
The Challenge of Relativistic Spaceflight - user_235711
http://www.icarusinterstellar.org/the-challenge-of-relativistic-spaceflight/
======
ryandrake
TL;DR: Chemical propulsion is a dead end. But, the alternatives require
matter/energy of ridiculous scale (hundreds of times the power output of human
civilization, launching hundreds of millions of tons of matter into orbit).
We're not going anywhere, any time soon.

~~~
Tloewald
Not just magnitude but duration. Name one machine that works without major
overhaul for more than 100 years. For bonus points, name a machine that's
significantly more complex than a clock.

~~~
Houshalter
Name one machine that's _designed_ to work for over 100 years.

Many of NASA's spacecraft have survived well beyond their intended death
dates, because they were constructed so well, and because space is cold,
static, and good at preserving things.

~~~
Tloewald
There are plenty of simple, well-made machines designed to work indefinitely
-- e.g. doorknobs, window assemblies. Even simple, robust, well-maintained
machinery tends not to last a very long time. There's a stone bench somewhere
that Thomas Jefferson supposedly used to sit on that has become curved over
time.

~~~
GFK_of_xmaspast
Are you seriously going with "a stone bench" as your example of the durability
of "robust well-maintained machinery".

~~~
rm445
I'm pretty sure he's taking the opposite view, that (a) building elements have
indefinite design lives but don't last that long, and (b) Even stonework
doesn't endure indefinitely.

I'm not sure I really agree with the second point in this context - stonework
tends to endure. We have Norman cathedrals that are looking good at nearly a
thousand years old, comparable to the timescales under discussion to
spaceflight. More to the point, there's no reason to believe that the basic
structural elements of, say, a hollowed nickel-iron asteroid wouldn't be
durable enough for spaceflight.

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ackydoodles
The numbers only become science-fictiony large if you want to go fast. Why not
go slowly?

The only reason humanity is obsessed with speed is because of our short life
spans, but that is a solvable problem.

All we have to do is to eliminate aging and it's associated diseases, and then
we can take our time going to the stars.

The most difficult part may be accepting limits upon our appetites, so that we
are not driven to consume everything and we can live sustainably. This is an
issue aboard a starship, where we will have to take a chill pill on
consumption of resources, just as it is an issue on starship Earth.

~~~
kjs3
Ignoring the whole "we'll just cure mortality...how hard can it be?", people
tend to go batshit crazy after spending a couple of months in confined
conditions looking at the same faces day after day. Think they're going to do
better mentally when they look forward to the same for a 100 years.

~~~
userulluipeste
Then we have to address this newly pinpointed problem - to somehow make people
not „go batshit crazy”. Maybe practicing some kind of meditation? I admit that
it's not as exciting as some technical overhaul we all expect, but still...

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cousin_it
What's the point of these huge generation ships? It's not like there's not
enough atoms on other planets. You should send a tiny fast robotic ship, maybe
with an uploaded mind if your AI tech isn't good enough. It will mine
materials at the destination and build a receiver antenna. Then you can send
more uploaded minds by radio, which will arrive at the speed of light with low
energy cost.

Another reason why you shouldn't send human bodies in tin cans, or even grow
them from eggs on the spot, is that human bodies are not adapted to the
conditions in space or at the destination, so they would need an unreasonable
amount of life support equipment. If you really want a colony of biological
creatures with human minds for some reason, bioengineer the right kind of
bodies on the spot and download minds into them.

~~~
snowwrestler
If we're going to stipulate fantastic concepts like "uploaded minds" then
let's just invent a hyperspace engine too and solve all the problems at once.

In the real world, we want to send human bodies because that's what human
minds are. Cartesian duality is a religious/philosophical concept for which no
scientific basis has yet been found.

~~~
cousin_it
I think you have "fantastic" and "real world" backwards. The Blue Brain
project is planned to have an uploaded rat brain this year (2014). Uploading
human minds is very likely to be closer than capturing the whole energy output
of the Sun, which is discussed in the OP.

Though uploading will likely cause so many changes that space exploration will
seem insignificant in comparison, see Robin Hanson's "The crack of a future
dawn" [1] and Carl Shulman's "Whole brain emulation and the evolution of
superorganisms" [2]. In general I think most people don't take this scenario
seriously enough, the authors I mention are the rare exceptions.

[1] [http://hanson.gmu.edu/uploads.html](http://hanson.gmu.edu/uploads.html)

[2] [https://intelligence.org/files/WBE-
Superorgs.pdf](https://intelligence.org/files/WBE-Superorgs.pdf)

