nyrath
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Posts posted by nyrath
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You could use ion engines and loads of xenon, and get insane amounts of Dv, but the ion engines have so little thrust that it takes forever to do a maneuver, and will require multiple passes to do large orbit modifications.
Try building your upper stage like this:
It has 5623m/s of Dv in there!
Dang! That's a sweet rocket!
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Well, delta-V depends upon two things, and two things only: the engine(s)'s Isp, and what percentage of the spacecraft's mass is fuel. You increase the Isp by using a better engine, and you increase the fuel percentage by adding more fuel tanks. You also can increase the fuel percentage by staging.
There is a complicating factor, though. Gravity. In space all your acceleration turns into delta-V. But during lift-off, each second while you are climbing into orbit imposes a "gravity tax" of 9.81 meters per second. This means your acceleration has the gravity tax subtracted from it before it is added to your delta-V. Obviously if your acceleration is less than 9.81, your ship is just going to vibrate on the launch pad while burning a hole in the ground.
To have lots of acceleration you need a large T/W ratio, which means a high thrust.
The dirty little secret of spacecraft propulsion is that systems with high thrust have low Isp, and vice versa. (Except for Zubrin's nuclear salt water rocket, and most rocket scientists are very skeptical that it will actually work. Remember the the Project Orion ship that uses a series of nuclear detonations? Imagine a drive that is a continuously detonating Orion. Ouch)
What does this mean? It means that the best propulsion for lifting into orbit is NOT going to be the best propulsion for traveling orbitally from planet to planet. You will want the Kerbal ion engine for orbit to orbit, and the others for lift-off. Especially the atomic rocket engine.
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What about the one from Destination Moon? I've not yet watched it myself, but the film has your Seal of Approval for an accurate portrayal of an atomic rocket.
Oh, yes, how could I forget the Luna ? Good catch.
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If i remember correctly the Starfury's from babylon 5 were fairly accurate physics wise. Using 16 engines to control flight in all dimensions in space, and having to burn retro to arrest relative motion.
Yes, plus the engines were at the end of long wings. This increased the lever arm that the thrust acts over.
They also are the only ships I recall that demonstrated that the rocket does not necessarily have to travel in the direction the nose is pointing. In an early episode, raiders are chasing Garabaldi, and he flips his starfury over and fires right into the raider's face, all the while with the ship's vector unchanged.
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The sole and only somehow "realistic" Sci-Fi movie I know is "2001: A Space Odyssee"
Having a giant, ion-powered monstership with artificial gravity and hibernation chambers sounds realistic to me.
That was good. But the ship from Avatar was pretty good as well. It even had heat radiators.
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First: What do you mean by no propulsion but an altitude control system?
I mean it has what Kerbal calls a RCS Thruster Block, but no propulsion systems. So it cannot change its vector very much, but it can spin in place for the purpose of aiming its shrapnel warhead at the target.
Second: Well, this Site is about hiding spaceships - a rocket needs no life-support and could be launched almost at "space-temperature" (2.7 k) if well isolated from the Ship. My idea was (why I used the word hurl), that the Ship takes care of this part (coil gun or something like that) so that the rockets stay cool. If everything else fails - I just hide them in a buch of you terrain-building kinetic weapons
Well, first off, this is a railgun launching a projectile:
https://en.wikipedia.org/wiki/File:Railgun_usnavy_2008.jpg
Good luck insulating the projectile so its 2.7 K temperature stays intact.
Coilguns are almost as bad.
Second off: unless you are hiding behind a planet, there is no horizon to hide behind. The coilgun launch will be visible over most of the solar system. Your opponent will notice the launch, paint you with active radar, and notice the projectiles. If you are hiding behind the planet, you cannot launch the projectiles at your target. Also: hiding behind the planet presumes your opponent does NOT have space stations, observation posts, and spy satellites scattered all over the solar system. The more they have, the harder to be "behind the planet" with respect to all of them.
Third off: the farther away you launch your projectiles, the more you are depending upon your opponent to travel exactly the way you want. The longer the travel time, the bigger the chance the target will make a course correction, a trajectory change, or something that will put the target outside of the projectiles engagement envelope.
Fourth off: hiding an "invisible" weapon inside a cloud of visible weapons is counter-productive. Or in "terrain". The target will see the visible weapons, avoid them, and in doing so also avoid the invisible weapon.
