Reports that Matter

Columbia Accident Investigation Board Report, Volume I · 2003

3.5 On-Orbit Debris Separation – The "Flight Day 2" Object

Section 21 of 80

3.5 On-Orbit Debris Separation – The "Flight Day 2" Object

Immediately after the accident, Air Force Space Command began an in-depth review of its Space Surveillance Network data to determine if there were any detectable anomalies during the STS-107 mission. A review of the data resulted in no information regarding damage to the Orbiter. However, Air Force processing of Space Surveillance Network data yielded 3,180 separate radar or optical observations of the Orbiter from radar sites at Eglin, Beale, and Kirtland Air Force Bases, Cape Cod Air Force Station, the Air Force Space Commandʼs Maui Space Surveillance System in Hawaii, and the Navy Space Surveillance System. These observations, examined after the accident, showed a small object in orbit with Columbia. In accordance with the International Designator system, the object was named 2003- 003B (Columbia was designated 2003-003A). The timeline of significant events includes:

  1. January 17, 2003, 9:42 a.m. Eastern Standard Time:

Orbiter moves from tail-first to right-wing-first orientation 2. January 17, 10:17 a.m.: Orbiter returns to tail-first orientation 3. January 17, 3:57 p.m.: First confirmed sensor track of object 2003-003B 4. January 17, 4:46 p.m.: Last confirmed sensor track for this date

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  1. January 18: Object reacquired and tracked by Cape

Cod Air Force Station PAVE PAWS

  1. January 19: Object reacquired and tracked by Space

Surveillance Network

  1. January 20, 8:45 – 11:45 p.m.: 2003-003B orbit decays. Last track by Navy Space Surveillance System

Events around the estimated separation time of the object were reviewed in great detail. Extensive on-board sensor data indicates that no unusual crew activities, telemetry data, or accelerations in Orbiter or payload can account for the release of an object. No external mechanical systems were active, nor were any translational (forward, backward, or sideways, as opposed to rotational) maneuvers attempted in this period. However, two attitude maneuvers were made: a 48-degree yaw maneuver to a left-wing-forward and payload-bay-to-Earth attitude from 9:42 to 9:46 a.m. EST), and

ON-ORBIT COLLISION AVOIDANCE

The Space Control Center, operated by the 21st Space Wingʼs

1st Space Control Squadron (a unit of Air Force Space Command), maintains an orbital data catalog on some 9,000

Earth-orbiting objects, from active satellites to space debris, some of which may be as small as four inches. The Space

Control Center ensures that no known orbiting objects will transit an Orbiter "safety zone" measuring 6 miles deep by

25 miles wide and long (Figure A) during a Shuttle mission by projecting the Orbiterʼs flight path for the next 72 hours

(Figure B) and comparing it to the flight paths of all known orbiting or re-entering objects, which generally travel at

17,500 miles per hour. Whenever possible, the Orbiter moves tail-first while on orbit to minimize the chances of orbital debris or micrometeoroids impacting the cabin windscreen or the Orbiterʼs wing leading edge.

  • If an object is determined to be — 25

within 36-72 hours of collid- mi s ing with the Orbiter, the Space le

Control Center notifies NASA, and the agency then determines a maneuver to avoid a collision.

There were no close approaches to Columbia detected during

STS-107.

Figure A. Orbiter Safety Zone

Figure B. Protecting the Orbiterʼs flight path

a maneuver back to the bay-to-Earth, tail-forward attitude from 10:17 to 10:21 a.m. It is possible that this maneuver imparted the initial departure velocity to the object.

Although various Space Surveillance Network radars tracked the object, the only reliable physical information includes the objectʼs ballistic coefficient in kilograms per square meter and its radar cross-section in decibels per square meter. An objectʼs radar cross-section relates how much radar energy the object scatters. Since radar cross-section depends on the objectʼs material properties, shape, and orientation relative to the radar, the Space Surveillance Network could not independently estimate the objectʼs size or shape. By radar observation, the objectʼs Ultra-High Frequency (UHF) radar cross-section varied between 0.0 and minus 18.0 decibels per square meter (plus or minus 1.3 decibels), and its ballistic coefficient was known to be 0.1 kilogram per meter squared (plus or minus 15 percent). These two quantities were used to test and ultimately eliminate various objects.

~12" ~ 9.0"

~ 8"

~10.5" ~4"

RCC Panel Fragment 37736 RCC Panel Fragment 2018 (From STS-107 Right Wing (From STS-107 Right Wing panel #10) panel #10) mi les Figure 3.5-1. These representative RCC acreage pieces matched the radar cross-section of the Flight Day 2 object.6 Quoted in Jenkins, Space Shuttle, p. 171. Press, 1996). 7 18 Memorandum from J. Fletcher to J. Rose, Special Assistant to the See John M. Logsdon, "Return to Flight: Richard H. Truly and the President, November 22, 1971; Logsdon, John, "The Space Shuttle Recovery from the Challenger Accident," in Pamela E. Mack, editor, Program: A Policy Failure?" Science, May 30, 1986, Volume 232, pp. From Engineering to Big Science: The NACA and NASA Collier Trophy 1099-1105. Research Project Winners, NASA SP-4219 (Washington: Government miles

In the Advanced Compact Range at the Air Force Research Laboratory in Dayton, Ohio, analysts tested 31 materials from the Orbiterʼs exterior and payload bay. Additional supercomputer radar cross-section predictions were made for Reinforced Carbon-Carbon T-seals. After exhaustive radar cross-section analysis and testing, coupled with ballistic analysis of the objectʼs orbital decay, only a fragment of RCC panel would match the UHF radar cross-section and ballistic coefficients observed by the Space Surveillance network. Such an RCC panel fragment must be approximately 140 square inches or greater in area to meet the observed radar cross-section characteristics. Figure 3.5-1 shows RCC panel fragments from Columbiaʼs right wing that represent those meeting the observed characteristics of object 2003-003B.10

Note that the Southwest Research Institute foam impact test on panel 8 (see Section 3.8) created RCC fragments that fell into the wing cavity. These pieces are consistent in size with the RCC panel fragments that exhibited the required physical characteristics consistent with the Flight Day 2 object.

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Findings:

F3.5-1 The object seen on orbit with Columbia on Flight Day 2 through 4 matches the radar cross-section and area-to-mass measurements of an RCC panel fragment.

F3.5-2 Though the Board could not positively identify the Flight Day 2 object, the U.S. Air Force ex- clusionary test and analysis processes reduced the potential Flight Day 2 candidates to an RCC panel fragment.

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