Interplanetary Staging and OSRU

[Duxwing]

How would combining on-site resource use (OSRU)* with reusable staging affect propellant requirements for the following mission profile?

Profile

1 | 2-staged craft begins empty in Low Minmusian Orbit

2 | Minmusian OSRU system resupplies stages and payload, giving second stage only enough propellant to correct inclination and course and capture.

3 | First stage puts craft on Hohmann trajectory to target

4 | First stage corrects course once craft leaves Kerbinar SOI

5 | First stage is jettisoned with enough fuel to so correct its course as to later aerobrake at Kerbin and be reused.

6 | First stage rendezvous burn

7 | Second stage corrects inclination

8 | Second stage corrects course near target SOI

9 | Second stage corrects course in target SOI

10 | Second stage captures in appropriate orbit

11 | Target OSRU refuels second stage; payload operates

12 | Second stage transfers itself and perhaps payload to Kerbin

Hypothesis

Staging decreases propellant requirements by increasing mass fraction. Beginning empty at Minmus allows the craft to reach LKO 'dry'--and therefore lighter--and removes the costly need to ship propellant from LKO. Giving the second stage just-enough propellant for maneuvering and capture lessens the first, which need not be replaced because it can instead be re-used. OSRU at the target further lessens the second stage by enabling it not to propel return propellant. The thereby-lightened second stage will need fewer engines for necessary TWR, decreasing dry mass and therefore propellant mass.

-Duxwing

*I write "OSRU" because I think the usual term for using stuff found where you go--in-situ resource utilization--is pretentiously verbose.

[merendel]

*I write "OSRU" because I think the usual term for using stuff found where you go--in-situ resource utilization--is pretentiously verbose.

In-situ is pretty much Latin for on site. Not sure simply translating the standard term into a modern language and coining a new acronym for it is less pretentious.

On to the actual topic of your post. I'm assuming from the wording of your profile that there already exists ISRU facilities at the target and said equipment is not being shiped with the second stage. I'm not sure your actually saving all that much adding that first stage into the mix. As stated the second stage, once refueled is capable of returning to kerbin on its own. If it can get back chances are it could reach the target as well and refuel once it arrives, do its mission, and top off its tanks once more before returning. All adding that first booster stage is doing is adding the weight of an extra engine, fuel tank, control systems, and enough fuel to return to kerbin. Unless your sending something particularly huge on a one way trip I dont see this as a net gain in anything but added complexity.

I think a more practical profile would be a transfer stage and a payload stage. Transfer stage gets the payload(empty of fuel if possible) out to the target. the whole ship docks with the local ISRU facility which refills transfer stage and if apropreate the payload stage. Payload stage does its mission a(landing/orbital manuvers/0g billiards) and then returns to the fueling platform. Any parts being returned to kerbin are reattached to the transfer stage and returned. Transfer stage and if applicable the payload aerobreak and remain in orbit for refueling and reuse while any detachable payload (science/crew) returns in a dedicated droppod.

[Duxwing]

In-situ is pretty much Latin for on site. Not sure simply translating the standard term into a modern language and coining a new acronym for it is less pretentious.

Why use Latin when the rest of the phrase is English? Why write "utilization" when "use" means the same? Hence my recoining.

On to the actual topic of your post. I'm assuming from the wording of your profile that there already exists ISRU facilities at the target and said equipment is not being shiped with the second stage. I'm not sure your actually saving all that much adding that first stage into the mix. As stated the second stage, once refueled is capable of returning to kerbin on its own. If it can get back chances are it could reach the target as well and refuel once it arrives, do its mission, and top off its tanks once more before returning. All adding that first booster stage is doing is adding the weight of an extra engine, fuel tank, control systems, and enough fuel to return to kerbin. Unless your sending something particularly huge on a one way trip I dont see this as a net gain in anything but added complexity.

I think a more practical profile would be a transfer stage and a payload stage. Transfer stage gets the payload(empty of fuel if possible) out to the target. the whole ship docks with the local ISRU facility which refills transfer stage and if apropreate the payload stage. Payload stage does its mission a(landing/orbital manuvers/0g billiards) and then returns to the fueling platform. Any parts being returned to kerbin are reattached to the transfer stage and returned. Transfer stage and if applicable the payload aerobreak and remain in orbit for refueling and reuse while any detachable payload (science/crew) returns in a dedicated droppod.

You're right. Neither should I start at Minmus: possible SOI shenanigans are endless. Well, darn.

-Duxwing

[magnemoe]

This work well, however I would rather start from LKO, Starting from Minmus, tend to increase dV requirements at least to Jool and other high dV locations. Yes last I tried it was 2500 m/s from orbit close to Minmus, more expensive than to aerobrake down into LKO.

