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#76 2020-06-28 06:25:33

Registered: 2018-04-27
Posts: 2,827

Re: Orbital Mechanics

For GW Johnson re 2 year orbit plan and Aldrin Cycler

Your presentation on Blogspot developed the 2 year orbit concept you revealed here in greater detail.

By any chance, have you written up a comparison of your plan to the Aldrin Cycler concept (and it's many variations)?  I note that your plan delivers a travel time of 4.26 months, compared to the longer Aldrin Cycler travel time of 4.87 months.  Your plan would appear to be faster, with the distinct advantage over most alternatives of a safe return to Earth if stopping at Mars is not possible for some reason.

In another post, I inquired about the feasibility of setting up a return vehicle to pass by Mars a month after the expedition arrives there using your 2 year orbit concept.  What I'm not clear on is if your orbit design only works when the planets are aligned in a certain way.

Edit#1: The Starry Night astronomy package comes in four flavors ... The $80 Enthusiast level includes orbit input.

Add & Edit Objects With The Orbit Editor

Presumably a student of orbital concepts for Mars / Earth transits could design an orbit, determine the element set needed, input that into the Starry Night program, and watch the behavior of the object with respect to Mars and the Earth using the speed-up feature.

This might be an inexpensive way to acquire a subset of the capability of the mission planners at NASA or SpaceX.

So! For GW Johnson ... can your 2 year orbit concept be written in Keplerian Orbital Elements?

I asked Google if there is anything available to convert to keplerian Orbital Element sets, and got back a (to me surprising) number of responses.

The search string I used was "orbit elements calculator".

Search Results
Web results

Convert between orbital elements and state › formulas › OrbitalElements
This calculator converts between orbital elements and state vectors, also known as Cartesian coordinates. It is recommended that you set your prefered units ...

Orbital Elements
Is the argument of periapsis, meaning the angle from the line of the ascending node to the point at which the satellite is closest to focus of the orbit. It is defined ...

Orbital Mechanics Calculator: Calculator - Elaine › orbital-mechanics-calculator › cal...
Let's get started! Convert Earth-Centered Inertial (ECI) Cartesian Coordinates (State Vectors) to Keplerian Orbital Elements; More Coming ...

Effortlessly convert orbital elements to position and velocity › orbits › elements › convertframe
Changing the Elements Help File. This program allows you to convert between orbital elements and position and velocity vectors in cartesian coordinates. The one ...

Orbital Elements - Ulysses - › web › ulysses › orbital-elements
The Ulysses Orbit: Classical Orbital Elements ... Peter Duffett-Smith's book "Practical Astronomy with your Calculator" (3rd Edition, Cambridge, 1988), or on the ...

Orbit of a satellite Calculator - High accuracy calculation - › exec › system
Calculates the orbital radius and period, and flight velocity from the orbital altitude.

Edit#2: I decided to follow up the idea of using Starry Night to evaluate Solar System mission designs.  The ancient Backyard version of Starry Night I have included an editor to allow input of Keplerian orbital elements, but considering the time frame of that edition (ca 2000), it is not surprising (to me at least) that it didn't work properly.  I am confident that in 20 years, the Starry Night company would have worked out whatever bugs might have existed.

Accordingly, I wrote to their Education division to ask if the current Enthusiast version can support evaluation of mission designs.

This inquiry may reveal a new line of business for the Starry Night corporation, or it may turn out you are already serving it, and I am simply unaware of it.  The ** primary ** purpose of this inquiry is to confirm that the edit-add-keplerian-element-sets feature of Starry Night Enthusiast edition can be used to demonstrate the famous Aldrin Cycler plan for Earth-Mars-Earth transportation.  The over arching purpose of this inquiry is discover if Starry Night Enthusiast edition is capable of assisting an instructor of orbital mechanics to provide a computer assistant for students to complete assignments.
Thanks for your Backyard version, which I have been using since (about) 2000. (th)

Edit#3: In re-reading the collection of citations for element set calculators, I was reminded that the orbit GW Johnson (and Buzz Aldrin) designed were ** Sun ** centric, so any software that would be useful for planning Solar System navigation would ** have ** to be Sun centric.  I'm not at ** ALL ** confident the Starry Night implementation of the Add-Orbit Edit feature supports Sun based element sets.

Edit#4: This reply was received from the Education division of Starry Night:

Your submission was received.  We will be in touch soon.  Thanks!


Last edited by tahanson43206 (2020-06-28 12:42:09)


#77 2020-06-28 08:37:21

From: New Hampshire
Registered: 2004-07-22
Posts: 18,863

Re: Orbital Mechanics

Orbital resonance comes to mind when we say cycler... But part of the issue is control of speed as the loop changes distances. Its similar to free return as well.

