Slow Re-entry

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arne97

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Aug 7, 2005, 10:54:43 AM8/7/05
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The shuttle, as well as most other space vehicles, enter the
atmosphere in a blaze of heat.
I assume that this is a method of shedding speed.
The moon lander , lacking an atmosphere, depended on rockets to
slow descent.
What with broken tiles and what-not, isn't there a better way to
get a ship down those last 200 miles than turning it into a meteorite ?
What about expendable drag devices ?
How much fuel would be needed to slow the vehicle in orbit to a
relatively safe landing speed?

Arne

Doc O'Leary

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Aug 7, 2005, 2:17:54 PM8/7/05
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In article <1123426483....@g44g2000cwa.googlegroups.com>,
"arne97" <gahad...@yahoo.com> wrote:

> What with broken tiles and what-not, isn't there a better way to
> get a ship down those last 200 miles than turning it into a meteorite ?

Not according to the rocket scientists. But what do they know, right?

> What about expendable drag devices ?

And in space it precisely will drag against what? Or what would you
propose they stick out in the high atmosphere that would be both
reliable and expendable at over Mach 20? Bonus points if you can
actually pack it small enough to fit in the Shuttle itself. This leads
to the "black box" joke: Why don't they just make the whole Shuttle out
of it? They did!

> How much fuel would be needed to slow the vehicle in orbit to a
> relatively safe landing speed?

Slightly less fuel than was needed to get the vehicle into orbit in the
first place. Well, a lot less if you consider how much fuel you'd have
to burn to get that fuel in orbit in the first place, but the point
stands. You'd have to build what amounts to a launch vehicle for the
current launch vehicle.

Simon Morden

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Aug 7, 2005, 2:40:41 PM8/7/05
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Doc O'Leary wrote:
> In article <1123426483....@g44g2000cwa.googlegroups.com>,
> "arne97" <gahad...@yahoo.com> wrote:
> >
>> What with broken tiles and what-not, isn't there a better way to
>>get a ship down those last 200 miles than turning it into a meteorite ?
>> How much fuel would be needed to slow the vehicle in orbit to a
>>relatively safe landing speed?
> >
> Slightly less fuel than was needed to get the vehicle into orbit in the
> first place. Well, a lot less if you consider how much fuel you'd have
> to burn to get that fuel in orbit in the first place, but the point
> stands. You'd have to build what amounts to a launch vehicle for the
> current launch vehicle.

If LEO is something like 4.5km/s, that's the amount of delta V you need
to shed. Either aerobrake or reverse thrust.

There's nothing magical about orbit - look up some of the high-altitude
jumps which were made in glorified space-suits. The reason those guys
didn't turn into fireworks was that they weren't moving that fast...

Simon Morden

Stephen Horgan

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Aug 7, 2005, 5:38:01 PM8/7/05
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You have to shed the velocity. Doing it slowly implies the use of
reaction mass, which you then have to carry. There is nothing wrong
with the principle as far as I know but the engineering problem with
current technology is formidable.
--
Stephen Horgan

"intelligent people will tend to overvalue intelligence"

Erik Max Francis

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Aug 7, 2005, 5:53:01 PM8/7/05
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arne97 wrote:

Orbital speed is 7-8 km/s. You need to shed that much speed in order to
avoid burning up in the atmosphere. Furthermore, you need to shed it
fast, because reducing your speed will make you drop inward due to
orbital mechanics, which means that you'll touch the atmosphere if you
don't shed it all quickly.

On the contrary, using reentry is a very effective and efficient way to
get to the surface of a terrestrial planet with an atmosphere from orbit
safely and effectively.

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
It is one thing to praise discipline, and another to submit to it.
-- Cervantes

Mad Bad Rabbit

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Aug 7, 2005, 8:51:58 PM8/7/05
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"arne97" <gahad...@yahoo.com> wrote:

> What with broken tiles and what-not, isn't there a better way to
> get a ship down those last 200 miles than turning it into a meteorite ?

Yes, a space-elevator ; but we need several thousand kilometers
of superstrong cable that we're not able to manufacture just yet.

--
>;k

Edward Cherlin

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Aug 7, 2005, 8:51:10 PM8/7/05
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arne97 wrote:

> The shuttle, as well as most other space vehicles, enter the
> atmosphere in a blaze of heat.
> I assume that this is a method of shedding speed.

Yup.

> The moon lander, lacking an atmosphere, depended on rockets to
> slow descent.

Yup. It can do that in the lower gravity of the moon.

> What with broken tiles and what-not, isn't there a better way to
> get a ship down those last 200 miles than turning it into a meteorite ?

Definitely not if it's the Shuttle. But all landings on Earth, Mars, and
Titan have used aerobraking in the high atmosphere, even if they used
parachutes lower down. Venus also, I believe.

> What about expendable drag devices?

They're called tiles.

If you can come up with a parachute that can operate at several thousand
degrees, and cords that can hold it to the Shuttle at those temperatures
and at 25,000 mph, feel free *NOT* to post your kookery here or anywhere
else on Usenet. When you have a working prototype, we'd be delighted to
read about you on the news.

> How much fuel would be needed to slow the vehicle in orbit to a
> relatively safe landing speed?

One humongous external tank and two solid rocket boosters should do it. Same
delta-V going down as going up, same gravity well.

> Arne

Jim Burns

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Aug 7, 2005, 10:20:47 PM8/7/05
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The space elevator is certainly the solution I want, mostly
because it seems to me that I'll be more likely be able to
pay for a ticket into space via the space elevator than via
some descendant of the Space Suttle.

How about Spaceship One, though? When I saw them on 60 Minutes,
my impression was (1) they're using a revolutionary design
to passively orient the ship for proper re-entry, and (2)
they don't look like they're using NASA-style ceramic-foam tiles.
OK, so all they've done so far is pop out of the atmosphere
and drop back in, but I would think their engineers are
designing for a future with true orbital flight -- and
return from orbit. Do they have a Clever Plan to make the
heat of re-entry not quite so hot?

Jim Burns

Hop David

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Aug 7, 2005, 10:31:05 PM8/7/05
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Jim Burns wrote:
> Mad Bad Rabbit wrote:
>
>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>
>>> What with broken tiles and what-not, isn't there a better
>>>way to get a ship down those last 200 miles than turning it
>>>into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.
>
>
> The space elevator is certainly the solution I want, mostly
> because it seems to me that I'll be more likely be able to
> pay for a ticket into space via the space elevator than via
> some descendant of the Space Suttle.
>
> How about Spaceship One, though? When I saw them on 60 Minutes,
> my impression was (1) they're using a revolutionary design
> to passively orient the ship for proper re-entry,

For a suborbital re-entry. Orbital re-entry is a completely different
animal.

--
Hop David
http://clowder.net/hop/index.html

Lorenzo L. Love

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Aug 8, 2005, 12:07:18 AM8/8/05
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Google >rotating space tether<


Ben Bradley

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Aug 8, 2005, 1:05:55 AM8/8/05
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On Sun, 07 Aug 2005 22:20:47 -0400, Jim Burns <burn...@osu.edu>
wrote:

>How about Spaceship One, though? When I saw them on 60 Minutes,
>my impression was (1) they're using a revolutionary design
>to passively orient the ship for proper re-entry, and (2)
>they don't look like they're using NASA-style ceramic-foam tiles.
>OK, so all they've done so far is pop out of the atmosphere
>and drop back in,

That's the secret. I didn't see 60 minutes, but I wouldn't be
surprised if they glossed over the difference between a suborbital and
orbital flight, and the differences in re-entry (it being TV, I'd be
very surprised if anyone other than Miles O'brien got it right). Space
Ship One, when coming back down from essentially a dead stop 60 miles
high, reached a speed of (just a ballpark guess) Mach 2 to Mach 3.
Something coming into the atmosphere from orbit is going at about Mach
23. It's a huge difference in speed and the amount of kinetic energy
being turned into heat.

>but I would think their engineers are
>designing for a future with true orbital flight -- and
>return from orbit. Do they have a Clever Plan to make the
>heat of re-entry not quite so hot?

I doubt it. Their plans are probably just like everyone else's:
figure out how to deal with the heat.

