How long your first stages last?

[The Aziz]

Out of curiosity. And I mean altitude rather than burning time.

Mine typically reach 15-20km high, and, as I'm trying to play with recovery, it's pretty hard to aim for land from there. As a result, so far 90% of my first stages ended up in water.

[Cpt Kerbalkrunch]

Unless you count boosters, my first stage usually gets me to 70-80km. I don't like to start my second stage engines until I hit vacuum.

This depends on launch profile, of course. Sometimes I come up short and have to burn the second stage for a few seconds to get out of the atmosphere.

Edited July 29, 2017 by Cpt Kerbalkrunch

[Curveball Anders]

2 hours ago, Cpt Kerbalkrunch said:

Unless you count boosters, my first stage usually gets me to 70-80km. I don't like to start my second stage engines until I hit vacuum.

This depends on launch profile, of course. Sometimes I come up short and have to burn the second stage for a few seconds to get out of the atmosphere.

Same for me.

SRBs burn out at around 20km, then main post breaking 70 and pre full orbit (automatic de-kesslerisation ).

[purpleivan]

Typically my first stages burn out at 10-20km, generally high enough for the atmospheric pressure sensitive engines to be working fairly efficiently.

But if I'm launching some massively asparagus staged beast then all bets are off... it could be as low as around 300m.

[Tyko]

3 hours ago, Cpt Kerbalkrunch said:

Unless you count boosters, my first stage usually gets me to 70-80km. I don't like to start my second stage engines until I hit vacuum.

This depends on launch profile, of course. Sometimes I come up short and have to burn the second stage for a few seconds to get out of the atmosphere.

Vacuum engines achieve near-100% vacuum efficiencies at fairly low altitude - the Terrier and the Poodle are at 97.9% efficiency (TWR & ISP) at 20Km 

Edited July 29, 2017 by Tyko

[Laie]

How long is a piece of string?

Depending on purpose and other factors, my fist stage may be kick-off boosters that provide tremendous acceleration for just a few seconds, or a slow burner that takes me most of the way to orbit, or anything in-between.

But for anthing "reasonable" or realistic-looking it often ends up being 10-15km or thereabouts.

@Cpt Kerbalkrunch: you're aware that vacuum doesn't need to be absolute, are you? In terms of air pressure and ISP effects, 10km is already most of the way to space; even poodles work well at that altitude, KR2L's even more so.

[fourfa]

I happened to be looking at this recently with a reusable winged lifter system powered by one Mainsail and one Rhino.  

The Rhino has better ISP than the Mainsail by 8500m.

[SchwinnTropius]

I try to aim for SSTO for my vertical launches, it's a nice challenge even for early career when only part count is a limiting factor. Usually I'll just barely make it, but if I fudge the launch and I don't quite make orbit I'll end up staging above the atmosphere.

[Cpt Kerbalkrunch]

1 hour ago, Laie said:

 

@Cpt Kerbalkrunch: you're aware that vacuum doesn't need to be absolute, are you? In terms of air pressure and ISP effects, 10km is already most of the way to space; even poodles work well at that altitude, KR2L's even more so.

Sure. I'm not simply aiming for vacuum affect on engine performance. Aerodynamics plays a role as well. The moment I leave atmosphere I can dump the launch vehicle and pop the nosecones from all my stacks to dump as much mass as I can. I also feel that, since you're using a more powerful engine to lift your rocket, I'd rather keep feeding it fuel to get me where I'm going before I dump it. Also, I assume we all build stages job-specific. My first stage's job is to get me out of the atmosphere; which is what it does.

And I'm sure you're aware that if you stage your launch vehicle at 20km, it's pretty tough to recover it without a mod. By leaving the atmosphere before staging, it makes it much easier to recover the launch vehicle intact. If you're so inclined.

