Why does it take so long to get to Mercury?

<a href="https:&#x2F;&#x2F;www.reddit.com&#x2F;r&#x2F;space&#x2F;comments&#x2F;1ktjfi&#x2F;deltav_map_of_the_solar_system&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.reddit.com&#x2F;r&#x2F;space&#x2F;comments&#x2F;1ktjfi&#x2F;deltav_map_of...</a> is another way of looking at the problem. Once you&#x27;re in Earth orbit, you need 2.4+.68+.14+.68+1.73 = 5.63 km&#x2F;s to get to the moon. But you need 2.4+.68+.09+.28+2.06+6.31+1.22+3.06= 16.1 km&#x2F;s to get to Mercury.<p>So if you don&#x27;t use gravitational slingshots (which can be modeled as ramming your spaceship into a planet&#x27;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.<p>In theory, you could just use a rocket that&#x27;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&#x2F;robots and a Starship with fuel to get enough fuel into orbit for a trip to various parts of the Solar System.<p>[edited to fix units]

This reminded me of Kim Stanley Robinson&#x27;s &quot;2312&quot; and the idea of standing on Mercury in the narrow hospitable belt, looking at the sun, and experiencing solar rapture.<p>Apparent size of the sun from the planets <a href="http:&#x2F;&#x2F;www.astronoo.com&#x2F;en&#x2F;children&#x2F;sun-apparent-size.html" rel="nofollow">http:&#x2F;&#x2F;www.astronoo.com&#x2F;en&#x2F;children&#x2F;sun-apparent-size.html</a>

I&#x27;m so curious what the navigation department for a place like NASA&#x2F;JPL consists of. Each probe&#x2F;satellites mission is so custom, do they have a software suite that they&#x27;ve refined over the last 50 years, is it a couple physics professors etc, are there two teams working independently to make sure no one messes up?

It’s a decent explanation for a phenomena that is not intuitively obvious just by looking at a diagram of the solar system. I wonder just how much fuel is needed to go directly without gravitational slingshots.

The short version: it takes much more fuel to fly directly from the earth into the sun than it does to escape the solar system. Because of this you need to use longer and slower methods.

&quot;There is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. ... Clearly, it is this second part, the missing, that presents the difficulties.&quot;<p>-- The Guide<p>Turns out that missing the Sun is much much easier.

This is super cool. I recommend reading the article and then watching the animation. I&#x27;m no physicist, but it looks like the fundamental idea is to use elliptical orbits to slip in front of a planet along it&#x27;s orbital track, and have the planet&#x27;s gravity slow the probe, and then get out of the way fast as the planet passes. It&#x27;s kind of the opposite of a cyclist drafting.

If you had a thousand (or million) satellites doing this, could you actually measurably modify the orbits of planets? Mercury is small enough that presumably 1000 satellites each doing 9 gravity assists could change it in some way?

Yes! This was a surprise to me to learn as well. I mean, it was in a different context (how to get to the sun), but the same issue applies, of having to shed a ton of angular momentum&#x2F;orbital energy.<p>(If you&#x27;re curious about the opposite direction, of objects with the least angular momentum, that would be either bosons, or Texas&#x27;s four-day-long &quot;rotating&quot; power outages.)

I wonder how hard it would be to build a big shock absorber and fire it directly at Mercury. Maybe delicate electronics and sensors could survive the impact if the force is spread out over a long enough time.

This reminds me of a fun brain teaser:<p>Of all the planets, which is Earth closest to on average?

How much energy do we have to shed? Are we making the earth fall towards the sun every time we launch a space craft?

Ahem. Unclear if this is intentional or an artefact of their blog software, but I couldn’t help but notice that the phrase “vacuum of space” in the article has an extraneous &amp;nbsp;. It is quite visible to the naked eye.<p><i>Shurely shome mishtake?</i>

Delta-v