Blimps In Space
Michael Ash
http://www.msnbc.msn.com/id/5025388/
I never heard of this idea or this company before, but maybe someone has.
Short version of the interesting part: JP Aerospace plans to put things
into orbit by floating a gigantic blimp to the edge of space, then
thrusting with an ion drive over the course of several days to get up to
orbital speed. The earlier parts of the plan are in testing, the later
parts are still very vague; they're projecting that it could be ready
within seven years.
So, my question to the group: is this thing reasonable? It sounds
completely insane. It sounds like something that was invented by someone
who took too many interesting chemicals, and yet, it seems like it might
just be possible.
Erik Max Francis
> So, my question to the group: is this thing reasonable? It sounds
> completely insane. It sounds like something that was invented by
> someone
> who took too many interesting chemicals, and yet, it seems like it
> might
> just be possible.
It sounds at least possible (based on your description, the URL gave me
an error).
--
__ Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ There never was a good war or a bad peace.
-- Benjamin Franklin
John Schilling
>As seen on Slashdot:
>http://www.msnbc.msn.com/id/5025388/
The Hypersonic Ion Zeppelin strikes again!
Your answer from the group, this group and the regulars over in the
sci.space heirarchy: This thing is not reasonable. It is completely
insane. Smart, knowledgeable people who have run the numbers find
that, at any altitude where either aerodynamic or bouyant lift can
support the thing, aerodynamic drag will limit it to speeds much,
much lower than orbital velocity unless they have a propulsion system
with much, much more thrust than any ion engine can provide.
Either the JP Aerospace folks are really planning on doing something
completely different and very clever, using the Hypersonic Ion Zeppelin
bit as a cover story, or they are making a stupid mistake. Which means
that they are making a stupid mistake regardless, because the Hypersonic
Ion Zeppelin is a stupid cover story.
The most likely explanation is, alas, just plain ordinary stupidity,
rather than stupidity covering extreme cleverness. Everything JP has
said is consistent with having made a common, intuitively obvious newbie
misconception as to how hypersonic aerodynamics works (the free-molecular,
specular reflection model, FWIW). If hypersonic aerodynamics actually
worked that way, the Hypersonic Ion Zeppelin would work as described.
But note that this criticism is specific to the Hypersonic Ion Zeppelin
itself, not to the Ascender airship or the so-called Dark Sky Station.
Those appear to be sound applications of high-altitude balloon technology,
and JP Aerospace appears to be competent in that regime. It's only when
they venture into the field of hypersonics and spaceflight, that they
appear to have fundamentally goofed.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *
Stan
}Michael Ash wrote:
}>JP Aerospace plans to put things into orbit by floating a gigantic
}>blimp to the edge of space...
}> So, my question to the group: is this thing reasonable? It sounds
}> completely insane. It sounds like something that was invented by
}> someone
}> who took too many interesting chemicals, and yet, it seems like it
}> might
}> just be possible.
}
}It sounds at least possible...
Ummm...the blimp won't go any higher than the weight of the air that
the blimp & it's cargo displaces, right?
And then accelerate up to orbital speed? In a thin (but still capable
of significant air resistance) atmosphere? Seems highly unlikely,
unlees the payload is small and the use of some exotic fuel.
Oh, yeah...the blimp is going to heat up a bit, isn't it?
Stan.
Erik Max Francis
> Ummm...the blimp won't go any higher than the weight of the air that
> the blimp & it's cargo displaces, right?
> And then accelerate up to orbital speed? In a thin (but still capable
> of significant air resistance) atmosphere? Seems highly unlikely,
> unlees the payload is small and the use of some exotic fuel.
Well, if you're talking about an ion drive, then your fuel is already
fairly exotic (using something like Ag or Xe) ...
John Schilling responded in more detail; I only had the one-sentence
description to go on. From a high-level description it doesn't seem
totally impossible in the way that, say, trying to reenter this way
would be -- you need to bleed off that speed, which turns otherwise into
heat, but you're already going fast. Here you're starting out slow and
speeding up.
It'd certainly require something peculiar like a spacecraft that started
out as a balloon and then ended up more like a lifting body. If you're
using an ion drive, you have low thrust, so you're by definition going
to be slowly increasing your speed, rising into higher "orbits," until
you actually leave the atmosphere. It doesn't seem impossible a priori
that you could do this if the numbers and altitudes worked out right.
But I haven't been exposed to the idea other than the short description;
if John Schilling says it's been analyzed and doesn't work, I wouldn't
doubt that for a bit.
--
__ Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ But who shall dwell in these worlds if they be inhabited?
-- Johannes Kepler
Stan
}
}It'd certainly require something peculiar like a spacecraft that started
}out as a balloon and then ended up more like a lifting body.
UNLESS, you could come up with a way to have a lifting body without
a rigid-ness that uses structure, thus keeping it light enough to
act like a blimp (while looking like a flying wing or close).
For the life of me, I can't think of any techn in the not-too-distant
future that will allow a balloon to rigidly hold a shape without the
need for structure.
Stan.
