Long time away from KSP. How's SSTO's like now?

[diegzumillo]

Hi all

Long time player here. Long time away also! I can see a lot has changed, so, anyone wants to throw some hints at me? just to put me up to date with the new mechanics. I noticed a few things. The aerodynamics is a lot more realistic. We didn't have to worry about drag that much. I mean, we had, but it was all very simplistic, and now too much drag at the front of the plane puts it off balance. I also noticed air breathing engines have an oxygen dependent thrust. This is a lot more realistic and I feel it's what causing the major changes to the rules of designing SSTOs.

I can actually get a simple SSTO on orbit using RAPIERs but just barely. I'm trying to make one with a nuke engine as a first step to make a single stage to the mun or other planets.

Anyway, hints?

[bewing]

SSTOs are trickier now. Getting them into orbit using nuke engines is the hardest trick of all. Nuke engines are heavy and have relatively low thrust.

Basically, you have 4 problems getting to orbit: Having enough fuel, keeping your drag as low as you reasonably can, having enough lift for all your engines and fuel -- and the nastiest one of all is that there is a heating "barrier" at 1300 to 1400 m/s in atmosphere.

MK1 parts now have reduced drag, so that's nice. Fuel and lift are just matters of experimentation, of course. One hint is that shockwave heating is actually sophisticated enough that putting a blunt front end on your SSTO will cause a detached shockwave, and very little heating. This gets you through the heating barrier, but you need more engine to handle the extra drag from the blunt front end. Shielded docking ports work well in this fashion. Or you can just be very careful about getting through the heating barrier quickly while climbing (with some extra thrust at the crucial moment, perhaps).

On reentry, you have 3 problems: at 35 km altitude, you are facing the same heating problem again from the other direction. Stability control -- a homebuilt spaceplane may tend to swap ends on you, or tumble. And third, landing. Wheels are a bit of an issue with the brand-new 1.1.0 release. (They will certainly be better when the hotpatch shows up.) And there has been some drag reduction in the plane parts. If you come in heavy, and try to land at 190 m/s, you may roll right off the end of the runway. Which may mean that it's wise to land going in the other direction on the runway -- where rolling off the end is not a disaster.

 

[Alshain]

Single Stage SpacePlanes aren't all that hard, you just have to bring them up on a slow and steady climb.  Finding the right balance of speed and climb is the hardest part.

Edited April 29, 2016 by Alshain

[diegzumillo]

Thanks I'll continue the experiments here.

(off: why is the forum in a question-answer format? it's weird)

[AeroGav]

I joined this game after it went live so some of the pre 1.0 SSTO feats make me shake my head.   I have no issue with NERV-powered spaceplanes, it's my preferred way of doing things,  but whether it's possible to truly single stage to minmus without abusing clipping, dropping any external tanks or booster engines, or use mods to overcome the ludicrous drag the game now assigns to struts and fuel ducts has yet to be proven.

Yes, atmo heating is much stronger than in 1.04 and previous, but that just means you need to hit max airbreathing speed (mach 4.5,  pointless going above that as the RAPIER thrust/velocity curve falls off a cliff above it - if you're able to, you're carrying too many engines) above 22km which you really should do anyway to avoid wasting fuel on fighting air resistance.

[bewing]

1 hour ago, AeroGav said:

whether it's possible to truly single stage to minmus without abusing clipping, dropping any external tanks or booster engines, or use mods to overcome the ludicrous drag the game now assigns to struts and fuel ducts has yet to be proven.

Really?? I find going to minmus and back to be very simple with a stock ssto and no cheats. What kind of proof do you want?

[AeroGav]

7 hours ago, bewing said:

Really?? I find going to minmus and back to be very simple with a stock ssto and no cheats. What kind of proof do you want?

I'd done it before with a ship that used TacFuelBalancer and KerbalJoint Reinforcement but I'd gotten discouraged when my last couple of attempts to make a 100% stock SSTO only made orbit with a little over 1000dV remaining, which isn't enough is it?  The designs were all quite different yet yielded very similar results , which made me feel there was a "glass cieling".