Maybe a super-duper rocket engine that operates in outer space will
be developed that gives a large enough thrust to slow down something
with the mass of the Shuttle so that it can just 'drop' into the
atmosphere, and have much less stringent hull designs for re-entry.
The engine would have to go down with the spacecraft, or perhaps it's
detachable and can then accelerate itself back to orbital speed to
rendevous with and decelerate another craft. Perhaps a nuclear powered
device would have enough power, but it's going to need reaction mass
from somewhere, and it's too expensive to to send it up from Earth.
Reaction mass might come from the Moon or the Astroid belt.
But making such an engine is surely beyond current budgets of
organizations such as NASA, much less the Space Ship One people. It
also has its pitfalls. If it fails after firing for 10 percent of what
it normally would take to 'stop' something in orbit, that something
will enter the atmosphere at near full orbital speed, perhaps without
being designed to do that.
To bring something like Space Ship One out of orbit, the engine
would also have to bring it down to 60 miles and leave it at a
standstill. If the craft were dropped from the usual LEO height (110
to 300 miles), it would have had at least 50 extra miles of freefall
acceleration due to gravity before hitting the atmosphere.

It takes something like ten or 20 times the energy to get something
going horizontally at orbital speed than it does to get it 100 miles
above the Earth's surface. Likewise, you have to slow down from the
orbital speed to come back (unless you want to make a supersonic
landing).

>Jim Burns

-----
http://www.mindspring.com/~benbradley

Steve Charlton

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Aug 8, 2005, 2:48:57 AM8/8/05
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In article <1123426483....@g44g2000cwa.googlegroups.com>,
arne97 <gahad...@yahoo.com> writes
Two space craft A and B, orbiting in opposite directions. They snag each
other as they pass with a very very strong and very very stretchy bungie
cord. Ssstttrrreeetttccchhh. They both stop relative to each other, they
both release the cord (at the same time) and drop vertically into the
atmosphere (as does the cord). Much less energy to shed. Much less heat
build up (the cord might get a tad warm).

Alternatively, if A releases the cord and B doesn't, tttwwwaaannnnggg! A
drops safely into the atmosphere and B + cord go zooming away at almost
twice the original speed.

Of course, when we can make a bungie cord that good, an orbital tether
will be no problem.

[Early morning review: I seem to need either more sleep or less alcohol
or both, but I'm leaving this last in anyway. Its not like this is a
serious thread.]

I don't recall anyone proposing an orbital bungie before so here goes.
Take two big masses (asteroids say) one on either end of the cord. Their
centre of mass would be in geo-stationary orbit. One is moving towards
Earth, the other away. The inbound one, decelerated by the bungie, just
touches the ground, everybody on it jumps off, everybody who wants a
really wild ride jumps on and up you go! An hour or 3 later the other
mass, with its passengers, touches down briefly and the situation
repeats. Of course, you'd need motors on the rocks, to keep everything
balanced, stop them hitting each other, smashing the odd city, etc.
There's even a tag-line for the T.V. advert - "Disney World Orbital -
what a ride!" B-)

--
Steve Charlton | You may have trouble getting
st...@gnirekoms.freeserve.co.uk | permission to aerobrake or
hint: ^^^^^^^^^ | lithobrake asteroids on Earth!
reverse this | - James D Nicoll

Marten Kemp

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Aug 8, 2005, 10:58:51 AM8/8/05
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arne97 wrote:

I wonder if sticking a whopping big ablative heat shield
(the kind of thing that was used for all the re-entry
capsules from Mercury to Apollo) on the bottom might
work. You'd have to replace it after each flight but
you wouldn't have to fiddle with those pesky tiles.

The weight differential is something upon which more
knowledgable people than I can comment.


--
-- Marten Kemp
(Fix name and ISP to reply)

Alcore

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Aug 8, 2005, 11:58:06 AM8/8/05
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On Mon, 8 Aug 2005, Marten Kemp wrote:

[snip]


>I wonder if sticking a whopping big ablative heat shield
>(the kind of thing that was used for all the re-entry
>capsules from Mercury to Apollo) on the bottom might
>work. You'd have to replace it after each flight but
>you wouldn't have to fiddle with those pesky tiles.
>
>The weight differential is something upon which more
>knowledgable people than I can comment.

[snip]

My thought on the subject was the concept of a re-entry "sled"...

Essentially, construct the entire high-heat re-entry portion of the
vehilcle as a one-piece shell that is "snap on" replaceable.

I like the notion of an ablative ceramic or metalic "belly shield" that
can be swapped out by 3 guys with screw-guns and a lifting rig for the
ship in about 20 minutes.

Gene P.
Slidell, LA

--
Alcore Nilth - The Mad Alchemist of Gevbeck
alc...@uurth.com


Edward Cherlin

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Aug 8, 2005, 1:10:32 PM8/8/05
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Alcore wrote:
>
> On Mon, 8 Aug 2005, Marten Kemp wrote:
>
> [snip]
>>I wonder if sticking a whopping big ablative heat shield
>>(the kind of thing that was used for all the re-entry
>>capsules from Mercury to Apollo) on the bottom might
>>work. You'd have to replace it after each flight but
>>you wouldn't have to fiddle with those pesky tiles.
>>
>>The weight differential is something upon which more
>>knowledgable people than I can comment.

What I want to know is how you get the shield *up* each time. You can't fold
it up and put it in the glove compartment. Besides, every kg of mass of the
thing comes out of payload.

> [snip]
>
> My thought on the subject was the concept of a re-entry "sled"...
>
> Essentially, construct the entire high-heat re-entry portion of the
> vehilcle as a one-piece shell that is "snap on" replaceable.
>
> I like the notion of an ablative ceramic or metalic

Metals conduct heat well, so they don't work as heat shields. Most of them
melt or oxidize at high temperatures, or both.

> "belly shield" that
> can be swapped out by 3 guys with screw-guns

Not metal screws, obviously, so what were you thinking?

> and a lifting rig for the
> ship in about 20 minutes.

I get it. Instead of the fiddly little tiles that have to be glued on one at
a time (and a large fraction of them break in the process because they have
to be so thin and light), we go for one humongous but equally thin
full-belly shield that breaks before you can get it into its shipping
crate, or even out of the mold where it's made. And then we only screw it
on in as many other places as we can do in what's left of our 20 minutes,
so that it will flap against the ship and break into little bitty pieces on
lift-off, and we won't have to worry about the weight on reentry.

Oh, wait, that means that it won't be there to shield the ship. Rats. It was
such a great idea. And we could have used the shipping crates for
low-income housing.

> Gene P.
> Slidell, LA


Stan

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Aug 8, 2005, 2:29:50 PM8/8/05
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Steve Charlton <st...@nospam.freeserve.co.uk> wrote:

}In article <1123426483....@g44g2000cwa.googlegroups.com>,
}arne97 <gahad...@yahoo.com> writes
}> The shuttle, as well as most other space vehicles, enter the
}>atmosphere in a blaze of heat.
}> I assume that this is a method of shedding speed.

(snip)


}Two space craft A and B, orbiting in opposite directions. They snag each
}other as they pass with a very very strong and very very stretchy bungie
}cord. Ssstttrrreeetttccchhh. They both stop relative to each other, they

}both release the cord (at the same time) ...

"Two space craft A and B, orbiting in opposite directions..."

So, to descend from the orbit of the space station, the shuttle would
have to "bungie-snag" something the same size orbiting in the exact
opposite direction. Hmmm...with the craft traveling a bit more than
5 KM/sec (someone check my orbital mechanics; I was never really good
at it) this means they would be passing each othe at more than 10 KM/sec.

More importantly, it would be that the space station would have a "visitor"
going by at a speed (& how many times a day?) that would surely make the
inhabitants a bit nervous.

Stan.

No 33 Secretary

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Aug 8, 2005, 2:41:31 PM8/8/05
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stan...@delete-this-crap-xprt.net (Stan) wrote in
news:stanleyh-080...@pdx-ppp131.pop1.net:

Plus, even slowing down by "bungee cord" would have to take long enough for
both objects to re-enter the atmosphere at high speed before they're done
slowing down. Because if they don't, the passengers are going to be tomato
paste from deceleration.

--
Terry Austin
www.hyperbooks.com
Campaign Cartographer now available

Gene P.