Michael Ash
> Michael Ash wrote:
>
> > So, my question to the group: is this thing reasonable? It sounds
> > completely insane. It sounds like something that was invented by
> > someone
> > who took too many interesting chemicals, and yet, it seems like it
> > might
> > just be possible.
>
> It sounds at least possible (based on your description, the URL gave me
> an error).
Odd. I tried the URL from my post again and it worked fine. Try again?
Michael Ash
> The Hypersonic Ion Zeppelin strikes again!
[snip excellent post]
> The most likely explanation is, alas, just plain ordinary stupidity,
> rather than stupidity covering extreme cleverness. Everything JP has
> said is consistent with having made a common, intuitively obvious newbie
> misconception as to how hypersonic aerodynamics works (the free-molecular,
> specular reflection model, FWIW). If hypersonic aerodynamics actually
> worked that way, the Hypersonic Ion Zeppelin would work as described.
Thanks for that great post. My question now is, why hasn't anybody pointed
this out to them yet? If somebody has, why haven't they listened?
John Schilling
Half the regulars in the sci.space.* heirarchy were in the audience when
JP Aerospace first revealed this concept; we did put them on the spot
with the relevant questions. Their answers, mostly weren't.
Either they are cluelessly overconfident, or they are concealing something
clever, both of which could explain their being unresponsive to critical
questioning of their stated design.
John Schilling
>Stan wrote:
>> Ummm...the blimp won't go any higher than the weight of the air that
>> the blimp & it's cargo displaces, right?
>> And then accelerate up to orbital speed? In a thin (but still capable
>> of significant air resistance) atmosphere? Seems highly unlikely,
>> unlees the payload is small and the use of some exotic fuel.
>Well, if you're talking about an ion drive, then your fuel is already
>fairly exotic (using something like Ag or Xe) ...
>John Schilling responded in more detail; I only had the one-sentence
>description to go on. From a high-level description it doesn't seem
>totally impossible in the way that, say, trying to reenter this way
>would be -- you need to bleed off that speed, which turns otherwise into
>heat, but you're already going fast. Here you're starting out slow and
>speeding up.
>It'd certainly require something peculiar like a spacecraft that started
>out as a balloon and then ended up more like a lifting body. If you're
>using an ion drive, you have low thrust, so you're by definition going
>to be slowly increasing your speed, rising into higher "orbits," until
>you actually leave the atmosphere.
This is indeed the concept they described, including the transition from
bouyant to aerodynamic lift.
>It doesn't seem impossible a priori that you could do this if the numbers
>and altitudes worked out right. But I haven't been exposed to the idea
>other than the short description; if John Schilling says it's been analyzed
>and doesn't work, I wouldn't doubt that for a bit.
The fundamental problem is that aerodynamic lift in a real gas, always
comes with a proportionate ammount of aerodynamic drag. The ratio of the
two, is a function of geometry and mach number and a few similarity
parameters like the Reynolds and Knudsen numbers, but *not* of density,
pressure, or altitude[1]. So as long as you are depending on aerodynamic
lift to keep from falling out of the sky, i.e. until you have actually
*reached* orbit, there's a certain irreducable ammount of drag you have
to overcome to continue accelerating, and no ammount of playing with
the numbers and altitudes will change that - climb high enough to make
the drag go away, and the lift goes away as well and you fall right back.
Increase speed, wing area, and/or angle of attack to regain the lift, and
you regain the drag in the same proportion.
The absolute best hypersonic lifting bodies anyone has even come up with
on paper, much less carved in metal, have a lift:drag ratio of maybe 10:1.
So a hypersonic, aerodynamic vehicle needs to have a thrust:weigh ratio
of at least 0.1:1 in order to accelerate. JP Aerospace has specified an
off-the-shelf ion thruster, and while they didn't state make and model,
nothing presently on the shelf can deliver even 0.001:1 thrust:weight.
So unless JP Aerospace has achieved such an aerodynamic miracle as to
improve the aerodynamics of their Hypersonic Ion Zeppelin by at least
two orders of magnitude, in practice more like three, over anything seen
or even theorized before, their vehicle will not be able to accelerate
in the suborbital hypersonic regime.
[1] Except to the extent that increasing density and reducing altitude
changes the Reynolds, Knudsen, etc, numbers. Which it does, but
alas weakly and in the wrong direction.
Eivind Kjorstad
> pressure, or altitude[1]. So as long as you are depending on
> aerodynamic lift to keep from falling out of the sky, i.e. until you
> have actually *reached* orbit, there's a certain irreducable ammount
> of drag you have to overcome to continue accelerating, and no ammount
> of playing with the numbers and altitudes will change that - climb
> high enough to make the drag go away, and the lift goes away as well
> and you fall right back. Increase speed, wing area, and/or angle of
> attack to regain the lift, and you regain the drag in the same
> proportion.
Sure. The only effect sligthly changing this is that as your speed gets
high enough to start to aproach orbital velocity at that altitude your
needed lift goes down. Which allows you to increase heigth, which
decreases drag (and lift), which increases speed, which means you need
even less lift.
Not that I believe their numbers, I agree that there seems to be a few
orders of magnitude missing somewhere.
Sincerely,
Eivind Kjørstad