Friendly Reminder

[Laie]

On 6/23/2016 at 10:43 AM, eddiew said:

Delta-v is delta-v, regardless of how many engines you have. There are no drag losses in a vacuum, so you can take as long as you like over burns.

No, it doesn't work like that.

Try sending something to Jool on 0.1g. Then do the same with 0.5g. For both runs, compare dV before/after and tally how much you actually spent.

0.1g doesn't require angelic patience: about 35 minutes of raw burn time, plus however long it takes you to set up the maneuvers. Periapsis-kicking is strongly recommendend.

[eddiew]

3 hours ago, Laie said:

No, it doesn't work like that.

Physics disagrees... Travel far, far out from the sun. 5km/s is the same however long or how many orbits it takes to achieve. Outside of the gains due to the oberth effect (or failure to harness), whether KSP agrees with physics is not really my responsibility or fault 

[Laie]

2 hours ago, eddiew said:

Physics disagrees...

I gather you're so sure of yourself, you think you know the outcome without trying?

 

[eddiew]

20 hours ago, Laie said:

I gather you're so sure of yourself, you think you know the outcome without trying?

On further thought, it depends on whether we're talking about sending it with the same fuel mass, or with the same delta-v... the conversation has seemed rather ambiguous to date. To me, it seemed like the latter.

I will agree that the most efficient use of a given mass of fuel is to burn it as fast as possible. If you have 10 solid weights with which to change direction, then throwing them in sequence means the first is pushing against the craft plus 9 weights, the second against the craft plus 8, etc. Gluing them together and throwing them out as a lump results in ten weights pushing against just the craft. (Although if you want to really go nuts, you could consider whether you're should account for the Oberth effect with a sequential election, since you will be going slightly faster each time resulting in that last weight being even better than expected.)

On the other hand, I'd need to a good thought experiment to explain why a 1.0 TWR ship with 3km/s available and a 0.1 TWR ship with 3km/s available won't end up both going 3km/s faster than they started when their manoeuvres are complete  

[Laie]

3 hours ago, eddiew said:

I'd need to a good thought experiment to explain why [...]

Why do you insist on thought experiments when you have a sufficiently capable simulator available?

But as you seem to be loath to just put your hypothesis to the test: your two hypothetical vessel would both gain 3km/s if they were to perform the burns in empty space. All the integration stuff would not change the outcome. However in KSP we're not in empty space: we typically depart from, and arrive at, places where there's significant gravity. That makes all the difference.

The way we're doing maneuvers assumes that all impulse happens at a single moment in spacetime; if you need more than a moment to perform the burn, there will be losses of some sort of another (oberth, steering, whatever). More often than not this can be ignored, but if you were to try a Jool mission on 0.1g, you'd find that it becomes pretty noticable.

[Megadeath]

It might be possible to use periapsis kicks to significantly reduce losses on an insertion burn (that's the departure, right?) but it seems to me that a low twr inherently means greater loss in the capture burn from burning longer before and after. 

I'm far from a rocket scientist, so constructive criticism appreciated. That's sorta the gist I'm getting from smarter people's arguments.

[MalfunctionM1Ke]

TWR is great but piloting skill is more important.

Always go full throttle until you reach the terminal velocity. And reach it fast or you will waste fuel.

Terminal Velocity discribes the speed where you begin to be "held back" by the atmosphere you are dashing through.
I.E. the highest speed an object would reach by falling to the ground.
Or in other words: You would actually rather aerobrake by going faster than your terminal velocity than launching.

The terminal Velocity will also change with atmospheric pressure (higher speed in thin air and lower speed with high angle-of-attack or blunt leading parts)

Kerbal Engineer Redux can give you a read-out for this.

Edited June 26, 2016 by MalfunctionM1Ke

[Norcalplanner]

Having a minimum TWR of 0.3 will make life much easier for any craft transferring to a different SOI, whether the Mun or Jool.