2 hours ago, Tyko said:

Vacuum engines achieve near-100% vacuum efficiencies at fairly low altitude - the Terrier and the Poodle are at 97.9% efficiency (TWR & ISP) at 20Km 

 

[RoadRunnerAerospace]

about half way through the ascent

[Superfluous J]

Depends on the payload, really.

Generally for small payloads, I dump the launch stage right before circularization (so it burns up in atmo), so it's as close to an SSTO as you can get without actually doing the O part.

For larger payloads where I have to actually put thought into the launcher, I like the first stage to get me up maybe 20km or so where I'm really starting to flatten out, because I'm no longer fighting gravity and the air is thin enough to basically be in space, so you can switch to the more efficient, less beefy engines with no problems.

[MythicalHeFF]

There goes the perfect 400,000 posts on KSP Discussion...

[Gargamel]

As I frequently over engineer my rockets, my core first stage usually ends up with 300-700 dv left to use in the transfer burns to wherever I am going after wards.  If my target is LKO, I try to have my first stage drop right before the circularization burn, or right at the end of it, so I don't have a huge drop in thrust midway through the burn.  

I am an aspargus fanboy, a carryover from the old versions where it was common to make 12 stage boosters, but now at best I'll have two booster stages (4 rockets + a core), but that's only if I'm launching very heavy stuff.  Usually I'll have SRB's drop off anywhere from 5k to 25k, depending on the booster and the rocket. 

I use a mod (MJ) to limit my TWR, so it will throttle down the liquid fueled engines as the TWR of the SRB's increases.  This will usually allow me to get more core stage to LKO with no problem, and the boosters drop low enough so the recovery mods can grab them. 

[adsii1970]

Until it runs out of fuel.

 

[kerbinorbiter]

my boosters usualy last until they hit the ground or explode

[cratercracker]

Until i hit the spacebar..

[DeltaDizzy]

Until I hit Alt-H, which I do A LOT.

[kerbinorbiter]

Until KSP crashes

[NSEP]

Depends. Sometimes i have a first stage that boost me to 1km and the other day its mostly in orbit.

[Human Person]

Well bejond max Q, the rest is up to you.

[kerbinorbiter]

57 minutes ago, NSEP said:

Depends. Sometimes i have a first stage that boost me to 1km and the other day its mostly in orbit.

whats the point in having a stage to 1km?

[Regor]

Sometimes orbit with 200m/s to spare

[Frozen_Heart]

Previously they got me around 1.8km/s and 50km high. Now i'm using a reusable first stage more like 1km/s and 40km high.

[magnemoe]

14 hours ago, Cpt Kerbalkrunch said:

Sure. I'm not simply aiming for vacuum affect on engine performance. Aerodynamics plays a role as well. The moment I leave atmosphere I can dump the launch vehicle and pop the nosecones from all my stacks to dump as much mass as I can. I also feel that, since you're using a more powerful engine to lift your rocket, I'd rather keep feeding it fuel to get me where I'm going before I dump it. Also, I assume we all build stages job-specific. My first stage's job is to get me out of the atmosphere; which is what it does.

And I'm sure you're aware that if you stage your launch vehicle at 20km, it's pretty tough to recover it without a mod. By leaving the atmosphere before staging, it makes it much easier to recover the launch vehicle intact. If you're so inclined.

 

One issue with dropping first stage low is that the short upper stage might flip around the fairing. 
30-35 km is safe distance here. You can keep fairing after this, I typically drop it at 45. 

Very large and small payloads as in small satellites and huge spaceship or bases tend to use their build in engines to circulate. In this case you want a bit oversize first stage for satellite, more so as an T-45 engine will pretty much make it an SSTO anyway. 
The spaceship / base tend tend to have a bit low TWR so you want it up to 50 km before it take over. 
 

[Urses]

From time as i began to use USI i build mostly SSTO class first stages and disassemble them in the orbit for MaterialKits to inflate all modules in-situ.

And i have mostly halffull tanks in orbiters to completly reuse the remainings of ascenders.