Eve One - Soliciting advice for an Eve Ascent Vehicle

[capi3101]

Greetings, fellow Kerbonauts.

For the last few days I've been toying once again with the notion of attempting to build an Eve ascent vehicle, with the goal of delivering one Kerbal to the surface of Eve and returning him to orbit safely. I haven't actually thought seriously about an Eve attempt since 0.19, but I remember the basic delta-V requirement being about 12,000 or so and the trick being to have sufficient TWR all the way up. Lately there's been some talk about Eve ascents on the forums, and one thing I kept hearing over and over is "don't take along unnecessary mass", "don't take along unnecessary mass", "don't take along unnecessary mass"...

Today I calculated a craft that could potentially do the job - except for one little snag, that being the fact that the first stage (dependent on a pair of Skipper engines) had a TWR of 0.99. Frustrated to be so close and yet so far, I thought "I wonder if I could replace the Skippers with an engine cluster that would give me slightly better performance".

An hour later, I had written down the basic idea for what I called the Skipjack Cluster (names are really not my thing): using an X200-16 as a structural base (because my calculations called for an X200-32 and X200-16 in each stage), I attached a total of 25 48-7S engines onto the bottom. The end result - 2.5 tonnes of engines, 750 kN of thrust and the same specific impulse characteristics as a Skipper, a lighter and more powerful substitute; only downside is a vastly increased part count. Tonight I built the booster craft I calcuated. Here's the end result:

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Based on the results of the test flight and the information KER is giving me, I'm fairly confident that the craft as is could make an Eve ascent, but I wanted to get the opinions of any Eve veterans out there.

Questions then:

1) Can the craft make a successful ascent as I've designed it, or am I still a little short on delta-V?

2) What do I need to add to it to get it down onto the surface? I know both large chutes and drogues (on decouplers) will be necessary along with lander legs (again, on decouplers); any idea how many?

3) How would you handle a ladder system for the craft? What's there now is a proofing payload; the ultimate idea is to replace the large probe core and battery banks with a Mk1 Lander Can.

[cantab]

The engine clusters look gorgeous. However, I fear your TWR is still too low for an efficient ascent, and considering you've showed vacuum not atmospheric delta-v you might fall short unless you're careful to land on high ground.

[marauder78]

1) Depends on where you land on eve and if the craft is full of fuel at the moment you land. Most of the ascend on eve are in atmosphere so you'd be better off designing a craft that can do 12K delta-V in atmosphere.

2) Depends on how you plan your decent. Chutes are a good option but the gravity on eve will rip your ship to pieces if you don't design it well enough. As for how many: depends on your landing weight and velocity.

3) Mk1 lander can is very heavy and you'll be having a hard time getting the right Delta-V. Weight is everything. As for ladders: the gravity on eve is allot higher as Kerbin, so if your ladder doesn't reach the ground you'll strand your kerbal on EVE.

[Capt. Hunt]

Delta-V is going to be crucial for that ascent, Since your prototype showed a tendency to shed engines, I would pack a few more then your calculations tell you that you'll need. Otherwise, you may find your Kerbalnauts stranded in the event of a failure.

[Jouni]

2) There are two critical moments in landing on Eve: deploying drogue chutes and touchdown. If the drogues are badly attached, they will tear off, possibly taking other parts with them. You can't really test this on Kerbin, because the forces will be much higher on Eve. On the other hand, if the ship survives with most of the drogues still attached, deploying main parachutes will probably not be a problem. On touchdown, pretty much anything can fall off (in my case it was the Aerospike engines in the core stage), so you may have to soften the impact with a short burn from the engines.

3) The final stage of your lander is very massive (2.5 tonnes of engines, 3 tonnes of empty fuel tanks, and 0.6 tonnes of payload). If you add a small additional stage on top of it (maybe a X200-8 fuel tank and a few 24-77 radial engines), you can probably lift a Mk1-2 Command Pod into orbit.

It seems that there is not enough room for a kerbal to climb between the stages. I would probably use a horizontal ladder from the core stage to the top of one of the inner boosters, and then add ladders to that booster.

[Red Iron Crown]

I've found aerospikes better than 48-7Ss for Eve ascent in testing. The better Isp in atmosphere lets you get enough extra dV from your fuel to offset the lower TWR, plus it reduces part count.

Use atmospheric dV for your calculations, this will give you a bit of margin for error or inefficiency in your ascent.