Yes the best would be to drop Pe down to 100 km at a time you can burn at Pe to be on your way, this is a good idea even if you use 100 m/s to pull the Ap inside Mun SOI to avoid problems.

You can use a satelite in low orbit to find the phase angels for burn so you can leave minmus at right time, the most important thing is to get the Pe located correctly

However in this setting you will leave Kerbin SOI after a 100-300 m/s burn and will not have much point in a first stage.

Now if you launch a payload from Kerbin, then refueled in LKO and used a reusable first stage (tug) this has multiple benefits.

First you save a lot on the payload as most of its weight tend to be fuel too, this reduce launcher demands a lot.

Secondly the refueling is free or a one time cost of getting the miner and tug into orbit.

One tips is to dock the 25x4 engine on a large core stage this way you can decople the engine and you have a huge fuel tank you can move with a tug you take this to Minmus an refill then leave in LKO as a depot.

http://i.imgur.com/t6hNAYH.png this is one of my tugs moving a huge miner to an refueling depot, the miner barely made it to orbit.

[Duxwing]

This work well, however I would rather start from LKO, Starting from Minmus, tend to increase dV requirements at least to Jool and other high dV locations. Yes last I tried it was 2500 m/s from orbit close to Minmus, more expensive than to aerobrake down into LKO.

Odd. I always thought that the benefit of beginning higher equaled the cost from lost Oberth effect.

Yes the best would be to drop Pe down to 100 km at a time you can burn at Pe to be on your way, this is a good idea even if you use 100 m/s to pull the Ap inside Mun SOI to avoid problems.

You can use a satelite in low orbit to find the phase angels for burn so you can leave minmus at right time, the most important thing is to get the Pe located correctly

However in this setting you will leave Kerbin SOI after a 100-300 m/s burn and will not have much point in a first stage.

That mission profile sounds too complex to be reliable because the properties of the trajectory from Minmus to Kerbin interact with the properties of the transfer trajectory; the transfer burn would also have to be brief to maximize the Oberth effect. I suspect that the added costs of moving the tug and maintaining the OSRU would exceed the savings of building smaller lifters.

Now if you launch a payload from Kerbin, then refueled in LKO and used a reusable first stage (tug) this has multiple benefits.

First you save a lot on the payload as most of its weight tend to be fuel too, this reduce launcher demanThatds a lot.

Secondly the refueling is free or a one time cost of getting the miner and tug into orbit.

Bringing propellant from Minmus to LKO would be much cheaper than lifting it from Kerbin to LKO.

One tips is to dock the 25x4 engine on a large core stage this way you can decople the engine and you have a huge fuel tank you can move with a tug you take this to Minmus an refill then leave in LKO as a depot.

http://i.imgur.com/t6hNAYH.png this is one of my tugs moving a huge miner to an refueling depot, the miner barely made it to orbit.

[LethalDose]

In-situ is pretty much Latin for on site. Not sure simply translating the standard term into a modern language and coining a new acronym for it is less pretentious.

This.

Why use Latin when the rest of the phrase is English? Why write "utilization" when "use" means the same? Hence my recoining.

Because it's done all the time in science and medicine. The Latin phrases are usually briefer and more clear than their English counter-parts, translate more cleanly across languages, and cleanly translate a general concept.

On to the actual topic of your post. I'm assuming from the wording of your profile that there already exists ISRU facilities at the target and said equipment is not being shiped with the second stage. I'm not sure your actually saving all that much adding that first stage into the mix. As stated the second stage, once refueled is capable of returning to kerbin on its own. If it can get back chances are it could reach the target as well and refuel once it arrives, do its mission, and top off its tanks once more before returning. All adding that first booster stage is doing is adding the weight of an extra engine, fuel tank, control systems, and enough fuel to return to kerbin. Unless your sending something particularly huge on a one way trip I dont see this as a net gain in anything but added complexity.

I think a more practical profile would be a transfer stage and a payload stage. Transfer stage gets the payload(empty of fuel if possible) out to the target. the whole ship docks with the local ISRU facility which refills transfer stage and if apropreate the payload stage. Payload stage does its mission a(landing/orbital manuvers/0g billiards) and then returns to the fueling platform. Any parts being returned to kerbin are reattached to the transfer stage and returned. Transfer stage and if applicable the payload aerobreak and remain in orbit for refueling and reuse while any detachable payload (science/crew) returns in a dedicated droppod.

You're right. Neither should I start at Minmus: possible SOI shenanigans are endless.

