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# Suggestion on space station altitude

## Question

I'm planning to put to orbit a space station/orbital habitat/refuelling station. I want to ask, what would be the most optimal altitude to put my station in...

I also use MechJeb if that helps...

Many thanks.....

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23 hours ago, Temstar said:

It's not 50/50, you should start the burn later than the 50/50 time. The reason is the during the burn your orbit steadily shifts towards the ideal ejection path and your TWR increases. At some point starting a burn earlier than node time results in an ejection angle that EXACTLY match the ideal ejection angle and that's what you want. Of course under this condition although your ejection angle is exactly correct you will be displaced position-wise from the ideal instant velocity change orbit. But we're talking about a change in position on the order of kilometers over a trip that will take months so it's trivial to correct.

The hard part is to work out the correct time split. The burn definitely start later than the 50/50 burn time but the exact timing is different for each ship and probably different again even for the same ship but different burn lengths.

If you are following prograde, then perhaps you should start slightly later than 50/50 split time. I haven't done the math, but I can see how that might be right. But as discussed in this thread where OhioBob did a bunch of tests, following prograde is less accurate than following the node.  Additionally, if you are following the node, starting before the 50/50 split gives better approximation of your final orbit to the planned orbit.  As a first approximation, splitting the delta-v 50/50 is better than splitting the time 50/50.

I gave an approximation for the split time in that thread: t = T (m/mf) (1 - sqrt(1 - mf/m)), where t is how soon to burn before the node, T is the total expected burn time, mf is the mass of fuel the burn requires, m is the initial total mass. Alternatively, you can rewrite that as: t = T (1-exp(-dv/(2 Isp g0))) / (1-exp(-dv/(Isp g0)), where dv is the delta-v of the maneuver.

The most accurate burn is somewhere between following the node and following prograde, probably varying from initially mostly on the node to finally mostly prograde. Having said all that, 50/50 time, prograde, is accurate enough for me for most purposes.

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As to the real topic on hand, don't decide based on efficiency.  Decide based on what you feel like doing.  There is very little penalty in this game for wasting resources. Therefore the best way to do something tends to fall along two lines:  1) practicality (rondezvous time, time warp limits, cpu limits, etc), and 2) whim/fun/novelty.  I say put up multiple stations, and see which ones you like the best or use the most.

Edited by Yasmy
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Another thing to keep in mind for orbits around Kerbin is that the high/low orbit boundary is at 250km altitude.  So if you want low-orbit situation, stay below that.

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22 hours ago, StarManta said:

I can't believe no one has challenged this statement. That's ridiculous.

The theme among all of the reasons this statement is wrong is planning. If you have every single aspect of your space program planned from here to the end of time, then maybe your statement can be correct. If you can perfectly calculate your delta-V for every mission with little fuel wasted (whether by hand or by mod), then you may not have a use for a place to stash surplus fuel left over after launch or at the end of a mission. If your ships never have an emergency that requires you to quickly deliver them fuel before they crash into the Mun or get ejected from the system, then sure, you won't need that fuel stash around the Mun. If every new craft design you come up with works perfectly on the first go, then you wouldn't see any benefit from having a single design fine-tuned for efficiently launching to a station at a known and practiced orbit, at which point it can be refueled for the rest of its journeys elsewhere.

If all of those conditions describe you, then you won't benefit from having a space station.

I would agree with Geschosskopf

Kerbin stations don't have to much use. Fuel is very cheap and refueling from station take a long time and need parts (RCS, docking rings...). There are other ways to optimize cash.

As for your statement of planing trips, a simple satellite can do as nicely.

I have space stations around nearly every planetary body from Moho to Eeloo. I love them. The only one I don't use is the oldest : the Kerbin station, even if it's the biggest of all.

Well, this is not totally true, I used it once to refuel my space plane so it could rescue badly designed return vehicles from Dres and Jool stations on a high eccentric Kerbin orbit. But without the stations, I would have created a simple rocket and do the same. It was purely RP.

We've discussed a lot on the refueling from Minmus or Mun that take a lot of time and gives very little benefits.

A Kerbin space station would be useful if you decide to use and reuse planetary transfer stages. Futher more, if experiences and contracts would not be validated only when landing on kerbin, but also docking with orbiting station, that would add a RP dimension to the need of Kerbin space stations.

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I've yet to find a use for a Kerbin space station, other than to fulfill a contract.  Of course I usually do one-off missions, i.e., I've yet to build up any kind of space infrastructure. Perhaps in the future I'll discover some useful purpose for a space station, but so far I don't see it.

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14 hours ago, Geschosskopf said:

Well, actually, my ships always do work the 1st time and never run low on fuel

For the second part of that to be true then without using orbital refuelling all your ships must either be single-shot, expendable, vehicles or SSTOs that drag all their atmospheric bits and pieces around space with them.  Both approaches are very wasteful.

If, on the other hand, you DO use orbital refuelling but not stations then i) you have to launch exactly the fuel required when it is required by each single ship that requires it, ii) any excess fuel is wasted when a ship lands back on Kerbin.  Both approaches are quite wasteful.