Upper staging is critical, make your final stages as small and light as possible. My Eve landing prototype's final stage is a lander can, a FL-T100 tank, a 48-7S, an RTG and a docking port.

Your booster will be more efficient if you use more and smaller asparagus stages based on 1.25m parts. You end up carrying less empty tank, increasing dV.

Arrange your landing equipment (parachutes, landing gear, science parts) in such a way that they can be jettisoned immediately after liftoff, no sense carrying that dead weight up.

[capi3101]

The engine clusters look gorgeous. However, I fear your TWR is still too low for an efficient ascent, and considering you've showed vacuum not atmospheric delta-v you might fall short unless you're careful to land on high ground.

Weird thing about that - I could've sworn I took a screenie with the KER window fully open for both atmo and vacuum. I guess I'll have to do that tonight when I get a chance; I haven't really given y'all all of the information.

I think it has just short of 11,000 atmospheric if I remember correctly. I'll have to look again.

1) Depends on where you land on eve and if the craft is full of fuel at the moment you land. Most of the ascend on eve are in atmosphere so you'd be better off designing a craft that can do 12K delta-V in atmosphere.

2) Depends on how you plan your decent. Chutes are a good option but the gravity on eve will rip your ship to pieces if you don't design it well enough. As for how many: depends on your landing weight and velocity.

3) Mk1 lander can is very heavy and you'll be having a hard time getting the right Delta-V. Weight is everything. As for ladders: the gravity on eve is allot higher as Kerbin, so if your ladder doesn't reach the ground you'll strand your kerbal on EVE.

Alright, well, I already know it's less than 12k atmospheric.

Going off the craft file this morning, the ship as is breaks down like this -

1 RC-L01 RGU (0.5t)

12x FTX-2 External Fuel Duct (0t)

13x X200-16 (117t)

13x X200-32 (234t)

168x Cubic Octagonal Strut (0t)

175x 48-7S (17.5t)

1x Clamp-O-Tron (0.05t)

1x TR-2V Decoupler (0.015t)

2x Z-1k Batt (0.05t)

36xEAS-4 Strut (0t)

6 TT-38K (0.15t)

6 TT-70 (0.3t)

6x Seperatron (0.435t)

6x Skipper (24t)

TOTAL ESTIMATED MASS: 394T

I plugged that into the parachute calculator and it's telling me for a parachute landing on Eve to land at about 5 m/s at sea level, I'll need twelve drogue chutes and 73 Mk-16XLs. Based on that it doesn't look like I'll be able to do a landing with just chutes. Now, if I shoot for a higher touchdown speed, it may be more feasible; with a dozen drogues and just 16 Mk-16XLs, I can touch down at 9.78 m/s, but then I'll have to make sure and sturdy up the lander legs. I was considering just going with I-beams anyway

I know that if the ladder doesn't go into the ground I'd have a problem; whole reason why I asked that particular question.

Delta-V is going to be crucial for that ascent, Since your prototype showed a tendency to shed engines, I would pack a few more then your calculations tell you that you'll need. Otherwise, you may find your Kerbalnauts stranded in the event of a failure.

Yeah, that was those TT-38Ks at work. I added the Seperatrons to try and combat that but they didn't help much. Based on the extra mass of a Seperatron versus the mass difference between a TT-38K and a TT-70, I might just replace the 38Ks with more 70s. They'd add less mass than the Seperatrons.

2) There are two critical moments in landing on Eve: deploying drogue chutes and touchdown. If the drogues are badly attached, they will tear off, possibly taking other parts with them. You can't really test this on Kerbin, because the forces will be much higher on Eve. On the other hand, if the ship survives with most of the drogues still attached, deploying main parachutes will probably not be a problem. On touchdown, pretty much anything can fall off (in my case it was the Aerospike engines in the core stage), so you may have to soften the impact with a short burn from the engines.

3) The final stage of your lander is very massive (2.5 tonnes of engines, 3 tonnes of empty fuel tanks, and 0.6 tonnes of payload). If you add a small additional stage on top of it (maybe a X200-8 fuel tank and a few 24-77 radial engines), you can probably lift a Mk1-2 Command Pod into orbit.

It seems that there is not enough room for a kerbal to climb between the stages. I would probably use a horizontal ladder from the core stage to the top of one of the inner boosters, and then add ladders to that booster.

Where would you recommend I attach the drogues given the design as is now? And what would be a generally safe landing speed to aim for? I've already mentioned what the parachute calculator generated for me.

