
How hard is space travel, in principle? - timf
http://michaelnielsen.org/blog/how-hard-is-space-travel-in-principle/
======
AngryParsley
The guy is right. If you can send stuff to Mars, sending stuff to Saturn isn't
much harder. In fact, we already do send probes around the solar system.

The problem is moving _people_ in space. Space is the ultimate desert. People
need all kinds of supplies to stay alive and healthy (air, water, food,
gravity, etc). They also need to be shielded from cosmic rays and solar
events.

I've said it before and I'll say it again: I doubt large numbers of biological
humans will ever participate in interplanetary travel. I bet brain-in-vat or
uploading technology will show up before payload costs get low enough for
average people to buy tickets to Mars. A brain in a vat doesn't need gravity
or exercise or space to roam around in. It needs less food and water than a
full human body, and it can be shielded easily.

~~~
rlpb
If my brain were in a vat, my need to travel would be significantly reduced.
The only reason I can think of would be if I wanted to interact with a distant
environment with less latency.

~~~
AngryParsley
Good point, but I think it's more general than that: A brain in a vat's need
be in a particular location is significantly reduced. Interaction with remote
things is limited only by light speed, and possibly bandwidth.

Travel costs for brains in vats are significantly reduced. Not only is travel
cheaper monetarily, but the experience of travel can be completely hidden.
Instead of sitting in a seat and looking out a window, you could spend your
time in a VR world or interact via robots. The only reason you would want to
stay in one place is to interact with the nearby environment at low latency.

In the end, uploads are the way to go. You can run them faster and travel cost
is just data transfer cost.

------
ANH
Regarding his underplaying of fuel mass, check out the rocket equation to get
an idea of how hard it is to achieve the delta-v required for various
maneuvers (e.g. suborbital, orbital, escape):
<http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation>

Essentially, your fuel mass requirements increase exponentially as you need
more delta-v. It's very much harder to get into orbit than to stay sub-
orbital. And you will need a significant amount of fuel left over if you wish
to orbit or land at your destination. You can mitigate that with atmospheric
aerobraking, but that's not possible on, say, the Moon.

------
bjelkeman-again
Halfway to anywhere: A really good book on the subject, including an
interesting story about development of low cost space launch capability. It is
a bit old now with SpaceshipOne and SpaceX in progress, but still worth a
read:
[http://www.nss.org/resources/books/non_fiction/review_013_ha...](http://www.nss.org/resources/books/non_fiction/review_013_halfway.html)

I was actually expecting some analysis on interstellar space travel. But you
can find an entertaining attempt at this by Charles Stross:
[http://www.antipope.org/charlie/blog-
static/2007/06/the_high...](http://www.antipope.org/charlie/blog-
static/2007/06/the_high_frontier_redux.html)

~~~
arethuza
I found myself reading Charlie's article and thinking that 400Mt of energy to
get something the size of a family car up to 10% of light wasn't that bad.

Of course, any real propulsion mechanism is going to require a lot more energy
than that but that actually sounds _reasonably_ achievable - at least if we
allow Orion style ships.

------
adaml_623
I think really this should be titled, 'How hard is moving an object in space,
in principle'.

For me space travel involves humans in space and that's really difficult.
Think about being in a little bubble of air surrounded by hard vacuum that
would kill you in seconds. Plus the cold/radiation/general plumbing problems.
Space travel is really hard.

------
Jabbles
_In fact, nearly all of the energy expended by modern rockets goes into
lifting the rocket fuel itself, and only a small amount into the payload._

Which would mean the fuel needed is quadratic in the GPE needed, which would
put Saturn right back up there at ~100 times harder to reach than the moon
(ignoring constants).

------
retube
"In fact, nearly all of the energy expended by modern rockets goes into
lifting the rocket fuel itself, and only a small amount into the payload. An
unfortunate consequence of this is that you need a lot more than four times as
much fuel"

Yes this is where theory != practice, and why in fact, it's incredibly
difficult and expensive to get somewhere like Mars.

------
rlpb
There seems to be an assumption here that the difficulty of going somewhere is
proportional to the energy required.

What about time, and provisions for life support during that time? What about
launch windows, in terms of the amount of waiting time required before a
return trip and the difficulties of a rescue mission?

Others have already mentioned that the amount of fuel/weight you need is worse
than linearly proportional to the energy required.

------
jpa
Really, really good book on this subject:
[http://en.wikipedia.org/wiki/The_Millennial_Project:_Coloniz...](http://en.wikipedia.org/wiki/The_Millennial_Project:_Colonizing_the_Galaxy_in_Eight_Easy_Steps)

[http://www.amazon.com/Millennial-Project-Colonizing-
Galaxy-E...](http://www.amazon.com/Millennial-Project-Colonizing-Galaxy-
Eight/dp/0316771635)

The book does a nice job of capturing all the hard engineering problems. His
proposed solutions are interesting but a bit superficial.

------
icegreentea
If your willing to take a loooooong time, you can take the interplanetary
highway. Basically, by carefully picking your path, you can essentially move
from Lagrange point to Lagrange point, where changing directions is nearly
free.

------
RyanMcGreal
>In theory there is no difference between theory and practice. In practice
there is.

\-- Yogi Berra.

