Revised Orbital Debris Assessment Report REPLY by Spaceflight, Inc. SAT-STA-20150821-00060 SHERPA ODAR v2 FILED

SHERPA ODAR v2 FILED

REPLY submitted by Spaceflight, Inc.

Revised Orbital Debris Assessment Report

2015-11-02

This document pretains to SAT-STA-20150821-00060 for Special Temporal Authority on a Satellite Space Stations filing.

IBFS_SATSTA2015082100060_1113791

SHERPA Orbital Debris Assessment Report
(ODAR)
This report is presented in compliance with NASA-STD-8719.14, APPENDIX A.

Report Version: 1 , 1 0 / 2 7 / 2 0 1 5

Document Data is Not Restricted.
This document contains no proprietary, ITAR, or export controlled information.

DAS Software Version Used In Analysis: v2.0.2

SHERPA Orbital Debris Assessment Report (ODAR)

VERSION APPROVAL and/or FINAL APPROVAL*:

Jason Andrews/ Curt Blake

*Approval signatures indicate acceptance of the ODAR-defined risk.

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SHERPA Orbital Debris Assessment Report (ODAR)

Table Contents

Self‐assessment of the ODAR using the format in Appendix A.2 of NASA‐STD‐ 8719.14:............................. 4
Assessment Report Format: .......................................................................................................................... 5
ODAR Section 1: Program Management and Mission Overview ................................................................... 5
ODAR Section 2: Spacecraft Description........................................................................................................ 6
ODAR Section 3: Assessment of Spacecraft Debris Released during Normal Operations ............................. 7
ODAR Section 4: Assessment of Spacecraft Intentional Breakups and Potential for Explosions. .................. 8
ODAR Section 5: Assessment of Spacecraft Potential for On‐Orbit Collisions ............................................. 12
ODAR Section 6: Assessment of Spacecraft Post‐mission Disposal Plans and Procedures ......................... 13
ODAR Section 7: Assessment of Spacecraft Reentry Hazards...................................................................... 16
ODAR Section 8: Assessment for Tether Missions ....................................................................................... 18

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SHERPA Orbital Debris Assessment Report (ODAR)

Self-assessment of the ODAR using the format in Appendix A.2 of NASA-STD- 8719.14:
A self assessment is provided below in accordance with the assessment format provided in Appendix A.2 of NASA-STD-8719.14.

Orbital Debris Self-Assessment Report Evaluation: SHERPA Mission

Launch Vehicle Spacecraft

Requirement # Compliant
Not
Incomplete
Standard
Non
Compliant Not
Incomplete
Comments
Compliant or N/A Compliant
Compliant
4.3-1.a No Debris Released in LEO. See note 1.
4.3-1.b No Debris Released in LEO. See note 1.
4.3-2 No Debris Released in GEO. See note 1.
4.4-1 See note 1.
4.4-2 See note 1.
4.4-3 No planned breakups.
4.4-4 No planned breakups.
4.5-1 See note 1.
4.5-2 See note 1.
4.6-1(a) See note 1.
4.6-1(b) See note 1.
4.6-1(c) See note 1.
4.6-2 Spacecraft does not go to GEO.
4.6-3 Spacecraft does not go beyond LEO.
4.6-4 See note 1.
4.7-1 DAS reports human casualty probability < 1:10,000
4.8-1 No tethers used.
Notes:

1. This launch has several spacecraft manifested and the SHERPA spacecraft is not the primary mission.

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SHERPA Orbital Debris Assessment Report (ODAR)

ODAR Section 3: Assessment of Spacecraft Debris Released during
Normal Operations
Identification of any object (>1 mm) expected to be released from the spacecraft any time
after launch, including object dimensions, mass, and material: There are no intentional
releases other than payload deployments (see Mission Overview).
Rationale/necessity for release of each object: N/A.
Time of release of each object, relative to launch time: N/A.
Release velocity of each object with respect to spacecraft: N/A.
Expected orbital parameters (apogee, perigee, and inclination) of each object after release:
N/A.
Calculated orbital lifetime of each object, including time spent in Low Earth Orbit (LEO):
N/A.