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Aug 8, 2005, 3:06:39 PM8/8/05
to

On Mon, 8 Aug 2005, Edward Cherlin wrote:

>What I want to know is how you get the shield *up* each time. You can't fold
>it up and put it in the glove compartment. Besides, every kg of mass of the
>thing comes out of payload.

Attatched to the ship, just like we do now, of course.

>> [snip]
>>
>> My thought on the subject was the concept of a re-entry "sled"...
>>
>> Essentially, construct the entire high-heat re-entry portion of the
>> vehilcle as a one-piece shell that is "snap on" replaceable.
>>
>> I like the notion of an ablative ceramic or metalic
>
>Metals conduct heat well, so they don't work as heat shields. Most of them
>melt or oxidize at high temperatures, or both.
>
>> "belly shield" that
>> can be swapped out by 3 guys with screw-guns
>
>Not metal screws, obviously, so what were you thinking?

Okey dokey... How about carbon fiber retaining pins then? You know,
something strong, reasonably heat resistant (they will be on the *inside*
of the shield, after all), and lightweight...

>> and a lifting rig for the
>> ship in about 20 minutes.
>
>I get it. Instead of the fiddly little tiles that have to be glued on one at
>a time (and a large fraction of them break in the process because they have
>to be so thin and light), we go for one humongous but equally thin
>full-belly shield that breaks before you can get it into its shipping
>crate, or even out of the mold where it's made. And then we only screw it
>on in as many other places as we can do in what's left of our 20 minutes,
>so that it will flap against the ship and break into little bitty pieces on
>lift-off, and we won't have to worry about the weight on reentry.
>
>Oh, wait, that means that it won't be there to shield the ship. Rats. It was
>such a great idea. And we could have used the shipping crates for
>low-income housing.

I'm thinking somebody needs some decaf.

Who said *anything* about using the same ceramic material as the existing
shuttle tiles? That stuff is designed to survive re-entry intact... not
ablate. It has *serious* structural and material properties deficiencies
for use outside of it's design envelope.

So let me try again... It's a *disposable* *easy-to-replace* heat shield.

Choose *new* materials that meet those guidelines.

(I have real trouble believing that, given the materials science
improvements since the Shuttle system selected its heat shield material in
the 70's, we aren't capable of some more advanced engineering today.)

Gene P.
Slidell LA

John Schilling

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Aug 8, 2005, 3:55:51 PM8/8/05
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In article <42F6C17F...@osu.edu>, Jim Burns says...

>
>
>Mad Bad Rabbit wrote:
>>
>> "arne97" <gahad...@yahoo.com> wrote:
>>
>> > What with broken tiles and what-not, isn't there a better
>> > way to get a ship down those last 200 miles than turning it
>> > into a meteorite ?

[...]

>How about Spaceship One, though? When I saw them on 60 Minutes,
>my impression was (1) they're using a revolutionary design
>to passively orient the ship for proper re-entry, and (2)
>they don't look like they're using NASA-style ceramic-foam tiles.

That's because they don't fly any faster than an SR-71. World
of difference between Mach 3 and Mach 30.

Yes, kudos for the revolutionary design providing passive stability
during re-entry, but that was only for *stability*. It had nothing
to do with the thermal protection issue. Rutan's passively-stable
vehicle, re-entering from Low Earth Orbit, would need the "ceramic
foam tiles" or something equivalent.


>OK, so all they've done so far is pop out of the atmosphere
>and drop back in, but I would think their engineers are
>designing for a future with true orbital flight -- and
>return from orbit. Do they have a Clever Plan to make the
>heat of re-entry not quite so hot?

Perhaps, but not that they are talking about. It's a hard problem;
one that we know how to solve, but not one that we know how to make
trivial.


--
*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" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

John Reiher

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Aug 8, 2005, 4:33:55 PM8/8/05
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In article <Xns96AC76EFAFC63ta...@216.168.3.50>,

No 33 Secretary <taustin...@hyperbooks.com> wrote:

> Plus, even slowing down by "bungee cord" would have to take long enough for
> both objects to re-enter the atmosphere at high speed before they're done
> slowing down. Because if they don't, the passengers are going to be tomato
> paste from deceleration.

When they did the tethered satellite experiment on the shuttle, the
tether generated a large voltage. This occurred because the tether was
moving through the earth's magnetic field. Theoretically you can pull
power from a tether and decelerate the attached ship. The more you pull,
the more you decelerate.

This may be a way to slow down a ship without using fuel.

--
The Kedamono Dragon
Pull Pinky's favorite words to email me.
http://www.ahtg.net
Have Mac, will Compute

Check out the PowerPointers Shop at:
http://www.cafeshops.com/PowerPointers

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Erik Max Francis

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Aug 8, 2005, 5:08:04 PM8/8/05
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John Reiher wrote:

> When they did the tethered satellite experiment on the shuttle, the
> tether generated a large voltage. This occurred because the tether was
> moving through the earth's magnetic field. Theoretically you can pull
> power from a tether and decelerate the attached ship. The more you pull,
> the more you decelerate.
>
> This may be a way to slow down a ship without using fuel.

It'll certainly slow your ship, since the electrical energy must come
from your orbital kinetic energy. But, as was pointed out earlier, low
Earth orbit is not very far from the atmosphere, so you must shed your
orbital speed very quickly to avoid hitting the atmosphere at high
speed. To shed your orbital speed rapidly through this fast means
you'll be generating tremendous amounts of electrical energy in a very
short period of time. Turned to heat, which it ultimately must be, that
will liberate as much energy as would have been liberated in you hitting
the atmosphere at orbital speed, since energy is conserved. That's
still very, very bad.

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis

I only regret that I have but one life to lose for my country.
-- Nathan Hale

No 33 Secretary

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Aug 8, 2005, 5:10:47 PM8/8/05
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John Reiher <kedamo...@Narf.mac.com> wrote in
news:kedamono.Poit-4A4...@text-west.newsfeeds.com:

> In article <Xns96AC76EFAFC63ta...@216.168.3.50>,
> No 33 Secretary <taustin...@hyperbooks.com> wrote:
>
>> Plus, even slowing down by "bungee cord" would have to take long
>> enough for both objects to re-enter the atmosphere at high speed
>> before they're done slowing down. Because if they don't, the
>> passengers are going to be tomato paste from deceleration.
>
> When they did the tethered satellite experiment on the shuttle, the
> tether generated a large voltage. This occurred because the tether was
> moving through the earth's magnetic field. Theoretically you can pull
> power from a tether and decelerate the attached ship. The more you
> pull, the more you decelerate.
>
> This may be a way to slow down a ship without using fuel.
>

You just completely missed my point, didn't you? Yes, you did.

If you slow down _slowly_, you will fall out of orbit before you are done
"slowing down." When you fall out of orbit, you will fall in to the
atmosphere. Not when you want to - when you're done "slowing down," but
much, much quicker, because you are no longer in orbit.

It's physics, and there's no clever way around it.

John Reiher

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Aug 8, 2005, 7:36:36 PM8/8/05
to
In article <_IidnSoTXdw...@speakeasy.net>,
Erik Max Francis <m...@alcyone.com> wrote:

> John Reiher wrote:
>
> > This may be a way to slow down a ship without using fuel.
>
> It'll certainly slow your ship, since the electrical energy must come
> from your orbital kinetic energy. But, as was pointed out earlier, low
> Earth orbit is not very far from the atmosphere, so you must shed your
> orbital speed very quickly to avoid hitting the atmosphere at high
> speed. To shed your orbital speed rapidly through this fast means
> you'll be generating tremendous amounts of electrical energy in a very
> short period of time. Turned to heat, which it ultimately must be, that
> will liberate as much energy as would have been liberated in you hitting
> the atmosphere at orbital speed, since energy is conserved. That's
> still very, very bad.

I'm not saying it was perfect, but it is an alternate to other methods.

As for the power being generated, you either have some hellacious
capacitors or you use it somehow.

Use the power to run an Ion drive? A mass driver? Running a laser and
vaporizing LEO garbage? Beam the power at another tether ship to boost
it into a higher orbit?

Yeah, it's problem, but, it is a novel way to resolve the problem.

