Reusable space programme - refuelling and crew return?

[RizzoTheRat]

Anyone here focussing on reusability?

So far I have had a reasonable success with my reusable SSTO lifters, and have a lander & rover design that has worked on the Mun, Duna and Ike.  I'd like to reach the point where I have orbital stations as fuel dumps, comms relays, and crew stopoffs around each planet, so I only need to ferry crews, and possibly fuel around.  a couple of things I've not quite worked out yet though....

For a post launch fuel dump I'm thinking a mining/refining station on the Mun with an orbital refuelling station in a relatively high orbit.  Clearly Minmus would involve using less fuel refilling the station from the surface, but is it worth it for the extra hassle of being on a inclined orbit compared to the rest of the solar system? Plus it's 6 day orbit presumably makes hitting transfer windows easier than Minmus's 49 day orbit?

What do people do about crew returns?  So far when I've been to Duna/Ike I've lugged a small craft based on a Mk1-2 pod to get the grew home.  What I'd like to do is have a reusable vehicle that transfers them to somewhere relatively close to Kerbin, and then a separate reusable lander to get them down.  Not tried it yet but I'm assuming the Mun's inclination makes it a lot easier to aerobrake around Kerbin and get in to a Mun orbit than it would to get to a Minmus orbit, or is it generally going to easier to just carry enough to fuel to get in a Kerbin orbit with limited aerobraking? 

[Brainlord Mesomorph]

Almost everything I do is designed for reuse. I specialize in nuclear landers that double as interplanetary tugs.

dV to land and take off from the Mun will burn a lot of fuel. Minmus is a better choice for fueling up interplanetary missions. The plane change to Minmus is what 20 or 30 m/s? 

aerobraking in to orbit from other planets is difficult.  (aerobraking to reentry is far more reliable.) I usually use thrusters to park reusable ships in orbit. then send up planes to bring down Kerbals.

 

BTW :permanent orbital fuel stations waste a lot of fuel. Once they're empty getting that giant tanker to maneuver up to it and dock with it will burn a quarter of the fuel you're trying to deliver. I send up single-use fuel tankers with extra docking ports. they serve as stations, but when they are empty I deorbit them.

Edited January 18, 2018 by Brainlord Mesomorph

[RizzoTheRat]

Nuclear Lander/Tug is exactly the way I've been heading too.  So far this game I've only been as far as Duna and Ike but my lander towed a fuel dump out to Duna orbit which followon missions to Duna and Ike have used.

I'm being thick on the inclined plane complication as I just realised I can refuel at Minmus and then lift them out of Minmus orbit to a high non-inclined Kerbin orbit at an ascending/descending node before the interplanetary window, but won't I still have issues with the 49 day orbit meaning I miss optimum windows for other planets?  Or does the fuel saving from being out there negate the extra used from being 25 days or so out from the optimum?

As I'm potentially waiting a fair while for the interplanetary window, I'm not too bothered taking a lot of orbits to intercept a space station (I've decided against using life support on this game), so docking doesn't need a massive amount of fuel, with enough time you can get an intercept with only a coupe of pretty small changes.  I'm only looking at a refuelling station in Minmus orbit though as the interplanetary and SSTO crew transfer vehicles can just meet up in Kerbin orbit, and possibly fuel dumps around other planets.  At the moment my lander has it's own drills and refining capability but I don't think that's the most efficient way to do multiple landings.

[Atkara]

I don't use orbital fuel dumps, but orbital refineries instead. Refining ore on demand and converting it into whatever each craft needs (Lf, LOX, Monoprop) on the spot, seems much more versatile to me. Kerbin, Mun & Minmus currently have one around them.

Mun & Minmus refineries are being supplied by ISRU equipped surface miners. I used to supply Kerbin's refinery also, from Minmus. But later on I opted for a combination of a spaceplane and an ore drone. If something is too big to dock with the refinery (which is often the case), the same spaceplane that carries ore, can be configured to bring up fuel, where the corresponding fuel drone will deliver the stuff.

Spaceplanes also bring up crew (and often tourists, since I play career) to LKO and either set for the refinery, where they change vessels, or meet up straight with the vessel -whatever suits the situation better. The same happens with the returning crews/passengers.

With multiple flights typically going on, I rarely have time for aerobraking so, I just get the returning vessels to circularize on their own.

