More Delta-V on Orbital Lifter ?

[John Kermin]

Hi,

I have a problem. I have build a huge Rocket that i want to use to lift other things into Orbit, because i am tired of having to over engineer my deep space vessels just so they can get out of Kerbin atmosphere.

I used tweak scale so the Rocket is positively massive, which it must be since it has has to carry whole spaceships inside. Preliminary tests seemed promising. But since i added actual payload i can't seem to get into LKO before my fuel runs out. Which makes since, because now i am lifting more mass then before. But nothing i do seems to have any real effect, getting to about 70k Apoapsis and then my fuel is gone, not enough for circularization let alone deorbit burns. I tried adding Boosters, adding engines to get higher TWR, removing engines to get closer to 1.2 TWR and most importantly doubling and tripling the tank. But nothing seems to work. What can I change so the thing does its job ? I dont think i can getter better ISP, its 315 and everything with more isp has to too little thrust.

 

 

Edited October 4, 2016 by John Kermin

[Waseemq1235]

I actually noticed that tweak scale-ing parts to a bigger size actually makes the parts less powerful (for engines)

Try strapping a bunch of non-scaled boosters on it, and maybe make the payload lighter.

[John Kermin]

Ok I enlarged the Tank by 50% and cut the payload by half and i still run out of fuel before circular orbit is achieved. Not sure how i am going to do the engines. I dont have a mounting bracket that can support more than 7. The boosters i use are procedural, not tweak scale. And that didn't work either.

From my experience there is a limit with booster size, at which point they simply lift themselves, if that. I tried adding 4 50m x 7m Boosters. It was ridiculous and even that didn't help. (Apart from the fact that the whole point of the craft is to have one reusable stage.)

Edit: Ok I added some ramjet engines and changed the ascent so that i am longer in the upper atmosphere. Its not elegant and the ramjet run for all of 90 seconds but it saves enough fuel so that i at least reach 80km circular orbit..

Edited October 4, 2016 by John Kermin

[DD_bwest]

 if your open to mods, you could download the real scale boosters lol they have some high thrust engines with ISP over 400.

 

but some may call that "cheating"  lol

[Aegolius13]

Is the core rocket single stage to orbit?  I don't use tweakscale, but I know in stock it's very hard to put any kind of payload into orbit on an SSTO rocket.

I would suggest scandalously enormous, radially mounted LF boosters.  That way you're still getting some of the benefits of staging.  

[Kelderek]

The DV needed to get to orbit is the same regardless of the size of your craft.  So if you have enough DV but can't attain orbit then the problem would have to be somewhere else.  Your vessel could have too much drag or your ascent path is not optimal.  Also, make sure you are looking at the sea level (ASL) numbers for stats like delta-V and ISP and not vacuum numbers.  You'll want at least 3200 delta-V ASL, perhaps even 3500+ depending on your design and target orbit altitude.  For the stock game, engines have ISP ratings around 290 ASL and only get above 300 when higher in the atmosphere or in a vacuum - I'm not sure how that changes if at all for mods.  Also take a look at your TWR, if that is too low then you waste fuel fighting against gravity.

[sjbuggs]

7 hours ago, John Kermin said:

I dont have a mounting bracket that can support more than 7. 

Another option would have been to use cubic struts surface mounted on the bottom of the tank to give attachment points for engines without an adapter.  Used this for 6x and 8x vector designs for a ssto rocket  

Look for tutorials on engine clustering for more.

[John Kermin]

Thank you for your answers

[GoSlash27]

John Kermin,

 For best results, the rocket should be designed from the outset to impart the required DV and t/w to your payload. Attempting to crutch a lifter that's insufficient for the payload will generally result in a bodged design... assuming you get it to work at all.

 You will have a lot more success if you design from the top down instead of the bottom up. Payload first so you know what you're dealing with, then rocket. Many players create lifters by payload rating, but even then they start with a boilerplate payload and design the lifter under it.

 A little tip: When launching a ship, I use the ship itself as it's upper stage. It's got tanks 'n engines, so why not put 'em to use? Once in orbit, it's a simple matter to refuel it and send it off to wherever.

 I hope this helps, and welcome to the fascinating world of rocket science!

Best,
-Slashy

 

 

 

Edited October 8, 2016 by GoSlash27