Assessment of spacecraft compliance with Requirements 4.3-1 and 4.3-2 (per DAS v2.0.2)
4.3-1, Mission Related Debris Passing Through LEO: COMPLIANT
4.3-2, Mission Related Debris Passing Near GEO: COMPLIANT

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SHERPA Orbital Debris Assessment Report (ODAR)

ODAR Section 4: Assessment of Spacecraft Intentional Breakups and
Potential for Explosions.
Potential causes of spacecraft breakup during deployment and mission operations:
There is no credible scenario that would result in spacecraft breakup during normal
deployment and operations.
Summary of failure modes and effects analyses of all credible failure modes which may
lead to an accidental explosion:
In-mission failure of a battery cell protection circuit could lead to a short circuit resulting
in overheating and a very remote possibility of battery cell explosion. The battery safety
systems discussed in the FMEA (see requirement 4.4-1 below) describe the combined
faults that must occur for any of seven (7) independent, mutually exclusive failure modes
to lead to explosion.
In addition to the battery protection mentioned about, the SHERPA battery unit features
two thermal switches that completely isolate the battery electrically if the temperature gets
too high.
Detailed plan for any designed spacecraft breakup, including explosions and intentional
collisions:
There are no planned breakups.
List of components which shall be passivated at End of Mission (EOM) including method
of passivation and amount which cannot be passivated:
No components require passivation at EOM.
Rationale for all items which are required to be passivated, but cannot be due to their
design:
SHERPA’s battery charge circuits include overcharge protection and a parallel design to
limit the risk of battery failure. However, in the unlikely event that a battery cell does
explosively rupture, the size, mass, and potential energy of these small batteries is such
that while the spacecraft could be expected to vent gases, debris from the battery rupture
should be contained within the battery housing / containment device due to the lack of
penetration energy. Note that SHERPA does not have solar panels or any means to
charge the battery while on-orbit.

Assessment of spacecraft compliance with Requirements 4.4-1 through 4.4-4:
Requirement 4.4-1: Limiting the risk to other space systems from accidental explosions
during deployment and mission operations while in orbit about Earth or the Moon:

For each spacecraft and launch vehicle orbital stage employed for a mission, the program
or project shall demonstrate, via failure mode and effects analyses or equivalent analyses,
that the integrated probability of explosion for all credible failure modes of each
spacecraft and launch vehicle is less than 0.001 (excluding small particle impacts)
(Requirement 56449).
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SHERPA Orbital Debris Assessment Report (ODAR)

Compliance statement:

Required Probability: 0.001.
Expected probability: 0.000.

Supporting Rationale and FMEA details:
Battery explosion:
Effect: All failure modes below might theoretically result in battery explosion
with the possibility of orbital debris generation. However, in the unlikely event
that a battery cell does explosively rupture, the small size, mass, and potential
energy, of the selected COTS batteries is such that while the spacecraft could be
expected to vent gases, most debris from the battery rupture should be contained
within the battery housing / containment device due to the lack of penetration
energy.
Probability: Extremely Low. It is believed to be a much less than 0.1%
probability that multiple independent (not common mode) faults must occur for
each failure mode to cause the ultimate effect (explosion).

Failure mode 1: Internal short circuit.
Mitigation 1: Qualification and acceptance shock, vibration, thermal cycling, and
vacuum tests followed by maximum system rate-limited charge and discharge to
prove that no internal short circuit sensitivity exists.
Combined faults required for realized failure: Environmental testing AND
functional charge/discharge tests must both be ineffective in discovery of the
failure mode.

Failure Mode 2: Internal thermal rise due to high load discharge rate.
Mitigation 2: Cells were tested in lab for high load discharge rates in a variety of
flight-like configurations to determine like likelihood and impact of an out of
control thermal rise in the cell. Cells were also tested in a hot environment to test
the upper limit of the cells capability. No failures were seen.
Combined faults required for realized failure: Spacecraft thermal design must be
incorrect AND external over-current detection and disconnect function must fail
to enable this failure mode.

Failure Mode 3: Excessive discharge rate or short circuit due to external device
failure or terminal contact with conductors not at battery voltage levels (due to
abrasion or inadequate proximity separation).
Mitigation 4: This failure mode is negated by a) qualification-tested short circuit
protection on each external circuit, b) design of battery packs and insulators such
that no contact with nearby board traces is possible without being caused by some

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SHERPA Orbital Debris Assessment Report (ODAR)

other mechanical failure, c) obviation of such other mechanical failures by proto-
qualification and acceptance environmental tests (shock, vibration, thermal
cycling, and thermal-vacuum tests).
Combined faults required for realized failure: An external load must fail/short-
circuit AND external over-current detection and disconnect function failure must
all occur to enable this failure mode.

Failure Mode 4: Inoperable vents.
Mitigation 5: Battery vents are not inhibited by the battery holder design or the
spacecraft.
Combined effects required for realized failure: The final assembler fails to install
proper venting.

Failure Mode 5: Crushing.
Mitigation 6: This mode is negated by spacecraft design. There are no moving
parts in the proximity of the batteries.
Combined faults required for realized failure: A catastrophic failure must occur
in an external system AND the failure must cause a collision sufficient to crush
the batteries leading to an internal short circuit AND the satellite must be in a
naturally sustained orbit at the time the crushing occurs.