Orbital refineries like these, will be eventually distributed across "my" solar system. They'll be tasked with refueling the landers I'll eventually send there, and the 16-32seater (not counting the MK3 Cockpit in front) "space liners" I've also finalized and scheduled to launch, when the network is complete.

Surface miners have accompanied my expeditions on Duna, Gilly, Moho & Dres. Coming up next is propably Eeloo and then, Jool and it's moons, where I finished satellite deployment last night and boy, was that a task... my head is still ringing

Edited January 18, 2018 by Atkara

[Guest]

I've gone for "waste not, want not" in my current career. So far, apart from a few disposable LF boosters early in the career, all I've wasted is drop tanks and interstage scrap, everything else has been either reusable, recoverable, or durable.

I've developed a heavy lifting SSTO capability so there's no point refining fuel in the Kerbin system; it's easier to loft it up in quantity when needed. However I am building an ISRU station on Pol to support my Jool operation. We will see how that goes.

One thing I've never attempted is asteroid mining, and I have a feeling it might make the Jool activities a fair bit easier as round trips to Pol are not cheap in dV.

[XLjedi]

Is there a benefit to an orbital refinery?   I sorta assumed that converting 30t of ore would result in 5-10t of fuel or far less?   Is there some magical conversion factor built into KSP that some how allows for 100% fuel conversion (or greater) efficiency?

If so, I would certainly opt for an orbital refinery... as it is now, I keep mobile ISRU vehicles on the nice flat "sea" of Minmus for refueling.

 

[RizzoTheRat]

40 minutes ago, Brikoleur said:

I've developed a heavy lifting SSTO capability so there's no point refining fuel in the Kerbin system; it's easier to loft it up in quantity when needed.

That's a good point.  My current SSTO lifter puts 45 tonnes in orbit pretty cheaply, so that's more than an orange Rockomax per launch, but like the idea of refuelling outbound craft a thousand m/s or so further out from Kerbin.

 

48 minutes ago, Atkara said:

I don't use orbital fuel dumps, but orbital refineries instead.

Am I right in thinking ore gives more than it's own weight of fuel when refined so it's more efficient to lift ore than fuel?  I hadn't really thought about that but it rings a bell from ages ago.  I launched a trial Mun mining base and tanker last night, but maybe I need a rethink, however I suppose it still makes sense to have some refining capability on the ground so the tanker doesn't need to land with enough fuel to get to orbit again.

[Guest]

3 minutes ago, RizzoTheRat said:

That's a good point.  My current SSTO lifter puts 45 tonnes in orbit pretty cheaply, so that's more than an orange Rockomax per launch, but like the idea of refuelling outbound craft a thousand m/s or so further out from Kerbin.

Due to the Oberth effect that'll only make sense for certain interplanetary operations though. If you're going to Jool for example it'll cost you about 2000 m/s from LKO but about 2500 from Minmus orbit.

[qzgy]

14 minutes ago, XLjedi said:

Is there a benefit to an orbital refinery?   I sorta assumed that converting 30t of ore would result in 5-10t of fuel or far less?   Is there some magical conversion factor built into KSP that some how allows for 100% fuel conversion (or greater) efficiency?

If so, I would certainly opt for an orbital refinery... as it is now, I keep mobile ISRU vehicles on the nice flat "sea" of Minmus for refueling.

 

Might be some part of an engineer perk? IDK. I do know they convert fuel significantly aster, although I don't know if theres an "ore to fuel" bonus.

For me, my strategy is just stick an ISRU system on when possible. Most of the time I have no need for large scale minmus base refineries or orbital refineries. This is mostly cause I play sandbox.

[XLjedi]

1 minute ago, Brikoleur said:

Due to the Oberth effect that'll only make sense for certain interplanetary operations though. If you're going to Jool for example it'll cost you about 2000 m/s from LKO but about 2500 from Minmus orbit.

Interesting point...  can't say that I knew that.  I have an SSTO that can make LKO with maybe 2100-2200-ish DV to spare (with my rather crude piloting skills).  This particular craft also carries ISRU equipment and can make low Minmus orbit with 4000-4400 DV available.  I had not taken into consideration the Oberth effect, but still seems a better option to stop at Minmus if it's only a 500 dv gain?

