Heavy SSTO with 45 Ton payload.(wip)

[Jakalth]

Download and info about the craft can be found: HERE, in the 10th post.

Well, I've been working on two different heavy lift SSTO's in the new aerodynamic system and I can say I am getting very close. I am slowly teasing secrets out of this new aero model that are making it easier to get heavy craft into space, and back again. Right now, I feel confident enough in this design to give you guys a sneak peak at what I've been able to make so far.

I present to you all, the -------. Well, it doesn't really have a name yet, it's still simply designated as Jak-102. It is, a 305 ton, 34 engine equipped(26 rapiers, 8 lv-n's), 45 ton payload hauling SSTO. I've been able to get it orbital already with an empty cargo hold and i'm currently tweaking the design a bit to get it orbital with a 45 ton refueling pod in it's cargo hold. It can already break atmosphere with it's full payload and still re-enter atmosphere intact. The flight profile for getting it orbital is a bit strange, coming from KSP 0.90 and earlier, but from what I've read, it's quite similar to it's smaller brethren. The design it's self is meant to act as an orbital mothership once orbit is reached, hence the LV-N rockets. And with a full refueling, it's got 19K Delta-V for the LV-N's.

A bit of the info I have been able to tease out(and some of this may already be known):

1: The wings only need a total lift rating of 10% of the crafts weight to fly, not really well though. But a total lift rating of at least 25% is needed to give it a manageable glide profile. 50% allows it to fly completely level/horizontal. Anything more then 50% lift rating per ton is just extra drag.

2: In order to go supersonic, a thrust to weight ratio of 1.25 seems to be the absolute minimum needed. Even at this amount, it requires going into a shallow dive to gain enough extra speed to break the sound barrier before the engines can spool up to full thrust. This is true for both the Turbo Ramjet and the Rapier engines. A thrust to weight ratio of 1.40 will allow the craft to break the speed of sound and go supersonic in a shallow climb. And in level flight, a TWR of 1.40 allows it to go supersonic at low altitudes. Once the craft breaks the speed of sound, even with the minimim 1.25 TWR, the craft can still maintain supersonic flight while going into a much steeper climb, or even keep accelerating if you let it.

3: The medium sized MK3 cargo bay has a fairly weak connection strength to the rear fuel tank, making it a primary failure point. Trying to reinforce this connection using struts that go from the fuel tank to the cargo bay cause instant structural failure the moment it is launched. BUT, connecting struts from the fuel tank, to a separate part, and then connecting struts from this separate part to the cargo bay, does allow the connection to be reinforced successfully.

4: The gimbaling on the Rapiers is a bit silly. Sometimes it is too strong, other times it is not enough. KSP, your drunk...

5: With large aircraft like this, a gentle stick is very important. Pulling up to hard causes an aerodynamic hit on the wing surfaces that can tear them apart. Turning on the other hand, they don't seem to mind so much.

6: speed.... yeah... Over speed is a very dangerous drug. For this craft, the top safe speed is 1100m/s @ 9000m. It's actual top speed @ 9000m is somewhere above 1300m/s, moments before it's wings start melting off and it eats its own air intakes. heh heh

7: Brakes, air brakes are important. When you've got enough thrust to go supersonic, it's even harder to slow down... I still need to find the right spot to add them to my SSTO, but they are very important for re-entry. Every little bit of speed you can bleed off early in the re-entry, saves your wings from being burned off, and air brakes work very well at giving you that little extra drag you need. And yeah, they have that nice sci-fi feel to them as well.

8: Reaction Wheels. Yeah, they only help once you breach the 20K altitude mark, otherwise your wings and tail fins should suffice. But when your craft weighs over 300 tons, you're going to need quite a few of them...

9: Last of all, intakes. For the Rapiers at least, having 2 rapiers per ram air intake seems to be the ideal amount when your craft can go supersonic. I always end up having plenty of air intake left(ok, maybe not plenty, but some...) once the craft pierces the 20K altitude mark and switches too closed cycle. The Turbo Ramjets seem to have similar properties but I haven't tested them as much due to this design needing the Rapiers for their duel modes.

Tip from Kagame:

10: when attaching cargo to your cargo bay be careful of the slightly buggy attachment point snap. if attaching the cargo to the front or back of the cargo bay, it can sometimes attach to the fuselage part in front/back of the cargo bay instead of the cargo bay it's self. This can cause the cargo bay to detach on launch, breaking you craft. If this happens, try re attaching your decoupler/docking port to its mounting point and see if it connects to the cargo bay correctly this time. (I can confirm this issue, I've had the same problem when adding large reaction wheels to the JAK-102. It effects more parts then just the cargo hold it seems)

Edited May 12, 2015 by Jakalth

[DMSP]

Nice!

