Getting to Duna - Fastern than Hohmann

[Kobymaru]

Hi!

I have played this game for quite some time now, and I have accumulated dozens and dozens of trips from Kerbin to Duna and back. So far, I have been doing this with the good old Hohmann transfer: cheapest in terms of Delta-V, but a little bit awkward timing-wise, and flight-time wise: the transfer windows are spaced a bit over 2 years apart, and the flight time ad minimum dV is 250 days.

I am getting increasingly dissatisfied with this business. I am willing to pay more Delta-V (potentially a lot more), to be able to get there more often and quicker.

How do the people around here get to Duna? Do you guys only go when you get minimum dV, or do you have some "fast-track" methods of transfer?

Edit: Since my goal is to create a sustainable Duna Kolony for Kerbals, I want to offer convenient flights, as often and as fast as possible. This obviously includes the traffic back from Duna!

Out of curiosity, what about Eve? How is the Fast-Track situation there?

Edited September 16, 2016 by Kobymaru

[Sharpy]

Use this:

https://alexmoon.github.io/ksp/

Set up the parameters - start date, initial orbit, target body, etc.

If you don't want to wait, open Show Advanced Settings and type end date a day away from your current game time. You may reduce the bottom 'Time of flight' value too.

 

Disregard the found optimal point.

Hover over the image; it shows up how much delta-V it will cost. The vertical scale is time of flight. Hover as close to the bottom as you dare

If you set up start date as 'today', hover right next to the left edge to have the departure ASAP.

When you have a point that is satisfactory in terms of delta-V and travel time, click. Parameters for the transfer will show up.

 

Edited September 16, 2016 by Sharpy

[Kobymaru]

2 minutes ago, Sharpy said:

Use this:

https://alexmoon.github.io/ksp/

Set up the parameters - start date, initial orbit, target body, etc.

Thanks, I do know about this. This is still almost exclusively Hohmann transfers, and I'm still severely limited by the transfer window. Although I'm willing to pay "extra", the off-season price of 5 km/s to 18 km/s seems quite far off.

What I was referring to were some mid-transfer maneuvers, or some magic gravity assists. And just to know how you people around here do to get over to Duna quickly.

 

 

 

[Streetwind]

What you are looking for is sometimes called a "high energy transfer". It cuts travel time by accelerating more than necessary at the start, and then braking harder at the end. In other words, you have to pay extra dV twice, which makes this kind of thing rather inefficient. But if you have fuel available... *shrug* The logical conclusion of the idea of high energy transfers is a "torchship", which is a spacecraft that accelerates continuously for half the trip, flips over in the middle, and brakes continuously for the second half. It thereby minimizes the travel time achievable by its available engine TWR.

Alexmoon's planner is perfectly capable of producing high energy transfers, if you properly restrict it to short travel times. You know you have something that is not a Hohmann transfer when the solution is plastered against the upper edge of the porkchop plot, indicating that you could save fuel by going slower.

As for being limited by the transfer window: that is planetary alignment for you. Even if you have a torchship, the trip will take a lot longer and cost vastly more fuel if the planets are far apart than if they are lined up right next to each other. You will never find a transfer type that is not affected by planetary alignment; it is physically impossible.

(Okay, I lied: there is one transfer type that always takes the same amount of time, called a periodic cycler. But it achieves this by sacrificing travel time - it is one of the slowest possible routes of them all, taking a full Duna year between each Duna encounter. Which is why I reckon you won't care about it. )

Edited September 16, 2016 by Streetwind

[Sharpy]

7 minutes ago, Kobymaru said:

Thanks, I do know about this. This is still almost exclusively Hohmann transfers, and I'm still severely limited by the transfer window. Although I'm willing to pay "extra", the off-season price of 5 km/s to 18 km/s seems quite far off.

What I was referring to were some mid-transfer maneuvers, or some magic gravity assists. And just to know how you people around here do to get over to Duna quickly.

You are absolutely not limited by transfer window, except within the 30 minutes or so of LKO period. Can't you really wait 30 minutes?