Erik Max Francis

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Aug 8, 2005, 7:44:39 PM8/8/05
to
John Reiher wrote:

> I'm not saying it was perfect, but it is an alternate to other methods.
>
> As for the power being generated, you either have some hellacious
> capacitors or you use it somehow.
>
> Use the power to run an Ion drive? A mass driver? Running a laser and
> vaporizing LEO garbage? Beam the power at another tether ship to boost
> it into a higher orbit?
>
> Yeah, it's problem, but, it is a novel way to resolve the problem.

Except it doesn't resolve the problem. Again, the amount of energy you
need to liberate is so large and you need to get rid of it so quickly
(you need to shed almost all your kinetic energy before you start to dip
in the atmosphere, and as soon as you start shedding it you descend into
a lower orbit) that even if you were try to use this method to convert
the kinetic energy into electrical energy and then get rid of it, the
conversion process qualifies as an explosion.

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis

History is a set of lies agreed upon.
-- Napoleon Bonaparte

No 33 Secretary

unread,
Aug 8, 2005, 7:46:59 PM8/8/05
to
John Reiher <kedamo...@Narf.mac.com> wrote in
news:kedamono.Poit-9E8...@text-west.newsfeeds.com:

> In article <_IidnSoTXdw...@speakeasy.net>,
> Erik Max Francis <m...@alcyone.com> wrote:
>
>> John Reiher wrote:
>>
>> > This may be a way to slow down a ship without using fuel.
>>
>> It'll certainly slow your ship, since the electrical energy must come
>> from your orbital kinetic energy. But, as was pointed out earlier,
>> low Earth orbit is not very far from the atmosphere, so you must shed
>> your orbital speed very quickly to avoid hitting the atmosphere at
>> high speed. To shed your orbital speed rapidly through this fast
>> means you'll be generating tremendous amounts of electrical energy in
>> a very short period of time. Turned to heat, which it ultimately
>> must be, that will liberate as much energy as would have been
>> liberated in you hitting the atmosphere at orbital speed, since
>> energy is conserved. That's still very, very bad.
>
> I'm not saying it was perfect, but it is an alternate to other
> methods.

No. It's not. It presents exactly the same problems with heat on reentry as
the present methods. Only worse. Plus other, even more deadly problems.


>
> As for the power being generated, you either have some hellacious
> capacitors or you use it somehow.
>
> Use the power to run an Ion drive? A mass driver? Running a laser and
> vaporizing LEO garbage? Beam the power at another tether ship to boost
> it into a higher orbit?
>
> Yeah, it's problem, but, it is a novel way to resolve the problem.
>

No. It's not. It's not even a novel way to kill our astronauts.

John Reiher

unread,
Aug 8, 2005, 9:08:23 PM8/8/05
to
In article <kpSdnQ2LS6j...@speakeasy.net>,

Erik Max Francis <m...@alcyone.com> wrote:

> > Yeah, it's problem, but, it is a novel way to resolve the problem.
>
> Except it doesn't resolve the problem. Again, the amount of energy you
> need to liberate is so large and you need to get rid of it so quickly
> (you need to shed almost all your kinetic energy before you start to dip
> in the atmosphere, and as soon as you start shedding it you descend into
> a lower orbit) that even if you were try to use this method to convert
> the kinetic energy into electrical energy and then get rid of it, the
> conversion process qualifies as an explosion.

Point taken. However, the tethered power generation system is a means to
move satellites and even the ISS about in orbit:

http://science.nasa.gov/newhome/headlines/ast08sep97_1.htm

It's even been considered for deorbiting boosters for satellites. It's
technology that will be used as it reduces the need for fuel to maintain
orbit in LEO.

But yeah, for "slow landing", it's not feasible, too much power is
required.


So, what about a big-arsed balloon? You need drag, so how about
inflating a balloon about 1km in diameter around the thing you want to
deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
generate a manure load of drag.

Erik Max Francis

unread,
Aug 8, 2005, 9:20:19 PM8/8/05
to
John Reiher wrote:

> Point taken. However, the tethered power generation system is a means to
> move satellites and even the ISS about in orbit:
>
> http://science.nasa.gov/newhome/headlines/ast08sep97_1.htm
>
> It's even been considered for deorbiting boosters for satellites. It's
> technology that will be used as it reduces the need for fuel to maintain
> orbit in LEO.

No one disputed that tethered systems, electromagnetic or not, can move
things around into higher and lower orbits. But an electromagnetic
tether system cannot deorbit from low Earth orbit to a soft landing.

> So, what about a big-arsed balloon? You need drag, so how about
> inflating a balloon about 1km in diameter around the thing you want to
> deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
> generate a manure load of drag.

How does that solve the problem? The big balloon either enters too
steep and burns up or enters too shallow and skips off. Reentry
vehicles are the shape they are because that provides sufficient lift to
keep the vehicle at the right entry corridor so that it doesn't burn up
and it manages to shed its speed enough so that it can make a soft landing.

These things aren't accidents, reentry systems work the way they do for
a good reason. If there were an easy, obvious alternate solution, we'd
be using it!

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis

All of your moonlight whispers / Counterfeit, counterfeit love
-- Lamya

Arthur Kimes

unread,
Aug 8, 2005, 9:44:23 PM8/8/05
to
On Sun, 07 Aug 2005 14:53:01 -0700, Erik Max Francis <m...@alcyone.com>
wrote:

] Orbital speed is 7-8 km/s. You need to shed that much speed in order


to
] avoid burning up in the atmosphere. Furthermore, you need to shed it
] fast, because reducing your speed will make you drop inward due to
] orbital mechanics, which means that you'll touch the atmosphere if you

] don't shed it all quickly.

I've heard entry angle is critical. Too steep, you burn up real
fast. Too shallow, you skip off.
I have a question about that "too shallow" deal. So you skip
off. You've used up some delta-v and are still going to re-enter the
atmosphere real soon (depending on how far you skipped off). Assuming
you can orient the ship - couldn't you do a series of re-entries at a
too-shallow angle so that when you were finally going too slow to skip
off you had a lot less speed to burn off?

Somebody else mentioned ablative shielding. What's the
difference in weight between the current fragile tiles and a old
fashioned mercury-gemini shield big enough for the shuttle? I'm
assuming ablative shielding was so heavy that they resorted to tiles
instead but I'm curious as to what the difference was.

**Hello, My name is Inigo Montoya; You stole my tagline; Prepare to die.**

Erik Max Francis

unread,
Aug 8, 2005, 9:59:58 PM8/8/05
to
Arthur Kimes wrote:

> I've heard entry angle is critical. Too steep, you burn up real
> fast. Too shallow, you skip off.
> I have a question about that "too shallow" deal. So you skip
> off. You've used up some delta-v and are still going to re-enter the
> atmosphere real soon (depending on how far you skipped off). Assuming
> you can orient the ship - couldn't you do a series of re-entries at a
> too-shallow angle so that when you were finally going too slow to skip
> off you had a lot less speed to burn off?

Keep in mind the entry angle is not the orientation of your ship
(although obviously that's important too), but the angle of your ship's
velocity vector relative to a tangent. If you're in orbit, attempt a
reasonable deorbit and choose too shallow of an angle, you'll skip off,
and yes, you'll reintersect the Earth's atmosphere again, but it's
unlikely that your entry angle on your second attempt will be any
better. If you burn enough fuel you can of course change that, but it's
not just orientation, it's your velocity at interface.

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis

uray

unread,
Aug 8, 2005, 10:05:28 PM8/8/05
to
"Arthur Kimes" <ar...@yahoo.com> wrote in message
news:42f80a32...@news.la.sbcglobal.net...

> On Sun, 07 Aug 2005 14:53:01 -0700, Erik Max Francis <m...@alcyone.com>
> wrote:
>
> ] Orbital speed is 7-8 km/s. You need to shed that much speed in order
> to
> ] avoid burning up in the atmosphere. Furthermore, you need to shed it
> ] fast, because reducing your speed will make you drop inward due to
> ] orbital mechanics, which means that you'll touch the atmosphere if you
>
> ] don't shed it all quickly.
>
> I've heard entry angle is critical. Too steep, you burn up real
> fast. Too shallow, you skip off.
> I have a question about that "too shallow" deal. So you skip
> off. You've used up some delta-v and are still going to re-enter the
> atmosphere real soon (depending on how far you skipped off). Assuming
> you can orient the ship - couldn't you do a series of re-entries at a
> too-shallow angle so that when you were finally going too slow to skip
> off you had a lot less speed to burn off?

