When will launch pad accept larger craft?

[strider3]

I am currently under size / mass restrictions at the launch facility (30 parts, mass 18t, height 20m, etc). I have been unable to get into orbit under these restrictions? I just can't seem to carry enough fuel to "close" the orbit after reaching apoapsis of 75,000 to 100,000 meters? So, actually a 2 part question...anybody gotten into a closed orbit under these size restrictions? If so can ya help a guy out with the craft you used? Also would still like to know when launch pad limits get raised?

 

Thank you.

Vic...the Newbal

[OhioBob]

You should be able to easily get into orbit under those restrictions.  Below is a good tutorial on how to design a rocket.

http://forum.kerbalspaceprogram.com/index.php?/topic/128838-how-to-build-a-rocket-ship-for-a-mission/

If you can you post an image of your rocket design, we might be able to tell what you're doing wrong.

Increasing the part/mass/size restriction requires upgrades to the Launch Pad and Vehicle Assembly Building.  Just right click on the building and select upgrade, however funds are required to do this.  If you can't get to orbit, then you're not likely to be able to complete the contracts needed to raise the funds.

The Level 2 upgrade to the Launch pad costs 75,000 funds and allows 36-m high and 140-ton vessels.

The Level 2 to upgrade to the Vehicle Assembly Building costs 225,000 funds and allows 255-part vessels.

 

Edited March 19, 2016 by OhioBob

[OhioBob]

Below is a rocket that can easily get to orbit using early career game technology.  Only 13 parts and 9.8 tons.

Edited March 28, 2016 by OhioBob

[Plusck]

Although OhioBob is absolutely correct, I distinctly remember finding it hard at the time too...

Basically, after working your way out of the atmosphere into suborbital hops, you'll find that less is more. As soon as you unlock the Terrier, orbiting becomes vastly simpler. Terrier+ FL-T400 can get you very very far - you just need a first stage to get that Terrier up to a minimum of about 1000 m/s. Or Terrier + FL-T200 + FL-T400 and enough first stage to get it up above about 10-12 km, if you don't mind the lower thrust in the later stage.

[strider3]

Here is just a recent attempt:

Parts, in order, top to bottom:

MK16 parachute

MK-1 command pod

FL-T100 fuel

LV-909 "Terrier" LF engine

FL-T100 fuel

T-400 fuel

T-400 fuel

T-400 fuel

LV-T30 "Reliant" lf engine

RT-5 solid engine

RT-5 solid engine

RT-10 solid engine

I am using the RT-10 and 5's in the initial lift stages to reduce speed while in atmosphere?

My basic flight: Fire until apoapsis is 75,000+, then "drift" until apoapsis is reached. Turn pro-grade and fire "max" liquid fuel engines in an attempt to complete a "closed" orbit...I never get there.

Any and all suggestions are greatly appreciated

Vic...the "Newbal".

[strider3]

OhioBob...can you tell me what engines you are using here?

I really feel like I'm overkilling the entire thing??

 

[strider3]

I feel like my entire procedure may be wrong, after reading yours and others comments? I have read the "How to get into orbit" post at the wiki...but It hasn't helped me?

I will, of course, keep trying.

Vic...the Newbal

[Reactordrone]

Those solid boosters aren't doing much for you since your TWR on the pad is so low. You'd be better off ditching all of the solid boosters and increasing the size of the fuel tank on the final stage to an FL-T400. That should easily get you into orbit with enough fuel left over to do a Mun flyby (not an orbit).

 

[Snark]

One thing to bear in mind about SRBs is that they have a crappy Isp, meaning that in general you really don't want them anywhere except the first stage off the launchpad.  So if you use SRBs, use them all at once off the launchpad, not one after the other as you've got here. (Also, suggest not using the Flea at all, once you have the Hammer and Thumper available.  It just doesn't have enough oomph, and its Isp is even worse than the other SRBs.)

I would say that your Reliant is over-fueled and your Terrier is under-fueled.  Give the Terrier a 2-ton tank instead of a 0.5-ton tank.  Replace the Reliant with a Swivel, and reduce its fuel supply to 4 tons.  Use a single Hammer off the pad, with its thrust limiter tweaked to give you a launchpad TWR of 1.5.

(I've found that 2 tons of fuel seems to be the sweet spot for the Terrier.  An upper stage of Mk1 command pod, 2-ton tank, and Terrier has well over 2000 m/s of dV, in a small/cheap/light package.)

That ought to get you to orbit quite handily.

[OhioBob]

1 hour ago, Victor3 said:

OhioBob...can you tell me what engines you are using here?

I really feel like I'm overkilling the entire thing??

Yeah, I think you're over complicating things.  If you are just trying to get to Kerbin orbit, there is no reason why you would ever need more than two stages.

