• 0
MoridinUK

Efficient ascent.

Question

I need help...

I've been following the advice here:
 

In a ship of this design:

Parachute, two mystery goo's, a temp sensor and pressure measure, a service bay with kerbal engineer inside, heatshield.  FL-t400 fuel then lv-909, decoulper, then 2x fl-t400 and an LV-t30 - dv 3.8k.  I try the method above and I simply go wrong!  I just don't make it to orbit!  I assume my turn went too fast, as I got heated up too!

Any advice other than just practice?

Share this post


Link to post
Share on other sites

29 answers to this question

Recommended Posts

  • 0

i did not read the advice you mention and also i am not playing in Kerbol system anymore its to small compare to earth and delta V required to reach orbit is to small compare to real earth so i am playing Real solar system 

but to have efficient ascent you need three things 

1- make sure the rocket is very aerodynamic 

this is very important because the shape of your rocket can greatly increase drag of rocket and so the the delta V losses 

the shape of rocket most resemble something like missiles and real life orbital rockets otherwise the delta v losses will increase the more bad shape and not aerodynamic the more harder it will be to reach orbit and more delta v needed 

2 - make sure you add more delta v for the drag losses in atmosphere   

the amount of delta v losses Inside atmosphere depends on several factor like the gravity turn 

the amount of mass launching to orbit 

and the aerodynamic shape of rocket 

so always add extra delta v 

and i advice you to use Kebral engineer mod which gives data about the amount of delta v the exact mass of rocket and many more valuable data 

3- you most know how much delta v you carrying and when to start gravity turn 

you most know the amount of delta v your rocket carries and how much you need to reach orbit for kerbal if i have not forgotten it most be something around 2300 m/s with out drag losses so with drag losses i think it will be something around 2500 m/s or 2600 m/s if i remember correctly 

and for gravity turn always begin in low altitude below 200 m around 100 m and even 80 m slowly turn toward east and you most reach in 45 Degree around 10000 m if i remember correctly 

and remember when you are in max Q ( maximum aerodynamic ) or in lower part of atmosphere never turn your rocket hard the atmosphere pressure combined with drag will easily turn your rocket upside down this is personal experience so  be careful 

i hope this help you on your journey toward space 

and good luck up there 

Share this post


Link to post
Share on other sites
  • 0

The first important "landmark" when you are gravity turning is your altitude when you hit a 45 degree tilt angle. You will get various numbers, but I like it in the 8 to 10km range. If you are turning too fast, click your SAS mode to "stability" -- that will stop it from turning further until you think the time is right. Then click back to prograde mode when the time is right.

 

 

Share this post


Link to post
Share on other sites
  • 0

My kerbal's can't follow prograde yet!  They need to get into and out of orbit first! lol

 

Share this post


Link to post
Share on other sites
  • 0
10 minutes ago, MoridinUK said:

My kerbal's can't follow prograde yet

Usually, it doesn't matter in atmosphere. Aerodynamically stable craft can hold itself on prograde.

Share this post


Link to post
Share on other sites
  • 0

It sounds like it wasn't just your turn that went too fast, but the rocket itself. Try slowing down a bit. My launches got a lot better when I learned you don't need to floor it all the time. You don't wanna go too slow either, though. :)

Unfortunately, I think practice is the answer (for just about everything). I fly each rocket a bit differently; by "feel", I guess. You'll learn when it's time to turn and, just as important, when to speed up or slow down.

Share this post


Link to post
Share on other sites
  • 0
Posted (edited)

make the first stage bigger, maybe 3 or 4 FL-T400 tanks. you don't need that kind of acceleration.

Edited by Physics Student

Share this post


Link to post
Share on other sites
  • 0
5 hours ago, MoridinUK said:

I just don't make it to orbit!

In general, when you have a problem in KSP such as not being able to make it to orbit, the problem will, broadly speaking, be one or more of the following:

  • You're building it wrong.  (e.g. inefficient design, or just not enough dV, or what-have-you)
  • You're flying it wrong.  (e.g. gravity turn not executed well)

You could have one of these problems, or the other, or both; so to be able to narrow in on just where the problem lies, we'll need some more information.