I actually really like using Minmus as a staging point for my interplanetary missions. Using Minmus as your starting point allows you to add a little less than 1000 m/s of dV to your mission, because when you get to the Kerbin Pe, you're only a few m/s shy of escape velocity. And if you can use IRSU to replenish fuel stores at Minmus, it'd be way easier than sending shipments of fuel from the surface of Kerbin.

The SoI change for Minmus -> Kerbin doesn't need to be precise at all, because your going to drop your Pe down to 70km above Kerbin, and Minmus moves so slowly that twitchy SoI transitions won't screw up your phase angle.

Edit: Well, ninja'd in part above. Including a trip to Minmus prior to an interplanetary trip makes the overall mission profile cost more dV, which is what it seems the detractors of this maneuver always seem to cling to. However, if you refuel at Minmus, the burns to escape Minmus and then drop your Pe around Kerbin are super cheap, and you can leave Kerbin's SoI with more overall dV.

Edited July 13, 2014 by LethalDose

[Duxwing]

Because it's done all the time in science and medicine. The Latin phrases are usually briefer and more clear than their English counter-parts, translate more cleanly across languages, and cleanly translate a general concept.

ISRU is not an example of latinization because, like I said before, ISRU is not all-Latin. Nor is it simple: "resource utilization" is a baffling mouthful to non-native speakers. It does not translate cleanly across languages--especially to Latin--and even knowing what the individual words meant when I first heard "in-situ resource utilization," I was baffled. If you want important scientific concepts to be succinct, easily-translatable, and Latin, then be consistent and write "uti natura," which abbreviates to "UI" and means "to use nature".

This semantic discussion is getting out-of-hand...

I actually really like using Minmus as a staging point for my interplanetary missions. Using Minmus as your starting point allows you to add a little less than 1000 m/s of dV to your mission, because when you get to the Kerbin Pe, you're only a few m/s shy of escape velocity. And if you can use IRSU to replenish fuel stores at Minmus, it'd be way easier than sending shipments of fuel from the surface of Kerbin.

I intuit that starting altitude is irrelevant if the craft is fueled there: am I right? Which is easier, hauling the fuel Mi->K or the craft K->Mi?

The SoI change for Minmus -> Kerbin doesn't need to be precise at all, because your going to drop your Pe down to 70km above Kerbin, and Minmus moves so slowly that twitchy SoI transitions won't screw up your phase angle.

How can this maneuver be made consistent?

Edit: Well, ninja'd in part above. Including a trip to Minmus prior to an interplanetary trip makes the overall mission profile cost more dV, which is what it seems the detractors of this maneuver always seem to cling to. However, if you refuel at Minmus, the burns to escape Minmus and then drop your Pe around Kerbin are super cheap, and you can leave Kerbin's SoI with more overall dV.

A staged system could further decrease the craft's size: a tug would drop the craft's periapsis, making the craft not need to carry propellant for that maneuver.

-Duxwing

[LethalDose]

ISRU is not an example of latinization because, like I said before, ISRU is not all-Latin. Nor is it simple: "resource utilization" is a baffling mouthful to non-native speakers. It does not translate cleanly across languages--especially to Latin--and even knowing what the individual words meant when I first heard "in-situ resource utilization," I was baffled. If you want important scientific concepts to be succinct, easily-translatable, and Latin, then be consistent and write "uti natura," which abbreviates to "UI" and means "to use nature".

This semantic discussion is getting out-of-hand...

There are dozens if not hundreds of Latin phrases that are commonly used in scientific and medical fields in association with non-Latin words & phrases. These include ad libitum water, pro re nata (PRN, for Rx's), in vitro insemination, in vivo experimentation, a priori parameterization, post hoc analysis, etc.

(hehe, that last one works on two levels)

Their appropriate and/or widely accepted use not pretentious. Trying to tell others that the appropriate use of said terms is pretentious is itself pretentious, as is stating a new term is needed.

I'm sorry if you find the term ISRU confusing, but it was coined long before KSP was a twinkle in HarvestR's eye.

I intuit that starting altitude is irrelevant if the craft is fueled there: am I right? Which is easier, hauling the fuel Mi->K or the craft K->Mi?

I don't know what "starting altitude is irrelevant" refers to. Lower orbits are better parking orbits, around both Kerbin and Minmus. Though Minmus orbits are so slow, it makes very little difference.

If a ship is going to leave Kerbin's SoI, I think it's easier to haul the ship to Minmus, because the vessel then gets to keep that potential energy it gained in the haul. If you have to haul the fuel from Minmus' orbit to LKO, then you have slow the fuel down to put it into LKO so you can dock it to your IP craft, killing all that potential energy. Even if you're aerobreaking the fuel, the PE is still gone.

