What happened to 4500m/s^2 delta-V to LKO?

[Temstar]

Having come back to KSP after being away for a long time I realised immediately it's a lot easier to reach LKO now than it use to be. Back when I was playing around 0.20 it took around 4500m/s^2 of delta-V to reach 75kmx75km LKO. Now I'm seeing boosters with 3500m/s^2 and lower reaching that orbit.

Standard gravity looks to be the same to me at 9.82m/s^2, what happened? Is the new delta-V to LKO all because of the new aerodynamic model?

It's a pretty big change, since we know that reaching orbit means you're halfway to anywhere slicing 1000m/s^2 off that requirement means everything else about the game is now a lot easier.

[jaredkzr]

Aerodynamic updates! The atmospheric soup no longer exists!

[Dispatcher]

Depends on how good one is at designing and flying a ship to orbit. For me, the old dV values are about right. :blush:

[Goody1981]

I believe it's now doable for around 3200ms-1. Ish.

[Temstar]

6000m/s^2 from Eve's surface to orbit now? Damn that's low, it use to take 13,000m/s^2 or so to reach orbit from Eve sea level.

[Venusgate]

[quote name='Temstar']
It's a pretty big change, since we know that reaching orbit means you're halfway to anywhere slicing 1000m/s^2 off that requirement means everything else about the game is now a lot easier.[/QUOTE]

"Easier" being a bit of an arbitrary term.
Ascent profiles are more flight skill weighted than just design skill weighted (over what it used to be: the diff between 45@10k and a perfect ascent profile was like 300m/s, now it's more like make or break, if not 500m/s+)

Also, since the most recent atmo update, you have to be cautious on your descent as well, even with el basic command pod and mk-16; the lower 10k isn't going to feather you like before.

[FancyMouse]

Don't forget engine is rebalanced (read: nerfed) at the same time.
For Eve, don't forget the bug of engine constant max thrust (w.r.t atm pressure) is fixed (RCS is not fixed as of 1.0.4). Some engines will just produce zero thrust on surface of Eve.
All those are changes in 1.0

[Temstar]

[quote name='Venusgate']
Ascent profiles are more flight skill weighted than just design skill weighted (over what it used to be: the diff between 45@10k and a perfect ascent profile was like 300m/s, now it's more like make or break, if not 500m/s+)[/QUOTE]
Yeah I've noticed this. New drag model also gives cool features like if your booster doesn't have center of drag behind center of mass (say unaerodynamic payload) it's quite prone to flipping tail first, particularly when doing violent pitch maneuvers. That said the game does give you more tools to deal with this as well with the new SAS capability to follow prograde and less BANG BANG steering from the SAS. We use to have to fight that SAS from shaking apart our wet noodle rockets all the way to orbit.

[QUOTE]Also, since the most recent atmo update, you have to be cautious on your descent as well, even with el basic command pod and mk-16; the lower 10k isn't going to feather you like before.[/QUOTE]
No complaint from me, it's a great change. Although I hope interplanetary aerocapture is still possible (even if it requires a specially designed tug stage)

[FancyMouse]

Interplanetary aerocapture is definitely possible. However, it doesn't just involve design of the tug. It's about design of the whole ship. Back in 1.0.4 I really had fun designing ship for zero-burn aerocapture on Eve. Haven't got a chance in 1.0.5 but I'm looking forward to it.

[Xyphos]

2250 for sub-orbit, another 150 to circularize, another 950 to escape SOI. 3450 total. you're still going to have to bring 3500 dV either way.
the major change is the atmosphere, it's not so "soupy" anymore, and (hopefully) you're not losing a lot of dV to drag

[Bluegillbronco2]

The Soup they called an atmosphere has been fixed. But now we have to have a good accent profile to get into orbit efficiently. I think its a good trade off...

[Meithan]

Yep, as others have said, the new Δv-to-orbit values are due to the new aerodynamic model. The tl;dr version of it is that KSP now attempts to correctly estimate how streamlined a body is.

You see, the aerodynamic drag force experienced by most flying objects is [url=https://en.wikipedia.org/wiki/Drag_(physics)#Drag_at_high_velocity]proportional to its "cross-sectional area"[/url] (the "frontal area" it presents to the airflow). Before 1.0, this area was not properly calculated (it depends on the geometry and orientation of the craft), but simply computed directly from the [i]mass[/i] of the ship: KSP assumed that the cross-sectional area was 8 m^2 per tonne of mass, regardless of shape and orientation.