Kerbin LKO departure will always be a tangential burn, because any other would be a pure waste at no benefit except maybe the up to 30 minutes. So will be Duna insertion burn. But look at the trajectories between Kerbin and Duna SOI. These are definitely not Hohmann if performed at non-optimal time. You will both leave Kerbin at a trajectory that is not tangent to Kerbin orbit, and arrive at Duna not tangentially to Duna orbit.

Mid-course burn makes sense only for plane change (and there's an option for that in the planner), otherwise Oberth effect says the same fuel is better spent in LKO or Duna orbit, buying you more speed and shorter transfer - so no, no maneuvers exist that involve acceleration/deceleration (as opposed to plane change) anywhere outside low orbits. Also, with good heatshields and air drag surfaces, you will be able to perform aerocapture, so feel free to uncheck 'insertion burn', and spend the delta-V on accelerating out of LKO - you'll still get more bang for the buck than spending that fuel anywhere else.

 

Delta-V optimal transfers (except for specific situations like bielliptic) are Hohmann transfers. Time-optimal transfers are dead simple, just burn at full speed halfway towards the point of encounter, retrograde the other half, straight ahead. But they have prohibitively high delta-V requirements. You need a hybrid - shorter time on a fixed delta-V budget, and it will be hybrid between the two - a transfer that is not entirely tangential to both orbits, but also not entirely perpendicular. This is what you get from the planner if you click near the bottom.

[pincushionman]

You can get

- to anywhere

- from anywhere

- -at any time

as long as you are willing to pay through the nose in dV. It's the approach New Horizons took - they said "we need to get to Pluto in ten years," found the biggest rocket they could afford, put down on the smallest probe they could afford, and went like a bat out of hell.

And couldn't make a braking burn, because the radial velocity at target was far, far too large. You're going to face the same challenge with your high-energy maneuver, so you're going to need some redonkulous plan to stop.

Also, remember that while the most efficient windows may come around every two years, one that is good enough may arrive sooner; it's just a more aggressive Hohmann. This is particularly important to keep in mind for the more remote targets. There's no sense waiting 40 years for an optimal transfer when it's only slightly better than what you can get this orbit.

[Jonfliesgoats]

That launch window planner is great for fast transfers as well as economy transfers.

[magnemoe]

6 minutes ago, Streetwind said:

What you are looking for is sometimes called a "high energy transfer". It cuts travel time by accelerating more than necessary at the start, and then braking harder at the end. In other words, you have to pay extra dV twice, which makes this kind of thing rather inefficient. But if you have fuel available... *shrug* The logical conclusion of the idea of high energy transfers is a "torchship", which is a spacecraft that accelerates continuously for half the trip, flips over in the middle, and brakes continuously for the second half. It thereby minimizes the travel time achievable by its available engine TWR.

Alexmoon's planner is perfectly capable of producing high energy transfers, if you properly restrict it to short travel times. You know you have something that is not a Hohmann transfer when the solution is plastered against the upper edge of the porckchop plot, indicating that you could save fuel by going slower.

As for being limited by the transfer window: that is planetary alignment for you. Even if you have a torchship, the trip will take a lot longer and cost vastly more fuel if the planets are far apart than if they are lined up right next to each other. You will never find a transfer type that is not affected by planetary alignment; it is physically impossible.

(Okay, I lied: there is one transfer type that always takes the same amount of time, called a periodic cycler. But it achieves this by sacrificing travel time - it is one of the slowest possible routes of them all, taking a full Duna year between each Duna encounter. Which is why I reckon you won't care about it. )

I do this sort of burns all the time with orion nuclear pulse engines, most trajectories are solar escape.
The burn to midpoint and then brake is only relevant if you don't use any fuel as in solar sails where its no reason not to use it for trust. 

Know the distance well, using orion to Duna its perfect to start then Duna is a bit ahead, then you want to go back Kerbin has overtaken Duna and you have an short trip home. If Duna is on the other side of the sun it take many times the time to go to Duna. Going to Jool or Eeloo the position is less impostant as the distance is far longer than diameter of kerbin orbit. 
just make sure you don't fly to close to the sun

Mecjeb has an porkshop graph build in. 
Note that this is even more practical going between Mun and Minmus or between Jool moons as the dV budget is far lower, using 100 m/s can save a lot of time. 
Same for going to or returning from minmus, it don't cost that much to cut the travel time to the half.


