Difference between revisions of "Tutorial: Earth-Moon Aldrin Cycler"

Latest revision as of 22:44, 6 May 2020

Buzz Aldrin invented a class of orbits that allow a ship to continuously transit between two bodies with little or no orbit adjustments. It's an extension on the classic Hohmann Transfer orbit. Aldrin's name is most popularly associated with Earth-Mars Cyclers but he did his early work on Earth-Moon Cyclers.

• Length: hours to days
• Difficulty: extreme
• For version: 1.8.1 with RealSolarSystem mods

Youtube Video Tutorial: Aldrin Cycler

Click Link to see Images

I can't upload any images for this page so I put them on my google drive. They can't be display on the page but you can click the IMAGE:xyz links to access them.

Prerequisites

This tutorial assumes you already know how to

• use Kerbal's Orbit Maneuver node controls
• alter a circular orbit into an elliptical orbit
• change the plane of your orbit
• install the RealSolarSystem mods
• execute a Kerbin-Mun or Earth-Moon Hohmann transfer orbit

Why create an Earth-Moon Aldrin Cycler

IMO an Aldrin Cycler cruise ship is the next logical step for space tourism after LEO Hotels. Tourism has much deeper pockets than our current science and industrial uses of space. Just look at the size of cruise ships and Earthly hotels! My dream of the future is that space can lay claim to some of those delicious tourist dollars.

When visiting space, tourists want more than just a trip in a tin can. They want Windows! They also want private suites, open spaces to enjoy zero-G activities and adventure services like space walks. These services require high mass infrastructure that is best left in a stable orbit requiring little or no delta-V. Launching this equipment with the tourists and deorbiting it does not make sense. Thus the obvious first destination is hotels in LEO.

After LEO tourism gets rolling a trip to the Moon is the next obvious destination. But we still want windows and zero-G fun on our week long trip. Aldrin Cycles are orbits that transit between celestial bodies and require minimal delta-V to maintain stability. This lets us create an Earth-Moon cruise ship.

This tutorial demonstrates a low delta-V orbit where cruise ships could cycle repeatedly between the Earth and the Moon.

Lunar Cycler Background

In 1985 Buzz Aldrin laid out the first example of a stable orbit that would allow heavy assets to cycle freely between the Earth and the Moon. Over the years his original concept has been expanded to include Earth-Mars Cyclers and a variety of Earth-Moon Cycler orbits.

3 Orbit Shamrock Cycler

The foundation for this tutorial is this AAS Paper: Circumlunar Cycler Orbits for a Manned Earth-Moon Space Station PDF. It describes a number of variants. The 3 orbit Shamrock Cycler was chosen for this tutorial.

IMAGE: 3 orbit Shamrock Cycle.

The Cycler starts with a typical figure 8 Hohmann transfer orbit to the Moon. Unlike the Apollo missions we don't transfer into lunar orbit as our objective is a free return to Earth and then future free returns to the Moon. So our cruise ship will simply drift around the Moon and fall back to Earth. Again unlike Apollo, we do not deorbit into the Earth's atmosphere. We carry on around the Earth toward the Moon again.

Unfortunately on our second trip out the Moon isn't there! Don't despair. The Moon has gone around 1/3 of it's orbit. On our 3 orbit the moon has finished 2/3 of its orbit. On our 4th orbit, the first of the next cycle, the Moon is back!

When looked at in a rotating Earth-Moon reference frame, this looks like a 3 lobed Shamrock. See diagrams above.

The Shamrock cycler orbit is not a clean & stable orbit. It requires a series of low delta-V maintenance burns. In Kerbal Space we have to eyeball our maneuvers so don't expect to hit the minimum delta-Vs described in the paper. Only real orbital mechanics can get those results.

Kerbal System Setup

This tutorial currently requires the RealSolarSystem mods. When written, 1.8.1 was the newest Kerbal Space version able to run RealSolarSystem. See Kerbal RealSolarSystem Releases. While Aldrin Cycle orbits can be setup in the Kerbol solar system, I haven't done that yet.

Any ship with a reasonable fuel supply can be used for this mission. I recommend a lower thrust engine for easier adjustments on low delta-V burns. I used the following

• Ravenspear Mk4 (stock space plane)
  • remove everything except the cabin
• Add
  • Rocomax 64 fuel tank
  • LV-909 "Terrier" Engine

Mission phases

Initialization

Skip the Launch

Your mileage may vary. These steps worked for me when starting from a clean Sandbox with the RealSolarSystem mods.

From Key Bindings use Mod+F12 Debug/Cheats Menu => Set Orbit to place your ship in orbit.

Due to the inclination of the Moon's orbit, it's easiest to start this operation from lunar orbit. Set the SemiMajor Axis to 4,738,000 which becomes a Lunar PE of 3,000,000 meters. Set the inclination to -158 degrees. This matches the inclination of the Moon's orbit but leaves your vessel orbiting in the opposite direction, appropriate for setting up a Hohmann figure 8. Set eccentricity to 0.001 to stabilize the orbit display in map mode.

