You are not logged in.
For GW Johnson re return of Austin Stanley after decades (2002 > 2008 (long pause) 2025 (17 years)...
I've started reading the posts by Austin Stanley from 2002, and am still ** in ** 2002 when I found this:
https://newmars.com/forums/viewtopic.php?pid=6265#p6265
Please comment upon this interesting idea. I have no idea if adding thermal energy as he suggests would make any difference.
Since we (generally) need propellants to be in a liquid state (ie, extremely cold) the idea would probably not help in practice.
However, that aside, I'm hoping you will comment upon the general idea of adding thermal energy to a chemical combustion process.
(th)
Offline
Like button can go here
At Sunday's Google Meeting, GW Johnson showed us work he is doing in planning Lunar missions, including ones to the poles.
This post is a follow up .... it occurred to me that an ordinary gyroscope might be helpful to someone trying to understand how to do an orbital plane change of 90 degrees, from equatorial (like Apollo) to polar. I asked Google's Gemini to consider the question, and if found a web site where we can view a video about orbital plane change.
Conversation with Gemini
Plane Change Gyroscope Teaching Aid? - Hi Again! Thanks for all your help with numerous previous requests! This one should be fun for you (I hope so). I am trying to help a professor of aerospace engineering (retired but very active) explain how to do a plane change while circling the Moon in an equatorial orbit, such as the one used by Apollo. The goal is to show how to land at the poles. Ordinary paper drawings don't quite seem to work for this. It occurred to me that an ordinary toy gyroscope, or perhaps even a spinning bicycle wheel, or perhaps something you can think of might work. Perhaps you can find an online animation that shows how to do a plane change while in orbit? The Professor is trying to explain that to do a plane change at the Moon, it is best to use an elongated orbit (such as NASA's Gateway orbit) to most efficiently accomplish a plane change. However, ** then ** we are hitting a snag as we contemplate the rocket burn needed. The professor is arguing for a 45 degree change as sufficient to reach the poles. In preparing your response, please show where the Lunar poles are located (as we look at the Moon from Earth). Many readers may not know where the poles are located.
Query successful
That is a fantastic and challenging problem for a teaching aid, especially connecting the physics of a gyroscope to orbital mechanics! You are absolutely on the right track; the principle of a spinning gyroscope resisting a change in the direction of its spin axis (rigidity in space) is the perfect analogy for understanding an orbital plane change.
Here are a few thoughts on the teaching aid and the orbital mechanics of a lunar plane change:
Gyroscope as a Teaching Aid
Ordinary Toy Gyroscope: A regular spinning gyroscope works well for a qualitative demonstration of rigidity in space. Once spinning, if you try to tilt its axis, it will resist and precess (move in a direction 90 degrees to the applied force).
Analogy: The spinning wheel represents the spacecraft in orbit. The plane of the wheel is the orbital plane. The force you apply to the axis represents the rocket burn's thrust. For a plane change, the thrust needs to be perpendicular to the velocity vector (i.e., directed "out" of or "into" the orbital plane). The gyroscope's resistance mirrors the massive ΔV (change in velocity) cost of a plane change.
Spinning Bicycle Wheel: This is a classic and very dramatic demonstration, better illustrating the magnitude of the angular momentum. Hold the wheel by its axle while an assistant spins it quickly. Try to tilt the axle; the force of precession is much more pronounced than on a toy gyro.
The key limitation of a simple gyro is that it only models a pure plane change where the speed is kept constant. In reality, a burn changes both speed and direction.
Orbital Plane Change Efficiency and the Gateway Orbit
Your professor is correct about using an elongated, or elliptical, orbit for efficiency. This is a crucial concept:
Minimizing ΔV: The rocket burn (ΔV) required for a plane change is directly proportional to the spacecraft's orbital velocity (v) and the angle of the change (Δi), as approximated by the formula: Δv≈2vsin(2Δi).
The Advantage of Apoapsis: For a fixed change in inclination (Δi), the required ΔV is minimized by performing the maneuver where the orbital velocity (v) is at its absolute minimum. In an elliptical orbit, the velocity is slowest at the apoapsis (the point furthest from the central body, which is the Moon in this case).
Gateway Orbit Analogy: The Gateway (NRHO) is a highly elongated orbit designed to pass over the lunar south pole region. This makes the ΔV for a plane change at apoapsis much lower than it would be from a low circular (like Apollo's equatorial) orbit. Using a high, elongated orbit for plane changes is often referred to as a Bi-Elliptical Plane Change.
Lunar Poles as Seen from Earth
To help non-experts, here is where the lunar poles are:
Lunar North Pole: Appears at the top of the Moon when viewed from Earth's Northern Hemisphere.
Lunar South Pole: Appears at the bottom of the Moon when viewed from Earth's Northern Hemisphere.
Since the Moon is tidally locked, we always see the same face. The poles are on the edge, or limb, as viewed from Earth, though slight wobbling (libration) allows us to see slightly more than 50% of the surface over time. The rotation axis is very nearly perpendicular to the plane of the orbit, so the poles are not easily visible face-on. The famous landing sites for the upcoming Artemis missions (and the current focus for resource exploration) are in the South Polar Region. A 45-degree inclination change from an equatorial orbit (like Apollo's) would get a spacecraft well into the mid-latitudes, and from a low lunar orbit (LLO), a 45-degree change would definitely allow a landing at 45 degrees latitude. To land at the pole (90-degree latitude) from an equatorial orbit (0 degrees inclination) requires a 90-degree plane change, which is very expensive in ΔV. However, a 45-degree change could be the final maneuver after a much larger inclination change was performed efficiently at a high apoapsis, or the 45 degrees might be the remaining angle to reach a target near the pole from a highly inclined, non-equatorial orbit.
This video provides an academic overview of the plane change maneuver, including the ΔV calculation, which may be helpful for your professor's detailed explanation. Plane Change Maneuver - Space Mechanics
Plane Change Maneuver - Space Mechanics - YouTube
AHMAD SALAHUDDIN BIN MOHD HARITHUDDIN / ENG · 6.8K views
https://www.youtube.com/watch?v=Xzl6gBcwtHI
Thank you for your explanation, for identification of the locations of the poles as seen from Earth, and most of all, for the gift of a link to a video about plane change in orbit. I will post your reply so everyone (who is interested) can see it.
That's wonderful! I'm glad the information was helpful, especially the video link. Teaching complex orbital mechanics is a challenge, and I hope the combination of the gyroscope analogy and the orbital mechanics concepts helps the professor illustrate this critical maneuver.
Good luck with the class and the project!
(th)
Offline
Like button can go here
Here is an image prepared by GW Johnson to show what is involved in changing plane at the Moon.
This image is part of a paper GW is working on, and he was willing to share it here for those who might be interested.
Since this is a pre-publication release, feedback is welcome.
http://40.75.112.55/phpBB3/download/file.php?id=48
(th)
Offline
Like button can go here
Repeating to ask for feedback from NewMars
Dr. Johnson has asked for feedback on this image. The question is whether you think this image would help a person without prior exposure to orbital mechanics to understand how it is possible to change the plane of rotation about the Moon by 90 degrees.
***
Here is an image prepared by GW Johnson to show what is involved in changing plane at the Moon.
This image is part of a paper GW is working on, and he was willing to share it here for those who might be interested.
Since this is a pre-publication release, feedback is welcome.
http://40.75.112.55/phpBB3/download/file.php?id=48
(th)
Offline
Like button can go here