Lowest cost per ton to Jool Intercept

KerikBalm · July 25, 2018

I've seen plenty of lowest cost per ton challenges for stock Kerbin orbit, but I haven't seen cost per ton challenges beyond that.

So why not a Jool intercept challenge? *

Rules:

#1) Must be all stock, Skiff and Wolfhound from Making history are not allowed.

#2) Commnet may be disabled

#3) No ISRU permitted

#4) Recovered craft parts may be deducted from the total cost (feel free to make SSTO designs)

#5) No exploits such as ladder drives,, kraken drives, or "getting out and pushing"

#6) Payload must not play any function role for the craft prior to decoupling.

Leader board: 500 funds per ton to Jool Intercept

* @Marschig

* @nickifr 5393 funds/ton

* @purpleivan 9008.5 funds per ton of payload to Jool

*

* Actually I'd like to do a 3x kerbin lowest cost to orbit challenge, but then that would limit participation, and if 3x only refers to the SMA around Kerbin's sun, and the radius of kerbin, that leaves the settings of atmosphere height, mountain height, and rotation period which would further limit entry. The dV requirements for getting to orbit on 3x kerbin are similar to the requirements for getting a Jool intercept in stock, so this challenge is a bit of a 3x lowest cost to orbit proxy.

Thus I'll make a sub category with requirements to make it a better proxy:

#7) No gravity assists prior to Jool intercept

#8) TWR must generally remain above 0.8 (relative to kerbin's surface): a dV of no more than 1,000 m/s is allowed to be generated at an acceleration in the 1-8 m/s^2 range.

#9) Orbital assembly is not allowed, recovery of parts that reach kerbin orbit, but don't reach Jool intercept are not subtracted from the cost.

3x Proxy leaderboard:

*

Edited September 8, 2018 by KerikBalm

OHara · July 26, 2018

Good idea. This should be interesting.

6 hours ago, KerikBalm said:

#5) No exploits such as [...]

The base category invites a space-plane that re-configures ~~to ion drive~~, which is likely to inspire a few designs that you may or may not consider exploits. Do you want to define any these of these as exploits or not before we get started?

* Ion drives stack by default, the thrust from one passes through another ion drive, giving a summed thrust.

* Ion drives thrust through anything else stacked upon or enclosing their outputs; they thrust through closed cargo bays.

* Other engines, Rapers, Vectors, etc., can form stack with all producing thrust if you offset them.

6 hours ago, KerikBalm said:

Thus I'll make a sub category with requirements to make it a better proxy:

#7) No gravity assists prior to Jool intercept

I don't know what "3x kerbin" means. Is it reaching an orbit 3x that of Kerbins around the sun? SSTO from 3x gravity? from Kerbin scaled 3x, with normal surface gravity?

The sub-category rule would seem to allow a Tylo gravity assist, if done after intercepting Jool, and I'm not sure if 'intercept' means entering the SoI or passing a periapsis with Jool.

Edited July 26, 2018 by OHara
looked up the price of Xenon for ion drives

KerikBalm · July 26, 2018

Ions would be allowed, their propellant costs are rather high, I'm not sure it would necessarily be worth it.

For now, I wouldn't enforce any part clipping rules, except part clipping things to avoid drag: which it normally doesnt effect except iin cases where you clip a bunch of stuff into a small service bay or something like that.

3x kerbin would be using the mod kopernicus (and perhaps sigma Dimensions to make the rescale simpler) that maintains the same surface gravity, but has an 1800 km radius instead of 600km, and has an SMA of 40.8 million km instead of 13.6 million km. Note 1800/600 = 3, also 40.8/13.6 = 3

And yes, a tylo gravity assist would be allowed, you only need to intercept Jool's SOI. You can use a tylo gravity assist if you want to help return a reusable craft.

Rescale links;

Note they have 2.5 and 3.2... I do my own 3x parameters.