First Figure 8 Hohmann

IMAGE: Start the first figure 8 from Lunar orbit

The first step toward an Earth-Moon Cycler is building a Hohmann figure 8. In this case we're starting from the Moon and looping around the Earth.

In Map mode, at the point in your Lunar orbit opposite the Earth setup a prograde burn of about 700m/s. Your target is an Earth PE of 3,000,000. If you're not familiar with Map mode and Maneuver nodes, you should read the other Kerbal tutorials about changing orbits.

It's important to ensure that your Earth-Moon orbits remain coplanar with the Moon's orbit. Check the plane of your orbit during each maneuver. Add out-of-plane components to your burns to correct any errors.

Tip: I always turn on SAS and use the automatic controls to point my ship in the right direction.

This completes the setup phase. The next maneuvers are repeating parts tuning the Cycler's orbit.

Repeating cycle of Cycler orbit adjustments

Set the Moon as your target for the all subsequent maneuvers. L-click the Mouse when pointing at the Moon and "Set as Target".

Using Lunar PE as the start of the cycle, you vessel will perform two highly elliptical orbits around the earth before re-intercepting the Moon on your third orbit. ... if all goes according to plan ...

Set the Ellipse duration

IMAGE: Set Ellipse Duration

The first recurring Cycler maneuver is a retrograde burn that reduces the AP of your highly elliptical Earth orbit. Coming from the Moon back to the Earth the orbit has too much energy and the next ellipses will take too long. The Cycler's non-Moon-intercepting ellipses need to have a duration just below 1/3 of the Moon's orbit duration. ... to intercept the Moon in your 3rd orbit around the Earth. Kerbal won't show you the next Lunar encounter until it's less than one orbit in the future. So we need to set the elliptical orbit duration now without navigation assistance.

At Earth PE setup a retrograde burn that brings the PE to AP time down to 4d 21h. This is just a guess! Save the game as you may need to adjust this timing. Zoom out to see the whole orbit. Hover over the AP marker to see the time to AP. Tip: Keep your mouse over the AP marker and display the AP time as you complete your burn.

Check your intercept

Perform the burn and check that your AP will occur in about 4d 21h. Warp around to just after AP. Warp around to just after the next AP. And warp around a third time to see the position of the Moon relative to your orbit's AP. Your goal is that the Moon should be 0 to 15 degrees counter clockwise when you get to AP. If you're very lucky final orbit will already intercept the Moon.

What to do if the Moon is in the wrong position when you get to the third AP? Revert to your saved state prior to setting up the AP time. Readjust your orbit duration. - If the Moon passed you, reduce your PE-AP time - If the Moon didn't reach you, increase your PE-AP time

Saving each variant lets you track how your burns change your arrival position relative to the Moon.

Pre-Hohmann setup burn

IMAGE: Pre Hohmann Earth PE setup Burn

When you get the Moon into a good position on the 3rd orbit, revert to your saved ellipse setup burn and setup for the final burn of this cycle.

Warp ahead to just before your final Earth PE prior to re-intercepting the Moon.

Setup a maneuver at Earth PE. Futz with the controls until you get a figure 8 Hohmann around the Moon AND the next Earth PE is about 3,000,000 meters. You may need to adjust both your prograde and radial velocities to obtain a good solution.

Rinse and repeat

Because we're just eyeballing these maneuvers your first attempts will likely result in fairly high delta-V. After a few attempts I got it down below 70m/s.

Simplifications

When compared to the AAS paper I took a couple shortcuts. I simplified the orbital plan down to two maneuvers instead of 3 and I loosened the constraint on Lunar PE.

Why create an Earth-Moon Aldrin Cycler

IMO an Aldrin Cycler cruise ship is the next logical step for space tourism after LEO Hotels. Tourism has much deeper pockets than our current science and industrial uses of space. Just look at the size of cruise ships and Earthly hotels! My dream of the future is that space can lay claim to some of those delicious tourist dollars.

When visiting space, tourists want more than just a trip in a tin can. They want Windows! They also want private suites, open spaces to enjoy zero-G activities and adventure services like space walks. These services require high mass infrastructure that is best left in a stable orbit requiring little or no delta-V. Launching this equipment with the tourists and deorbiting it does not make sense. Thus the obvious first destination is hotels in LEO.

After LEO tourism gets rolling a trip to the Moon is the next obvious destination. But we still want windows and zero-G fun on our week long trip. Aldrin Cycles are orbits that transit between celestial bodies and require minimal delta-V to maintain stability. This lets us create an Earth-Moon cruise ship.

This tutorial demonstrates a low delta-V orbit where cruise ships could cycle repeatedly between the Earth and the Moon.

Lunar Cycler Background

In 1985 Buzz Aldrin laid out the first example of a stable orbit that would allow heavy assets to cycle freely between the Earth and the Moon. Over the years his original concept has been expanded to include Earth-Mars Cyclers and a variety of Earth-Moon Cycler orbits. The foundation for this tutorial is this AAS paper. Circumlunar Cycler Orbits for a Manned Earth-Moon Space Station PDF describes a number of variants.

