Orbital drag question

This may be a bit OT for this group, but I'll ask anyway...

Atmospheric drag causes everything in LEO to eventually
re-enter and burn up, correct? I assume that smaller, denser
items take longer, but the eventuality is always the same.
So, is there an altitude where it's generally decided that
drag no longer presents a meaningful problem? I know that
geostationary would meet that, but what about lower than that?

Given this, why would space trash from previous operations
in space present a long-term problem?

JazzMan
--
************************************************** ********
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
************************************************** ********
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
************************************************** ********

I've wondered this myself, I'd guess that for all intents and purposes,
around 400 miles might be a good start.

Is the tailing off of the density linear or logarithmic, I wonder.

As far as junk is concerned, surely some things will have lots of drag and
come back fast, while others will be up for ages.

I noted with a little dismay that during the space walk from the ISS,
several items were discarded by simply shoving them away, or so it seemed.
So what stops these becoming a problem later on?

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"JazzMan" wrote in message
...
This may be a bit OT for this group, but I'll ask anyway...

Atmospheric drag causes everything in LEO to eventually
re-enter and burn up, correct? I assume that smaller, denser
items take longer, but the eventuality is always the same.
So, is there an altitude where it's generally decided that
drag no longer presents a meaningful problem? I know that
geostationary would meet that, but what about lower than that?

Given this, why would space trash from previous operations
in space present a long-term problem?

JazzMan
--
************************************************** ********
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
************************************************** ********
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
************************************************** ********

nmp wrote:

Op Sat, 03 Sep 2005 19:36:08 +0000, schreef Brian Gaff:

I noted with a little dismay that during the space walk from the ISS,
several items were discarded by simply shoving them away, or so it seemed.

Interesting, I didn't see that - but I was not watching so very closely
all the time. Are there pictures, has there been any talk about it?

So what stops these becoming a problem later on?

I guess at low orbit these "items" (what were they?) will fall out of
orbit fast enough to never be a problem? Or anyway, perhaps this is the
justification used by astronauts to not care about them?

It would seem to me that discarding small items from the station
would be easily done by just throwing it back along the orbital
path. The station gets a microscopic boost, the trash rapidly
decellerates and burns up, leaving more room for hauling
stuff back on return vehicles. I could even see a hand-wound
spring catapult used for the same purpose.

JazzMan
--
************************************************** ********
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
************************************************** ********
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
************************************************** ********

Brian Gaff wrote:
I've wondered this myself, I'd guess that for all intents and purposes,
around 400 miles might be a good start.

It depends on what timescale you are talking about, and the ballistic
coefficient of the object in question.
Is the tailing off of the density linear or logarithmic, I wonder.

As far as junk is concerned, surely some things will have lots of drag and
come back fast, while others will be up for ages.

Remember that there is a cube / square relationship here. Your surface
area (and hence drag) goes up by the square radius, while volume (and
thus mass) goes up by the cube. It should be clear that as the
difference in radius gets larger, this will swamp most other effects.
All else being even remotely close to equal, small things will deorbit
faster.
I noted with a little dismay that during the space walk from the ISS,
several items were discarded by simply shoving them away, or so it seemed.
So what stops these becoming a problem later on?

There have been a number of hand launched satellites and medium sized
objects (tens of kilograms) discarded this way, both from ISS and Mir.
The crew is instructed to throw them back along the velocity vector.
Apparently, this is enough to prevent significant risk form recontact.
Of course, if they did recontact, the the relative velocity would be
quite small.

An interesting combination of trash and hand launch satellite is coming
up described here http://www.arrl.org/news/stories/2004/10/19/1/?nc=1


The plan is to turn a expired Orlan space suit into a small amateur
radio satellite, and shove it off from ISS.

"Brian Gaff" wrote in message
.uk...
I've wondered this myself, I'd guess that for all intents and purposes,
around 400 miles might be a good start.

Is the tailing off of the density linear or logarithmic, I wonder.

As far as junk is concerned, surely some things will have lots of drag and
come back fast, while others will be up for ages.

I noted with a little dismay that during the space walk from the ISS,
several items were discarded by simply shoving them away, or so it seemed.
So what stops these becoming a problem later on?

Brian

You have to remember the velocity of the space station and its orbit. No
other orbiting objects come within what is it? 0.2 degrees of each other.
This ends up being about 100km. So they have about 100km in the anti normal
direction when throwing stuff away before its a problem. In the low earth
orbits the stuff would definatly be pulled down before it driffed this far,
even if the astronaut threw it hard.

"JazzMan" wrote in message
...
This may be a bit OT for this group, but I'll ask anyway...

Atmospheric drag causes everything in LEO to eventually
re-enter and burn up, correct? I assume that smaller, denser
items take longer, but the eventuality is always the same.
So, is there an altitude where it's generally decided that
drag no longer presents a meaningful problem?

I think the Shuttle term for this altitude during re-entry is "Entry
Interface" or E.I. the point where the shuttle hits the atmosphere.

JD

The high altitude density of the atmosphere also depends on the state of
the solar sunspot cycle. When the sun is at the maximum of it's
approximately eleven year cycle the increase in solar radiation causes
the earth's atmosphere (ionosphere) to expand. This is why Skylab came
down. During the years it was in orbit the solar cycle reached the
maximum and the atmospheric drag increased enough to decay it's orbit.

Brian Gaff wrote:

I've wondered this myself, I'd guess that for all intents and purposes,
around 400 miles might be a good start.

Is the tailing off of the density linear or logarithmic, I wonder.

As far as junk is concerned, surely some things will have lots of drag and
come back fast, while others will be up for ages.

I noted with a little dismay that during the space walk from the ISS,
several items were discarded by simply shoving them away, or so it seemed.
So what stops these becoming a problem later on?

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________

"JazzMan" wrote in message
...
This may be a bit OT for this group, but I'll ask anyway...

Atmospheric drag causes everything in LEO to eventually
re-enter and burn up, correct? I assume that smaller, denser
items take longer, but the eventuality is always the same.
So, is there an altitude where it's generally decided that
drag no longer presents a meaningful problem? I know that
geostationary would meet that, but what about lower than that?

Given this, why would space trash from previous operations
in space present a long-term problem?

JazzMan
--
************************************************** ********
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
************************************************** ********
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
************************************************** ********

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

nmp wrote in
news

Does anyone have a list of *all* probes, satellites,
spacecraft etc. that have ever been launched, which ones
are still up there, and which of those are no longer
operational?



Don't know if this is what you're look for but...
http://planet4589.org/space/logs/satcat.txt

Larry