Interplanetary How do you do it (not Eve or Duna)

[SwissSpace93]

Hello

I want to start a Moho-Mission Program in Sandbox, i was already on Duna and deployed MapSat's arround Eve.

My idea was, to build a Rocket that do the escape Burn to Kerbin SOI edge. Then i decouple the Interplanetary stage and recover the Orbit-Rocket.

Or is it better to assemble a Transfership in Low Kerbin Orbit and travel with this directly?

Delta-V maps are telling me i need about 16km/s to bring back the Crew (i added some delta-V as reserve), i saw Videos from poeples travelling to Moho with little Planeshaped Vessels and other peoples that are using big Rockets with Nuclear enignes to travel.

[Aegolius13]

15 minutes ago, SwissSpace93 said:

My idea was, to build a Rocket that do the escape Burn to Kerbin SOI edge. Then i decouple the Interplanetary stage and recover the Orbit-Rocket.

It's better to do your entire burn in low Kerbin orbit,  due to the Oberth effect.  If the burn takes too long,  you can split it into several passes (periapsis kicking). 

 

17 minutes ago, SwissSpace93 said:

Or is it better to assemble a Transfership in Low Kerbin Orbit and travel with this directly?

There is no compelling reason  to assemble your ship in orbit,  as opposed to launching it in one big piece.   You certainly can if you find it fun,  but you'll spend delta v rendezvousing, have floppier joints,  etc.  But anyhow,  as mentioned above, best to do your whole burn from LKO.

You may also want to look into the alternative method to get to Moho, by launching when Kerbin is at an ascending or descending node relative to Moho. There are a few threads on here explaining the details. 

[SwissSpace93]

37 minutes ago, Aegolius13 said:

It's better to do your entire burn in low Kerbin orbit,  due to the Oberth effect.  If the burn takes too long,  you can split it into several passes (periapsis kicking).

That makes sense, but when i burn at Periapsis then the Oberth is working like when the Rocket is in a LKO.

My Idea was this:

[Zhetaan]

8 minutes ago, SwissSpace93 said:

That makes sense, but when i burn at Periapsis then the Oberth is working like when the Rocket is in a LKO.

That's actually nominally better than burning at LKO.  Coming down from a higher orbit means that you are going faster when you reach periapsis.  Of course, most of the advantage is lost because you had to burn to get the high apoapsis in the first place (Oberth gives much better multipliers on hyperbolic flyby trajectories), but by splitting the burn into multiple parts and doing both at the periapsis, you do get a bit of extra benefit.  That type of manoeuvre is called a periapsis kick.

I will warn you, however, that your timing will be close.  You may not have the time to both de-orbit your booster and complete your next kick unless you have a mod that takes care of de-orbiting for you, such as StageRecovery; you may prefer to let your booster go round again and de-orbit it after your transfer stage leaves Kerbin's SOI.

Edited November 21, 2017 by Zhetaan

[Aegolius13]

16 minutes ago, SwissSpace93 said:

That makes sense, but when i burn at Periapsis then the Oberth is working like when the Rocket is in a LKO.

My Idea was this:

Ahhh, I see.  I thought you actually meant barely leaving the Kerbin SOI, and then doing the rest of the burn to Moho out in deep space. 

Your actual plan looks good.

[SwissSpace93]

12 minutes ago, Zhetaan said:

You may not have the time to both de-orbit your booster and complete your next kick unless you have a mod that takes care of de-orbiting for you, such as StageRecovery; you may prefer to let your booster go round again and de-orbit it after your transfer stage leaves Kerbin's SOI.

That was only an example i can deorbit the booster when the Spaceship is on Escape or Transfer then i have enough time for this

[Helmetman]

2 hours ago, SwissSpace93 said:

Hello

I want to start a Moho-Mission Program in Sandbox, i was already on Duna and deployed MapSat's arround Eve.

My idea was, to build a Rocket that do the escape Burn to Kerbin SOI edge. 

As stated by aegolius13, it's better to make use of the Oberth effect. Some basic calculus will evaluate this, but just see Wikipedia for some basic to mid depth information on the maneuver.
Burning closer to the Pe of the departure planet (Kerbin in this case, but accounts to every gravitational body) for a escape trajectory is more efficient then doing the interplanetary burn later on.