I see that Kopernicus may not be working in 1.4 yet... I haven't updated to 1.4 yet. That would be another issue for a real 3x kerbin payload to orbit challenge... Definitely a proxy challenge is a better idea

Edited July 26, 2018 by KerikBalm

Laie · July 27, 2018

I wonder if I should submit an entry based on my recent recent Jool-5. I guess I could calculate the cost of the LV vs what arrives at Jool. But being a throw-away launcher, I guess it won't be competitive in the end. What do you say, would this be the kind of entry you even want to see? I pretty certain it couldn't do a x3 ascent, at any rate.

purpleivan · July 29, 2018

Here's my crack at this. Nothing complicated, just a Spark sitting on top of a Kickback.

Cost was 5515 funds and mass of 24.880 tons, which works out at 224.076 funds per ton

Just a basic attempt this, so expecting it to be given a thorough spanking. Actually I've been messing around with vertically launched SSTO's for the last couple of days, and the upper stage of this would fit nicely in the cargo bay of one of those.

So might be giving this another attempt later.

In VAB

Kickback most of way to orbit.

Circularise on the Spark

In orbit.

Burn for Jool.

On its way out.

Course adjustment to swing by Tylo, to bring vehicle into Jool orbit.

Hi guys.

Passing Tylo.

In Jool orbit.

Marschig · July 29, 2018

2 hours ago, purpleivan said:

Cost was 5515 funds and mass of 24.880 tons, which works out at 224.076 funds per ton

Maybe the mass at Jool was meant? Because

On 7/25/2018 at 8:27 PM, KerikBalm said:

Payload must not play any function role for the craft prior to decoupling.

purpleivan · July 29, 2018

7 hours ago, Marschig said:

Maybe the mass at Jool was meant? Because

Ah... didn't notice that. I was thinking that it was a bit strange that the total mass was the one that counted.

Ok, here's the revised stats.

Total cost = 5515 funds and a mass arriving at Jool of 0.28 tons, so a total of 19696 funds per ton. Definately going to have another go at this with an SSTO launcher.

Scrub that, just realised that the mass at Jool has to be minus anything related to getting the payload there, so the spark and tanks would have to be deducted too.

Started a spaceplane mission that suffered the same issue, so I'm going to re-start with a payload specific section, that is detached at Jool for clarity.

Edited July 29, 2018 by purpleivan

KerikBalm · July 29, 2018

@purpleivan

I'm sorry, but I thought it was clear that I was talking about the cost per ton of *payload*

Your entry delivers a mostly empty vessel to Jool intercept, with most of that mass playing a functional role. Being generous, you got 1.96 units of fuel and oxidizer to Jool intercept, which is about 0.01 tons of mass that didn't play a role in reaching Jool, which at a starting cost of 5515 funds means.... over 550,000 funds per ton to Jool intercept

On 7/27/2018 at 4:26 AM, Laie said:

I wonder if I should submit an entry based on my recent recent Jool-5. I guess I could calculate the cost of the LV vs what arrives at Jool. But being a throw-away launcher, I guess it won't be competitive in the end. What do you say, would this be the kind of entry you even want to see? I pretty certain it couldn't do a x3 ascent, at any rate.

Sure. One final addendum in case it wasn't clear: The cost of the payload is not to be included in the cost per ton - it shouldn't matter if you deliver 5 tons of Ore that is dirt cheap, or 5 tons of xenon gas, or 5 tons of RTGs.

The mass of the payload divided by the cost of the launch & transfer vehicle to get the payload to jool.

Your entry may be competitive, throwawy vehicles would be much more competitive here vs to just LKO (as the dV requirement increases, staging gets more and more apprealing=

purpleivan · July 30, 2018

Ok... attempt number 3 (I bailed on the 2nd when I realised it didn't really match the rules).

This is an entry that uses a spaceplane to place a payload of 235kg in orbit of Jool, at a cost of 9008.5 funds/ton

Here are the pics salient to the challenge entry.

Mass of the payload at Jool

Cost of the probe 1606.

Cost of the spaceplane wet 31,640.

Cost of the spaceplane dry 31,129 (so fuel cost of 511)

Total cost of mission 511+1606, to put 0.235 tons in Jool orbit = 9008.5 funds/ton.

If there's anything missing or wrong here, let me know. I'll blame doing this far too early in the morning (started putting vehicle together at 6:30am).

Here's a few scenic pics (full Imgur album here).

