Why does it take so long to get to Mercury?
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esa.int
So if you don't use gravitational slingshots (which can be modeled as ramming your spaceship into a planet's gravitational field and bouncing off in the other direction), then you need ~3x the delta-v to get to Mercury compared to the moon. And getting to the Moon required one of the most powerful rockets in human history.
In theory, you could just use a rocket that's 3x as powerful as the Saturn V to get enough fuel into orbit to get to Mercury via a direct route. But this runs into engineering issues with creating a rocket that big. Alternatively, you could develop a way to refuel rockets in orbit and then launch 3x Saturn Vs with one space probe and 2 fuel tanks. This is the plan for SpaceX where they will launch a Starship with humans/robots and a Starship with fuel to get enough fuel into orbit for a trip to various parts of the Solar System.
[edited to fix units]
You don't need 16.1 m/sec to get to mercury, there's a 'k' missing. To put it another way: that's off by about a factor of 1000.
Also somewhat fun is the idea of "solar sailing." Both the particulate solar wind and the raw solar radiation have momentum, and by redirecting either one you can get a push. Since increasing / decreasing the "height" of your orbit is actually a function of causing acceleration in the direction of orbit (or opposite that direction), we should be able to change the shape of a vessel's orbit by deflecting outward-streaming sunlight and particles so they're facing along the orbital path (i.e. a 90-degree turn, with a 45-degree-angle mirror). You'd need a lot of surface area for a reasonable amount of delta-V in a human timeframe, but nothing we know of makes this approach impossible. JAXA demonstrated it can work (https://en.wikipedia.org/wiki/IKAROS); the Planetary Society has been looking into it (https://www.planetary.org/sci-tech/lightsail).
Could you put it on one of the poles?
Traveling anywhere outside of Earth's gravity means you are always going to fall into a well, so the smaller the better. The problem with Mercury is to get there you have to fall into the Sun's gravity well.
The sun has the biggest gravity well around, and Mercury is deep down inside of it. If Mercury was bigger it would actually be even harder to get there, since you'd then also have to fall down it's large well too.
A delta-v map will usually include atmosphere as a separate route from the raw energy requirements of entering and exiting gravity wells. Some of the counterintuitive aspects of these flight plans involve “very nice, ok! But how do you plan to slow down when you get there?”
On arrival to the moon or mercury (or Minimus) you have to be able to stop under your own power, which you have necessarily brought in your tanks. And therefore mass.
Too bad the resonant microwave propulsion thing was more likely a poorly designed experiment (acceleration without propellant). But… it violated our understanding of physics, so we’re stuck with bringing our gas everywhere.
Bringing your own gas is fine. The real problem with space travel is you need to bring your own roads. Because what you're short of isn't energy, it's something to push against.
Hey, this is just a share to see if anyone shares my interest. In my spare time, I have been kind of been making a videogame based on this question. (I’ve worked on sims professionally, but it is not most of my career.)
A “floating origin” and using alt dynamics is nothing new, but I’m a bit obsessed with weird sim physics in games. I had been playing around with a kinetic quadracopter dogfighting concept in godot engine for about a year.
Then the “tic-tac UFO” videos resurfaced, and I’ve been having a lot of fun imagining “how those physics would work” if reality happened to be as interesting as what Commander Fravor says he saw.
I doubt the UAP news is what anyone thinks it’s about, but I’ve made little simulations involving everything from spacetime warping to matrix-style “if you fly close to c.”
Sadly, it’s not a very rewarding game concept beyond “woah neat!” Gets me back to why I started programming, though.
I think you should keep exploring it. Maybe this is how folks get an intuition for orbital mechanics.
5.63 m/2 vs 16.1 m/s ?
Neither 5.63 meters divided by 2, nor 16.1 meters per second can be right, from context.
https://space.stackexchange.com/questions/370/can-you-tack-a...
I'm not versed in solar-particle-physics, but I doubt the Bernoulli's principle applies to solar particles.
What you want to do is accelerate either parallel or antiparallel to your orbital velocity (ie. tangent to the orbit). With a solar sail you do this simply by orienting the sail at a roughly 45° angle relative to the sun, allowing you to either accelerate or decelerate depending on which way you reflect the photons (the resulting force will be normal to the sail so in practice solar sailing is more complicated than that, but you get the point).
I'm a bit confused. I have a vague memory that due to the Tsiolkovsky rocket equation the amount of fuel needed to reach a delta-v grow exponentially. How is it possible that you need a 3x bigger rocket to reach 3x the delta-v?
