Mission to Moho. any tips?

[Callmedave]

In my 1.1.2 career mode i have picked up a remote tech contract to get satellite network set up around Moho.

Ive built a single launch vehicle with 4 satellites attached which is proven (same design for Kerbin, Mun and Minmus sats) The delivery section can be used as a fifth satellite too if required.

Ive adapted it to have enough Dv (with about 20% surplus) 

Does anyone have any tips for this contract. I'll post an image of the craft and contract when i get back home if anyones interested.

[Foxster]

Umm, general tips? Well, every time I take a craft to Moho I seem to use loads more dV than I thought I needed. It's a long way, there's no atmosphere for aero braking but you come in fast, the gravity is fairly high and the terrain rugged, which all means dV is easy to waste. So, I tend to pack the biggest margin of dV I can. 

[Hodari]

Never had much luck with Moho, so all I can say is that the capture burn will probably take WAY more dV than you think, so be prepared for that.

[Aegolius13]

I just got my first probe into Moho orbit after two... let's just call them flybys (one mission I was actually able to salvage by redirecting to Eve).  I would echo the suggestion of bringing way way more delta-v than the launch planner says you're going to need.  With the huge velocities involved, even a small deviation from the ideal launch can lead to much larger capture burns.

On that topic, if you're not going automatic with MechJeb or whatnot, fine-tune the crap out of your maneuvers to make sure your transfer orbit is as close to tangent to Moho's orbit as humanly possible.  Once I get an encounter, I like to check this by putting a maneuver node at Moho periapsis and seeing how much retrograde delta-v it takes to get a stable orbit.  Of course, you will probably need to fine-tune after each burn along the way.

It helps to have a decent TWR on the capture burn, since you'll and you'll be flying by very fast and will have a short time to lay down the necessary braking burn.  I'm sure people had done it with an ion thruster, but sounds like a very tricky proposition.  Which is too bad - Moho could otherwise be great ion probe territory due to the massive delta-v requirements and ample solar energy.  

Finally, I know some folks have come up with plane change tricks to avoid a huge plane change burn in solar orbit.  I haven't really figured this out yet, but it's discussed here:

http://forum.kerbalspaceprogram.com/index.php?/topic/134892-whats-the-best-way-to-get-to-moho/

 

[Violent Jeb]

For moho, the capture burn is almost the same as your transfer burn. if you want exact numbers its around

2k dv to transfer and

2k dv to pull into orbit

I believe your orbital velocity is around 700 m/s, so if you'd like to land you'll need a good 800dv for a suicide burn to land.

Note that you'll be moving pretty quick when you get to moho, so you'll need a twr at least .6 or so in order to slow down close to apo, without incurring big losses.

The transfer time is short, the encounter isn't too terrible, and iirc moho has the most frequent optimal transfers of any other planet, so you can basically expect an optimal transfer within 30 days at any given time.

Edited June 24, 2016 by Violent Jeb

[Vaporized Steel]

 

Violent jebs DV estimates are correct. But if you use a normal homan transfer for Moho you will need more then that.
What you can do to get to that 2K dv estimate is in 2 ways.
Either you can directly transfer to moho from kerbin orbit. To do this launch your rocket on to a inclination around Kerbin. How much is dependent on where you'll meet Moho. Moho is on a inclined orbit around the sun, thus has a incline orbit against the ecliptic. Don't know what the Ecliptic is. Google it?

That means either south or north depending on whether Moho is North at the position of intercept versus the ecliptic or south. Using maneouvre node this can be 35 north or south. That means you don't want to launch to the west 90degrees on kerbin but either 125 degrees [South] or 55 degrees [North]

Also you want to make sure you meet Moho at it's periapsis around the Sun when you encounter it. Moho goes around the sun several times so you can't eyeball where it will be. You will need the interplanetary guide and calculator.

I can't remember the best time to launch to moho to meet it at it's periapsis as I haven't travelled to Moho in quite some time. But the best launch windows are stated on the internet. Maybe someone else can eleborate on that.

On that launch window you'll meet Moho at a certain place and time that is in some way inclined to the ecliptic. If you know how much that is at that time, you'll know in which direction you'll have to launch from kerbin in between 55degrees North or 125 degrees south.