In the case of returning from Earth orbit, yes. I believe with Apollo it
was a different story, their velocity was so high they really would "skip
off" into Solar orbit.

It's all a matter of balancing economics and technology over estimated
risks. To much redundancy and the vehicle never leaves the pad, not enough
and it blows up. I'm not an expert but my best guess is that a "Skipping
return" would involve a lot more complexities in planning and execution.
Each of those complexities adds an element of risk. Those complexities could
result in the Shuttle trying to land in the middle of the Pacific ocean :(

The question is: Which gives the higher overall chance of successfully
achieving the mission goals while minimizing the risks?

It's not an easy question to answer and hopefully a lot of people brighter
than me are considering it.


uray

unread,
Aug 8, 2005, 10:33:07 PM8/8/05
to
"John Reiher" <kedamo...@Narf.mac.com> wrote in message
news:kedamono.Poit-9E8...@text-west.newsfeeds.com...

> In article <_IidnSoTXdw...@speakeasy.net>,
> Erik Max Francis <m...@alcyone.com> wrote:
>
>> John Reiher wrote:
>>
>> > This may be a way to slow down a ship without using fuel.
>>
>> It'll certainly slow your ship, since the electrical energy must come
>> from your orbital kinetic energy. But, as was pointed out earlier, low
>> Earth orbit is not very far from the atmosphere, so you must shed your
>> orbital speed very quickly to avoid hitting the atmosphere at high
>> speed. To shed your orbital speed rapidly through this fast means
>> you'll be generating tremendous amounts of electrical energy in a very
>> short period of time. Turned to heat, which it ultimately must be, that
>> will liberate as much energy as would have been liberated in you hitting
>> the atmosphere at orbital speed, since energy is conserved. That's
>> still very, very bad.
>
> I'm not saying it was perfect, but it is an alternate to other methods.
>
> As for the power being generated, you either have some hellacious
> capacitors or you use it somehow.
>
> Use the power to run an Ion drive? A mass driver? Running a laser and
> vaporizing LEO garbage? Beam the power at another tether ship to boost
> it into a higher orbit?

All the fancy ideas require a lot more pieces. It's proving very difficult
to beat the original and tried and true method of re-entry, simple and
effective. A capsule with a heat shield protected from launch damage and
equipped with redundant parachutes for final descent. Works on land as well
as at sea. In fact, it will land just about anywhere, screw the damn ground
controllers.


Jim Burns

unread,
Aug 8, 2005, 10:39:23 PM8/8/05
to

Erik Max Francis wrote:
>
> John Reiher wrote:
>

> > So, what about a big-arsed balloon? You need drag, so how about
> > inflating a balloon about 1km in diameter around the thing you
> > want to deorbit slowly? Even in the next to vacuum of LEO, a
> > 1km balloon should generate a manure load of drag.
>
> How does that solve the problem? The big balloon either enters
> too steep and burns up or enters too shallow and skips off.
> Reentry vehicles are the shape they are because that provides
> sufficient lift to keep the vehicle at the right entry corridor
> so that it doesn't burn up and it manages to shed its speed
> enough so that it can make a soft landing.

I seem to remember being told that the shuttle is a lifting body.
Of course, every time I hear a description of piloting the
shuttle, someone uses a phrase close to "glides like a brick."
I'm guessing, though, that the longer time spent in atmosphere
gave us a lower maximum "braking" temperature and that this
was part of a plan to give us a re-usable heat shield.

How far could that be taken? You give two options here:
a steep drop into the atmosphere or a skip out of the atmosphere.
What about hypersonic gliding in the very thin upper atmosphere?
It seems to me that if there is enough force in the atmosphere
to slow a ship down, there could be enough force to provide
lift.

Of course, the kind of wing shaped for hypersonic gliding
in near vacuum would most likely be very different from
pretty much any kind of flight in the lower atmosphere.
But let's just say NASA finally pried that Area 51 technology
loose from the DoD and the new shuttle reconfigures its
wings for the different conditions on the way down:

1) Am I right in thinking that extending the reentry would
lower the maximum skin temperature of the reentry vehicle?
2) /Is/ hypersonic flight in a near vacuum theoretically
possible?
3) Do we (someone) know how to do it?
4) How different would the wings be from something that could
fly lower down and land?
5) Suppose DoD doesn't give up it's Wierd Tech. How crazy would
you have to be to build a ship to try to fly on top the
atmosphere, inside it and land?

> These things aren't accidents, reentry systems work the way they
> do for a good reason. If there were an easy, obvious alternate
> solution, we'd be using it!

Ah, but that was before we had the Area 51 technology!

For me, making suggestions like this isn't a way of
suggesting those engineers were idiots or that I am the
Gigantic Brain (true though that may be). It's fun!
It's educational! And, at my most serious, it's a lot
like panning for gold in a played-out mine. I know ...
I'm not going to find anything worth my time, but
I can dream.

Jim Burns

Hop David

unread,
Aug 9, 2005, 12:00:27 AM8/9/05
to

Say you instantly shed 7.7 km/sec and dropped like a stone from 350 km
altitude. It would take you about 4 minutes to reach an altitude of 80
km. The mesosphere starts at that altitude and that is where meteors
start burning up.

Shed velocity gradually and it would take you longer to reach the
mesosphere since you still have angular velocity and are enjoying the
lift of centrifugal force over most the burn. Losing 7.7 km/sec over 5
minutes would subject the occupants to about 2.6 g. Not comfortable but
it certainly wouldn't make passengers "tomato paste".

I believe that presently an 80 meter/sec burn is done from 350 LEO and
that drops the perigee into the mesosphere. It takes about 45 minutes to
reach the perigee.

>
> It's physics, and there's no clever way around it.
>


--
Hop David
http://clowder.net/hop/index.html

Hop David

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Aug 9, 2005, 1:13:54 AM8/9/05
to

uray wrote:
> "Arthur Kimes" <ar...@yahoo.com> wrote in message
> news:42f80a32...@news.la.sbcglobal.net...
>
>>On Sun, 07 Aug 2005 14:53:01 -0700, Erik Max Francis <m...@alcyone.com>
>>wrote:
>>
>>] Orbital speed is 7-8 km/s. You need to shed that much speed in order
>>to
>>] avoid burning up in the atmosphere. Furthermore, you need to shed it
>>] fast, because reducing your speed will make you drop inward due to
>>] orbital mechanics, which means that you'll touch the atmosphere if you
>>
>>] don't shed it all quickly.
>>
>>I've heard entry angle is critical. Too steep, you burn up real
>>fast. Too shallow, you skip off.
>>I have a question about that "too shallow" deal. So you skip
>>off. You've used up some delta-v and are still going to re-enter the
>>atmosphere real soon (depending on how far you skipped off). Assuming
>>you can orient the ship - couldn't you do a series of re-entries at a
>>too-shallow angle so that when you were finally going too slow to skip
>>off you had a lot less speed to burn off?
>
>
> In the case of returning from Earth orbit, yes. I believe with Apollo it
> was a different story, their velocity was so high they really would "skip
> off" into Solar orbit.

A skip would shed some velocity. Apollo would have to be going faster
than escape velocity. Seems to me unlikely.

Do you have a cite?

Michael Ash

unread,
Aug 9, 2005, 2:58:59 AM8/9/05
to
Hop David <hopspageHA...@tabletoptelephone.com> wrote:
>>
>> In the case of returning from Earth orbit, yes. I believe with Apollo it
>> was a different story, their velocity was so high they really would "skip
>> off" into Solar orbit.
>
> A skip would shed some velocity. Apollo would have to be going faster
> than escape velocity. Seems to me unlikely.

Even going slower than escape velocity, a skip would leave Apollo on a
trajectory that would take a significant amount of time to return to the
Earth, probably hours or days. The command module simply wouldn't have had
enough supplies for the occupants to have survived that long, even if the
next reentry would have been at a suitable angle.

That said, this kind of reentry is apparently practical and has been used.
According to the Wikipedia entry
(http://en.wikipedia.org/wiki/Skip_reentry), it was used on the Zond lunar
explorers.

