Best place for an interplanetary launch facility?

[leptoon]

What would you say is the best place near Kerbin or on/near one of its moons to launch interplanetary spacecraft from? I've already begun a base on Minmus but gravity is so low combined with an icy surface, I have to weigh the modules down at least 25 tons just to keep them from sliding around.

Edited July 17, 2015 by leptoon

[Evanitis]

In my opinion, Minmus surface is the most convenient for fueling while LKO is the most convenient for launching. I used a station on Minmus orbit for a while, but I found it too tedious to shoot for ideal ideal transfer angles from that inclination. These days I refine on LKO. Getting the ore there might be a hassle, but I don't have to do that too often and it's easy compared to an interplanetary mission. It would be the same if I kept the ISRU on Minmus and I only transfered the fuel. I believe that's the most cost-effective way, as the ships I launch only have to carry enough fuel to reach Kerbin orbit.

[leptoon]

I see... Thanks for the input.

Edited July 17, 2015 by leptoon

[Wemb]

Yup, I'd say minmus too - easy to get to, low dV to move fuel up from the surface - big flat open areas for landing on, low dV to get out of it's orbit, and when you're there, you're already most of the way out of Kerbin's system too.

Low gravity can be a problem with things moving about - but the good news is that reaction wheels can generally be enough to correct anything that's beginning to topple over when you land - and, if battery and solar power allows, can be enough to keep a vessel perched in some every funny angles even when landed on a slope.

You do have to be careful eva-ing - I've pushed rockets over by accident myself..

Wemb

[Nich]

What is the most cost effective way to leave Miniums? Burn down to Kirbin for oberith effect or just leave directly from Minimus?

[Wemb]

What is the most cost effective way to leave Miniums? Burn down to Kirbin for oberith effect or just leave directly from Minimus?

To get a slingshot. But getting the timing and trajectory right to do without having to do more expensive corrections afterwards? Might be more difficult than it's worth.

Sorry - edit - not a slingshot - forgot that they're not the same thing. But still - getting the end tradjectory right might be too difficult to make it worth much.

Wemb

Edited July 17, 2015 by Wemb

[Red Iron Crown]

To get a slingshot more Oberth Effect. But getting the timing and trajectory right to do without having to do more expensive corrections afterwards? Might be more difficult than it's worth.

Fixed for you. Might seem pedantic but slingshots and the Oberth Effect are really confusing at first, conflating the terms only makes things worse.

[Jouni]

My standard orbits for interplanetary departures are (just above) 120 km, 160 km, 240 km, and 600 km. Higher orbits are more expensive to reach, but low-TWR transfer burns are more accurate from them. Transfer burns require essentially the same delta-v from all of these orbits.

Higher orbits are also useful, because they allow higher time warp multipliers (at 120 km, 240 km, 480 km, and 600 km), and rendezvousing with ships at them requires less waiting. The 160 km orbit also reduces lag, because the games starts using a less detailed model of Kerbin beyond it.

[Yasmy]

Here's the rough delta-v cost for going interplanetary either via dipping down to the parent for a powered slingshot, directly from a moon, or from low orbit around the parent. These calculations assume no inclination changes and zero eccentricity orbits, so it can be significantly off. I post it more as a general guideline.

I'm going to agree with others that departing from LKO is easiest. Bringing fuel from Minmus to an LKO depot is a lot more wasteful, but so much easier. Fuel tugs, being almost all tankage, tend to be much easier to fly and dock than interplanetary vessels, and can have fabulous total delta-v. Timing is also trivial from LKO. That said, if your interplanetary vessel is low on total delta-v, topping off at Minmus could enable you to complete a mission which you couldn't if you departed directly from LKO.

Transfer burn delta-v [m/s]. Does not include capture at the target.