5 hours ago, MoridinUK said:

In a ship of this design:

Parachute, two mystery goo's, a temp sensor and pressure measure, a service bay with kerbal engineer inside, heatshield.  FL-t400 fuel then lv-909, decoulper, then 2x fl-t400 and an LV-t30 - dv 3.8k.

Thanks for the description, though it would help to have a screenshot (sometimes a picture is worth a thousand words).  For example, how is this controlled?  I don't see any mention of either a command pod or a probe core.  (Or is the kerbal engineer a command component, like a probe core?  I don't know, since I never run KER myself).

For example, without seeing a picture of your ship, it's hard to tell whether it's aerodynamic or not, which in turn could affect how much of your dV you waste due to aerodynamic losses.

4 hours ago, bewing said:

The first important "landmark" when you are gravity turning is your altitude when you hit a 45 degree tilt angle. You will get various numbers, but I like it in the 8 to 10km range.

^ This.  This right here.  Try a launch, and note the situation when you hit 45 degrees.  Specifically,

  • what's your altitude?
  • how fast are you going?

The ideal shape of the curve will depend somewhat on your TWR, but in general you should be hitting 45 degrees somewhere in the 8-10 km range for most TWR ranges, and at that point you should be going 300 m/s (or significantly faster).

If your gravity turn is too aggressive, you end up hitting 45 degrees too low and too slow.  You end up flying sideways really fast through the thick soup of the lower atmosphere, and waste all your dV fighting drag rather than climbing to space.

If your gravity turn is too timid, you end up climbing too steeply and don't hit 45 degrees until you're really really high up, which means you're not making efficient use of your dV-- essentially you're blowing a big wad of it in climbing mostly vertically to a high altitude, then doing a right angle turn to accelerate sideways.  That can work, but it is making very inefficient use of your dV, and will require more dV to get to orbit than a well-executed turn would.

5 hours ago, MoridinUK said:

I assume my turn went too fast, as I got heated up too!

Not necessarily.  What you really care about is "how much dV am I losing to drag?"... and you should be aware that visual Mach and flame effects in KSP have almost no relation to how much drag you're actually experiencing, particularly in the upper atmosphere.  In particular, when you're in the 25-45 km zone, you can have spectacular flame effects, even when the actual drag force is negligible.  It's just eye candy, and harms nothing as long as you don't heat up so much that you actually explode.

That doesn't mean that drag isn't real, or that you don't have to worry about it-- just that you shouldn't rely on "how dazzling the flames are" as a guide to "how bad is the drag problem".

What really matters there is, 1. how aerodynamic is your ship (for which we'd need to see a screenshot), and 2. how fast you're going at what altitudes (for which we'd need more information about your trajectory).

 

So, @MoridinUK, it would help if you could provide the following information:

  • A screenshot of your ship.  Also, what's your total ship mass?
  • When your ascent hits 45 degrees, how fast are you going and what's your altitude?
  • When your ship finally runs out of fuel, what does your trajectory look like?  (A screenshot of your trajectory, in map view, would be most useful.)

 

Share this post


Link to post
Share on other sites
  • 0

A lot of good advice already, although perhaps a bit technical for someone trying to make orbit for the first time(...efficiently?)

While it's very cute to follow instructions that tell you how to make orbit with minimal use of SAS, I don't think it's a good habit in the long run since it's actually a pretty intense balancing act and a lot of it depends on several different factors: drag/shape, CoM, TWR, etc.

What I've found to be efficient enough is to keep SAS on, experiment with tipping the rocket east (very important, changes your dV requirements if you try to go for an orbit in the other direction) between the 500m and 1km mark and try to keep it tipping slowly so that you reach 45 degrees around the 10km altitude mark. (For maneuverable rockets, turn fine control on (caps lock) to avoid brutal changes.)