While this may be difficult to understand, and I hope your willing to learn what inclined orbits versus the ecliptic mean to know your orbit inclination around Kerbin there is a simpler way imho which still requires you to learn something which is gravity assists.

The 2nd method is that, gravity assists!

This also saves alot of extra Delta V.

You can launch in a 90 degree equatorial orbit around Kerbin and launch to Eve, and use Eve as a gravity assits to both lower your periapsis around the Sun to get close to Moho (you still need some extra delta V to raise it lower), and to change your inclination around the Sun to reach Moho.

When you use a normal Hohman transfer without changing your inclination around the Sun to match Mohos you will have alot more velocity to cancel when you reach Moho, not 2K but more like 3 to 4K delta V just to get into orbit, not to mind landing.
I use ION engines when I get to MOHO. This makes you a very light vehicle with loads of delta V to get the job done. But I do use the method always whereby I get into Kerbin a inclined orbit around Kerbins equator. Thus I don't launch 90 degrees so that when I get to moho I don't have to burn extra delta V in a plus or minus radial direction to deduct inclination velocities.

You may not want to go to the technical stuff of things, thus you'll use a Hohman transfer. The same you'll use to get to Duna, eve or the Mun for instance. If so, make sure you have atleast 3.5K delta V just to get into Moho orbit (not mentioning The DV to get there or landing stage to get back home)

 

Edited June 24, 2016 by Vaporized Steel

[DD_bwest]

what i always do,  is go overboard on the Ions,   Because of how close you get to the sun, your panels will be pumping out the juice,  so you can get away with using more and more ion drives.

i also go overboard on the deltaV, so that i can just circ rather close to moho, then make an encounter so that my approach speed is significantly shorter.

[Jarin]

4 hours ago, Aegolius13 said:

It helps to have a decent TWR on the capture burn, since you'll and you'll be flying by very fast and will have a short time to lay down the necessary braking burn.  I'm sure people had done it with an ion thruster, but sounds like a very tricky proposition.  Which is too bad - Moho could otherwise be great ion probe territory due to the massive delta-v requirements and ample solar energy.  

As a general idea if you do go ion... quicksave an hour or two outside of Moho's SOI. I had to burn more than 30 minutes before SOI changeover with my last ion probe. If you don't like quicksave/revert, just remember that "half estimated burn time" does NOT work for long burn captures. If you have an hour burn, you'll be hurtling past PE with 30 minutes left on your burn and keep sailing right on by. 

[KerikBalm]

It is very important t get the transfer burn right.. if you aren't coming in tangent to Moho's orbit, you're going to have a bad capture burn.

Moho is much less forgiving of deviances from the optimal transfer.

If you come in at a 5 degree angle to Jool's orbit... its not a big deal... but its a huge deal for moho... plot your course well.

[Der Anfang]

I've had encounters where capture burns require more than 4k dv... is that right?? Is that normal?

[Superfluous J]

31 minutes ago, Der Anfang said:

I've had encounters where capture burns require more than 4k dv... is that right?? Is that normal?

Not really, were you doing the plane change and encounter at the same time? Was your periapsis around Sun at Moho's orbit or was it well within it?

[Firemetal]

Ok I have been in orbit around Moho a number of times. (never landed though) Use Nukes and make sure your DV in LKO is something like 5000 m/s or more if you are doing satellites. If you are landing and return, I'd suggest 8000+ m/s in LKO and do it Apollo style. (Landing and return modules are separate.

Hope this helps.

Edit: Try Eve assists!

Edited June 25, 2016 by Firemetal

[Lunar Sea]

How about trying to intercept Moho at the AN or DN? 

[Hotel26]

[Ion engines suggested above is a good idea]

I found Maccollo's post below very helpful:

 

I ended up actually putting a fuel dump into 6Gmx6Gm helio-orbit at the required 7-degree inclination.  And then rendez-vous'ing there to refuel for the Moho intercept.

I have considered also using aero-breaking at Eve to pay for some of my descent into the gravity well.  (I think Eve is at 8 gigameters, from memory?)

In any case, you need a lot of good timing on your side to get to Moho in one shot and then you need a massive deceleration to catch it.  So I prefer a multi-step plan.