For more, read the link I sent.
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Well, just think of the sheer material that would be used needed to produce such a "terrain" - that quite inefficient.
That depends upon the range. On the other hand, you can replace dumb rocks with smart rocks. Throw kinetic weapons that have no propulsion, but they do have targeting sensors, an attitude control system, and a spacecraft sized shotgun shell on the nose. With these you do not have to fill an area with dumb rocks to create terrain. The weapon's engagement envelope fills out the terrain.
If I could come up with a weapon to defeat other, capital spaceships, I would hurl a swarm of stealth-rockets in the general direction of the enemy from several hundred km away. During the cruise, they would be inactive. After a set time (or I could send an activation signal) the rockets would activate (as close to the enemy as possible), indentify their targets and attack them in the most efficient way. This way they would be safe from interception during cruise.
sigh, here we go again.There ain't no stealth in space
http://www.projectrho.com/public_html/rocket/spacewardetect.php#id--There_Ain't_No_Stealth_In_Space
It is a truth universally acknowledged that any thread that begins by pointing out why stealth in space is impossible will rapidly turn into a thread focusing on schemes whereby stealth in space might be achieved. -
I saw an actual shot of US fighter planes attacked an Japanese cruiser during WW2, they was doing multiple passes over the ship, first thought was Stat Wars.
That is because the space battles in A New Hope were based on filmed World War I and World War II dogfights.
http://en.wikipedia.org/wiki/Star_Wars_sources_and_analogues#Film
(ninth point)
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If it was all about firing missiles from one ship to another, then it wouldn't make any sense, since to track another ship in space, the missile would have to be its own maneuverable spacecraft, and it could just be fired from the carrier vehicle.
The missile would also have the advantage that its design does not have to include mass for a life-support system, consumables, a habitat module, crew members, or propellant to return to base. The target does not have that luxury. So if you shot the missile at the target, it could follow the target through the entire solar system, for months. And it would eventually catch the target because it has a much better mass ratio. The only thing the target can do is try to take out the hostile missile with antimissiles or a point-defense system.
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I can't imagine how tedious a film or book would be if it actually adhered perfectly to reality.
I gather you were not a big fan of Saving Private Ryan? That one was so close to reality that it induced flash-backs in veterans.
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This will be very useful to deal with all those idiots who want star citizen to become a realistic game. Thank you!
And be sure to check out the various pages on space combat.
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I guess space fighters appeal to us so much, because essentially they are manly, fast, sleek, deadly machines of war. But intellectual inertia plays a role too. First trains looked like stagecoaches put on rails. First cars looked like carriages without the horses. First planes looked a lot like kites (or tried to emulate shapes of bird wings or floating seeds). When something completely new appears, we like to compare it to something well known, comfortingly familiar. And at first we don't really know how to do it better.
Well, not to put too fine a point on it, but the first moon ship, the Apollo Comand/Service module and the Lunar module, did not particularly look like an airplane.
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I'd say that the best weapon for space-warfare are self-guided missiles. Direct energy is unpractical and simple kinetic weapons to easy to dodge if you are fighting over hundreds of kilometers. Also just think of the recoil of a Battleship-class gun on a spaceship - the mounting for these guns would be massive, otherwise they would rip the ship to parts - and heavy stuff is be avoided. So, selfguided missiles - no recoil to handle and even at long range they are accurate. With sufficienty advanced computers on board they could even go after vulnerable parts of the enemy ships like sensors, engines or radiators...
In some spacecraft combat simulations I've seen, kinetic energy weapons are not weapons so much as they are terrain. The idea is that you spew a hail of shrapnel or buckshot into the vectors that you want to discourage your target from using. You are sort of using them to herd your target in the direction you want it to travel, counting on the fact it wants to dodge away from the weapons fire. Generally there is no terrain in space other than the odd planet or two, but clouds of kinetic weapon fire will count as such.
Directed energy weapons, kinetic energy weapons, and missiles. Ken Burnside compared it to a policeperson armed with a service revolver, a shotgun, and a police dog. The revolver (beam weapon) cannot be dodged or outrun, but can miss. The shotgun (kinetic weapon) is more likely to hit, but with reduced lethality. The dog (missile) can be dodged or outrun (or shot, that would correspond to point defense), but the blasted thing will chase you, and will always hit unless you actively prevent it.
