
Station Crew Docks Dragon Capsule to ISS - mzaccari
http://www.nasa.gov/content/station-crew-grab-themselves-a-dragon/index.html
======
readerrrr
And that is their second launch within 14 days. The previous launch was a
satellite to a geostationary orbit.

~~~
bfe
This 14-day interval between Falcon 9 launches was the fastest consecutive
launch since Gemini 7 & 6A in December 4 & 15, 1965.

SpaceX plans to beat that record soon with launches a week apart becoming
routine.

~~~
ewoodrich
Gemini 7 and 6A were manned launches on human-rated launch vehicles, so it
isn't quite comparable yet.

~~~
bfe
Still, modern launch vehicle human ratings were only developed after the
second Shuttle disaster, and are far beyond 1965 standards.

[http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_...](http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_8705_002B_)

Falcon 9 v1.1 is almost certainly safer than the Titan II Gemini Launch
Vehicle. As with prior Dragon flights, humans could have flown and been just
fine.

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ANH
Of note, there is an Earth observation instrument, RapidScat, being carried in
the Dragon's trunk, which will be (has been?) plucked off the capsule by
operators on the ground. This one measures wind. Another, called CATS, will be
similarly deployed on the outside of the ISS in December-ish; it will measure
clouds and aerosols.

These are part of a collection of low-cost (well, lower than a full satellite)
Earth observation instruments to take advantage of the external mount points
on the ISS. NASA recently had a media briefing about this:
[http://www.nasa.gov/press/2014/september/nasa-hosts-media-
br...](http://www.nasa.gov/press/2014/september/nasa-hosts-media-briefing-to-
announce-new-earth-observing-role-for/)

------
MrBra
Is it common to use metric system when launching rockets to space or is it a
peculiarity of SpaceX? I heard the speaker on SpaceX channel always referring
to kilometers and kilometers per second when talking about height and speed.

~~~
antimagic
It's common for pretty much all of engineering really. It's ludicrous to make
calculations a bit more complicated by using weird non-SI units.

The fact that NASA managed to crash a probe into Mars because they hadn't yet
learned the lesson says it all really. Just use SI units and stop worrying
about it.

~~~
Ankaios
No, the important lesson is to always label your units, and another one might
be to always be careful passing dimensionful numbers between codes and teams.
You can run into the same problem by accidentally even forgetting to convert
between, e.g., newtons and millinewtons.

~~~
Tloewald
SI units don't include millinewtons, so the problem wouldn't arise. That's
part of the point.

You measure mass in kg, not g, not tonnes.

You measure distance in metres. Not kilometers. Not nautical miles.

You measure time in seconds.

A Newton is a derived SI unit — 1 kg m / s^2

Incidentally, this is why engineering notation works the way it does. You pick
your units and you get the significant figures from the mantissa and the
descriptive prefix (giga, nano, micro, kilo, etc.) from the exponent.

~~~
pimlottc
His point (I believe) is you always need to label units regardless of system.
You could have the same problems with microseconds vs nanoseconds.

~~~
jjoonathan
Tloewald's point was that microseconds and nanoseconds are not SI base units,
so standardizing on base units eliminates the ambiguity (the second alone is
the SI base unit of time). Of course additional mechanisms of double and
triple checking are probably still warranted to account for human fallibility.

~~~
jessaustin
That's fine until you start using floating point values in order to satisfy
this SI fetish. (I guess you like farads and henries too.) It's much better to
use fixed point and keep track of your multiplier. A sufficiently advanced
type system could do this, but at some point it will require careful thinking
about precision.

~~~
Tloewald
Using fixed point and tracking your multiplier is exactly like using floating
point.

~~~
jessaustin
Floating point is treated differently by compilers, involves different
components of the processor, generates different types of errors, and has
different performance. Perhaps there is some perspective from which that
proposition is true?

~~~
jjoonathan
A perspective where one is more familiar with IEEE754 than your in-house
custom fixed-point implementation of choice?

