[1.2] Real Solar System v12.0 Dec 8

[jrandom]

Is it just me, or is the sky rendering a little too high at the horizon? Should it be bright-white like that?

[NathanKell]

You know what? I think you're right....

Given how .23 changed things, though, don't think I can change outerRadius...

[Starwaster]

Is it just me, or is the sky rendering a little too high at the horizon? Should it be bright-white like that?

You know what? I think you're right....

Given how .23 changed things, though, don't think I can change outerRadius...

I think it depends on the altitude. I've seen very very high altitude photos where there was a white haze/glare on the horizon but not so thick and I think we're getting it lower than we should be.

Also, what exactly changed Nathan? I've been wanting to look into this myself but I just haven't had the time to start, especially since I'm trying to work on something myself.

[skykooler]

Is it just me, or is the sky rendering a little too high at the horizon? Should it be bright-white like that?

http://i.imgur.com/nSASdWb.png

This is in part because of the limited dynamic range available in computer graphics. In real life, the horizon is a blue many times brighter than the zenith; but KSP runs out of bright blues and has to make it white to make it bright enough for the atmospheric model.

[dlrk]

I'm finding it very difficult to figure out a good ascent profile. I either wind up pitching over too significantly, too soon, or overshooting and getting an excessively high apoapsis and a periapsis in the atmosphere.

What is a recommend gravity turn profile?

[AbeS]

1- Start with a TWR of 1.2, don't throttle.

2- When you reach 60-100 m/s you pitch to 85deg.

3- When you reach around 160 m/s pitch to 80 deg.

4- Pitch gradually to 70 deg until you reach like 270 m/s.

5- After that you could turn off SAS and it will pitch gradually by itself if your vessel is kind of aerodynamic. If it doesn't, pitch gradually until 45 deg and around 1300 m/s.

6- By then you will be pretty high so you can go to 0 deg gradually with an angle of attack of like 10.

7- Circularize, I usually stay at 0 deg until I reach Ap and pitch up a bit if I start going down.

[jrandom]

I'm finding it very difficult to figure out a good ascent profile. I either wind up pitching over too significantly, too soon, or overshooting and getting an excessively high apoapsis and a periapsis in the atmosphere.

What is a recommend gravity turn profile?

I've been getting to orbit using the following profile:

(I have no idea how efficient this profile is, only that it works.)

1. Launch at a TWR of 1.2
   
2. Go straight up until rocket hits 100m/s
   
3. Reach 22.5-degrees tilt by 15km
   
4. Reach 45-degrees tilt by 30km
   
5. Reach 90 degrees tilt by 70km
   
6. Kill thrust when apopsis reaches 250km
   
7. Circularize when appropriate
   

You shouldn't need to alter your throttle setting during your first ascent stage. If you can build your rocket so that its TWR at sea-level is 1.2 at full-throttle, that's preferred.

Edited December 30, 2013 by jrandom

[Starwaster]

I've been getting to orbit using the following profile:

(I have no idea how efficient this profile is, only that it works.)

1. Launch at a TWR of 1.2
   
2. Go straight up until rocket hits 100m/s
   
3. Reach 22.5-degrees tilt by 15km
   
4. Reach 45-degrees tilt by 30km
   
5. Reach 90 degrees tilt by 70km
   
6. Kill thrust when apopsis reaches 250km
   
7. Circularize when appropriate
   

You shouldn't need to alter your throttle setting during your first ascent stage. If you can build your rocket so that its TWR at sea-level is 1.2 at full-throttle, that's preferred.

Unless your TWR is like 4 or something, then throttling back starts to look attractive....

(I can't help it! I overbuild my first stage )

[NathanKell]

Wow, y'all have high-TWR upper stages.

I generally fly my ascents on mechjeb (I know, I know). The key points to remember are:

*Set your turn start based on your liftoff TWR, such that your turn begins anywhere 80-100m/s (depending on later TWR). 1.2 liftoff TWR with a decently-large upper stage (so your lower stage burnout TWR isn't too high) and you should probably start your turn at 1.4km or so. 1.7 TWR and a fast increase, better start at like 200m.

*Set your turn end and turn shape based on (a) your upper stage's TWR (<1TWR upper stage, you better have a high turn end and maybe even a >0 turn end angle) and ( such that you will stay aimed at the surface-prograde marker throughout the ascent.

