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Need some help with circularisation burn RSS/RSS/RP1


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Need some help with circularisation burn RSS/RSS/RP1

Hello guys, this is the first time I play RSS/RO/RP1, I’ve been studying a lot of stuff, other vessels designs, ideas, physics and math; just to be as professional as could be. However, with the above I still have problems getting to orbit even I have 9.792 DV with KER and 9587 with Mechjeb; so here is the think:

My first stage is a NAA-75-110A series 
Second stage is the AJ10-27 (include RCS and separator motor to reduce ullage) 
Third stage is the XASR 1

[DV](https://i.imgur.com/H3zKIm9.jpg)
[Upper Stage ](https://i.imgur.com/mzxeVQq.jpg)
[staging ](https://i.imgur.com/vV2Bup5.jpg)


I’be tried the following orbital methods:
1. Perform gravity turn with Mechjeb and some seconds before reaching target AP turn off MJ, continue with SAS looking for a flat profile; before reaching AP T- 1:25 start rotating to get spin stabilization, T-1:00 start burning with a pitch between 3 and -10 degrees (have tried almost all pitch degrees); if you look at the design stage 2 and 3 must burn consecutively due to ullage.

2. Fly PVG with coasting, and repeat almost the same procedure as above starting with the spin stabilization.

With any of the above can’t get a stable orbit, must of them with a PE of -60 KM or 70 Km

Really appreciate the help

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Need some help with circularisation burn RSS/RSS/RP1

Hello guys, this is the first time I play RSS/RO/RP1, I’ve been studying a lot of stuff, other vessels designs, ideas, physics and math; just to be as professional as could be. However, with the above I still have problems getting to orbit even I have 9.792 DV with KER and 9587 with Mechjeb; so here is the think:

My first stage is a NAA-75-110A series 
Second stage is the AJ10-27 (include RCS and separator motor to reduce ullage) 
Third stage is the XASR 1

[DV](https://i.imgur.com/H3zKIm9.jpg)
[Upper Stage ](https://i.imgur.com/mzxeVQq.jpg)
[staging ](https://i.imgur.com/vV2Bup5.jpg)


I’be tried the following orbital methods:
1. Perform gravity turn with Mechjeb and some seconds before reaching target AP turn off MJ, continue with SAS looking for a flat profile; before reaching AP T- 1:25 start rotating to get spin stabilization, T-1:00 start burning with a pitch between 3 and -10 degrees (have tried almost all pitch degrees); if you look at the design stage 2 and 3 must burn consecutively due to ullage.

2. Fly PVG with coasting, and repeat almost the same procedure as above starting with the spin stabilization.

With any of the above can’t get a stable orbit, must of them with a PE of -60 KM or 70 Km

Really appreciate the help

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Sounds like you need more dV. Note that KER and MechJeb are assuming vacuum isp when calculating your dV, and combined with losses due to gravity during the initial stages of the launch, you will need to account for that with more fuel.

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Use the ‘insert image from URL’ button to insert the images instead of just putting text links. 9500m/s should be enough to reach some kind of orbit.

Instead of those squat, fat upper stage tanks, try building them long and thin- 0.3-0.4m diameter and long enough to burn the engines 5 seconds beyond their rated burn times. Swap the top stage to the AJ configuration and make the avionics on top as light as you can as well as streamlined so you can ditch the heavy fairing.

The way I did this contract was- RD103 engine (though the NAA should be fine), decouple the avionics from the first stage when it burns out and use that with RCS to point, spin and ullage the upper stages, then 2x AJ10-27 upper stages to get into orbit plus a further six AJ10-27s as first stage boosters. I’ve been documenting my own blundering through RP-1, here’s how I got into orbit: https://imgur.com/a/fHNFYSZ 

 

Most of what I’ve been doing is based on Next Small Step, you should take a look at it as it contains a lot of useful hints and tips:

 

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Welcome !

Sadly the images didn't embed at all.

Spoiler

just to help anyone else if they want to see it, if OP didn't edit the post.

H3zKIm9.jpg
mzxeVQq.jpg
vV2Bup5.jpg

I have a feeling that perhaps the dV is too close to the minimum requirement... while it's true that you need about 9.5 km/s of dV available for orbiting in RSS/RO, there'll most likely be losses if one consider that the launch trajectory isn't necessarily the most efficient for the rocket (esp. if you mention that you need to coast - most RSS liquid rocket launches, as does RL launches, shouldn't need to, unless if it's a solid rocket motor upper stage or something similar). The dV figures given by the in-game dV calculator only sums up to ~8.5 km/s and that might be one indicator.

Edited by YNM
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