Failure Mode 6: Low level current leakage or short-circuit through battery pack
case or due to moisture-based degradation of insulators.
Mitigation 7: These modes are negated by a) battery holder/case design made of
non-conductive plastic, and b) operation in vacuum such that no moisture can
affect insulators.
Combined faults required for realized failure: Abrasion or piercing failure of
circuit board coating or wire insulators AND dislocation of battery packs AND
failure of battery terminal insulators AND failure to detect such failure modes in
environmental tests must occur to result in this failure mode.

Failure Mode 7: Excess temperatures due to orbital environment and high
discharge combined.
Mitigation 8: The spacecraft thermal design will negate this possibility. Thermal
rise has been analyzed in combination with space environment temperatures
showing that batteries do not exceed normal allowable operating temperatures,
which are well below temperatures of concern for explosions.

Combined faults required for realized failure: Thermal analysis AND thermal
design AND mission simulations in thermal-vacuum chamber testing AND over-
current monitoring and control must all fail for this failure mode to occur.

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SHERPA Orbital Debris Assessment Report (ODAR)

Requirement 4.4-2: Design for passivation after completion of mission operations while
in orbit about Earth or the Moon:

Design of all spacecraft and launch vehicle orbital stages shall include the ability to
deplete all onboard sources of stored energy and disconnect all energy generation
sources when they are no longer required for mission operations or postmission disposal
or control to a level which can not cause an explosion or deflagration large enough to
release orbital debris or break up the spacecraft (Requirement 56450).

Compliance statement:
SHERPA battery charge circuits include overcharge protection and a parallel
design to limit the risk of battery failure. However, in the unlikely event that a
battery cell does explosively rupture, the small size, mass, and potential energy,
of these small batteries is such that while the spacecraft could be expected to vent
gases, most debris from the battery rupture should be contained within the vessel
due to the lack of penetration energy.

Requirement 4.4-3. Limiting the long-term risk to other space systems from planned
breakups:

Compliance statement:
This requirement is not applicable. There are no planned breakups.

Requirement 4.4-4: Limiting the short-term risk to other space systems from planned
breakups:

Compliance statement:
This requirement is not applicable. There are no planned breakups.

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SHERPA Orbital Debris Assessment Report (ODAR)

ODAR Section 5: Assessment of Spacecraft Potential for On-Orbit
Collisions
Assessment of spacecraft compliance with Requirements 4.5-1 and 4.5-2 (per DAS v2.0.2,
and calculation methods provided in NASA-STD-8719.14, section 4.5.4):
Requirement 4.5-1: Limiting debris generated by collisions with large objects when
operating in Earth orbit:
For each spacecraft and launch vehicle orbital stage in or passing through LEO, the
program or project shall demonstrate that, during the orbital lifetime of each spacecraft
and orbital stage, the probability of accidental collision with space objects larger than 10
cm in diameter is less than 0.001 (Requirement 56506).

Large Object Impact and Debris Generation Probability:
Collision Probability: 0.00011; COMPLIANT.

Requirement 4.5-2: Limiting debris generated by collisions with small objects when
operating in Earth or lunar orbit:
For each spacecraft, the program or project shall demonstrate that, during the mission of
the spacecraft, the probability of accidental collision with orbital debris and meteoroids
sufficient to prevent compliance with the applicable post-mission disposal requirements is
less than 0.01 (Requirement 56507).

Small Object Impact and Debris Generation Probability:
Collision Probability: 0.0000; COMPLIANT.

SHERPA’s mission duration of <12 hours is so short that the probability of collisions with small
objects in Earth orbit affecting its mission is effectively zero.

Identification of all systems or components required to accomplish any postmission
disposal operation, including passivation and maneuvering:
SHERPA has no post-mission maneuvering or disposal operations. Post-mission
passivation consists of draining battery power. SHERPA has no propellant or pressure
vessels.

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SHERPA Orbital Debris Assessment Report (ODAR)

ODAR Section 6: Assessment of Spacecraft Post-mission Disposal Plans
and Procedures
6.1 Description of spacecraft disposal option selected: The satellite will de-orbit naturally by
atmospheric re-entry. For atmospheric drag / re-entry calculations in DAS, a cross-section drag area of
3.383 m² was assumed. This was determined via analysis of 180 equally-spaced orientations of a 3D
model of the spacecraft.

6.2 Plan for any spacecraft maneuvers required to accomplish postmission disposal:
SHERPA does not have propulsion or attitude control. There is no plan for post-mission disposal
maneuvers..

