Tips for Dres return archive as mission is over

[Guest]

Ah Dres... The dwarf planet that no-one likes. It's the Dwarf Mun planet. It's inclination isn't the best. And it's ugly...

mission over no longer needs to be opened

Edited June 26, 2019 by Guest

[Foxster]

One obvious thing is to minimise your payload i.e. just put man in a can on the surface and bring him back. Adding anything else, such as a rover, is going to greatly increase the dV requirement.  Also dumping anything not needed for the return journey (landing struts, science stuff, etc) will help. 

 You could also consider mining at Dres to reduce the need for fuel hauled to Dres and back. 

Another thing is to just have more dV. It is a mission that seems to suck up more dV than the dV maps say. Live with longer burn times and overload on the stageable tanks. I sometimes use just a few nukes and a repeatable stack of stageable big LF tanks like this...

  

Edited June 16, 2019 by Foxster

[Aegolius13]

23 hours ago, The Doodling Astronaut said:

Best way how to get there (Maneuver nodes and when I should change inclination)

I would just to a regular Hohmann transfer -- I don't think Dres is situated that well for a gravity assist.  If you choose to do one, I'm thinking Kerbin-Kerbin might be the best bet (i.e., leave the Kerbin SOI, and flyby it again in one year).

The optimal plane change may depend on where your launch position is relative to Dres' AN/or DN.  If you're luck enough that Kerbin is right at a node as you're leaving, then you can combine the plane change with your injection burn, and get a nice "pythagorean" savings.  Even if you're not right at a node, you can often use this method to at least reduce the inclination at minimal delta-v cost. 

Whatever you can't do when leaving Kerbin, I'd just do around halfway between the planets.  

23 hours ago, The Doodling Astronaut said:

Cheapest circulization (EX: Is closer better)

Yes, a closer periapsis is always better when circularizing, due to the Oberth effect.  Even if you want to go into a high orbit, you're still best off doing your insertion burn as close to the surface as possible, bringing your apoapsis down to the desired altitude, and then circularizing at the apoapsis.  if you're planning to circularize into a low orbit and/or land, then it's even simpler.

Also worth noting that there's nothing wrong with splitting your circularization burn into several passes -- this can save delta-v since you can keep your burns closer to the maneuver node. (This is a bigger deal on higher-gravity worlds, though).  Though of course you have to at least capture on the first pass or you'll be doing a fly-by.

 

23 hours ago, The Doodling Astronaut said:

Dres total fuel amount

On 6/15/2019 at 11:44 AM, The Doodling Astronaut said:

If I am a little bit frustrated on these answers it's generally because I am running out of time before I am on a camping trip with friends following surgery.

UPDATE: I will attempt another attempt in a few days so before then would be nice

No offense, but you're asking for something that it's really hard for anyone else to provide.  The delta-v maps show a more-or-less best-case flight from a typical launch window, but in practice that's often hard to do. How far you end up deviating from that budget depends mostly on how meticulous you are in setting up maneuvers.  E.g., 2500 m/s seems pretty high on an injection burn; Jool typically only takes 2,000.  1,600 is pretty spot-on.  So you may be able to save a lot by hitting the launch window dead-on and executing a clean Hohmann transfer.  Perhaps combining plane change with ejection will save some delta-v as well. Also, if you can heat-proof your craft for Kerbin reentry, you can probably avioid needed any Kerbin insertion burn at all.

But I think your own experience is the best guide for how much more you need.  If you think you'll fly similar to the previous mission, and ran short there, adding one more stage and ~3,000 m/s seems like a reasonable start.  

[Guest]

On 6/16/2019 at 12:55 PM, Aegolius13 said:

I would just to a regular Hohmann transfer -- I don't think Dres is situated that well for a gravity assist.  If you choose to do one, I'm thinking Kerbin-Kerbin might be the best bet (i.e., leave the Kerbin SOI, and flyby it again in one year).

The optimal plane change may depend on where your launch position is relative to Dres' AN/or DN.  If you're luck enough that Kerbin is right at a node as you're leaving, then you can combine the plane change with your injection burn, and get a nice "pythagorean" savings.  Even if you're not right at a node, you can often use this method to at least reduce the inclination at minimal delta-v cost. 

Whatever you can't do when leaving Kerbin, I'd just do around halfway between the planets.  

Yes, a closer periapsis is always better when circularizing, due to the Oberth effect.  Even if you want to go into a high orbit, you're still best off doing your insertion burn as close to the surface as possible, bringing your apoapsis down to the desired altitude, and then circularizing at the apoapsis.  if you're planning to circularize into a low orbit and/or land, then it's even simpler.

Also worth noting that there's nothing wrong with splitting your circularization burn into several passes -- this can save delta-v since you can keep your burns closer to the maneuver node. (This is a bigger deal on higher-gravity worlds, though).  Though of course you have to at least capture on the first pass or you'll be doing a fly-by.