The numbers are completely made up and based on my time playing KSP (https://xkcd.com/1356/) rather than real rockets so change the numbers as you see fit. But my core point is that orbital refueling greatly extends the usable delta-v of a rocket once it's prepared in orbit since it's easier to build 3x of a normal rocket than a rocket with 3x the payload.
This doesn't sound right. Orbital and escape velocities for the earth should depend only on the mass of the earth.
You need about 11-12 km/s to relative to the Earth to escape Earth's gravitational pull from LEO (only a bit more than it takes to reach the moon). Earth itself is orbiting the sun at about 30 km/s. To not get re-captured, the spacecraft needs to be far enough in distance or the difference in velocity needs to be large enough. How much is "enough" depends on the time scale, but for spacecraft we're talking several km/s.
I wonder why the chart doesn't consider the possibility to aerobreak into the sun.
[1] I feel that lithobreaking is slightly more correct than lithobraking.
That's if you want to slingshot yourself to Mercury with no fuel though, right?
If you have fuel then you can keep going to Mercury at a steady 0.1 km/s by constantly firing rockets to maintain that speed, and get there eventually.
You don't need escape velocity to leave the Earth either; you only need escape velocity if you want to maintain orbit without constantly firing rockets.
I think your comment misunderstands inertia and orbital dynamics, but it's hard to follow what you propose doing differently than your basic earth escape + transfer.
I understand the confusion, though, because Δv in a space dynamics context is different than in a physics one. It is not a direct measure of added velocity as you’d expect from kinematics, but instead required impulse per unit of mass in order to achieve the desired outcome, which is ever so slightly different and considers additional impactful variables. Remember, the question being answered is really about fuel, so how much impulse you lose to any number of factors goes into your Δv budget as if you needed the extra anyway.
I’m assuming LEO is 9.4 on the map (won’t load for me for some reason), and if it is, that’s the best number for space people. Physics would instead tell you that it can be done in 8. Different questions.
Apparent size of the sun from the planets http://www.astronoo.com/en/children/sun-apparent-size.html
For high-efficiency chemical propulsion (e.g. hydrogen - which, note, non-storable!) that's about 3.5-4x the exhaust velocity, meaning around 98-99% of your spacecraft's mass needs to be fuel.
For electric propulsion (which has issues because of low thrust and electrical power requirements), it's only about 0.5-1x the exhaust velocity, so only maybe 50-70% of spacecraft mass needs to be fuel.
In any case, it's a LOT.
Good specific impulse plus good thrust is a combo that requires nuclear-explosion-scale energy, ie Project Orion or Nuclear Salt Water Rockets (an option that is, shockingly, even more insane than Orion).
The Parker Solar Probe, for example, pulled the trick off of getting a high-eccentricity orbit around the sun by slingshotting Venus seven times (the transfer orbit from Earth to Venus is about 3 km/s delta-v).
There's a pretty good overview of the math at the Space stackexchange: https://space.stackexchange.com/questions/38612/how-much-les...
-- The Guide
Turns out that missing the Sun is much much easier.
But if your goal is to move the planet farther from the sun because it becomes more luminous and threatens to scorch the earth and you need to move away to cancel it, it is probably doable.
A 1km radius rock asteroid, which is nowhere close to the maximum, weighs an order of magnitude more than this.
According to Wikipedia Mercury weighs about 3.285 × 10^23 kg, about 10^20 times more than most satellites. You'd need much more than 1000 satellites (or have much heavier satellites) to significantly impact the orbit. OTOH, if you'd have sensitive enough instruments you could measure the effect of even a single gravity assist.
Summary is no for Jupiter, even the entire planet Earth wouldn't affect it that much. Mercury is much smaller though, so it might be possible to make a significant change, though you're probably still talking about sending a significant fraction of the mass of the whole planet Earth.
You might be able to alter the orbit like that without destroying the Earth if you figure out how to gather a ton of mass already in space, asteroids or something maybe. But now you've got to figure out how to redirect their orbit into the exactly right one without throwing most of their mass around, and do it with a reasonably-sized mission from Earth.
So, if each satellite changes speed by 10 km/s, then Mercury's orbital speed will change by 10^-14 m/s, or about 0.03mm/century.
Doesn't seem like we'll notice it.
(If you're curious about the opposite direction, of objects with the least angular momentum, that would be either bosons, or Texas's four-day-long "rotating" power outages.)
Of all the planets, which is Earth closest to on average?
:)
Shurely shome mishtake?
The purpose is, so folks can look up delta-v and start to understand. It's not necessary to recapitulate everything on the web in a post. For instance I google 'orbital mechanics delta v' and the whole story is right there for the taking.