In the image that I posted, the bottom engine is a LV-T45 "Swivel" and the upper engine is a LV-909 "Terrier".  Those engines have plenty of thrust to spare.  You can easily add another FL-T400 fuel tank to the first stage*, which would give you another 500 m/s to play around with.  (You can even add a FL-T100 to the second stage for another 200 m/s.)  You don't need that extra fuel just to reach orbit, but once there you'll have plenty of fuel to fly around and perform orbital maneuvers.

Once you've made it to orbit and have a design that you know works, you can then start playing around with different variations.  You'll figure out what works and what doesn't, and in the process you'll make better and better rockets.

(* By "first stage" I mean the bottom stage, i.e. the first to burn.  I am not referring to the staging sequence numbers as seen in the VAB.)

 

Edited March 20, 2016 by OhioBob

[Plusck]

3 hours ago, Victor3 said:

Here is just a recent attempt:

Parts, in order, top to bottom:

MK16 parachute

MK-1 command pod

FL-T100 fuel

LV-909 "Terrier" LF engine

FL-T100 fuel

T-400 fuel

T-400 fuel

T-400 fuel

LV-T30 "Reliant" lf engine

RT-5 solid engine

RT-5 solid engine

RT-10 solid engine

I am using the RT-10 and 5's in the initial lift stages to reduce speed while in atmosphere?

My basic flight: Fire until apoapsis is 75,000+, then "drift" until apoapsis is reached. Turn pro-grade and fire "max" liquid fuel engines in an attempt to complete a "closed" orbit...I never get there.

Any and all suggestions are greatly appreciated

Vic...the "Newbal".

Yes, you're overcomplicating things.

The final stage is excessively puny. The terrier is the engine that is capable of giving you the most velocity in the high atmosphere, but you're limiting it with a puny fuel tank. Quadruple the fuel it has (FL-T400 instead of 100) and you can get rid of most of the stage just underneath it.

Remember that an engine carried but unused is just dead weight. The terrier is terrible in the lower atmosphere, but it works just fine above about 10-12km. Don't carry it all the way to orbit just because its "atmospheric" stats are bad !

You don't seem to have radial decouplers, but that doesn't stop you surface-attaching things. Rather than two SRB stages, you can surface-mount a few together (i.e. one under a stack decoupler, and two radially attached on the sides). Not really necessary, but if you really want a boost it's the easy way to go.

But in fact, the reliant should be enough on its own. Don't overload the craft and it'll do fine. Give the reliant two T-400s or two 400s and one 200, and no more, and it'll get your Terrier more than high enough to shine !

A Reliant plus 2.5 T-400s then a Terrier with a T-400 are more than enough to get to orbit. Just be sure to start your gravity turn a few degrees off the launchpad, stick to prograde and you should reach orbit (and more) without any boosters being needed.

[OhioBob]

@Victor3 I just noticed also that you have a heat shield on your command pod.  If you are just going to low Kerbin orbit, then the reentry heat won't be great enough to require a heat shield.  Delete the heat shield and you won't need as much rocket to get your pod to orbit.

Heat shields are only needed for high speed reentries from either a high orbit or from interplanetary space.  And even in that case it may not be necessary to carry the full amount of ablator.  If you right-click on the heat shield there is a slider that allows you to decrease the ablator mass.  A 1.25m heat shield has a maximum ablator mass of 200 kg.  For a return from Mun or Minmus, you can safely dial that back to 60 kg, maybe less.  For a return from high orbit, the rule of thumb I use is that I set the ablator mass to 5% of the reentry vehicle mass.  For interplanetary transfers, the entry velocities can be much greater.  In that case you may need 100% ablator. 

[strider3]

Thanks for all the suggestions! Using the "Less is More" philosophy I was able to "close" the orbit...but then exploded!!! LOL. I think I "fat-fingered" the keyboard at that stage but will try again with same craft and get back to you.

Vic...the newball

[strider3]

Success!! Thank you all for getting me past this step! The craft was as follows:

MK16 parachute

MK-1 command pod

(no heat shield, as suggested)

FL-T400 fuel

FL-T400 fuel

FL-T100 fuel (as suggested)

LV-909 "Terrier"

FL-T200 fuel (as suggested)

FL-T400 fuel

FL-T400 fuel

LV-T30 "Reliant" (I tried the T-45 "Swivel" but seemed to come up a bit short? Probably me doing something wrong in flight).

I had just enough fuel to burn my way into re-entry.

 

Beautiful, gang...just awesome. Thank you!!!!!!!!

Vic...the Newbal

[OhioBob]

Congratulations!  That's a nice milestone to get out on the way.  Now that you've done it once, you can do it again, practice, and get better.  Having a design that is known to work is a good starting place.  You can now tweak it to see if you can make it better.  Once you have something that you're really happy with, you can use it as a template for future rockets.  At some point you should try experimenting with side-mounted boosters.

