Heavy SSTO Efficiency Challenge

[icedown]

Heavy SSTO Efficiency Challenge

 

Purpose:

There are several challenges to build a SSTO and they have produced some very awesome results.  This challenge is designed around efficiency though.  The payload is two(2) standard orange jumbo tanks of fuel to orbit.  The target orbit is 300km with AP/PE +- 5.  This will also include a return to Kerbin. Scoring will be based on costs per mission in fuel.  Landing distance from KSC will be taken into account.  Landing AND stopping on the runway will give 0% penalty, on KSC grounds 5% and linear up to 50% penalty at maximum distance from KSC.  Score will be in credit value of fuel.

Rules:

1. The craft must not lose any parts during any phase of the flight with the exception of the jettisoning of the two(2) FULL Rockomax Jumbo-64 Fuel Tanks at the 300km orbit.  This does not have to be done but the craft must be capable of it.
2. The craft must lift off horizontally from the runway and land the same way, as with a normal aircraft. Parachutes are allowed for assistance stopping.
3. The craft must reach an orbit of 300km +-5km both AP/PE
4. The craft must have functional RCS to allow for docking and a usable docking port
5. All fuel tanks, wings, engines, and external parts must be stock, no tweakscale either
6. Craft must be capable of sustaining its own power requirements through either solar panels or fuel cells (Fuel cell fuel burn will count against score)
7. KJR is allowed.

Scoring:

Scoring will be accomplished by calculation of fuel used during the entirety of the trip.  Values will be in Kerbin's standard monetary unit. Values are stock and are as follows

• 0.80 per unit of liquid fuel
• 0.18 per unit of oxidizer
• 0.60 per unit of solid fuel
• 1.20 per unit of monopropellant
• 4.00 per unit of Xenon

For scoring purposes, screenshots are required showing starting and ending fuel, as well as required orbit and jettison of the 2 tanks.  Screen shots showing landing position as well as coordinates if not landed at KSC.  Videos are appreciated as are craft files.

Scoring will be done by LOWEST score.    Leader board will be posted here and I am currently working on a forum sig badge.

 

Top Entries

1. Orange Clockwork III by Kroshan                                                                                                11,238.72
2. Cargo 2 by mk1980                                                                                                                         11,671.80

 

Gate Crashers

Stingray Orange by Nefrums To efficient for government work

SSTO Double Jumbo by Mikki Forgot to turn on locator beacon and is MIA

 

Edited June 14, 2016 by icedown
Updated Leaders

[mk1980]

I think i'll make an entry to that challenge when I have some time to spare. One question though:

"4. The craft must have functional RCS to allow for docking and a usable docking port"

I usually dock my spaceships without RCS, and I don't really see why a cargo lifter plane that delivers tanks to orbit should even need to dock at all. I mean, if you intend to dock the craft, it's pointless to put the tanks in a cargo bay - that only adds the mass of the cargo bay on top of the mass of the tank. makes more sense to transfer the fuel from the internal tanks of the craft and not use cargo bays at all.

not going to start an argument here, though. a few MP tanks and RCS thrusters won't make or break the design anyway

[AviatorTrainman]

I've never even been able to take one orange tank up, but I'll try this challenge anyway, since I focus better when I have an actual tangible goal.

[icedown]

Building an SSTO is not an easy task.  One that can carry this load is even harder. It took me quite a while to build one that could achieve orbit with this kind of load. The purpose of the odd rules of this challenge is to make an efficient station and interplanetary builder.  The requirement to be able to jettison the tanks stems from the fact that this ship will be capable of hauling not only that mass, but that size to orbit, and not necessarily just fuel. Think of them as placeholders.  To be able to return without the fuel means that the ship doesn't care what's in the cargo bay.   The requirement for the RCS is because some people (Including me) do dock a lot with RCS.  When on orbit building a station, it may be necessary to move around it.  The reason for the 300km orbit is to have room for maybe a little heavier payload or some mistakes on the climb through the atmosphere.

