Lowest Delta-V SSTM

[cubinator]

After my first Jool-5 ISRU mega-SSTO thing, other people started doing similar things. One thing I noticed was that while I barely managed to get to Minmus with 5300 m/s of deltaV, astrobond managed it with a very similar rocket that only had 4860.

Now that got me wondering:

What is the minimum Delta-V to Minmus?

The delta-V map I use says the absolute optimal deltaV for getting from Kerbin to Minmus is 4470 m/s. As far as I know, this has never been done before. So now I challenge you:

Build a Single Stage Rocket which can travel to Minmus. wait, did I just mimic the KSP contract format? huh.

-It can be a plane, rocket, or even a turtle.

-It must be propelled with rocket engines.

-It must be Single-Staged, meaning nothing is decoupled. (If you want to use decouplers for some purpose other than decoupling, go for it. Just don't separate anything.)

-Either use an informational mod like KER to display delta V values, or give me the full/dry masses, TWR, and Isp of engine(s) used so I can calculate it myself. It's easier to keep track of if you just use a mod.

-Remember, this challenge is not about least fuel to Minmus, it's about least delta-V.

-Delta-V values in the leaderboard are in vacuum.

-Please submit screenshots of every important moment such as launch, orbit, transfer, landing, as well as one in VAB with dV info tabs open, if you have them. Videos are ok too.

-No refueling as part of the submission, ISRU points are because it's hard to make a ship with a big ISRU unit and get it somewhere.

-No EVA landings, the lander itself must arrive at the surface (intact).

-No cheaty mods like Hyperedit may be used. Not sure what kind of engine mods will help you here, so you can use them if you want and I will judge how cheaty they are. Kraken propulsion/warp drives are not accepted as this is a rocket-based challenge.

-Bonus points* if you make an SSTO turtle

-If your ship has an ISRU system (no refueling during submission, your ship is graded based on how much it can go on one full (set of) tank(s)

-If you bring lots and lots of SCIENCE!!!

-If your ship can get back to Kerbin from Minmus without refueling

-If it can go EVEN FURTHER than Minmus without refueling

*not really a point system, just an honorable mention in the leaderboard.

Leaderboard:

1. PLAD (4097 m/s, Mammoth engine cluster, less fuel made it better(?!))

2. killakrust (4351 m/s, Mainsail engine, 3 Kerbals to Minmus surface)

3. PLAD (4440 m/s, Mammoth engine cluster, 1 Kerbal to Minmus surface with 309 m/s to spare!)

4.

5.

Frequently Asked Questions:

-Why haven't you banned OP engine mods?

A:OP engines will not affect delta-V usage; in fact, most of them make it more which is bad for this challenge.

Hope you enjoy the challenge! Let me know if anything is unclear and I will attempt to clarify it when my occasionally busy schedule allows it.

Edited November 6, 2015 by cubinator

[Van Disaster]

Well it's certainly been done in 0.90 ( check the submissions to this as an example and remember that was there & back again ) - question is, how about FAR? Shouldn't make any difference to orbit dV for rockets, but I refuse to fly a plane without it...

[Foxster]

Just checking...This is a single stage craft launched from Kerbin that then without refuelling goes on to land in one piece on Minmus?

BTW...that minimum dV number of 4470 is not necessarily for a single stage craft.

[cubinator]

Here is an example submission:

Javascript is disabled. View full album

It was just something I put together in a few minutes, and it worked remarkably well. Aerodynamics must be the key here...

- - - Updated - - -

how about FAR?

FAR is ok. I can't really think of any mod that would actually disqualify, as long as the ship is actually flown with rockets go ahead.

- - - Updated - - -

Just checking...This is a single stage craft launched from Kerbin that then without refuelling goes on to land in one piece on Minmus?

That's right.

[Kagame]

Thinking about it. Tried a direct intercept-to-landing, succeeded at maybe 200 m/s shy of astrobond's mark, only for me to be an idiot and lock the suspension of my landing legs, causing the stack to.... well.... "poing" upon landing. And since it was a mighty big ol' rocket, I couldn't recover before it came back down to Minmus xD

Update: Is advanced lithobraking allowed? Like, USI floaties with 200 m/s of impact tolerance?

Edited October 31, 2015 by Kagame

[Van Disaster]

On Minmus you tend to just bounce off.

[cubinator]

Is advanced lithobraking allowed? Like, USI floaties with 200 m/s of impact tolerance?