Underway to Duna the fast way. 

[eddiew]

20 minutes ago, Sharpy said:

You are absolutely not limited by transfer window, except within the 30 minutes or so of LKO period...

I think this is probably the right answer

A "window" isn't a binary thing. Taking a quick screen grab Alexmoon as suggested above, its output is this porkchop:

For fuel economy, we consider the darkest blue area to be our 'window' - but it is a window of efficiency, not of time. It only closes when you no longer have enough fuel to travel. If you had a fuel budget of, say, 2km/s, then you have a gap between 213 and 230 days from now, which will arrive about 230 to 270 days after launch. If we want to burn in just 200 and reduce the travel time to something similar, we can still travel, but it will cost twice as much fuel. You can transfer even during the red zone if you want to. 

The process is exactly the same in all cases: put a manoeuvre node on the night side of Kerbin and add prograde until you get some sort of intercept. (I suspect the red zone above is when you would have to burn at noon, against Kerbin's orbital momentum, into a retrograde solar orbit, which really will cost a lot more. The insertion burn would be equally devastating, since you have to shed your own solar-orbit speed, and then equalise with Duna's.)

If you want in game tools to help, Mechjeb has "Advanced transfer to another planet" which will give you a porkchop plot as above, and simply lets you click on it to set a manoeuvre node up. Alternatively, Transfer Window Planner will give you some idea of how much it will cost while you're planning the mission on the ground. In either case, be wary of your arrival burns as well as your departure!

@Sharpy is spot on about the LKO period being a thing to watch out for. Sometimes Kerbin is in the direction you need to burn, and sometimes your orbit around Kerbin is swinging you backwards. You do need to wait until you are on the right side of the planet before you kick the engines

(I suspect the majority of players use low consumption routes because, well... timewarp. Sip your tea and you've arrived. The only reason to step on the gas is if you're using life support mods, but that means trading LS mass for fuel mass and doesn't really get you anywhere.)

Edited September 16, 2016 by eddiew

[Sharpy]

12 minutes ago, eddiew said:

@Sharpy

(I suspect the majority of players use low consumption routes because, well... timewarp. Sip your tea and you've arrived. The only reason to step on the gas is if you're using life support mods, but that means trading LS mass for fuel mass and doesn't really get you anywhere.)

Most of the time.

Yesterday I burned hard from Minmus to LKO, as arrival of the Class E is looming sooner, and Bill *just* finished construction of the base and was needed on Claymore presto. Actually, spent maybe 100m/s extra, reducing transfer time from weeks to some 4 days.

Except I didn't check first, and Bill, before getting into Claymore, had to kick out the engineer who was already in there. Boy was that a surprise!

Anyway, one extra redundant engineer, hooray! I'm always short on them.

 

[Mike Mars]

You can always download Impossible Innovations.

It's fusion engines are impossibly powerful.

My record trip to Duna was 12 days.

MM

[Kobymaru]

 

1 hour ago, Sharpy said:

You are absolutely not limited by transfer window, except within the 30 minutes or so of LKO period. Can't you really wait 30 minutes?

I can wait 30 minutes, I can not wait over 2 years

 

1 hour ago, Streetwind said:

What you are looking for is sometimes called a "high energy transfer". It cuts travel time by accelerating more than necessary at the start, and then braking harder at the end.

1 hour ago, pincushionman said:

You can get to anywhere from anywhere at any time as long as you are willing to pay through the nose in dV.

So this seems to be the consensus here. Thanks for the tips, I will keep using the Transfer Planner and just budget more dV.

However, wasn't there a guy who did a whacky duna Sprint that involved an Eve flyby? I can't find the link anymore, unfortunately.

 

Quote

Also, remember that while the most efficient windows may come around every two years, one that is good enough may arrive sooner; it's just a more aggressive Hohmann. This is particularly important to keep in mind for the more remote targets. There's no sense waiting 40 years for an optimal transfer when it's only slightly better than what you can get this orbit.

Good point. I do that on my remote probes, but this is something to consider for Duna as well.

 

1 hour ago, eddiew said:

A "window" isn't a binary thing.