Keep tipping slowly (idea is to not leave or go very far out of prograde, keep your attitude inside the circle as much as possible, but along the "right edge") until you reach 30km. Then, the atmosphere should be thin enough for you to switch to map view safely(and make significant attitude adjustments depending on the situation). From there you can watch your apoapsis and time to apoapsis. As soon as your Ap gets above 70km, you can pretty much turn 90 degrees (towards the horizon). Also, if your time to apoapsis gets above a minute, you may want to throttle way down or stop your engine depending on your altitude and wait until you are closer to apoapsis (less than a minute, or even closer as TWR allows) to turn your throttle back up.

...and that's pretty much it with any rocket. With 3,8km/s dV and a reasonnable design, you should make orbit every time like this. The key is really pacing your turn from the pad to 45 degrees at 10km.

Share this post


Link to post
Share on other sites
  • 0
Posted (edited)
7 hours ago, MoridinUK said:

then 2x fl-t400 and an LV-t30 - dv 3.8k

Not enough dV - KER shows the VAC-Value!

Click "Atmospheric" in KER (VAB) and look at your dV:

orbiterwronglboeh7d5ar.jpg

[Edit: just noticed that i used a reliant instead of a swivel for the above pic - dV is less with a swivel]

When the first stage is ditched you are still in atmo. (12-15km i guess?) and the Terrier is very weak below 25km. More dV loss. Your first stage need to burn longer.

Also set KER to Partless, then you dont need the KER Part. (And if for some reason of a new KSP version your KER doesnt work anymore you are still able to load your save games in stock - if you never use the KER-part)

Remove it and the service bay. If you just want to go orbital and return remove the heatshield also. MK1 Pod is fine for reentry from LKO. Also remove the monoprop from the capsule - 40kg dead and unusable weight :wink:

Add at least one FL T 400 (2 are better) to the first stage and 2 radial booster. Set the thrust of the booster so that your TWR in atmo is 1.5

(Ignite booster and mainengine together)

Maybe add 4 fins to the bottom.

Try:

orbiterwrong290b3fkapyr.jpg

Note that the KER is wrong for the last stage, you are near VAC when 1st stage is ditched. So for a real value switch "Atmospheric" off (and note that now KER is wrong with the first stage :wink: then)

The vessel in the 2nd pic has ~4800dV, enough to reach orbit even if you are really bad doing ascends.

Allways reach at least 20km, better 25km before using the Terrier.

 

Edited by Draalo

Share this post


Link to post
Share on other sites
  • 0

I have a very simple but very effective trick (learned practicing ascents with Gravity Turn Continued). Always keep an eye to the Time-to-Apoapsis (TtA) indicator (uncomfortably with the Apoapsis marker in map mode in stock KSP; much handier having KER or other similar add-ons windows open).

Apply full throttle at launch and make the vessel pitch down (generally to 85° is enough, vessels with very high TWR may pitch down more) eastwards as soon as you leave the ramp. Engage the SAS to hold prograde mode (and never leave it until in orbit). Only apply lateral correction as needed to obtain the required launch inclination, but otherwise don't try to steer the vessel, ever.

What you have to do is to modulate throttle so to keep TtA = 50 seconds during all ascent from KSC (aiming for LKO). At first you'll go full throttle and TtA will steadily climb; once at 50 start closing throttle and aim to keep that value. Of course keeping prograde at all times, the vessel will follow a gravity turn. Only when close to the orbital speed (> 2000 m/s) reduce throttle further so to progressively reduce TtA to 0 (should more thrust be applied at this point, Apoapsis altitude will increase and TtA shift farther away).

Share this post


Link to post
Share on other sites
  • 0
11 minutes ago, Draalo said:

Not enough dV - KER shows the VAC-Value!

Click "Atmospheric" in KER (VAB) and look at your dV:

 

3800 vac deltav is fine to reach LKO with an efficiently built rocket, with the right engines on the lower stage.

the swivel and reliant are the right engines at early game.

Share this post


Link to post
Share on other sites
  • 0
21 minutes ago, Draalo said:

Allways reach at least 20km, better 25km before using the Terrier.

