SSTO to laythe and beyond

[Val]

... As i am struggling to get TWR above 0.08 in my ship. I experimenting with a 2/8 Raipier/Ion setup.

I think the problem with Ions is that you have many open stack connectors. It creates so much drag, that you need an unreasonable amount of Air Breathing thrust to lift it to orbit.

How much does your ship weigh?

I managed to create some pretty awesome (if I say so myself) designs where a single Rapier can lift a craft with a starting weight of 26.8t to orbit, weighing 18.6t once in orbit.

SSTL U-5 Dart Mk.5

Does your ship weigh more than that to require 2 Rapiers?

[Red Iron Crown]

I tried a Rapier/ion plane when prototyping for the mission, the most efficient (if slightly cheaty) way to bring them up is in a cargo bay. Open the doors and they thrust just fine. That plane was doomed by low TWR and difficulty generating power out near Jool.

That's a super lean design, Val, well done! I didn't think a Rapier could push that much mass to orbit.

[Nefrums]

The ship weight is around 25t.

It also needs more oxidizer to get into orbit as the ions have so low thrust, and also have some left for the Laythe assent.

The drag of the ions is a big problem. Just got an idea... Ionspikes.

I use PB-NUKs and lots of batteries to power the ions.

[Val]

That's a super lean design, Val, well done! I didn't think a Rapier could push that much mass to orbit.

Thanks. Took me every evening since my failed Laythe attempt to work out that design. Went trough a lot of iterations to figure out especially:

• Optimal placement of each component, to keep thrust through CoM and keep the CoM from moving too much when fuel is drained
  
• How much wing is needed and at what angle to the body, to keep drag as small as possible while passing through the Mach barrier.
  

Would probably have saved a lot of time doing this with a 2:2 engine layout. Would have been so much easier to get thrust through CoM. A 1:1 layout is much like a rocket with boosters only on one side. Kinda like the Space Shuttle.

Some concepts I tried.

Actually. I may give some new 2:2 or 3:3 designs a go. With all that I learned, I think I could reach 6 km/s dV and TWR > 0.3 in LKO.

The ship weight is around 25t.

A single Rapier should be able to lift that.

It also needs more oxidizer to get into orbit as the ions have so low thrust, and also have some left for the Laythe assent.

Hmm. With nukes you don't need Oxidizer on Laythe. I could get up to 1600+ m/s Airbreathing with Apoapsis at 75 km. I wonder if that would be enough for Ions?

The drag of the ions is a big problem. Just got an idea... Ionspikes.

Heh. I was going to suggest just that. Edited July 10, 2015 by Val

[Nefrums]

I had mixed up the weights 25 t at lko. Takeoff is 34t.

Just tested the ionspikes. Took away most of the drag.

Still not enough fuel in Lko to take of laythe. Needs some more work...

[Nefrums]

Finally after several days of trying, I succeeded in making a design I'm happy with. And that can get to LKO with enough fuel for a Laythe assent: StarFlare

[Val]

Finally after several days of trying, I succeeded in making a design I'm happy with. And that can get to LKO with enough fuel for a Laythe assent: StarFlare

That is a very nice looking craft. And impressive Dv too. The TWR gives me shivers though

[Red Iron Crown]

That does look pretty cool, Nefrums. Care to show us the power system that I assume is in that cargo bay? That TWR is low, but I think after your Laythe ascent, when the ship is much lighter, you could land on Bop or Pol on ion power alone and still return. The landing itself would be tricky, though.

[Nefrums]

http://i.imgur.com/NhRoQ19.jpg

The power system in the cargo bay there are 25 PB-NUKs, 36 Z400 batteries and one XL solar array.

It can power all the 10 ions for ~4 min. The PB-NUKs power 2 of the ions and the solar panel another 2 of them (at kerbin)

It is a bit hard to find a good balance of power and weight. There is no obvious solution.

PB-NUKs are heavy, solar panels don't work on jool, batteries run out.

I think a Pol landing should be doable. Not sure about Bob as the ship cant sustain the TWR for long enough

Edited July 11, 2015 by Nefrums

[PLAD]

These SSTO spaceplanes have been superb examples of form and function. So until I get better at spaceplanes here is a minimalist entry for a 1-way SSTO to Laythe. 9 parts and 7.7 tons at launch. I used my trusty KEKKJ route, this time using Kerbal time instead of Earth time. Some notes on that path:

-On the Kerbin-Eve leg KSP's path predicter keeps switching between showing an Eve closest approach before and after solar periapsis. You need to use the post-periapsis encounter (at UT Year 2 D353.6 +/-1, 198.6 +/-1 K-days after leaving Kerbin on Y2 D155). So sometimes it won't show the right Eve encounter but you can figure out where it should be.