Technically not, but anything above 10 km/s basically means "nope, you're not going". I'm not *that* much in a hurry

 

Quote

(I suspect the majority of players use low consumption routes because, well... timewarp. Sip your tea and you've arrived. The only reason to step on the gas is if you're using life support mods, but that means trading LS mass for fuel mass and doesn't really get you anywhere.)

Well yes, timewarp. But I have quite a few things going on and one of the few things that irk me about KSP in general is that the the effort-reward is so extremely disconnected. I start "a thing", and until this "thing" is finished, I had dozens of maneuvers for other, completely unrelated "things". Since I don't play taht often, long transfer times sometimes translate to weeks in real time.
It would just be nice to cut down the in-game travel time to bring "I want to bring these kerbals to duna" and "i brought those kerbals to duna" closer together in real time.

 

Quote

And couldn't make a braking burn, because the radial velocity at target was far, far too large. You're going to face the same challenge with your high-energy maneuver, so you're going to need some redonkulous plan to stop.

Yeah, that's the other problem

 

1 hour ago, magnemoe said:

I do this sort of burns all the time with orion nuclear pulse engines, most trajectories are solar escape.

18 minutes ago, Mike Mars said:

You can always download Impossible Innovations.

It's fusion engines are impossibly powerful.

Not quite what I was going for

Edited September 16, 2016 by Kobymaru

[eddiew]

18 minutes ago, Kobymaru said:

Well yes, timewarp. But I have quite a few things going on and one of the few things that irk me about KSP in general is that the the effort-reward is so extremely disconnected. I start "a thing", and until this "thing" is finished, I had dozens of maneuvers for other, completely unrelated "things". Since I don't play taht often, long transfer times sometimes translate to weeks in real time.
It would just be nice to cut down the in-game travel time to bring "I want to bring these kerbals to duna" and "i brought those kerbals to duna" closer together in real time.

To be fair, that's just a play style thing. I used to have the exact same problem, and through all of 0.90 I hardly left Kerbin SoI because I felt compelled to launch *something else* whenever there was a gap of more than a week. I think I had one single trip to Duna, and it took ten real-time days to arrive. Which wasn't actually very fun, since the intercept vanished somewhere en-route and I had to hyperedit it back on track.

This career, I became a bit more brutal with myself. I am allowed only one crewed, non-station mission at any time. Yes, I have probes bound for Neidon and Sarnus (I think) but they won't arrive for another 8 years. Meanwhile, if I want to go to Duna or Moho or Jool - I can do that in a few hours, because I'm not allowed to send up a second ship while they're away and I might as well timewarp. Result; I have been to Duna and Moho and Jool, two of them being personal firsts!  

My 2p; try to restrain from too many parallel missions. You actually get less done by being too keen ^^

[Leafbaron]

46 minutes ago, eddiew said:

My 2p; try to restrain from too many parallel missions. You actually get less done by being too keen ^^

@eddiew This, well said.

 I recently and by recently I mean months ago got Kerbal Alarm Clock. I thought "oh this will be awesome, I can run parallel missions and keep track of everything!" which is true, you can. However, it really limits how much you can time warp and you still need to make sure you don't have two maneuver nodes setup to burn at the the same time. But i thought i would be able to get so much done, and really you get more done in kerbin SOI but less far trips done. if you don't care about how high the game clock reaches and your progression just time warp the excrements out of those Duna missions. Or get the interstellar mod pack, there is an high energy fusion reactor engine that delivers like 40k DV and 3g acceleration. With those stats you could start orbiting Kerbol Retrograde and meet up with Duna in a real hurry.

Edited September 16, 2016 by Leafbaron

[Deddly]

Looks like there are already some great answers here, but it seems to belong in Gameplay Questions, so I moved the discussion there.

[Chaos_Klaus]

 

 

1 hour ago, Kobymaru said:

Thanks for the tips, I will keep using the Transfer Planner and just budget more dV.

 

@Kobymaru

I have this feeling that you are not using the transfer planner to its full extent. When you click "Plot it!" it shows you this porkchop plot with the black crosshairs. You can actually click around in this plot and it will give you the transfer parameters. Every point in this plot represents a different transfer. You can even click and drag too scroll around. That planner can give you the exact parameters of any transfer you want. It just gives you the most efficient one by default.

