sgt_flyer

guess that could be a good interrogation before anyone thinks of exploiting the moon - based on what's remaining of 'easily' extractable resources on earth, and known moon resources - outside of He-3, is there some resources that could soon become interesting enough on the moon that it would become cheaper to go mine it there rather than extracting it on earth ? (after all, once easily avaible resources become depleted, trying to get those from less accessible deposits is going to drive extraction costs up) once the overall costs tips in favor of the moon for any resource, guess we would see things hapenning

well, if we build either an elevator or a maglev track on the moon, it will be in order to support an already ongoing exploitation of the moon anyway - and you'll already need some form of industrial processing before shipping those materials. (sending refined materials would be more useful than sending raw ones - especially if the materials are meant for some kind of orbital factory - at least, you could bury radiators in the moon's soil to get rid of industrial process waste heat more easily than you could 'in space) -so you'd have some form of light industry already in place for that. as for fully self-replicating machines, i'd guess that we would at first keep on making most of the electronics here on earth, while the machines on the moon would focus on making most of the mechanical parts (having to only send the electronics would drastically reduce the payloads we'd have to send to the moon, after sending the first machines able to recreates their own mechanical parts, most likely some sort of 3d printer. once we get enough of those, we'd start making specialised machinery) still, with the known moon's elemental composition, i'd guess parking asteroid in orbit or at L1 (doubles as a potential elevator counterweight) with an elemental composition to make up for what the moon is lacking (ex, copper / carbon) would be useful.

thought of of maglev deceleration too (at least,a variation of it, with a 'maglev car' that has a deployable docking system , which would have to match the incoming spacecraft speed's, catch it then slow both of them down - simply to give a wider clearance for the spacecraft -can work in reverse too - and the maglev car itself could be used for rapid transit between the two extremities of the very long track)) basically, the interrogation i was given is this : Can your spacecraft finetune his orbit with enough precision (with all N-Body problems) to get his periapsis just above your maglev track without risks of hitting the moon (because slightly too sideways or too low) at least, if you can have a precise enough orbit, if the maglev's track malfunction during the spacecraft approach, you would simply let the spacecraft continue on it's original orbit .

only way you could 'stop' the thrust without 'turning off' the black hole would be to be able to adjust the mirrrors so your hawking radiation is evenly expelled on opposing sides of the spacecraft. (so both thrust vectors would cancel each other)

@fredinno maybe for the same reasons - GEM60's are only used on delta-IV - you need to keep ATK's production lines running to keep the experienced personnel for making the boosters and casting the fuel. (at least until Atlas V GEM63's are operationnal - current Atlas V AJ-60A are built by Rocketdyne, but GEM63's are coming soon, and later GEM63's XL are meant for vulcan.) and you need your assembly crew to keep the experience of attaching those

could the gravitation come into play too, or those involved masses would still be too small to have an effect? theoritical blackhole ships are supposed to have the same mass as the blackhole they hold - if the blackhole 'pushes' the starship away, their gravitation should tend to attract each other - so the ship would be towing the blackhole. (problem is - how do you prevent thrust ? ^^ - you can't stop the blackhole ^^ - unless you place the blackhole at the ship's exact center of mass, and change your mirror configuration to send the radiation to opposite sides of the starship instead only out of the back)

Maybe the DOD does that simply to keep the dual launcher capability, in case a problem grounds atlas V for months ? - if no one else purchases delta IV, they still need to give to the people working on delta-IV a job to do - to preserve an experienced workforce (these kind of people would be hired elsewhere). - you don't want a workforce entirely made of people with no delta-IV building experience the day they would really need delta-IV - hiring a workforce with no delta-IV experience only in case of atlas V failure would increase building time, increase failure risks. (And before you even restarting building deltas, you need to train those new hires, delaying even more the next launch) - and the same goes for the whole supply chain behind it - if the suppliers don't have demands for Delta-IV parts, no need to keep the tools and workers at the ready at all time for those.

mmh - a delta IV with no booster with a 4m upper stage and 1,5tons payload has only a TWR of 1,26 at sea level. - the difference between sea level and vacuum ISP for the RS68A is quite big too - (360s SL, 412s vacuum) - so maybe they only propose the delta-IV with boosters so they can limit a bit the gravity losses - and only have limited variations of the same trajectory to compute. still, guess the main reason could be simply to keep a 'steady' and knowledgeable workforce for both delta-IV and ATK factories, so the DOD can keep two different launchers. (afterall, if you never launch delta-IV except if Atlas has a problem, you would lay off the delta-IV workers, and the day you need delta, you would have to rely on new hires with no experience - bad for reliability.)

that, or they can transfer the fuel through a wormhole - in that case, why have a 5 units limit ^^

just tested, given the kerbal's weight do not change, either the backpack is not taken into the calculations, (so 95kg + 20kg) or the EVA fuel does not weight anything - which would completely throw off any calculations still regarding densities, we're on kerbin - a planet largely smaller than earth - yet with the same surface gravity

actually, KSP's monoprop density has been calculated as 4kg /l - if ksp's units are indeed liters - still, even if ksp's units are not liters, you would end up with 20kg of monopropellant with this weight, you end up with an isp of 336s (if the 20kg are in addition of the 95kg of the kerbal) besides, what is the kerbal's weight before and after expending it's propellant ? unless, of course, if the kerbals modify the monoprop fuel into eva fuel before putting it in their suits.