-Using Mun is much harder than a direct to Eve flight. No matter how well you set up the TMI burn there will be a big error you have to correct right after the burn.

-I needed 3 tiny course adjusts between the 2 Kerbin flybys. It is tricky to get the right Jool approach without having to fly by Kerbin too low the 2nd time.

-I always adjust to the 1/100th of a m/s even though the rocket can't be nearly this accurate. This way I confirm that the right path is there somewhere even if I can't get on it just yet.

-KSP's path predictor can't see more than 2 flybys ahead (usually) so you should use a flyby tool (Flyby Finder or Arrowstar's TOT) to plan a route with more than 2 flybys in it.

I can see some advantages to using a plane instead of a rocket are that a plane can have TWR lower than 1, and you don't have the brutal gravity losses while going up. On the other hand I like the high TWR for the ejection boost. I do not think my Rapier-only approach will be able to get to Laythe and back because its ISP and TWR are not high enough though. On the other hand getting from Laythe orbit back to Kerbin shouldn't cost more than about 900m/s. Maybe.

Javascript is disabled. View full album

Edited July 12, 2015 by PLAD
said 200. meant 900.

[Val]

Impressive feat, PLAD. Such a small ship. So little dV.

[Nefrums]

That is some nice gravity assists.

I'm half way through my SSTL mission now.

http://imgur.com/a/PT7J7

[selfish_meme]

These SSTO spaceplanes have been superb examples of form and function. So until I get better at spaceplanes here is a minimalist entry for a 1-way SSTO to Laythe. 9 parts and 7.7 tons at launch. I used my trusty KEKKJ route, this time using Kerbal time instead of Earth time. Some notes on that path:

-On the Kerbin-Eve leg KSP's path predicter keeps switching between showing an Eve closest approach before and after solar periapsis. You need to use the post-periapsis encounter (at UT Year 2 D353.6 +/-1, 198.6 +/-1 K-days after leaving Kerbin on Y2 D155). So sometimes it won't show the right Eve encounter but you can figure out where it should be.

-Using Mun is much harder than a direct to Eve flight. No matter how well you set up the TMI burn there will be a big error you have to correct right after the burn.

-I needed 3 tiny course adjusts between the 2 Kerbin flybys. It is tricky to get the right Jool approach without having to fly by Kerbin too low the 2nd time.

-I always adjust to the 1/100th of a m/s even though the rocket can't be nearly this accurate. This way I confirm that the right path is there somewhere even if I can't get on it just yet.

-KSP's path predictor can't see more than 2 flybys ahead (usually) so you should use a flyby tool (Flyby Finder or Arrowstar's TOT) to plan a route with more than 2 flybys in it.

I can see some advantages to using a plane instead of a rocket are that a plane can have TWR lower than 1, and you don't have the brutal gravity losses while going up. On the other hand I like the high TWR for the ejection boost. I do not think my Rapier-only approach will be able to get to Laythe and back because its ISP and TWR are not high enough though. On the other hand getting from Laythe orbit back to Kerbin shouldn't cost more than about 900m/s. Maybe.

http://imgur.com/a/82Kbh

I think if you had a mk1 inline cockpit and a shockcone instead of the capsule and the two radial intakes you would increase your in orbit dv by a substantial amount. You would be able to airbreathe longer and at a higher speed. Same number of parts. Radial parachute would need to be behind the cockpit.

[Red Iron Crown]

These SSTO spaceplanes have been superb examples of form and function. So until I get better at spaceplanes here is a minimalist entry for a 1-way SSTO to Laythe. 9 parts and 7.7 tons at launch.

Great mission, you're the king of slingshots! One trick I've learned for VTOL Rapier-powered craft if you want to lift a bit more with them is to burn in closed cycle mode off the pad, this gives a higher TWR until you accumulate enough speed to switch back to air-breathing mode and keep climbing (Not my trick, someone used it in the payload fraction challenge).