I guess that the rationale behind that choice was that, very roughly, in general heavier ships are "bigger" and thus have a larger cross-sectional area. But this assumption fails to acknowledge the fact that we can build things to be streamlined: simply make rockets tall and slim and you can make them quite heavy without increasing the cross-sectional area.

Before, your small 20 tonnes rocket (at launch) had an effective cross-sectional area of 160 m^2: that's as if it had a frontal diameter of 14.3 meters! Anything heavier than a few tonnes was essentially considered a pancake flying face-on for drag purposes. Hence the soup-o-sphere.

Now KSP does an honest try to correctly calculate the cross-sectional area of your ship, and thus streamlined shapes (like most of our rockets) now fly with considerably less drag.

[Hannu]

[quote name='FancyMouse']Don't forget engine is rebalanced (read: nerfed) at the same time.[/QUOTE]

Not significantly. Now it is easy, practical and economic to achieve an orbit (or very near) with one liquid stage and couple of SRBs. Before the new atmosphere 2 stage rocket (with SRBs at start) was the most practical. It is sad, because I like staging. I do not want souposphere back, but maybe I should try some mod which make planets larger.

[Alshain]

[quote name='Hannu']Not significantly. Now it is easy, practical and economic to achieve an orbit (or very near) with one liquid stage and couple of SRBs. Before the new atmosphere 2 stage rocket (with SRBs at start) was the most practical. It is sad, because I like staging. I do not want souposphere back, but maybe I should try some mod which make planets larger.[/QUOTE]

2 Liquid, stacked and a couple of SRB's actually reduces overall cost. You have to take advantage of the fact your upper stage engine, (be it the Terrier, Poodle, Skipper, Rhino, or something else), typically gets far more efficient high atmosphere thrust than your lower stage engine. This means more delta V and less fuel tanks, and since the upper stage engines are a lot cheaper (relatively speaking), it usually means reduced cost over a single stage LFO with SRB's (assuming you dispose of everything). Just make sure the first stage + SRBs gets you to 30-40km. Edited November 20, 2015 by Alshain

[Luis]

Not meant as snark, but delta V is expressed as a velocity in metres per second (m/s), not metres per second squared (m/s^2). The latter would be an acceleration and implies that you jump from zero to orbital velocity in a single second! :wink:

[KerikBalm]

I was going to comment on that, and also make another correction.
"aScent" is what we are talking about, ie basically going up
"aCcent" is a variation in the way you talk.

dV is reduced because the atmosphere is less draggy, only atmospheric portions of the game were made easier.
Meanwhile the across the board ISP nerfs (the LV-N' vacuum Isp was spared, but its TWR and atmospheric Isp suffered badly, the Ion engine's vacuum Isp was spare, but its vacuum Isp suffered badly) mean that its harder to get the dV you need for everything else.

Engines that use to get 390 Isp are now getting between 340-350 Isp

Engines that used to get 370 Isp are now getting between 300-320 Isp

Make a pancake shaped rocket, and you'll need a similar amount of dV as before.

[Rune]

[quote name='Temstar']Having come back to KSP after being away for a long time I realised immediately it's a lot easier to reach LKO now than it use to be. Back when I was playing around 0.20 it took around 4500m/s^2 of delta-V to reach 75kmx75km LKO. Now I'm seeing boosters with 3500m/s^2 and lower reaching that orbit.

Standard gravity looks to be the same to me at 9.82m/s^2, what happened? Is the new delta-V to LKO all because of the new aerodynamic model?

It's a pretty big change, since we know that reaching orbit means you're halfway to anywhere slicing 1000m/s^2 off that requirement means everything else about the game is now a lot easier.[/QUOTE]

Hey Temstar, welcome back! We have grown mighty in your absence. :)

And yeah, all kinds of aerodynamic goodness, like SSTOs with less than 1 TWR that actually use their wings for something, sane ascent paths (5-10º AoA works best to climb now), rockets that flip over because they drain the fuel in incorrect fashion, becoming bottom-heavy, and ascent paths that actually look like a true gravity turn. Oh, and aerobraking is now scary on account of heating... All in all, the atmosphere now works like it's supposed to... and intake spamming is dead!


Rune. Temstar is the guy that taught [I]me[/I] how to build bases. :) Edited November 20, 2015 by Rune

[Dafni]

[quote name='Luis']Not meant as snark, but delta V is expressed as a velocity in metres per second (m/s), not metres per second squared (m/s^2). The latter would be an acceleration and implies that you jump from zero to orbital velocity in a single second! :wink:[/QUOTE]

Thank you. I didn't want to be the guy pointing out details like that, but it sure irked me.