I'm looking for ships that will fill the gap of multipurpose reusable heavy lifters.  To often we cover up inefficiencies in our ships with the "MOAR BOOSTERS!" mentality, but this challenge is designed to showcase ships that are efficient designs.  We have some awesome ship builders in this community and this is a tall task, but I think that everyone will learn from these ships how to build larger, stable SSTOs that are usable outside of one prize mission. These are probably the more complex and harder machines to build well in KSP. and I'm really hoping to see some awesome designs.  I learned a ton from looking at the K-Prize ships.  I designed this to be a workhorse extension of that prize.

Edited June 9, 2016 by icedown

[mk1980]

getting there. been messing around a bit. basic design is an mk3 plane with 8 rapiers. got it to 300x200 orbit when the fuel ran out. had ~1000 oxidizer left over. with better fuel balance, it might get to the 300x300 orbit. will need a bit more fuel for the retro burn, though.

it's trickier than i expected. that plane could probably get the tanks to a 75x75 km orbit and return without any changes. maybe i'll have to reconfigure. add some more LF and maybe some extra engines. a pair of nukes would be nice for the orbital maneuvers i guess.

i'm done for today, but will continue tomorrow if time permits

[Cinocal]

This gives me motivation to finish flight testing one of my recent designs. I've never test flown it without FAR.

[KroShan]

Well - i didnt think i works out on my PC but 1.1. does wonders
THX for the Challange i wouldn't have tried it without- my biggest SSTO sofar was a design for a bit more than one orange tank.

I basically copied my design from Skylon - first i didn't want to, but in the end the high mass of the engine cluster forced me to put it near the Center of Mass for balanced empty flight.

 

"The Orange Clockwork" has 126 parts and 252.9 t (including 72t Payload) on takeoff.
It has
19,430-(2*2880)= 13,670 LF
14,091-(2*3520)=   7,051 Ox
to spend.
Dry mass is around 77.3t.
So the first entry has 13,670*0.8 + 7,051*0.18 - 398*0,8 = 11,886.78 points

Especially the deorbit (from 80x80 without aerobraking, i had 1509LF before deorbit equals around dV=730m/s), reentry and landing was far from fuel efficient so it would be easy to save another 400LF. It can withstand a pretty tough reentry.
On the Design-side one could spare one or two rapiers or one Whiplash per side.

Maybe i should get also a K-Prize for it

Edited June 10, 2016 by KroShan
dry mass & dV - payloadmass 76t

[mk1980]

i guess that skylon-like setup will be a common sight. the plane i've been playing around with looks quite similar to yours. a bit shorter and with less engines, but i haven't gotten it to the target orbit yet, so i may also have to slap on some extra engines and longer tanks to acutally make it work.

[mk1980]

after some more messign around, my design made it. didn't change much. just replaced one Mk3 LF/O tank with a pure LF tank and added a pair of nukes for orbit

here's the album. hope i captured all the required footage. i forgot to ask if kerbal engineering is allowed. let me know if not. doesn't make much of a difference, tbh. i guess i could re-do the whole flight without the mod if necessary (and without the stupid cloud mod that almost killed me in the final landing approach...)

fuel spent:

14610 LF total (ignoring the 5760 units in the cargo tanks) - 518 remaining after landing

8030 oxidizer

13 Monoprop (120 - 107 remaining). wasn't necessary but i fired the thrusters for a few seconds to get away from the cargo tank after dropping it off)

score:

14092 * 0.8 = 11273.6 (LF)

+ 8030 * 0.18 = 1445.4 (Ox)

+7 * 1.2 = 8.4 (MP)

=> 12727.4 total

 

conclusion: not worth it to try and minimize engine count too much. getting a ~72 ton payload to a 300 km orbit with just 8 rapiers and 2 nukes is possible, but you waste too much fuel to the low thrust to weight ratio (taking off at a TWR of 0.32 is painful). also takes way too long to get to orbit that way.