~~~
darkmighty
The Blue Brain project will have a rat brain _model_. It reproduces some of
the responses you'd expect from a real. That's orders of magnitude of
technical progress away from what an upload would require. We don't even know
for sure if it's physically possible to perform an upload (due to quantum
mechanics), much less have a device which can come close to measure a
significant part of the quantum state of a working brain (i.e. the technical
problems beyond physical feasibility).

~~~
jessedhillon
Can you point to some introductory reading about the quantum mechanical
effects at work in the brain? I've read The Emperor's New Mind but was left
with the impression that it was more conjecture than research.

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josh-wrale
Master the art of "the transporter" with information being sent via optics.
Send a ship out into space. Aboard will be an environment for humans and a big
receiver on the side. Send the ship. Wait until it reaches it destination.
"Beam" humans to the ship. If boredom ensues, reverse the transmission. Leave
the "Stargate" behind. :)

Edit: see quantum entanglement

Edit 2: Thinking aloud about quantum entanglement. I understand that we can
slow and stop light by passing it into a Bose-Einstein condensate. Can we
thereby suspend two entangled particles, each in its own BEC? That way, we can
send our ship out into space, unfreeze light (time?) and proceed to transmit
Data (heh).

Edit 3: Transmit, that is: faster than the speed of light. (thinking not) :)

Edit 4: Now, I want to know what happens when a BCE containing stopped light
travels at or near the speed the speed of light.. Ah never mind. I'm not a
physicist. Cold and fast don't go together easily, either. :)

Edit 5: Do watch:
[https://www.youtube.com/watch?v=-8Nj2uTZc10](https://www.youtube.com/watch?v=-8Nj2uTZc10)

Edit 6: By the way, if Edit 2 is used, no big receiver would be required.
Hmm.. Send the quantum receiver to a Class M planet.. Skip the on-ship
environment. Terraform to taste.

~~~
teraflop
You can't use entanglement to do FTL communication.

[http://en.wikipedia.org/wiki/No-
communication_theorem](http://en.wikipedia.org/wiki/No-communication_theorem)

~~~
josh-wrale
Glad to learn something new. Thanks.

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higherpurpose
I think we'll need fusion to make intra-solar system travel (really) possible,
where we just transport stuff through-out the entire system, with a speed of
at least 1/100 of the speed of light. Achievable in ~50-100 years.

For inter-stellar space travel, say to the closest 20-100 star systems, we'll
need either an anti-matter powered ship or a black-hole powered one (a bit
more likely) that can travel to these stars in only a few years to a decade,
and then another few years to a decade back, with the speed of 30-50 percent
of the speed of light. Achievable in ~200-300 years (remember technological
progress is exponential not linear).

For whole galaxy exploration we'll definitely need something like a warp
engine. When we'll get this is harder to predict, but it will probably take at
least 1,000 years to do it.

Things that could definitely help with space exploration: figuring out
immortality against aging, which could also make us more interested in
100-year old projects, transferring our consciousness to machines/more
resilient avatars not just for space travel, but also for living on new
dangerous planets, and quantum Internet so we can rapidly communicate through
long distances.

If we do the last one, we might not even need to travel ourselves or transfer
into other bodies, to go to those places. We'd just send robots that we
control absolutely and very precisely, just like we were there
(Avatar/Surrogates-style).

~~~
jp555
> (remember technological progress is exponential not linear)

No it is not. For example, airliners fly about as fast as they did a
generation ago, and if you buy a desktop computer today it won't be noticeably
faster than the ~3 year-old one you're using now.

Do you really think the next TV you'll buy will be _exponentially_ bigger than
the one you have today? Prepare to be disappointed.

warp-engine would require FTL travel, which is not possible. How can you
travel a distance less than zero? At C all distances are zero.

DNA is already a pretty good way to travel the stars, a human ovum (the
largest human cell) has a low enough mass to get out of Earth's gravity well
using only electrostatic or solar-pressure forces, no fuel required. If it
were somehow interstellar-vaccum-hardened and able to modulate the energy
gradient it uses to change direction, it could travel to the stars.