(edit)

Did you really have two FL-T400 + one FL-T100 fuel tanks on the second stage?  If so, that might be a bit too much.  That would give your upper stage a thrust-to-weight ratio at ignition of only 0.93.  You can make that work with the right trajectory, but it's lower than I typically like for my second stage.  Why don't you try one FL-T400 + one FL-T200 on the second stage (TWR=1.26)?  I think the higher stage 2 acceleration will allow you to fly a trajectory that is a bit more forgiving.  Additionally, the higher TWR will allow for a modestly heavier payload.  With the lighter second stage you can probably also try switching back to the Swivel engine.

I think the following would work really well.  Plenty of Δv and good TWR.

MK16 parachute
MK-1 command pod
Decoupler
FL-T200 fuel
FL-T400 fuel
LV-909 "Terrier"
Decoupler
FL-T200 fuel
FL-T400 fuel
FL-T400 fuel
LV-T45 "Swivel"

There is enough rocket there that you could add a heat shield (60 kg ablator) and perform a Mun flyby.  Of course that's assuming you fly an efficient enough ascent that you're not wasting Δv.  That's the next thing you should practice, getting to orbit efficiently.  Flying the above rocket on a really good trajectory should allow you to get your command pod (no heat shield) to low Kerbin orbit with about 1500 m/s Δv remaining.  If you are way worse than that, then you have some work to do on your piloting skills.  (I just did a test launch and got into a 78 km orbit with 1507 m/s Δv to spare.)

 

Edited March 21, 2016 by OhioBob

[mrclucks]

On 3/19/2016 at 7:49 AM, Victor3 said:

My basic flight: Fire until apoapsis is 75,000+, then "drift" until apoapsis is reached. Turn pro-grade and fire "max" liquid fuel engines in an attempt to complete a "closed" orbit...I never get there.

Any and all suggestions are greatly appreciated

Vic...the "Newbal".

This seems like you are actually going straight up instead of performing a gravity turn.  

If this is the case then you need to nudge your craft over a bit shortly after taking off(anywhere between 100m/s and right after launch depending on how much you nudge it) and then follow the prograde vector.  This provides alot of the sideways momentum you need to establish an orbit and would reduce your circulation burn to a few hundred dv at most(30 m/s is my best).

Look up gravity turns on YouTube and the forums and try out different methods a few times untill you get the feel for it and establish a method that is fairly reliable

[Streetwind]

@Victor3 - if you want to practice piloting a little, try the following craft:

Parachute
Capsule
Decoupler
FL-T400
FL-T400
FL-T400
FL-T400
Swivel

This is an 8-part, 11.5 ton, single stage to orbit rocket. If you have the FL-T800, it even takes only 6 parts (half as many fuel tanks). Flown well, this rocket has enough fuel to establish a stable orbit, and then deorbit itself again before decoupling the capsule for reentry. However, for a beginner, the margins may feel a bit tight, and the large engine a little unruly towards the end... which is a good thing. Because if you can get this thing into some sort of a stable orbit and back, you can pat yourself on the back and say with confidence that you understand how to fly rockets reasonably well.

(For the curious, it has about 3.7 km/s vacuum dV.)

Edited March 21, 2016 by Streetwind

[Plusck]

19 hours ago, OhioBob said:

I think the following would work really well.  Plenty of Δv and good TWR.

MK16 parachute
MK-1 command pod
Decoupler
FL-T200 fuel
FL-T400 fuel
LV-909 "Terrier"
Decoupler
FL-T200 fuel
FL-T400 fuel
FL-T400 fuel
LV-T45 "Swivel"

 

100% agree. I'm a bit puzzled by the "as suggested" in the upper stage part of Victor3's post because it seems that there has been a misunderstanding somewhere.

I personally tend to underuse the Swivel, and stick to the Reliant instead due to its higher thrust, lower weight, and better Isp at sea level. This isn't necessarily a good idea since the Swivel rapidly overtakes the Reliant's stats as it climbs the atmosphere. And the Swivel gives more control (but sometimes too much...). However, if you have controllable fins (and I'd recommend fins at the base of the rocket anyway, to err on the safe side) the Reliant does seem to make everything smoother.

Edited March 21, 2016 by Plusck

[OhioBob]

1 hour ago, Plusck said:

100% agree. I'm a bit puzzled by the "as suggested" in the upper stage part of Victor3's post because it seems that there has been a misunderstanding somewhere.

 

I fairness to Victor3, he got quite a few suggestions, so it's not entirely surprising that he might have gotten a bit confused.  I'm actually the one that suggested adding (to the sample rocket shown in the third post) a FL-T100 to the second stage, but that was after suggesting adding a third FL-T400 to the first stage.  I've since reconsidered that configuration and now prefer the configuration listed in my last post.  The more recent configuration provides almost as much Δv but with 0.5 t less propellant, and I think it also has better TWR numbers.
 