Bryan Derksen

unread,
Aug 9, 2005, 3:22:28 AM8/9/05
to
On Sun, 07 Aug 2005 19:51:58 -0500, Mad Bad Rabbit
<madbad...@yahoo.com> wrote:

>"arne97" <gahad...@yahoo.com> wrote:
>
>> What with broken tiles and what-not, isn't there a better way to
>> get a ship down those last 200 miles than turning it into a meteorite ?
>

>Yes, a space-elevator ; but we need several thousand kilometers
>of superstrong cable that we're not able to manufacture just yet.

Actually, I don't think a space elevator would be too useful to
something that's in a 200 mile orbit. The elevator's not moving at
orbital velocity, so to dock with it at the 200 mile mark you'd need
to kill your velocity with respect to the ground. That's the problem
that we're trying to deal with anyway.

For something in geosynchronous orbit or close to it, yes, a space
elevator is ideal. For lower orbits a rotating tether might work okay.

Bryan Derksen

unread,
Aug 9, 2005, 3:43:01 AM8/9/05
to
On Mon, 08 Aug 2005 22:39:23 -0400, Jim Burns <burn...@osu.edu>
wrote:

>Of course, the kind of wing shaped for hypersonic gliding
>in near vacuum would most likely be very different from
>pretty much any kind of flight in the lower atmosphere.
>But let's just say NASA finally pried that Area 51 technology
>loose from the DoD and the new shuttle reconfigures its
>wings for the different conditions on the way down:

I recall once long ago reading an article about "hypersonic
waveriders", hypothetical aircraft designed for ultra-high-speed
flight in the upper atmosphere. Perhaps they could be inverted to be
negative lifting bodies generating a high pressure zone _above_
themselves, pushing themselves downward so that they wouldn't go
hurtling off into space. They would essentially be in a low-altitude
powered orbit. A spacecraft reentering on a shallow "skip-off"
trajectory could perhaps use this effect to hold itself down in the
upper atmosphere instead.

http://www.aerospaceweb.org/design/waverider/main.shtml has some
information about waveriders in general, but doesn't discuss this
aspect of their use so I have only my fallable memory to rely on now.
Sorry.

Steve Charlton

unread,
Aug 9, 2005, 3:50:50 AM8/9/05
to
Secretary <taustin...@hyperbooks.com> writes

>stan...@delete-this-crap-xprt.net (Stan) wrote in
>news:stanleyh-080...@pdx-ppp131.pop1.net:
>
>> Steve Charlton <st...@nospam.freeserve.co.uk> wrote:
>>
>> }In article <1123426483....@g44g2000cwa.googlegroups.com>,
>> }arne97 <gahad...@yahoo.com> writes
>> }> The shuttle, as well as most other space vehicles, enter the
>> }>atmosphere in a blaze of heat.
>> }> I assume that this is a method of shedding speed.
>> (snip)
>> }Two space craft A and B, orbiting in opposite directions. They snag
>> each }other as they pass with a very very strong and very very
>> stretchy bungie }cord. Ssstttrrreeetttccchhh. They both stop relative
>> to each other, they }both release the cord (at the same time) ...
>>
>> "Two space craft A and B, orbiting in opposite directions..."
>>
>> So, to descend from the orbit of the space station, the shuttle would
>> have to "bungie-snag" something the same size orbiting in the exact
>> opposite direction. Hmmm...with the craft traveling a bit more than
>> 5 KM/sec (someone check my orbital mechanics; I was never really good
>> at it) this means they would be passing each othe at more than 10
>> KM/sec.
More like 20km/s.

>>
>> More importantly, it would be that the space station would have a
>> "visitor" going by at a speed (& how many times a day?) that would
>> surely make the inhabitants a bit nervous.
Stan,
Nobody said do it just outside the space station (see below) and anyway,
computers are already good at orbital mechanics, plotting such an
intercept should be child's play for them by the time we can make such
extraordinary materials.

>Plus, even slowing down by "bungee cord" would have to take long enough for
>both objects to re-enter the atmosphere at high speed before they're done
>slowing down. Because if they don't, the passengers are going to be tomato
>paste from deceleration.

TAustin,
There are 300 miles to fall from the space station to the top of the
atmosphere and only 100 miles of atmosphere. I believe it's only the
last 50 miles or so that really slows a spacecraft down. What makes you
think that the bungie can't slow them down without squashing the crew
with g-forces while they fall 300 miles, when atmospheric drag can do it
in 50 miles or so?

Back of an envelope calculations follow: I know, I know, I missed a lot
out; rotation of the Earth, fall off in g with height, variable
elasticity of the bungie as it stretches, etc. but I think its close
enough. I also took easy approximations and dropped fractions. Its late
and I haven't checked them, its also been a long time since college.
Feel free to check me if you want.

Deceleration from initial velocity of 10,000 m/s
v = at. 10,000 = at. (1)

We need to know how long we've got (t). Lets get that.

Distance to fall = 300 miles = 480km = 480,000m

Time to fall 480,000m under gravity
D = 0.5at^2. (2)
D = 480000m, a = g = 10m/s^2,

Rearranging gives:-
t = (2D/a)^0.5 = (960000/10)^0.5 = 96000^0.5 = 310s

Now we know how long we have for the ACME bungie to do its stuff - 310s.

Substitute t into (1).

10000 = a*310,

rearranging gives
a = v/t = 10000/310 = 32m/s = just over 3g - so no tomato paste
passengers then.

Actually, you'd want to start from a lower orbit, otherwise you'll hit
atmosphere too fast (approx. 3000m/s). You'd get too much heating. If we
raise the g-limit we can fall for less time. Six g would probably be the
limit. Using that we can fall for 160 seconds, which means a fall of
128,000m = 128km = 80 miles and we hit atmosphere at 1600m/s, so we
could get quite close to the top of the atmosphere and still only need
to pull 6g for 160s. That would bring the 2 space craft into the
atmosphere at only Mach 4. I guess we'd want pick somewhere between 3g
and 6g.

I'm pleased to see my idea would work after all. I'd been worried.
That's what you get for writing to usenet while both tired and under the
influence. Must try Irish Coffee next time. B-)
--
Steve Charlton | You may have trouble getting
st...@gnirekoms.freeserve.co.uk | permission to aerobrake or
hint: ^^^^^^^^^ | lithobrake asteroids on Earth!
reverse this | - James D Nicoll

Erik Max Francis

unread,
Aug 9, 2005, 5:38:19 AM8/9/05
to
Michael Ash wrote:

> Even going slower than escape velocity, a skip would leave Apollo on a
> trajectory that would take a significant amount of time to return to the
> Earth, probably hours or days. The command module simply wouldn't have had
> enough supplies for the occupants to have survived that long, even if the
> next reentry would have been at a suitable angle.

That's right. According to the NASA mission reports for Apollo XI,
entry interface was at 36 194 ft/s at an altitude of about 400 000 ft;
that's 11.034 km/s at an altitude of about 120 km, or just a shade under
escape speed from Earth. That's an extremely elliptical orbit from the
Earth, and even if the results of other bodies' gravity (like the Moons)
wouldn't perturb it -- it would be highly unwise.

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis

There is another world, which is not of men.
-- Li Bai

Michael Ash

unread,
Aug 9, 2005, 9:15:44 AM8/9/05
to
Bryan Derksen <bryan....@shaw-spamguard.ca> wrote:
> On Sun, 07 Aug 2005 19:51:58 -0500, Mad Bad Rabbit
> <madbad...@yahoo.com> wrote:
>
>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>> What with broken tiles and what-not, isn't there a better way to
>>> get a ship down those last 200 miles than turning it into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.
>
> Actually, I don't think a space elevator would be too useful to
> something that's in a 200 mile orbit. The elevator's not moving at
> orbital velocity, so to dock with it at the 200 mile mark you'd need
> to kill your velocity with respect to the ground. That's the problem
> that we're trying to deal with anyway.

Consider that something in low orbit doesn't need to boost to geosync, it
just needs to boost into an elliptical orbit where the high end of the
orbit is at the same speed as the space elevator at that altitude. I don't
know what kind of savings that gets you, but I expect it would be
significant. It's still more fuel than dropping altitude enough to hit the
atmosphere, but it's better than coming to a complete stop.

