Early Light Orbital Rocket Tutorial (P&LC) - KSP-RO/RP-1 GitHub Wiki

Note: This tutorial was written for RP-1 P&LC 3.21, and is based on https://github.com/KSP-RO/RP-1/wiki/Early-Orbital-Rocket-Tutorial

Introduction

After you've completed your sounding rocket development, the next big step is to launch a satellite into orbit. To demonstrate one way of accomplishing this important milestone, this tutorial will show you how to build an early orbit-capable rocket fit for the Early Satellites (Light) program. Please note that this is simply one way of progressing in an RP-1 career. There are many paths to success!

Figure 1 - The completed rocket.

This will be a two-stage rocket, using an XLR35-RM-1 upper stage and an LR79 lower stage. The XLR35-RM-1 is an upgraded config of the XLR-11, unlocking in the Early Rocketry node. Compared to the baseline XLR11-RM-3 config, the XLR35-RM-1 adds gimballing and a turbopump, saving weight by not having to use a high-pressure fuel tank. The LR79 is unlocked in the 1956-57 Orbital Rocketry tech node. The rocket will also use isogrid fuel tanks, which are lighter and more capacious compared to earlier conventional (separate structure) fuel tanks. The finished rocket will mass around 53 tons, and its launch complex will take approximately 150 days to build. Be sure to construct your Launch Complex in time in time for your first orbital launch attempts.

Figure 2 - The launch complex cost.

Payload

Figure 2 - Payload.

Let's design the rocket from the top down. For the purposes of this tutorial, we will be launching a 260kg mass simulator into a 180x180km 28.5 degree inclination orbit. Feel free to customize your own satellite with whatever you may need to accomplish a particular mission, such as antennas, solar panels, or experiments that don't fit inside the probe core.

Decoupler and fairing

Figure 3 - Payload decoupler and fairing.

Next, we're going to add a decoupler, fairing base, and two fairing halves. The use of a separate decoupler allows us to save a significant amount of mass. The fairing base with the decoupler enabled weighs 69kg, but only 17kg without. In contrast, the small 20cm decoupler weighs only 4kg, saving us a total of 48kg that can now become payload!

Figure 3 - Decoupler mass savings.

This rocket uses a 1.2m diameter for the payload fairing. There are a couple reasons for doing this, including reutilizing existing 1.25m tooling that you'll already have if you've been flying X-planes. There is a 4% leeway up and down for diameter tooling, meaning that 1.25m tooling gets you any diameter between 1.2m (0.96*1.25) and 1.3m (1.04*1.25). Additionally, we'll make some edits to the Procedural Fairing settings. Make sure you have bought the Aluminum Fairings and Stringers upgrade in the Early Materials Science node in R&D, as this will allow you to reduce your fairing mass from 46kg to 34kg. Every kg counts on early rockets! Beyond the mass reduction, the fairing also has a custom pointy shape. Feel free to try your own shapes, and observe the aerodynamics and aesthetic effects.

Figure 4 - Fairing mass reduction upgrade.

Upper stage

Figure 5 - Upper stage configuration

Once you've placed the fairing base and fairing halves, it's time for avionics which can actually control the upper stage. In this tutorial, all avionics units are colored orange. Select a procedural avionics part and attach it beneath the fairing, adjusting it to 1.2m diameter. Configure the avionics to use the Near-Earth Avionics Prototypes configuration, and set the controllable mass to be around 6 tons. Add 2000 kJ of batteries to power the avionics, and under Communication edit the antenna to be a TL0 20 dBm VHF antenna. This will save some cost, mass, and power.

Next, select a Modular Tank (Isogrid Structure) fuel tank, and place it beneath the avionics. Increase the diameter to 1.8m and the length to 1.7m. The default utilisation will be 95 percent. Always make sure this slider is maxed out to take full advantage of a fuel tank's capacity. You may have noticed that 1.2m and 1.8m diameters do not match. We will solve this by clicking the Select Nose button in the PAW, and selecting the 3:2-Short nose. A bit of math tells us that 1.8*(2/3) = 1.2, which is the 1.2m of our fairing.