That, however, is still easier than hauling fuel up from Kerbin's surface. And it's the exact reason ISRU should be part of the freakin' game.

How can this maneuver be made consistent?

What's inconsistent about it, and why does it need to be more consistent? Leave Minmus, using as little dV as possible with the lowest possible periapsis around Kerbin, and then drop your PE to just above the atmosphere. Remember what Emerson said: "a foolish consistency is the hobgoblin of little minds." It would be foolish to impose consistency where none need exist.

A staged system could further decrease the craft's size: a tug would drop the craft's periapsis, making the craft not need to carry propellant for that maneuver.

I guess, but after you're in space, the efficiency gained by staging is minimal, unless you're doing it on a large scale, or you have to squeeze maximal benefit out of each bit of resource (e.g. a Moho mission).

oh look, e.g., exempli gratia, another place where it's not pretentious to use a Latin phrase with non-Latin words.

Edited July 13, 2014 by LethalDose

[magnemoe]

Odd. I always thought that the benefit of beginning higher equaled the cost from lost Oberth effect.

That mission profile sounds too complex to be reliable because the properties of the trajectory from Minmus to Kerbin interact with the properties of the transfer trajectory; the transfer burn would also have to be brief to maximize the Oberth effect. I suspect that the added costs of moving the tug and maintaining the OSRU would exceed the savings of building smaller lifters.

Bringing propellant from Minmus to LKO would be much cheaper than lifting it from Kerbin to LKO.

Or just use ion engines to move the propellant.

-Duxwing

PS - Should English not be your first language, tell me if you want help.

Me two, I knew I would loose out lot on the Oberth effect however I was already 1000 m/s out of the gravity well so I estimated 1500 m/s, It was closer to 2500 m/s, not sure as I had only 2200 m/s. Eve and Duna should work better as the dV requirements is half of Jool.

The drop down operation is not so hard, use a satelite in LKO to set up the trajectory, mechjeb is nice here.

Now plan your exit from Minmus so your Pe is close the the burn point, You can even adjust the time you pass Pe by lowering Ap however some hours off is no big deal.

I have only done this a few times but it worked well. Done the same a lot within the Jool system, that is aerobraking into an Layte orbit who just keep Ap inside SOI, her the issue is that a 50 m/s burn tend to take you outside of Tylo orbit.

An ion engine is not a good choice for moving 150 ton fuel. An tug with 4-6 LV-N works well here.

---

The real point here is that using a reusable first stage on interplanetary missions is an good idea. However not if you start from Minmus as it will end up in interplanetary space after 200 m/s burn.

Starting from LKO it can burn 1000 m/s and get an free return to LKO, you can also get it cheap to minmus if you are willing to wait and keep watch for Mun.

Now if you send stuff to Duna one way you could just add a drop tank on the lander to give it 500 m/s extra, Eve is often a bit more expensive.

Edited July 13, 2014 by magnemoe

[Duxwing]

There are dozens if not hundreds of Latin phrases that are commonly used in scientific and medical fields in association with non-Latin words & phrases. These include ad libitum water, pro re nata (PRN, for Rx's), in vitro insemination, in vivo experimentation, a priori parameterization, post hoc analysis, etc.

(hehe, that last one works on two levels)

Your reasoning that scientists should Latinize important ideas does not support these combinations of Latin and English because many scientific and medical terms involve no Latin or language whatever; e.g., both such old elements as Gold, Iron, and Copper and such common medical tools as scalpel, cast, and syringe have vulgar common names. Scientific etymology therefore is not, like I think you believe, Latin but at least English and Greek if not also the hodge-podge of culture wherefrom the names of recent chemical discoveries are chosen; e.g., "Rutherfordium" and "Higgs' Boson". Latin and Greek may only simplify some terms--e.g., "post-hoc reasoning" is simpler than "inventing axioms after learning what horrors your previous ones wrought"--and not complicate them when vulgar cognates exist; and these vulgarities should be concise.

These two points are especially-true of ISRU, which uses both unnecessary Latin and fancy English: in situ and on site are cognates, and "utilization" means the simpler noun "use". Hence my point that OSRU is better-understood than ISRU. My lab notebook aptly describes the logical extreme of your principle: the elements would be renamed "Unium, Duim, Trium, ...". And yet... the idealist in me would like one language for the whole world. It would be phonetic and compilable and have no exceptions, homonyms, homophones, slang, figures, etc.

So, in principle, I think we agree.

Their appropriate and/or widely accepted use not pretentious. Trying to tell others that the appropriate use of said terms is pretentious is itself pretentious, as is stating a new term is needed.

That I dare challenge convention is pretentious? Whether my challenge happens to be right or wrong is entirely independent of whether one may challenge convention. Though I probably should not have jumped to the jugular by calling it pretentious... sorry.