rechecked a bit the last posts @tater - in vacuum, there's one thing you want to avoid at almost all costs - High friction. (due to using wheels + mechanical brakes or skids) - because friction transforms kinetic energy into heat - without an atmosphere, you don't have convection to help you dissipate the heat. so that would leave mostly magnetic based braking. still - even a very long maglev surface (even longer than 40km - there are several Maglev projects here on earth that are 200km+ long) would surely cost much less than a space elevator hanging from the Earth - moon lagrangian point - besides, under the moon's gravity, you could build the thing on top of bridge pillars much more spaced and high than what's possible here on earth.

i think the kerbal's MMU RCS ISP is way much higher than real world ones - MMU's use nitrogen cold gas thrusters - with a miserable ISP of around 73s ! (but it allows them to go without risking contamination of the science equipments they fly around ;)) contrary to KSP, real RCS exhausts don't magically pass through anything in their path ^^

@Redjoker it's a bit better, but i still have the lower half of the text horribly mixed (Chrome, Win 10) there must be something really wrong somewhere within the text itself - something the Wisywig editor misses guess we'll have to copy paste this mess in notepad

@cantab quick note on the moon quench gun - if you are shipping stuff from the moon back to earth, shouldn't it be possible to directly send it to earth without needing to circularise around the moon (or even needing to spend any dV for the spacecraft outside of RCS attitude) ? as the moon is tidally locked to earth, you only have to wait for the correct time on earth to fire the quench gun, and accelerate the payload directly on a path towards atmospheric reentry. (or if you just want to ship to leo, limit a bit the gun power, so the payload aerobrake , then once you lowered you orbit enough, circularise in leo - for much less dV than having to do the transfer manoeuvers.)

oh, the idea i was talking about was for something akin to a reduced size launch loop on the moon, where you can't aerobrake for landing - depending on the size, with the moon's reduced gravity and no atmospheric perturbation, it might even be feasible to build without needing 'active' power hungry support components like those a launch loop or a space fountain would need on earth.

you'll need a quite long maglev structure / railgun in any case - simply to limit the G forces during acceleration and deceleration - the automated maglev car alone could sustain much higher G forces, but when you have to accelerate / decelerate a manned payload , you don't want the crew to sustain too much G forces. now, such structure will be long for sure, but on the moon it should be within the realm of feasability with today's materials - if you pick the right spot to have things as flat as possible. now, as for precision, you'll of course need several observation systems all along the orbital path on the moon's surface, capable of precisely determining the spacecraft's orbital parameters,then use a feedback loop system to adjust. if we can determine and track orbital trajectories of passive debris threatening ISS, a spacecraft with active comms systems would be much easier to track

Yup, a passive structure like a bridge would be impossible over such spans. An active structure, that's another story though (You basically have a giant maglev continuously accelerating mass so it has a ballistic trajectory 'higher' than the track's curve - so such a structure would be held through tension too (as the accelerated mass would tend to 'press' upwards onto the magnetic track). You'll just need tethers on the side of the track to prevent sideway movements - that's the launch loop concept. (Because a launch loop could be also used as a bridge as well as an orbital launch system - start acceleratng on a separate track, match the speed and 'latch' onto one of the outgoing maglev elements - the maglev element would transport you at very high speeds towards the other end - where you 'unlatch' the maglev to get onto a slow down separate track. (in the meantime, on each extremity of tehe launch loop you have a looped track to send back maglev elements back in the launch loop with limited impact on their speeds) Note, in the concept, the launch loop is meant to span over oceans anyway - in case of failure however, of course, the permanent energy requirements to keep such a structure afloat would be quite tremendeous - have a power failure, and the thing would break apart under it's own weight. An interesting concept, but building the 'starter' track onto which you build the rest to increase the loop's capacity would be hard - not including the constant energy requirements to keep such a structure in the air.

at the moment you catch the incoming spacecraft, both vehicles are supposed to move at the same speed. at this point, the orbital curvature is low enough than an adjustable deployable system from the maglev can match the orbital curvature (especially if the section of the maglev track where you catch spacecrafts has a curve parallel to the orbital curvature) would give you more time to catch the incoming spacecraft. when you know the inbound spacecraft velocities and how much time you need for your maglev to accelerate to match the speed, timing it down for rendez-vous is not an extraordinary feat

with a good spacecraft guidance, you could also use the railgun track (more like a maglev track in fact;)) to decelerate for moon landing. The structure's shape would be quite similar to a launch loop which is another proposed orbital launch system) (ramps on both ends with a high altitude flattened curve section in the middle) . - high enough above the surrounding natural formations that you can lower your periapsis down to the maglev track without risking impacting the moon's surface. for landing an inbound spacecraft, you time and accelerate a maglev car on the track until it matches the spacecraft speed and position, the maglev car then use a deployable system to bridge the gap between the track and the spacecraft at it's periapsis, catch the spacecraft then the maglev car slows down the spacecraft on the remaining of the track. in case of problem with the maglev car / the track during the spacecraft approach, the spacecraft would simply continue it's orbit. of course, you can also launch with such a track - accelerate the maglev car with the spacecraft attached to it, deploy the spacecraft, and release it when you reached your desired orbital speed. the maglev car then slows down on the rest of the track.