 

 

 

[KroShan]

I did a next attempt with a bit more wingsurface four Rapiers less, so 8 instead of 12. Worked out pretty nice until a reload. Two wings broke of there after a kraken attack (i managed landing anyway).

Points would have been:
19,430-5,860=13,670
13,678-7,040=  6,638

(13,670-551)*0.8+(6,638-85.2)*0.18=11,675pts (screenshot available if required)

Also a big issue is the massive drag while having high Angle of Attack i will mix up the two designs and going for higher TWR. The few funds won't hurt any careergame and its more forgiving for flying errors and also faster in RL.
 

 

Edited June 11, 2016 by KroShan
typos

[kcs123]

Something out of contest. Those two orange tanks are not full. Only one and a half filled with fuel. More payload mass require more engines and more fuel. I created this one for myself and goal was to create SSTO with minimal amount of engines. It was created few days back, before this chalange is created.

Payload capacity ~60t with 1000 m/s dV to spare in LKO.
Part count (payload included): 60 parts
Crew cabin with 6 seats, if you also count pilot that is 7 kerbonauts on craft
Cost: 327502 kerbobucks - might look expencive, but at the time you unlock parts for it, it should not be a problem
Cargo bay is created with 3 x 6m wide B9 S3 parts - offering decent room for anything that is within 60t limit.
You could put a bit more, but runway length become problem during take off.
 

Same craft in orbit, screenshot taken in one of test flights.

I belive that I'm near limit with this design. Craft use one medium sized SABRE engine and four small sized SABRE engine. Whole available thrust is same as two medium SABRE engines. That small bump over canards is shielded docking port.
Resource panel also show decent number of monopropelant fuel to be used for docking.

Mods used: FAR, B9 Aerospace, B9PW, KJR, mechjeb used only for info purposes.

Sorry, I didn't save all of screenshots taken on test flight to orbit and back, need to do another trip for that.
Probably usage of other mods disqualify craft for this chalange, but I wanted to share it, to inspire someone to create craft with more wings instead of more engines. Not necessary all craft have to share similar skylon look.

 

[KroShan]

11 hours ago, kcs123 said:

...
I belive that I'm near limit with this design. Craft use one medium sized SABRE engine and four small sized SABRE engine. Whole available thrust is same as two medium SABRE engines. That small bump over canards is shielded docking port.
...
Mods used: FAR, B9 Aerospace, B9PW, KJR, mechjeb used only for info purposes.
...
Probably usage of other mods disqualify craft for this chalange, but I wanted to share it, to inspire someone to create craft with more wings instead of more engines. Not necessary all craft have to share similar skylon look.

 

Nice craft, with all the fuel dV left it should be possible to get to 300x300km orbit. Why do you have 1100 monoprop on it, this is dead weight. Exchange it for fuel in the tank and you get 72t payload up to orbit.
obey rule no.5:
as stock player i have no clue what" medium" Sabre means - looks like it is a very large 2,5m engine. It is totally not comparable with stock also because of FAR. Maybe it could get comparable when you list the TWR of this craft.

More lift definitly helps keeping low AoA and therefore keep drag low. But in stock are only relativly small wings available that can stand the reentry temp. So you need a lot of parts and this impacts very high on performance. Also finding the optimum between drag of lifting surfaces and drag due to AoA is a lot of work.

Edited June 11, 2016 by KroShan

[Mikki]

Must payload be attached inside a cargobay?

[kcs123]

SABRE-S engine is comparable to stock RAPIER, although, engine is heavier than RAPIER but have better ISP.  4 x SABRE-S engine have same mass and provide same thrust as one SABRE-M engine. Yep, you are right it is large 2.5m engine.