[Sharpy]

1 hour ago, Kobymaru said:

So this seems to be the consensus here. Thanks for the tips, I will keep using the Transfer Planner and just budget more dV.

However, wasn't there a guy who did a whacky duna Sprint that involved an Eve flyby? I can't find the link anymore, unfortunately.

Oh, gravity assists can save a lot of delta-V - which you can sacrifice towards speeding up.

The problem is the opportinities for these appear on their own schedule.

Do you want to "fly to Duna fast" or do you prefer to "arrive at Duna soon"?

If it's the former, then you wait a couple years for the most opportune planet alignment (there was a 'flyby finder' tool somewhere, use your google-fu), and you're getting a transfer considerably faster than on fuel alone. This may be important if you're playing with exhaustible life support resources or such.

But for most people it's more about 'not waiting forever for the transfer window, then for the transfer to end, then transfer window back, then transfer back to end' - launch fast, and launch soon. And in this scenario you have no time to hitchike assists all over the system, waiting for the planets to align just right. You just burn to your destination.

[Kobymaru]

5 minutes ago, Chaos_Klaus said:

I have this feeling that you are not using the transfer planner to its full extent. When you click "Plot it!" it shows you this porkchop plot with the black crosshairs. You can actually click around in this plot and it will give you the transfer parameters. Every point in this plot represents a different transfer. You can even click and drag too scroll around. That planner can give you the exact parameters of any transfer you want. It just gives you the most efficient one by default.

Thanks, I already knew about these features

I was just kinda hoping for a bit more orbital creativity than "click into the red area". Something along the lines of the rich purnell maneuver

 

Just now, Sharpy said:

Do you want to "fly to Duna fast" or do you prefer to "arrive at Duna soon"?

The latter. 

 

Just now, Sharpy said:

If it's the former, then you wait a couple years for the most opportune planet alignment (there was a 'flyby finder' tool somewhere, use your google-fu), and you're getting a transfer considerably faster than on fuel alone. This may be important if you're playing with exhaustible life support resources or such.

But for most people it's more about 'not waiting forever for the transfer window, then for the transfer to end, then transfer window back, then transfer back to end' - launch fast, and launch soon. And in this scenario you have no time to hitchike assists all over the system, waiting for the planets to align just right. You just burn to your destination.

Why not both? Fly-by's when opportune, high-dV when necessary.  The problem is, i do not have good experiences with fly-by finder tools. I tried the Matlab-one and the Pascal-one, and they are both kinda icky and complicated to use, and I'm not sure how to tune the parameters to get what I want. But maybe I should give them another go.

 

[Aegolius13]

You can see the same concept when planning a trip to the mun or Minmus.  Particularly for the latter, it only costs a few delta v to speed up your trip a lot.  So I seldom do a Hohnann transfer, but rather overshoot and the brake a little more to insert.

But since your Kerbin orbit is so much closer to the center of the orbit than an interplanetary transfer, the launch window issues don't apply.

[Mike Mars]

2 hours ago, Leafbaron said:

@eddiew This, well said.

 I recently and by recently I mean months ago got Kerbal Alarm Clock. I thought "oh this will be awesome, I can run parallel missions and keep track of everything!" which is true, you can. However, it really limits how much you can time warp and you still need to make sure you don't have two maneuver nodes setup to burn at the the same time. But i thought i would be able to get so much done, and really you get more done in kerbin SOI but less far trips done. if you don't care about how high the game clock reaches and your progression just time warp the excrements out of those Duna missions. Or get the interstellar mod pack, there is an high energy fusion reactor engine that delivers like 40k DV and 3g acceleration. With those stats you could start orbiting Kerbol Retrograde and meet up with Duna in a real hurry.

I've actually gotten up to 86K DV with the standard fusion engine from Impossible Innovations. The high efficiency engine will give you 48K easy.

MM

[Leafbaron]

3 minutes ago, Mike Mars said:

I've actually gotten up to 86K DV with the standard fusion engine from Impossible Innovations. The high efficiency engine will give you 48K easy.