I'm sorry if you find the term ISRU confusing, but it was coined long before KSP was a twinkle in HarvestR's eye.

You need not be sorry: we're just disagreeing. And I knew how old ISRU was.

I don't know what "starting altitude is irrelevant" refers to. Lower orbits are better parking orbits, around both Kerbin and Minmus. Though Minmus orbits are so slow, it makes very little difference.

"starting altitude is irrelevant" means that the Oberth effect is so inversely proportional to altitude that one cannot save propellant by descending from higher orbits to lower ones or vice-versa.

If a ship is going to leave Kerbin's SoI, I think it's easier to haul the ship to Minmus, because the vessel then gets to keep that potential energy it gained in the haul. If you have to haul the fuel from Minmus' orbit to LKO, then you have slow the fuel down to put it into LKO so you can dock it to your IP craft, killing all that potential energy. Even if you're aerobreaking the fuel, the PE is still gone.

Kepler proved two-body orbits reversible, eliminating our need to consider direction of movement. Instead we need only consider our maneuvers and the masses thereby moved. We should consider the relevant facts:

1 - Sending propellant from Minmus to LKO will require moving more mass because propellant will mostly comprise the mass of interplanetary rockets powered by stock engines.

2 - Sending craft from LKO to LMiO* will require more dV (not necessarily more propellant) because Minmus' lacking an atmosphere necessitates that craft must burn more to reach and much more to capture at Minmus.

3 - Sending fuel from LMiO to LKO seems less-efficient because it requires moving and aerobraking massive, expensive tankage and massive re-entry equipment.

4 - Sending craft from LKO to LMiO seems more sensible because these craft are designed to handle easily, aerobrake safely, and generally be tough.

5 - Sending craft from LKO to LMiO seems more dangerous because I want to minimize maneuvering of manned craft, which could fatally crash.

*I abbreivated Minmus to Mi because I generally abbreviate bodies's names to their first and, if necessary, second letter and "Minmus" and "Mun" share a first letter, necessitating using their second letters.

That, however, is still easier than hauling fuel up from Kerbin's surface. And it's the exact reason ISRU should be part of the freakin' game.

Right-on!

What's inconsistent about it, and why does it need to be more consistent? Leave Minmus, using as little dV as possible with the lowest possible periapsis around Kerbin, and then drop your PE to just above the atmosphere. Remember what Emerson said: "a foolish consistency is the hobgoblin of little minds." It would be foolish to impose consistency where none need exist.

It could be inconsistent because it involves many fine maneuvers, and it should be consistent because Kerbals will do it.

I guess, but after you're in space, the efficiency gained by staging is minimal, unless you're doing it on a large scale, or you have to squeeze maximal benefit out of each bit of resource (e.g. a Moho mission).

KER says that one stage, much propellant, and much more patience can accomplish any non-trivial Moho mission: in other words, a payload atop a huge fuel tank atop an LV-N, raising orbits enough not to hit atmosphere during transfer burns.

oh look, e.g., exempli gratia, another place where it's not pretentious to use a Latin phrase with non-Latin words.

That phrase is so archaic that I never knew it was Latin until now, thinking instead that it meant "examples given". Anyway, can we discuss Kerbal instead of nomenclature?

-Duxwing

[merendel]

you could potentialy save on your fuel margins a bit by sending the tug to minmus first although probably not overall fuel. It only takes about 170 dv or so to leave from a low minmus orbit to an atmosphere skiming Pe around kerbin. Your still spending the fuel to get it to minmus but if you can refuel there at low cost you can send the ship off with a smaller fuel tank. top off at minmus, eject back to kerbin SOI at the right time, get full use of the oberth effect at kerbin Pe and be able to eject from the SOI spending only 200ish dv from your tank + whatever the actual transfer dV is. You'll also be going significantly faster during your ejection burn than normal for a LKO makeing the burn to reach your eventual target even more efficent.

On the flip side your adding alot of complexity to your burn calculations. You have to plan to leave minmus a couple kerbin days ahead of your planed burn. Minmus might also be on the wrong side of the planet forceing you to accept a suboptimal launch window as you wait for it to reach position for you to get your Pe in the right place. Minmus's inclination will also likely effect how much you need to adjust for your targets inclination. It could help you or hinder you, depends the system conditions at the time of the launchwindow.

I dont think its worth it to design a tug where your cuting the fuel margins so close that you'd see much benifit considering the challanges of leaving from minmus over LKO. The point of a reuseable tug is to reuse it. Unless its ment for a dedicated ferry mission to a single location with identical payload mass each time your probably going to want a slightly overengineerd tug. This lets you send variable payloads to variable locations with the same spaceframe. you can still send it with the tank half empty if your only going to duna instead of to jool if you desire. you could play games with modular fuel pods as well.

