Can anyone help improve my rocket? - Duna and Back

[Gameslinx]

Hello! I've been a KSP player for some time but I have never really be inclined to exit the Kerbin-Mun-Minmus system until today. I'm beginning to approach the mid-end of the Career mode and I'm starting to need science from beyond the KMM system. I've made this rocket specifically for Duna and back (still needing to attach a service bay with science stuff) but it doesn't quite have the kick to slow down at Kerbin intercept on the way back.

I've tried landing with parachutes on Duna (which is what I intend to do with this rocket) and it has worked so far. Nuclear engines are not favourable for me since I don't like them (no gimbal) and people are saying they're not necessary for duna, so I'd like to avoid using them until further in the career.

Could anyone provide some feedback/improvement on my rocket? (attached below as a .craft)

Stage stats of the rocket:

- Strong lifter with asparagus staging

- 2.5m transfer stage

- 1.25m lander stage

- the lander should be able to get back to Kerbin since the Transfer stage can be used as a lander if there's fuel left, meaning extra fuel in 2 stages to get back.

- aerobrake reentry

 

Craft is attached below.

https://www.dropbox.com/s/p2szuiimqo7yftt/Sylver.craft?dl=0

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions. 

[Gameslinx]

Just now, Vanamonde said:

This question about how to play the game has been moved to Gameplay Questions. 

OK sorry. Thanks for moving

[Vanamonde]

No problem.

[Mjarf]

I took a look at your craft and it seems like you're at the knife's edge delta-v wise, KER states 8774 m/s delta-v total. It may be enough if you fly extremely efficiently, but it leaves no margin for error. I would use drogue chutes instead of aerobrakes myself, but using aerobrakes isn't wrong, it's just a different way of doing things. Your lander has 4 landing legs, 3 is enough really, and saves a little bit of weight, giving you a tad more delta-v and twr. You'll gain about 200 m/s on the lander stage delta-v  by switching to a single terrier engine instead of 4 Twitch engines. You'll also get slightly better TWR. Removing one landing leg brings the lander delta-v up to 2025 m/s, with a new total of 9023 m/s, that alone makes things a bit easier.

Your lifter stage looks pretty solid, you could probably lose one of the reaction wheels though. I'd add a couple of the small solar panels to the lander, they're very light and it sucks to run out of electricity.

 

I'm not gonna criticize your craft too much, as I respect others ways of doing things, and I do not do things efficiently at all myself. I primarily play science mode as I don't like to be limited by economics.I adore the NERV engine myself, it excels at chewing fuel and producing delta-v all day long. Yes it has no gimbal and has a terrible power to weight ratio, but you can't overlook it's superior ISP. The lack of gimbal isn't that relevant once your outside the atmosphere IMO, as you don't have to fight drag and such.

Edited October 9, 2016 by Mjarf

[Gameslinx]

7 minutes ago, Mjarf said:

I took a look at your craft and it seems like you're at the knife's edge delta-v wise, KER states 8774 m/s delta-v total. It may be enough if you fly extremely efficiently, but it leaves no margin for error. I would use drogue chutes instead of aerobrakes myself, but using aerobrakes isn't wrong, it's just a different way of doing things. Your lander has 4 landing legs, 3 is enough really, and saves a little bit of weight, giving you a tad more delta-v and twr. You'll gain about 200 m/s on the lander stage delta-v  by switching to a single terrier engine instead of 4 Twitch engines. You'll also get slightly better TWR. Removing one landing leg brings the lander delta-v up to 2025 m/s, with a new total of 9023 m/s, that alone makes things a bit easier.

Your lifter stage looks pretty solid, you could probably lose one of the reaction wheels though. I'd add a couple of the small solar panels to the lander, they're very light and it sucks to run out of electricity.

 

I'm not gonna criticize your craft too much, as I respect others ways of doing things, and I do not do things efficiently at all myself. I primarily play science mode as I don't like to be limited by economics.I adore the NERV engine myself, it excels at chewing fuel and producing delta-v all day long. Yes it has no gimbal and has a terrible power to weight ratio, but you can't overlook it's superior ISP. The lack of gimbal isn't that relevant once your outside the atmosphere IMO, as you don't have to fight drag and such.

