Optimal TRW from Kerbin?

[Spricigo]

13 minutes ago, StrandedonEarth said:

Okay, now I'm going to have to try that. Just set the initial pitch attaching it to the launch clamps, and then fire-and-forget if you set it right?

Just wait a bit when loading,  physics kicking in will shake the rocket and small deviations may cause huge differences.  

Also let me provide a working example: https://kerbalx.com/Spricigo/Auto-Orbiter (search for @Snark's Osumi challenge for even better examples.) 

Edit: for the typical put a satellite around Kerbin contract there is the add convenience of the orbit well outside the atmosphere.  Allows for climb on SRBs followed by insertion/circularization on efficient vacuum engines. Brute force then finesse. 

Edited April 9, 2017 by Spricigo

[Alshain]

On 04/08/17 at 4:23 AM, Streetwind said:

Well, with a high TWR rocket, you just turn over sooner and harder at launch, that circumvents this issue nicely. Look at some of the videos posted in relation to "minimum dV to orbit" challenges. The winners generally have huge amounts of thrust and pitch sharply right off of the pad. So there's absolutely no mechanic that invalidates the concept of "high TWR reduces dV cost to orbit".

Maybe if you turn off heat but I don't see that working under normal circumstances.

[Red Iron Crown]

22 minutes ago, Alshain said:

Maybe if you turn off heat but I don't see that working under normal circumstances.

Careful choice of the frontmost part can mitigate that, the designs I've seen that work this way use the shielded docking port. 

[Snark]

5 hours ago, StrandedonEarth said:

Okay, now I'm going to have to try that. Just set the initial pitch attaching it to the launch clamps, and then fire-and-forget if you set it right?

Yup.  As @Spricigo alluded to, here are some examples of ships that literally fly themselves to orbit with no autopilot (other than a couple of parts from "Smart Parts" that activate staging-- one that stages on a timer, one that stages when fuel runs out):

Example of a (very simple, not particularly optimal) ship that does this:

[Razorforce7]

There are so many variables in this that there are many answers. I think on most ordinary designs a twr of 1.4 through 1.5 is recommended. However, this is completely different for spaceplanes. They usually only require a TWR of atleast 0.66 (preferably more). That is about twice as much to lift of the ground, atleast when given a rather averaged looking wing design.

On some designs I put wings flat on the radial surfaces of my fuel tanks. I do this on reusable rockets. TSTO or simply a 2 stage recoverable rocket which has said wings surfaces on the first stage.
This first stage also has alot of TWR (around 2 through 2.5+)
Due to the wings it can curve quite sharply at higher airspeeds through thinner air as long as I keep the speed not to slow/fast. So with all that extra thrust I can still guide my ascent curve. Only thing to make sure is that all your parts have high heat resistance (which most wing parts do anyway)
Higher TWR is always better for least amount of Delta V to orbit. But with a least delta V design you usually have so many engines that your total dead weight in orbit is actualy higher.
And since more weight is more fuel and parts which in turn cost most funds the range of 1.5 TWR with the available engine types is quite a well estimated and average statistic when taking all aspects in consideration. 
There are alot of pics on this site about different rocket designs. Some will perform better over the 1.5 thrust range and some under it.
But anything below 1.2 for a rocket seems unlikely to be a efficient design, no matter what it is your launching.


 

Edited April 10, 2017 by Razorforce7

[GoSlash27]

On 4/8/2017 at 5:47 AM, CSE said:

To go into more detail for determining the ideal TWR for each stage, @GoSlash27 had a good post that laid out a mathematical design approach, which I can't now remember/find.

CSE,

 My approach is geared towards optimizing each stage for the DV requirement, not the optimal t/w. That's the "reverse rocket equation", outlined here:

 

For t/w requirements, I use more crude "rule of thumb" figures.

Atmospheric SRB first stage: 1.2:1
Atmospheric hybrid first stage: 1.3:1
Atmospheric liquid fuel first stage: 1.4:1
Launch transstage 0.7:1
Orbital insertion/ interplanetary stage 0.5:1
Vacuum lander/launch stage 1.5:1 local

 Of course, all of this is out of date now. I've been out touring Iowa on my blue scooter instead of playing KSP...

Best,
-Slashy