Download though?

Also, it's for 1.0.2, right?

[Jakalth]

I'm waiting on uploading it for download until I can get it orbital with a payload. Hopefully soon I'll have that part adjusted and ready. And yeah, it's for KSP 1.0.2. It also still needs a name.

[Kagame]

I've also experienced some problems with the cargo bay/fuel tank linkage. In my experience, it's actually due to accidentally attaching the decouplers for whatever payload you're using to the fuel tank instead of the actual cargo bay. Try detaching everything but the cargo bay, then attaching your payload to the cargo bay's little green dots, then attaching everything else again. If that fails, begin all over again, you've got a part clipped funny somewhere. It also seems like you have an abnormally high amount of those nukie engines and intakes- my preference is to use Sabres alone and double the amount of fuel you're using. My last Mk. 3 cargo ship needed about fourteen of them, if memory holds. I'm trying out a trimaran layout to add SABRE mounting points and overall craft rigidity, I'll get back to you on whether that works or not. Finally: Dude, use the FAT-455 control surfaces. In fact, add control surfaces overall. That's probably the reason you've got issues getting it into orbit, because you can't get there in the first place! =P. And add RCS thrusters, as air tends to act... silly... past 20K. (This is based off of my experiences in 1.0, though, yours may differ.)

EDIT: Still working on the trimaran layout. It is an absolute pig to fly, it rolls given the slightest provocation.

Edited May 10, 2015 by Kagame

[Jakalth]

@Kagame That is some good advice, I've added it to the list of tips. As for the thrust part, the 26 rapier engines are needed to get the TWR high enough to go supersonic. You can't see all 26 due to careful clipping of the engines to keep it from getting to big and to keep the engines from over heating each other. The 8 LV-n's are needed due to it's heavy weight, but they are only ment to be used for orbital transfers once an orbit has been achieved. Without a cargo it can already reach a minimal orbit of 76,000m and from there transfer to a higher orbit, or even make a Mun run. It's just the added weight of the cargo has reduced it's current delta-v, which I'll fix when I next load up the game. As for the FAT-455, that is what the center-ish wing already is. That's the pivot point of the front half of the craft making that a good spot to have that wing. The smaller canard on the nose is for fine adjustments and to reduce the over control it was suffering from.

Also, the only mod I have installed is Kerbal Engineer, so I do not have access to the Sabre engines.

[Roflcopterkklol]

Jaka 4 turbo jets where 2 of those rapiers are would help a lot, give you that push over the 320m/s barrier and once you switch the engine modes you will not need the extra rapiers anywho, i have gone to putting turbo jets into the designs of all my SSTO's, seems to be the best way, 1 turbo jet for every 2 rapiers is a good rule i have found (This rule only works in toe with nuclear engines 4 rapiers and 2 turbo jets per nuke i found for smaller SSTO's, could go more nukes the bigger the craft is) without nuclear engines there is no point using them though.

Edited May 11, 2015 by Roflcopterkklol

[Jakalth]

I'll have a downloadable version available tomorrow when I get home from work. It has a bunch of airbrakes added to help it slow down during re-entry(16 of them, 8 wasn't quite enough, might not be enough yet). The cargo bay holds a single orange fuel tank, which gets used up during the ascent so it is kind of pointless... It does have some issues with going orbital though, mostly with the 2 FAT-455 wings having such low heat limits(only 1200 while most other wings can handle 2000) so over heating of those parts is a bit of an issue. But, once you spool up the rapiers, at 8000m, it'll push its self up to over 1000m/s while still in air breathing mode.

I'll add a suggested ascent plan with the link to the craft tomorrow.

[Crikeycrapper]

Man, this SSTO is HUGE. You say it could lift up an orange tank, huh? Try posting this to my Mk3 SSTO thread when you get a chance!

thread: http://forum.kerbalspaceprogram.com/threads/120511-Showcase-Show-off-your-Mk3-SSTOs!

[Capt. Hunt]

you probably don't need the LV-Ns unless you're going to use it for interplanetary missions, 19km/s is a lot of Delta-V.

[Jakalth]

Ok, pretty much finalized the ssto. It didn't quite reach the potential I was hoping it would reach, but it is still orbital and is a good learning tool. The SSTO can still carry an orange tank into orbit, but for now, it burns the fuel out of it to help with orbital ascent. Without the orange tank, it still reaches orbit with basically the same amount of fuel left. I had to change a few things around on it again to fix a problem I didn't notice at first due to it only happening during re-entry. The changes have altered its flight profile a little, reducing it's pitch authority, but not enough to alter its ability to go orbital.

