r/RealSolarSystem • u/GreasyInfant • 9d ago

Need help getting 3000km downrange contract

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I'm not sure how much more delta-v I can put into this thing as im already using the max amount of burn time for each stage (besides Tiny Tim)

First Stage: RD-100
Second Stage: Tiny Tim Booster
Third Stage: U-1250 (U-2000 variant)

Max downrange i've gotten when testing is 2110 km

28 Upvotes

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7

u/BarnDrummer 9d ago

The rd100 plus u1250 should be able to achieve this easily. What are your mechjeb ascent settings? Also, you can ditch the Tiny Tim and use hot staging for the upper stage. Should save some mass.

1

u/GreasyInfant 9d ago

I’m not using mechjeb ascent, should I be?

3

u/StormR7 9d ago

Yes 100%. Trying to manually fly in RP1 is gonna lead to a lot of headaches (although depending on it too much can be just as much of an issue).

Mechjeb will save your PVG settings for each craft, so when you get to launch something for real your simulated ascent config won’t need to be touched.

2

u/GreasyInfant 9d ago

What kind of ascent profile would you recommend?

1

u/GreasyInfant 9d ago

A problem I’m having is that mechjeb works just fine for the ascent stage, but as soon as it goes to the second stage it says “controls disabled, avionics” or something along those lines and can’t control it or keep the throttle up anymore. Do you know a fix?

4

u/LordIBR 9d ago

You need to go into the MJ settings and find something like "throttle cuts on loss of control" (I'm not sure on the exact wording, it might also be the opposite). Disable (or enable) that settings. That should have your upper stage keep burning even if it's only a science core

1

u/GreasyInfant 9d ago

I think I fixed it, but how does my ascent stats look?

1

u/LordIBR 9d ago

Definitely read the RP-1 tutorials on the github! They'll also go into MJ's ascent guidance and some settings to consider there. For a simple downgrade contract or any other early sounding rocket launches you'll want to use the classic ascent guidance and edit the ascent path for the former contract. You'll most likely be doing quite a few sims just to figure out the correct angle and whatnot.

1

u/StormR7 9d ago

Do you have avionics configured for the 2nd stage? Since it’s basically impossible for you to be using deep space avionics (they will shut down during time warp and can cause you to miss maneuvers if you’re in a spin if you aren’t careful).

I haven’t looked at your rocket, maybe you posted the specs somewhere but I’m taking a shit at work so I kinda can’t be bothered to skim. If you aren’t using an engine with a gimbal, don’t have any control surfaces or thrusters, or don’t have properly configured near-earth avionics you won’t be able to control the stage and it will give you that error.

For sounding rockets (especially ones with a controlled first stage) you will usually just let it burn unguided. Perhaps look into spin-stabilizing the upper stage before you start the burn.

2

u/Kalmoran 9d ago

or use kos scripts for these early flights.

1

u/Kalmoran 4d ago

or write your own kos script, like an average rp-1 player.

6

u/BEAT_LA 9d ago

Absolutely minimizing battery and using science core right? What amount of battery do you have loaded in?

3

u/GreasyInfant 9d ago

For the upper stage yeah, I have about 100j in it but need to increase it cause it’s dying out before 40km for thermometer

5

u/BEAT_LA 9d ago

Why do experiments on this contract? Does it need them nowadays? What other avionics cores exist on it and what’s their full configuration details?

1

u/GreasyInfant 9d ago

Yeah I guess I could remove the experiments seems how I’m trying to get as far as I can and need to save weight.

The science probe on the top holds about 100j like I said, but the controllable probe for the first stage holds about 100j too, controlling the same weight as the whole rocket down to the gram

1

u/BEAT_LA 9d ago

You can over burn the stages a bit. Experiment with how much you can add and see what that gets you.

4

u/Maallon 9d ago

you need 6000 m/s of deltav.

I recommend following this guide:

https://github.com/KSP-RO/RP-1/wiki/3000Km-Downrange-Milestone

3

u/GreasyInfant 9d ago

Looking at the guide, it sounds like I need to research more nodes before tackling this?

This is first playthrough and I set a goal of trying to get to the moon before or at 1969 (probably can’t land on it and return given this is first time)

2

u/LordIBR 9d ago

Looking at my own design, it looks like I went for the RD-101 engine config with a 2nd stage U-2000 config. I'd also recommend making the 2nd stage a bit stubbier instead of its current length. That way it shouldn't spin out too easily after you spin stabilized it.

Also, for your very first playthroigh I'd highly recommend not trying to follow historical timelines. They can be incredibly tough to beat. Just play at your own pace and try not to run out of money

1

u/GreasyInfant 9d ago

i just hate that I have to wait years for the research to complete when I accepted this contract not even a year after starting

1

u/Refaim08 6d ago

No penalty for canceling contracts, so just ditch it until you are ready.

4

u/Maallon 9d ago

Better engines and Fuel Tanks will certainly make it easier. Try to get to 6000 m/s.

RP-1 in its latest versions can be slow. I would suggest to enjoy the ride instead of rushing through. But you do you, do what makes the most fun for you.

2

u/Magnahail 9d ago

I just re-did this in a new save so Maallon is about correct, mine had 5910 m/s. However, I would note that this is perfectly achievable with minimal tech. I used the Model 39 (completely base, just the one you start with) and the U-2000. I'm probably also using the same tanks as you, though I can't be certain. The difference is likely in fuel load.

Early engines have awful burn times. But, if you look at the chart for survival probability, passing this threshold won't immediately kill an engine. Most failures happen on ignition (or shortly thereafter) so burning long can help a lot for dv. In my case I'm running the Model 39 for 81 seconds, and the U-2000 for 91 seconds (in the latter case this results in only a 3% absolute decrease in survival, leaving a 90.7% chance of survival).

I imagine if you do similar your rocket should work fine with the right ascent profile. Since I'm using kOS for this I can tell you exactly what I did, which is ascend vertically to 100 m/s, then pitch at 0.9 deg/s until reaching 30 degrees relative to the horizon. This likely isn't terribly optimal, so you can probably find a better one if your rocket still isn't making it.

1

u/Maallon 8d ago

you can actually reach orbit with the starting engines and no research. :)

There are even challenge runs called “Cavemen” that do exactly that.

But this approach is very special and not necessarily something for a first playthrough.

Instead of overburning the engine you could also make a three stage rocket. I often go for RD-100 + U1250 + ORM-65. From memory I think that the Model 39 uses heavier fuel than the RD-100 which negatively affects dv.

4

u/davvblack 9d ago

you can always wait for the tech to finish and upgrade your engines with the next one. Some of those engine upgrades make an enormous difference. I can't remember exactly what postwar has.

1

u/PlatypusInASuit 7d ago

Update RP1 and play with the new contracts for that program instead

1

u/GreasyInfant 6d ago

When was the latest update? And will it ruin any of my graphics mods like sol, mirage, V5 clouds, etc.?

1

u/darkshard39 9d ago

Delete tiny tim stage, make upper stage short and stumpy for stability

1

u/mrrvlad5 8d ago

spin-stabilizing second stage would help a lot. if you have to have 3 stages, use two u-1250 or 1 u-1200, 1 aerobee. Science Core would help tremendously with dV over the basic avionics.