  Moon -> Target:  Moon->Parent->Target Moon->Target Parent->Target
 Gilly ->   Moho:            776             1367          1643
 Gilly -> Kerbin:            507              497          1373
 Gilly ->   Duna:            775             1364          1642
 Gilly ->   Dres:           1308             2476          2176
 Gilly ->   Jool:           1648             3048          2517
 Gilly ->  Eeloo:           1786             3264          2655
   Mun ->   Moho:           1135             1509          1699
   Mun ->    Eve:            462              348          1024
   Mun ->   Duna:            498              414          1060
   Mun ->   Dres:            987             1279          1550
   Mun ->   Jool:           1361             1840          1924
   Mun ->  Eeloo:           1520             2065          2084
Minmus ->   Moho:            943             1958          1699
Minmus ->    Eve:            270              440          1024
Minmus ->   Duna:            306              567          1060
Minmus ->   Dres:            795             1700          1550
Minmus ->   Jool:           1168             2319          1924
Minmus ->  Eeloo:           1328             2559          2084
   Ike ->   Moho:           1970             2159          2118
   Ike ->    Eve:            908              975          1055
   Ike -> Kerbin:            464              421           611
   Ike ->   Dres:            658              671           806
   Ike ->   Jool:           1158             1266          1306
   Ike ->  Eeloo:           1382             1518          1529
Laythe ->   Moho:           2228             1273          3135
Laythe ->    Eve:           2109             1131          3015
Laythe -> Kerbin:           2049             1063          2955
Laythe ->   Duna:           1979              986          2886
Laythe ->   Dres:           1906              909          2812
Laythe ->  Eeloo:           1893              896          2799
  Vall ->   Moho:           1835             1334          3135
  Vall ->    Eve:           1715             1099          3015
  Vall -> Kerbin:           1655              980          2955
  Vall ->   Duna:           1586              844          2886
  Vall ->   Dres:           1512              702          2812
  Vall ->  Eeloo:           1499              678          2799
  Tylo ->   Moho:           1807             1298          3135
  Tylo ->    Eve:           1688             1141          3015
  Tylo -> Kerbin:           1627             1067          2955
  Tylo ->   Duna:           1558              988          2886
  Tylo ->   Dres:           1484              913          2812
  Tylo ->  Eeloo:           1472              901          2799
   Bop ->   Moho:           1452             1652          3135
   Bop ->    Eve:           1332             1275          3015
   Bop -> Kerbin:           1272             1068          2955
   Bop ->   Duna:           1203              811          2886
   Bop ->   Dres:           1129              510          2812
   Bop ->  Eeloo:           1116              455          2799
   Pol ->   Moho:           1335             1739          3135
   Pol ->    Eve:           1216             1332          3015
   Pol -> Kerbin:           1156             1104          2955
   Pol ->   Duna:           1086              815          2886
   Pol ->   Dres:           1013              462          2812
   Pol ->  Eeloo:           1000              394          2799

Edited July 17, 2015 by Yasmy

[Sharpy]

Departure from Minmus kills the benefits of Oberth effect. Transfer from LKO to Duna can be only 80m/s more than from LKO just outside the Kerbin SOI. And transfer to Duna from outside Kerbin SOI is more than transfer from LKO - even counting the dV needed for escape of Kerbin SOI.

Probably the best transfer would be dropping from Minmus into LKO (after refuelleing) without circularizing, just depart on the right trajectory with a small burn at the periapsis. Although timing that right may be more than tricky...

Edited July 17, 2015 by Sharpy

[Yasmy]

Higher orbits are also useful, because they allow higher time warp multipliers (at 120 km, 240 km, 480 km, and 600 km), and rendezvousing with ships at them requires less waiting. The 160 km orbit also reduces lag, because the games starts using a less detailed model of Kerbin beyond it.

I do this around other bodies as well. I place my station or return vessel just high enough to get the minimum warp I need to maintain sanity. I hate having to switch vessels to warp fast enough to do something.

[xtoro]

If your plan is to refuel before leaving Kerbin's SOI, Minmus is best. Yes you need to correct inclination on the way, sometimes, but if you compare having a mining facility on the Mun to Minmus, you'll spend more dv launching from the Mun than from Minmus+inclination change.

[Yasmy]

- even counting the dV needed for escape of Kerbin SOI.

Everything else you said was correct, but this isn't. Duna doesn't cost too much to get to from interplanetary space near Kerbin. Same goes for Eve. Occasionally going from a moon directly interplanetary is cheaper than going from LKO, and sometimes it is even cheaper than dipping down to LKO to perform the burn. For instance, going directly to Duna or Eve from the Mun is cheaper than dipping down to Kerbin.

Edited July 17, 2015 by Yasmy
spelling

[ajburges]

LKO

+ Optimal Oberth effect

- logistics of refueling

MKO (250 km)

+ Oberth effect

+ higher timing tolerance

+ higher acceleration tolerance

+ lower resolution textures used for Kerbin at higher altitude. Less lag during assembly

- fuel logistics

- less Oberth effect

Launch from Minmus

+ simple fuel logistics

+ different/delayed launch windows

- very little Oberth effect

- orbital inclination

Kerbin gravity assist from Minmus

+ simple fuel logistics

+ even more Oberth effect

+ enroute inclination correction

- very complex manuvers with tight timing

Pick the one whose advantages align to your needs. Due to part counts, you never want to assemble a multi module behemoth in LKO. Once you assemble in MKO just launch from there. OTOH a single launch mission from Duna is simplest to burn straight from LKO. If you don't want to maintain a fuel convoy to LKO to support refueling, you either need to burn funds on refuel missions from the surface or visit Minmus. (or capture a large asteroid)

[Red Iron Crown]

You can't use Kerbin for a gravity assist when leaving from Minmus.

[xtoro]

You can't use Kerbin for a gravity assist when leaving from Minmus.