The big problem I generally have with ladders is "going over the rim". I think I know how to handle this now, but it's definitely something I intend to test out on Kerbin before heading out. I'll try your suggestion for placement. I do worry about what'll happen when it comes time to ditch the things (don't want them shooting into one of the outer fuel tanks).

I've found aerospikes better than 48-7Ss for Eve ascent in testing. The better Isp in atmosphere lets you get enough extra dV from your fuel to offset the lower TWR, plus it reduces part count.

Use atmospheric dV for your calculations, this will give you a bit of margin for error or inefficiency in your ascent.

Upper staging is critical, make your final stages as small and light as possible. My Eve landing prototype's final stage is a lander can, a FL-T100 tank, a 48-7S, an RTG and a docking port.

Your booster will be more efficient if you use more and smaller asparagus stages based on 1.25m parts. You end up carrying less empty tank, increasing dV.

Arrange your landing equipment (parachutes, landing gear, science parts) in such a way that they can be jettisoned immediately after liftoff, no sense carrying that dead weight up.

My original design actually called for an Aerospike in the core stage. The fuel load changed that, but going through my calculator routine this morning, you're right - a quad of aerospikes should produce higher delta-V for a comparable TWR. That might not work for all the stages, but it is something else I could try.

I know it'd be more efficient to use the smaller parts, unfortunately part count is an issue. Which then begs the response of "explain that engine cluster to me again", of course...

Y'all have given me a lot to think about and I appreciate the responses so far. I'll do some tweaks tonight and report back how it all goes.

[Jouni]

Where would you recommend I attach the drogues given the design as is now? And what would be a generally safe landing speed to aim for? I've already mentioned what the parachute calculator generated for me.

There are 12 good spots for drogues on top of the boosters. Radial attachment might also work, but I don't have that much experience with it.

With such a heavy ship, you'll probably want to spread the drogues and regular parachutes evenly across the boosters. That may cause some problems when ejecting the parachutes, because there are not too many safe ejection angles from the inner boosters.

Safe landing speed really depends on the ship. Some ships can survive massive impacts, while others break when touching down slower than 5 m/s, for no apparent reason.

[capi3101]

What would you say to a quad adapter on top on the boosters, with two drogues and two big chutes each, set in place on top of a large rockomax decoupler and with a pair of seperatrons on the side of the decoupler? The idea being that once the ship was down, the whole assembly could be ejected off. Getting the chutes on the adapter might be a trick but I think I could handle it if I placed them one at a time on a subassembly. I'd definitely test it out on Kerbin before making it operational. Do you think that might do the trick?

[Kryxal]

I wonder if a 2*2 plate on top of a decoupler, attached by girder to another 2*2 plate with nothing underneath and a couple of seperatrons to help pull it off would do the trick...

Oh, add struts, and you might well be able to add extra chutes on that other plate!

[capi3101]

Alright, guys - progress reports from last night.

First off, I took a screenshot with the ship as it was, set to Eve and Atmospheric stats:

The ship as is gives me 10,273 m/s and an average initial TWR of 1.47. According to the wiki, that would be sufficient for takeoff if I didn't put down any lower than 2,000 meters. My intent is not to land in the sea, obviously, but I'm looking at Kerbal maps and saying to myself "there seems to be an awful lot of this planet that's lower than 2000 meters elevation"...

Second shot is the ship adjusted for aerospikes in the core.

That gives me 10,375 m/s, the highest delta-V of any of the attempts I made last night, but reduces the average TWR to 1.40. One of y'all harped on me for already having an inefficient ascent, so that didn't seem like something I wanted to keep. So I ditched that configuration - sitting here this morning, it seems to me that I might want to restore central aerospikes in the final configuration.

The third shot shows the original ship with the Sepratrons removed and the outer TT-38Ks replaced with TT-70s. The impetus here was to put a little more space between the inner and outer booster ring, to avoid losing engines in seperation events:

This configuration gives me essentially the same performance as the original configuration (with a grand total extra delta-V of 1 m/s); the benefit is peace of mind of a clean separation.

The last shot kept the outer TT-70s and replaced the Skippers with aerospike quads.

Average TWR stayed the same, at 1.47; the benefit here is the increase of delta-V to 10,345. Which is where I left things.

I think tonight I'll try different combinations involving aerospikes - though I have to ask, as long as the TWR stays up above...say, 1.2 or so, and the delta-V requirement is there, does it really matter?

