I hope it doesn't outlast my delete key!
On Sat, 6 Aug 2011 11:57:57 -0400 "James" [email protected] writes:
What is the life expectancy of ARISat-1? How long till the orbit degrades and it burns away?
73! James KB7TBT www.kb7tbt.com
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Thank you for your informative contribution..
Anyone with a real answer?
73! James KB7TBT www.kb7tbt.com
I hope it doesn't outlast my delete key!
On 8/6/11 8:55 PM, James wrote:
Thank you for your informative contribution..
Anyone with a real answer?
Well, an educated guess can be made by looking at a plot of ISS altitude vs time:
http://www.heavens-above.com/IssHeight.aspx
The ISS is periodically reboosted, accounting for the sudden jumps in this sawtooth-like graph. Obviously ARISSat-1 won't be reboosted, so if you extrapolate the downward-sloping parts of the graph you can get a rough idea of what will happen.
The ISS orbital decay rate varies with changes in upper atmospheric density with solar activity, but also because of changes in its attitude and the operation of the solar panels.
The orbital decay rate also depends on qthe ballistic coefficient of the object. This has units of mass divided by area -- the mass of the object divided by the cross-sectional area it presents in its direction of flight. The larger the ballistic coefficient, the less its deceleration from drag as it flies through the thin upper atmosphere.
The ISS probably has a larger ballistic coefficient than any other satellite simply because it's so huge. The volume of most objects increases as the cube of the size while the cross-sectional area increases with the square. Since mass is usually a function of volume, a large object will generally have a higher ballistic coefficient and last longer in a given orbit than a small object.
Obviously there are exceptions to the "large lives longer" rule such as the "Echo" balloons. The actual ballistic coefficient for any given satellite has to be computed from its actual mass and dimensions and its orientation relative to its velocity vector. The ISS is a huge satellite, but it also has lightweight solar wings that greatly increase its cross-sectional area without increasing its mass very much, so they decrease its ballistic coefficient somewhat.
ARISSat-1 is far smaller than the ISS, but it is fairly heavy for its size and it lacks large solar wings that create a lot of drag. This will reduce its decay rate, but it will still probably decay more quickly than the ISS.
It was tossed out the back of the ISS against the velocity vector, and that immediately put it in a lower energy orbit with a higher mean motion. But any further increase in mean motion will be due to orbital decay, and from that we should be able to estimate its ballistic coefficient and how it will likely behave in the future. Determining an exact lifetime would be difficult because of the difficulty of predicting solar activity, but a good estimate can probably be made.
--Phil
I note that, lifetime-wise, this deployment delay has actually left us much better off. The ISS had some big reboosts in June and is now at an altitude of about 387 km. Had we been deployed in February as originally scheduled, the ISS would have been at an altitude of only about 352 km.
73, Phil KA9Q
If anything, maybe this calls for another Chicken Little Contest to see who can come the closest to predicting re-entry.
73,
Jeff WB3JFS
----- Original Message ----- From: "Phil Karn" [email protected] To: "James" [email protected] Cc: [email protected] Sent: Sunday, August 07, 2011 12:34 AM Subject: [amsat-bb] Re: Life Expectancy ARISat-1
On 8/6/11 8:55 PM, James wrote:
Thank you for your informative contribution..
Anyone with a real answer?
Well, an educated guess can be made by looking at a plot of ISS altitude vs time:
http://www.heavens-above.com/IssHeight.aspx
The ISS is periodically reboosted, accounting for the sudden jumps in this sawtooth-like graph. Obviously ARISSat-1 won't be reboosted, so if you extrapolate the downward-sloping parts of the graph you can get a rough idea of what will happen.
The ISS orbital decay rate varies with changes in upper atmospheric density with solar activity, but also because of changes in its attitude and the operation of the solar panels.
The orbital decay rate also depends on qthe ballistic coefficient of the object. This has units of mass divided by area -- the mass of the object divided by the cross-sectional area it presents in its direction of flight. The larger the ballistic coefficient, the less its deceleration from drag as it flies through the thin upper atmosphere.