Do scroll down to and read Maccollo's article in the post cited above though.  The main point is that you want to go when you can perform the inclination change simultaneously with the transfer burn (Kerbin departure)

Edited July 25, 2016 by Hotel26
clarity

[Geschosskopf]

On 6/24/2016 at 9:37 AM, Callmedave said:

Does anyone have any tips for this contract. I'll post an image of the craft and contract when i get back home if anyones interested.

The 1st thing to understand about Moho is that, due to its rather steep inclination, not all transfer windows are created equal.  Transfer windows are determined simply by the relative positions of the 2 planets when looking down on the solar system from above.  This ignores the 3rd dimension.  Moho is often far above or below Kerbin's ecliptic plane and the greater this distance, the more dV you have to spend on the transfer to account for its inclination.  So what you want is one of the RARE windows when you will meet Moho when it's near the ecliptic.  But there's not really anything to tell you this apart from a porkchop plot and associated software than can find the minimal dV path (including both capture and transfer).  

The 2nd thing to understand about Moho is that the amount of dV needed to capture there is VERY sensitive to the angle at which your ship's trajectory crosses Moho's orbit.  You need this angle to be a small as possible, so your path is essentially tangent to Moho's orbit.  Being even a little bit off there VASTLY increases the amount of dV needed to capture.  This is what gives Moho its evil reputation in the forum.  Folks who meet Moho at like a 45^ angle might need 5-6 thousand m/s to capture there.  This is why focusing on the minimum dV for just the transfer, while ignoring the capture cost, is a big mistake.  Many have been lured to their doom by going for the low-cost transfer and then been unable to capture.

With that out of the way, there are 3 ways to get to Moho.  From worst to best, they are:

1.  Conventional Direct Transfer from Kerbin (either Hohmann or ballistic).
This is going to Moho the same as you would any other planet.  While it's possible to do this without getting yourself into an impossibly huge capture burn, it requires picking the correct window out of many, and very precise execution in both nod placement and creation, and doing the burn.  This precision is beyond the abilities of many people, especially the part about knowing when to leave.  Trying this method usually results in another frightful tale of a massive capture burn, which is why the other methods are considered better.

 

2.  Gravity Braking off Eve
Here, you leave Kerbin on an Eve window and do a conventional transfer to Eve.  When you get to Eve, you pass it on the sunny side, which is where the braking comes from.  On the way there, you adjust your Eve Pe so, once you leave Eve's Pe, your trajectory's inclination will be as close to matching Moho's as possible.  Going by Eve like this will lower your post-Eve Ap from the vicinity of Kerbin's orbit to the vicinity of Eve's orbit, and should also put your post-Eve Pe somewhere near Moho's orbit.  You will now probably have to do a somewhat expensive maneuver to get a Moho encounter perhaps several solar orbits after you pass Eve.  However, because your orbit now has a much smaller diameter and is rounder than if you come direct from Kerbin, you meet Moho at a nicely small angle, so the capture burn is very reasonable.  This method is usually considerably cheaper than what you normally get with a conventional transfer, but is more expensive than the last method.

 

3.  Meeting Moho at it's AN or DN.
Here you totally ignore any and all transfer windows.  Instead, you watch the map and leave Kerbin when Kerbin is on the line connecting Moho's AN and DN.  Do your burn so that your trajectory just kisses Moho's orbit at either its AN or DN, whichever is on the other side of the sun from where Kerbin is now.  This totally eliminates the need to apply any inclination change into the transfer burn.  It's highly unlikely that Moho will be at that node when you get there, however, so what you then have to do is a burn to lower your Ap from the vicinity of Kerbin's orbit down to somewhere between Eve and Moho.  Then you just wait a few solar orbits until you sync up with Moho so you'[l both be at the node (where your Pe is) at the same time.  To speed things up, you'll probably have to do some tweak burn at some point to get an encounter, which means you won't meet Moho exactly on the node, but as long as you keep the encounter very close to the node, you'll be OK.  In this situation, the capture burn is usually less than 1000m/s.

[Gordon Fecyk]

On ‎7‎/‎25‎/‎2016 at 1:17 PM, Geschosskopf said:

3.  Meeting Moho at it's AN or DN.
Here you totally ignore any and all transfer windows.  Instead, you watch the map and leave Kerbin when Kerbin is on the line connecting Moho's AN and DN.

Does this also apply when returning? As in, leave Moho when it's on the line connecting Kerbin's AN and DN, put the AP somewhere near Kerbin's AN or DN, and wait a few solar orbits until you get reasonably close?

