Tutorial:Aeris 4A mission

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The Aeris 4A ready to start

This guide will help you fly the Aeris 4A into orbit, and land back at the KSC runway.

The Aeris 4A is an SSTO spaceplane that has air-breathing Turbo Ramjet Engines for use at lower altitude and speed, while a Toroidal Aerospike Engine takes over when the ramjets become ineffective.

For simplicity, this guide will call the Turbo Ramjet Engines “jet engines”, and the Toroidal Aerospike will simply be called “rocket engine”.

This guide assumes that you have never flown a spaceplane into orbit before, but some of the details here should be interesting for experienced KSP players as well. Hopefully, this guide will help you become familiar with the operational principle of air-breathing SSTO spaceplanes, allowing you to not only be able to fly the Aeris 4A, but also design much better vehicles of your own.


Before we get into space, the Aeris 4A takes off and flies just like a regular plane.

  • 01. Activate SAS
  • 02. Activate Jet Engines (Default Hotkey: 5)
  • 03. Throttle to 100% (Default Hotkey: Z)
  • 04. Pull up after speed reaches 70m/s
  • 05. Gear up after altitude reaches 80m

  • Note on 04:
    • It is impossible to suffer a tail strike in the Aeris 4A no matter how hard you pull up during takeoff, but it is still good form to pull up gently.
  • Note on 05:
    • The KSC Runway has an altitude of 70m. However, your altitude is calculated from your cockpit, so when the altitude reads 71m, it doesn’t mean your whole plane has left the ground, it just means the cockpit has tilted up. Thus it is safe to wait until altitude reading is 80m before retracting landing gear.

Ascent to Orbit

In case you didn’t know, being in orbit means spinning around the planet so fast that the centrifugal force fully counteracts gravity.

You will need a velocity of around 2270m/s to create that much centrifugal force. You will also want to be above 70km; under 70km, air resistance will slowly eat away at the speed you worked so hard to gain; above 70km, there is no air resistance, and your speed won’t be lost. Thus, you stay in space forever without having to expend fuel.

So let’s start spinning around our planet by heading eastward.

  • 06. Maintain a heading of 90 (East)
  • 07. Keep aircraft nose pointed 15 degrees above the horizon
  • 08. When altitude exceeds 18km, and speed exceeds 1380m/s, active rocket engine (Default Hotkey: 6)
  • 09. Keep aircraft nose pointed 10 degrees above the horizon
  • 10. Go into map view (Default Hotkey: M)
  • 11. When apoapsis reaches 80km, cut throttle to 0% (Default Hotkey: X)
  • 12. Keep aircraft nose pointed prograde
  • 13. Coast toward apoapsis
  • 14. About 10 seconds before arriving at apoapsis, throttle back up to 100% again, and keep nose pointed prograde
  • 15. When periapsis rises to about 80km, set throttle to 0%

Congratulations, you flew a plane into orbit! You can now stay in space forever, until you voluntarily fire your engines to deorbit yourself.

  • Note on 06:
    • Because the planet Kerbin spins eastward at 175m/s, it means that you get 175m/s for free when entering into a west-to-east orbit. While the Aeris 4A is capable of entering into a different orbit, the procedure will be different, and this guide will only cover getting into the simplest west-to-east orbit.
  • Note on 08:
    • The Aeris 4A’s jet engines are 11 times more fuel efficient than the rocket engine. So, we want to be in jet-only mode for as long as possible. However, at 18km altitude and a velocity of 1350m/s, the Aeris 4A’s jets start to become ineffective, and thus we are forced to use the rocket engine for the rest of our journey.
    • 1380m/s is already more than half orbital speed. We have already traveled more than half of the ascent, while expending fuel at 11times the efficiency of a pure rocket: this is the advantage of air-breathing vehicles.

Orbital Mission

The stock Aeris 4A can be used to perform theses missions:

  • Create crew reports and EVA reports, then send them back to Kerbin for Science Points.
  • Transporting one Kerbal to another ship or space station.
  • Docking with and refueling another ship or space station.

If you want to get back to Kerbin from an 80km by 80km circular orbit, you will need this much fuel: 66 oxidizer and 54 liquid fuel.

Deorbit and landing

This part is hard. I am sorry to say that the Aeris 4A’s Mk1 cockpit is not very heat resistant, and very prone to burning up during reentry.

To ensure safety, I suggest a long and arduous “skip reentry”.

We will first get low in the atmosphere, bounce off (skip) to a pretty high altitude again, and then perform a second descent. The long and winding path traveled will spread the heat over a greater amount of time, and ensure survival.

The long and winding path will also make an accurate landing at the KSC runway difficult. However, with practice, accurate unpowered landings can be consistently done.

Here is the procedure:

  • Between the KSC continent, and the continent west of the KSC continent, there is an ocean, and the middle point in the ocean, we will call Location A.
  • Pretend you are on Location A, go westward along the equator for a distance equal to 1/4 of the total equator. This position, we will call Location B (this location is coincidentally very close to the giant impact crater).
  • 16. When your orbital path takes you right above Location B, start burning retrograde.
  • 17. When your current projected path ends at Location A, stop the burn.
  • 18. Deactivate all engines, and set throttle to 0%.
  • 19. Keep your nose pointed prograde as you descend through the atmosphere.
  • 20. When your altitude reaches 35km, start pulling up gently.
  • 21. When your nose is stable at about 10 degrees above the horizon, pull up hard, and keep your stick completely pulled up.
  • 22. The high speed combined with the large delta wing will ensure you won’t backflip, and if you eased into this maneuver gently, your nose won’t oscillate up and down.
  • 23. Keep the stick pulled up to maximum. Your altitude will drop to about 30km; and then you will ascend back to about 43km; and then you will descend again. Now, you should no longer keep the stick fully pulled up.
  • 24. Nose up if you think you will undershoot the KSC runway; nose down if you think you will overshoot. Make yaw adjustments as needed. If you need to lose speed, use the “nose up and down” maneuver, but don’t do it too hard, or you will rip your wings off.
  • 25. For a gentle landing, you should hit the runway at less than 100m/s airspeed, and less than 5m/s vertical speed. Apply wheel brakes (Default Hotkey: Hold B) to come to a full stop.

Congratulations! You went to orbit and back! In a plane! And you didn’t jettison any parts during the journey!

  • Note on 18:
    • Because jet engines don’t work in space, you may not realize your jet engines are on. This will come back to bite you when you are trying to slow down in the lower atmosphere: your jet engines suddenly come back to life, and instead of slowing down, you are speeding up.
  • Note on 24:
    • I have followed my own guide to the letter, and made perfect unpowered landings at the KSC every time. However, I understand reentry and landing is hard for beginners, and some practice may be needed.
    • If you end up really off course, but still have some fuel left, you can reignite your jet engines and do a powered flight back to the KSC. Naturally, the unpowered glide is the most fuel efficient.
    • If you really can’t make it to the KSC runway, pick any flat piece of ground and land. Landing back on the planet is still a great achievement!