The ISS probably has a larger ballistic coefficient than any other satellite simply because it's so huge. The volume of most objects increases as the cube of the size while the cross-sectional area increases with the square. Since mass is usually a function of volume, a large object will generally have a higher ballistic coefficient and last longer in a given orbit than a small object.
Obviously there are exceptions to the "large lives longer" rule such as the "Echo" balloons. The actual ballistic coefficient for any given satellite has to be computed from its actual mass and dimensions and its orientation relative to its velocity vector. The ISS is a huge satellite, but it also has lightweight solar wings that greatly increase its cross-sectional area without increasing its mass very much, so they decrease its ballistic coefficient somewhat.
ARISSat-1 is far smaller than the ISS, but it is fairly heavy for its size and it lacks large solar wings that create a lot of drag. This will reduce its decay rate, but it will still probably decay more quickly than the ISS.
It was tossed out the back of the ISS against the velocity vector, and that immediately put it in a lower energy orbit with a higher mean motion. But any further increase in mean motion will be due to orbital decay, and from that we should be able to estimate its ballistic coefficient and how it will likely behave in the future. Determining an exact lifetime would be difficult because of the difficulty of predicting solar activity, but a good estimate can probably be made.
--Phil
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
I would prefer having a set of orbital elements that actually correctly predicts AOS/LOS times for a couple of days to start my "SWAG" on when it will reenter.
Sent from my iPad
On Aug 7, 2011, at 3:47 AM, "Jeff Yanko" [email protected] wrote:
If anything, maybe this calls for another Chicken Little Contest to see who can come the closest to predicting re-entry.
73,
Jeff WB3JFS
----- Original Message ----- From: "Phil Karn" [email protected] To: "James" [email protected] Cc: [email protected] Sent: Sunday, August 07, 2011 12:34 AM Subject: [amsat-bb] Re: Life Expectancy ARISat-1
On 8/6/11 8:55 PM, James wrote:
Thank you for your informative contribution..
Anyone with a real answer?
Well, an educated guess can be made by looking at a plot of ISS altitude vs time:
http://www.heavens-above.com/IssHeight.aspx
The ISS is periodically reboosted, accounting for the sudden jumps in this sawtooth-like graph. Obviously ARISSat-1 won't be reboosted, so if you extrapolate the downward-sloping parts of the graph you can get a rough idea of what will happen.
The ISS orbital decay rate varies with changes in upper atmospheric density with solar activity, but also because of changes in its attitude and the operation of the solar panels.
The orbital decay rate also depends on qthe ballistic coefficient of the object. This has units of mass divided by area -- the mass of the object divided by the cross-sectional area it presents in its direction of flight. The larger the ballistic coefficient, the less its deceleration from drag as it flies through the thin upper atmosphere.
The ISS probably has a larger ballistic coefficient than any other satellite simply because it's so huge. The volume of most objects increases as the cube of the size while the cross-sectional area increases with the square. Since mass is usually a function of volume, a large object will generally have a higher ballistic coefficient and last longer in a given orbit than a small object.
Obviously there are exceptions to the "large lives longer" rule such as the "Echo" balloons. The actual ballistic coefficient for any given satellite has to be computed from its actual mass and dimensions and its orientation relative to its velocity vector. The ISS is a huge satellite, but it also has lightweight solar wings that greatly increase its cross-sectional area without increasing its mass very much, so they decrease its ballistic coefficient somewhat.
ARISSat-1 is far smaller than the ISS, but it is fairly heavy for its size and it lacks large solar wings that create a lot of drag. This will reduce its decay rate, but it will still probably decay more quickly than the ISS.
It was tossed out the back of the ISS against the velocity vector, and that immediately put it in a lower energy orbit with a higher mean motion. But any further increase in mean motion will be due to orbital decay, and from that we should be able to estimate its ballistic coefficient and how it will likely behave in the future. Determining an exact lifetime would be difficult because of the difficulty of predicting solar activity, but a good estimate can probably be made.