MM

Yes, and I believe as throttle goes down, ISP goes up. so if you don't mind minscule thrust you can squeeze more dV out of it.

[septemberWaves]

Due to wanting to practice calculations for a college project (consisting of designing a Mars exploration program) I've recently been looking into using a cycler. I'm currently in the process of designing a heavily-modded Duna-Kerbin mothership that can be placed into a cycler orbit and stay there.

A cycler orbit, for those who are unfamiliar with the concept, is an orbit that passes by two celestial bodies (e.g. Earth and Mars) for a high-energy transfer window in both directions, and is an exact multiple of the synodic period between both destinations (time it takes for both bodies to be in the same position relative to each other) so that they are in the same place relative to each other at the same point on the cycler's orbit. Usually a vessel in a cycler orbit will stay beyond the Hill Sphere (SOI) of each body to minimize changes to the orbit (though some corrections have to be made, usually to account for orbital eccentricity in the destinations' orbits). This is a good choice of mission profile for multiple repeated crew missions, as it can help to minimize the crew's time in microgravity as well as meaning that an incredibly massive mothership can be placed in the cycler orbit and then never need to expend large amounts of propellant on entering or exiting orbit around either Earth or its destination. Most cycler orbits will have an apoapsis above the orbit of the higher planet, and a periapsis below the orbit of the lower planet. An ideal cycler orbit has an orbital period exactly equivalent to the synodic period between its destinations, so that both transfer windows occur every orbit.

The plan I have for my college project (which I will be replicating to some degree in KSP) involves the MCV (Mars Cycler Vehicle) which will be assembled in Earth orbit and then transferred using an autonomous nuclear thermal propulsion module which will be moved into a graveyard orbit once no longer needed. The MCV will have all necessary life support and habitation capabilities for the crew, and will pass by both Earth and Mars at a specific high-energy transfer window in both directions. For every orbit the MCV makes (for the duration of the Mars exploration program) it will be resupplied and be able to facilitate a new mission. The resupply vehicle will be fully autonomous, but will need to have the same reliability rating as a crew-rated vehicle because the crew would not survive without the success of the resupply mission.

There will be a HTV (High-energy Transfer Vehicle) to take the crew to/from the cycler. This will consist of a reusable crew module, and a high-efficiency propulsion module that will be replaced with every mission. The HTV will stay in HEO (High Earth Orbit) between the magnetic fields for the duration of its stay at Earth (where it will be refurbished and the propulsion module replaced) and in LMO (Low Mars Orbit) for the duration of the crew's time at Mars. There will also be a replacement HTV ready for launch each time so that in the event of the HTV returning and being unable to be reused, the Mars exploration program can still continue. I will aim to have it spend no longer than 4 weeks travelling between the MCV and either planet. This means that the propulsion module will need rather high efficiency, and will probably involve the use of either magnetoplasma thrusters or a high-efficiency chemical engine (such as a tri-propellant engine). I also want to ensure that it is capable of supporting the crew in LMO for the entire time period between the arrival at Mars and the departure for Earth, in case there is any issue that would mean that the surface mission cannot be conducted.

For each mission, there will be a new MDV (Mars Descent Vehicle), MAV (Mars Ascent Vehicle) and MSH (Martian Surface Habitat). They will each be transported to LMO before the mission that will use them (much like in The Martian) and the MAV and MSH will be landed at whichever landing site is chosen for that particular mission. The MSH will be sent with all necessary surface equipment, and a pressurized rover.

Some of the missions (I will be proposing four out of the ten total) will also involve landing on both Deimos and Phobos using the DPEV (Deimos/Phobos Exploration Vehicle). This will be transported to LMO in the preparation phase of each relevant mission. The Deimos and Phobos landings will occur at the end of 

Before any of the crewed equipment, there will be a satellite network set up. A constellation of MPS (Martian Positioning System) satellites will be deployed in Mars orbit along with three larger satellites to serve as relay links back to Earth (there are three for redundancy). There will also be a relay satellite positioned at Mars's L4 point, and another at its L5 point, and two relay receiver satellites in Earth orbit. This will ensure a continuous communication link to all vehicles involved in the Mars exploration program.