My preferred space tugs consist of a rocomax 200x8 core with LVN's on outriger girders with fuel lines from the core (number depends on how much thrust I want usualy 2-4). A probe core, reaction wheel,power system, and enough RCS for docking rounds out the tug. Payload gets attached to the underside between the engiens so the tug pulls it through space instead of pushing. If required an additional fuelpod of apropreate size is inserted between the tug and the payload. in the 2 engien config its 7tons dry (4.5 of that the engiens) bit over 11 fueled and has about 3.4k dv with no payload/tanks and can easily sling even the new 3.75m tanks underneth if required to haul a payload to the target. Several tugs can be stacked with careful alignment of engiens if more thrust is desired for a mission. Modular, versital and efficent for any misson with a payload greater than a couple tons. for 1-2 tons or less I just stick it on a small thrust pod to get it wherever.

[Duxwing]

@merendel

Tugging and aerobraking the ship from LMiO to LKO would simplify my transfers while giving me almost the benefit of what you describe. My mission profile would be:

0 - Ship in LKO; tug in LMiO; fuel in LMiO.

1 - Ship transfers from LKO to LMiO.

2 - Tug docks with ship.

3 - Tug brings ship to fuel.

4 - Tug and ship refuel.

5 - Tug puts ship on Kerbinar aerobraking trajectory.

6 - Tug quickly undocks from ship and returns to LMiO.

7 - Ship aerobrakes to LKO

8 - Ship performs interplanetary transfer

-Duxwing

[LethalDose]

Your reasoning that scientists should Latinize important ideas does not support these combinations of Latin and English because many scientific and medical terms involve no Latin or language whatever; e.g., both such old elements as Gold, Iron, and Copper and such common medical tools as scalpel, cast, and syringe have vulgar common names. Scientific etymology therefore is not, like I think you believe, Latin but at least English and Greek if not also the hodge-podge of culture wherefrom the names of recent chemical discoveries are chosen; e.g., "Rutherfordium" and "Higgs' Boson". Latin and Greek may only simplify some terms--e.g., "post-hoc reasoning" is simpler than "inventing axioms after learning what horrors your previous ones wrought"--and not complicate them when vulgar cognates exist; and these vulgarities should be concise.

These two points are especially-true of ISRU, which uses both unnecessary Latin and fancy English: in situ and on site are cognates, and "utilization" means the simpler noun "use". Hence my point that OSRU is better-understood than ISRU. My lab notebook aptly describes the logical extreme of your principle: the elements would be renamed "Unium, Duim, Trium, ...". And yet... the idealist in me would like one language for the whole world. It would be phonetic and compilable and have no exceptions, homonyms, homophones, slang, figures, etc.

So, in principle, I think we agree.

No, we don't.

I don't, and won't, believe there's any problem with using established nomenclature to describe the established practices/concepts/etc that they describe, regardless of the what the source or sources of the nomenclature is, so long as the term is reasonably accurate (as is ISRU).

Your original statement, that a descriptive phrase with a four letter abbreviation is "pretentiously verbose" due to it's Latin source, and the position you continue to defend, is contrary to mine.

"starting altitude is irrelevant" means that the Oberth effect is so inversely proportional to altitude that one cannot save propellant by descending from higher orbits to lower ones or vice-versa.

I still don't understand what you're trying to say here, and I'm past trying to figure it out. For an ejection maneuver, you can save propellant by descending from a higher orbit to a low Pe. As I've stated repeatedly before (on this thread and at least two others) the "Minmus refueling station" strategy costs more dV than a direct ejection from LKO for any given ship, but the ship leaves Kerbin's SOI with more dV.

Kepler proved two-body orbits reversible, eliminating our need to consider direction of movement. /CLIP

Again, I'm really not sure what the point of this statement or the cited facts are, or even if it's supposed to be a counterpoint to my statement.

KER says that one stage, much propellant, and much more patience can accomplish any non-trivial Moho mission: in other words, a payload atop a huge fuel tank atop an LV-N, raising orbits enough not to hit atmosphere during transfer burns.

Yep, KER says a lot of things. Have fun trying to make those burns.

you could potentialy save on your fuel margins a bit by sending the tug to minmus first although probably not overall fuel. It only takes about 170 dv or so to leave from a low minmus orbit to an atmosphere skiming Pe around kerbin. Your still spending the fuel to get it to minmus but if you can refuel there at low cost you can send the ship off with a smaller fuel tank. top off at minmus, eject back to kerbin SOI at the right time, get full use of the oberth effect at kerbin Pe and be able to eject from the SOI spending only 200ish dv from your tank + whatever the actual transfer dV is. You'll also be going significantly faster during your ejection burn than normal for a LKO makeing the burn to reach your eventual target even more efficent.