Spoiler

 

1 Whiplash,  2 NERV,  4 Big S Delta wings = 1000dV in LKO

2

2 RAPIER, 2 NERV, 8 Big - S wings - 1100 dV

2 NERV, 1 RAPIER, 2 PANTHER (discarded) , 8 big S wings = 1300dV

2 NERV,  2 RAPIER and 2 PANTHER - the rapiers and panthers are discarded.   = 3700dV !

 

OK, the first two versions of my "manta ray" craft are a bit light on fuel.     I left the mk2 bicoupler empty since the NERV cannot access the contents so all it'd do is help mess up the CG.      Dropping engine stages only boosted my dV a little bit, on the evidence of those two flights (i know, small sample size).   The last was a true "maximum effort" version.  Not only does it discard the expensive RAPIER engines too, it also uses an inline cockpit with a 2:1 adapter and NCS adapter for extra capacity.  The bicoupler is filled,  the engine pre-coolers are replaced by  mk1 liquid fuel fuselages to mount the NERV to,  and the discarded airbreathing stages get their own mk1 liquid fuel fuselage each to draw fuel from, and radial intakes.

After lunch I'll try combining the expanded fuel capacity of the last version with the fully SSTO nature of the first, and see how i get on.

Stats - "Manta Ray" full SSTO

download S211 Manta Ray

Cost of discarded stages   N/A

Takeoff Fuel                       2480 units

Fuel Mass                          12,400kg

Dry Mass of Orbiter            21,556kg

Leftover fuel in orbit            669 units

dV in orbit                            >1000 m/s

 

Stats - "Javelin Heavy" w/boosters

https://kerbalx.com/AeroGav/S211-Javelin-Heavy

Cost of discarded stages   4800

Takeoff Fuel                       2480 units

Fuel Mass                          12,400kg

Dry Mass of Orbiter            19,556kg

Leftover fuel in orbit            663 units

dV in orbit                            >1100 m/s

 

Stats - "Shed 7 Ultra Heavy" 

*edit - accidentally deleted engines off this craft before uploading and i don't have a backup*

Cost of discarded stages   30,799

Takeoff Fuel                       5240 units

Fuel Mass                          26,200kg

Dry Mass of Orbiter            19,070kg

Leftover fuel in orbit            2322 units

dV in orbit                            >3700 m/s

 

 

Edited May 1, 2016 by AeroGav

[bewing]

Quote

my last couple of attempts to make a 100% stock SSTO only made orbit with a little over 1000dV remaining, which isn't enough is it?  The designs were all quite different yet yielded very similar results , which made me feel there was a "glass cieling".

Mine is a little tricky to get to orbit, but I don't have KER currently so I can't give you an LKO dV readout. If you want to try flying it you are welcome to see what it can do. I can give a (fairly) short list of launch instructions. I can either post the craft file here or email it to you.

Edited May 1, 2016 by bewing

[AeroGav]

OK,  I took my first , pure SSTO version of the "Manta Ray" and filled the fuselage tanks, swapped over the tail cones for NCS adapters which hold a bit of fuel,  and added an inline cockpit since this lets us fit another NCS adapter (80LF)  as well as a type 2 to type 1 adapter (180 LF) ahead of the cockpit.   Though actually, my main reason for using inline cockpits is crashworthiness.

Finally, I took the tailcones off the back of the NERVs and decided to make some external fuel tanks to attach here and be dropped on the way up.

Bill of materials for each item

Decoupler 180 Kredits

FT400 tank  230 Kredits when supplied empty

NCS Adapter  256 Kredits (empty)

Small nose cone 180 Kredits

Fuel Duct 150 Kredits

That's 1216 Kredits for each external tank holding just 480 LF - more than half the cost of a Panther engine !  I doubt somehow, that the drop tanks carried by today's jet fighters are more than half of the price of it's engine, but there we go.    With these "drop tanks",  the pure SSTO version has over 2k DV.  It could probably still reach Minmus without them if going for the strictest interpretation of re-usability.

I'm noticing the 2 rapier vs 1 rapier version of this ship maxes out at about 23km and mach 4.3, whereas the single rapier can only reach 21km and still hang on to mach 4.3.      The 2 panther/2 nerv/1 rapier version might get about 10% more delta V in orbit due to having 10% less empty weight once the panthers stage off.   It's also a little easier to fly in my experience, because thrust levels are more even throughout the flight profile.    There is more thrust on tap for penetrating the sound barrier when afterburner is toggled on, but once supersonic the incredible surge in power from the Rapier is blunted which makes it easier to follow the intended climb profile.   The other advantage of Panther boosters is their greater economy in Dry mode as will be used for much of the flight .   However, this could be less important given that they drain from external tanks anyway.

download S211 Manta Ray 2

I'm going to update the intermediate version of this craft with the extra fuel tanks, and then we'll have the definitve "Manta Ray" series..