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Min. Energy needed to launch to the sun?


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How much energy would it take to dump something on the sun?

 

So basically what does it take to bring something in lower orbit, low enough to make it eventually drop on the sun?

 

Using other planets/moon allowed. :cool:

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To drop it directly into the Sun you would need to change its velocity by nearly 30 km/sec. This works out to 450000000J per kilogram.

 

If you tried to use Venus for a gravity assist, it would take an initial change of velocity of 4.8 km per sec to drop to Venus' orbit, but even with a perfect 180° assist (not possible) you would only make up about 6km per sec, leaving you about 19 km/sec short of falling into the Sun. I suppose you could use multiple passes in order to trim velocity at each pass, but this would take very good timing and would be a long drawn out process.

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If you tried to use Venus for a gravity assist' date=' it would take an initial change of velocity of 4.8 km per sec to drop to Venus' orbit,...[/quote']

 

multiple passes by venus is a good idea to reduce the propulsion cost

 

Janus, could you please check your 4.8 km/sec figure?

I believe it is more like 2.5 km/sec

 

that would be delta-V to get started on a hohman transfer ellipse to fall in and flyby Venus

I think it is something around 2.5, maybe a little less, depending on details.

 

it is an intriguing possibility that gravity assist(s) from venus could slow the craft enough that it could reach mercury and use a mercury gravity assist

 

I know mercury does not have much mass but it is very dense and so one can fly close, and gravity assist might be worth something. a deflection into the sun maybe

 

why does the guy want to fall into the sun?

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why not just launch it at the sun?it doesn't have to go too terribly fast, just enough to leave orbit. gravity should do most of the work. it would take time, but it would work.

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Why not just point it directly at the sun, and not worry about orbit transfers?

 

to point a spacecraft's velocity vector directly at the sun is very expensive in rocket fuel because it will cost a delta-vee of at least 30 km/sec after leaving earth

 

(after leaving earth the craft still has the earth's 30 km/sec approx. circular orbit velocity. that must be killed and a small sunwards vector given, so the cost is 30+ km/sec)

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why not just launch it at the sun?

 

same answer as before

would need a 30+ km/sec change in velocity, that is a huge expenditure,

 

currently space missions like Galileo to Jupiter and Cassini to Saturn only require fuel enough to achieve a much smaller change in velocity, like 3 km/sec

 

Galileo got to Jupiter by slowing down by just a few km/sec and drifting in towards venus, hooking a gravity assist from venus, twice hooking a gravity assist from earth, and by then it was going fast enough to swing out to Jupiter. So the cost of getting to Jupiter was around 4 km/sec (I am not sure about the exact figure)

even that takes a considerable big rocket

it aint cheap just to get a few km/second change in velocity,

 

so your plan, of changing velocity by 30 km/sec so he could drop into the sun would be hellishly expensive in taxpayer dollars

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Can't we use the moon in any way?, why not?

 

Why I ask?, it's an interesting question because there are endless solutions, one better than the other.

Would a computer program be able to calculate it, I mean the min. cost? (including choosing time and route)

 

P.S 'the guy' has the name 'Kedas' here :)

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Can't we use the moon in any way?' date=' why not?

 

Why I ask?, it's an interesting question because there are endless solutions, one better than the other.

Would a computer program be able to calculate it, I mean the min. cost? (including choosing time and route)

 

P.S 'the guy' has the name 'Kedas' here :)[/quote']

 

OK Kedas, it sounds like you ask just because it is an interesting question to you, multifaceted. Not for a practical reason.

 

as a academic matter, any massive body can be used for its gravity

and how much good you get from it depends on

 

its mass

its density (which determines how close you can come to the center of mass in a flyby)

its velocity relative to where you are coming from and your destination.

 

I have thought about using the moon too, like you, but it does not seem very attractive to me because

 

it is low mass

it is only moderately dense (some 3.5 times water)

it is not moving very fast relative to earth

 

 

if one is leaving earth then the moon is not interesting because it is going very slow relative to earth, we want speeds that are at least several km/second but hopefully tens of km/second

 

if one is passing thru the Earth-Moon system from the outside, and one wants to hook a boost, then obviously the Earth is better than the moon because (both are going essentially the same speed of around 30 km/s and) the Earth is 81 times more massive and also more dense than the moon.

