ESS Beginner's Guide to Space Exploration

septemberWaves · September 9, 2016

Beginner's Guide to Space Exploration

When showcasing vehicles for my Eloquent Spacecraft Systems series, I have encountered a few players who are confused by how I achieve what I do. Questions about how I can create spacecraft to accomplish various goals are common enough that I feel the need to address them. So of course, in my usual style, I'm going completely overboard with it and thus this thread now exists. Over time, I will be putting together what is essentially a series of guides on how to achieve various accolades (from the simplicity of reaching Kerbin orbit to the immense task of exploring the Jool system), and particularly how to do it in style.

Things to note about these guides

I'll be using stock parts, but I have a couple of mods installed. MechJeb will provide detailed information beyond what the stock game can offer (and also includes various features that help with efficiently flying a spacecraft). Kerbal Alarm Clock and Trajectories are included for convenience with regards to planning missions. I also have Color Coded Canisters and Colorful Fuel Lines installed, which help to improve appearances of stock fuel systems. Finally, I have Kerbal Joint Reinforcement installed, and if you try to do some of the things that I do in this series without that mod then you will need a large quantity of struts.
I am very much in the habit of designing things for aesthetics, and whilst I will not be prioritizing appearances quite as much as I usually do, there will still be things that can be changed about my designs to improve efficiency.
Whilst you could play through much of the game simply by mimicking my designs, I very much do not recommend it. This thread is intended to help new players learn the basics (and the not-so-basics) of mission planning and spacecraft construction, but it's best to make your own vessels once you have a better understanding of where to start. Additionally, it may be most helpful to take inspiration from my designs but look into ways of improving them, since nothing I will create is perfectly optimized for anything other than appearances.

A list of existing guides in this thread

Spoiler

Kerbin

First Kerbal to Low Kerbin Orbit

Edited September 9, 2016 by eloquentJane

septemberWaves · September 9, 2016

First Kerbal to Low Kerbin Orbit

Once you're in orbit, you're halfway to anywhere (well, almost anywhere). So of course, getting to orbit is important.

Command Module Design

Spoiler

The first part of any rocket that you need to design is the payload. In this case, your payload is a kerbal, who will be sitting inside a Mk1 command pod. To design a safe and effective capsule, there are several things you need to consider:

Control
Launch Abort System (LAS)
In-orbit operations
Returning to Kerbin

The capsule has internal reaction wheels, but it is often a good idea to add an extra one to improve the speed that your vessel can turn.

You also need to include a parachute for the return. I'm attaching one using a cubic octagonal strut rather than the attachment node, and then clipping it into the reaction wheel, because I want to attach the LAS decoupler above. I have also attached some linear RCS ports to help with controlling the direction of the vessel.

I attached the decoupler upside-down (because the side that the arrows point to is the one that it detaches from) and then offset it upwards so that I could ensure that the parachute was attached correctly.

At this point I decided to add a docking port. Whilst not technically necessary on this particular vehicle, it's a good idea to get into the habit of including a docking port.

Now for the LAS. An octagonal strut with a nosecone above to keep the rocket pointy should suffice for the structural element.

A sepratron on either side makes a good LAS for this small pod. They are attached with mirror symmetry so that I can angle them both in the same direction (holding shift whilst using the rotate tool allows you to rotate at 5 degree intervals instead of the usual 15 degrees).

I then offset them into the nosecone so that they look better (holding shift when using the offset tool allows for smaller and more precise offsetting intervals).

It's important to make sure that the sepratrons stage at the same time as the LAS jettison decoupler, so that the entire LAS can be jettisoned with ease. The actual abort sequence will be set up as an action group later.

Aside from the parachute, there are two important things needed for returning to Kerbin. One of them is a heat shield, and the other is a method of slowing down enough to safely deploy the main parachute; this can be either a drogue chute, or (in this case) several solid rocket motors.

These sepratrons are angled and offset so that they are behind the heat shield. They will be set up to fire as the heat shield is jettisoned.

The staging for the heat shield can be toggled in the heat shield's right click menu.

The command module is complete. The next thing to design is the service module.

Service Module Design

Spoiler

The service module is the part of a spacecraft that includes things like propulsion and electricity systems, as well as fuel. Generally it sits directly behind the command module.

The first things I add are a decoupler and a fuel tank. I also attach a MechJeb core to the command module, so that the vessel data is visible at all times during flight.

You may be tempted to use a Terrier engine. For this payload and this fuel quantity, it provides 1140m/s of delta-v, and a thrust-to-weight ratio of 1.75.

However, there is a better option. A Spark engine, and a small toroidal fuel tank for the sake of appearances, provides a significant improvement on the amount of delta-v at the cost of thrust-to-weight. This is because the Spark, whilst less fuel efficient, is also significantly less massive than the Terrier, and the mass reduction makes a significant difference with this smaller payload (the Terrier is better suited to more massive payloads). I also added a pair of Twitch engines to increase vacuum thrust-to-weight. This isn't really necessary and decreases the delta-v total a little, but it does decrease burn times which is good.

The next thing to consider is the Attitude Control System (or Reaction Control System in-game, hence RCS). Center of mass is somewhat important here, but the additional reaction wheel on the command pod means that the vessel should be able to compensate fairly well. Because this vehicle isn't designed to dock to things and thus the RCS is just for improving maneuverability, I use linear ports at both ends and only have 4-way ports around the approximate center of mass. The center of mass will change as you burn fuel, but that's not really an issue with this vehicle.