I use ~100km and turn shape 45 for the Titan II (1.2 liftoff TWR, large comparatively-high TWR upper stage) and something more like 180km and 70 for the Saturn IB (with its moderate-TWR J-2 upper stage). For something with a Centaur (oy) you'll need to set turn end VERY high, and expect to circularize after apogee.

That will minimize steering losses (burning off-prograde) and aerodynamic forces (that might flip your rocket).

One more thing to consider: Even if it would be more efficient to turn early and have a high-TWR rocket, you also need to consider heating. You don't want your payload to burn up during ascent. This may force you to accept a rounder trajectory that goes up further and turns more gently.

[AbeS]

I totally understand Starwaster! I sometimes start with throttle at 1/4th to start with a TWR of 1.2 and then I have to throttle down when I get the "crew reaching G limit" message

[jrandom]

I totally understand Starwaster! I sometimes start with throttle at 1/4th to start with a TWR of 1.2 and then I have to throttle down when I get the "crew reaching G limit" message

With RealEngines giving minimum thrust to engines, I've been having to keep an eye on MechJeb's 'Maximum TWR' display to ensure that I don't accidentally kill my crew by having the launch stage end with a TWR of 14 at the end of its burn at minimum thrust. There've been a few close calls.

[metaphor]

I try to have all stages start at around 1-1.5 g's and end at 3-4 g's. That way I can full throttle the whole way. My ascent profile starts at 90 degrees until 1 km, and goes down 5 degrees down after that, adding 1 km to the intervals each time. So 1 km - 90, 3 km - 85, 6 km - 80, 10 km - 75, 15 km - 70, etc. When I get close to space, I try to keep the apoapsis about 1 minute ahead to have enough time to circularize.

[AbeS]

You are right jrandom! that was before!

I ran a test with Real Engines and the NP Bearcat with just a mk1-2 pod and fuel tanks, max TWR was like 40 so I started switching the engine on and off... they died for science just when there was only 10L of Kerosene left

[Starwaster]

What I do for my high TWR stages is set an acceleration throttle limit of 11-21 m/s. (11.784 would approximate a TWR of 1.2 on Kerbin....)

And... I'm watching my calico splashing around in the water bowl.... she looks like she's fishing for something... or maybe just doing it to drink the water off her paw. Now she's looking up at me as though she knows I'm talking about her.... such a strange little creature. (she came from a shelter that considered her unadoptable because she was fearful or unfriendly or something and she was in danger of being put down.... )

[dlrk]

Thanks for the help. It turned out the problem I was having was that the version of Stretchy SRB I was using was slightly out of date, and hadn't corrected the stretchy tank masses. I updated it, and it's good now, thanks.

I do have another question though. How do I get a geostationary orbit?

[jrandom]

How do I get a geostationary orbit?

Look up the geostationary orbit distance/time on wikipedia (this is what I used). Use Kerbal Engineer's Flight engineer so you can see your orbital period. Fly up to roughly the right orbital height, circularize, and then use RCS to fine-tune the orbit to the correct period (something like 23:56:04.1 or thereabouts).

[AbeS]

(something like 23:56:04.1 or thereabouts)

That is a semi-major axis of approximately 42,164,172.723 m (Or Ap = Pe = 35,793,172.723 m)

[jrandom]

Sounds about right. I tossed out my little reference card after I got my six comsats into orbit.

[dlrk]

So, the real life values can be used?

[Captain_Party]

Nathan, I'm still having the solar panels bug... Or you're telling me 3 1x6 stock panels isn't enough to power a probe core, a dish and one omni-attenae?

[dlrk]

Are the sidereal values, size values, etc available for the resize?

[NathanKell]

everything's in the RealSolarSystem.cfg file.

Captain_Party: Depends if you've rescaled RT2's settings, and if you're using Realism Overhaul. Expect only about 300W (0.3EC/sec) from those three panels. That may well be less than you need.

[dlrk]

Thanks, and one more GSO question. With RemoteTech, how do I launch my first GSO satellite, since Hohhman transfer can't be performed due to the lost connection?

[NathanKell]

Sure it can. Launch into a GTO with an apogee of 35786km, and a perigee above the atmosphere of Earth. Then keep orbiting until your apogee is directly over KSC, and circularize then.

[ferram4]

It's difficult to do with very low TWR upper stages. My solution was to put a relay sat in a 550km orbit and time the launch; use that satellite to relay the signal over the horizon to KSC.

An alternative is to have a very high TWR for your upper stage. That would allow you to get the burn done before losing contact.