SomeGuy12

Sweet. Sounds to me like we just weld together a set of metal propellant tanks, fill one with whatever fuel we happen to have handy, and the other with chlorine trifloride. Pressurize em both, open 2 valves, presto, rocket thrust! What could possibly go wrong? I see no need for further R&D, gonna order up the materials and CLF3 now. Bet I can have a rocket going by the end of the weekend. * *In light of certain news articles where people were taken out of context : yes, I'm kidding. I don't think you can order CLF3 from any chemical supply house anywhere, and I'm aware that even if you could get it into a tank, it would probably attack the welds or the seals inside the valves. Also, helium pressurization is not what they use on lower stages of rockets, pressurizing a tank to high pressure containing CLF3 sounds like a gold star Darwin Award. Finally, building any kind of rocket using the "hold my beer while I weld this together and get it fired up by the end of the weekend" method is going to result in disaster, even if you use a proven, simple design.

Doesn't diluting it ruin it as a fuel? For rocket flight you need the maximum energy content per mass and volume. You'd need a variant that flows smoothly in native form, especially after heating.

This is about the same as Rune's laser idea. You overcome it a similar way. You use filtered sensors that have extremely narrow fields of view, and they scan across the sky very rapidly, and you correlate the inputs from several such sensors to search the sky in 3 dimensions. You probably do this digitally with massive sensor arrays that are sensitive to the phase of incoming light. You can then digitally focus on different areas of the input and thus filter out the bright decoys. You reduce gain and use high dynamic range sensors so you don't get blinded.

Wedge, I agree with Kerik. Taking the position that "because we can't test X, my position Y is correct" is a fallacy. Even though we can't test X, from what we know now, stealth in space is not possible. You can only make reasoned opinions based on current knowledge. Maybe FTL travel is possible or you can escape to parallel dimensions to sneak up on a target, or maybe there's a way to have total omniscience about an area of space. You can't make a reasoned judgement on "maybes". When we say "there's no stealth in space", what we are saying is, "based on the best current knowledge of physics and thermodynamics and compact sensors, stealth in space is extremely unlikely". We don't care what your speculation about future knowledge is. If you have a meaningful opinion to give based on current scientific knowledge, I'd be glad to hear it, but speculating advances that are not currently known to be physically possible is a waste of time and space in this thread.

Rune : we discussed this. So you blind a few sensors. How many more does the enemy spacecraft have? No, you can't close with impunity. They can either devise laser light shielded sensors, sacrifice a sensor periodically to get targetting information on you, get the data relayed from other observers you aren't lasing, use your laser beam itself as a target and a sensor that has enough attenuation layers to analyze the light from it, etc etc etc. Or set a nuke off as an illumination flare and use shielded sensors. Heh. I think the only way to take a spaceship out of a fight is to destroy a system needed to fight in a way that cannot be quickly repaired. So burn a hole through their reactor, all their radiator wing-roots, etc. And yeah, it's a trap. To be invisible to infrared, Wedge has to use a gas with the same temperature as CBR. The way we'd spot his proposed stealth space battlewagons is when they blot out the sun from their enormous propellant tanks. It's also a trap in that using cold gas like that makes you colder than CBR...which is also spottable as a cold spot against the background. Whoops.

Keep going. Go through the exercise. What's the fastest gas you can use? If you permit it to expand, how fast will it leave the cylinder? How hot does the gas have to be? I know the answers, but I know you won't believe me unless you do the exercise yourself.

Well, ok, the problem I have as an engineer myself is that I wouldn't want to have the devices fail prematurely. Much better to have the device be reliable but if it is a limited time use product, have a sealed battery, internal to the chip, and use that battery to run a timer. When the timer hits zero, erase the firmware. Protect the firmware from reading (all modern microcontrollers and FPGAs have this protection). This is how you'd want to say, distribute anti aircraft and anti tank guided missiles to an ally you only marginally trust, such as Ukraine.

That's fairly obvious this will happen. Obviously the graphene has to be trapped inside something that won't covalently bond with the 2d graphene layer. You're saying you'd do this on purpose to make expiring circuits? What kind of lifespan are we talking about here? Why would you want circuits that fail eventually on purpose?

I agree. I guess what I was trying to get at is if you are thinking about going for a bigger mirror, or a petawatt of continuous beam power, the bigger mirror is a better idea. - - - Updated - - - Yes, liquid cooled. It's not as bad as it sounds - the "liquid cooling" just means one of these is against the sensor. So there's a sensor, a solar panel for power, a radiator panel to shed the heat, and some kind of low-vibration pumping system. And gyros for orientation and RCS. Probably a spacecraft the size of a trash can or so. Basically, a mini version of the James E Webb telescope without the massive focusing mirror, just a small one.