Edited July 30, 2018 by purpleivan

nickifr · August 8, 2018

Since there only seems to be a single entry on the leaderboard as of now, I decided to have a go at this myself.

I decided to go with a falcon-9-style rocket. As payload I used a few empty ore tanks, together exactly 1000kg.

So here are the stats:
Mass of payload: 1.000kg
Cost of payload: 2.188 funds
Cost of transfer stage: 2.679 funds
Cost of filled booster stage: 40.576 funds
Value of empty, landed booster (assuming empty tanks): 37.862 funds

Calculation (payload not included; Booster recovered with empty tanks): 2679+40576-37862=5393
This means the payload delivery cost for this rocket is: 5.393 funds/ton

Now to the screenshots:
Here are the two full imgur albums: VAB, Flight documentation
If you don't want to use them, here are some individual pictures since the imgur album embed is broken once again:

VAB views:

Spoiler

VAB view of payload (2.188 funds cost; Exactly 1.000kg)

VAB view of the transfer stage (2.679 funds, fully expendable)

VAB view of the booster (40.576 funds, fully recoverable; See the next picture to see how much your get from a recovery)

VAB view of the booster when empty (37.682 funds, this is how the booster is recovered and therefore how much I get back)

VAB view of the finished rocket.

Screenshots of the flight:

Spoiler

Liftoff!

Not doing a gravity turn with this rocket because I want to recover the booster

Booster seperation, slight boostback burn.

Multitasking (Booster is on a suborbital trajectory; I need to orbit the upper stage before the booster reenters the atmosphere, otherwise it despawns...)

Upper stage entering orbit while booster stage is still on a suborbital trajectory

Booster using the airbrakes to slow down

Booster landed and recovered, reclaimed 37.862 funds

Planning a transfer maneuver

Leaving kerbin behind

Transfer in progress (Transfers to jool always take forever... Note I'm using earth time instead of kerbin time)

Jool intercept, challenge completed! (Marked as debris because the 1000kg-payload doesn't have a probe core)

Payload deployed during jool intercept! Exactly one ton of payload flying by jool. Should have brought a few cubesats with me instead, would have been more fun.

According to the challenge rules you only have to intercept jool, not orbit it, so that's all I did here. Doesn't seems as clean to do as performing a proper orbit, but I completed the challenge.

I guess there are still a few possibilities to reduce the cost/ton here. You could for example use a cheaper probe core (but loose reaction wheels), remove a few struts (but loose launch stability), have a bit less fuel in the upper stage (but reduce safety margins), ditch the battery (but risk probe blackout) or use a cheaper engine on upper stage (but reduce time you have left to land the booster). Definitely happy with this design, though.
Or, if you're really insane, you could do a BFR-type rocket, basically using a recoverable booster stage to get you to orbit, then transport the payload to jool with the second stage which you also return to kerbin. Uuh, maybe not.

Edited August 9, 2018 by nickifr
Imgur albums don't work... Replacing with multiple individual screenshots and added a bit more description, also put them all in a spoiler bracket to reduce space taken up by my post

KerikBalm · August 13, 2018

Nice entry, I've been really busy lately (new job, moving to new apt, wedding in 2 months), so sorry for not adding it sooner.

I've been meaning to take one of my 3x SSTO designs, and test it out on stock size kerbin, I figure I can dump a lot of oxidizer and use nukes to get a really good entry, but nothing so far...

and for a really good entry... have the spaceplane stage detach and wait (years) in orbit to recover a nuke stage much later.... that's an idea at least

Marschig · August 16, 2018

KM-T craft https://kerbalx.com/Marschig/KM-T

Inspired by VM-T

Spoiler

554.27 funds per t., screenshots and calculations below: https://imgur.com/a/HgNZb5Q

Spoiler

Fully assembled craft: 105409 funds, 104.477 t.

Payload: 34875 funds, 16.97 t. This is a part of an orbital station, ISRU and Ore don't used before decoupling at Jool.

Carrier: 70534 funds, 87.507 t.