I'm half way through my SSTL mission now.

http://imgur.com/a/PT7J7

You are a more patient player than me, that escape from Kerbin took some time. You also mentioned in your captions:

The best solution that I found was Burning at a point between the maneuver and prograde and trying to keep PE height constant.

I have also found this to be the best compromise for long burns. Point at the node and you risk grazing the atmo and losing precious speed, point prograde and Pe gets raised too high, wasting Oberth effect. Cool that we arrived at the same solution independently.

Well done with your Laythe ascent, clever move to make the mode switch when you did to minimize excess LF or O. You've got a large dV budget remaining, gonna try to hit another moon before returning?

[Nefrums]

As many as I can :-)

Nice to hear that you found the same ejection burn method to be the best. Still 400 dV is alot to lose due to low TWR.

Btw. The spreadsheet you made helped alot. Thanks!

[PLAD]

Red Iron Crown-thanks, notice I used your Tylo capture method almost exactly, it is superb. By getting flung outward after the Tylo flyby you can tune your Jool apoapsis and thereby your arrival time at Laythe's orbit to whenever Laythe will be there. It's pretty universal as long as your Jool approach isn't too far out of Tylo's orbital plane. I tried paths that get flung inward but they make getting a future encounter much harder. I'm also going to try your suggestion of taking off with the Rapier in closed mode, in open cycle it sits there for about 10 seconds spooling up before it even moves.

Nefrums- Very nice mission so far, that is a lot of dV still in the tank after returning to orbit from Laythe. It'll be interesting to see what you do with it.

selfish_meme- I'll try that too. I want to find the limit of the dV I can get to orbit with a single Rapier using a vertical ascent, I suspect the maximum possible is around 1600m/s but it would take about 2300m/s to do a Laythe-and-return.

It looks to me like the fastest you can get in air-breathing mode with the Rapier is about 1500m/s on Kerbal (without exploding, anyway). Has anyone substantially beaten that? Next step up is one Rapier and 1 nuke, I see Val has already made some high-dV ones of those with the Dart Mk5 and 6.

[Nefrums]

Mission success!

Album updated: http://imgur.com/a/PT7J7

[Red Iron Crown]

Nefrums: That is all kinds of awesome, you put that extra dV to good use! 30 minute suicide burns? You have more patience than I do.

[Nefrums]

Thanks!

I am never ever going to design a ship with less than 0.1 twr again!

[PLAD]

Nefrums, that is superb. A Jool-3 with a single stage! That would be phenomenally hard to beat.

[Nefrums]

Thanks! Getting a 4th landing at Jool would require another 1k dV at least, and 4x the TWR

[Val]

Mission update:

I got a U-6 Spirit Mk.3 to Jool with 4.2 km/s dV left in the tank, using PLAD's K-E-K-K-J route. Though, I'm not nearly as effecient. Still costs me ~1.3 km/s dV. But it was a big improvement over the 2.3 km/s dV a direct burn cost me on the previous attempt. Unfortunately I couldn't land at Laythe. No matter how I tried to aero-capture, either the Mk1 Pod kept exploding or I didn't slow down enough. So I gave up... again.

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I'm now trying with a Spirit Mk.6 which has more wing area for aero-capture and more radiators to keep cool. I'm using PLAD's route again, but I didn't hit the windows that well, so had to improvise and use a different 2nd Kerbin flyby, to hit Jool. And then I arrived a bit fast at Jool, so had to use a 32 m/s Jool PE retro-burn in combination with a Tylo gravity assist, to get captured. And i haven't had time to do more, so haven't tested the upgrades on the Mk.6 yet.

Misc.:

On a side note, I started wondering if I could build something that could bring some cargo to Laythe. And then this surprise happened.

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A Mk3 based SSTL with 9.5 t cargo and 4.1 km/s dV in LKO and 0.26 TWR. Or 5.1 km/s dV and 0.27 TWR with empty cargo hold.

I was just surprised a viable SSTL could even be built using Mk3 parts.

Edited July 17, 2015 by Val
Fix a couple of typos

[Val]

 

Adding new pictures as they happen. Maybe I should learn to stream...

Edit: I landed on Laythe, but I need to go sleep now.

Edit 2: Forgot to link craft files again.

Edit 3: Album updated with return journey

Edited December 15, 2015 by Val
Forum conversion format fix

[Red Iron Crown]

Impressive, Val! The missions so far have been "flags and footprints" style, looks like you are brought some useful cargo and the crew to use it.

[Quabbo]

Very nice to see!