I'm a little confused. 1. Are you saying you can't focus, with a big mirror on the order of 100 to 1000 meters radius, onto a target at a great distance using UV or X-rays? 2. Are you saying you actually need that kind of beam power if you can get a small, tight beam at whatever distance you are at? The whole idea is that if you are using a laser against an enemy vehicle in the same weight class, the enemy can shed just as much heat as you are sending. So you have to be able to focus the beam onto a small enough area to vaporize a hole in their systems. The vapor gets lost to space and so the enemy ship loses mass, and the functionality of whatever system the beam burned through. Burn a hole in the enemy power source or the enemy weapons or the enemy radiator junctions and you win. If you are forced to spread the light over their whole hull, you don't win. They can shed as much heat as you are sending, because by definition they have radiators about the same size, and your lasers are less than 50% efficient. (they basically have to be, because of that dreaded law of physics, entropy. An in phase laser beam focused in a single direction has very low entropy compared to the chaotic sea of high energy particles resulting from a fission, fusion, or antimatter reaction that is your power generator. So you have to shed the difference as high entropy heat) Your "petawatts of power" idea only works if the enemy is massively out-massed.

Describe for me a potential rocket engine design that has ISP above 100 and does not involve a massive thermal signature. This means you must have an exhaust velocity of 1 kilometer/second with respect to your ship. Keep in mind that the heat radiators to shed the waste heat from your energy source count as well as the exhaust plume. "Engine design" means all critical components - don't say a "photon drive" without including the power system.

Wedge, you're wrong. You cannot turn heat into electricity without releasing mostly heat because heat has more entropy than electricity. Go pick up a textbook and verify for this yourself. We aren't making wild guesses when we say the plume from a rocket engine has to be hot and thus the actual gas molecules will also radiate in infrared. No engine design that gives performance better than "pathetic and useless" exists that doesn't have a hot exhaust. And that's after 40 years of rocket science. The plume itself must be a massive stream of gas, because (1) with high ISP, the exhaust velocity of the gas must be very high and (2) with high thrust, there has to be a lot of it. That's all you have to detect.

Entropy says this won't work (see Shpaget's reply). As I said, you're not one of the posters that genuinely understands science and engineering, or you would have known this instantly.

You can set the beam to wide angle and gradually narrow it. (adjustable elements in the telescope). This lets you calibrate for conditions, as you can empirically discover the correct set of mirror settings this way. You could do the calibration much faster by using several laser frequencies and several sets of mirrors and adjusting each mirror asymmetrically. This will stop systematic errors that are constant during the calibration period. Once you are zeroed in and have a narrow patch of laser light impinging on the enemy hull, burning a hole or just warming the surface, you can correct for small attitude errors by adjusting as the beam tracks due to attitude error. Still, yeah, in some cases, I think the beam would kind of wobble over the enemy spacecraft, semi-randomly damaging different parts of it. Especially if your spacecraft is taking hits, causing outgassing and flexing as the whole structure bends back and forth chaotically.

Do you understand the concept of "an object hotter than the background glows in infrared". "Most of space is empty of all objects, glowing or otherwise". "A rocket exhaust stream is a stream of high velocity particles going the same direction." This is less entropy than the chaotic sea of high energy particles you get when you combust 2 chemicals, fuse or fission some atoms, or react matter and antimatter. Therefore, the entropy has to be rejected in the form of waste heat. Space has no particles to shed waste heat onto, so it must be radiated, as convection/conduction do not work. You have to radiate to a significant portion of the sky, or you are also creating an impedance in your heat rejection system by trying to radiate energy in a low entropy form. This is the reason. The RCS nozzles on the shuttle will glow. Any kind of higher energy system will glow much more brightly. No amount of technical trickery can obscure this, you might as well say "and then we invent anti gravity" as an explanation for why you think there will be stealth in space. You merely need several observer stations with IR detectors and the ability to sweep the entire sky. The reason you need several is that yes, someone could perform maneuvers if they knew where the observer was and were precisely in line with the sun. Similarly, it's vaguely possible to hide with a cooled front plate, if you aim it right at the target you are trying to sneak up on, so you need observers located at other angles to spot this trick. Your post indicates that you don't in fact have any such education, or you forgot what you allegedly know. So yeah, my call is correct. I believe that any tautology - a series of objectively correct statements linked by inescapable, correct logic - must be correct. So does every other objective/rational thinker on the planet. I just gave you a tautology above, and the tautology is self -verifying. Unless the statements I made above are not fundamental physics, or there is a weak link in the reasoning, it's correct, and it doesn't matter if everyone else on the planet has an opinion that disagrees...it is still correct.