In any case, I'm still about 1000 m/s short of a craft capable of landing and return from any point on the planet, about 400 shy of being able to take off from 1,000 meters.

I experimented around last night with a parachute "pack" that I might utilize for Eve. The basic design is what I indicated in a post yesterday (and I wish I'd taken screenies of its tests) - an upside-down rockomax decoupler with a quad adapter attached to it, with two drogue chutes and two big chutes in each space. I've also attached two radial chutes and four seperatrons to the sides of the decoupler. Seperatrons fire at the same time the decoupler fires, blowing the whole thing clear of the ship. Had pretty good range on Kerbin, though I might've liked a straighter flight path (I suspect the center of thrust of the assembly is too far below the center of mass). The plan is to stick one of these on each of the booster tanks, giving me 24 drogues, 24 radials, and 24 big chutes. I've plugged the craft's mass into the parachute calculator and had it calculate landing velocities for various elevations with that configuration of chutes. Here are the results:

2000 = 7.70 m/s

2500 = 7.98 m/s

3000 = 8.26 m/s

3500 = 8.55 m/s

4000 = 8.86 m/s

4500 = 9.17 m/s

5000 = 9.5 m/s

5500 = 9.84 m/s

6000 = 10.19 m/s

6500 = 10.55 m/s

7000 = 10.93 m/s

7500 = 11.32 m/s

It looks like I'll need a quick puff of the engines right on touchdown no matter where I land. The idea is to fire the chutes as soon as I hit atmo and let them "stage" their deployments, that way I get maximum benefit from each chute.

Well, that's pretty much been it for last night. Any new suggestions? Comments? Scathing criticisms?

[Red Iron Crown]

I would try replacing your middle ring stage's engines with aerospike clusters, too. Personally I would use cubic octagonal struts instead of the quad couplers for the clusters to reduce mass, too.

I would also suggest adding a small final stage atop your current large final stage. A pod, small tank, and a 48-7S would add over 1000m/s of dV, enough to get to your goal of having enough to ascend from almost any landing site.

May as well replace your placeholder payload with the final configuration for testing, it will help you avoid unpleasant surprises.

Keep your TWR at 1.2 or better, any lower and you'll waste dV fighting gravity for too long.

[capi3101]

Last night's frivolities - I only had about twenty minutes in which to do anything, but I did get a few things done.

First, for some reason I hadn't saved the changes from the night before, which was aggravating - the big loss being the outer tank TT-70s. I'll be fixing that one in the near future. Meantime I went ahead and did a launch with aerospike clusters centerline and outboard (and again, for some reason I don't have a screenie - the combination gave me slightly lower TWRs, about another 300 m/s of delta-V, and worse steering authority). Lost an engine again due to the reverting of the TT-70s to TT-38Ks.

Somehow that configuration didn't perform as well as the initial one. I think it was due to some bad piloting on my part (on account of an engine getting knocked off, on account of TT-38Ks instead of TT-70s again). I'll replace the decouplers and try again when I can.

I did go ahead and try adding a small final stage - on my proofing payload, I added an FL-T100 and a 48-7S, another .6 tonnes of mass or so. Knocked the total delta-V down to about 8,000. So no.

Other big thing for the night was the testing of the parachute ejection system I'd worked up before on the actual ship:

Worked well except for one slight detail...

That would be the center stack disintegrating and the proofing payload falling to its doom. Some kind of collision going on with the central X200-32. Going to have to look into how that's happening. Meantime, what do you all thing of the chute setup? This is the same one for which I calculated my numbers yesterday.

Still haven't begun approaching lander legs. Still leaning towards I-beams, honestly.

Tonight I'll try a launch with just aerospikes. Going to have to figure out how to steer with that; I've had problems with the spikes on that score before.

[Red Iron Crown]

Mine has 18 aerospikes and an LVT-45 on 1.25m tanks arranged asparagus style, and control authority was a problem until the outer ring of stages was gone. My solution was to add two reaction wheels to the last of the outer stages.

Did you stage your small final stage properly? Seems like it should have increased total dV, seeing as the stage itself would have over 1300m/s of atmospheric dV.

[capi3101]

Don't know if I did or not - I just pulled the last stage off the proofing payload by the decoupler, added the extra equipment and then stuck it back on. The game does have an annoying habit of jacking up asparagus when you go to make changes, so I'll give it another shot.