Recovered Part without Fuel: 60928 funds, 20.157 t

So, maximum cost of mission (no fuel left after landing) is 70534-60928=9606 funds

4.2 m/s^2 at Start

267.4 m/s to acceleration > 8 m/s^2

When atmospheric engines becomes weak, rocket engines prevent drop acceleration below 8 m/s^2

Transfer Fuel to Jool Intercept Stage

Separation

Landing

250 Fuel left. So mission cost is 9606-250*0.8 = 9406

Cost per t. = 9406/16.97 = 554.27

Planning Jool Intercept. dV = 1793.6+111.2 = 1904.8 m/s

KER shows strange value 5559 m/s as stage dV, but real stage dV is 1964 m/s

Start acceleration is 6.81 m/s^2. To 8 m/s^2 burned 1793.6-1253.1 = 540.5 m/s

267.4+540.5 = 808 m/s < 1000 m/s allowed acceleration below 8 m/s

At Jool:

Edited August 17, 2018 by Marschig

FleshJeb · August 17, 2018

On 7/25/2018 at 10:27 AM, KerikBalm said:

#8) TWR must generally remain above 0.8 (relative to kerbin's surface): a dV of no more than 1,000 m/s is allowed to be generated at an acceleration in the 1-8 m/s^2 range.

I'm curious as to the rationale for that rule. My most efficient spaceplanes in 1x scale typically start with a closed-cycle TWR of 0.2, and as a whole, only get above 0.8 TWR when the open-cycle Rapiers are near full performance. This won't work as well in 3x, but you'd be shocked what you can get to orbit with a ridiculous amount of wings.

KerikBalm · August 17, 2018

@Marschig Very nice entry... I think we're starting to zero in on the point where funds per ton cannot come down so dramatically anymore

19 hours ago, FleshJeb said:

I'm curious as to the rationale for that rule. My most efficient spaceplanes in 1x scale typically start with a closed-cycle TWR of 0.2, and as a whole, only get above 0.8 TWR when the open-cycle Rapiers are near full performance. This won't work as well in 3x, but you'd be shocked what you can get to orbit with a ridiculous amount of wings.

That's exactly why the rule is for the 3x Proxy sub category, and not the general challenge. Also... I think I intended that to be for the non-air-breathing dV, because in 3x, when airbreathing engines cutout, you still need a lot of dV to get to orbit, and LV-Ns alone won't cut it (whereas LF only designs work fine in stock gameplay) for most of the ascent (my 3x designs have LV-Ns firing from before the switch to closed cycle, and they keep firing the rest of the way to orbit, whereas the rapiers go closed cycle, but then cutoff a few-several hundred m/s before orbit is achieved)

Marschig · August 25, 2018

Optimized version: https://kerbalx.com/Marschig/KM-TM

KS-25 and one J-X4 were changed to two LV-T45, unnecessary tanks and intakes were removed

Cost per ton: (43808 - 35224 - 89.86*0.8 - 75.95*0.18) / 16.97 = 500.8

Acceleration below 8 m/s^2: 342 + (1260-1216) + (1816-1276) = 926 m/s < 1000 m/s

https://imgur.com/a/tEcGfOo

P.S. Cost per ton can be lowered to 488 by replacing LV-T45 with T-1

Edited August 26, 2018 by Marschig

KerikBalm · September 8, 2018

Well, I just took my heavy cargo SSTO that I used for 3x games... launched it with a bunch of full Ore tanks... I should have paid more attention to how much ore it was... 187 tons was more than I intended as the payload I put 1 too many ore tanks (11 instead of 10). I had launched outside of a launch window, and indeed an optimal launch window doesn't require a plane change, so I just got the AP out to Jool and decoupled... I forgot to transfer reserve fuel to the rear section which needs to redock for recovery... so its not a formal entry. I had about 200 m/s left after decoupling the payload that would in theory be used to arrange a kerbin return journey.

Cost full, no payload: 708,728

Cost completely empty: 644,902

Total cost assuming 100% recovery: 63,826 funds

Since it was 187 tons: 341.5 funds per ton.

Now... I didn't actually get the intercept, nor did I actually recover my SSTO, so its not an entry yet... but it shows promise.

I think when I try for real, I'll do it with just 10 ore tanks, for 375 funds/ton.

And it of course qualifies for the 3x proxy challenge... but I think I may do a dedicated variant that does it in 2 stages