Author: Tom Nardi / Source: Hackaday
On February 22nd, a Falcon rocket lifted off from Cape Canaveral carrying the Indonesian communications satellite Nusantara Satu. While the satellite was the primary payload for the mission, as is common on the Falcon 9, the rocket had a couple of stowaways. These secondary payloads are generally experiments or spacecraft which are too small or light to warrant a rocket of their own such as CubeSats.
But despite flying in the economy seats, one of the secondary payloads on this particular launch has a date with destiny: Israel’s Beresheet, the first privately-funded mission to attempt landing on the Moon.But unlike the Apollo missions, which took only three days to reach our nearest celestial neighbor, Beresheet is taking a considerably more leisurely course. It will take over a month for the spacecraft to reach the Moon, and it will be a few weeks after that before it finally makes a powered descent towards the Sea of Serenity, not far from where Apollo 17 landed 47 years ago. That assumes everything goes perfectly; tack a few extra weeks onto that estimate if the vehicle runs into any hiccups on the way.
At first glance, this might seem odd. If the trip only took a few days with 1960’s technology, it seems a modern rocket like the Falcon 9 should be able to make better time. But in reality, the pace is dictated by budgetary constraints on both the vehicle itself and the booster that carried it into space. While one could argue that the orbital maneuvers involved in this “scenic route” towards the Moon are more complicated than the direct trajectory employed by the manned Apollo missions, it does hold promise for a whole new class of lunar spacecraft. If you’re not in any particular hurry, and you’re trying to save some cash, your Moon mission might be better off taking the long way around.
Beginner’s Orbital Mechanics
Before we can understand the different methods used to reach the Moon, we need to know a bit about how spacecraft navigate. More specifically, how a spacecraft in orbit around one body can transition into orbiting around another. As you might expect, being literal rocket science, these concepts can be a bit tricky to master.
As such, we’re going to take a few liberties here to make things a bit easier to wrap the mind around. For one, let’s forgo the third dimension entirely and imagine that both the starting and destination orbits are on the same plane. Further, let’s say that the orbits are nicely concentric, that is, the orbit we’re looking to transition into is essentially the same as our current orbit, just at a higher altitude from our starting position.
Obviously the Moon does not have a perfectly flat and circular orbit around the Earth, but that being said, it’s not a terrible analogy. Once the basics of an orbital transfer are understood, it’s not much of a leap to see how they could be applied to the Moon’s actual orbit around our planet. Though we’ll leave applying these concepts to more distant destinations in our solar system as a exercise for the reader.
The other important thing to understand is how changes in velocity effect the orbit. When velocity is increased in the direction of travel, the altitude of the orbit on the opposite side of the burn is raised. The altitude and position at…
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