 

No offense, but you're asking for something that it's really hard for anyone else to provide.  The delta-v maps show a more-or-less best-case flight from a typical launch window, but in practice that's often hard to do. How far you end up deviating from that budget depends mostly on how meticulous you are in setting up maneuvers.  E.g., 2500 m/s seems pretty high on an injection burn; Jool typically only takes 2,000.  1,600 is pretty spot-on.  So you may be able to save a lot by hitting the launch window dead-on and executing a clean Hohmann transfer.  Perhaps combining plane change with ejection will save some delta-v as well. Also, if you can heat-proof your craft for Kerbin reentry, you can probably avioid needed any Kerbin insertion burn at all.

But I think your own experience is the best guide for how much more you need.  If you think you'll fly similar to the previous mission, and ran short there, adding one more stage and ~3,000 m/s seems like a reasonable start.  

Thanks for the data It's great people like you are out here. Thanks for the info...

On 6/16/2019 at 2:32 AM, Foxster said:

One obvious thing is to minimise your payload i.e. just put man in a can on the surface and bring him back. Adding anything else, such as a rover, is going to greatly increase the dV requirement.  Also dumping anything not needed for the return journey (landing struts, science stuff, etc) will help. 

 You could also consider mining at Dres to reduce the need for fuel hauled to Dres and back. 

Another thing is to just have more dV. It is a mission that seems to suck up more dV than the dV maps say. Live with longer burn times and overload on the stageable tanks. I sometimes use just a few nukes and a repeatable stack of stageable big LF tanks like this...

  

Thanks for the data it's great people like you are out there. Thanks for the info...

But mining I count as cheating as it isn't a real world solution (unless your elon musk)

 

Edited June 18, 2019 by Guest

[Guest]

 

So this video points out two things: ONE that the Dres glitch is happening (that which isn't the question in this one) TWO that Dres takes a big chunk of fuel to circulize {Not shown in video but it was a lot [3842 dV]}. Why does it take so much? I had a lander that only took about 1000 meters less and another that took 1000 meters MORE. So can anyone help me get the right encounters and angles of arrival? IMAGES PREFERRED

[sturmhauke]

You are transferring outside of the window, and arriving at an angle to Dres' orbit. This massively increases your dV requirements. For low dV transfers you want to leave inside the window, and arrive at a tangent such that your transfer Ap is inside Dres' SOI and in the same plane. I recommend using the Transfer Window Planner mod and referring to this tutorial (a general guide, but applicable to anything).

 

[Gargamel]

Overlapping threads have been merged, and moved to GP Q's, as it is about the game, not BG in particular. 

[Guest]

1 hour ago, sturmhauke said:

You are transferring outside of the window, and arriving at an angle to Dres' orbit. This massively increases your dV requirements. For low dV transfers you want to leave inside the window, and arrive at a tangent such that your transfer Ap is inside Dres' SOI and in the same plane.

So what do you mean I'm out of window? This trajectory was calculated using http://ksp.olex.biz/

Also apologies people for If I am a little mad with my answers. I have been spending hours on this topic and just tired 

Edited June 18, 2019 by Guest

[sturmhauke]

1 hour ago, The Doodling Astronaut said:

So what do you mean I'm out of window? This trajectory was calculated using http://ksp.olex.biz/

That tool (which uses the same math as the mod I mentioned BTW) gets you close, but you often still have to fiddle with your ejection burn a bit. Leaving a little sooner or later, from different altitudes at the origin, or from different angles can make a big difference.

[Guest]

2 minutes ago, sturmhauke said:

That tool (which uses the same math as the mod I mentioned BTW) gets you close, but you often still have to fiddle with your ejection burn a bit. Leaving a little sooner or later, from different altitudes at the origin, or from different angles can make a big difference.

Okay so first I don't or want to use mods so that's out of ballpark of ideas. Is the issue me not needing to change my inclination? For some reason the current ejection burn doesn't need to change inclination that much isn't that a little bit bad? I am going to start watching videos of how other people get there.

[Aegolius13]

1 minute ago, The Doodling Astronaut said:

Okay so first I don't or want to use mods so that's out of ballpark of ideas. Is the issue me not needing to change my inclination? For some reason the current ejection burn doesn't need to change inclination that much isn't that a little bit bad? I am going to start watching videos of how other people get there.

It's not about inclination; it's about where you and the target are relative to the sun (this is called a phase angle).  You know how when you do a simple transfer to the Mun, you need to start it at the right point in your orbit around Kerbin, so that the Mun is at the right place when you arrive?  It's the exact same thing with interplanetary, except instead of you going around Kerbin, you have to wait for Kerbin to go around the Sun until Kerbin is at the right spot in its orbit.  That is the primary thing the launch window planners provide, but they also help with inclination at a given launch window.  

[Guest]

2 minutes ago, Aegolius13 said:

It's not about inclination; it's about where you and the target are relative to the sun (this is called a phase angle).  You know how when you do a simple transfer to the Mun, you need to start it at the right point in your orbit around Kerbin, so that the Mun is at the right place when you arrive?  It's the exact same thing with interplanetary, except instead of you going around Kerbin, you have to wait for Kerbin to go around the Sun until Kerbin is at the right spot in its orbit.  That is the primary thing the launch window planners provide, but they also help with inclination at a given launch window.  