The Jak-102 "TopKnot", is a heavy ssto with a decent sized cargo bay for orbital activities. I couldn't think of a better name for the ssto, sorry... It might be possible to keep the orange tank full once in orbit, if you drop the LV-N's and engine necells they are attached to, but this might also leave it stranded in orbit with no oxidizer to deorbit and you'll need to add more air intakes to make up for the loss of the 8 on the LV-N necells.

This is the new look of the Jak-102. The LV-N's were moved forwards to help keep the center of mass from shifting so far backwards as the fuel is burned off. It has 24 airbrakes that are deployed only when the normal brakes are applied, or when the parking brake is turned on. This is to prevent them from slowing the craft down while maneuvering(if they even do that), and because that is simply how I wanted them to work. How it looks fully deployed can be seen below.

I know, the cargo bay doors clip through several parts, but that is simply how I had to do it with how this craft is built...

Flight profile:

Take off: Set the throttle to about 75% on the runway and let the craft run the length of the runway to build up speed. At the end of the runway, pull up lightly to get it flying, then pull up some more(more aggressively) until it is nosed up 20 deg from horizontal.

Climbing: Continue to fly at a 20 deg nose up. adjust the throttle to maintain speed under 300m/s as you climb for efficiency sake. At about 8000m, go to full throttle and nose down to between 5 and 10 deg, or until it's climb rate nearly stops. Let the craft build up speed. This can take some time due to it being a large and heavy craft, but it will eventually accelerate up to supersonic speeds. Let the craft accelerate up to about 1000m/s and watch the heat on the middle wings and ram air intakes, they are the first to overheat if it starts going too fast. At this speed, reduce thrust until it's acceleration pretty much stops. The craft at this point should be over 9000m, probably just shy of 11Km and climbing. Keeping a close eye on the heat of the middle wings, let the craft accelerate slowly to about 1100m/s as it continues to climb to 19Km. At this point, or a little sooner, it has probably switched to closed cycle on the rapiers. Throttle up enough to maintain speed on the rapiers and, as it continues to climb, little by little bring down the throttle when it starts accelerating again. Using minimal throttle to get to orbit should save you a little fuel for orbital burns later on.

Orbit: In orbit, swith to the LV-N's for orbital corrections. They are a lot more efficient, but take a lot longer to make corrections. In space, it changes direction slowly, using only reaction wheels to turn. RCS thrusters could be added to improve orbital maneuvering if you wish to do so. Deploy the 2 large solar panels, which are behind the middle wings, to generate power. Be sure to retract them before re-entry.

Re-entry: Set a re-entry orbit to graze the atmosphere at an altitude of 50,000m, but try not to go much deeper into the atmosphere then this. A shallow descent is needed to bleed off the orbital speed before the craft overheats. Once it has descended to 60Km, deploy the airbrakes by applying the parking brakes like you would on the ground. You can deploy them sooner, but they don't really help this early. Deploying them any later and you loose out on some of the initial drag they give that reduces how much the craft accelerates as gravity pulls it in. Keep the craft pointed prograde during the descent to reduce heating on some of the more sensitive parts of the craft and to help keep it stable. It is not recommended to go off prograde until the craft has slowed down to below 1000m/s. Once below 1000m/s you should be able to turn the rapiers back on and run them at low thrust to fly the craft around a bit. Just be careful flying the craft after re-entry, it is going to be rather nose light and will pitch up a bit easier then it should. Waiting until the speed is dropped to below 400m/s is recommended.

Landing: The craft is going to be a handful after burning off nearly all its fuel. It will want to pitch up most of the time but should be able to turn much tighter. Landing is best done at a very shallow descent, keeping the nose down so the landing gear can all touch fairly close to the same time. It will probably take a few tries to get it to land nicely, or you might be able to land it on your first try.

Do have fun playing around with this craft and I hope you learn a few things that help you with your ssto's, and atmospheric craft in general.

Action groups:

1: Rapiers turned on, LV-N's turned off

2: Rapiers turned off, LV-N's turned on

9: release the cargo from the docking port(in the cargo hold)

10: open/close the cargo bay doors("I can't do that Dave.")

Download: Jak-102 TopKnot

Edited May 12, 2015 by Jakalth

[Capt. Hunt]

what's the rear clearance like on those LV-Ns? Rockets in KSP don't perform well if there is anything in the path of the exhaust. That's probably why maneuvering with the LV-Ns is so sluggish. You could probably get away with using RCS and OMS instead, they'll have plenty of Delta-V for maneuvers or even a deorbit burn, especially if you ditch the NERVAs, and also, that'll allow you to dock it safely.

[Radam]

I find nervas somewhhat usefull as if they fire for 4 minutes, its a gain compared to rapiers.

Then. Again, my 36t cargo ssto weighs 120t.