THIIIIIIIIIIS! As stated above, more fuel is used overall, but you get to leave the SoI with more dV, which is what matters.

On the flip side your adding alot of complexity to your burn calculations. You have to plan to leave minmus a couple kerbin days ahead of your planed burn. Minmus might also be on the wrong side of the planet forceing you to accept a suboptimal launch window as you wait for it to reach position for you to get your Pe in the right place. Minmus's inclination will also likely effect how much you need to adjust for your targets inclination. It could help you or hinder you, depends the system conditions at the time of the launchwindow.

Well, yeah, also this. The good news the launch windows are usually very broad, and while Minmus does rotate pretty slowly, it's exceptionally rare to not have it in the correct position at any point during the window. Minmus' inclination usually doesn't matter at all because of how small your normal position and velocity (normal = perpendicular to the ecliptic) is compared to your orbital velocity around the sun. It's more likely that a Mun encounter during your drop will screw up your exit than Minmus' inclination.

Both methods (direct LKO ejection and Minmus refueling) are totally legitimate in stock KSP. Direct ejection uses less dV overall, and Minmus refueling station lets you leave with more dV. Pick your preference.

If you can produce fuel on Minmus with a mod, it doesn't really change much. If you want to send fuel back to LKO, super. If you want to refuel at Minmus, super. Hell, do BOTH. Get your vessel into LKO dry, send fuel and a tug from Minmus to push the vessel back to Minmus, then refuel it and send it on it's way!

[Duxwing]

No, we don't.

Yes, we do. You and I both want scientific language to be consistent, and we differ only in the implementation of that consistency.

I don't, and won't, believe there's any problem with using established nomenclature to describe the established practices/concepts/etc that they describe, regardless of the what the source or sources of the nomenclature is, so long as the term is reasonably accurate (as is ISRU).

I can understand "don't," but "won't" sounds like nothing could ever persuade you otherwise, and I don't think you meant that: refusing to believe something despite whatever argument may come is nuts. Assuming you meant to emphasize your point, I counter that language should be as simple as possible for the same reason works of engineering should be elegant. "on-site" is no harder to translate than "in-situ," which is harder to understand because English is lingua franca, and "utilization" is eight letters and four syllables longer than the equivalent word "use".

Your belief would justify absurdly replacing such words as "booster" with "delta-V increasing mechanism" or "decoupler" with "object separation mechanism". Every extra word, letter, and syllable makes scientific writing less clear and approachable, impeding the international collaboration we both want. And besides, who wants to write all that extra stuff?

I still don't understand what you're trying to say here, and I'm past trying to figure it out. For an ejection maneuver, you can save propellant by descending from a higher orbit to a low Pe. As I've stated repeatedly before (on this thread and at least two others) the "Minmus refueling station" strategy costs more dV than a direct ejection from LKO for any given ship, but the ship leaves Kerbin's SOI with more dV.

Why would descending save propellant? I agree that it would have more dV.

Again, I'm really not sure what the point of this statement or the cited facts are, or even if it's supposed to be a counterpoint to my statement.

It is a counterpoint because if orbits are reversible, then the increase in velocity due to descending equals the decrease in velocity needed to descend.

Yep, KER says a lot of things. Have fun trying to make those burns.

It's easy: just raise your orbit enough.

THIIIIIIIIIIS! As stated above, more fuel is used overall, but you get to leave the SoI with more dV, which is what matters.

[/qyite]

I'm agreeing with you here.

Well, yeah, also this. The good news the launch windows are usually very broad, and while Minmus does rotate pretty slowly, it's exceptionally rare to not have it in the correct position at any point during the window. Minmus' inclination usually doesn't matter at all because of how small your normal position and velocity (normal = perpendicular to the ecliptic) is compared to your orbital velocity around the sun. It's more likely that a Mun encounter during your drop will screw up your exit than Minmus' inclination.

Both methods (direct LKO ejection and Minmus refueling) are totally legitimate in stock KSP. Direct ejection uses less dV overall, and Minmus refueling station lets you leave with more dV. Pick your preference.

What is direct LKO ejection?

If you can produce fuel on Minmus with a mod, it doesn't really change much. If you want to send fuel back to LKO, super. If you want to refuel at Minmus, super. Hell, do BOTH. Get your vessel into LKO dry, send fuel and a tug from Minmus to push the vessel back to Minmus, then refuel it and send it on it's way!