Great post, but I disagree with this one statement.

Yes, Terrier is horrible at sea level.  But you don't need to go anywhere near 20 km to get good use out of it.  Terrier works great even at 10 km.

Reason:  what it cares about is "what percentage of an atmosphere do I have?"  At 10 km, atmospheric pressure is only around 10% of ASL, IIRC.  That means you're 90% of the way to a vacuum, and the Terrier gets very close to its vacuum Isp.

So, absolutely don't use a Terrier on the launch pad, but once you get over 10 km it's fine.  Even a little lower would probably be okay.

That said, this discussion's a bit of a red herring where the OP is concerned.  With a ship as described, I expect he'll be way higher than 10 km before the Terrier kicks in.  And if he's not, then the real problem will involve that, rather than how the Terrier does after he starts it.

@MoridinUK, what's your altitude when the Terrier starts?

Share this post


Link to post
Share on other sites
  • 0
Posted (edited)
31 minutes ago, Lelitu said:

3800 vac deltav is fine to reach LKO with an efficiently built rocket, with the right engines on the lower stage.

Yes, but the point is that he dont have 3800dV :wink:

The vessel in the 1st pic showed me ~3660dV in VAC, with atmo losses he may end at real ~3200dV

(Monoprop was removed in the pic)

@MoridinUK pls post a pic of your vessel in the VAB

Edited by Draalo

Share this post


Link to post
Share on other sites
  • 0
Posted (edited)
8 minutes ago, Draalo said:

Yes, but the point is that he dont have 3800dV :wink:

The vessel in the 1st pic showed me ~3660dV in VAC, with atmo losses he may end at real ~3200dV

(Monoprop was removed in the pic)

 

That is *not* what you said. You said that vacuum detalv isn't the right display. Technically, that's true, in that it won't show the actual deltav available. However, all the deltav maps available list vacuum deltav to orbit. Because the maps list vacuum deltav, it's easier to just use vacuum display and check against this value. This is done because vacuum deltav is easy to calculate and work with (vacuum isp doesn't change over time). Atmospheric deltav is a lot harder to work with mathematically, since you have to account for ascent profile due to ISP varying with atmospheric pressure. 

Also, no craft file or picture was provided by the OP, so we can't be completely sure of the available deltav.

Further, 3400 vacuum is about the limit i've been able to achieve with a well streamlined rocket, and good ascent profile. I'm nowhere near the best pilot ever either. 3800 is enough to get away with some inefficiency to orbit.

Edited by Lelitu

Share this post


Link to post
Share on other sites
  • 0

Right, and wow, thanks all for the responses... I love the kerbal community!

 

Firstly, I have been to orbit, I have been all over mun and minmus, but in 0.9... this is my first time trying to get serious since the atmosphere lost its soup!  So bare with me.

I'm so sorry I forgot the command pod in the description of the vehicle. (I shall have to think about where to host images as imgur doesn't want to hook in nicely!

http://imgur.com/a/SqCYp

Vac DV 3.8k ish,  Atmos 1.8k !!! So how have I actually managed to get this into orbit?  Have I been missing something big?  I have made it to a circularised 80k orbit with just under 300dv left in the tank...

My problem with the gravity turn (sas off) is that my rocket wonders off the east line slightly, especially after separating (I'm hitting about 20k I think before switching to the terrier...  which at that point only puts out 1.5 twr but that is good enough...  Also I notice the rocket starts to straighten up some times so returning, on its own, from about 15 degrees back to straight up!  The staging is really troublesome and sas HAS to go on for then or it just tumbles.

Time to AP methods... I try to sort this, but I don't want to hang about in the air.  I find I have to dip the nose below the horizon slightly to prevent it climbing higher as I keep pushing to get the PE to pop out of the surface.  Last attempe (my best) I had an AP of 82 and PE 56 before reaching the atmosphere!

My best run used an odd method, keep twr between 2 and 2.5, hit the turn turn to 5-10% early. leave Sas off and throttle back to not gain too much twr. I did have to use sas to keep the prograde from wondering as the rocket tilts northward for some reason... :(  

However, having noticed the engineer thinks I only have 1,8k dv at ground level, I think I'm actually doing better than I thought!