As for launch systems, I will mainly try to limit all modules to Falcon 9 and Falcon Heavy payload capacities (22.8 tonnes and 54.4 tonnes respectively), in an attempt to prioritize reusable launch systems (and at the same time help to test out and therefore improve the Falcon systems). For larger payloads I have allowed myself the option to use NASA's SLS rockets, for payloads of 70, 105, 130, and possibly 150 tonnes if development of the Pyrios LRBs goes ahead. The crew will be transported to the HTV on a Dragon 2 (possibly launched on a Falcon Heavy if it can't reach the necessary orbit altitude from launch on a Falcon 9).

It's an incredibly complicated method as far as KSP goes, but it's definitely interesting and will be quite fun to execute (I just have to figure out the synodic period between Kerbin and Duna).

[Kerbart]

9 minutes ago, eloquentJane said:

(...)

It's an incredibly complicated method as far as KSP goes, but it's definitely interesting and will be quite fun to execute (I just have to figure out the synodic period between Kerbin and Duna).

Those are definitely the main reason to build a cycler in KSP. In real life it means that you will only have to spend DV once for your transfer vehicle with life support, shielding, communications, energy supply, etc on board. In KSP none of these are particularly relevant (unless using the various mods) and is the practical advantage of a cycler far more limited. But never let that get in the way of having fun!

[Kobymaru]

 

@eloquentJane

Interesting concept, and that's exactly the kind of alternatives that I'm talking about!

Do I understand correctly that this needs a separate vehicle at Kerbin and Duna to get to the Cycler? If so, the velocities have to be matched, and there's not much benefit to a direct high-energy trajectory. Like Kerbart said, only shielding and Life-Support systems would be permanently in orbit. In KSP, that's not a lot of mass.

The biggest drawback that I see (in KSP at least) is that those constant gravity assist encounters need to be manually flown.. painstakingly corrected with 2-4 maneuvers per cycle, every year... That seems like quite a hassle.

Nevertheless, interesting project!

 

ps.: Are you in this video? 

 

[septemberWaves]

Well, one of the mods I'm using is Kerbalism, so there is quite a significant benefit to the cycler orbit (I chose to use it because the project is primarily an exercise in mission planning and I decided that I want some experience with resource management (I know it's more complex in reality but the extra challenge in-game is still fun)). I also anticipate that there wont be too many correction burns required, since I'll be keeping the MCV exclusively in Kerbol's SOI and orbits in KSP have far less error than in reality. Also, I only plan on running three Duna missions as opposed to the minimum of 10 Mars missions that I am going to propose for my college project, so the MCV in KSP won't see an enormous amount of use.

@Kobymaru yes, the HTV is the separate vessel that will be used to transport the crew to/from the MCV at both Earth and Mars. It has to conduct high-energy transfers to rendezvous with the MCV, and also to transport the crew from the MCV to Mars and later back to Earth. It will dock to the MCV and stay with it for as much of the transfer as possible. Because of this mission profile, the HTV has to keep the astronauts in a cramped microgravity environment (the MCV has centrifuges and reasonable living space as well as a lab) and I want to minimize the time spent in such an environment (which unfortunately means that the HTV requires a huge amount of delta-v and therefore will probably use low-thrust electric propulsion).

The alternative is a mission profile like in The Martian, where the Mars transfer vehicle will get into an orbit around both destinations. I chose to avoid this because the MCV is enormous due to the need to store 7 astronauts in deep space for several years in total (I'm not sure quite how large it will be yet but I anticipate it being significantly more massive than the ISS (largely due to the centrifuge modules)) and therefore the propellant costs for transferring it between SOIs would seriously add up even with high-I_sp thrusters. I also would anticipate that ethics councils would not allow the use of nuclear thermal propulsion on a crewed spacecraft, so the most effective method of transporting the MCV into its required orbit is not really an option for use when the crew are on board (hence why that transfer stage has to move into a graveyard orbit once the MCV is positioned safely). The other reason why I chose to use the cycler method is because it is rather interesting and doesn't require calculations on the same level of complexity as the spiral orbits of electronically-propelled vessels (which was the other propulsion option for the MCV and is its method of making course corrections).

Also, no, I am not in that video.