--Phil
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
On 8/7/11 12:47 AM, Jeff Yanko wrote:
If anything, maybe this calls for another Chicken Little Contest to see who can come the closest to predicting re-entry.
Absolutely!
As an old friend of mine used to say about his favorite game of backgammon, this will require a combination of luck and skill.
--Phil
I remember that a few years ago with some other bird Like Ande or something like that?
Joe WB9SBD
The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com
On 8/7/2011 2:47 AM, Jeff Yanko wrote:
If anything, maybe this calls for another Chicken Little Contest to see who can come the closest to predicting re-entry.
73,
Jeff WB3JFS
----- Original Message ----- From: "Phil Karn"[email protected] To: "James"[email protected] Cc:[email protected] Sent: Sunday, August 07, 2011 12:34 AM Subject: [amsat-bb] Re: Life Expectancy ARISat-1
On 8/6/11 8:55 PM, James wrote:
Thank you for your informative contribution..
Anyone with a real answer?
Well, an educated guess can be made by looking at a plot of ISS altitude vs time:
http://www.heavens-above.com/IssHeight.aspx
The ISS is periodically reboosted, accounting for the sudden jumps in this sawtooth-like graph. Obviously ARISSat-1 won't be reboosted, so if you extrapolate the downward-sloping parts of the graph you can get a rough idea of what will happen.
The ISS orbital decay rate varies with changes in upper atmospheric density with solar activity, but also because of changes in its attitude and the operation of the solar panels.
The orbital decay rate also depends on qthe ballistic coefficient of the object. This has units of mass divided by area -- the mass of the object divided by the cross-sectional area it presents in its direction of flight. The larger the ballistic coefficient, the less its deceleration from drag as it flies through the thin upper atmosphere.
The ISS probably has a larger ballistic coefficient than any other satellite simply because it's so huge. The volume of most objects increases as the cube of the size while the cross-sectional area increases with the square. Since mass is usually a function of volume, a large object will generally have a higher ballistic coefficient and last longer in a given orbit than a small object.
Obviously there are exceptions to the "large lives longer" rule such as the "Echo" balloons. The actual ballistic coefficient for any given satellite has to be computed from its actual mass and dimensions and its orientation relative to its velocity vector. The ISS is a huge satellite, but it also has lightweight solar wings that greatly increase its cross-sectional area without increasing its mass very much, so they decrease its ballistic coefficient somewhat.
ARISSat-1 is far smaller than the ISS, but it is fairly heavy for its size and it lacks large solar wings that create a lot of drag. This will reduce its decay rate, but it will still probably decay more quickly than the ISS.
It was tossed out the back of the ISS against the velocity vector, and that immediately put it in a lower energy orbit with a higher mean motion. But any further increase in mean motion will be due to orbital decay, and from that we should be able to estimate its ballistic coefficient and how it will likely behave in the future. Determining an exact lifetime would be difficult because of the difficulty of predicting solar activity, but a good estimate can probably be made.
--Phil
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
On 2011-08-07 09:34, Phil Karn wrote:
On 8/6/11 8:55 PM, James wrote:
Thank you for your informative contribution..
Anyone with a real answer?
Well, an educated guess can be made by looking at a plot of ISS altitude vs time:
http://www.heavens-above.com/IssHeight.aspx
The ISS is periodically reboosted, accounting for the sudden jumps in this sawtooth-like graph. Obviously ARISSat-1 won't be reboosted, so if you extrapolate the downward-sloping parts of the graph you can get a rough idea of what will happen.
The ISS orbital decay rate varies with changes in upper atmospheric density with solar activity, but also because of changes in its attitude and the operation of the solar panels.
The orbital decay rate also depends on qthe ballistic coefficient of the object. This has units of mass divided by area -- the mass of the object divided by the cross-sectional area it presents in its direction of flight. The larger the ballistic coefficient, the less its deceleration from drag as it flies through the thin upper atmosphere.