 

so the moon is not a very attractive prospect for any gravity assist

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to point a spacecraft's velocity vector directly at the sun is very expensive in rocket fuel because it will cost a delta-vee of at least 30 km/sec after leaving earth

 

(after leaving earth the craft still has the earth's 30 km/sec approx. circular orbit velocity. that must be killed and a small sunwards vector given' date=' so the cost is 30+ km/sec)[/quote']

 

Ooh, yeah. Forgot about that minor term. Serves me right for pretending to live in the earth-centered-inertial coordinate system of timekeeping. :rolleyes:

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multiple passes by venus is a good idea to reduce the propulsion cost

 

Janus' date=' could you please check your 4.8 km/sec figure?

I believe it is more like 2.5 km/sec

[/quote']Oops, Forgot yo take a squareroot while solving.

 

that would be delta-V to get started on a hohman transfer ellipse to fall in and flyby Venus

I think it is something around 2.5, maybe a little less, depending on details.

 

it is an intriguing possibility that gravity assist(s) from venus could slow the craft enough that it could reach mercury and use a mercury gravity assist

Well, a single pass wouldn't be enough, and the problem with multiple passes is that the more passes you add, the smaller your initial launch window is and the less room for error you have. Add in the fact that your last pass has to put you on a trajectory that intersects Mercury, and I think you'll find that available launch windows are few and far between.

 

I know mercury does not have much mass but it is very dense and so one can fly close, and gravity assist might be worth something. a deflection into the sun maybe

 

 

Even if Mercury was dense enough to allow for a hairpin, 180° assist, a single pass would not be enough. Adding multiple Mercury passes on top of multiple Venus passes would even further restrict available launch windows. At some point you have to ask when do lack of launch windows outweigh the saving in fuel.

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I surmise he's hoping to halt global warming by switching to nuclear power and is looking for somewhere to dump the radioactive waste.

 

If that is the case then why not just throw it out of the system entirely? As stated it takes a delta v of 30km/sec to drop something into the Sun. It only takes a little over 12 km/sec to attain escape velocity from the Sun. Use Jupiter as an assist and you can bring that down to under 6 km/sec. (You might not want to use the Galileo method, people screamed enough about a small nuclear power plant, imagine how they'd howl if it was a load of nuclear waste.)

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Why not just point it directly at the sun, and not worry about orbit transfers?

 

Directly? You mean where the sun "is" or where we see it. The image we have now of the sun depends on light that left the sun 500s ago. It's a similar problem to shooting at a transverse moving target. I imagine some careful calculating would be required.

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Even if Mercury was dense enough to allow for a hairpin' date=' 180° assist, a single pass would not be enough. Adding multiple Mercury passes on top of multiple Venus passes would even further restrict available launch windows. At some point you have to ask when do lack of launch windows outweigh the saving in fuel.[/quote']

 

I heartily agree about the rarity of launch windows and the difficulty of setting up a mission to take maximum advantage of encounters with other bodies. the impracticality here is partly due to Kedas.

 

My understanding it that he posed it as an academic problem, not a practical one.

 

Can't we use the moon in any way?' date=' why not?

 

Why I ask?, it's an interesting question because there are endless solutions, one better than the other.

Would a computer program be able to calculate it, I mean the min. cost? (including choosing time and route)

...[/quote']

 

I asked him and he didn't give any practical purpose (like waste disposal). I gather he simply wanted to know the minimum possible [delta-V essentially] to reach the sun! I suppose having to wait for 100 years for an ideal launch window would be no obstacle to him and that he is willing to assume highly accurate navigation. He wants to know, or indicates so anyway, the mathematical minimum cost of hitting the sun.

 

I can't calculate this, can only speculate and make rough estimates. wouldnt worry about infrequent launch windows though.

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If that is the case then why not just throw it out of the system entirely?

 

I agree with the spirit of Janus' post, but would suggest plunging the waste into Jupiter's atmosphere.

Humans will never want to live on Jupiter and it would make no difference anyway. The planet already has radioactivity and it has a huge volume.

 

there are three points:

 

it is easier (less costly) to hit Jupiter than to hit the sun

 

Jupiter and the sun are very similar destinations (big orbs where no one wants to go)

 

disposing anything toxic in space is risky because of the danger of a failed launch, so you get dispersal in the earth's atmosphere------so there is that danger regardless of what your planned target is

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You can't incinerate nuclear waste. It remains radioactive no matter how hot you heat it.

I'm speaking metaphorically. Also note that real 'incineration' is not 'so much cleaner' than conventional methods for conventional waste.

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