[amsat-bb] Dnepr Upper Stage Apogee

[M5AKA]

Thanks for that Dan, can you just confirm that the millions of items of debris that NASA was referring to are naturally occurring chunks of rock ? 


As you mention Weapons Testing in space has produced thousands of debris pieces in orbits around 800 km and below.

73 Trevor M5AKA



On Sunday, 6 July 2014, 8:03, Daniel Schultz <n8fgv at usa.net> wrote:
 


>I noticed that after the last Dnepr launch, it's upper stage was raised 
>to an apogee of 1454 km, putting it in a 1454 km x 609 km orbit with a 
>97.9 degree inclination, in order to avoid collision with any of the 37 
>satellites it released.

>There are, however, no legally binding requirements regarding debris
mitigation.


International agreement requires that objects in orbits lower than 2000 km
must exit that region within 25 years after end of mission. Objects in orbits
above 2000 km can remain there for longer than 25 years in a "disposal orbit",
but only a few missions have the excess propulsion capacity to reach that
orbit. Some US Government missions have disposed of upper stages to a higher
orbit to avoid the need to issue a Notice to Airmen concerning the falling
debris hazard. At least one polar orbiting weather satellite launch sent the
upper stage on an Earth escape trajectory for disposal.

It would seem that the Dnepr orbit is still too low to satisfy the
international requirement.

>In the case of amateur transponder satellites they can be assumed to have an
>operation lifetime of 40+ years (think OSCAR-7), as I recall debris
mitigation
>suggests re-entry within 25 years of the end of mission. For amateur
transponder
>satellites this might imply 65 years in orbit.

NASA is considering a revision to this policy to specify a total lifetime in
LEO of no more than 30 years regardless of mission lifetime. 

Other interesting facts from Scott Hull's July 1 colloquium at NASA Goddard
include:

1. There are about 22,000 objects larger than 10 centimeters in the NORAD
database, an estimated 500,000 objects between 1 and 10 centimeters which are
too small to track, and millions of objects less than one centimeter. The
Chinese Fengyun 1C disintegration in 2007 produced about 2850 trackable pieces
of debris. The new S-band space fence will be capable of tracking objects
larger than 5 centimeters when it becomes operational in 2018. 

2. There are about 4000 dead satellites on orbit, and about 1000 active
satellites. 

3. The debris population has peaks at 750, 900 and 1400 km. You would have to
go to Saturn to find a worse debris environment than that of a 750 km Low
Earth Orbit. Science missions can be difficult when you live in a minefield. 

4. Most spacecraft disintegrations are caused by battery and pressure vessel
explosions. Nickel hydrogen batteries are most susceptible to explosion but
NiCd and lithium ion batteries can also explode. A lithium ion battery must
NEVER be recharged after it has been fully drained. Rocket bodies left in GTO
are subject to explosion when the perigee height dips low enough to begin
atmospheric heating, which can cause remaining fuel in the tanks to explode.
Modern mission design requires that batteries be disconnected from solar
arrays and fully discharged and pressure tanks vented to space at the end of
the satellite mission. 

5. Space is still pretty big. We have been lucky so far. Statistics predict
another eight or nine major collisions in the next 40 years with just the
current population of debris. 

6. The movie "Gravity" did have a science adviser, and they did get a few
things right, namely that there were no loud sounds when the debris struck the
shuttle, and objects with lower area to mass ratio arrived first. Nevertheless
most NASA folks still consider the movie to be a comedy. If you have the DVD
there is an additional 20 minute documentary video about orbital debris on the
disk.

For more information see http://orbitaldebris.jsc.nasa.gov/faqs.html#6

73, Dan Schultz N8FGV









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