So getting into a escape trajectory and then doing a interplanetary burn is more costly Delta-V wise.
To get to Moho I would use Eve as a gravity assist to change your inclination around the ecliptic to match that of Moho's. You need next to no Dv for this other then a well executed fly by (gravity assist) of Eve.
Matching it's inclination (Moho's orbit angle around the sun) will deduce the Dv required to slow down at Moho.
It's also important that you match Moho on its Apoapsis around the Sun. Kerbin has a completely circular orbit. Moho has a somewhat considerable elliptical orbit of 6.3 million Kilometers by 4.2
 million kilometers around the Sun.

Adding to that is that Moho is much closer to the Sun overall. So the relative speeds are much greater on top of the previous mentioned fact. This also means that the penalty of slowing down between moho's Pe and Ap around the Sun is much greater then that of any other planet.
This means that with a inefficient approach when not minding inclination or Moho's Pe around the Sun but using a direct approach from Kerbin to Moho you can need as much as 6000 Delta V to get into Moho orbit upon arrival during a unfavourable launch window.
Taking the efficient approach when minding a inclination change and arrival at Moho's Ap then you can get as low as 3200 m/s Dv (maybe even less). For this you pick the right launch window and you'll use Eve to lower your Pe around the Sun and change the inclination.

2 hours ago, SwissSpace93 said:

 Then i decouple the Interplanetary stage and recover the Orbit-Rocket.

Not sure what you mean by this. Do you mean you have one stage burning to SOI escape, then undock and recover that stage back at Kerbin?
As in, is it a recoverable launch system your getting at?
 

2 hours ago, SwissSpace93 said:

Or is it better to assemble a Transfership in Low Kerbin Orbit and travel with this directly?

 So the answer to this is "Yes" 
Not just in Moho's case but in any case. 
Also, you don't need to assemble anything in LKO. It's perfectly possible to get crew and some science equipment to Moho in a single launch. Unless you have a potato computer that can't run on many parts, then I would do multiple launches and assemble what's required in Orbit.

2 hours ago, SwissSpace93 said:

Delta-V maps are telling me i need about 16km/s to bring back the Crew (i added some delta-V as reserve), i saw Videos from poeples travelling to Moho with little Planeshaped Vessels and other peoples that are using big Rockets with Nuclear enignes to travel.

The planeshaped vessels are probably SSTO's using ION engines or a combination of that with LF and LF/O engines (ION engines is the engine with the blue exhaust)
ION engines are often optimized for low volume, drag and weight. ION engines are very low powered and not much fun to play with if you value your real life minutes. But they're very efficient and only work fluently with a lighter less complicated vessel to deduce part count and weight.
Nuclear rockets may do the same but are bulkier due to stats (weight and isp) of the Nerva engine. So that's why the nuclear rockets are larger while doing the same.
Both methods can be used for transfer to Moho and back. ION engines are way to small for considerable payload. So if you bring multi tons to the scene, go the nuclear route and only use a ION on the latter stages if that turns out beneficial in deducing total mass, parts at launch. 
Moho missions using ION engines are often a probe or 1 to 2 crew vessels with the only intention to land a kerbal there and do a few small experiments and get back to Kerbin again.

You only need about 12.5 km/s Delta V to get to Moho and back.

3500 m/s to get into LKO. (can be less if your going for optimal efficiency)
1670 m/s to get a Moho encounter (can be less, about 1100 m/s using Eve as a gravity assist)
3200 m/s to slow down at Moho.
1800 m/s to land at Moho and return to Orbit.
2370 m/s to get back to Kerbin (1570 m/s Dv when using Eve to assist back to Kerbin)

So that's 3500 + 1670 + 3200 + 1800 + 2370 = 12.540 Dv and not 16 km/s. And it's going to be less if you take the Dv shortcuts using the gravity assists. But I haven't thrown spare Dv numbers into the mix so I'll add up a couple of hundred for the entire mission.
Have you verified the data of the Dv sheet posted (wherever the source of this Dv sheet is located)

 

 

 

Edited November 21, 2017 by Helmetman

[Spricigo]

Instead of the booster pushing the ship only to the edge of the SoI and decoupling you may boost all the necessary deltaV for the transfer and keep some extra fuel on the booster for bringing back inside the SoI and then recover/re-utilize the booster.

