ramana wrote: ↑24 Aug 2023 04:05
AmberG and team Kudos for high level discussions and explaining intricacies.
Ramana
Ramana and others ..Thanks.
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Let me comment on few of the items discussed here .mainly to provide some insight into basic math/physics/science of orbital mechanics.. again ignore if you wish. (will answer honest questions to clarify but for basic concepts see any good text book)..
Few questions/discussion are centered on the extra fuel - can that be used to bring PM to Earth etc..
1. With lunar gravity very low, returning to earth should consume much less thrust. What would be the ratio , is it 1:100?
2. Entering back to earth, how much thrust ratio needed compared to escaping the earth's gravity, my understanding is huge thrust is used for escaping the earth's gravity.
3. How easy it would be to launch rocket from moon to outer space compared to launching from earth, with moons low gravity advantage, provided we can generate rocket fuel from moon's water/gas/elements.
4. In case we make moon habitable, does building international space station become redundant?
First, let's cover some fundamental concepts. Honestly, some of the comments provided are not entirely accurate (and some, in my opinion, are quite peculiar) when it comes to basic physics.
The speed of the spacecraft in its current orbit around the Moon is approximately 1.6 km/s. This orbit is polar, meaning it is nearly perpendicular to the ecliptic plane (at around 90 degrees) and also nearly perpendicular (within 5 degrees) to the Moon's orbit around the Earth.
It's important to note that this velocity is a vector quantity. You cannot simply "add" a value of x to get "1.6 + x" in any direction.
The often-mentioned "escape velocity" (around 2.4 km/s) allows a spacecraft to break free from the Moon's gravitational pull. However, it's worth mentioning that even after escaping, the spacecraft would still follow an orbit around the Sun that is quite similar to Earth's and the Moon's orbit. In other words:
To travel to other planets, such as Mars, a spacecraft would still require a velocity of nearly 30 km/s. So, for interplanetary travel, a significant amount of fuel is still necessary.
If the intention is to return to Earth, thinking that a certain amount of fuel is needed to transition from 1.6 km/s to 2.4 km/s
misses a crucial point.
This analogy is akin to saying that all you need is a certain amount of energy to hit a six in cricket. You actually need precise timing (just as in scoring a hole in one in golf).
(Not only is an adequate change in velocity (delta-v) necessary, but the spacecraft must be launched in the correct orbital plane. Even more importantly, the timing has to be impeccable, ensuring that when the spacecraft reaches its highest point (apogee), it encounters Earth. This is incredibly difficult to achieve – hence why many of us refer to ISRO's orbit calculations as "magic," as timing is exceptionally complex.)
Regarding the CH3PM's rockets, I'm not well-versed enough to calculate fuel requirements accurately,
but I can calculate delta-v. As for timing calculations, those are exceedingly challenging. I would venture to guess that the practical chances of achieving the required timing are less than one in a million. (While ISRO might surprise me, I remain skeptical.)
Lastly, just as with Lunar Orbit Insertion (LOI), there must be a burn close to Earth. This maneuver comes with its own challenges – if the angle is too shallow, Earth's atmosphere could send the spacecraft back into space, akin to a pebble skipping on a lake's surface. Conversely, if the angle is too steep and there isn't a reliable heat shield, the spacecraft could burn up upon reentry.
--- Just for perspective:
TEI (Trans Earth Injection) burn for Apollo 11 lasted almost 6 minutes on 45,000 N engines using nearly 1200 Kg of fuel.
(And I am not counting mid course correction and breaking near earth fuel)
And for making the timing right ..( all that calculations *literally* took months of computer time (and all timing was predetermined) in 1960's when computers were not very fast and on-board computers had only 4K of RAM
Now ISRO can do magic, gravity can assist to save fuel, but WHY?
IMO we should be delighted that CH3PM will be there for years to come -- doing its SHAPE thingie...
May be some time in future ...it could be moved to a safer orbit or join a moon space station in the museum section .. who knows..
Now ISRO can do magic
3. How easy it would be to launch rocket from moon to outer space compared to launching from earth, with moons low gravity advantage, provided we can generate rocket fuel from moon's water/gas/elements.b][/b]
We will still need delta-V of about 30 Km/sec to, say go to Mars (unless, we do gravity assist with Moon or Earth etc) .. but from earth we need around 8 km/sec just to get to a space -station.. so savings are tremendous... besides since there is no air on moon, it is possible to have ground based shooting guns type launch to provide more efficiency than rockets. (On earth, you can not shoot with high velocity as the friction from air there ... so you need 2 or 3 stages...))
pic.twitter.com/xXkMWwLKwG