Figure 6 - Nose selection.

Next, we will an XLR11 engine variant to power this stage, specifically the XLR35-RM-1. Surface attach the engine to the bottom of the fuel tank, select the move tool (2 on the keyboard by default), verify it is in Absolute mode, and center the engine.

https://github.com/user-attachments/assets/56aaa3ab-a0cb-4c23-b273-5b353dc96688

Figure 7 - Engine placement.

After verifying the engine is centered, click the Engine Show GUI button in the PAW. A new menu will open, in which we will select the XLR35-RM-1 config. Take note of the information screen which appears when you hover over the engine config. It contains valuable information not found elsewhere, such as the TestedBurnTime=900 line. It is a commonly held belief that overburning your engines is always bad. Not so! Some engines have a TestedBurnTime value, meaning they lose much less reliability when burning beyond their rated burn time, which in the case of our XLR35-RM-1 is three minutes fourty seconds. This is what will allow our XLR35-RM-1 to burn for four minutes twenty-five seconds, which in combination with its high reliability will incur nearly no additional risk. Don't forget to actually add the fuel with the Fill: XLR35-RM-1: XLR11 button in the PAW.

Figure 8 - Engine selection.

In order to attach a lower stage, we will need an interstage. The reason we surface-attached our engine was to simplify attaching this interstage. Select a Hollow Interstage from the Coupling Category and configure it the Saturn Variant, MS-II core with a 1.8m Diameter and 1.3 V.ScaleAdj. Attach it to the bottom of the fuel tank.

Figure 8 - Interstage.

Lower Stage

Figure 9 - Lower stage.

Start the lower stage with a second procedural avionics unit, using the same Near-Earth Avionics Prototypes configuration as the upper stage. Increase the controllable mass to around 60 tons, and give it a few hundred EC so it won't run out of power during the launch. Disable the antenna. You only need the one in the upper stage.

Place another Modular Tank (Isogrid Structure) fuel tank beneath the avionics, with 95% utilization in standard Al Gridded Tank configuration. Make it 2.7m in diameter and increase the length of the tank to 7.6m. Then, like we did for the upper stage, switch to the 3:2-Short Nose. Finally, click the Select Mount button in the PAW and select the Shroud (XL) mount. This mount will improve both aerodynamics and aesthetics.

Select an LR79 engine and place it on the bottom of the rocket stack. Use the PAW of the tank to fill it with the correct mix of kerosene and liquid oxygen. Note that this engine will have the starting S-3 configuration, which is less powerful and less reliable than subsequent configurations. If you have configured your rocket correctly, the first stage burn time is half a second under three minutes, and the SLT (Sea Level Thrust) is somewhere in the range of 1.16. Please note that because the LR79 is a ground lit engine, depending on your version of Mechjeb, these stats will only be visible in the Delta-V Stats window once you have attached launch clamps, which we will do in the Finishing touches section. Upgrade the LR79 as soon as you unlock the 1958 Orbital Rocketry node. The second configuration ("S-3D") is more reliable and powerful, allowing you to launch larger payloads, provided you make other required adjustments (such as tank lengthening) to your rocket.

To finish up the lower stage, set the LR79 exhaust type to Jupiter and attach a S-3D Vernier Exhaust to provide roll control.

Figure 10. Roll control vernier.

Finishing touches

Figure 11. Launchpad parts.

Our engine can't ignite without any launch clamps, so you can either add some simple clamps to the sides, or properly dress up your rocket with some Modular Launchpad parts, as seen above.

Now that we've got all our parts placed, it is time to check our staging. Put the LR79 and S-3D Vernier Exhaust in the 5th stage, all the launchpad clamps and parts in the 4th, the XLR35-RM-1 in the 3rd, its corresponding decoupler in the 2nd, the fairing halves in the 1st stage, and the payload decoupler in the 0th stage. Having the engine and decoupler in different stages will allow us to hotstage, giving the XLR35-RM-1 engine time to spool up before the LR79 burns out. This improves attitude control.

Figure 12. dV stats and staging sequence.

