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Comment by joedrew | Hacker News Reader

Pluto in particular would be a problem, though, because it is a) very small, and b) very far away. In order to get there in a realistic time, your probe has to be going _very quickly_; in order to stay in Pluto orbit, the probe has to be going _very slowly_.

So, unfortunately, to stay in Pluto orbit, either you carry a lot of fuel with you to slow down (which makes launch incredibly difficult, because you need more fuel to accelerate the fuel you need to slow down, and then you need more fuel to accelerate _that_ fuel, and so on), or you wait a long time to get there.

The bigger, closer planets and planetoids, though, will see a lot more exploration as the cost of launch decreases.

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This is an interesting study that could get 20kg into Pluto orbit. It uses gridded ion engines coupled to multiple Radioisotope Thermal Generators.

PDF: http://www.esa.int/gsp/ACT/doc/PRO/ACT-RPR-PRO-ISTS2004-Plut...

>> to stay in Pluto orbit, either you carry a lot of fuel with you to slow down

Gravity assist can be used often used to speed up a spacecraft, but can also be used to slow it down.

  https://en.wikipedia.org/wiki/Gravity_assist

In addition, atmospheric drag can also be used to slow down a spacecraft passing a planet.

While both of those statements are true, Pluto is too small and its atmosphere is too thin for either of those approaches to slow down a probe enough.

Generally the gravity assists act on other planets on the way to the destination. For example, Cassini got assists off of Venus twice, then Earth, then Jupiter on its way to Saturn.

Note: I'm no astrophysicist, and this is just back of the napkin math

Uranus is the physically closest planet to Pluto at the minimum distance of 11AU (about 1,64 billion km). Pluto's escape velocity is about 1,2 km/s (putting the orbital velocity at about 0,7 km/s). So a naive brake on Uranus would need to put the craft such that it brakes down to less than 1 km/s. 1,65 billion km at 1 km/s is about 52 years. Which seems to be a like letting off the gas in a car while going up a hill to break, but then getting to the top and still needing to go 50 miles to your destination. So something else needs to be in place other than just relying on gravity assists/braking.

Or you send some self replicating stuff on the moon, build some factories and solar panels, and build and launch robots from there. We have the technology to do this right now if we are willing to put the money. And if we polish the moon we could beam excess energy to earth.

What do you mean by "polish the moon"?

Chrome the moon?

I can only assume it means creating a large, vigorously reflective surface. Not the whole moon, but presumably making a reflective, concave part large enough to send a focused beam of directed energy.

(NB: this doesn't sound like a good idea to me, or necessarily realistic, I'm just guessing that's what is meant.)

Cover it with solar cells.

Colonize it with Polish people, of course.

Just make sure to send the government up there first.

> Or you send some self replicating stuff on the moon [...] > We have the technology to do this right now

Do we? Self-replicating robots would be very exciting, even on Earth, but I thought we weren't close to being able to make them. Do you have a citation/link?

You have 3d printers that can print themselves. That is a cornerstone.

Everything except assembly, the motors, and the electronics. It's definitely getting closer but we don't have printers that can actually print themselves just yet.

FANUC factories.

2003:

http://money.cnn.com/magazines/business2/business2_archive/2...

2007 (?):

https://www.youtube.com/watch?v=-SREct28lJM

2010:

http://www.bloomberg.com/bw/magazine/content/10_49/b42060442...

2015:

http://www.wsj.com/articles/japanese-robot-maker-fanuc-revea... (put google in the referrer to avoid paywall)

They are just a industrial automation company. Why should they be able to build stuff on the moon?

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