Next Steps

Efficient for fuel but not for Tourism

In IMAGE: Pre Hohmann Earth PE setup Burn you'll see that swinging around the Moon causes the next ellipse to precess. This is a problem from a Tourism perspective. The impact is a number of Cycles where our passengers spend most of the time looking at a dark Earth and then the Lunar far side is also dark.

While this is the lowest energy fully recurring orbit there are ways and means to fix this problem. The first is spend more energy every cycle and always intercept the Moon at the same point in its orbit.

Another option is to allow the precession to carry through a few cycles and then perform a major orbit change to skip all the less desirable transits.

As for the 9 day ellipses out to deep space I think at least one of these can be fully utilized. See my Lunara Tours itinerary below.

So. Knock yourselves out creating these variants!

Cruise Ship Design

My dirty secret is that I couldn't build a Kerbal rocket if my life depended on it. I just love playing with orbital mechanics and ideas around Lunar tourism. So what would the ship of my dreams look like? Well, as much as like the Gateway Project's von Braun ring, I think we'll be setting up the first cruise ships as a linked set of Space-X BFRs (aka Starships).

But the dirt simple option won't address the need for Windows! Inflatables might do the job. I think everyone would need to wear space suits in case of a rupture. Which bring me to a crazy idea: What about rows of spacesuit helmets dotting the sides of the ship? Underneath each helmet could be a pressure sealed chamber for one person. Everyone could have their own view of the universe.

One way or another a large percentage of the outer hull should be some kind of clear material. Have you heard about transparent aluminum? Scotty invented it but ALON became real in 2018. And it's a great thermal conductor.

So here again, knock yourselves out. I'd love to see what other KSP aficionados come up with.

Lunara Tours Brochure

If I'm going into space as a tourist, I want WINDOWS! If I'm paying for a trip to the moon, I want to SEE the Moon.

At Lunara Cruise lines everyone gets a window. Whether you book into the Lunara Sunrise, our LEO hotel or our lunar cruise ship the Lunara Acropolis, you are guaranteed a window whenever you want one. We also have zero-G gymnasiums, an assortment of restaurants and other onboard amenities you expect from a luxury cruise line.

By far our most popular package, Moon on a budget is an 18 day adventure that takes you to the far side of the moon.

We also provide an Ultimate Lunar Excursion package that includes transfering to our Lunar orbit station and then landing at our Moon base.

Moon on a Budget Itinerary

Like any trip to space the adventure begins with your training. Training for space is itself an adventure. We also set aside plenty of time to tour the area and see all the sights. Our training center is located in the historic center of space travel, Cape Canaveral.

Day 8: Launch day is a rush in so many ways. Your personal launch steward will be with you every step of the way so just sit back and enjoy the ride. After launch is a bit of quiet time onboard your shuttle. We have half a day before docking at the Lunara Acropolis. This is very much like an overnight transcontinental flight. We turn the lights down and encourage everyone to catch their breath and a few zees.

Day 9: Embarkation. Your steward will help you navigate your first day in zero-G. Step one is get to your cabin. Step two is find the nearest window and drink in that awe inspiring view of the Earth.

Day 10-16: Deep Space. Get familiar with all the onboard amenities as the Lunara Acropolis heads out on the deep space leg of the journey. The Earth is still a great sight. Make good use of our 3 domed theatres. We also have center stage for watching zero-G acrobatic troup. Or learn some of zero-G moves yourself in our open gymnasiums. Sign up for laser tag. Enjoy the restaurants and casino.

Day 17: Earth Flyby. Orbits are strange things aren't they? To get to the Moon the Lunara Acropolis has to fly past the Earth again. While odd, this is a great opportunity. We missed Earth close ups during during launch and embarkation. So get out your cameras and find your favourite window.

Day 18-21: Transit to the Moon. Enjoy our hospitality as you watch the Moon get larger every day.

Day 22: Far Side of the Moon. Today is the climax of our trip. Grab some snacks and your camera. Watch the Moon take over the sky. See mountains and craters accentuated by the crisp airless shadows along the terminator. Feel the isolation as the Earth and everything you've ever known disappear. And the joyful reappearance of that Blue Marble contrasted from the start black and white of the Moon.

Day 24-27: Returning to Earth. Watch again as the Earth looms ever larger.

Day 28: Debarkation. Get a grand bonne voyage from the captain and crew as you get ready for reentry. Feel gravity creep back into your bones after almost 3 weeks in space.

OR add on an extra 9 day deeply discounted deep space loop before heading home.

Links

ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160004674.pdf Reference paper describing the Shamrock cycler used in this tutorial

AAS Copyright info I hope this lets us use the images found in the paper.

Kerbal Real Solar System Module is required to follow this tutorial exactly but the outline will work fine between Kerbin & Mun.

forum.kerbalspaceprogram.com/index.php?/topic/121166-buzz-aldrins-cycler-orbits-are-they-useful-in-ksp

[Category:Tutorials|Advanced Aldrin Cycler Orbit]