[RizzoTheRat]

I hadn't realised the Oberth effect had that big an impact  I'd never really looked at the relative velocities but I guess you're going a hell of lot slower out at Minmus

I tend to be using pretty low TWR craft though, so my burn time from Kerbin to Duna was something like 3-4 minutes for my last mission, presumably that's not going to get as much benefit from Oberth as a more powerful craft that can do more of it's burn at a lower altitude?  So in that case I'm better off spreading the burn over 2 or 3 orbits? I think I need to read up a bit on Oberth

 

[XLjedi]

27 minutes ago, qzgy said:

Might be some part of an engineer perk? IDK. I do know they convert fuel significantly aster, although I don't know if theres an "ore to fuel" bonus.

For me, my strategy is just stick an ISRU system on when possible. Most of the time I have no need for large scale minmus base refineries or orbital refineries. This is mostly cause I play sandbox.

I work in the energy industry and I have to admit, I really always just assumed a 1:1 (or greater) energy conversion ratio was not possible...  regardless of having an Engineer aboard. 

Loss of energy during a refining process is kinda one of those assumptions that is as certain as gravity.  I would be a bit disappointed if you could actually squeeze more juice out of rock than the actual weight of the rock.  I strongly suspect a surface refinery on Minmus or the Mun that lifts liquid fuels to orbit would be far more efficient. 

The idea of an orbital refinery makes no sense to me.  ...but I do admit, I have not vetted the ore/fuel conversion ratio.

Edited January 18, 2018 by XLjedi

[Guest]

3 minutes ago, XLjedi said:

Interesting point...  can't say that I knew that.  I have an SSTO that can make LKO with maybe 2100-2200-ish DV to spare (with my rather crude piloting skills).  This particular craft also carries ISRU equipment and can make low Minmus orbit with 4000-4400 DV available.  I had not taken into consideration the Oberth effect, but still seems a better option to stop at Minmus if it's only a 500 dv gain?

Sure, that makes sense.

I only use SSTOs as lifters. They don't go past LKO (exception: Laythe plane). In space, I have a variety of different types -- landers, shuttles, tankers, relays, probes of various kinds, and so on. The idea is that I loft what I want to loft to LKO and then continue from there; if I want to recover a lander, I fly it back to LKO, pick it up with my SSTO (designed to shield it on re-entry), then bring it back.  So SSTOs go up and down, space stuff goes around in space, and if I need to recover it, I fly it back down to low or medium KO and pick it up with an SSTO. So I haven't built 4000+ m/s planes; in fact my craft usually have at most 3000 m/s on them, with 2000...2200 much more typical. (So far the big exception to that is my reusable Tylo landing system, which has 5300 on the lander itself; tankers of course have theoretically way more but that doesn't really count.) 

@RizzoTheRat A 2-3 minute burn won't noticeably eat into your Oberth effect benefit. I just had an 8-minute burn for Jool and it ended up only maybe 10-20 m/s more than calculated, and I think most of that was cosine losses as I wasn't able to burn prograde the whole way. With time warp it's easy to forget that it'll typically take you 8-9 days to get to Minmus -- a few minutes of burn isn't much compared to that!

[Corona688]

4 hours ago, RizzoTheRat said:

For a post launch fuel dump I'm thinking a mining/refining station on the Mun with an orbital refuelling station in a relatively high orbit.  Clearly Minmus would involve using less fuel refilling the station from the surface, but is it worth it for the extra hassle of being on a inclined orbit compared to the rest of the solar system?

The extra incline is hardly noticeable once you leave Kerbin orbit, there's such a huge delta-V difference between you and the rest of the solar system anyway.

4 hours ago, RizzoTheRat said:

What do people do about crew returns?  So far when I've been to Duna/Ike I've lugged a small craft based on a Mk1-2 pod to get the grew home.  What I'd like to do is have a reusable vehicle that transfers them to somewhere relatively close to Kerbin, and then a separate reusable lander to get them down.

If you wanted to be systematic about it, you could run a shuttle loop between stations on Minmus and Kerbin, powered by fuel mined from Minmus.

4 hours ago, RizzoTheRat said:

Not tried it yet but I'm assuming the Mun's inclination makes it a lot easier to aerobrake around Kerbin and get in to a Mun orbit than it would to get to a Minmus orbit

I don't think it's that easy to hit the mun by aerobraking, unless you plan your mission to the minute and the joule.  The right orbit at the wrong time isn't much help.

4 hours ago, RizzoTheRat said:

or is it generally going to easier to just carry enough to fuel to get in a Kerbin orbit with limited aerobraking? 

