From: strider@clotho.acm.rpi.edu (Greg Moore)
Subject: Re: DC vs Shuttle capabilities
Organization: The Voice of Fate
Date: Tue, 22 Dec 1992 07:00:38 GMT

In article <ewright.724956784@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>In <b-p254n@rpi.edu> strider@clotho.acm.rpi.edu (Greg Moore) writes:
>
>>	Umm, so?  Tell me, did you see 3 aircraft landing at the same
>>time, or flying in formation?  Did you see baggage transferred between
>>them while in flight?  I'm not talking about on the ground, I'm talking
>>about in space.  If you recall, my original comment was about in-flight
>>satellite repair.
>
>You're being led astray by words.
>
>Both airplanes and orbiting spacecraft are said to be 
>"in flight."  That doesn't mean they have anything in 
>common, except that neither one is in contact with the
>Earth.  We also say that ships and islands are "at sea."
>That doesn't mean that ships and islands have very much
>in common. 
>
	Gee, thanks for clearing that up to me.  And I thought
the space shuttle needed wings so it could fly through the ether.
The key words in your rebuttal are "...neither one is in contact
with the Earth."  Exactly.  I can't just "walk" from a DC-10 in
flight to a 747.  I can't just "walk" from a DC-1 to another
DC-1 in flight either.
	I can recall only 1 (possibly 2) examples of astronauts
transferring between craft via EVA.  And in that case I believe
the craft were linked.  Ever note how careful NASA is when
it sends astronauts on EVA.  They make sure they are somehow
securred to the shuttle or the RMS so that they don't accidently
drift off.

	I don't doubt that someday we'll see EVA between
non-docked craft.  I also don't doubt that we'll see in-orbit
refuelling of cyrogenics.  I also don't doubt that we'll see
3 bodies maneuvering within a small space (say less than a couple
of meters between craft).  But, I claim it will take lots of
work and lots of practice.

>An orbiting spacecraft is not flying like an airplane.  
>There is no air rushing past the wings.  It isn't using
>aerodynamics to stay up and isn't using its engines to 
>maintain velocity.  If it runs out of fuel, it does not
>come crashing back to Earth like an airplane.
>
	Gee, and you mean all those Star Trek episodes where
if the engines failed the Enterprise crashed were a bunch
of howie?  Gee whillickers.
	And speaking of wings, when did wings come into
play.  I'm not complaining about wings, or the lack thereof.
I think you've mistaken me for someone else on this net.

>When two spacecraft touch each other, they are not "in 
>flight" relative to one another.  They are said to be
>"docked," like ships at sea.  So, if you want to base
>your analogies on words like this, you should argue that
>the US Navy is the only organization that can navigate
>two ships to the same dock, then transfer fuel from one
>to another.
>
	So, Intelsat VI and Endeavour were docked before
it was hard-down in the payload bay?  What about when
the astronaut bumped it with the bar?  Was that docked?
Or was that in flight relative to each other.  I think
NASA would like to know that gee, they were docked, and
tht the Intelsat was NOT set into motion by this contact.

And as for tranfering fuel while under way, my naval
knowledge is less, but I don't know too many groups of people
other than the military that do fuel transfers while in
motion.  It's generally a whole lot easier to come to a
dock, or at least anchor in calm water.
	(And, even then, it's somewhat easier than in
space since the water will tend to damp your motions if
you bump the other ship.)

>
>>	Ayup.  And the US Air Force is the ONLY one that regularly does
>>inflight air-refueling.  I haven't seen Delta or Virgin Atlantic do it.
>>Remember, again, we are talking about in-orbit, not on the ground.
>
>We aren't talking air-to-air refueling either.  In-space refueling
>does not require split-second timing, only hooking up the hoses
>properly.
>
	Only.  Given the current understanding I have of DC-1,
(and please, correct me wrong if I am) there is no mechanism
for a drogue or probe.  The drogue you could argue is part of 
the cargo fuel tanks.  The probe has to be added to the DC-1
you want to refuel.  Now, when designing this, you have to account
for any nudges your drogue may transmit.  As you transfer fuel
between craft, your mass changes, which means you have to actively
update your algorithm for active stabilization.  If you have a
rigid "arm" for your drogue, you can't have to much movement,
lest you break your "arm".  If you use a hose, you need someway
of attaching it. (Either a rigid arm or an astronaut).  A hose
introduces other problems related to a change in center of mass.

	Now, one way I see around this is to redesign the DC-1
so that two can accomplish a hard-docking of some sort.  In
this I mean something studier than a linkage carrying one or 
two fuel lines.  I make this requirement only because I think
stress on a much smaller arm would be too higher.

>So, what's so special about the ground?
>
	It's stable.  Things on it tend to find a stable point.
If I happen to lean against a DC-1 on the ground, or even push off
with some force, the worst that happens is I fall down.  I don't
drift off.  (Before you jump down my throat, no I don't think
the risk of a person drifting off is high at all.  However, I do
think the risk of induced motion to be high.)

>
>>	No, some people are telling me, DC-1 will do this, do that, and
>>hey, we can add this, we can add that... it's all going to be easy.
>>I'ms aying, "sounds good, but prove it."
>
>Again, I thought that was what we are doing.
>
	Sorry, but to me, and some others, it sounds like some
people ahere are trying to skip the prove it step and say, "take
our word for granted."

>What are *you* doing, except standing on the sidelines carping?
>
	I'm not insulting people.
	And I'm trying to A) get some answers for my own
use. B) Inject a little reality into this world.  A reality
where sometimes things don't work the first time.  Were some things
may never work.  A reality where a person is willing to say,
"Hey, wouldn't it be great if this thing is cheap enough to fly to
the moon!", not "Oh, we just fly over to our on-orbit depot, fuel
up, and fly over. It's a piece of cake."

	Trust, me, I'm a big fan of the DC-X and DC-Y programs.
I do have doubts about DC-1 though.

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