magic tech )

That's going to depend entirely on what form of propulsion and other tech are invented. If force fields and artificial gravity are invented, then things will be radically different from if they are not. The form of the ship will be dependent on the propulsion technology. So for a fictional universe, you have to start with the assumptions on what the basic tech will be. Otherwise the question is just too broad.

 

[Winner]

This is basically your one-stop shop.

Oh, I know Atomic Rockets well, a great site. Although I don't necessarily agree with their conclusions.

BTW, I'd recommend to read what this guy did in his sci-fi universe. It's much less hard SF, but he's definitely one who gave it a lot of thought and detail. I am stealing some of his idea shamelessly...

You might want to look at some of the early Larry Niven stuff. He had some pretty interesting concepts on space battles with physics in them. IIRC, the two best books for that were A World of Ptavs and Protector.

Definitely, especially the notion that powerful drive systems can in fact be used as weapons...

My personal opinion is that technology won't be the determining factor in the creation of armed spaceships (after all, the Soviets stuck a cannon on Almaz), but rather incentives. You would need a situation where there is a compelling reason to engage in space combat that creates results superior to sending a cruise missile at the enemy's spaceport here on Earth. Spaceships are very expensive things, and would presumably only be launched by relatively wealthy powers, not rogue states or space pirates.

I agree. The reason I see for armed space combat vessels is to control lines of communication (although I know that very term is problematic in space) and secure outposts around the Solar System against opportunistic attacks. Basically it would begin more as a police force than a navy as a dedicated combat force. From there, developments would continue due to arms race mentality.

The thing is, I am not even sure space combat is *possible* (this is a multi-faceted word, I don't want to go into too much detail here) without some pretty sci-fi technologies.

That's going to depend entirely on what form of propulsion and other tech are invented. If force fields and artificial gravity are invented, then things will be radically different from if they are not. The form of the ship will be dependent on the propulsion technology. So for a fictional universe, you have to start with the assumptions on what the basic tech will be. Otherwise the question is just too broad.

As I said, I want to first establish an ultra-hard SF baseline, i.e. what we think is *possible* based on our contemporary understanding of science, engineering and physics. I understand the question is too broad and hard to grasp, I am struggling with it enormously due to the quantum scale of possibilities.

Let's say we have a ship. The drive system is some sort IC (inertially-confined) fusion engine which gives the ship a considerable degree of flexibility in moving around the solar system. (I.e., it won't run out of propellant after three deep-space manoeuvres, it has A LOT of delta-v). But how would such a ship fight other ships?

The problem I am consistently running into is that battles in space would be extremely quick and deadly. You'd engage your enemy at ranges measured in hundreds of thousands of kilometres (with lasers) or (tens of) thousands of kilometres (with rail-guns, missiles and such). Even if nukes are not allowed in space (I see no reason why they *should* be except for human prejudice based on Earth experience), no ship can possibly carry enough armour to take much punishment. This means that manoeuvrability and acceleration will be be their armour (i.e. we're back to "not getting hit is the best armour protection" philosophy). This obviously goes badly if beam weapons are practical at very long ranges - if they always hit and they can blow you up with that one hit, then space combat is a most irrational proposition. This needs to be resolved, somehow - I am leaning towards nerfing beam weapons (i.e. inventing practical difficulties precluding them from becoming the main weapons of the spaceship).

Then there is the thing with fire-counterfire. In space, you can shoot at the projectiles the enemy is hurling at you, unless they're too fast. This means if your enemy launches a missile, you shoot it down - we're doing that even here on Earth with sea navies now. There's no way to hide, no practical stealth giving your missile a chance to approach secretly and hit. Space mines are a ridiculous proposition for that very reason. So, in order to hit with a missile, you need to launch A LOT of them, to saturate the enemy defences batteries - but that is a problem, since weight matters in space; a space ship cannot carry hundreds or thousands of missiles to be expended in just one engagement, even if cost wasn't an issue. So what should I do with this dilemma?

Lastly, fighter/bombers - Atomic Rockets killed the trope of the space fighter alá Babylon 5 or Battlestar Galactica. According to their reasoning, it makes no sense in space since it had none of the inherent advantages fighters have on Earth (i.e. they move in a different medium; in space its always vacuum). But I am not sure I want to give them up

Ah, ok. I asked because I was considering penning a short story where, after many years meticulously combing through Kepler data, they found a truly Earthlike planet (aka, an Earth analog or Earth 2.0, etc) in a jovian or superjovian's trailing Trojan point. Still trying to decide whether to give it its own large moon.

Go for it. If someone can do Rocheworld, this is absolutely realistic by comparison

 

[peter grimes]

OKAY! I found the thing about the [missing] washer:

Two videos, watch them in sequence with sound on so you don't miss the narration.

http://lessonslearned.faa.gov/ChinaAirlines120/ChinaAirlines120_Downstop_pop_up.htm

http://lessonslearned.faa.gov/ChinaAirlines120/ChinaAirlines120_Evacuation_pop_up.htm