Aerobraking will always be more economical than hauling 2km/s of fuel to Duna and back, but I think you should aim for a station in wide Kerbin orbit.  And be prepared to re-enter anyway, or you'll sometimes find yourself bailing out and making for safe orbits on suit RCS.

[Freshmeat]

Considering Minmus as fuel depot leads to a couple of interesting problems in orbital mechanics. I drop off from Minmus orbit timed so the periapsis will be at the correct angle to retrograde when the time comes for an interplanetary transfer. Given that Minmus is in an elliptical orbit, it ends up being a job for Excel. The initial periapsis is rather high so I can correct the inclination from Minmus and get a node with the correct inclination at periapsis. Then I adjust the apoapsis so I can lower the periapsis and hit it at the correct time for the final burn. How low depends on the actual craft, but my rule of thumb is that the burn should start at no more than 20 degrees before the burn, so low TWR interplanetaries tend to start from higher orbits. 

It makes an interplanetary launch an interesting adventure designed to save as much dV as possible, but you need to find it interesting enough to let one departure from orbit last an entire play session.

[XLjedi]

@Freshmeat  ...that's too compelcated for my simple mind to appreciate.

I kinda view an interplanetary launch from Minmus no different than trying to hit a planet from Kerbin.  The distances are so great, it just doesn't seem to matter that much, I'm just happy to hit something within the SOI of a given system!  Then again, I don't always hit my target either.  ;-D  ...mission saved by F5 once again.

 

[Atkara]

3 hours ago, RizzoTheRat said:

Am I right in thinking ore gives more than it's own weight of fuel when refined so it's more efficient to lift ore than fuel?  I hadn't really thought about that but it rings a bell from ages ago.  I launched a trial Mun mining base and tanker last night, but maybe I need a rethink, however I suppose it still makes sense to have some refining capability on the ground so the tanker doesn't need to land with enough fuel to get to orbit again.

No, I think it's the same. X tons of ore, convert to the same tonnage in fuel. It's versatility what I was after:

• If I'm fueling up a NERVA propelled vessel, I'll convert to Lf only.
• if it's conventional, I'll convert to LOX.
• if it's NERVA propelled but is equipped with verniers (which is often the case) I'll fire up Lf & Ox separately, since I rarely want to top the Ox tanks.
• if I'm in need of monoprop, I'll convert to that.

And I'll do this on the spot. Whether the vessel in question is docked on the refinery, or has met up with the miner (which carries it's own ISRU anyway) I'll convert to whatever I need, right there. In the case of the miner, if it has fuel to spare, I'll go hybrid.

Edited January 18, 2018 by Atkara

[Corona688]

3 hours ago, XLjedi said:

I work in the energy industry and I have to admit, I really always just assumed a 1:1 (or greater) energy conversion ratio was not possible...  regardless of having an Engineer aboard.

The full-sized ISRU only has a 1:1 ratio in meaningless "fuel' and "ore" units, work that out in tons and there's a 50% loss.  The ratio is fixed, engineers don't change efficiency just rate.

It's implied that the ISRU extracts hydrogen and oxygen from water in hydrated minerals and ice, so "ore" is inert anyhow, the fuel energy is supplied by solar cells.

Quote

The idea of an orbital refinery makes no sense to me.  ...but I do admit, I have not vetted the ore/fuel conversion ratio.

People will go to heroic lengths to avoid landing the full-sized ISRU, just because it's so obnoxious to design with.  You can't attach radial parts to it, so any traditional design becomes a top-heavy needle, a skycrane of trusses, or a base-assembly problem.

Edited January 18, 2018 by Corona688

[Atkara]

8 minutes ago, Corona688 said:

People will go to heroic lengths to avoid landing the full-sized ISRU, just because it's so obnoxious to design with.  You can't attach radial parts to it, so any traditional design becomes a top-heavy needle or skycrane of trusses.

I don't think my solution would win beauty contest, but I wouldn't call it ugly either...

Here's the orbital refinery too:

Spoiler

Alternate view

 

Edited January 18, 2018 by Atkara

[Corona688]

5 minutes ago, Atkara said:

I don't think my solution would win beauty contest, but I wouldn't call it ugly either...

I neglected a fourth alternative, "very large".  I always try to go small, sometimes pointlessly so, and the full ISRU was a rude shock I found a way eventually though:

Edited January 18, 2018 by Corona688

[XLjedi]

I seem to be spamming craft pics today... 