Wedge, the fact is, some of the posters on this forum know what they are talking about, and the majority don't. So calling an argument "unresolved" when the posters on one side of the argument don't know basic physics or engineering, and the posters on the other side do, is misleading. I know a lot of both and hold several degrees. Obviously that doesn't mean much unless I'm going to reveal my IRL identity, but from my perspective, the arguments are actually over. 1. I know, from my personal knowledge of physics and engineering, and the arguments given here, that ultimately laser weapons are the only way to go, because there is no way to stop the beams and if at least 2 beam frequencies are in use, no way to reflect them. However, I also know that the enormous pieces of equipment, weighing thousands of tons, needed to generate and focus even soft x-ray beams may mean there is a brief period of time before anyone invests that much money where simpler kinetic weapons may rule the day. 2. I know, again from both personal knowledge and the arguments give, that there is not any stealth in space except around the handful of places in space that give you cover, such as large planets. The rest of the time, it's a wide open battlefield, and range is king. The more efficient the rocket engine you devise, the bigger the flare of infrared light you must emit in order to use it. This is because kinetic energy of your rocket exhaust stream scales with the square of the exhaust stream velocity. Ergo, if you double ISP, you must quadruple the required energy, and a rocket exhaust stream has low entropy compared to the power source driving it. This means you must have gigantic heat radiators in order to use any kind of high performance rocket. This is why even the mediocre performance space shuttle RCS plumes can be seen from the asteroid belt, and a nuclear thermal rocket would be visible from anywhere in the solar system. And don't even think of cloaking a fusion or antimatter drive, either of which will glow like a star. You can't get into weapons range of someone if you don't maneuver, and the moment you maneuver, "bloop. contact detected, no IFF, mass estimate is warship class. Shall I arm weapons, commander?" So from my perspective, the arguments are resolved. I have not seen any arguments from a poster that are supported by actual facts and knowledge to dispute #1 and #2.

As I understand it, the only way water matters is it makes long term ISRU easier. That is, if you pay the enormous cost of sending some kind of mining equipment that can mine up the soil and then bake out the water, you would be able to collect, a drop at a time, water, which happens to contain the lightest element in the universe, hydrogen. This lets you make rocket fuel - methane or liquid H2 - entirely from resources found on Mars itself. It lets you fill the water tanks of a habitat without having to bring that water all the way from Earth. Or, you could just haul the lightest element, hydrogen, in tanks to Mars, and get the oxygen and carbon from Mar's atmosphere. For obvious engineering reasons, ISRU where you just have an air compressor and an air intake and a compact set of machinery sounds a heck of a lot more reliable and cheaper to develop than a set of mining equipment. Also, that mining equipment may end up just requiring human hands to keep it running. Certainly, present day automation isn't up to the task.

The reason to spam is when you are against a peer warship or some other hard target. Spy satellites don't have point defense or enough fuel for any real evasive maneuvers. This is what I was talking about - against a peer warship, one you aren't sure you are going to beat at all, missile spam makes sense. Might as well go all in. Naturally, this can create mutual kill scenarios, where at the end of the battle, both warships are dead from the huge swarm of missiles.

I'm saying, Rune, that sensors have become so light and cheap that there is literally no way to kill all the sensors able to detect the enormous signal of an IR plume from a space warship without blowing up the whole ship. I'm saying it's going to be literally the very last system to fail. Especially since radios are also light and cheap, and a space warship would be receiving a constant telemetry feed from as many as dozens of other small spacecraft, all updating the sensor picture as seen by the space warship's control systems. And that's today's technology. Totally plausible future nanoscale circuits and sensors could let you literally paint backup sensor systems onto every exterior surface of the ship. I think the way you take a space warship out of the fight is you kill the power. Specifically, both high velocity kinetic guns and lasers need enormous electricity supplies or they don't work. And the only energy source that makes any sense in an environment where every gram costs you propellant and money is nuclear. You punch a hole in one of the gigantic magnets that are part of a fusion reactor, or put a few holes in the primary loop for a fission reactor. (probably a space warship's fission reactor will only have a single loop) The warship's lasers and railguns stop firing and the battle is basically over. Batteries and fuel cells and RTGs might keep the sensors, life support, and short range chemical propellant point defense firing, but anything with the range to reach across thousands of kilometers would be down. So yeah, a space fight could end with a whimper, not a bang. Put a pencil sized hole in each of the enemy warship's nuclear power sources, and it's over. No dramatic explosion, and the disabled warship might appear almost completely undamaged...or not.