Also consider that there's almost no reason to be in a 200-mile orbit in
the first place if a space elevator is available. With the possible
exception of some military systems, almost everything you can do using
equipment put up in a really expensive launcher at 200 miles can be done
better using equipment put up in a cheap launcher a high altitude.

Gene P.

unread,
Aug 9, 2005, 10:30:26 AM8/9/05
to

On Mon, 8 Aug 2005, Erik Max Francis wrote:

[snip]


>How does that solve the problem? The big balloon either enters too

>steep and burns up or enters too shallow and skips off. [...]

"Skips off"... You've been watching too many movies.

Once you are in a closed orbit that intersects the atmosphere, you *will*
deorbit entirely. You might re-emerge once or twice, but eventually the
energy lost on each pass will lower the overall height of the orbit until
you *don't* re-emerge.

This myth is the result of the Apollo program moon returns. The moon
return orbit is so large (I.e. It's high enough to reach the moon!) that
if the capsule were to re-emerge, it's next pass could be days or weeks...
in which case the astronauts would surly have expired from exhaustion of
air and power supplies...

If I'm not mistaken, the lunar return orbit for Apollo 13 was actually an
escape trajectory... i.e. If they'd missed and not re-entered they had
enough speed to leave the Earth/Moon entirely. This was done so that they
would get back faster... before they ran out of air.

So, "skips off" is a myth. Once in an atmosphere intersecting orbit,
falling completely out of the sky is inevitable.

There is a problem with "skimming" the top of the atmosphere though.
Instead of a quick wash of the Dragon's Breath of re-entry, the process
becomes a slow roast... Each pass will generate some heat. And
unfortunately, once the ship has risen high enough to quit generating that
heat, it still has no easy way to shed it. It gradually soaks through the
insulation and bakes the ship.

If you do re-entry quickly, the outside skin gets so hot, that it
transfers a lot of the heat back to the atmosphere once the fast
heat-creating part of re-entry is done. This works because the air soaks
up and carries away the heat much better than the insulation underneath
the heatshield. There is no air to do this in space... so the insulation
heats up slowly until it's in equilibrium with the heat shield.

Ash Wyllie

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Aug 9, 2005, 9:38:35 AM8/9/05
to
Bryan Derksen opined

>On Sun, 07 Aug 2005 19:51:58 -0500, Mad Bad Rabbit
><madbad...@yahoo.com> wrote:

>>"arne97" <gahad...@yahoo.com> wrote:
>>
>>> What with broken tiles and what-not, isn't there a better way to
>>> get a ship down those last 200 miles than turning it into a meteorite ?
>>
>>Yes, a space-elevator ; but we need several thousand kilometers
>>of superstrong cable that we're not able to manufacture just yet.

>Actually, I don't think a space elevator would be too useful to
>something that's in a 200 mile orbit. The elevator's not moving at
>orbital velocity, so to dock with it at the 200 mile mark you'd need
>to kill your velocity with respect to the ground. That's the problem
>that we're trying to deal with anyway.

Beanstalks have, and cause, real problems for all objects not in
geosynchronous orbit.

>For something in geosynchronous orbit or close to it, yes, a space
>elevator is ideal. For lower orbits a rotating tether might work okay.


-ash
Cthulhu in 2005!
Why wait for nature?

No 33 Secretary

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Aug 9, 2005, 11:44:38 AM8/9/05
to
Hop David <hopspageHA...@tabletoptelephone.com> wrote in
news:42F82A5B...@tabletoptelephone.com:

>
>
> No 33 Secretary wrote:
>> John Reiher <kedamo...@Narf.mac.com> wrote in
>> news:kedamono.Poit-4A4...@text-west.newsfeeds.com:
>>
>>
>>>In article <Xns96AC76EFAFC63ta...@216.168.3.50>,
>>> No 33 Secretary <taustin...@hyperbooks.com> wrote:
>>>
>>>
>>>>Plus, even slowing down by "bungee cord" would have to take long
>>>>enough for both objects to re-enter the atmosphere at high speed
>>>>before they're done slowing down. Because if they don't, the
>>>>passengers are going to be tomato paste from deceleration.
>>>
>>>When they did the tethered satellite experiment on the shuttle, the
>>>tether generated a large voltage. This occurred because the tether
>>>was moving through the earth's magnetic field. Theoretically you can
>>>pull power from a tether and decelerate the attached ship. The more
>>>you pull, the more you decelerate.
>>>
>>>This may be a way to slow down a ship without using fuel.
>>>
>>
>> You just completely missed my point, didn't you? Yes, you did.
>>
>> If you slow down _slowly_, you will fall out of orbit before you are
>> done "slowing down." When you fall out of orbit, you will fall in to
>> the atmosphere. Not when you want to - when you're done "slowing
>> down," but much, much quicker, because you are no longer in orbit.
>
> Say you instantly shed 7.7 km/sec and dropped like a stone from 350 km
> altitude.

If you _instantly_ shed, well, pretty much any amount of velocity, you have
experienced infinite deceleration, and are not a fine red paste on the
front of the cabin.

Try again.

<stuff based on impossible, and deadly, mistake snipped as irrelevant>

No 33 Secretary

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Aug 9, 2005, 11:45:51 AM8/9/05
to
You have no idea what you're talking about.

John Reiher

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Aug 9, 2005, 1:37:25 PM8/9/05
to
In article <Xns96AD5927491FFta...@216.168.3.50>,

No 33 Secretary <taustin...@hyperbooks.com> wrote:

> You have no idea what you're talking about.

I agree... I'm not sure to what or about who, even if its me Austin's
talking about. :-)

I mean that's one reason for this group, to ask those "stupid questions"
and be "educated" in what may happen. (+/- 25%)

That brings up the other question: One man recovery vehicles.

http://www.astronautix.com/craftfam/rescue.htm

MOOSE is the most unique of the recovery systems postulated. I'm not
even sure it would work.

John Schilling

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Aug 9, 2005, 1:45:16 PM8/9/05
to
In article <kedamono.Poit-DB7...@text-west.newsfeeds.com>, John
Reiher says...

>So, what about a big-arsed balloon? You need drag, so how about
>inflating a balloon about 1km in diameter around the thing you want to
>deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
>generate a manure load of drag.

Which will cause it to slow down, which will cause it to fall out of
orbit, and so in a matter of minutes your big-arsed balloon will not
be in the near-vacuum of LEO, but in the upper atmosphere.

At that point, it will be generating much much more than a shitload of
drag, and a corresponding ammount of heat, and the only question is
whether it will be torn apart before it vaporizes or vice versa.
Either way, leaving the payload in the upper atmosphere at near-orbital
velocity, reducing the problem to one previously found to be Difficult.


--
*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" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

John Schilling

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Aug 9, 2005, 1:55:05 PM8/9/05
to
In article <kedamono.Poit-9E8...@text-west.newsfeeds.com>, John
Reiher says...

>
>In article <_IidnSoTXdw...@speakeasy.net>,
> Erik Max Francis <m...@alcyone.com> wrote:
>
>> John Reiher wrote:
>>
>> > This may be a way to slow down a ship without using fuel.
>>
>> It'll certainly slow your ship, since the electrical energy must come
>> from your orbital kinetic energy. But, as was pointed out earlier, low
>> Earth orbit is not very far from the atmosphere, so you must shed your
>> orbital speed very quickly to avoid hitting the atmosphere at high
>> speed. To shed your orbital speed rapidly through this fast means
>> you'll be generating tremendous amounts of electrical energy in a very
>> short period of time. Turned to heat, which it ultimately must be, that
>> will liberate as much energy as would have been liberated in you hitting
>> the atmosphere at orbital speed, since energy is conserved. That's
>> still very, very bad.

>I'm not saying it was perfect, but it is an alternate to other methods.

>As for the power being generated, you either have some hellacious
>capacitors or you use it somehow.

>Use the power to run an Ion drive? A mass driver? Running a laser and
>vaporizing LEO garbage? Beam the power at another tether ship to boost
>it into a higher orbit?

>Yeah, it's problem, but, it is a novel way to resolve the problem.

The problem is, a Space Shuttle using this technique to decelerate from
orbital velocity before falling into the atmosphere, will be generating
several *billion* watts of electric power.

