help me make my mun sattelite launcher smaller.

[putnamto]

alright so i have a craft capable of putting a sattelite in basically any orbit of the mun, but i feel this could be smaller/cheaper etc.

any ideas?

[steuben]

what is the mass of the satellite? 

[eddiew]

Well for one you could stack it as a single pillar, rather than side boosters. You have huge initial TWR, and I think one engine under two tanks would do just fine. You also wouldn't need the nose cones.

[Flavio hc16]

delta v required for putting a satellite on mun's orbit:

3200 for LKO( with a good gravity turn and a twr at the launch around 1.5)+850 for trans-mun+280 for mun injection, so you need 4350 ( bit of margin). You could almost do it without your side boosters

[Zhetaan]

4,600 m/s of dV should give you enough to reach any Mun orbit provided you time it correctly.

If the centre engine is a Terrier or equivalent (which I assume from the Stage 2 non-atmo TWR of .87), then you're actually wasting fuel on the centre engine by burning it at sea level, so this rocket is possibly less capable than it could be.

@eddiew's suggestion has a lot of merit to it; you get all the punch of one of the existing boosters and with fewer parts and less drag, too.  If one engine (as opposed to the two-and-one-half you have now) is not quite powerful enough to launch, try removing some fuel from the booster (or the upper stage); each booster provides approximately 500 m/s (possibly a bit more, but that gives you more room to remove fuel) and your current setup is about 1,400 m/s too rich.

Another possibility is to get rid of the side boosters entirely and switch to an SRB for initial ascent.  That would definitely be both cheaper and smaller.

[Starman4308]

Do not ignite the central Terrier on the ground. The Terrier is a vacuum engine: if used on the ground, it mostly just wastes LF/O. I suspect the earliest it should be ignited is somewhere in the 10-20km altitude range.

The upper stage is significantly under-fueled. It burns for just 1420 m/sec; given that it's likely the relatively high-specific-impulse Terrier in there, you should be burning that upper stage for more. You may also consider replacing the Terrier with a Spark engine: it has a bit less specific impulse, but masses 400 kg less, which may overcome the loss of Isp.

A common rule-of-thumb: stages with equal specific impulse should have about the same delta-V; stages with higher specific impulse should have more delta-V.

Overall, I'd convert this to a single axial stack with a longer upper stage, possibly shortening the second stage, and having just a single LV-T45 on the first stage. If the single LV-T45 isn't quite enough, you can stick a couple SRBs to the side of it, or possibly one underneath the LV-T45.

[GoSlash27]

What Steuben said. We need to know the mass of the payload.

Best,
-Slashy

[putnamto]

the sattelite is only 225 kg, its for a contract. im taking you guys input and redesigning it now, updated pics when im done.

i like this design



but my piloting skills arent nearly as good as they should be so i think im going to opt for this one instead. ill probably need that extra DV for when i accidently hit full throttle instead of half throttle, or end up going the wrong direction.



or i could just go with two FL-T800's on the bottom and have alot of DV to play around with.

thanks guys, wish me a safe flight.

EDIT: gravity turns with the last design are far more difficult that with the original, im constantly having to fight my pitch to stop from tumbling, but i was able to get into an LKO with 1300ish dv left so thats plenty to get my satelite where i need to.

im assuming the reason it became less stable is because of the higher COM and less width due to the the removal of the booster stage?

Edited March 15, 2018 by putnamto
i edit things alot

[GoSlash27]

Putnamo,
 I would go with this:

2nd stage: 48-7S Spark with an FL-T200 tank.
First stage:  4x24-77 Twitch, FL-T100 + FL-T200.

Aerodynamics become a pain when dealing with small lifters like this. You will need a fairing for the interstage to keep it clean.

An alternative design.
Parallel staging. Center core has an adapter to neck the fairing down to .625, 7 Oscar B tanks, and a 48-7S Spark.
The 2 side boosters consist of a nose cone, 3 Oscar B tanks, and a 48-7S Spark.
 
Best,
-Slashy
 

Edited March 15, 2018 by GoSlash27

[Spricigo]

2 hours ago, putnamto said:

the sattelite is only 225 kg, its for a contract. im taking you guys input and redesigning it now, updated pics when im done.

I suspect you can complete the mission with something like that:

Spoiler

https://kerbalx.com/Spricigo/SL60DC

 

[putnamto]

thanks guys, i was able to succesfully fullfill the sat contract, then i got three of the four temperature contracts i was aiming for, then i ran out of fuel.

a quick question though, once i reach the muns SOI im unable to set the mun as my target anymore, whatsup with that? ive tried setting maneuvers, deleting manuevers, going back to the space center, just about anything i could think of and it wouldnt let set the mun as my target again.

the contract would have been alot easier if i could see my AN and DN and i dont know how to tell that unless i have a target.

Edited March 16, 2018 by putnamto

[Flavio hc16]

Once you are in a body's SOI you  can't  targhet it anymore. However when you are given a contract,  you should see the targhet orbit  in game so it shouldn't  be hard  to reach it

[putnamto]

7 minutes ago, Flavio hc16 said:

Once you are in a body's SOI you  can't  targhet it anymore. However when you are given a contract,  you should see the targhet orbit  in game so it shouldn't  be hard  to reach it

how  can you discover the AN and DN once your in the SOI? and say im in a polar orbit, how would i change that to an equatorial orbit effectively? before i would just burn normal/antinormal at the DN or AN, but if im inside the planets soi how would i do this?

[Streetwind]

Without mods, all you can do is eyeball it. I often use the Mun's own orbit line as a visual guide, because it "hits" the surface right on the equator.

If you often have this problem around the same celestial body, you can launch a reference craft to it. Some tiny throwaway satellite. You invest a one-time effort to make that one as perfectly equatorial as possible. Then, all future missions can just target that craft as a reference point.

To make this extra easy, look for contracts like "position satellite in equatorial orbit of <body>". Then you even get paid for setting up your reference craft, and you have a target orbit showing you how to get perfectly equatorial!