[Frozen_Heart]

Though it takes 1k less dV to reach orbit, i'm finding the same rockets are no more effective than before due to the engine nerf. I've had to remove fuel from a lot of my rockets as well due to the lower ALS thrust.

[Pthigrivi]

[quote name='FancyMouse']Interplanetary aerocapture is definitely possible. However, it doesn't just involve design of the tug. It's about design of the whole ship. Back in 1.0.4 I really had fun designing ship for zero-burn aerocapture on Eve. Haven't got a chance in 1.0.5 but I'm looking forward to it.[/QUOTE]

It's definitely possible, just make sure you can stay behind that heat shield.

[BenCushwa]

[quote name='Meithan']Yep, as others have said, the new Δv-to-orbit values are due to the new aerodynamic model. The tl;dr version of it is that KSP now attempts to correctly estimate how streamlined a body is.

You see, the aerodynamic drag force experienced by most flying objects is [URL="https://en.wikipedia.org/wiki/Drag_(physics)#Drag_at_high_velocity"]proportional to its "cross-sectional area"[/URL] (the "frontal area" it presents to the airflow). Before 1.0, this area was not properly calculated (it depends on the geometry and orientation of the craft), but simply computed directly from the [I]mass[/I] of the ship: KSP assumed that the cross-sectional area was 8 m^2 per tonne of mass, regardless of shape and orientation.

I guess that the rationale behind that choice was that, very roughly, in general heavier ships are "bigger" and thus have a larger cross-sectional area. But this assumption fails to acknowledge the fact that we can build things to be streamlined: simply make rockets tall and slim and you can make them quite heavy without increasing the cross-sectional area.

Before, your small 20 tonnes rocket (at launch) had an effective cross-sectional area of 160 m^2: that's as if it had a frontal diameter of 14.3 meters! Anything heavier than a few tonnes was essentially considered a pancake flying face-on for drag purposes. Hence the soup-o-sphere.

Now KSP does an honest try to correctly calculate the cross-sectional area of your ship, and thus streamlined shapes (like most of our rockets) now fly with considerably less drag.[/QUOTE]

The downside of this is that there is now less drag available to slow you down during e-entry and aerobreaking. Plan accordingly, and pack your heat shields.

[KerikBalm]

[quote name='Frozen_Heart']I've had to remove fuel from a lot of my rockets as well due to the lower ALS thrust.[/QUOTE]
Yes, that is also worth pointing out,
Atmospheric TWR has been nerfed.
After getting to orbit, everything else is harder now due to the lower Isps (or lower TWR of the LV-N, which is now LF only).
Getting to orbit is different now... many people after 1.0 were complaining that they couldn't even reach orbit because of rockets flipping (use fins and don't try a rapid 45 degree turn in significant atmosphere... straight up to 10 km and then turn 45 degrees will flip your rocket). SSTOs were overheating and exploding durring ascent... if they made orbit, they wouldn't survive re-entry or landing.

While the calculated dV can be much lower now, you'll need a greater mass of engines for your first stage (although some engines like the vector and mammoth have great TWRs even at 1 atmosphere), and you'll need a higher fuel fraction to get the same dV because of lower Isp.

SSTOs in particular were nerfed, and made not so ridiculously insane.
No jet engine operates higher than 30km (on kerbin), whereas before a ramjet engine could get 40,000 Isp, they were nerfed down to 8,000 Isp, and their thrust was reduced. Then in 1.04, their thrust was halved, and their Isp was halved down to 4,000 Isp. The rapier (which can propel you faster, and higher), now has only 3200 Isp.
Additionally, whereas before they could accelerate a craft to nearly 2,400 m/s surface velocity, the best one (the rapier) can only get you to about 1,600 m/s... but at the altitudes it can do that... you're unlikely to survive very long due to the heating.
You now need roughly 1,000 m/s of dv from rockets for SSTOs now, before you needed about 10...

[herbal space program]

[FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT][FONT="Arial"][COLOR=#000000]The thing about the old aero that made it easier is that you could fly a dinner plate into orbit face-up if you strapped enough boosters to it. Now you actually have to think about how the thing will fly. My new Moho rocket has a great big bulging fairing at the top covering the upside down lander, and I still haven’t figured out how to make it not want to flip over when it hits the sound barrier.[/COLOR][/FONT]

[FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT]

[StormKat]

Welcome back Temstar. We missed you.

[Fenris]

[quote name='BenCushwa']The downside of this is that there is now less drag available to slow you down during e-entry and aerobreaking. Plan accordingly, and pack your heat shields.[/QUOTE]
I love it, I actually use drogue chutes now which I never needed before.