Depends how he's using the term. Doing the action of a gravity assist is not possible, but using Kerbin's gravity to assist you in accomplishing the Oberth Effect is correct

[Red Iron Crown]

Dropping periapsis to get more Oberth effect is not a gravity assist. That was sort of my point, and as I said earlier in thread it may seem pedantic but gravity assists and the Oberth Effect are confusing concepts for many (they certainly were for me when i learned about them), conflating the terms only makes things worse.

[xtoro]

Oh I know, was just joking, I'm sure he didn't mean it that way. The easiest way to explain, I think, is that you can't leave a body's SOI and use its parent's body for a gravity assist. Same as you can't use the Sun (Kerbol) for a gravity assist unless you're outside that sun's SOI to begin with. Those cases would be considered the Oberth Effect.

[jlcarneiro]

Great topic and better discussion, thanks!

Do you know of some tutorial (or video) that explains the difference between Oberth Effect and gravity assist? And (better yet) a video that shows such maneuver (e.g. from Minmus to Duna through Kerbin periapsis)?

[AaronLS]

You can't use Kerbin for a gravity assist when leaving from Minmus.

Being pendantic is fine if not discarding the essence of what was conveted. If you want to correct terminology then say "that is called X, Y is the wrong term for that". As is it sounds like you're challenging the essence of what others are proposing rather than clarifying terminology.

[xtoro]

Being pendantic is fine if not discarding the essence of what was conveted. If you want to correct terminology then say "that is called X, Y is the wrong term for that". As is it sounds like you're challenging the essence of what others are proposing rather than clarifying terminology.

Gravity assist is a tricky terminology and I wish it had its own name to make it clearer. But I do agree with Red that they are not the same thing...

Great topic and better discussion, thanks!

Do you know of some tutorial (or video) that explains the difference between Oberth Effect and gravity assist? And (better yet) a video that shows such maneuver (e.g. from Minmus to Duna through Kerbin periapsis)?

I explained it in the post above yours (may have been ninja'd)

[mhoram]

Do you know of some tutorial (or video) that explains the difference between Oberth Effect and gravity assist? And (better yet) a video that shows such maneuver (e.g. from Minmus to Duna through Kerbin periapsis)?

Here are two posts that try to explain how both work:

Oberth Effect

Gravity Assist

Edited September 26, 2015 by mhoram
typo

[ajburges]

You can't use Kerbin for a gravity assist when leaving from Minmus.

But if you also use your Oberth burn trajectory to modify ejection angle, it's back to being a gravity assist. Given a month long orbital period, chances are you want to play with your ejection angle as well as realize greater Oberth gains.

The two are not mutually exclusive manuvers (as if they weren't confusing enough in usage)

[Sharpy]

The "dumbed down" explanation would be that Oberth maneuver is a powered Gravity Assist, and vice versa.

A normal gravity assist requires entry and departure at specific angles relative to the assisting body's trajectory (in most intuitive way, if "front" is the direction towards which the body (a moon, a planet) is heading, passing "behind" speeds you up, passing "in front" slows you down).

Oberth effect only requires you to move fast - the faster you move the more actual speed/trajectory change you can squeeze out of the same delta-V. Both speeding up and slowing down (but not so much sideways). That means you can tweak your entry and exit angles as much as you like, just do it near periapsis to get the most out of your fuel.

Of course one doesn't exclude the other. You can get much more speed out of combining Oberth maneuver and a gravity assist than from either of them. It's also pretty hard to perform an Oberth maneuver without performing a gravity assist at the same time - after all you are flying by a body, and it will affect you *somehow* (possibly thwarting your Oberth maneuver benefits if you entered an assist that acts in the opposite direction than your burn...)

Also, while gravity assists are always about "smaller scale" flyby affecting a "larger scale" speed - a moon flyby affects your orbit around a planet, a planet flyby affects your orbit around the sun - you can't perform a Kerbin gravity assist to change your Kerbin orbit - Oberth maneuver is independent of these.

Say, you want to get a capture - enter orbit of Eve. If you only skirt its SOI, and start braking, you'll spend a lot of fuel to get the periapsis near the planet's atmosphere. But if you enter at such an angle that you're almost skirting its atmosphere, then burn retrograde at the periapsis, you'll get a capture (an orbit) in a fraction of the delta-V; as you approached it, its gravity was pulling you in and sped you up considerably, making your burn much more efficient - using Eve gravity for changing your velocity relative to Eve. (If you wanted to try capture using gravity assist, you'd have to use Gilly for braking. But Gilly being so small and light wouldn't be much of assistance - the heavier the body the stronger the effect, simply because you're "falling" faster.)

[Sharpy]

For instance, going directly to Duna or Eve from the Mun is cheaper than dipping down to Kerbin.

Mun yes, Minmus no. Mun is close to Kerbin enough that you need quite a bit of delta-V to drop your periapsis to LKO. Note how the farther the orbit the slower the orbital speed and the less you need to brake to get the periapsis all the way down. So, getting from Minmus to LKO periapsis is very cheap. And again, orbital speed of Mun is high enough that Oberth effect for departure is not insignificant.