TWR on take off is somewhere between 0.26 and 0.30, can't recall accurately, need to double check it in game. 1100 MonoProp on it ? Well, it was just test flight, fuselages offers a lot of combination and with minor adjustment you can reconfigure it as you need. I didn't spend much time in optimization of this craft. Just fooled around with various aircraft designs, because I would not have much time for career game before next KSP update.

It's just to find out proper ratio between wing surfaces lift/weight and between engine thrust/weight ratios. I was created similar crafts in past, so it is much easier to create new ones when you have some experience. IIR I spend one or two hours with this one, not perfectly optimized, but does job good enough.

Not realy comparable to full stock parts, advantage of mods used on this is ability to create large craft while keeping part count low adn still having decent performance. Also, parts offer better design choices.

[mk1980]

another attempt with a heavily modified plane. as i suspected, it worked a bit better with more rapiers (12 instead of 8). this time i only used one nuke. looks a bit silly since it s basically just tacked on the back end on the fuselage. other than that, i kinda like the aestehtics of the craft with the mk2 engine nacelles embedded in the wings. 

wings are more in the back this time. looks better (imo), but it's harder to keep under control in atmospheric flight (after reentry)

 

now for the fuel numbers:

LF: 13410 - 528 (left after landing) = 12882

Ox: 7590

score:

LF: 12882 *0.8 = 10305.6

Ox: 7590 * 0.18 = 1366.2

sum: 11671,8

 

conclusion: a few more engines and a bit less fuel seem to work better; wings at the back work "ok", but wings+engines centered around the mid section (ie. skylon style) are more stable in flight with empty tanks.

 

 

[mk1980]

5 hours ago, Mikki said:

Must payload be attached inside a cargobay?

i don't think the challenge requires that specifically. i guess it would be within the spirit of the challenge to build something that can (technically) also lift bulky cargo that doesn't fit into a cargo bay but can be packed inside a fairing that is attached to the lifter plane somehow.

i made something along that line a while back. in this case i used a bunch of ore tanks as the "placeholder" cargo (~120 tons), but the plane was designed with other payloads in mind that would be inside a fairing docked at the port behind the cockpit section.

i went with a more "traditional" design for the challenge because i don't think that an "open cargo format" plane design can compete (too much drag). would be interesting to see something like that specifically tailored to the requirements of the challenge, though.

[herbal space program]

6 hours ago, Mikki said:

Must payload be attached inside a cargobay?

I don't know, but I have a feeling  the naked tanks will have so much drag that a cargo bay will be necessary for good efficiency anyway. I'm going to try this later when I'm done with some work I have to do. I just finished building an all 0.625m SSTO, which was surprisingly difficult, so this will make an interesting contrast. I spent a long time working on the problem of maximum dV/acceptable TWR on orbit for a long-range, landing-capable space plane, and I think what I learned there should give me good starting point for this. That plane  was able to get 17 tons of fuel on orbit for 17 tons of LF/LFO. If I could maintain that ratio for a 4X scale-up, I thin I'd have a pretty competitive rig.

And FWIW as an additional comment on the scoring system, the price of LF seems excessive to me if you really want the most efficient design. Shouldn't that really be measured in tons of total propellant used rather than by making LF 4.5 times more expensive than Ox? I'm pretty sure  I suspect that with this system, what will win out is a design that uses Mainsail and Whiplash engines, not Rapiers and nukes, because TWR and using less LF will win out over absolute efficiency in terms of propellant mass. , If you re-scale the ISP of a Mainsail vs. a nuke engine in terms of your point system, it works out to around 575, because 1 ton of a Mainsail's propellant will cost only 54% of what one ton of a jet/nuclear engine's will. The Poodle's vacuum ISP actually works out to around 650. Given that, I believe that the high TWR of the more efficient LFO engines with an only slightly lower ISP under this system will trump the Nerv. It's a tougher call to make with the jet engines, since the phenomenal TWR of the Rapiers at the high end may outweigh their lower ISP and low-end thrust in air, and their ISP as rockets is pretty good under your system.  So it will probably either be all Rapiers or some combination of Rapiers, Whiplashes, and Aerospike/Mainsail/Poodle. We'll see...