@Corona688 "People will go to heroic lengths to avoid landing the full-sized ISRU, just because it's so obnoxious to design with.  You can't attach radial parts to it, so any traditional design becomes a top-heavy needle or skycrane of trusses. "

Mobile planet-side ISRU, bit of a monstrosity, but it's not too bad!

https://kerbalx.com/XLjedi/RLV-21-Magic-Hat

However, this whole idea of 1500 units of ore being equivalent to 3000 liquid units (even if conversion is happening in a vacuum?) and requiring zero electricity in the process does have me rethinking the idea of an orbital refinery.  However distastefully unrealistic that might seem, I'm usually quick to say, "Meh, it's just a game."

Edited January 18, 2018 by XLjedi

[Atkara]

2 minutes ago, Corona688 said:

I neglected a fourth alternative, "very large"

That's what you have to do, if you want to be in position to mine and lift 2700 units of ore (3.3k for this craft) from the surface of Ike and land it on Duna, as many, highly lucrative contracts often request. And if you can do that, why not build around it?

[XLjedi]

8 hours ago, Brainlord Mesomorph said:

Almost everything I do is designed for reuse. I specialize in nuclear landers that double as interplanetary tugs.

dV to land and take off from the Mun will burn a lot of fuel. Minmus is a better choice for fueling up interplanetary missions. The plane change to Minmus is what 20 or 30 m/s? 

aerobraking in to orbit from other planets is difficult.  (aerobraking to reentry is far more reliable.) I usually use thrusters to park reusable ships in orbit. then send up planes to bring down Kerbals.

 

BTW :permanent orbital fuel stations waste a lot of fuel. Once they're empty getting that giant tanker to maneuver up to it and dock with it will burn a quarter of the fuel you're trying to deliver. I send up single-use fuel tankers with extra docking ports. they serve as stations, but when they are empty I deorbit them.

A decent interplanetary nuke tug is something I've been kicking around lately...  Although I've been a bit torn between the idea of a larger sized mothership or to go with more of a "Jedi-ring warp drive" style smaller thing to just plug a lander into.

I also approve of that tanker approach for refueling!  I don't see a need to have to intercept and dock twice to get to the fuel.

[XLjedi]

6 hours ago, Brikoleur said:

Sure, that makes sense.

I only use SSTOs as lifters. They don't go past LKO (exception: Laythe plane). In space, I have a variety of different types -- landers, shuttles, tankers, relays, probes of various kinds, and so on. The idea is that I loft what I want to loft to LKO and then continue from there; if I want to recover a lander, I fly it back to LKO, pick it up with my SSTO (designed to shield it on re-entry), then bring it back.  So SSTOs go up and down, space stuff goes around in space, and if I need to recover it, I fly it back down to low or medium KO and pick it up with an SSTO. So I haven't built 4000+ m/s planes; in fact my craft usually have at most 3000 m/s on them, with 2000...2200 much more typical. (So far the big exception to that is my reusable Tylo landing system, which has 5300 on the lander itself; tankers of course have theoretically way more but that doesn't really count.) 

(snip)

I do really like the play-style/idea of dedicated "space stuff"...   I also have a hard time separating myself from the "coolness" component of space planes though.  I've been tinkering with a mothership-type class to move stuffs between planets.  In my latest attempt at a career playthru, I'm also trying to limit the number of items that I have floating around up there.  A science lab corvette that I can essentially move from place to place as I need to is also in the works, having a little trouble on the lifter for that one though.  It has some pretty cool "Orbital Science Attack Missiles" on it.  ...for shooting collected research back to the ground from orbit!  Just have to figure out how it's going to get into orbit to begin with? <sigh>

Edited January 18, 2018 by XLjedi

[RizzoTheRat]

3 hours ago, Corona688 said:

People will go to heroic lengths to avoid landing the full-sized ISRU, just because it's so obnoxious to design with.  You can't attach radial parts to it, so any traditional design becomes a top-heavy needle, a skycrane of trusses, or a base-assembly problem.

A lot of people don't like asymmetric designs either, the full size ISRU plus a medium Thermal Control System weighs 4.5 tonnes, the same as an empty Ore tank and a Hitchiker.  This was my now aborted design for a self landing Mun mining base, obviously it's not perfectly balanced but its close enough that the torque can handle it, it also wouldn't work if you were planning on taking off again with a load of ore, but it was only intended to land with the bottom tanks in use.