Go For Launch (or Simulation)

Figure 13 - On Pad w/ MechJeb PVG Settings

To test our design, we will simulate it with the Simulate button in the Integration Info window. You can use MechJeb Dev PVG with this design. You can find the settings for this rocket in the screenshot, in the Ascent Guidance, Ascent Settings, and PVG Settings windows. As this could be your first time launching and orbital rocket with PVG, I will briefly explain the important settings. Under Ascent Guidance, the important fields are Target Periapsis, Target Apoapsis, and Orbit inclination. We set Target Periapsis to our desired orbital height and leave Target Apoapsis at zero, so we will circularize. For the Orbit inc. we simply click the Current button, setting it to the latitude of our launchsite. Make sure the radio buttons for Ascent Settings and PVG settings are checked. In the Ascent Settings window verify Stop autostaging at stage # is set to 1 or lower, so Mechjeb can fully automatically complete all required staging actions. Additionally, make sure the radio button for Support hotstaging is enbled with a 1 second lead time, otherwise the second stage will not be able to spool up before stage seperation. Over in the PVG Settings window Last Stage is the final stage mechjeb will burn an engine in. Early Shutoff Stage is the stage mechjeb will turn off an engine in to hit the orbital parameters requested in the Ascent Guidance window. Booster Pitch start and Booster Pitch rate control the gravity turn (non PVG-controlled) part of the flight. As our SLT is low, we use and 80m/s Booster Pitch start and 0.7 degrees/s Booster Pitch rate to make sure we nicely transition into PVG-controlled flight, which begins once the dynamic pressure (Q) drops below the Q Trigger of 10kPa. Feel free to play around with some of the other settings to observe their effects. Experimentation is an excellent teacher. Be sure to configure your rocket and PVG settings before clicking Engage Autopilot. Once you click Engage Autopilot you should see approximately 830 m/s of dV excess. Most of this will be lost to external factors like gravity losses, steering losses, and drag. Once you're configured, stage to begin ascent.

If you're having problems with PVG, such as it burning up or down, please visit A Primer on Ascent.

Figure 14 - Ascent.

Figure 15 - Staging.

This demonstration rocket is launching into a 180x180km 28.55 deg inclination orbit. If you are delivering an actual payload, make sure to detach the satellite from the upper stage, or permanently disable the avionics of your remaining Near Earth avionics unit (otherwise the upper stage avionics will drain the batteries quickly), and you're done! If you're now in orbit for the first time (even just in a simulation), be sure to savor the moment.

Figure 16 - Payload in orbit.

Once you've figured out a launch profile that works, go back into the VAB and design a payload to fulfill whatever contract requirements you have. If you are a little short on dV for some orbits, add some HTP RCS to the upper stage along with an unguided final kickstage. Finally, tool everything, begin LC construction, and once that finishes place some rockets into the build queue. Hopefully the RNG will behave when it's time to launch for real, and your engines will function all the way to orbit. If they don't, just remember that every failure adds DU, increasing the chance the next rocket will succeed.

Evolution

After you've successfully launched your rocket to orbit and spent a few moments basking in your achievement, you may wonder what comes next. The answer, in a word, is "Evolution". Go back into the VAB, and start tweaking your rocket design. See how you can improve it. Upgrading your engines is always a good way. Replacing the XLR35-RM-1 with the RD-0105 from the 1958 Orbital Rocketry node, and upgrading the LR79 from the S-3 config to the S-3D and stretching the tanks will greatly improve the mass off payloads you can launch. Such a upgraded rocket should be able to bring up an unguided payload with 3400 m/s or more of delta V to orbit, enough to go to the moon. Try various upgrades and see just how far this rocket can take your space program.

This evolution is one of the reasons the tutorial uses the this design. There are many small tweaks you can make as you progress down the tech tree, so this design is a great starting point. You'll begin to see the utility of changes that were made historically, such as stretching fuel tanks, swapping out engines, adding SRBs to the first stage, and increasing the diameter of the upper stage.

Take the skills and concepts you've learned, fire up your RP-1 career, and go make your own history!