K^2, are X-rays lasers remotely near practical? I know you can get visible light lasers, they are basically a battle ready technology right now.

Rune...not this crap again. No stealth in space, and any competent space warship commander will have dozens of backup sensor systems and will deploy a fleet of drone spacecraft, far from the battle, that all also have sensors. They will, at a minimum, scan 100% of the sky in infrared at least once a minute so you cannot be surprised by anything under thrust. The drone spacecraft sensor net will all relay their data to the mothership, and will also give you views from other angles, so even if someone manages to mask their emissions in a narrow cone, they will be seen still. It's just not gonna happen. The only "stealth" that is plausible is that if you approach a planet and enter low orbit, someone could launch from the far side and come after you. You wouldn't know about the launch vehicles because you can hide on a planet with the mass of the planet and the planet's atmosphere to act like heat sinks and to scramble IR signals.

I dunno...It kind of sounds to me like you are going to need the mirror to be in a rigid mount (because your ship is under thrust in a battle. If you are stationary, someone could fire a shotgun kinetic round of tiny hypervelocity pellets. You have to be always under thrust juking sideways, and changing which direction you are juking to not get hit) The rigid mounted mirror is presumably going to contain thousands of tiny micro adjustment devices, probably some kind of wire that shrinks slightly when exposed to electric current or something, mounting on the back side of the mirror. The mirror is probably actively cooled as well, using some kind of vibration-free MHD coolant pump system. This is a lot of gear, more than you can throw out into space. You need all this equipment - the beam power of a laser mirror is enormous, measured in megawatts per square meter. As it heats during firing, you need to be continually adjusting the mirror to keep the focal spot at the target as small as possible. This is also why the mirror has to be cooled, since otherwise it will eventually overheat. Oh, and to deal with missiles, it may have to slew relatively violently between targets located several degrees apart. It all depends on assumptions. I'm assuming a "plausible mid-future" where the mirrors are only 5 to 10 meters across, limiting beam range to only a few thousand kilometers. Missiles can have closing speeds above 20 kilometers/second, higher if the firing ship uses it's high efficiency fusion drive to get a firing pass with a closing speed of 100 kps or more. That gives you a lot less time to react. In addition, in some engagements the firing ship or another warship has it's own lasers, within beam range of the victim warship. Victim warship unfurls delicate 5-10 meter, actively cooled mirrors, and the other warship burns off their outer coating, taking them out of the battle. I can see repairing the minor damage to the mirror - just a single molecule layer has been ablated off - mid battle, by replacing the mirror segments or even some kind of nanotechnology repair print head that moves over the mirror, fixing it. It's going to take time to do this, however, and if maximum beam range is 3000 kilometers and the missiles are closing at 10 kps, you have only 5 minutes.

Just boost the mass driver ISP by making the mass driver track longer. Get that ISP up to 10k or 100k and do this. Also, uh, better plan on waiting at least a century. 5 days is ridiculous.

Bomb pumped X-rays, or there is some kind of nuclear shotgun round. Both would need a missile to deploy the weapon since obviously the vehicle that uses it will be destroyed by the nuke going off. You might be able to set off the X-ray effect or the nuclear shotgun round outside the range of the enemy laser point defense. Another option is you move a warship to extreme laser range of the enemy warship and it launches missiles. See, at extreme laser range, laser mirrors themselves are fragile because their coatings are only tuned for an exact frequency. So the enemy warship is forced to uncover it's laser to fire at the missiles, but if it does that, it's laser mirrors get zapped. You could use missiles to force a decision this way. I think missiles might have their place for a while. X-rays are hard to focus as mirrors don't even work. Sure, eventually, it does sound like there will be nothing but really power lasers in kilometer+ mountings. An enormous warship will be to carry just 1 laser.

So I've realized something. If space warships are ever built, and they have missiles as a weapon, unlike on Earth, there's no reason you cannot send every single missile you have at the enemy at the same time. You would cold launch the missiles, sending them out into space near the launching ships, and they would use RCS to form up into a formation. When ready, every single missile would ignite it's main engine and hurtle towards the enemy warships simultaneously in order to overwhelm any defenses. For targets where you estimate this would be overkill, you would calculate the optimal number of missiles to eliminate the target and send only those. You can't do this on earth because missiles can't just float out in a vacuum near the mother ship, keeping up with it since there is no friction in space. Missiles have to burn fuel to stay in the air, so they have to head towards the enemy right away.