 

[SwissSpace93]

12 hours ago, Helmetman said:

Have you verified the data of the Dv sheet posted (wherever the source of this Dv sheet is located)

I dont checked the deltaV,but i aded very much dV today i'll start building the Rocket

(MapSat is easier because it need no return dV)

12 hours ago, Helmetman said:

14 hours ago, SwissSpace93 said:

 Then i decouple the Interplanetary stage and recover the Orbit-Rocket.

Not sure what you mean by this. Do you mean you have one stage burning to SOI escape, then undock and recover that stage back at Kerbin?
As in, is it a recoverable launch system your getting at?
 

i want to remove the Debris, to keep my Sandbox Universe clean. So i want to bring the booster back (if it is reusable or just blow it up in Kerbin athmosphere).

[Superfluous J]

I like your plan so much I may try it myself. You're basically doing a periapsis kick and stage at the same time.

A++ would transfer again.

[FancyMouse]

The biggest benefit of this plan is when there's a large inclination when ejecting. This method can correct inclination at apoapsis with minimal fuel, and then you can just burn prograde to eject, saving about up to a hundred m/s or so if the original burn (e.g. suggested by TWP) is like 2km/s prograde and 1km/s normal. It also allows an extra stage if one doesn't want to leave space debris. I do this plan a lot when leaving for Jool from Kerbin directly, for example.

It's pretty useless for helping super-low TWR ejection - the 1km/s to burn to edge of SoI is usually less than half of the total dV required (I assume by using Ions you would want to go somewhere further than Duna/Eve). So the final ejection still burns more than half the delta V, which doesn't make the situation any more reasonable.

[Laie]

On 11/21/2017 at 10:04 PM, Spricigo said:

Instead of the booster pushing the ship only to the edge of the SoI and decoupling you may boost all the necessary deltaV for the transfer and keep some extra fuel on the booster for bringing back inside the SoI and then recover/re-utilize the booster.

Done that a long time ago and, at least in the context of going to Jool (that is to say, ~2km/s transfer -- ain't Moho even more than that?), it was more effort than I expected at first. Still technically worthwhile, but... well. Done it once, won't do again.

At comparable effort, and much less fuel, you can send the booster on a cruise nearly as long as the main vessel, to come back and encounter earth again at a later time. Works well with destination Jool or Eeloo, not sure about the inner planets.

 

[Kryxal]

I might be a good idea to decouple your booster far earlier, and do a larger burn lower down to shorten the orbital period if you plan to deorbit it before doing the ejection burn.  For that matter, you could use a larger booster if you have the extra delta-v to abort your system exit.

[SwissSpace93]

My technology Kerbals have build a new Orange rockomax Fueltank, without oxidizer in it but with the 2x Liquidfuel.

They telled me something about copy folder and config editing, i dont know what they actually did.

Now i have 2 different Tank that looks sam, but have other fuels in it.

[SwissSpace93]

I have now 3 MapSat's arround Moho!

(i posted Images in the "What did you do today in KSP" -Topic)

The transferstage has 71m/s Fuel in it, when i was finished.

Now i want to do the Kerbaled "Moho-2", this is harder with Lifesupport but i have a plan. I use Eve as assist to keep the fuel for the return.

[wumpus]

On 11/21/2017 at 12:56 PM, Aegolius13 said:

It's better to do your entire burn in low Kerbin orbit,  due to the Oberth effect.  If the burn takes too long,  you can split it into several passes (periapsis kicking).

"Several passes" works on Duna/Eve, but going much further afield pretty much means you need as much delta-v going beyond Kerbin's SOI as you need to get to the edge.  Still, breaking it into 2 cuts the thrust needed in half (or your lack of Obereth gains in half).

I'd also look into Juno slingshots (to anywhere past Duna/Eve).  Of course, typically what you really need is an alignment change, so in that case it might be better to kick off Duna, Eve, or any you can reach while it intersects with the plane you need.

[SwissSpace93]

My Crew on Moho-2 played with the Throttle-switch and now they are in clockwise Orbit and the unmanned lander is against clockwise orbiting.

So they need the fuel to Rendevous and land on Moho, mit idea was now to send a Supplyship when Kerbin is at the AN or DN of Moho to get 0° Incclination and go to Moho.

This is my next KSP-Challenge

- Lifesupport for 3.5 Years from now

- No missing crew Respawn