 

 

Edited June 11, 2016 by herbal space program

[KroShan]

The next iteration "The Orange Clockwork III" has more wingsurface and again 12 Rapier and is even uglier and aerodynamicly more unrealistic.
Points:

(13570-1076)*0,8+(6638-174)*0,18= 11,159pts
 

 

[mk1980]

not sure about the comment on the scoring system. i doubt mainsails will be used - their vacuum Isp is garbage, so you might as well just use the rapiers and not add an extra engine.

i actually couldn't get my original plane to the target orbit with just rapiers, so i added a pair of nukes and switched an LF/O tank to pure LF. that worked. to get the same amount of deltaV out of the rapiers in closed cycle, a lot more fuel would have been required. and then additional engines to carry that weight. and then more wings to lift the whole thing up. so the whole things gets bigger and bigger. i guess i'll give it a try - instead of a nuke, i'll try to do it with just rapiers and see if i can get it to work.

i think the score system is not bad. the 300km orbit makes nukes for orbit the obvious choice. but with the adjusted score, we might actually see some creative solutions other than "enough rapiers to get to space + 1-2 nukes to get to the 300km orbit and back".

also, isn't that the price (in kerbal currency) of the fuels in game? 

[herbal space program]

1 hour ago, mk1980 said:

not sure about the comment on the scoring system. i doubt mainsails will be used - their vacuum Isp is garbage, so you might as well just use the rapiers and not add an extra engine.

 

I guess I agree about the Mainsail since it weighs so much and has only a very slightly better vacuum ISP than the Rapier. The Poodle and Aerospike engines, OTOH, have 3-4 times the thrust of the Nerv, weigh 1/3-half what the Nerv does, and under this system have an ISP (in terms of points) only slightly worse than that of the nuclear engine. Given the fairly small total dV required to reach a 300km vs. 70km orbit, I think the much better TWR and lower weight of those engines might offset their slightly worse ISP. For longer trips, the nuke will of course always win out in spite of its lesser ISP advantage in this system. The aerospike in particular might have the additional advantage that it makes a good "crutch" for the Rapiers, providing a decent ASL ISP to provide a short boost at takeoff/SB transition, and both better TWR and ISP than the Rapier or Nerv during the rocket-powered portion of the ascent, perhaps allowing one to get away with shipping fewer Rapiers. Also, if those scores do in fact reflect the in-game costs of the propellants, then I totally agree this scoring system represents as good a rationale as fuel mass, given that the whole rest of the system is recoverable. I don't really play career anymore, so I've never really thought about the cost of fuel.

Edited June 11, 2016 by herbal space program

[Nefrums]

I reused an old design i used on the stock payload fraction challenge.  It is a bit smaller than other designs shown here with a takeoff mass of 146t.

It spent 6071 LF and 2640 OX,  so i guess 5332p

 

 

 

 

[herbal space program]

12 minutes ago, Nefrums said:

I reused an old design i used on the stock payload fraction challenge.  It is a bit smaller than other designs shown here with a takeoff mass of 146t.

It spent 6071 LF and 2640 OX,  so i guess 5332p

 

Dang it, that looks very much like what I was thinking of building .  That's going to be hard to beat, but I might try something similar using an aerospike instead of a nuke.

 

 

 

Edited June 11, 2016 by herbal space program

[KroShan]

I did a Excel calulation of your assumption. It is true but not for the dV regime we need here. Its the other way around!
The more dV you need the more cost-efficient is the LF/OX-Engine! But the break even point for two craft
-1st) 162t (with 2xNerv an 4xRapier more than 2nd) and
-2nd) 150t(with 2x Dart) 
is around 2900m/s.