Or just send the tug and keep the fuel at Minmus.

-Duxwing

[LethalDose]

Okay, I'm going to leave everything else alone, because this:

It is a counterpoint because if orbits are reversible, then the increase in velocity due to descending equals the decrease in velocity needed to descend.

is either so incredibly unclear it's meaningless, or so incredibly wrong it's concerning.

The velocity you gain at periapsis, which is the only thing I can think of that you mean by "increase in velocity due to descending" absolutely does not equal the velocity it takes to descend!!! I read this in wikipedia, and most certainly does not say what you are citing here. The only statement I can see about "reversibility" appears to state that acceleration in one direction may be opposed by equal acceleration in the opposite direction.

And if you don't believe me, go try it.

Get into a circular orbit at the same altitude as Minmus. Your orbital velocity will be about 332.9 m/s (both at periapsis and apoapsis, because it's circular, it's all the same). Now, we're going to burn retrograde about 60 m/s (actually 59.18 m/s) to reduce the Pe to 75 km. When you get to that Pe, your speed will be 3216 m/s.

To recap: You loose 60 m/s dV at Ap, and gain nearly 2,900 km/s at Pe.

The decrease in velocity to descend (-60 m/s) nowhere near equals the velocity gained by the descent (2882 m/s).

Maybe that's not what you actually meant by that statement, but then you gotta clear that up because it's going to mislead the crap outta people who don't know better.

[Duxwing]

Okay, I'm going to leave everything else alone, because this:

is either so incredibly unclear it's meaningless, or so incredibly wrong it's concerning.

The velocity you gain at periapsis, which is the only thing I can think of that you mean by "increase in velocity due to descending" absolutely does not equal the velocity it takes to descend!!! I read this in wikipedia, and most certainly does not say what you are citing here. The only statement I can see about "reversibility" appears to state that acceleration in one direction may be opposed by equal acceleration in the opposite direction.

Thanks for correcting my misunderstanding!

And if you don't believe me, go try it.

Get into a circular orbit at the same altitude as Minmus. Your orbital velocity will be about 332.9 m/s (both at periapsis and apoapsis, because it's circular, it's all the same). Now, we're going to burn retrograde about 60 m/s (actually 59.18 m/s) to reduce the Pe to 75 km. When you get to that Pe, your speed will be 3216 m/s.

To recap: You loose 60 m/s dV at Ap, and gain nearly 2,900 km/s at Pe.

The decrease in velocity to descend (-60 m/s) nowhere near equals the velocity gained by the descent (2882 m/s).

Maybe that's not what you actually meant by that statement, but then you gotta clear that up because it's going to mislead the crap outta people who don't know better.

I did a similar experiment confirming your result.

-Duxwing

[LethalDose]

This is the major reason that refueling at Minmus before an interplanetary trip works so well. In addition to needing very little dv to reach Kerbin escape velocity after leaving Minmus, it's also very easy to escape from low Minmus orbit.

[Duxwing]

This is the major reason that refueling at Minmus before an interplanetary trip works so well. In addition to needing very little dv to reach Kerbin escape velocity after leaving Minmus, it's also very easy to escape from low Minmus orbit.

How can I consistently put my periapsis mid my long transfer burn?

-Duxwing

[LethalDose]

How can I consistently put my periapsis mid my long transfer burn?

Time the start of your burn so it's half done at the node, e.g. if your burn is 10 secs long, start it 5 s before the node or before Pe. This is easy to do and frequently done, unless you're talking about something else.

[magnemoe]

Time the start of your burn so it's half done at the node, e.g. if your burn is 10 secs long, start it 5 s before the node or before Pe. This is easy to do and frequently done, unless you're talking about something else.

I think its more about dropping from Minmus so your Pe is close to the transfer node.

My way to do this is to use an spotting satelite in LKO, use it to set up a burn,then leave Minmus a bit before minmus is on the opposite side of the node.

Now you usually have to wait for the burn until the time for the transfer burn, if its a long wait I pull Ap below Mun SOI as Mun has a high chance of messing with your orbit.

I only use this for ships build at a Mimus shipyard as its a bit complex. For refuelig I tend to drop the miner down into LKO, Using a dedicated tanker ship or a tank pushed by a tug. would be even more efficient.

[Duxwing]

I think its more about dropping from Minmus so your Pe is close to the transfer node.

My way to do this is to use an spotting satelite in LKO, use it to set up a burn,then leave Minmus a bit before minmus is on the opposite side of the node.

Now you usually have to wait for the burn until the time for the transfer burn, if its a long wait I pull Ap below Mun SOI as Mun has a high chance of messing with your orbit.

How can the ship see the node the spotting satellite created?

-Duxwing