I would prefer a soft landing, but I'm also interested in what ideas people come up with. I might make a separate category for lithobrakes.

[Kagame]

Oh, and one mod you'll want to ban from the start: Eskandare's Thermal Nuclear engine mod. It's a fairly realistic representation of a theoretical nuclear combined cycle engine. The problem is that nuclear combined cycle engines are DEAR GOD OP. You'd be able to SSTM with two LF fuselages, basically.

Edit:

-Instell Incorporated, I'll leave to your decision. It's possible to circularize on scramjets alone thnks to Kerbin's small radius, but it's incredibly difficult and still takes fuel- unlike Thermal Nuclear.

- Interstellar Extended may make things a bit too easy.

Edited October 31, 2015 by Kagame

[Van Disaster]

Oh, and one mod you'll want to ban from the start: Eskandare's Thermal Nuclear engine mod. It's a fairly realistic representation of a theoretical nuclear combined cycle engine. The problem is that nuclear combined cycle engines are DEAR GOD OP. You'd be able to SSTM with two LF fuselages, basically.

Well - that does bring up something I've not thought about fully; is it better to have a higher or lower ratio of fuel to structural mass? this is about dV cost rather than absolute fuel use, so in theory it shouldn't matter how OP your engines are as long as they actually use fuel and don't teleport you. Reporting dV with combined cycle engines like Rapiers is awkward though, more so when you have nuclear engines thrown in as well.

[cubinator]

Well - that does bring up something I've not thought about fully; is it better to have a higher or lower ratio of fuel to structural mass? this is about dV cost rather than absolute fuel use, so in theory it shouldn't matter how OP your engines are as long as they actually use fuel and don't teleport you. Reporting dV with combined cycle engines like Rapiers is awkward though, more so when you have nuclear engines thrown in as well.

I agree, OP engines won't help you in this challenge. I would like to stay away from jet engines and Rapier type engines, just to make things easier to calculate. Jet engines could actually hurt you, as the challenge is not about least delta-V used, it's about how much is actually in your ship, and jets can get some ridiculously high numbers sometimes.

[killakrust]

Ok, so here is my entry.

Made it to Minmus with 4351 DV in craft, used 4314.

Javascript is disabled. View full album

The trick seems to be reducing atmospheric drag on the Kerbin takeoff. I tried with a larger craft like cubinator, but the drag made me lose too much dv.

I'm not sure but I suspect a 1.25m craft with a powerful enough engine might be able to do better, but I don't think the stock engines are up to the job.

[cubinator]

Ok, so here is my entry.

Made it to Minmus with 4351 DV in craft, used 4314.

Good job! I too found that atmospheric efficiency is the key to this challenge.

[astrobond]

Ok, so here is my entry.

Made it to Minmus with 4351 DV in craft, used 4314.

http://imgur.com/a/RKsqs

The trick seems to be reducing atmospheric drag on the Kerbin takeoff. I tried with a larger craft like cubinator, but the drag made me lose too much dv.

I'm not sure but I suspect a 1.25m craft with a powerful enough engine might be able to do better, but I don't think the stock engines are up to the job.

Wow Excellent !

Better than the minimal required dV lol

Congrat's killakrust

Not a lot of time to try this challenge grrr... but i think some wings could also be something to test to minimise total dV needed....

[PLAD]

This is a very interesting challenge. I'm used to trying to do something with minimum mass, it turns out that is not always similar to trying to do it with minimum dV expended. As someone pointed out earlier, the key to this challenge is getting out of Kerbin's atmosphere with as little dV as possible. Using tricks like flying by Mun multiple times to set up the best Hohmann from there to Minmus, making low burns to maximize Oberth, etc. can save maybe 100m/s. But optimizing the ascent can save hundreds. At first I experimented with flat ascent trajectories and high acceleration to reduce gravity losses, but I kept hitting a wall at a bit under 3050m/s to LKO where the decreasing gravity losses where overwhelmed by the increasing drag losses (Mechjeb has a great option for tracking these, see my pictures). Then I discovered that a straight-up ascent solved both problems if your TWR is high enough! Normally straight up is a bad idea for several reasons-under a TWR of about 5 the gravity losses overwhelm any other advantage, and if you are going to land on Mun or intercept anything in orbit your lack of tangential velocity means the encounter will be at very high speed, also eliminating any dV advantage. It is also VERY hard to aim accurately, and especially to cut off the engine at a precise speed. At a TWR of 12 a 1-second delay in cutoff makes for a 120m/s error! But because I was aiming for a Mun flyby the lack of tangential velocity actually increased its effect, and the aim didn't have to be so precise as long as you do a correction shortly after cutoff. It all worked out. Normally getting to LKO would be at least 3010m/s, and the burn from there to a Mun flyby would have to be at least 845m/s, for a total of 3855m/s. But in this entry I got from LKO to the Mun flyby for only 3780m/s.