[Geschosskopf]

3 hours ago, Gordon Fecyk said:

Does this also apply when returning? As in, leave Moho when it's on the line connecting Kerbin's AN and DN, put the AP somewhere near Kerbin's AN or DN, and wait a few solar orbits until you get reasonably close?

Yeah, you definitely want to leave when Moho is at or near its AN or DN to avoid as much of the plane change dV as possible.  But otherwise, going back to Kerbin isn't as tricky as getting to Moho.  Kerbin in in a much wider orbit at a much lower velocity than Moho, so isn't nearly as picky about how tangentially you encounter it as Moho is.  Besides, Kerbin is one of the biggest rocks in the game, has a thick atmosphere, and has relatively big Mun conveniently to hand.  All 3 of these can be used alone or in combination to supply much of the braking required to capture at Kerbin.

The best thing is, Moho's "year" is only a bit over 100 days IIRC, so it hits one node or the other every couple of months.  Thus, you never have to wait very long when you want to leave, unless you want to go direct from Moho to Kerbin on a conventional transfer.  Then you have to wait for Kerbin to move to the appropriate place relative to one of Moho's nodes.  If you just want to go, then it's kinda the same as getting to Moho to begin with.  You leave Moho with it's in the right place without worrying about where Kerbin is, then maybe do a few laps around the sun to sync up with Kerbin.  Of course, out near Kerbin, these solar orbits will take nearly 1 year so a lot of game time (and hence life support) can go by while you wait.  So you generally get home faster waiting on Kerbin to reach the proper phase angle with one of Moho's nodes.

[Lunar Sea]

On 7/25/2016 at 1:17 PM, Geschosskopf said:

 Instead, you watch the map and leave Kerbin when Kerbin is on the line connecting Moho's AN and DN. 

How does one get these lines to show up? I have a ship waiting in Mun equatorial orbit, but even when I select Moho as the target it doesn't show me the AN or DN, much less the lines. Although I do get time to relative AN/DN in KER, but those figures aren't making sense to me. 

Edited July 28, 2016 by Lunar Sea

[Superfluous J]

40 minutes ago, Lunar Sea said:

How does one get these lines to show up? I have a ship waiting in Mun equatorial orbit, but even when I select Moho as the target it doesn't show me the AN or DN, much less the lines. Although I do get time to relative AN/DN in KER, but those figures aren't making sense to me. 

Create a maneuver node to exit Kerbin equatorially. Your ship's projected Sun orbit will have the AN/DN lines so long as Moho is your target (or Dres, or Eeloo, or whatever target you want though those 3 are the only ones where this plan is reasonable, and due to how insanely long it would take, Eeloo is likely better to just suck it up and do the mid course burn).

Also, you can focus the map on Sun and just tilt it and eyeball it. Though getting the Sun orbit is more precise.

Note: Don't execute this burn, just plot it to see where the line is.

Edited July 28, 2016 by 5thHorseman

[Geschosskopf]

12 hours ago, Lunar Sea said:

How does one get these lines to show up? I have a ship waiting in Mun equatorial orbit, but even when I select Moho as the target it doesn't show me the AN or DN, much less the lines. Although I do get time to relative AN/DN in KER, but those figures aren't making sense to me. 

You just have to eyeball it.  Orient the map so Kerbin's orbit is edge-on and looks like 1 line.  Then rotate the view until Moho's orbit also looks like a single line crossing Kerbin's line.  IOW X marks the spot.  Then warp until Moho is at the center of the X.

[Lunar Sea]

On 7/28/2016 at 4:52 PM, Geschosskopf said:

You just have to eyeball it.  Orient the map so Kerbin's orbit is edge-on and looks like 1 line.  Then rotate the view until Moho's orbit also looks like a single line crossing Kerbin's line.  IOW X marks the spot.  Then warp until Moho is at the center of the X.

I managed to get an encounter within 1000km or so of the AN but the nodes tell me I'm still looking at 3000dv or so for the capture burn

This is the idea right? 