Quote

I personally tend to underuse the Swivel, and stick to the Reliant instead due to its higher thrust, lower weight, and better Isp at sea level. This isn't necessarily a good idea since the Swivel rapidly overtakes the Reliant's stats as it climbs the atmosphere. And the Swivel gives more control (but sometimes too much...). However, if you have controllable fins (and I'd recommend fins at the base of the rocket anyway, to err on the safe side) the Reliant does seem to make everything smoother.

I probably underuse the Reliant.  I've always preferred the Swivel because of the thrust vectoring, but there are likely applications where the Reliant might be a better choice.  I should probably really think about using it more often.

 

Edited March 21, 2016 by OhioBob

[Snark]

1 hour ago, Plusck said:

I personally tend to underuse the Swivel, and stick to the Reliant instead due to its higher thrust, lower weight, and better Isp at sea level. This isn't necessarily a good idea since the Swivel rapidly overtakes the Reliant's stats as it climbs the atmosphere. And the Swivel gives more control (but sometimes too much...).

 

50 minutes ago, OhioBob said:

I probably underuse the Reliant.  I've always preferred the Swivel because of the thrust vectoring, but there are likely applications where the Reliant might be a better choice.

I tend to go with the Swivel all the way, mainly because I prefer to design my rockets to take off on SRBs only, and my liquid-fueled engine doesn't kick in until the SRBs burn out.  The SRBs typically take me to at least 10 km altitude, at which point I'm 90% of the way to vacuum and will be getting essentially vacuum Isp from my engines.  Thus the Swivel works better for that.

If I were using liquid fuel right off the pad, I'd probably use the Reliant more.

[OhioBob]

30 minutes ago, Snark said:

I tend to go with the Swivel all the way, mainly because I prefer to design my rockets to take off on SRBs only, and my liquid-fueled engine doesn't kick in until the SRBs burn out. 

I see now why you prefer a liftoff TWR of 1.5.  When I'm using all solids to launch off the pad, I too prefer a TWR up around 1.5.  However, my tendency is to use a liquid-fuelled first stage (yes, I know it is more expensive but I just like it better).  In that case I like to load up on propellant to bring the TWR down to about 1.3-1.4.

[Snark]

1 hour ago, OhioBob said:

I see now why you prefer a liftoff TWR of 1.5.  When I'm using all solids to launch off the pad, I too prefer a TWR up around 1.5.  However, my tendency is to use a liquid-fuelled first stage (yes, I know it is more expensive but I just like it better).  In that case I like to load up on propellant to bring the TWR down to about 1.3-1.4.

Yah, I like taking off on SRBs-only, partly because of the burn-the-lowest-Isp-fuel-first thing, and also for the purely irrational reason that I just really like SRBs on a visceral level and get a thrill from roaring off the pad on a spectacular column of flame. 

I usually smooth out the ride a little by arranging my radial SRBs in two symmetry groups rather than one (e.g. two groups of 4 rather than 1 group of 8), with one group having a higher thrust limiter than the other.  Take off on all of them together, but the high-thrust ones burn out first and are jettisoned while the second group continues to burn a while longer.  (I call it "poor man's asparagus".)  Smooths out the ride, TWR doesn't slam so hard near the end of the SRB burn.  Gives the SRB portion of the flight some legs.

[pincushionman]

On March 19, 2016 at 5:49 PM, Victor3 said:

…My basic flight: Fire until apoapsis is 75,000+, then "drift" until apoapsis is reached. Turn pro-grade and fire "max" liquid fuel engines in an attempt to complete a "closed" orbit...I never get there…

Please describe your gravity turn! You should start turning slowly before you even get to 100 m/s - And with a small ship like you need, you should be getting to that speed almost right off the pad. 45 degrees by 10-15 km, follow prograde most of the rest of the way. You should be well downrange by the time your apo reaches 70 km.

I agree with @mrclucks - it sound like you're trying to haul your heavy ship straight up to apo and trying to get all your horizontal speed once you get there. By going diagonally you essentially get some of your horizontal speed for free.

[superstrijder15]

On 19-3-2016 at 6:03 AM, OhioBob said:

Heat shields are only needed for high speed reentries from either a high orbit or from interplanetary space.  And even in that case it may not be necessary to carry the full amount of ablator. 

Or you're like me and you never ever use a heat shield but instead go for really tedious aeorbraking with 5-30 passes before you reenter... maybe I should try a heat shield on the next thing I build.

[Deddly]

@Victor3, I tink you've recieved some good advice here already, but the most important advice you've been given is actually how to fly. I recreated your very first rocket, including the head shield, and I can confirm that your design is able to reach orbit with a decent fuel margin. 

Edited April 10, 2016 by Deddly