Total dV from Kerbin launch to Minmus landing: 4079m/s. And I landed standing up!

Now I'm trying to find a way to get back to Kerbin with the 309m/s left in the tank. I've never done it with less than 390 so I think I'm doomed.

Javascript is disabled. View full album

PS-How's that parachute for optimism? We had to put it there to convince Jeb to fly the thing.

Edited November 3, 2015 by PLAD
Said radial, meant tangential.

[astrobond]

This is a very interesting challenge. I'm used to trying to do something with minimum mass, it turns out that is not always similar to trying to do it with minimum dV expended. As someone pointed out earlier, the key to this challenge is getting out of Kerbin's atmosphere with as little dV as possible. Using tricks like flying by Mun multiple times to set up the best Hohmann from there to Minmus, making low burns to maximize Oberth, etc. can save maybe 100m/s. But optimizing the ascent can save hundreds. At first I experimented with flat ascent trajectories and high acceleration to reduce gravity losses, but I kept hitting a wall at a bit under 3050m/s to LKO where the decreasing gravity losses where overwhelmed by the increasing drag losses (Mechjeb has a great option for tracking these, see my pictures). Then I discovered that a straight-up ascent solved both problems if your TWR is high enough! Normally straight up is a bad idea for several reasons-under a TWR of about 5 the gravity losses overwhelm any other advantage, and if you are going to land on Mun or intercept anything in orbit your lack of radial velocity means the encounter will be at very high speed, also eliminating any dV advantage. It is also VERY hard to aim accurately, and especially to cut off the engine at a precise speed. At a TWR of 12 a 1-second delay in cutoff makes for a 120m/s error! But because I was aiming for a Mun flyby the lack of radial velocity actually increased its effect, and the aim didn't have to be so precise as long as you do a correction shortly after cutoff. It all worked out. Normally getting to LKO would be at least 3010m/s, and the burn from there to a Mun flyby would have to be at least 845m/s, for a total of 3855m/s. But in this entry I got from LKO to the Mun flyby for only 3780m/s.

Total dV from Kerbin launch to Minmus landing: 4079m/s. And I landed standing up!

Now I'm trying to find a way to get back to Kerbin with the 309m/s left in the tank. I've never done it with less than 390 so I think I'm doomed.

http://imgur.com/a/Xf52h

PS-How's that parachute for optimism? We had to put it there to convince Jeb to fly the thing.

Awesome !!!

[killakrust]

This is a very interesting challenge. I'm used to trying to do something with minimum mass, it turns out that is not always similar to trying to do it with minimum dV expended. As someone pointed out earlier, the key to this challenge is getting out of Kerbin's atmosphere with as little dV as possible. Using tricks like flying by Mun multiple times to set up the best Hohmann from there to Minmus, making low burns to maximize Oberth, etc. can save maybe 100m/s. But optimizing the ascent can save hundreds. At first I experimented with flat ascent trajectories and high acceleration to reduce gravity losses, but I kept hitting a wall at a bit under 3050m/s to LKO where the decreasing gravity losses where overwhelmed by the increasing drag losses (Mechjeb has a great option for tracking these, see my pictures). Then I discovered that a straight-up ascent solved both problems if your TWR is high enough! Normally straight up is a bad idea for several reasons-under a TWR of about 5 the gravity losses overwhelm any other advantage, and if you are going to land on Mun or intercept anything in orbit your lack of tangential velocity means the encounter will be at very high speed, also eliminating any dV advantage. It is also VERY hard to aim accurately, and especially to cut off the engine at a precise speed. At a TWR of 12 a 1-second delay in cutoff makes for a 120m/s error! But because I was aiming for a Mun flyby the lack of tangential velocity actually increased its effect, and the aim didn't have to be so precise as long as you do a correction shortly after cutoff. It all worked out. Normally getting to LKO would be at least 3010m/s, and the burn from there to a Mun flyby would have to be at least 845m/s, for a total of 3855m/s. But in this entry I got from LKO to the Mun flyby for only 3780m/s.