Edited July 31, 2016 by Lunar Sea

[Norcalplanner]

On 7/25/2016 at 11:17 AM, Geschosskopf said:

2.  Gravity Braking off Eve
Here, you leave Kerbin on an Eve window and do a conventional transfer to Eve.  When you get to Eve, you pass it on the sunny side, which is where the braking comes from.  On the way there, you adjust your Eve Pe so, once you leave Eve's Pe, your trajectory's inclination will be as close to matching Moho's as possible.  Going by Eve like this will lower your post-Eve Ap from the vicinity of Kerbin's orbit to the vicinity of Eve's orbit, and should also put your post-Eve Pe somewhere near Moho's orbit.  You will now probably have to do a somewhat expensive maneuver to get a Moho encounter perhaps several solar orbits after you pass Eve.  However, because your orbit now has a much smaller diameter and is rounder than if you come direct from Kerbin, you meet Moho at a nicely small angle, so the capture burn is very reasonable.  This method is usually considerably cheaper than what you normally get with a conventional transfer, but is more expensive than the last method.

Today I used this method to successfully get to Mercury in RSS for the first time, getting a gravity brake off of Venus.  I had a monster ship with 26 km/s of delta V taking a large satellite and three landers (in part to fulfill a Strategia contract) and had repeated failures with a direct Hohman transfer.  I'd arrive with 8 km/s left in the tank, and the capture burn would be 15 km/s.  Using a gravity brake off of Venus, I arrived with 11 km/s in the tank, and the capture burn was only 6 km/s.  So my massive rocket (over 10,000 tons) which was woefully insufficient for a direct journey to Mercury, was grossly overbuilt when using a Venus assist.  Definitely some of the most difficult yet satisfying gameplay I've had in quite a while. 

[Geschosskopf]

8 hours ago, Lunar Sea said:

I managed to get an encounter within 1000km or so of the AN but the nodes tell me I'm still looking at 3000dv or so for the capture burn

This is the idea right? 

This looks like a direct transfer from Kerbin to Moho, and is essentially optimal for that method.  You're meeting Moho on the opposite side of the sun from where you left Kerbin so you're the encounter is as tangential as it can get, and you're hitting Moho at a node so you eliminated the plane change cost.  Bravo!  And because it's a direct transfer, the travel time is minimized.  That's about the best possible result with the direct transfer method.

It's just that the opportunities to do it this way are few and far between.  Normally, when Moho is at the correct phase angle from Kerbin, the encounter won't be anywhere near one of Moho's nodes.  This is why folks do the other methods more often, resigning themselves to making several solar orbits and thus accepting much longer travel times.

 

7 hours ago, Norcalplanner said:

Today I used this method to successfully get to Mercury in RSS for the first time, getting a gravity brake off of Venus.

Yay!  Be sure to post up a mission report of that.

[Lunar Sea]

7 hours ago, Geschosskopf said:

This looks like a direct transfer from Kerbin to Moho, and is essentially optimal for that method.  You're meeting Moho on the opposite side of the sun from where you left Kerbin so you're the encounter is as tangential as it can get, and you're hitting Moho at a node so you eliminated the plane change cost.  Bravo!  And because it's a direct transfer, the travel time is minimized.  That's about the best possible result with the direct transfer method.

It's just that the opportunities to do it this way are few and far between.  Normally, when Moho is at the correct phase angle from Kerbin, the encounter won't be anywhere near one of Moho's nodes.  This is why folks do the other methods more often, resigning themselves to making several solar orbits and thus accepting much longer travel times.

 

Well it's direct to the AN but there's no encounter the first time; I'm trying method 3 as above. Once I hit the AN the first time is when I lower my Ap and get the encounter for the 2nd time around on it. However the Ap is still out past Eve so I wonder if I'm still going too fast at the encounter since no matter how I slice it the capture burn is showing 3000dv or so

Edited July 31, 2016 by Lunar Sea

[Geschosskopf]

1 hour ago, Lunar Sea said:

Well it's direct to the AN but there's no encounter the first time; I'm trying method 3 as above. Once I hit the AN the first time is when I lower my Ap and get the encounter for the 2nd time around on it. However the Ap is still out past Eve so I wonder if I'm still going too fast at the encounter since no matter how I slice it the capture burn is showing 3000dv or so

OH, you said you already knew the capture burn so I was thinking you had an encounter.  Anyway, yeah, if you're planning on waiting for an encounter at the node, you've done the 1st step perfectly.  Now when you get to your solar Pe, bring your solar Ap down inside Eve so you don't accidentally get ejected by it, and then it's a waiting game.