 

Share this post


Link to post
Share on other sites
  • 0
Posted (edited)

 

1 hour ago, MoridinUK said:

Right, and wow, thanks all for the responses... I love the kerbal community!

 

Firstly, I have been to orbit, I have been all over mun and minmus, but in 0.9... this is my first time trying to get serious since the atmosphere lost its soup!  So bare with me.

I'm so sorry I forgot the command pod in the description of the vehicle. (I shall have to think about where to host images as imgur doesn't want to hook in nicely!

http://imgur.com/a/SqCYp

Vac DV 3.8k ish,  Atmos 1.8k !!! So how have I actually managed to get this into orbit?  Have I been missing something big?  I have made it to a circularised 80k orbit with just under 300dv left in the tank...

My problem with the gravity turn (sas off) is that my rocket wonders off the east line slightly, especially after separating (I'm hitting about 20k I think before switching to the terrier...  which at that point only puts out 1.5 twr but that is good enough...  Also I notice the rocket starts to straighten up some times so returning, on its own, from about 15 degrees back to straight up!  The staging is really troublesome and sas HAS to go on for then or it just tumbles.

Time to AP methods... I try to sort this, but I don't want to hang about in the air.  I find I have to dip the nose below the horizon slightly to prevent it climbing higher as I keep pushing to get the PE to pop out of the surface.  Last attempe (my best) I had an AP of 82 and PE 56 before reaching the atmosphere!

My best run used an odd method, keep twr between 2 and 2.5, hit the turn turn to 5-10% early. leave Sas off and throttle back to not gain too much twr. I did have to use sas to keep the prograde from wondering as the rocket tilts northward for some reason... :(  

However, having noticed the engineer thinks I only have 1,8k dv at ground level, I think I'm actually doing better than I thought!


 

Biggest thing that rocket needs is some fins. 3 of the smallest fins placed right at the bottom of the lowest tank will sort out most of the prograde wander. Moving some of that fuel from the second to the first stage will help as well. The terrier is very efficient, but low thrust, so pushing a FL-T200 tank, instead of the FL-T400 will work better, put an FL-T200 in the first stage, and you'll have the same fuel total, but will get significantly higher and faster before switching over to the terrier. 

If there's room, move the goo canisters into the service bay, along with anything else sciency on the pod. the drag isn't helping, but isn't the biggest problem. it's the fins.

If it drifts a degree or two off perfectly equatorial, don't bother fighting it, the losses are trivial.

Edited by Lelitu

Share this post


Link to post
Share on other sites
  • 0
3 hours ago, Lelitu said:

 

Biggest thing that rocket needs is some fins. 3 of the smallest fins placed right at the bottom of the lowest tank will sort out most of the prograde wander. Moving some of that fuel from the second to the first stage will help as well. The terrier is very efficient, but low thrust, so pushing a FL-T200 tank, instead of the FL-T400 will work better, put an FL-T200 in the first stage, and you'll have the same fuel total, but will get significantly higher and faster before switching over to the terrier. 

If there's room, move the goo canisters into the service bay, along with anything else sciency on the pod. the drag isn't helping, but isn't the biggest problem. it's the fins.

If it drifts a degree or two off perfectly equatorial, don't bother fighting it, the losses are trivial.

If anything else,  I would suggest to change the Swivel for a Reliant. This will make the initial tilt more difficult to do right,  but after the rocket get up to speed aeroforces will be enough to keep it in the right direction. 

Anyways,  that further steep can wait until the pilot build confidence in doing the initial tilt accurately.  For now the gimbal is useful for corrections in case of a less than perfect initial tilting. 

5 hours ago, MoridinUK said:

My best run used an odd method, keep twr between 2 and 2.5, hit the turn turn to 5-10% early. leave Sas off and throttle back to not gain too much twr. I did have to use sas to keep the prograde from wondering as the rocket tilts northward for some reason... :(  

There is little, if any, advantage to limit TWR to build up.  Gravity loss beat  drag loss for most launch vehicles nowadays.  If your trajectory is not too steep and the rocket is stable just get to orbital velocity ASAP. 