The service module is complete (actually I forgot the solar panels but I realized this later in pre-launch checks), but it needs a special way to decouple from that engine whilst keeping the rocket aerodynamic enough. I disable the shroud on the Spark (all engines with shrouds have the option to disable the shroud in the right-click menu) and add a decoupler beneath.

This isn't remotely aerodynamic, so the next thing to add is a fairing. An interstage fairing can be created by closing the fairing when it contacts a suitable part (such as the bottom of that white fuel tank).

Finally, to ensure a clean stage separation, I attach a pair of sepratrons to the fairing base, offset them to be inside the fairing, and angle them slightly outwards to avoid damaging the service module.

Launcher Design and Pre-launch Checks

Spoiler

Now that the payload (command/service module) is complete, the next step is to design a launch system. It takes around 3500m/s for a good pilot to get into low Kerbin orbit. For less experienced pilots it's good to aim for around 3800m/s, plus a little more for a de-orbit burn. My target orbit for this launch is 80km and I'm not going to be flying a perfect gravity turn, so 3800m/s is my goal. The service module has around 1150m/s (the 195m/s shown as stage 1 is not counted because that's part of the landing system on the capsule) meaning that the launcher needs around 2650m/s.

I start off by adding in a reaction wheel and two fuel tanks. The reaction wheel isn't always necessary, but I want to use a Reliant engine which lacks any gimballing range and therefore can't steer the rocket, so an additional reaction wheel is desirable. The Reliant is a good lifting engine because it has reasonably high thrust and is quite efficient in Kerbin's lower atmosphere.

With this fuel tank configuration, the thrust-to-weight ratio at sea level (under SLT on the MechJeb display) is good, but there is not enough delta-v.

The obvious solution is a few extra fuel tanks. SLT is still above 1.0 (which is required for the rocket to lift off) but now the delta-v meets the requirement.

In order to improve stability, I added a couple of fins. This slightly decreased the total delta-v, but I am experienced enough with gravity turns that this won't be a problem.

Finally, a couple of launch stability enhancers are added (out of the way of the fins) to prevent the rocket from crashing into the launch pad and experiencing a rapid unscheduled disassembly (not usually a problem with low-mass rockets like this, but it's a good habit to get into).

Technically this rocket is ready to launch. However, there are a couple of things that must be checked. Firstly, it must be ensured that stages are configured correctly, because the game does not always do this properly.

Next, critical systems need to be checked. It turned out that I had overlooked the solar panels, so I added them in. Again, this lowers my delta-v margins slightly, but it's not a major issue.

And finally, action groups must be set up. In this case, the only major action groups to set up are the solar panels and the Launch Abort System. I like to set solar panels to the "1" key.

The abort action group has it's own on-screen button, which is found next to the altitude meter. In this case, the LAS sepratrons and the decoupler beneath the command module must be staged for the launch abort sequence.

Flight

Spoiler

Now that the spacecraft design is complete, it's time to fly it. I'll be using MechJeb's autopilot to get a fairly efficient gravity turn, but it's easily doable without the autopilot once you're used to it. The target orbit for this launch is 80km with zero eccentricity and zero inclination (within reasonable error).

The first step is pre-launch checks on the launch pad. Ensure that staging is correct, everything is fully fueled, and the crew are where they should be. And if you're using MechJeb like I am, this is also the time to configure the autopilot.

Once all checks are performed and the vessel is go for flight, throttle up and launch.

Once launched, it is usually convenient to roll the rocket until the North marker on the navball is to the left. This is entirely optional but I find it convenient because it means that the gravity turn uses primarily the "w" and "s" keys. Travel straight up until surface velocity reaches about 100m/s, then begin to tilt to the East.

This rocket turns quite slowly due to the lack of engine gimballing, which means it loses some delta-v to gravity and can't conduct a perfectly efficient gravity turn. This is not a problem because I included some extra delta-v to compensate, but usually you want to be at an angle of 45 degrees from the surface by the time you reach 8km in altitude.

Main engine cutoff. Time for the stage separation.

The stage separation on this rocket actually consists of two staging events. The first jettisons the interstage fairing, and the second separates the launch stage and activates the sepratrons to push the launch stage away from the spacecraft.

Service module engine ignition.

Here the apoapsis is shown as it approaches space at 70km. The intended apoapsis is at 80km.

The intended apoapsis is reached and the service module engine throttles down.

Here the LAS is jettisoned, as it is no longer needed.

Once in space, deploy solar panels and prepare a maneuver node to circularize at apoapsis.

Execute the maneuver node to circularize the orbit.

Now a stable orbit has been achieved, with 32m/s of delta-v remaining. It's usually better to have more, but this is plenty for a de-orbit burn.

Since 32m/s won't lower my periapsis to 20km (which is a good altitude for a quick de-orbit), I instead schedule a 32m/s retrograde burn to consume all of the remaining fuel, and then move it so that my landing site (as estimated by the Trajectories mod) is close to the KSC. It's best to overshoot landings if you want to be precise.

Unfortunately the burn had to be executed in darkness, but it had the intended effect.

Upon re-entering the atmosphere, the service module is jettisoned. Stability assist can be turned off at this point, because the heavy end of the capsule (where the heat shield is) will naturally point forwards when aerobraking.

With this capsule design, aerobraking can commence without any input from the controls. The following screenshot includes the parachute highlighted in its clipped position.

Ablator is heavy and usually not much is consumed. I didn't limit it on this flight because it's best to test out how much of it gets used, but on future missions the ablator amount can be limited to save mass and increase delta-v.