Question on landing weight to fuel consumption. please check

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Question on landing weight to fuel consumption. please check

Post by Engineer » Thu Dec 08, 2011 8:27 pm

Well, I decided just to make a quick reference table on the Apollo 17 stats on the weight landed to the amount of fuel used to use as a basic reference on how much weight we can land (about) on the lunar surface using the falcon heavy. using the Apollo 17 mission, I think I found the ratio for their orbit of 47 Nautical miles. please note that I am not going to include the assent stage fuel consumption because the probe, geck, or what ever is going to be sent there won't be returning.
total weight of the LM descent with water and fuel: 23113 (from wikipedia)
total weight of the LM assent with water and fuel: 10385 (from wikipedia)
total fuel sent in Apollo 17 landing: 19,564 (http://history.nasa.gov/SP-4029/Apollo_ ... Status.htm)
total LM weight: 33,498
total fuel weight:19,564
total ratio: 1.7
in other words, it would take 1 pound of fuel to land 1.7 lbs on the moon. so in total, with its on weight included, only a 7th the mass of the fuel can be landed. this sounds wrong to me, so please check it to make sure.
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Post by RaresH » Fri Dec 09, 2011 4:51 am

As far as I know the mass ratio corresponds the percentage of fuel to try mass. So take your number of 1.7 that means that for every 1ton of LM ther's 1.7tons of fuel

Is the LM weight of 33,498 the total weight including fuel?

From my references R=M/Me or R=(Mpt/M)+1

So in this case an 33,497(mass w/propellant) / 13,933(Mass empty) = 2.4(mass ratio)

so for every kilo of Lunar Lander you need 2.4 of propellant.

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Post by Engineer » Fri Dec 09, 2011 7:08 am

thats highly inefficient. are you sure that isn't backwards? 2.4 lbs for every lb of fuel? if that is so, the total weight we can land on the moon (assuming the weight loaded is 15k) we'd only land 6250 lbs on the moon. I think. math was my favorite subject, but could never grasp some concepts.
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and yes, the total weight was with fuel and water, but not sure if it included humans and supplies.
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Post by RaresH » Fri Dec 09, 2011 7:55 am

I did indeed mean 1lb for every 2.4lbs of fuel. But don't take my word for it since my math was not my favorite subject, haha.

I get my figures from Atomic Rockets. Maybe you've heard of the site; http://www.projectrho.com/rocket/engine ... d--Delta-V

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very upset now

Post by Engineer » Fri Dec 09, 2011 6:32 pm

so, with room for error, only 3 tons can be landed on the moon with the heavy. that using the figures from the Apollo missions, of course, but still. very maddening. if that is the best they could do, and with scientific improvements all in all, maybe that number can be 6500. that's what I would place my hopes on. some times I wish the conservation of momentum wasn't real. so, that will include the lander, the payload, and the guidance computers. not exactly a Saturn 5, but restrictions = innovation.
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Post by joertexas » Sat Dec 10, 2011 12:18 am

The best way to calculate performance for space vehicles is by the amount of Delta Vee a particular maneuver requires. For example, the Apollo landers had something like 2.3km/s of fuel, and used about 1.9 - 2.1km/s during their landings. The weights involved can be derived from there, starting from how much thrust the engines put out.

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This is a relatively stupid question

Post by Engineer » Mon Dec 12, 2011 5:29 pm

is there a current list of all engines and their output exhaust out put or is it a search and hope to get lucky?
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Post by joertexas » Tue Dec 13, 2011 5:21 am

[quote=""Engineer817""]is there a current list of all engines and their output exhaust out put or is it a search and hope to get lucky?
:cool: [/quote]

I have a spreadsheet on rocket engine specifications, but I have no clue where it came from..

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:::Brain leaking out of ear into puddle on floor:::

Post by Engineer » Tue Dec 13, 2011 6:53 am

where at? I could defiantly use that. I've been racking my brain over delta v and other aspects of landing equipment on the moon. Its beyond my level of understanding at the moment but I haven't given up on it.

this is what I've come up with so far in terms of information. the link given to me (http://www.projectrho.com/rocket/engine ... d--Delta-V) gave the the delta V equation and a basic understanding of it. what I can't figure out is: isn't this equation for getting off the ground? I'm trying to get an accurate answer on what we can land from a falcon heavy. not what we can lift off.

second, I found a spreadsheet calculator so to speak here (http://www.asi.org/adb/06/07/03/01/leo- ... ample.html) this is the exact opposite of what I needed. well, opposite is a little off. perhaps backwards is better. my questions on this are the delta V is preset to 20,000. :confused: I'm wondering if you could explain that to a dumb person. (not that I know any).

Third, from what I understand, the 16000 lbs to tli is basically meaning on its way to the moon. (from Wikipedia on a chart of orbital launch vehicles) however, looking through the references at number 35 I came to a pdf document from space X that was sited for the information on the TLI numbers. I did not see those numbers at all. I have downloaded the PDF for future reference. is there a specific ratio of leo to tli? in terms of fuel and as such some on can point me at? :confused:

lastly, I require a basic orbital mechanics equation. this is completely concerning parking breaks. what can I put in lunar orbit from the weight in TLI?:confused:

I know the general consensus is mining right off the bat, but I'd just like to see for myself the options in terms of weight are.

And if there is an answer already made for my main question, don't tell me it just yet. I'd like to try figuring this out with some help. Thanks in advance.
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Post by RaresH » Wed Dec 14, 2011 3:07 am

That first link I sent you is the Delta-V equation that's used to determine Delta-V budget for any given ship.

The equation for getting off the ground and escaping a planets gravity well is sqrt[(2*G*Pm)/Pr]. The meanings for the letters in the equation and other useful equations can be found in the mission page here; http://www.projectrho.com/rocket/mission.php.

In our case we can just use various delta-v charts available online to derive our Delta-V mission budget; http://www.projectrho.com/rocket/missio ... lta-V_Maps

And coupled with exhaust velocity of any available engine we can then guess what mass ratio is best for our Mission. It's pretty cool once you get a grip on the bath.

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