Soooooooooooo My inclination doesn't matter as long I get an encounter with it my time I leave was from the Online Calculator I posted earlier so what am I doing wrong? I'm confused what I am doing wrong 

[Guest]

 

I watched this video and realized he got the same encounters I did but had lower cost burns...  Making me more confused

[sturmhauke]

On 6/16/2019 at 1:32 AM, Foxster said:

One obvious thing is to minimise your payload i.e. just put man in a can on the surface and bring him back. Adding anything else, such as a rover, is going to greatly increase the dV requirement.

Not exactly. dV is short for delta-V, which means "total change in velocity". The dV requirement to transfer from one body to another does not change with the mass of the vehicle. What does change with vehicle mass is how much fuel is required to get a certain potential dV from that vehicle.

[mystifeid]

49 minutes ago, The Doodling Astronaut said:

I watched this video and realized he got the same encounters I did but had lower cost burns...  Making me more confused

His transfer AP is close to the orbit of Dres. Your AP (at the 5 sec mark in your video) looks like it is out near the orbit of Jool.

[Vanamonde]

Dres takes a lot of dV to circularize for two reasons. Firstly, it has no atmosphere to assist with aerobraking, and secondly, it has little gravity to help bend your trajectory into a curve around the planet. 

[sturmhauke]

43 minutes ago, The Doodling Astronaut said:

 

I watched this video and realized he got the same encounters I did but had lower cost burns...  Making me more confused

Your phase angle (relative position of Kerbin and Dres) is about right, but your ejection angle (how you leave Kerbin) looks like it might be off. For outbound transfers, you want to start your ejection burn in approximately the same direction as the orbit of your starting body, to benefit from its velocity. (The exact ejection angle can be tweaked to get a better encounter, but mostly just make sure it's in the ballpark.) This might mean starting half an orbit off from your theoretical ideal ejection time, if you would be facing the wrong way.

[Aegolius13]

2 hours ago, The Doodling Astronaut said:

Soooooooooooo My inclination doesn't matter as long I get an encounter with it my time I leave was from the Online Calculator I posted earlier so what am I doing wrong? I'm confused what I am doing wrong 

They both matter (this comes with a 3-dimensional universe), but the phase angle is more important when choosing when to leave.*   As I mentioned a while back, it's generally not too expensive to fine-tune your inclination via a halfway-point correction burn.  But you can't really do that if your phase angles are wrong, without overshooting like in your prior attempt.

Important thing to note - you do NOT always need to match the plane of your target.  It's nice to keep things simple, but not mandatory.  What you do need to do is make sure you intercept the target's orbit at the time you capture (otherwise you'll be above or below the target and miss).  In other words, if you can't match planes, you want to put your ascending or descending node over the target.  

You've probably done all this without thinking about it when going to Minmus.  If you get lucky, you can hit Minmus without a normal/antinormal burn, but that only works when Minmus' orbit happens to cross the your original orbit at the right time.  More often, you need to do a normal/antinormal adjustment along the way.  Again, the only thing that's really different when going interplanetary is that you have to time things around Kerbin's point in its orbit.

 

*Except, arguably, when going to Moho.  But that's another topic entirely.

[Guest]

Thank you for all the answers I will be flying to Dres soon and this will come in handy so I have all the info I need so this post will be able to come to a close...

16 hours ago, mystifeid said:

His transfer AP is close to the orbit of Dres. Your AP (at the 5 sec mark in your video) looks like it is out near the orbit of Jool.

Thank you for the difference

[Guest]

Can someone tell me if 2600 Meters per second is enough to return to kerbin?

@Aegolius13 @sturmhauke @mystifeid anyone?

[Foxster]

I think you can do it with about 2000dV. Obviously depends on how good a transfer you take. You'll want to go straight for re-entry rather than Kerbin orbit, right? 

[mystifeid]

13 minutes ago, The Doodling Astronaut said:

Can someone tell me if 2600 Meters per second is enough to return to kerbin?

You should be able to find a transfer of 1500m/s or less. But your remaining fuel may not be enough for capture without some aerobraking.

[Guest]

Just now, mystifeid said:

You should be able to find a transfer of 1500m/s or less. But your remaining fuel may not be enough for capture without some aerobraking.

So I won't to be able to circularize at kerbin but can aerobrake?

[mystifeid]

You definitely won't be able to circularize.

Looking at a pork chop plot for two transfers:

Transfer 1

Transfer Burn - ~1500m/s

Capture Burn - ~ 2000m/s

Total - ~3500m/s

Transfer 2

Transfer Burn - ~1250m/s

Capture Burn - ~3250m/s

Total - ~ 4500m/s

The numbers for the capture burns may be exaggerated but I think you can expect a toasty return to Kerbin.

[Guest]

*Facepalm* @mystifeid... How fast do you except the aerobrake to be?

 

Theoretically I can set it up for aerobrake and fire the engines as much as possible, but sound from what you're saying it won't help that much if I have like 600 dV when I come back or so.