An idea what might have happened with the chutes?

[Red Iron Crown]

If I were to guess I would say the sepatrons cooked something in your core stage. Did you check the mission report (F3)?

[capi3101]

Yeah - there were a lot of "damaged by" entries - a lot of them. I just kinda skimmed through them all, didn't notice the big one if it was there. I suppose it probably overheated and exploded. I might try having the inboard stacks shoot off an an angle that still gets them clear of the central stack without necessarily having the engine fire shooting right into the central stack.

[immelman]

Perhaps you should first build your lander aiming to land above 5000 m? This will knock down the deltaV needs by a lot. The region of Eve with the tallest mountain has a number of areas above this that are quite flat. You can drive up it or use MJs landing predictor for a pin point landing.

To make lifting your lander off Kerbin and transfer to Eve easier look at ditching aero spikes completely and using all 48-7s attached by cubic struts to 400 or 800 tanks asparagus style. A ratio of 1 landing leg per 4 tones works.

I have lifted off a lander can on a 44T lander using this setup.

[capi3101]

Day 4:

Yesterday I had a thought - it was a pretty simple question I asked myself, actually. "Where do I need the most thrust?" Well, the answer to that is obvious to anybody who designs rockets; you need it at the bottom, right at launch. So, it occurred to me that where I needed the thrust my Skipjack cluster offered was at the beginning - in the outboard boosters. So I rebuild the ship entirely; I added Red Iron Crown's final stage suggestion, put the asparagus back together strictly with TT-70s, put aerospike clusters center and inboard and Skipjacks outboard, set KER to Eve Atmospheric and this happened:

Looks like I'm finally there. The TWRs are a little low but as long as they're above 1.2 I should be golden.

So now that I know I can get the ship up, it was time for me to worry about how to get it down intact. Impact and chute testing. Lots of this going on:

I did learn a lot about how I should approach the final landing. I was ripping chutes off with the full load on Kerbin, so I can be pretty much guaranteed to need to be burning when the chutes open (drogues, then main chute sequence).

Chute ejection went better today; reaiming in the Sepratrons did the trick.

It did occur to me later that I probably should not stage the chutes in the same stage as the lander legs...

Getting a good set of lander legs is also going to be a concern - here's what I have so far.

That might hold, though it is a bit flimsy.

I had a thought on how I was going to get Jeb out of the can when the time came - it'd involve mods so it's kinda cheatsy, but it would save me from having to build a convoluted ladder system that might or might not work.

Yep. All so far is going exactly to plan...

[Red Iron Crown]

You should turn on infinite fuel in the Alt-F12 menu when testing your chutes, otherwise the lander will get significantly lighter as it ascends.

Realchutes is a good mod that makes the parachutes behave more realistically (no 50G jolt when they open), if that's something you'd be interested in.

Good to see you're getting there with your lander, methodically fixing problems as they arise. Keep it up!

[KerikBalm]

Hmm, my plan was just to use two rings, asparagus staged, of FL-T800 tanks with aerospikes, the central tank with a LV-T45 engine (so I can stack it on top of a mainsail asparagus booster to get it into orbit and on its way to Eve). Drogue chutes on top of the inner asparagus ring + radial chutes (large chutes along the outer ring).

On top of the central fuel tank, I've got a FL-T400 fuel tank with a LV-909, and on top of that I've got 3 oscar-B fuel tanks feeding a 48-7s engine. on top is a probe core, strapped to the sides in 2 fold symetry are two command seats.

Of course, lots of struts and a ladder system to get them to the command seats. I was going to do just 1 seat for 1 kerbal, and maybe even use jet pack fuel to get into orbit, I don't use any mods that tell me how much dV the ship has, and I haven't tested yet.

Then I decided I'm going to send down a lab based rover to get more Science!!! in case the return vehicle doesn't make it (and to get the Science!!! faster, and to provide a plausible habitat, so that they only need to breifly scramble from the labe module, and into their command seats, before leaving the densest parts of Eve's atmo), and to try and get some liquid readings as well.

As I figure it, Aerospikes will basically always have 390 ISP, while 48-7s and skippers will basically have 300 ISP (since Eve's atmo takes a long time to drop below 1.0 atms).

30% more ISP is worth the extra engine weight methinks (meanwhile nukes won't have better ISP until nearly 14km, and are much heavier).

Also the key to the most dV is to have the smallest upper stage, hence the tiny diameter stages.

