Sending something to the Moon

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Hello,

I was doing some google searching regarding sending something into space / to the moon and I came across a now-closed thread on these boards.

I know it's a far-fetched idea but I'm interested to know what you all think it would take to send something to the moon.

Here are just a few questions I have:

- How hot would the object become exiting our atmosphere?

- How cold would the object become once in space?

- How would you calculate the trajectory of the object to reach the moon?

- How long would such a journey take?

- How much power would you need in order to reach the moon?

- Would you need constant power or could you tap into gravity?

Those are just a few of my questions, of course. I think it's a good starting point, though. I am guessing that this venture would cost far more than I could afford so I'm primarily looking at this from a hypothetical standpoint. (Though there is no doubt, I would lo achieve such a feat!")

Cheers,

Cody

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How hot? Depends on the object itself- The geometry, the materials and how fast it's going.

How cold? Since there is no air in space, it would only lose heat by radiation so it would cool more slowly than it would on earth. Exactly how fast it cools depends on the geometry of the object.

Calculating the trajectory is in principle, fairly simple.

The time would probably take a couple of days, but it depends on how fast you go.

Essentially all of the energy is used escaping the earth. So it depends how fast you go, how big your object is, how much energy you dissipate in heat.

Once you get to a certain distance, the moon's gravity will pull you in the rest of the way. After you escape earth's gravity, almost no energy is required.

In principle, going to the moon is easy. Practically, it's much harder.

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Here are just a few questions I have:

1/How hot would the object become exiting our atmosphere?

2/ How cold would the object become once in space?

3/How would you calculate the trajectory of the object to reach the moon?

4/How long would such a journey take?

5/How much power would you need in order to reach the moon?

6/Would you need constant power or could you tap into gravity?

i numbered the uestions to make it easier to follow.

1/ not very. most of the speed is gained where the air density is so low frictional heating is minimal. 2-300*C would be tops even on the most extreme launch trajectory.

2/ about 120*C on the sun facing side and about -200*C on the space facing side. rotation will minimise thermal expansion/contraction and temperature difference.

3/read up on orbital mechanics. you'll be wanting to do a hohmann transfer from LEO(Low earth orbit).

4/depends, what is the fuel limitations and equipment limitations. the apollo missions took a couple of days. some probes can do it faster, others slower.

5/ depends on the size of the craft.

6/ gravity cannot be tapped into. but you wouldn't need a constant level of thrust.

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Thank you for your responses.

Here are a few more questions:

What is [are] the equation(s) to determine speed, and distance if thrust and mass are known? (Let's say mass is 8 lbs and thrust is 215 Newtons.)

What I'm getting at is, how can I determine how much thrust I will need to reach LEO (Low-Earth Orbit) which is approx. 1500 km above the Earth. I don't want to go too far and have my rocket run outside LEO, at the same time I do not want the craft to come hurtling back to the earth. (Given that it will have a parachute feature for such an occasion, nevertheless, what if that fails???)

Also, as far as sending communication back to the Earth from the craft, how could I manage this? How does NASA do it? Could I use the internet? A private server? Something else?

Cheers,

Cody

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You're require the equation of motion for the rocket, there are many ways of calculating this, the most common way is newtonian mechanics using F=ma, but I'd be tempted to use Legrangian mechanics.

You would calculate the energy required to get into orbit by working out the energy required to get to that hight, and the energy required to maintain the orbit. Of course you'd have to take friction into account to get some realistic numbers, as this would be important.

If it falls in an uncontrolled manner, it will burn up...

You would need to use some radio transmitter/receiver.

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• 1 month later...

i have some accelerometers that i've tested at sonic speeds (less than 1500fps), which record the Cd as the pressure spikes during the flight. assuming a hypersonic vehicle could be built (it's beyond my capabilities), i have no doubt my electronics could record atmospheric pressure changes, as well as changes in the weight/drag of my rocket in relation to the atmosphere at mach 5, 6, 7...etc...the fastest rocket i feel i could make without failure would be mach 2ish. mach 3 would be pushing it, but hypersonic is out of the question for now. (for me anyway).

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if it leaves the hypothetical stage you might want to give the FAA a head's up first before anything leaves the ground

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• 8 months later...

Warning: Noob Question.

What type of thrust would you need to send something into orbit (around earth) from the ground?

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depends on the mass of the object. the more mass the more thrust needed.

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how about a ... meter long rocket weighing in at 25lbs w/o fuel

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won't make it. too small.

iirc for every kilogram of mass you want to put up there you need about 10kg of fuel.

so, a 25lbs rocket(assuming single stage) would need about 250lbs of fuel. although that is a rule of thumb and generally applies to larger rockets, i'm not sure how well it scales.

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wow, are there equations or formulas for this? where?

