Significant Increase in Satellite Breakups During 2006 (Forwarded)

[From Vol. 11 No. 1, January 2007 issue ORBITAL DEBRIS QUARTERLY NEWS, page
2, NASA JSC]

Significant Increase in Satellite Breakups During 2006

Although no satellite breakups were detected for nearly a year during the
period from June 2005 to the first of May 2006, the remainder of 2006
witnessed eight satellite breakups for a rate of one per month. Not since
1993 had so many breakups occurred in one year. Half of these breakups
occurred in the final quarter of the year and included one Japanese and two
U.S. rocket bodies and one Russian spacecraft. Fortunately, the debris from
these latest four satellites, with ages ranging from less than one hour to
more than 17 years, should be relatively short-lived.

On 14 September 2006 the Russian Federation launched Cosmos 2423
(International Designator 2006-039A, U.S. Satellite Number 29402), the
eighth of a series of Earth observation spacecraft which began in 1989 with
Cosmos 2031. The nearly 7-metric-ton spacecraft normally operate between an
altitude of 200 km and 350 km for periods of up to four months. A
distinctive feature of this class of spacecraft is an apparent detonation of
the vehicle at the end of mission. Debris clouds with as many as 180
members, with apogees as high as 1100 km, have been detected. Fortunately,
the low altitude of these spacecraft at the time of fragmentation leads to
very limited orbital lifetimes for the debris.

After a flight of 64 days, Cosmos 2423 completed its mission on 17 November
and generated numerous debris, of which 28 were quickly cataloged by the
U.S. Space Surveillance Network (SSN) (Satellite Numbers 29604 - 29631)
before reentering the atmosphere. Some debris were thrown into orbits with
apogees of more than 850 km, but all known debris had fallen out of orbit
within 30 days.

While the fragmentation of Cosmos 2423 had been expected, the release of at
least 62 debris by a Delta IV second stage (International Designator
2006-050B, U.S. Satellite Number 29523) soon after launch on 4 November was
not. As reported on page 3 in this issue, this rocket body successfully
completed a controlled reentry burn about an hour and a half after
delivering its payload into a 850 km, sun-synchronous orbit. However,
sometime after orbital insertion and before the de-orbit maneuver, the stage
ejected all the aforementioned debris in a retrograde direction.

The nature of the debris and the cause of their release are not yet
understood, but an investigation is underway. The primary objective is to
identify the debris generation mechanism and to implement any necessary
countermeasures to prevent a reoccurrence on future Delta IV missions.
Although the two debris thrown into the lowest orbits decayed quickly, the
orbital longevity of the remaining debris might be significantly greater,
particularly under the current low level of solar activity.

The surprise of the rapid fragmentation of the Delta IV second stage was
matched by the 3 December breakup of a Delta II second stage which had been
dormant in a low Earth orbit for 17 years. Moreover, the stage
(International Designator 1989-089B, U.S. Satellite Number 20323), which had
been used to launch NASA's COBE spacecraft, had been passivated at the end
of its mission and, therefore, should not have contained any energy sources
that could have caused the breakup. At the time of the event, the ~900 kg
stage was in an orbit of 685 km by 790 km with an inclination of 97.1 deg.

By the end of December, no debris had been officially cataloged by the U.S.
SSN, but more than 30 debris were being tracked. On a positive note, the
debris were decaying rapidly, despite their moderate altitude. Such behavior
suggests that the debris possess a high area-to-mass ratio. Observations of
the stage after the event indicated that it was tumbling rapidly. Potential
reasons for the breakup, including impact by a small object, are under
evaluation.

The final satellite breakup of 2006 involved the second stage of an H-2A
launch vehicle (International Designator 2006-037B, U.S. Satellite Number
29394), which had been in orbit for less than four months. At the time of
the event, the rocket body was in an orbit of 430 km by 490 km with an
inclination of 97.2 deg. Less than 20 debris were detected by the U.S. SSN.
The breakup bore several similarities with the fragmentation of another H-2A
second stage in August (Orbital Debris Quarter News, 10-4, p. 1). All the
debris were expected to reenter within a relatively short time.

*****

[From Vol. 11 No. 1, January 2007 issue ORBITAL DEBRIS QUARTERLY NEWS, page
3, NASA JSC]

Delta IV Performs Successful Controlled Reentry

The latest flight of the Delta IV launch vehicle has demonstrated a new
capability to execute a controlled reentry of the second stage from a
relatively high orbit. The operation not only removed the vehicle from a
long-lived orbit, where it might have been a later source for
collision-induced debris, but also eliminated any risk of injury or property
damage which might have followed an uncontrolled reentry.

The Delta IV launch system was introduced in 2002 and through October 2006
had been used on six missions to a variety of Earth orbits. The seventh
mission, carrying a U.S. meteorological spacecraft (DMSP 5D-3 F17), called
for a direct insertion of the second stage and the payload into a
sun-synchronous orbit near an altitude of 850 km. Fifteen minutes after
launch from Vandenberg Air Force Base on 4 November, the spacecraft and the
Delta IV second stage reached the target orbit and were separated about
three minutes later.

After coasting for another hour and a half, the second stage was restarted
for a final three-minute burn. Without its payload, the stage was able to
fly an extremely steep trajectory and reenter the atmosphere only a few
minutes later, rather than the leisurely 30-plus minutes normally seen with
other satellite reentries. Consequently, the debris impact footprint over an
uninhabited region of the Pacific Ocean was substantially reduced.

This demonstration proved that, given adequate residual propellants, the
Delta IV second stage has sufficient electrical power and attitude control
accuracy following payload release to conduct a controlled reentry. This
capability is of particular interest since reentry risk assessments for both
types of Delta IV second stages (with nominal dry masses of either 2.9 or
3.5 metric tons) have indicated that the amount of debris expected to
survive an uncontrolled reentry would pose a human casualty risk in excess
of the value of 1 in 10,000 set forth in the U.S. Government Orbital Debris
Mitigation Standard Practices.