Total dV from Kerbin launch to Minmus landing: 4079m/s. And I landed standing up!

Now I'm trying to find a way to get back to Kerbin with the 309m/s left in the tank. I've never done it with less than 390 so I think I'm doomed.

PS-How's that parachute for optimism? We had to put it there to convince Jeb to fly the thing.

Yeah, fantastic job.

You might even save a bit more DV if you ditch the fins on the bottom of the craft. I'm sure it helped my attempt a tiny bit.

[cubinator]

in this entry I got from LKO to the Mun flyby for only 3780m/s.

Total dV from Kerbin launch to Minmus landing: 4079m/s. And I landed standing up!

Now I'm trying to find a way to get back to Kerbin with the 309m/s left in the tank. I've never done it with less than 390 so I think I'm doomed.

http://imgur.com/a/Xf52h

PS-How's that parachute for optimism? We had to put it there to convince Jeb to fly the thing.

Good job! Interesting idea with the direct ascent path, it really does save fuel, doesn't it? I know that landing high up can save some fuel, but 309 m/s sounds tough.

Theoretically, if you can get to a Mun intercept, you can get out to solar orbit, then later get a gravity assist with Kerbin again, then transfer to Duna, use an Ike gravity assist to slow into an eccentric orbit, then aerobrake in Duna's atmosphere as many times as needed to bring your apoapsis down and eventually land...

BTW I read off of vacuum delta-V for the leaderboard, so that puts you in second place with 4440 m/s. Most of the time is spent in space (at least in all the successful space missions I've heard of), so that's where I take the delta-V numbers from.

Edited November 5, 2015 by cubinator

[PLAD]

OK, I could not get that last ship back to Kerbin. So I decided to make another run using what I learned from the first one, and this time landed with exactly zero fuel left (it ran out at 5m altitude and landed at about 4m/s, so survived). Changes were:

-Removed fuel to reduce takeoff vacuum dV to 4092m/s. This cut the total mass by 10% and increased the acceleration, thus dropping the gravity losses by about 50m/s.

-Launched 1 minute later, at 2:31:00, to raise Mun flyby altitude and cut Minmus SOI arrival speed by 18m/s.

-Landed at 3080 meters instead of 2665.

-Running out of fuel just before landing was also handy, slowly lowering the ship the last few meters uses a lot of dV, as long as you kill all but the last 5m/s or so low above Minmus you should be OK. If you have a large SAS! It tilted 18 degrees from vertical before the SAS saved it from falling over. I'm glad I wasn't sitting up in that cockpit.

So this is my final entry, 4092m/s. I am intrigued by how much more could be cut by using a monstrous high-acceleration ship, but balancing the drag losses of sticking more motors on against the reduced gravity losses would be a trick.

I tend to uses dV expended as recorded by Mechjeb as a guide, though it's complicated to confirm the numbers using the rocket formula because the iSP changes as the rocket leaves the atmosphere. But I would say that this mission got from Kerbin to Minmus' surface with an expended dV of 4037m/s. Your way is more useful for planning a mission though, since the number you are given by Mechjeb or KER as you design the ship is the vacuum dV. (Or the 0-altitude atmosphere dV, which is kind of less use for a rocket.)

Javascript is disabled. View full album

[herbal space program]

So this is my final entry, 4092m/s. I am intrigued by how much more could be cut by using a monstrous high-acceleration ship, but balancing the drag losses of sticking more motors on against the reduced gravity losses would be a trick.

I tend to uses dV expended as recorded by Mechjeb as a guide, though it's complicated to confirm the numbers using the rocket formula because the iSP changes as the rocket leaves the atmosphere. But I would say that this mission got from Kerbin to Minmus' surface with an expended dV of 4037m/s. Your way is more useful for planning a mission though, since the number you are given by Mechjeb or KER as you design the ship is the vacuum dV. (Or the 0-altitude atmosphere dV, which is kind of less use for a rocket.)

I think there still must be some way to improve TWR/drag, but you totally nailed so many other aspects of this that I think you’re going to be very tough to beat in practice.