 

BTW, 1,8km/s atmospheric is considering the terrible Isp of the Terrier at sea level (and mediocre Swivel's sea level Isp).  It would just read "bananas"  for the relevance sea level Isp actually have. 

Share this post


Link to post
Share on other sites
  • 0

I got it into orbit with a bit over 300m/s left in the tanks so it's definitely do-able with that rocket. You may just need more practice with the new atmosphere model as it takes a little while to get used to it after 0.90. Steerable fins would help with controllability and don't be afraid to turn fairly sharply after launch when you have a high  TWR.

Share this post


Link to post
Share on other sites
  • 0

Thanks all!  Is that a Swivel I put on it? It was supposed to be the Reliant!  

I've got to orbit with 270ish left, so I'm not far off!  I'm not sure I've unlocked controllable fins just the winglet things... I'll give that a try and see if I can move the science into the bay, I just like being able to access experiments without having to open anything! 

I may try it at full thrust, but the reason to limit, I thought, was because going faster slows the gravity turn?

Share this post


Link to post
Share on other sites
  • 0

It does slow the turn indeed. But if you go from 0 to 45 degrees in the first 8 to 10 km, and you want to go from 45 to 80 degrees at 45km -- then you need to slow the turn a bit, anyway. So it works out all right. Let's say -- you want to get to 1600m/s ASAP. After that, you can reduce the throttle to keep your Ap from going too high.

 

Share this post


Link to post
Share on other sites
  • 0

With suggestions to move fuel fro. The terrier stage, wouldn't that mean carrying more mass for longer or is the extra twr worth it? I can't wait to try some of the suggestions! 

Share this post


Link to post
Share on other sites
  • 0
9 hours ago, MoridinUK said:

Thanks all!  Is that a Swivel I put on it? It was supposed to be the Reliant!  

The swivel has gimbal. That means the engine can steer. The reliant has better isp at sealevel but doesnt has gimbal.

The swivel is your coice for a steerable mainengine, reliant is your choice for Lf-boosters - use it as mainengine only if you have controll surfaces to steer.

Share this post


Link to post
Share on other sites
  • 0
9 hours ago, MoridinUK said:

Thanks all!  Is that a Swivel I put on it? It was supposed to be the Reliant!  


I may try it at full thrust, but the reason to limit, I thought, was because going faster slows the gravity turn?

Well,  personally I didn't check it,  just carry on with what others said before me.  So probably my mistake. 

If you rocket is aerodynamic stable the rate of turn will be limited by velocity. Since higher TWR get up to velocity quickly it means you need a more aggressive initial tilt.

But that is all,  just get the initial tilt right and a stable rocket will fly itself to orbit,  no control input (nor SAS)  necessary. Reducing the thrust later is just a way to give time to a rocket that initially wasn't tilted enough to orient itself. 

Share this post


Link to post
Share on other sites
  • 0
23 minutes ago, Draalo said:

The swivel has gimbal. That means the engine can steer. The reliant has better isp at sealevel but doesnt has gimbal.

The swivel is your coice for a steerable mainengine, reliant is your choice for Lf-boosters - use it as mainengine only if you have controll surfaces to steer.

Actually both are the rookie engines to use before you learn to launch with a pure SRB 1st stage pointed in the right direction. There is something very satisfying in pressing spacebar and watch the rocket flying itself to orbit. 

Share this post


Link to post
Share on other sites
  • 0
8 hours ago, MoridinUK said:

With suggestions to move fuel fro. The terrier stage, wouldn't that mean carrying more mass for longer or is the extra twr worth it? I can't wait to try some of the suggestions! 

Moving fuel from the terrier to the first stage means a greater fuel mass in the first stage, and smaller payload mass in first stage (stages 2+ are payload for stage 1). This gets you more deltav out of stage 1, but less out of stage 2.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now