Flight Profile:
Okay, here’s the concept. If you have ever tried to play paddle-ball, the one that has the rubber ball attached to the paddle with an elastic cord, you’ve seen this maneuver.
If you are like me, when you try to hit the ball on its first return, it zooms past, and then comes back with even more momentum when you pull it back with the elastic cord.
Well, that’s what we’re going to do with the Moon. I know it looks like a ball, but it’s going to be our paddle.
We’re on the ball, or at least I hope we are. We don’t want to actually impact the Moon, we want to go zooming past.
Our first pass going around the Moon will begin stretching our tether. As we get farther and farther from the Earth/Moon system, the gravitational bond will be stretched more and more, storing a great deal of potential energy.
Then when we return toward the Moon, it will already have moved in its orbit around Earth. It is that motion which will give us extra velocity toward Mars. We’re going to steal some of the Moon’s momentum.
That’s only fair. It has been stealing Earth’s momentum for millennia, in the form of tides. The transfer of momentum between the Earth and the Moon slows the Earth, and pushes the Moon higher in its orbit.
Our little theft will not be noticeable, or even measurable, but it will give us a kick in the pants as we go by on the second loop. We won’t feel it, for we will be in free fall, but it will make our trip to Mars much faster.
The free fall referred to above will not mean we have to hang on to things. We will still be rotating for artificial gravity. It just means we will be going faster without expending reaction mass.
There is a price to pay, of course. We will arrive in the Martian sphere of influence with quite a bit of extra momentum. Our cometary orbit path will have to be modified by rocket propulsion after we get there, rather than before.
You may well ask, why hasn’t NASA done it this way? The answer is, NASA doesn’t think this way. To use reaction fuel at the end of the journey, rather than at the beginning, is counter-intuitive to everything they are familiar with.
“Of course you have to use a lot of fuel at the beginning, and every pound of fuel you need at the end of the journey has to be purchased with ten to a hundred pounds of fuel at the beginning. You can’t re-write the Laws of Physics!”
Ahem. Well, no. We’re not rewriting physics. We’re just using some different applications of it. The Earth-Moon system is a double planet. If you could imagine a bar of iron stuck through their respective bodies, and extended out into space, you would see that the end of it, way beyond the Moon, would be whipping around at a pretty good clip, even though the Moon orbits only once a month.
If you launched your vessel from the end of that imaginary iron bar, it would already have a good velocity, and it would come at the expense of the angular momentum of the Earth-Moon system.
Clear as a bell, right?
Okay, we swing around the Moon sometime tonight, giving a new use for a New Moon, and we head off toward that balance point in space where we would be equidistant from the attraction of the Earth and Moon, and the gravitational attraction of the rest of the Universe.
Then we will slow, and stop, and gradually begin falling back toward the Earth again. We will supplement that acceleration with a steady rocket thrust, and build up a tremendous velocity, spurred by the gravitational attraction of the Moon.
I’m using the Moon in particular because it has so much less orbital debris floating around it. It would be virtually impossible for a vessel this size to do a slingshot maneuver around Earth without impacting something in orbit. That would not be a good thing.
So we’ll use the Moon as our paddle, and its gravity as our elastic tether, until we build up so much speed that we just go zipping along toward the next planet out, which would be Mars.
My calculations indicate we should arrive sometime in late April.
Then we’ll have some fun, as we try to slow down enough to be captured by the Martian gravity. At least it’s a quicker trip.
Piece-of-cake, right? Child’s play, really.
Okay, the best view of the Moon will occur after we pass it, when it will be brilliantly illuminated by the Sun.
We’ll go from a dark, New Moon to a bright Full Moon in a matter of seconds. Nail-biting seconds, for some. No need to worry, though. If we impacted, we would all be killed before we had a chance to blink, even.
After we zip past the Moon, we’ll have a few days to set up the rotation of the Thrust Ring, for our reverse thrust procedure, but I’ll explain that later. Just continue with your regular chores, or vacation activities.
Wellnow! I feel relieved...NOT!!!
I'm a very nervous passenger, Bob, due to my car accident a bazillion years ago...I could have gone the entire trip without reading that...:o|
Sounds complex, but I'm sure you'll handle it excellently!
I have to go mediate a dispute about crayons. Martyred sigh.
"No need to worry, though. If we impacted, we would all be killed before we had a chance to blink, even."
What me worry?
Happy New Year NmB!
Not fair, and not true, actually -- NASA's looked at using the moon for gravity assists, and has actually used it before. The downside is that for the present, NASA is constrained to launching from the ground, and using the moon would unduly constrain the launch window to a few days/month, which is undesirable when you've already got a very tight launch window to begin with.
I've seen them do some truly mind-boggling gravity assist profiles -- for example NASA has used them extensively with the Cassini and Galileo missions around Saturn and Jupiter, respectively. (And FWIW, they used gravity assists from Venus and Earth to get to the outer planets in the first place...)