The ISS probably has a larger ballistic coefficient than any other satellite simply because it's so huge. The volume of most objects increases as the cube of the size while the cross-sectional area increases with the square. Since mass is usually a function of volume, a large object will generally have a higher ballistic coefficient and last longer in a given orbit than a small object.
Obviously there are exceptions to the "large lives longer" rule such as the "Echo" balloons. The actual ballistic coefficient for any given satellite has to be computed from its actual mass and dimensions and its orientation relative to its velocity vector. The ISS is a huge satellite, but it also has lightweight solar wings that greatly increase its cross-sectional area without increasing its mass very much, so they decrease its ballistic coefficient somewhat.
ARISSat-1 is far smaller than the ISS, but it is fairly heavy for its size and it lacks large solar wings that create a lot of drag. This will reduce its decay rate, but it will still probably decay more quickly than the ISS.
It was tossed out the back of the ISS against the velocity vector, and that immediately put it in a lower energy orbit with a higher mean motion. But any further increase in mean motion will be due to orbital decay, and from that we should be able to estimate its ballistic coefficient and how it will likely behave in the future. Determining an exact lifetime would be difficult because of the difficulty of predicting solar activity, but a good estimate can probably be made.
--Phil
Actually the TLEs give you the values for the drag (First Time Derivative of the Mean Motion) and for the ballistic coefficient (BSTAR drag term). Note that in the TLEs the definition of the ballistic coefficient is the inverse of Phil's definition, i.e. the higher the BSTAR value, the higher the drag.
When comparing the latest TLE sets for the ISS and for ARISSat-1, it appears that the drag for the satellite is roughly twice as high as for the ISS. But since the values for the drag vary a lot from one TLE set to the next, it helps to use average values over a number of TLE sets.
73, Nico PA0DLO
On 8/7/11 3:40 AM, Nico Janssen wrote:
Actually the TLEs give you the values for the drag (First Time Derivative of the Mean Motion) and for the ballistic coefficient (BSTAR drag term). Note that in the TLEs the definition of the ballistic coefficient is the inverse of Phil's definition, i.e. the higher the BSTAR value, the higher the drag.
I did know that, but I didn't mention it because I thought the satellite is probably too new for these values to be especially accurate, and in the past they've always seemed rather noisy. But if they do settle down to meaningful average values then they should be useful in predicting lifetime, yes.
When comparing the latest TLE sets for the ISS and for ARISSat-1, it appears that the drag for the satellite is roughly twice as high as for the ISS. But since the values for the drag vary a lot from one TLE set to the next, it helps to use average values over a number of TLE sets.
Twice as high - now that's a very interesting data point. What are those average values?
I know that the ISS performs some drag-avoidance maneuvers with its solar arrays, such as a "night glider" mode where they're turned parallel with the velocity vector at night to reduce drag when they're not doing anything anyway. I've also noticed that rarely do they all track the sun even in the daytime. Perhaps they're off-pointed to reduce drag when maximum power is not needed.
I've always thought the ISS should do something more with all its trash than stuffing it into cargo ships and sending them back into the atmosphere. Imagine a big electrically powered slingshot that fires the trash against the velocity vector, giving a forward impulse to the ISS while simultaneously deorbiting the trash...
Phil, KA9Q
"Fast Forward" your predix software and watch it crash.
On 08/07/2011 03:55 AM, James wrote:
Thank you for your informative contribution..
Anyone with a real answer?
73! James KB7TBT www.kb7tbt.com
I hope it doesn't outlast my delete key!
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Fast Forwarding using the current keps, it first kisses the earth in central Africa on 2013/06/24 at 11:26Z
participants (8)
-
James -
Jeff Yanko -
Joe -
k6yk -
Nico Janssen -
Nigel A. Gunn, W8IFF/G8IFF -
Phil Karn -
Robert McGwier