The physics principle behind orbital resonance is similar in concept to pushing a child on a swing, where the orbit and the swing both have a natural frequency, and the other body doing the "pushing" will act in periodic repetition to have a cumulative effect on the motion. Orbital resonances greatly enhance the mutual gravitational influence of the bodies, i.e., their ability to alter or constrain each other's orbits. … Cycles.pdf … clers.html

Nasa free return … 018049.pdf


#78 2020-06-28 09:19:00

GW Johnson
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,982

Re: Orbital Mechanics

I'm no expert in orbital mechanics.  I have never understood any of the "cycler" concepts,  including Aldrin's,  because I cannot see how any of them ever come close to Mars,  except at very long-isolated intervals.  That assumes orbit perihelion is at Earth's orbit,  and the period is exactly 2 years,  so that the Earth is always there at perihelion passage.  The apohelion is out near the inner edge of the asteroid belt,  and Mars's period is 688 days,  not any sort of multiple of anything to do with the transfer orbit. 

I may or may not have estimated the transit time to Mars correctly at the 4.26 months.  I dunno,  I am no expert,  and this is by-hand stuff,  not software.  Period is controlled by the semi-major axis length "a",  independent of the perihelion distance you select.  If you select a perihelion inward of Earth's orbit,  then more of your transit path is along the slower portion of your orbit,  and you get a longer transit.  But,  I don't understand how you can make the Earth-orbit rendezvous every two years,  unless that is your perihelion at Earth's orbit.  Maybe there is a way,  I dunno,  but I do not understand how that might be done.

As I said,  I'm no expert in orbital mechanics.  But I do understand the basics.

My computer is on the fritz.  I have no access to my data while using my wife's computer to correspond.  So,  I'm a bit crippled for a while.


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"


#79 2020-06-28 11:01:29

Registered: 2018-04-27
Posts: 2,827

Re: Orbital Mechanics

For SpaceNut re #77 .... thanks for links to Resonance topics. 

For GW Johnson re #78 ...

First ... best wishes for finding a way to bring your trusty system back online!   

Second, thanks for your engaging modesty about your two year orbit suggestion.  It would be fun to (somehow) draw younger folks who are closer to the current state of the art into this forum, but I admit chances of that happening seem small.  Still, as the recent appearance of LiveForever on the forum makes clear, folks who set up an ID years ago may suddenly decide a topic is of interest.

I am hoping the Starry Night folks decide to consider my mission planning suggestion for their software.

If their software can display object motion based upon Sun-centered Keplerian Orbital Element sets (which is not at all guaranteed) then I'd be interested in upgrading from my (nearly) 20 year old (and very reliable) copy of Backyard Starry Night.

What I can visualize (if the program can perform as described) is inserting various orbit designs (yours is of particular interest of course) and setting them into motion using the animation that Starry Night provides.  ** That ** part of their program is one I have used extensively, to discovery when planets such as Mercury will be visible from my location.

From what little I've been able to glean from the Aldrin Cycler write-ups is that the ship's Navigator would ** really ** earn their Galactic Credits by having to perform exceedingly precise maneuvers during object encounters to keep the cycler headed for the next appointment.

From what I am able to pick up from your images in the blog, and your text on the 2 year orbit concept, is that the orbit is designed to ** always ** insure a safe return to Earth, but that the expedited travel time to Mars can only occur when Mars is in a specific location with respect to Earth.  If that understanding is correct, then the orbit can be used no more frequently than the Hohmann design. 

In an earlier post I had inquired about the feasibility of sending a return vehicle on one of your two year orbits ** ahead ** of the mission with astronauts, so that the earlier mission would be passing close to Mars a month after the astronauts arrive at Mars.  However, if the mission plan you have designed can ONLY work once a Mars orbit, then sending the return vehicle ahead of the expedition would appear not to make sense.

There ** is ** another possibility ... the Two year orbit design could be launched ** any ** time (a vehicle without passengers) and just stopped in a position slightly above Mars' orbit, so that Mars trundles along and eventually catches up.  This would put a return vehicle, fully loaded with supplies and fuel, as a resource available for retrieval by the expedition in case it is needed.  If the resource is not needed for a safety return, it could be collected/commandeered for some other purpose.

Edit#1: After re-reading the above, I realized the return vehicle could be sent ** four ** years ahead ... it would complete a full two year cycle and pass by Earth just as the new expedition launches.  The two could then travel in tandem, the one as backup for the other.  Whether there is any advantage over just sending two vehicles is not clear, but at least it is a possibility.


Last edited by tahanson43206 (2020-06-28 11:06:31)


#80 2020-06-29 18:37:58

Registered: 2018-04-27
Posts: 2,827

Re: Orbital Mechanics

Here is a two part reply from Starry Night ...

Part 2

To follow up from the previous reply, our engineers wanted me to tell you that Starry Night will not perform the exact operation that you are seeking.  They want to add it to the list of features for a future update.

Thank you again,


Simulation Curriculum
Starry Night | SkySafari | Layered Earth | BeyondLabz

Part 1

Starry Night Pro (not Enthusiast) is used by JPL and NASA for purposes such as this but they have not provided all of the details. 

Amazing that you are still using SN Backyard!

Thank you

Simulation Curriculum
Starry Night | SkySafari | Layered Earth | BeyondLabz


Last edited by tahanson43206 (2020-06-29 18:39:35)


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