(Holger Bjerre begs to differ. He points out that kinetic weapons are less likely to hit since it can be dodged, beam weapons lose lethality with range just like shotguns, and kinetic weapons do not lose lethality with range just like revolvers. Well, no analogy is perfect...)
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Aiming at and hitting a target at extreme ranges in space combat is not a trivial problem given that you're constrained on how quickly you receive information by the speed of light
Yes, light speed lag does complicate things. It can put an upper limit on the maximum percentage chance to hit the target. It depends upon the target's cross section, the target's current maximum acceleration, the range to the target, and the velocity of the weapon you are firing at the target.
Equation here:
http://www.projectrho.com/public_html/rocket/spacewardefense.php#id--Evasive_Maneuvers
Also, while armour would provide little protection against a direct hit by a nuclear weapon, explosions do not propogate through vacuum very well meaning that armour could quite comfortably provide reasonable protection against proximity detonation of nuclear weapons.That's what I thought as well, until I learned about the dreaded Casaba Howitzer. Nuclear detonations do have their destructive potential fall of drastically with range, due to the fact they are radiating all their destruction spherically. Inverse square law is a harsh mistress.
But what if you could make the blast radiate in one direction. A nuclear shaped charge. This changes everything. Among other things is can make armor more and more pointless.
I'd like to find more details about the casaba howitzer, but after fifty years the blasted thing is still classified.
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Thanks!
Forum says (You must spread some reputation around before giving it to Rune again)
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"So What If I Broke Twelve Laws Of Physics? It's Only Science FICTION"
This opinion implies that the word "fiction" nullifies the word "science." Since it is "fiction", and fiction is by definition "not true", then we can make "not true" any and all science that gets in the way, right?
Nonsense. By the same logic, the term "detective fiction" gives the author license to totally ignore standard procedures and techniques used by detectives, the term "military fiction" allows the author to totally ignore military tactics and strategy, and the term "historical fiction" allows the author to totally ignore the relevant history.
Imagine a historical fiction novel where Napoleon at Waterloo defeated the knights of the Round Table by using the Enola Gay to drop an atom bomb. It's OK because it is "fiction", right?
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Its called Telemachus I downloaded it last night. Just about to finish work and go have a play about with it.
Apparently they used Telemachus on the Mission to Duna, and they said they could not have completed the mission without it.
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Wow! They did a second mission to Duna!
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I feel like I should be the one congratulating (and thanking!) you. I discovered your "Project Rho" website some years ago, and was inspired by your conversational and engaging writing to try to make basics of rocket science understandable to kids. Until KSP, I lacked the proper tools (I tried a few times to lead classes for older kids with model rockets with very limited success). In a sense, I hope that my daughter will teach me what I need to know before attempting to figure out how to reach broader audiences more effectively.
Things I try to do on my website to make it understandable and engaging:
- Break up walls of text with lots of amusing pictures
- Understand the concepts enough so you can translate them from Science-ease into Colloquial English (though USA slang will confuse international readers)
- Use humorous images in your explanations
- Give some examples of practical consequences of the abstract principles
- Add a few sarcastic jokes when appropriate
Example:
Hydrogen gives the best exhaust velocity, but the other propellants are given in the table since a spacecraft may be forced to re-fuel on whatever working fluids are available locally (what Jerry Pournelle calls "Wilderness re-fuelling", Robert Zubrin calls "In-situ Resource Utilization", and I call "the enlisted men get to go out and shovel whatever they can find into the propellant tanks").
Example (where the kinetic energy weapon equation is illustrated by the deadly effect of used kitty-litter impacting at 12.24 kilometers per second):
http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Kinetic_Kill_Weapons--Equations
- Break up walls of text with lots of amusing pictures
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This has probably been posted already, but I cannot seem to find it with the search function.
A group of avid Kerbal Space Program fans wondered if you could launch a pilot to the Mun and back using maths rather than the in-flight orbital planning. The pilot flies upstairs, locked in cabin-view (IVA) while mission control directs him via skype downstairs. Hijinks ensue.
So the pilot was playing the game on his computer, locked in cabin-view. The mission control team had no access to the computer. They used a large white board, lots of math, and tools like Innsewerants Space Agency's ISA Mapsat readouts to calculate where the pilot and his ship was, and directed him to a save touch-down on Mun.
This would be an incredibly educational exercise for a group of gifted students.