I suppose you have misunderstood quantum entanglement, as it does not offer
any way to communicate instantaneously over vast distances. It's more like
when the light-standard in front of you turns green, you know INSTANTANEOUSLY
that the "entangled pair" light-standard perpendicular to your view is red.

~~~
parksy
How would the ovum develop and be nurtured? Sympathetic alien surrogates?

Why not seed more simple lifeforms, such as genetically modified bacteria,
upon hundreds of "candidate" planets so that by the time our generation ships
arrive there's a good chance some basic terraforming has already occurred.

~~~
ForHackernews
> How would the ovum develop and be nurtured? Sympathetic alien surrogates?

You could send along artificial wombs and some kind of computer/AI to raise +
educate the first generation born.

~~~
kjs3
Never been a parent, eh?

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ForHackernews
\ _shrug\_ It's all sci-fi tech anyway. Artificial wombs probably aren't
_that_ far off: [http://www.popsci.com/scitech/article/2005-08/artificial-
wom...](http://www.popsci.com/scitech/article/2005-08/artificial-wombs)

There's a clear demand for advanced reproductive technology, and it would
offer the secondary advantage of neatly sidestepping the current abortion
debate.

~~~
kjs3
You're missing my point (which I suppose I really didn't make, so my bad). A
child raise by machines is likely to be one seriously emotionally messed up
child.

~~~
icambron
Well, all kids are raised by machines, just usually machines called Mom and
Dad. The question is whether the machines we could make to replace us as
parents are better or worse. It's hard for us now to imagine artificial
machines being better at it than we are, but, you know, so is relativistic
spaceflight.

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adrianN
One efficient way to convert mass to energy is using the Hawking radiation of
artificial black holes. This seems to by allowed by the laws of physics
according to this paper:

[http://arxiv.org/abs/0908.1803](http://arxiv.org/abs/0908.1803)

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TrainedMonkey
What I got out of that is first company or nation to manage useful self
replication technology in space will gain immense power.

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rwmj
Doesn't your spaceship get ground down or blown to bits by interstellar dust?

~~~
seiji
Use a very tiny, highly reinforced spaceship about the size of a standard 330
ml can.

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ceautery
I think he may have meant 1/12th rather than 1/2th of the speed of light, but
I must say I'm very tempted now to start calling one half a "tooth" instead.

~~~
shasta
Maybe not "tooth", but why do we use the phrases "a third" and "a fourth" for
fractions, but not "a second" for half?

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arethuza
Perhaps because of the potential confusion with "a second" being used to mean
"another" i.e. 2X rather than 1/2X.

e.g. I could eat a second pizza

Do I mean another pizza or half a pizza?

[OK it should be phrased as "a second of a pizza" \- but that is rather close
to "a second pizza"]

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jperras
Not that I have a better answer, I believe the phrase "a third of a pizza" is
just as confusing.

~~~
arethuza
You are, of course, quite correct.

I should make a mental note to comment on HN while actually focusing on
something else..... :-)

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drjesusphd
Is continually accelerating at 9.8 m/s^2 necessary? Sure, that's what's needed
to get off the ground, but it seems excessive for a whole interstellar
journey.

~~~
sp332
Well if you accelerate slower, then you travel slower, then the relativistic
effects of your speed are exponentially slower. So it's good to accelerate as
quickly as possible.

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asgard1024
One challenge to relativistic spaceflight is computing. If you put a CPU into
a vehicle, which goes close to speed of light, it may not work properly,
because the energy pulses in the device will become unsynchronized when going
in different directions.

~~~
ryandrake
Special relativity says the speed of light is the same in all reference
frames. In the reference frame of the moving CPU, it would operate correctly.

~~~
JoshTriplett
While the speed of light is the same, relativity also has a lot to say about
_accelerating_ reference frames.

That said, if you were accelerating fast enough to affect the behavior of a
CPU, you'd be experiencing G-forces comparable to the tidal forces of a black
hole; computation would be the _least_ of your problems.

~~~
scarmig
Hmm, suggests a vaguely related question to my mind. Generally speaking, do
black holes have any implications for computations? E.g. does having a black
hole at your disposal let you solve any problems you wouldn't be able to
otherwise?

~~~
oakwhiz
What you are describing is a form of hypercomputation. It is not yet known
whether hypercomputation is even really a "thing." A hypercomputer, if it
existed, would be able to solve the halting problem.

[http://en.wikipedia.org/wiki/Hypercomputation](http://en.wikipedia.org/wiki/Hypercomputation)
[http://en.wikipedia.org/wiki/Malament-
Hogarth_spacetime](http://en.wikipedia.org/wiki/Malament-Hogarth_spacetime)