There are plenty of applications where it makes sense to do something
different because you need to accommodate special hardware (e.g. FPGAs),
because you want a different representation density/range, or because external
policy effectively dictates the most natural format (e.g. finance). But in the
absence of a pressing concrete reason to ditch 754 floats, they are BY FAR the
best option for high performance, reproducible, portable, debuggable math with
abundant documentation and pre-existing pools of expertise. They're far from
trivial but so is the fixed-point code you would replace them with.

If someone couldn't be bothered to learn the relevant intricacies of IEEE754,
why do you expect them to do a better job re-implementing the stuff on top of
integer math (or picking apart the in-house attempt to do so)? Shifting from
problems of the "intern forgot to reset the rounding mode" variety to the
"Newton's method code erroneously terminates one cycle too early if the last
bit is a 1" variety hardly seems productive.

------
aidos
Whenever I see ISS dockings I wonder why the arm isn't computer controlled.
There's no specific information on this page but I'm assuming it was a manual
docking. Can anyone explain why the process is still manual?

~~~
FranOntanaya
I bet the trainers that certify an astronaut is precise enough to get it done
are a lot cheaper than the engineers required to certify a computer wouldn't
karate chop the station.

~~~
icegreentea
The arm almost certainly has a control system that can resolve that. Since
humans suck at higher order control, the arm almost certainly has a control
system that takes the operator's desired output (which will be a series of
joint angles), and converts into the required motor torques. In this process,
the control system almost certainly also does sanity checks to prevent self-
intersections, collision with the space station, overtorqeuing the motors, and
etc.

Replacing the human with a computer program therefore likely doesn't literally
involve verifying that it will not karate chop the station - lower level
control will take care of that for you.

However, as anyone who has worked with robot manipulators before, actually
getting good performance out of them in variable environments (ie, not a
controlled factory assembly line) is quite a bit of work - work that probably
isn't worth it.

------
markab21
Does anyone know what happens to the pod after a shuttle-craft docks and
delivers cargo?

Do they push it back to earth? Into space, leave it in orbit?

~~~
andyjohnson0
It will stay at the ISS for a month to allow cargo transfer [1]. Then it
returns to earth under its own power and is re-used after refurbishment [2].

[1] [http://www.nasa.gov/content/expedition-41-trio-waits-for-
dra...](http://www.nasa.gov/content/expedition-41-trio-waits-for-dragon-and-
new-soyuz/index.html#.VCF3zvldV2s)

[2] [http://www.spaceflight101.com/dragon-spacecraft-
information....](http://www.spaceflight101.com/dragon-spacecraft-
information.html)

~~~
Zuph
Although the Dragon is reusable, SpaceX's contract with NASA stipulates that
new capsules be used for each resupply mission. Not sure if the contract
allows SpaceX to refurbish the capsules for other commercial missions, but the
other CRS Dragons are being used for showpieces at the moment.

~~~
andyjohnson0
Interesting - I didn't know that. Do you know if this is due to NASA being
general cautions with a new, relatively unproved vehicle? Or is it a condition
of human-rating the Dragon?

~~~
rst
NASA was unwilling to believe any discount offered for use of a refurbished
spacecraft until they'd actually done it, so the bid was made on the basis of
a new capsule for each mission.

(The human-rated Dragon is going to be a different version anyway, with
altered docking support, much beefier propulsion, altered solar panels, and of
course, internal controls and life support. Current plan is new spacecraft
permission there, too, though, perhaps for the same reason.)