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How did they do that? Do I sense a MP mod?
No they didn't (and don't say the "M" word).
It only worked because KSP is so close to reality. The way I understand it, the pilot was locked in a room with the computer playing KSP. He locked the game into IVA mode, where he could only use cockpit controls and see using a small viewport window.
Meanwhile, the mission control people were in a separate room, with synchronized watches. They had a big white board, and tools like Innsewerants Space Agency's ISA Mapsat readouts. They also had a web cam aimed at the pilot, and a cell phone. The mission control capsule communicator was the only member of the team who could use the cell phone to communicate with the pilot.
The mission control people just used mathematics to calculate the required trajectories, and passed the settings to the pilot. They had no access to the computer running KSP.
Read the link for details. It worked quite well. And this would be incredibly educational for a group of gifted students.
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Powerful computer users, powerful computer users everywhere...]
I feel for you. I could not play KSP at all until recently. My antiquated computer was not even up to the task of assembling a spacecraft in the first tutorial (the parts would drag very slowely). But my new computer has the power.
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Every day I find something new and astonishing about KSP!
In this case, it is how the original poster intuitively stumbled over the need for orbital fuel depots.
You can try teaching people about such things, but it sort of bounces off their brains. But here, playing KSP, it soon becomes obvious as a natural extension of playing the game. Such "self discovered" knowledge sticks with the player.
http://www.projectrho.com/public_html/rocket/infrastructure.php
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Thats why it is called science FICTION; some people still seem to forget that this is made to entertain, i can suspend my disbelief if there is some "magic-tech" that has been introduced (like the Hyperdrive, artificial gravity field. etc. Dead Space did a good job at that, actually). I cannot, on some points, contain myself about out-of-nothing rule breaking of physics laws. (Alien : Resurrection; the re entry at the end would have compromised the whole vessel, if i remember correctly)
Sigh.
http://www.projectrho.com/public_html/rocket/respectscience.php
sigh, here we go again.
Movie Space ships compared to the real deal
in KSP1 Discussion
Posted · Edited by karolus10
Another goodie was Independence War from Particle Systems.
http://en.wikipedia.org/wiki/I-War_(1997_video_game)
Full Newtonian physics. None of this silly spaceships-acting-like-fighter-planes nonsense. You learned Newton's Third Law the hard way. The ship would respond to your controls much like an over loaded 18-wheeler at high speed on a road covered with black ice.
Karolus10: Multiple posting, rest of post has been removed and merged bellow - please using "Edit Post option", thank You.
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POST_2:
Absolutely!
But my point is that we have George Lucas to thank for the misconception that combat spacecraft will act like atmospheric fighter planes. Since Mr. Lucas thought it would be cinematically dramatic to use WWI and WWII fighter plane footage as a model for the actions of the X-wings and TIE fighters, this was seared into the minds of SF fans. And latter productions like Battlestar Galactica and Buck Rogers followed suit.
This is similar to the other Hollywood misconception that handguns have magazines containing an infinite number of bullets.
POST_3:
Heinlein rulz, man. My website is full of his quotes.
Frau im Mond is also a classic, for reasons you mentioned. And if I remember correctly, it was the first occurrence of the now standard "count down to zero". Not bad for a 1929 silent movie.
POST_4:
Yes, _The Reality Dysfunction_ is good.
But for scientifically realistic combat I recommend _Through Struggle, the Stars_ and _The Desert of Stars_ by John Lumpkin.
http://www.projectrho.com/public_html/rocket/atomicnovel.php#id--John_Lumpkin
And not just because I gave him technical advice.
POST_5:
Wow! A Kerbal Starfury!
Once again, KSP astonishes me with its physics engine. You used KSP to recreate a starfury, and experimentally discovered their control issues. Cool!
This means when B5 fans scoff at your assertion, you can say you speak from experience.
POST_6:
Well, yes, it is a nice retcon, but it is still a retcon. The point is that there is no need, unless your ship plans on doing belly landings. And the fact it introduces a problem: if the power to the grav plates fails, suddenly the rear wall is the floor, and the control panels are on a pillar halfway up the walls. Why not have the grav plates on the thrustward side of the habitat module, so if the power fails to the grav plates you won't notice?
Again, the problem appeared when Matt Jeffries designed the Starship Enterprise, and couldn't shake the "spaceships are boats" fallacy.