[meteorite-list] Threat From Retired Satellite Exceeds NASA Standards

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 26 Jan 2012 10:04:49 -0800 (PST)
Message-ID: <201201261804.q0QI4n72019256_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/news/n1201/26rxtereentry/

Threat from retired satellite exceeds NASA standards
BY STEPHEN CLARK
SPACEFLIGHT NOW
January 26, 2012

The Rossi X-ray Timing Explorer, a NASA satellite retired from service
Jan. 5, will present a 1-in-1,000 chance of harming someone when it
makes an uncontrolled fall from Earth orbit some time after 2014, a
level ten times riskier than NASA now requires for re-entering
spacecraft, according to an agency spokesperson.
 
The forecast for the satellite's re-entry calls for a return between
2014 and 2023. Fluctuations in solar activity cause the atmosphere to
expand and contract, making it difficult to accurately predict when
uncontrolled satellites will re-enter.

The satellite, launched in December 1995, was designed before NASA
issued standards for public safety from re-entering spacecraft. NASA
satellites must now have a probability of striking a person of less than
1-in-10,000.

"This satellite was launched four months before the first NASA standard
on orbital debris mitigation and re-entry risk management was issued,"
said Beth Dickey, a spokesperson at NASA Headquarters in Washington. "As
such, it was not subject to the re-entry risk guideline, since it had
already been built."

NASA's Upper Atmospheric Research Satellite, or UARS, re-entered the
atmosphere in September, spreading debris over the unpopulated Pacific
Ocean. It carried a risk of 1-in-3,200 of a human casualty, but the
event caused no injuries or damage.

"Later, NASA did evaluate the re-entry risk for RXTE and found it to be
on the order of 1-in-1,000, or about ten times the maximum desired risk
level," Dickey told Spaceflight Now.

Satellites with the risk of RXTE typically re-enter ever few years. No
one has ever been reported hurt by falling satellite debris.

The RXTE spacecraft does not carry propellant, so leftover rocket fuel
and tanks are not a concern, according to NASA officials.

Germany's ROSAT X-ray observatory uncontrollably crashed back into
Earth's atmosphere in October with a 1-in-2,000 risk of harming a
person. There were no reports of casualties from ROSAT's re-entry.

RXTE is circling 294 miles above Earth in an orbit that passes over
regions between 23 degrees north and south latitude. When the
7,000-pound satellite falls from orbit, it will only threaten areas
lying under its equatorial flight path.

During its 16-year mission, RXTE gave researchers glimpses of the inner
workings of black holes and neutron stars.
Received on Thu 26 Jan 2012 01:04:49 PM PST