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that was a very very rough estimate. to get a better one we will need to know the geometry of the rocket, the mass distribution, the type of fuel used, the nozzle design, the exhaust velocity, the orbit it is trying to achieve and where it is launched from and in what direction.

all these and more will have an effect on the fuel required.

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The thrust of a rocket is expressed in N. It's a force, which (if it's larger than the force of gravity) will lead to an acceleration.

The trick with a rocket is therefore twofold:

1. Make enough thrust to accelerate (to overcome gravity)

2. Continue to accelerate long enough to get into orbit, meaning you need to reach something like 6-7 km/s (kilometers per second!).

$\mathbf{T}=\frac{dm}{dt}\mathbf{v}$ (source: wikipedia)

In that formula, $\frac{dm}{dt}$ is the amount of mass you push out of the rocket engine. This can be expressed in kg/s. It can be calculated in many ways, but probably the most common is to simply look at how fast you burn the fuel.

The harder part is to estimate the exit velocity of the gas. This is described pretty well on wikipedia, on the "De Laval Nozzle" site. Wiki's rocket engine nozzle site gives additional info. The formula you need is:

$V_e = \sqrt{\;\frac{T\;R}{M}\cdot\frac{2\;k}{k-1}\cdot\bigg[ 1-(P_e/P)^{(k-1)/k}\bigg]}$

The only thing not explained on the wikipedia site is how to calculate the pressure that is developed from the propellant. But a little googling got me also a site which seems to explain that one: http://www.nakka-rocketry.net/th_pres.html - search for the "steady-state chamber pressure".

That all is needed to calculate the nozzle velocity. From there on it's a matter of $F=m\cdot a$, and you shouldn't forget to correct for the air-friction that you'll encounter while you are in the atmosphere (it is definitely significant enough to take into account, but since the pressure and velocity is not constant, it is another nasty formula).

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• 2 years later...

Well, this is my old thread from a long time ago.

I am still fascinated with the idea of sending something to the moon. My latest idea is to use a high-altitude weather balloon as a launchpad for a small space sounding vehicle.

In other words...

Ascend to ~35km using weather balloon > launch vehicle into hohmann transfer orbit to the moon > retrorockets to slow the payload down before soft landing

Doable?

Cheers,

Cody

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• 1 year later...

Well, this is my old thread from a long time ago.

I am still fascinated with the idea of sending something to the moon. My latest idea is to use a high-altitude weather balloon as a launchpad for a small space sounding vehicle.

In other words...

Ascend to ~35km using weather balloon > launch vehicle into hohmann transfer orbit to the moon > retrorockets to slow the payload down before soft landing

Doable?

Cheers,

Cody

The same idea popped in my head today. Hence finding your post.

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Based upon the date of the OP and of the last post it would appear that even the outline planning for such a project takes in excess of four years.

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The same idea popped in my head today. Hence finding your post.

Here's the problem.

Launching a rocket to the Moon from a height of 35 km would take 10.73645 kg of fuel per 1 kg of rocket mass, vs 10.8623 kg if launched from the surface (assuming a direct to transfer orbit launch). This is only a savings of ~0.125 kg of fuel per kg of rocket.

This also means that for every kg of rocket, your balloon would have to lift 11.73645 kg. The lifting power of Hydrogen when used in a balloon is 1.202 kg/m^3. The density of hydrogen at STP is 0.09 kg/m^3. Thus you would need 0.8788 kg of hydrogen filling your balloon to lift the 1 kg of rocket plus the fuel (this is not even taking into account the weight of the balloon material itself). This is 7 times more than the savings in fuel you would get from launching at 35 km vs. the surface.

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• 1 month later...

Did it occer to anyone that even if you get in to space the moon is around 6 months travel from us in a nasa built space ship. I would be happy if i could just be burried in space, and know that would be a fact for when my time comes.

As for flying to the moon, Liquid Oxegen, Liquid Hydrogen and lots of it.

Edited by yojojo12
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Did it occer to anyone that even if you get in to space the moon is around 6 months travel from us in a nasa built space ship. I would be happy if i could just be burried in space, and know that would be a fact for when my time comes.

It takes 6 months or longer if you use a low-thrust solution such as ion propulsion or solar sails. It took SMART-1 over a year to get to lunar orbit, and that required the vehicle to be firing its engines about 2/3 of the time.

It takes only 3 days or so to get from low Earth orbit to low lunar orbit if you use a high-thrust solution such as was done with the Apollo missions, and that requires the firing the engines for only ten minutes or so.

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• 9 months later...

Here's the problem.

Launching a rocket to the Moon from a height of 35 km would take 10.73645 kg of fuel per 1 kg of rocket mass, vs 10.8623 kg if launched from the surface (assuming a direct to transfer orbit launch). This is only a savings of ~0.125 kg of fuel per kg of rocket.