[herbal space program]

I agree, OP engines won't help you in this challenge. I would like to stay away from jet engines and Rapier type engines, just to make things easier to calculate. Jet engines could actually hurt you, as the challenge is not about least delta-V used, it's about how much is actually in your ship, and jets can get some ridiculously high numbers sometimes.

I think OP engines will definitely help you if they have better TWR values than stock does for similar ISPs. As PLAD has shown us, the fundamental parameter of this challenge is how high TWR/drag is for your stack when it takes off. AFAICT, everything else is execution, although that part is by no means trivial. By my reckoning, this number will depend linearly on both the TWR and ISP of the engine in question, since the former dictates the acceleration on takeoff for a given mass and the latter how large that mass will have to be. Other than those, drag is the only real structural consideration.

[cubinator]

I think OP engines will definitely help you if they have better TWR values than stock does for similar ISPs..

I think the only engine that would give a significant advantage is one with super high TWR, and an Isp that is super high in atmo, but goes way down to normal in vac, because I measure delta-V in vacuum so your atmospheric efficiency wouldn't matter.

[herbal space program]

I think the only engine that would give a significant advantage is one with super high TWR, and an Isp that is super high in atmo, but goes way down to normal in vac, because I measure delta-V in vacuum so your atmospheric efficiency wouldn't matter.

I think ISP is important both in atmosphere and vacuum because it indirectly affects the critical parameters of both TWR and drag. Here’s how I see the physics: Clearly the biggest source of deltaV loss in this exercise is getting off of Kerbin. Getting off of Kerbin entails possible losses from two sources: atmospheric drag and fighting gravity. The ideal solution to the first issue is to launch the most streamlined stack you possibly can as straight up as you can, minimizing the total amount of air you have to go through and how much energy you transfer to it. The solution to the second would be to instantaneously deliver the entire impulse required to get you where you’re going on the ground so that you can coast all the way to your destination. You could escape an airless Kerbin that way for around 3.4 km/sec, and whatever fraction of that it takes to reach the Mun SOI plus the drag losses is the absolute floor of how much dV you need to expend to get to Minmus. So what you need to do is accelerate as quickly as possible from the moment you take off, on a near-vertical trajectory that tops out just at the right spot on the inner edge of the Mun’s SOI. Your acceleration will depend on the TWR of the whole stack on the pad and on how much drag it has. The intrinsic TWR of the engine is one critical component of the first parameter, but its ISP is also critically important because it dictates how heavy the whole stack will be. The less fuel you have to boost, the faster you will accelerate. Less fuel also means less total drag, so ISP affects that as well. I don’t know what the correct formula to optimize this relationship is, but I Imagine it works out to something along the lines of maximizing TWR*LN(ISP)/drag coefficient. I think I might try applying that formula to all the available engines and seeing if any of them beat out the Mammoth. I also note the PLAD had an actual capsule on the ship, and you didn’t specify that there had to be a Kerbal aboard, so there could be some dV shaved off there by using a probe core. Anyway, I agree with PLAD that this is indeed a very interesting challenge.

[Red Iron Crown]

I think the ideal engine for this challenge would have atmo and vacuum Isps as close in value as possible (while still being able to lift enough fuel). Every m/s of atmo dV used will cost less vacuum dV that way.

[herbal space program]

I think the ideal engine for this challenge would have atmo and vacuum Isps as close in value as possible (while still being able to lift enough fuel). Every m/s of atmo dV used will cost less vacuum dV that way.

Yes I was just figuring this out. Having everything based on vacuum dV kind skews the calculation. I was thinking that aerospikes might stand a chance of edging out the Mammoth, but their higher vacuum ISP will penalize them. One thing that might offset this is the fact that values close to vacuum ISP are reached pretty quickly. I monitored the ISP of the Mammoth on a stack very similar to PLAD’s, and found that it reached 310 at about 22 sec in, and engine cutoff was at 57 sec, so most of the burn actually happens at very close to vacuum ISP. I’m going to spend a little time investigating this.

I’m also going to investigate the optimal atmospheric ascent speed a bit more. It seems like too fast too low might cause excessive drag losses that will more than offset the gravity losses of going a bit slower at first.

[Red Iron Crown]

I’m also going to investigate the optimal atmospheric ascent speed a bit more. It seems like too fast too low might cause excessive drag losses that will more than offset the gravity losses of going a bit slower at first.

IME experience gravity losses trump drag. Getting sideways as soon as possible is the best play dV-wise, just have to be careful to avoid burning up.