The cost difference on these spacecrafts for a 200m/s burn is only 150 Funds but cheaper with the Nerv. From mass perspective you would spend 2.05t vs 4.43t of fuel.

m_1=	1
	e^(dV/(v_u)
	m_0

Spoiler

OXcost /unit	LFcost /unit	ISP Nerv v_u/9,81	ΔV	m_0	m_1	ΔM_Nerv	Nerv m_1/m_0	cost_Nerv	ISP Dart v_u/9,81	m_03	m_1_Dart	ΔM_Dart	Dart m_1/m_0	cost_Dart	cost-ratio
0,18	0,8	800	1	162	161,98	0,02	1,000	3,30	340	150	149,96	0,04	1,000	4,13	0,800
0,18	0,8	800	10	162	161,79	0,21	0,999	33,01	340	150	149,55	0,45	0,997	41,22	0,801
0,18	0,8	800	100	162	159,95	2,05	0,987	328,18	340	150	145,57	4,43	0,970	406,72	0,807
0,18	0,8	800	200	162	157,92	4,08	0,975	652,20	340	150	141,27	8,73	0,942	801,42	0,814
0,18	0,8	800	800	162	146,30	15,70	0,903	2511,99	340	150	118,01	31,99	0,787	2936,52	0,855
0,18	0,8	800	1000	162	142,62	19,38	0,880	3100,99	340	150	111,14	38,86	0,741	3567,04	0,869
0,18	0,8	800	2000	162	125,56	36,44	0,775	5830,99	340	150	82,35	67,65	0,549	6210,05	0,939
0,18	0,8	800	2900	162	111,95	50,05	0,691	8007,59	340	150	62,88	87,12	0,419	7997,93	1,001
0,18	0,8	800	8000	162	58,45	103,55	0,361	16567,47	340	150	13,63	136,37	0,091	12518,95	1,323
0,18	0,8	800	10000	162	45,30	116,70	0,280	18671,43	340	150	7,48	142,52	0,050	13083,16	1,427

Edited June 12, 2016 by KroShan
plot

[herbal space program]

16 minutes ago, KroShan said:

I did a Excel calulation of your assumption. It is true but not for the dV regime we need here. Its the other way around!
The more dV you need the more cost-efficient is the LF/OX-Engine! But the break even point for two craft 162t (with 2xNerv an 4xRapier more than) and 150t(with 2x Dart)  is around 2900m/s.

The cost difference on these spacecrafts for a 200m/s burn is only 150 Funds but cheaper with Nerv.

m_1=	1
	e^(dV/(v_u)
	m

 

Unfortunately I don't have time right now to completely work through this analysis, but something has to be out of whack in what you found. The more dV you need, the more advantage a higher ISP engine will confer, period. The heavy, high ISP engine might lose out at the low end because its higher mass offsets the smaller amount of fuel required, but eventually you'll get to the point where the additional fuel mass required for the lower ISP engine will exceed the additional mass of the higher ISP one. This just has to get better and better for the nuke as dV increases. While this challenge's points calculation regime does greatly reduce the advantage of the Nerv in this regard, it does not eliminate it, so AFAICT what you concluded can't be correct.  I think what you're not taking into account is that changing engines will affect the starting mass, both in terms of the engine weight and fuel mass, but alas I don't have time to work that out now.

[KroShan]

The math is correct. You are also.

I took into account that the enginecluster with NERV is havier - but the whole spacecraft wouldn't be because it needs less fuel.
The assumption that a vessel without OX would have the same starting mass is wrong.
The effect we see here is, that the massratio is that high that the vessel(LF/OX) would have a very tiny "drymass" so every m/s gets really cheap whereas the Nerv driven craft still has a lot more mass and needs more LF for the same m/s velocity change.

6 hours ago, herbal space program said:

The more dV you need, the more advantage a higher ISP engine will confer, period.

By stating this - why do you want to try it anyway ^^

I try to figure it out on the basis of Nefrums ingenius work. I totally forgot about the payload fraction challenge an how great this designs there are

Edited June 12, 2016 by KroShan