The system that can effectively use several billion watts of electric
power, will not fit inside a space shuttle. The system that can simply
store power being pumped in at several billion watts, will not fit inside
a space shuttle. The system that can even just harmlessly dissipate
several billion watts of electric power, will not fit inside a space
shuttle. Just the wiring harness to deliver several billion watts of
electric power to the load, will not fit inside a space shuttle.

The best you can hope for, is to melt the tether the moment you turn it on.
Billions of watts of power in one place calls for brute-force thermodynamics,
not playing around with electricity.

George W Harris

unread,
Aug 9, 2005, 2:28:47 PM8/9/05
to
On 9 Aug 2005 10:45:16 -0700, John Schilling <schi...@spock.usc.edu>
wrote:

:In article <kedamono.Poit-DB7...@text-west.newsfeeds.com>, John


:Reiher says...
:
:>So, what about a big-arsed balloon? You need drag, so how about
:>inflating a balloon about 1km in diameter around the thing you want to
:>deorbit slowly? Even in the next to vacuum of LEO, a 1km balloon should
:>generate a manure load of drag.
:
:Which will cause it to slow down, which will cause it to fall out of
:orbit, and so in a matter of minutes your big-arsed balloon will not
:be in the near-vacuum of LEO, but in the upper atmosphere.
:
:At that point, it will be generating much much more than a shitload of
:drag, and a corresponding ammount of heat, and the only question is
:whether it will be torn apart before it vaporizes or vice versa.
:Either way, leaving the payload in the upper atmosphere at near-orbital
:velocity, reducing the problem to one previously found to be Difficult.

Clearly the answer isn't just one balloon, but
many concentric balloons. Say, ninety-nine lift balloons.
--
e^(i*pi)+1=0

George W. Harris For actual email address, replace each 'u' with an 'i'.

Hop David

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Aug 9, 2005, 4:33:51 PM8/9/05
to

Michael Ash wrote:
> Hop David <hopspageHA...@tabletoptelephone.com> wrote:
>
>>>In the case of returning from Earth orbit, yes. I believe with Apollo it
>>>was a different story, their velocity was so high they really would "skip
>>>off" into Solar orbit.
>>
>>A skip would shed some velocity. Apollo would have to be going faster
>>than escape velocity. Seems to me unlikely.
>
>
> Even going slower than escape velocity, a skip would leave Apollo on a
> trajectory that would take a significant amount of time to return to the
> Earth, probably hours or days. The command module simply wouldn't have had
> enough supplies for the occupants to have survived that long, even if the
> next reentry would have been at a suitable angle.

And that would be an earth orbit even if it does take awhile to return
to perigee. Uray was saying it would skip off into Solar orbit.

>
> That said, this kind of reentry is apparently practical and has been used.
> According to the Wikipedia entry
> (http://en.wikipedia.org/wiki/Skip_reentry), it was used on the Zond lunar
> explorers.

Hop David

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Aug 9, 2005, 4:49:21 PM8/9/05
to

No 33 Secretary wrote:

> <stuff based on impossible, and deadly, mistake snipped as irrelevant>
>

You just completely missed my point, didn't you? Yes, you did.

It would take 4 minutes to reach the mesosphere in a worst case
scenario. 5 minutes if deceleration is more gradual.

5 minutes is plenty of time to shed 7.7 km/sec without being squished to
tomatoe paste.

Hop David

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Aug 9, 2005, 5:00:59 PM8/9/05
to

No 33 Secretary wrote:
> You have no idea what you're talking about.
>

No. It is you who don't know what you're talking about.

There is plenty of time to lose your orbital velocity before you drop
into the mesosphere.

You can salvage your credibility one of two ways:

You can admit you're wrong.

You can support your argument with physics, math and numbers.


I'm predicting you'll respond with ad hominem.

If you fulfill my prediction it will be time to plonk your pathetic
troll ass.

No 33 Secretary

unread,
Aug 9, 2005, 5:31:06 PM8/9/05
to
news:42F916D1...@tabletoptelephone.com:

>
>
> No 33 Secretary wrote:
>
>> <stuff based on impossible, and deadly, mistake snipped as irrelevant>
>>
>
> You just completely missed my point, didn't you?

You are an idiot.

> Yes, you did.
>
> It would take 4 minutes to reach the mesosphere in a worst case
> scenario. 5 minutes if deceleration is more gradual.
>
> 5 minutes is plenty of time to shed 7.7 km/sec without being squished to
> tomatoe paste.
>

Now address the discussion of how much energy needs to be shed, and how,
and how you fit the equipment to do so in to a vehicle smaller than the
equipment.

You are an idiot. Your idea is stupid.

No 33 Secretary

unread,
Aug 9, 2005, 5:31:42 PM8/9/05
to
news:42F9198B...@tabletoptelephone.com:

>
>
> No 33 Secretary wrote:
>> You have no idea what you're talking about.
>>
>
> No. It is you who don't know what you're talking about.

I know you are, but what am I?


>
> There is plenty of time to lose your orbital velocity before you drop
> into the mesosphere.
>
> You can salvage your credibility one of two ways:
>
> You can admit you're wrong.
>
> You can support your argument with physics, math and numbers.
>
>
> I'm predicting you'll respond with ad hominem.
>
> If you fulfill my prediction it will be time to plonk your pathetic
> troll ass.
>

That is correct. You _will_ killfile me, because I do not allow retards to
read my posts.

Hop David

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Aug 9, 2005, 5:41:42 PM8/9/05
to

No 33 Secretary wrote:
> Hop David <hopspageHA...@tabletoptelephone.com> wrote in
> news:42F916D1...@tabletoptelephone.com:
>
>
>>
>>No 33 Secretary wrote:
>>
>>
>>><stuff based on impossible, and deadly, mistake snipped as irrelevant>
>>>
>>You just completely missed my point, didn't you?
>
>
> You are an idiot.
>
>
>>Yes, you did.
>>
>>It would take 4 minutes to reach the mesosphere in a worst case
>>scenario. 5 minutes if deceleration is more gradual.
>>
>>5 minutes is plenty of time to shed 7.7 km/sec without being squished to
>>tomatoe paste.
>>
>
> Now address the discussion of how much energy needs to be shed, and how,
> and how you fit the equipment to do so in to a vehicle smaller than the
> equipment.

Completely irrelevant to your contention that there is no time to
decelerate before hitting the mesosphere.

>
> You are an idiot. Your idea is stupid.
>

*plonk*

Erik Max Francis

unread,
Aug 9, 2005, 6:00:47 PM8/9/05
to
Gene P. wrote:

> "Skips off"... You've been watching too many movies.
>
> Once you are in a closed orbit that intersects the atmosphere, you *will*
> deorbit entirely. You might re-emerge once or twice, but eventually the
> energy lost on each pass will lower the overall height of the orbit until
> you *don't* re-emerge.

No one said anything about a deorbiting object skipping off into solar
orbit; in fact, we've talked at great length about how that _doesn't_
happen in a too-shallow deorbit burn. You could stand to read a bit
more of the thread before jumping in.

"Skips off" just means that it rises back up, before rising back down
again. When people talk about skipping rocks off lake, do you think
they mean that the rock rises up into the stratosphere? No.

--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis

Life is a predicament which precedes death.
-- Henry James

Erik Max Francis

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Aug 9, 2005, 6:02:48 PM8/9/05
to
Jim Burns wrote:

> I seem to remember being told that the shuttle is a lifting body.
> Of course, every time I hear a description of piloting the
> shuttle, someone uses a phrase close to "glides like a brick."

Well, it _is_ a lifting body. It's just not a great one compared to a
plane. If it weren't a lifting body, it wouldn't glide at all; it would
fall like a rock.

Erik Max Francis

unread,
Aug 9, 2005, 6:03:39 PM8/9/05
to
John Reiher wrote:

> MOOSE is the most unique of the recovery systems postulated. I'm not
> even sure it would work.

It would sure be a hell of a ride.

Erik Max Francis

unread,
Aug 9, 2005, 6:04:34 PM8/9/05
to
George W Harris wrote:

> Clearly the answer isn't just one balloon, but
> many concentric balloons. Say, ninety-nine lift balloons.

Guards!

Dr John Stockton

unread,
Aug 9, 2005, 5:23:55 PM8/9/05