This also means that for every kg of rocket, your balloon would have to lift 11.73645 kg. The lifting power of Hydrogen when used in a balloon is 1.202 kg/m^3. The density of hydrogen at STP is 0.09 kg/m^3. Thus you would need 0.8788 kg of hydrogen filling your balloon to lift the 1 kg of rocket plus the fuel (this is not even taking into account the weight of the balloon material itself). This is 7 times more than the savings in fuel you would get from launching at 35 km vs. the surface.

Sorry for reviving an old thread but today I was also thinking of the cheapest way to land an object on the moon, take a few pictures and somehow transmit them back.

I was just wondering, why are the savings of fuel so small? I though that the main need for thrust was to get out of Earth's gravity?. Which also brings me to the next question: At what speed does an object need to be traveling after it has escaped Earth's atmosphere, to not get pulled back into Earth? I'm guessing it would either need to be high enough speed to escape Earth's gravity before the velocity becomes negative or to have a thrust that counters mg.

Also realisticly, is it possible to have a motor that is light and powerful enough to pull a 1kg "rocket" into low earth orbit? Or to phrase it differently: (How much thrust power would you need to lift 1kg into LEO?)

I'm not very knowledgeable on these things but have recently been very curious so excuse the newb questions.

Now I know that such a project is pretty much impossible anyway but I do not understand why even consider engines using fuel to send a small object in LEO and maybe even to the moon as surely an engine capable of using fuel will add a lot of extra weight and thus require even more fuel which would increase the weight to a point where the rocket is too big but not big enough to have the capabilities of achieving anything? Is it possible to use a battery/solar powered motor instead?

Finally, lets say that somehow the rocket managed to get to the moon, the cameras managed to take some pictures, how easy would it be to transmit the pictures and detect the radio signals from so far away?

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Sorry for reviving an old thread but today I was also thinking of the cheapest way to land an object on the moon, take a few pictures and somehow transmit them back.

I was just wondering, why are the savings of fuel so small? I though that the main need for thrust was to get out of Earth's gravity?.

at 35 km gravity has only dropped by ~1%

Which also brings me to the next question: At what speed does an object need to be traveling after it has escaped Earth's atmosphere, to not get pulled back into Earth? I'm guessing it would either need to be high enough speed to escape Earth's gravity before the velocity becomes negative or to have a thrust that counters mg.

~11 km/sec Even at the "edge of the atmosphere" you are deep in Earth's gravity well.

Also realisticly, is it possible to have a motor that is light and powerful enough to pull a 1kg "rocket" into low earth orbit? Or to phrase it differently: (How much thrust power would you need to lift 1kg into LEO?)

In terms of thrust, anything over 9.8 N would get you there eventually. However, the less the thrust, the more time fuel just spent supporting the weight of the rocket. It is much more efficient to get up to speed quickly, and for that you need more thrust.

I'm not very knowledgeable on these things but have recently been very curious so excuse the newb questions.

Now I know that such a project is pretty much impossible anyway but I do not understand why even consider engines using fuel to send a small object in LEO and maybe even to the moon as surely an engine capable of using fuel will add a lot of extra weight and thus require even more fuel which would increase the weight to a point where the rocket is too big but not big enough to have the capabilities of achieving anything? Is it possible to use a battery/solar powered motor instead?

As far as lift off and getting into orbit goes, solar energy just won't cut it. the solar panels just can't produce the energy to lift even their own weight. Besides, any rocket still needs reaction mass (something to throw to produce thrust). With chemical rockets, the fuel and reaction mass are one in the same.

Now there is such a thing as a solar powered ION engine. They produce very low thrusts, so they are only useful once you've gotten into a free fall environment. The advantage of an ION engine is that it has very high exhaust velocity, and the higher the exhaust velocity, the more efficient the rocket (the less reaction mass needed to reach a certain speed). But, as I said, the high efficiency comes with low thrust.

Edited by Janus
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• 8 years later...

Hi all my name is Andredi.

I want to piggy back on this conversation and pose it a different way in a question form asking for a proposed solution, rather than discussing the limitations in the hopes that we may come upon a clever idea.

1. How can I send a 1kg object to the moon for under \$10,000.  All crazy ideas welcome.  But seriously, how.  Travel time doesn't matter.  State of the object on landing or "hitting the moon" semi matters as all I want is for it to have the ability to let me know it landed and ping so i can determine where.

Think outside the box please but using existing technology that is plausible.

Also, the 1kg object can have accoutrements to get it to the moon that make it weigh a total of 2.2kg or 5lbs.

I know there is a way.

Looking forward to any ideas.

Also, open to reconfiguring the parameters to make it a smaller object, even nano sized, with the caveat that it has to land and we can determine where it landed and identify it.

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