------
mariocesar
Tomorrow is happening today

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s369610
"support 255 research investigations", I hope that 255 is just a coincidence
and that research isn't limited by 8 bits

------
bvm
It's technically a berthing, not a docking as it mates under the power of the
Candarm, not under its own steam.

~~~
idlewords
MATES UNDER THE POWER OF THE CANADARM

~~~
Intermernet
Out of context, this sounds like a line from a very bad book. Have an upvote.

~~~
possibilistic
To both parent and GP:

Please don't comment on HN like you would on Reddit. If you don't have
questions or information to add to the thread, you should probably use that as
a cue to refrain from posting.

Joke posts might not seem bad, but in aggregate they lower the signal to noise
ratio we have come to appreciate about HN. Additionally, once these kinds of
jocular posts start, it becomes infectious.

I'm not trying to be mean; I'm guilty of making posts like this too. Many of
us simply do not want to see HN devolve into the equivalent of a spammy
subreddit. It's important that we all remind each other of the value of this
community so that we can protect it from spiraling into a bad state.

~~~
idlewords
Please don't tell others how to post. It's patronizing. There's a voting
system you can use to express your concern.

~~~
tedks
The reason why hacker news is good is because it remains serious.

It's important to remember that Hacker News is _not_ a democracy. There isn't
a voting system so people can democratically decide what content is good or
bad. Rather, Hacker News is a dictatorship, controlled by Paul Graham and the
Y Combinator. Within this space, the Y Combinator has absolute control over
all content.

In a democratic system like Reddit, there might be objections to changing the
titles or shadowbanning trolls (reddit does shadowban, but mods can't
shadowban people for disturbing the quality of a subreddit). On Hacker News,
these features are welcomed because they raise the quality of discourse.

Your only choice when it comes to hacker news is to stay and be a productive
member, or leave. You are free to leave. Nobody is forcing you to stay here.
The source code for Hacker News is even publicly available; if you want to
make Joker News you're free to do so.

In this way, Hacker News circumvents tyranny of the majority in favor of
quality of content. (I suspect that it also has to do with the Y Combinator's
libertarian politics -- Hacker News is an excellent example of what the world
could be like it if were organized into voluntary units with absolute internal
control, but free choice and movement between those units.)

~~~
ceejayoz
> There isn't a voting system so people can democratically decide what content
> is good or bad.

I'm confused. Comments have up/down voting, and posts have up voting and
flagging.

> In a democratic system like Reddit, there might be objections to changing
> the titles or shadowbanning trolls (reddit does shadowban, but mods can't
> shadowban people for disturbing the quality of a subreddit). On Hacker News,
> these features are welcomed because they raise the quality of discourse.

I've seen both people posting "you're hellbanned and it doesn't look
warranted" and productive, moderator-accepted complaints about changing
titles.

~~~
tedks
>I'm confused. Comments have up/down voting, and posts have up voting and
flagging.

The voting system exists so that the community can raise productive comments,
and lower unproductive comments. It's impossible for Paul Graham himself to
come to every thread and say which comments are good and bad. We have to help
how we can.

>I've seen both people posting "you're hellbanned and it doesn't look
warranted" and productive, moderator-accepted complaints about changing
titles.

The Y Combinator is reasonable, and human. It has a set of rules it attempts
to operate by, but human agents occasionally violate their own rules.
Ultimately, all decision-making authority rests with them, not the community.

But the fact they exist is difference enough to demonstrate my point.

~~~
ceejayoz
"The voting system exists so that the community can raise productive comments,
and lower unproductive comments" sounds like "a voting system so people can
democratically decide what content is good or bad". What's the distinction
you're trying to make?

~~~
tedks
The community does not decide what is good or bad. Paul Graham has already
decided that. There is no democracy.

~~~
reelgirl
I am new to HN, but you say Paul Graham has already decided.

Check out this article: [http://techcrunch.com/2014/03/29/after-stepping-
aside-from-y...](http://techcrunch.com/2014/03/29/after-stepping-aside-from-y-
combinator-paul-graham-hands-over-the-reins-at-hacker-news/)

Also, your comment was still allowed to post.

~~~
possibilistic
I accidentally downvoted you when attempting to pinch-zoom on my phone. I'm
sorry! I didn't mean to make that mistake. I wish we had the feature to undo
things like that.

