"John Doe" wrote in message
...
Jeff Findley wrote:

True, but my argument is that it is a desire to return an entire
experiment
rack to the earth more so than a hard requiremnet.


The whole point of developping the ability to return racks was to enable
experiments that would have required the rack be returned. Just because
they haven't yet scheduled such experiments doesn't mean that the need
wouldn't have become "hard requirement" later on.

In other words, this was a capability in search of a requirement.

Because the shuttle and MPLM's (or something like them) were assumed to be
available until the end of the life of ISS, the ability to return entire ISS
racks to earth was a no brainer to implement. However, this assumption has
changed, so it's time to re-evaluate whether this was really a hard
requirement or just a desire.

I have this sort of argument with our "product marketing" people all the
time when I'm told to implment some bit of functionality. If I don't know
of any customer who needs this functionality, I'll tell them, show me a real
customer/user workflow that requires this functionality.

I'm not going to spend weeks, months, or even years developing new
functionality without a real customer workflow. In years past when we've
implemented such capability without a real user workflow, all we've ended up
with is unused functionality which doesn't make the company money.

And remember that some
experiments may have devices that are too big to fit through the russian
hatches, so they couldn't be disposed of.

Again, HTV will take care of disposal. Disposal of hardware is a
requirement which is separate from returning mass to earth. Shuttle/MPLM is
a solution to both problems, but that does NOT mean that the same vehicle
has to do both requirements simultaneously.

Remember that while so far, "experiment" has been a term associated with
watching crystals grow in a test tube, the real experiments in the
station are getting systems to work reliably. Didn't the russians hitch
a ride on a shuttle to return a failed Elektron unit after a replacement
had been sent by Progress ?

True, because they wanted it back on earth for failure analysis and repair
since Elektron's are rare hardware. Such a requirement could be fulfilled
by Space-X's Dragon.

But not every bit of failed hardware has to be returned to earth. A failed
laptop on ISS is arguably far cheaper to replace with a new one than it is
to return the failed one and refurbish it. It would also be foolish to
require that every failed light bulb be returned to earth. You might want a
couple returned for failure analysis, but that's about it.

If you have a failed unit, and you are required to disassemble it to fit
in a return vehicle, then the act of disassembling it might disrupt the
conditions and skew any analysis done on earth when the unit is examined .

Then NASA had better hope that Dragon works and is available soon, hadn't
they?

BTW, JAXA has a few pages in english for HTV:

http://iss.jaxa.jp/en/htv/operation/

It mentions first launch in 2009. But the rocked is still under
development. Anyone hae some background on the readyness of that rocket ?

Often, such web sites were built many years ago and not really updated
with new schedules.

I'm not sure what the current schedule is. Even NASA websites are sometimes
bad about updating such information. The Mitsubishi website says first
launch in 2008. :-P

That said, you'd think that JAXA would want to get it flying sometime soon,
considering that the JEM is now in orbit. When ISS is expanded to a six
person crew, I'd think that they'd want HTV flying a.s.a.p. :-)

Jeff
--
"Many things that were acceptable in 1958 are no longer acceptable today.
My own standards have changed too." -- Freeman Dyson