Perhaps you just have half-empty tanks/ships scattered around the system in any old orbit.  I'd say those are just being hard-to-reach stations, since they aren't doing anything else.  Rendezvous and dock, suck fuel, not full yet rendezvous and dock with another one, suck fuel, rendezvous and dock with SSTO bringing new crew into orbit.  A very complicated and time-consuming (but not necessarily wasteful) way to do things.

I have a small station around most bodies.  When I have any vehicle coming into a system I know it needs to rendezvous and dock with that one thing, in a known and tweaked orbit.  There will be fuel and crew waiting there (unless the ship is bringing them to the station, of course).  My space-vehicles never land, just top-up and move on.  My SSTOs are each designed for the body they operate from.

THAT's efficiency.

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4 hours ago, Pecan said:

#1:  For the second part of that to be true then without using orbital refuelling all your ships must either be single-shot, expendable, vehicles or SSTOs that drag all their atmospheric bits and pieces around space with them.  Both approaches are very wasteful.

#2:  If, on the other hand, you DO use orbital refuelling but not stations then i) you have to launch exactly the fuel required when it is required by each single ship that requires it, ii) any excess fuel is wasted when a ship lands back on Kerbin.  Both approaches are quite wasteful.

#3:  Perhaps you just have half-empty tanks/ships scattered around the system in any old orbit.  I'd say those are just being hard-to-reach stations, since they aren't doing anything else.  Rendezvous and dock, suck fuel, not full yet rendezvous and dock with another one, suck fuel, rendezvous and dock with SSTO bringing new crew into orbit.  A very complicated and time-consuming (but not necessarily wasteful) way to do things.

#4:  I have a small station around most bodies.  When I have any vehicle coming into a system I know it needs to rendezvous and dock with that one thing, in a known and tweaked orbit.  There will be fuel and crew waiting there (unless the ship is bringing them to the station, of course).  My space-vehicles never land, just top-up and move on.  My SSTOs are each designed for the body they operate from.

THAT's efficiency.

#1.  Um, no, wrong on all counts.  I make neaerly zero expendable ships (other than irresistibly lucrative contract stations and bases within Kerbin's SOI, which I never plan to use myself).  Most of my ships are put in space to be employed permanently or to be reused at some other planet.  And I only make the odd Kerbin-based SSTO spaceplane for coolness because they are just as useless as stations and refueling systems in Kerbin's SOI.  Kerbin spaceplanes can't lift the stuff I need shoved to other planets without WAY more trouble than it's worth.  I do, however, make lots of SSTOs (rocket and spaceplane) for other planets, where they make sense, just as do stations and refueling operations out there.

#2.  I never refuel anything in Kerbin orbit, and very few of my ships return to Kerbin.  I'm in the colonization business.  Colonization means permanent, self-sufficient occupation of other planets.  Self-sufficiency requires reusability and thus refueling, but at other planets.  It is NOT efficient to do any of these functions at Kerbin.  And designing ships with excess fuel is inefficient on its face.

• Optimist:  The glass is half full
• Pessimist:  The glass is half empty
• Engineer:  The glass is too big for the job it's doing

#3.  I'm proud of my litter-free space program.  Thanks to TAC Self-Destruct, I leave zero expended boosters floating around in space.  And when I say "expended", I mean it.  See #2 above.  If they've got some dregs left in the tank when I blow them up, it's less than I'd spend chasing them down to reclaim, and definintely not worth the price of the ship needed to do that, nor the investment of my playing time when I could be doing other things.  Within Kerbin's SOI, if you can't already easily afford to buy and lift fresh fuel from the ground by the time you unlock the technology needed to chase down and suck out the dregs in expended boosters, then you're BADLY mismanaging your space program.  And outside Kerbin's SOI, you're making your own fuel while you sleep so there's even less point in chasing down expended stages.

#4.  I do the same thing at other planets, as should be clear by now.  But that's all beside the point.  This thread is about stations in Kerbin's SOI.  I say they're a bad idea unless either you've got very juicy contracts to build the useless things or you're just doing it for potlatch.  If neither of those conditions is true, then I strongly advise against building a station anywhere within Kerbin's SOI.  The numbers (whether measured in the various game currencies or in the amount of your personal time required) just do not justify stations in Kerbin's SOI.

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19 hours ago, Geschosskopf said:

This thread is about stations in Kerbin's SOI.  I say they're a bad idea unless either you've got very juicy contracts to build the useless things or you're just doing it for potlatch.  If neither of those conditions is true, then I strongly advise against building a station anywhere within Kerbin's SOI.  The numbers (whether measured in the various game currencies or in the amount of your personal time required) just do not justify stations in Kerbin's SOI.

And I would say that is entirely dependent on your preferred play-style of ISRU at other planets and ships that never return to Kerbin SOI.  That's all fair enough, of course, but it's only one play-style.

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101,307m. It passes over KSC once every 36 minutes, allowing simplified launch windows for rendezvous and reentry based on time of day. 1° of longitude is traversed every 6 seconds.

Best,

-Slashy

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