Thanks for your feedback. I will do the changes you said. Is there any chance I can sneak in a second 2.5m Rockomax tank in the transfer stage? Or some radial mounted tanks on the lander?

[Plusck]

I took a look too. My conclusions are slightly different: your only real problem is in your final (lander) stage: there is no way you'll get home with it, even though your transfer stage will be virtually full of fuel when you ditch it.

The two sets of reaction wheels at the top of the lifter stage are unnecessary and you can remove them altogether. You have plenty of fins for aero control and gimbal for upper atmosphere/vacuum control. The single reaction wheel at the top can easily get you lined up for the transfer burn on its own. That also lets you get rid of the struts holding the craft together around those weak reaction wheel joints.

You should make LKO with about 1000 m/s left on the Twin Boar - so your transfer to Duna can be done with the lifter stage. That leaves over 2km/s just to get into Duna orbit. The problem is that without docking ports, you can't use the transfer stage to refuel for the return home. Your lander has about 1700m/s, which is just too tight (you'll certainly need some of that to land on Duna, so you'll be nearly dry on returning to orbit). If you use a pair of docking ports to attach to the transfer stage, and a basic probe core to stop if from being automatically treated as debris, you can meet up in orbit, transfer fuel across and be laughing for the return home.

 

edit: just re-read the original post. You're right that the transfer stage can be used to land, but you'll have no landing legs and you need to at least start the return to orbit using the transfer stage if you're going to have enough fuel to get back to Kerbin. If you plan on doing that, you can put parachutes/drogues on the 2.5m section, airbrakes too if you want, and leave the final stage light and clean (plus a couple of photovoltaic panels) so it can get home on its own.

Edited October 9, 2016 by Plusck

[AeroGav]

I like that rocket, it flies much nicer than mine do , it looks good and is also quite a real-world design.

I can only echo what the others said, that NERV is the way to go.    I did a quick bit of maths a few months ago that showed that a Terrier makes sense if fed with an FT400 or smaller,  but if the burn duration gets any longer than that, you get more delta v for your combined engine + fuel mass by switching to NERV.   The only problem you might have is that an LV-N/Mark1 LF Fuselage transfer stage will make your rocket even longer.

I've never actually been to Duna with a rocket however,   since I'm better at building partially reusable spaceplanes like this this -

https://kerbalx.com/AeroGav/WhippyNerv-II

EDIT - just did a test design for a NERV transfer stage.    

MK1 liquid fuel fuselage with a NERV right behind it, radially attach mk0 liquid fuel fuselage. Wet mass 10.08 Tons, Dry 5.08 Tons,  over 15k delta V,  it has a TWR over 1 on Duna.    Looks like a separate lander isn't necessary..

Edited October 11, 2016 by AeroGav

[Gameslinx]

2 hours ago, AeroGav said:

I like that rocket, it flies much nicer than mine do , it looks good and is also quite a real-world design.

I can only echo what the others said, that NERV is the way to go.    I did a quick bit of maths a few months ago that showed that a Terrier makes sense if fed with an FT400 or smaller,  but if the burn duration gets any longer than that, you get more delta v for your combined engine + fuel mass by switching to NERV.   The only problem you might have is that an LV-N/Mark1 LF Fuselage transfer stage will make your rocket even longer.

I've never actually been to Duna with a rocket however,   since I'm better at building partially reusable spaceplanes like this this -

https://kerbalx.com/AeroGav/WhippyNerv-II

EDIT - just did a test design for a NERV transfer stage.    

MK1 liquid fuel fuselage with a NERV right behind it, radially attach mk0 liquid fuel fuselage. Wet mass 10.08 Tons, Dry 5.08 Tons,  over 15k delta V,  it has a TWR over 1 on Duna.    Looks like a separate lander isn't necessary..

Thanks for the reply! I believe I can use a similar design of that lander in my own rocket, but I may add a lot of parachutes for accurate aerobraking