yup, those bridges basically use a tube with a lot of small cables inside it. (the cables bear the loads, not the tube) - and they can even go at an extremity of the tube, to replace the individual cables as needed. besides, those suspensions have good margins and are not meant to be used near their structural limits. an important infrastructure like a space elevator would have even wider margins Still, what would make me afraid of such a space elevator, is if the cable breaks near it's counterweight in space - imagine the tons and tons of cable that would fall across the earth (i doubt the cable would fall straight down - and with various orbital velocities... - basically anything around the equator would be at risk...

mmh at 100 feet, it would make the baserunner roughly 50% longer than our biggest Haul trucks - and those are on wheels, like the baserunner. (for quarries and such, where you generally have unstable ground ;)) https://en.wikipedia.org/wiki/Terex_33-19_%22Titan%22 https://en.wikipedia.org/wiki/BelAZ_75710 now, one unknown, would be : what is Kharak surface gravity ? if it's lower than earth, you could build bigger things without risks to see it sink in the sand (for fun, 1 german tank concept which would have been bigger than the baserunner https://en.wikipedia.org/wiki/Landkreuzer_P._1000_Ratte) (though, of course, Nasa's Crawlers are even bigger than the german tank ^^) edit : found another long wheeled vehicle, the MZKT 79221, which serve as the Transport Erector Launcher for the Topol-M missile. (Still shorter than 100 feet though ;))

@RocketSquid in interplanetary spaceship cases, docking events (especially on a mars mission) basically occurs only before departure and after arrival so i guess you can allow a spin down of the spaceship / hab ring at these occasions (besides, while the crew is down there on mars, there's supposed to be nobody inside the ship, so you can let your ship without rotation). the same for 'important' burns, you can allow a spin down too it won't kill the astronauts to be in weightlesness for the duration of a planned burn sidenote, for 'supply' crew only before departure, they are only there to unload stuff, and for a short duration stay only - so they most likely won't need artificial gravity.

i guess that having a mechanical seal big enough to let a man go through it between a fixed section and a rotating section is going to be really annoying to have a reasonable leakage rate. (afterall, needing to have both mating parts so perfectly adjusted over all the circumference) - which is why people are proposing an enclosure (if you need a fixed habitable section) but still why would we need both a fixed and a rotating section ? having only one of the two entirely removes the need for such a mechanical seal. so either : - rotating the whole ship, with the need to get antennas, solar panels, potentially radiators, and maybe engines on a system allowing them to keep pointed in a fixed direction (with their connections to the spaceship needing to take into account the rotation) , - having only the habitable section spin (you either only connect to the docking hub when the ring is stopped, or the docking hub is integrated in the hab ring,with the docking port lined up with the axis of rotation (so a docked spacecraft doesn't create an imbalance when the ring is spun) - again, you need a way to interface the rest of the ship with the hab ring, so those connections have to take the rotation into account. in both cases, you would only have to deal with small connections, much easier to perfectly adjust than one big mechanical seal. we could also add having the whole habitable structure wholly fit within an enclosed fixed section, which would create it's own engineering problems (additionnal weight for the whole structure notably and such a huge fixed housing structure would surely need to be inflatable to be able to fit in a launcher fairing, then you have to assemble afterwards the rotating hab structure within the inflated housing) in any of those 3 cases, you'll need to deal with the torque / friction between the rotating and non rotating elements. even if one part has a tiny mass compared to the rest, needing to compensate for friction will still induce opposite movements in both sides (even with ferrofluid seals - as you still need bearings alongside it, so you have to compensate for that. on another note, just for ISS, for installing a rotating habitable ring on ISS, didn't they plan to have sets of airtight doors on both sides ? so any leakage occuring in the space between the rotating and fixed sections would be limited to this tiny space between the two doors - and you only open the doors when you need to get from one section to the other, greatly limiting the effects of the increased leakage rates.

i'm wondering - if we could slow down the light to really low speeds these entangled pairs of photons, would it break entanglement ? (some managed to really slow down light to a crawl) http://www.photonics.com/m/Article.aspx?AID=28520 Combined with the technique presented in this thread, you first create your entangled pair, then slow down both sets of entangled photons, move one set while it's still in it's slowing medium. If entanglement is still preserved in this case, then wouldn't it be possible to : - Place the image you went to send on one side (maybe something akin to a QR code if you want to send data) then on the other side, wait until a predetermined time (as you should be able to determine in advance when the entangled pair of photons exits both slowing down medium) to record the result. Though, of course, that means preparing in advance the entangled pairs, just changing the image on one side and recording the result on the other side could be made at a pre set time. (So no need to transmit synchronisation information at all time through conventionnal means) still, it's just an hypothesis guess either slowing down the light or moving the medium containing it would break the entanglement anyway