My eve mission in the planning stages involves 3 launches:

#1) the lander as described above, that will descend unmanned to Eve's surface

#2) The science rover that will descend to Eve's surface, and the return stage that will stay in orbit

#3) an interplanetary booster stage that will dock with the lander (via a part held underneath the lv-T45 by a decoupler), and get it to Eve.

[capi3101]

^^^

You're going to come up short on TWR; it's the LV-909 stage that'll get you. Your TWR at that point with the load you've described on top of it, assuming an OKTO2 probe core, is 0.928. Design overall has 11,355 m/s as written.

I'd humbly suggest that you replace the LV-909 with a combination of an 48-7S and a pair of 24-77s. It'd improve the TWR of that stage to 1.29 and give a small but noticeable boost to TWR to all downstream stages (your central stack is below 1.2), and it will only cost you 4 m/s of delta-V. Wiki says you need 11,282 to take off from the ocean, so you should have enough delta-V that you can spare that amount.

Rest of the craft has TWR comfortably above 1.5.

Edited March 16, 2014 by capi3101

[capi3101]

My own mission plan goes something like this:

1) Launch a series of four Barn Burners and dock them to a Thunderbolt in orbit. A Barn Burner is 2.5 Jumbo 64s equivalent, while a Thunderbolt is essentially a nuclear thruster pack. Test it for delta-V before sending it on to Eve. Include a return stage adapter with the Barn Burner train; this will include a KAS container with a chute or two for the lander's command pod.

2) Using TAC to balance the tanks and override the fuel lines, launch the lander from Kerbin and send it on to Eve under its own power. Lock staging before I launch.

3) Rendezvous the lander and the Barn Burners in Eve orbit. Refuel and land. Unlock the staging before Eve entry.

4) Using Crew Manifest, transfer Jeb from the central stack command pod to another command pod closer to the bottom of the craft. Have him climb down from there. Plant a flag and do the usual business.

5) Have Jeb climb aboard, use Crew Manifest to transfer him to the central stack command pod. Make sure he's there before proceeding.

6) Ditch chutes, side command pods and solar panels. Take off and ditch lander legs.

7) Ascend to orbit.

8) Send return stage to rendezvous with the command pod once orbit is acheived. Jeb climbs out and affixes chutes.

9) Return to Kerbin.

[Red Iron Crown]

I really need to install and mess around with TAC. I've been slapping a couple of drop tanks onto the lander for its ascent into LKO, but the TWR falls off so much its tricky to circularize. Overriding the fuel lines sounds like exactly what I need.

[KerikBalm]

^^^

You're going to come up short on TWR; it's the LV-909 stage that'll get you. Your TWR at that point with the load you've described on top of it, assuming an OKTO2 probe core, is 0.928. Design overall has 11,355 m/s as written.

I'd humbly suggest that you replace the LV-909 with a combination of an 48-7S and a pair of 24-77s.

Hmmm, I would have though that by the time I got to the Lv-909 stage, TWR wouldn't be so important, and I'd be in the upper atmo soing my gravity turn.

Also, the dV seems uncomfortably low - I'm thinking either 1 more oscar B fuel tank in the upper stage, or perhaps on the Fl-t400 stage I could add 2 FL-T200 tanks on radial decouplers with 48-7s(?) Lv-909s(?) - no cross feeding to improve the TWR of the core (since when its the core alone thrusting, it won't have a full fuel load).

I know 48-7s are more efficient than LV-909s for low masses (its better to push around a lot less mass at a little less ISP, than to push around a lot of mass with higher ISP), but I'd think with the stage above it, that 48-7s wouldn't be what I'd want here.... but if I only lose 4 m/s, its not such a big deal.

This suggestion, and the OP's engine cluster, illustrate one thing that sort of bugs me about KSP.

For gameplay considerations, bigger doesn't have to be better, but it certainly shouldn't be worse.

By this I mean that using multiple small parts shouldn't be better than using one large part - if for nothing else than to reduce part count. I'm very tempted to go non-stock, and just do very simple mods using the rescale factor (and mass and thrust) to make proportionately larer "small parts" ie scale up the aerospike to be larger so I can use 1 large aerospike instead of a quad adaptor and 4 of them. Doing this with the 48-7S would improve computer performance even more, as all those cubic struts would be gone too.

But a scaled up 48-7s (to the large size) would completely replace the mainsail....