6.3 Calculation of area-to-mass ratio after postmission disposal, if the controlled reentry option is
not selected:
Spacecraft Mass: ~603 kg
Cross-sectional Area: 3.383 m2 (arithmetic mean for random tumbling)
Area to mass ratio: 0.0056103 m2/kg (arithmetic mean for random tumbling)
6.4 Assessment of spacecraft compliance with Requirements 4.6-1 through 4.6-5 (per DAS
v 2.0.2 and NASA-STD-8719.14 section):
Requirement 4.6-1: Disposal for space structures passing through LEO:
A spacecraft or orbital stage with a perigee altitude below 2000 km shall be disposed of by one
of three methods:
(Requirement 56557)
a. Atmospheric reentry option:
 Leave the space structure in an orbit in which natural forces will lead to atmospheric
reentry within 25 years after the completion of mission but no more than 30 years after
launch; or
 Maneuver the space structure into a controlled de-orbit trajectory as soon as practical
after completion of mission.
b. Storage orbit option: Maneuver the space structure into an orbit with perigee altitude greater
than 2000 km and apogee less than GEO - 500 km.
c. Direct retrieval: Retrieve the space structure and remove it from orbit within 10 years after
completion of mission.

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SHERPA Orbital Debris Assessment Report (ODAR)

for atmospheric re-entry analysis. Even if SHERPA trimmed to its minimum drag
configuration for the entirety of its post-mission lifetime, DAS reports that it will re-
enter in 19.8 years.

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SHERPA Orbital Debris Assessment Report (ODAR)

ODAR Section 7: Assessment of Spacecraft Reentry Hazards
Assessment of spacecraft compliance with Requirement 4.7-1:
Requirement 4.7-1: Limit the risk of human casualty:
The potential for human casualty is assumed for any object with an impacting kinetic
energy in excess of 15 joules:
a) For uncontrolled reentry, the risk of human casualty from surviving debris shall not
exceed 0.0001 (1:10,000) (Requirement 56626).

Summary Analysis Results: DAS v2.0.2 reports that SHERPA is compliant with the
requirement. According to DAS calculations, there is a low probability that some1 spacecraft
components (the ESPA Grande ring itself with bolted-on aluminum adapters) may reach the
ground (see DAS input data below for input parameters). However, the DAS software does not
currently allow explicit modeling of a the specific geometries for these components, so these
numbers are expected to be larger than anticipated due to conservatism in the inputs provided to
DAS. Total human casualty probability is reported by the DAS software as 1:18,900 for each
SHERPA spacecraft. This is expected to represent the absolute maximum casualty risk, as
calculated with DAS's limited modeling capability.

Analysis (per DAS v2.0.2):

10 27 2015; 15:09:22PM DAS Application Started
10 27 2015; 15:15:05PM *********Processing Requirement 4.7-1
Return Status : Passed

***********INPUT****
Item Number = 1

name = SHERPA-Zero
quantity = 1
parent = 0
materialID = 5
type = Cylinder
Aero Mass = 603.000000
Thermal Mass = 603.000000
Diameter/Width = 3.000000

name = ESPA_assembly
quantity = 1
parent = 1
materialID = 9
type = Cylinder

1
Other components that were modeled (i.e. wire harnesses, PM struts, shim, etc.) are not likely to survive reentry due to
the inability to accurately model these with sufficient fidelity within the limitations imposed by DAS. Even with these
components accounted for, SHERPA is still compliant with this requirement.
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SHERPA Orbital Debris Assessment Report (ODAR)

Aero Mass = 445.500000
Thermal Mass = 445.500000
Diameter/Width = 1.574800
Length = 1.420000

name = QP
quantity = 21
parent = 1
materialID = 9
type = Box
Aero Mass = 7.500000
Thermal Mass = 7.500000
Diameter/Width = 0.272000
Length = 0.404000
Height = 0.272000

**************OUTPUT****
Item Number = 1

name = SHERPA-Zero
Demise Altitude = 77.993621
Debris Casualty Area = 0.000000
Impact Kinetic Energy = 0.000000

*************************************
name = ESPA_assembly
Demise Altitude = 0.000000
Debris Casualty Area = 4.390694
Impact Kinetic Energy = 800968.750000

*************************************
name = QP
Demise Altitude = 69.397441
Debris Casualty Area = 0.000000
Impact Kinetic Energy = 0.000000

*************************************

=============== End of Requirement 4.7-1 ===============

Requirements 4.7-1b, and 4.7-1c below are non-applicable requirements because
SHERPA does not use controlled reentry.

4.7-1, b) NOT APPLICABLE. For controlled reentry, the selected trajectory shall
ensure that no surviving debris impact with a kinetic energy greater than 15 joules is
closer than 370 km from foreign landmasses, or is within 50 km from the continental
U.S., territories of the U.S., and the permanent ice pack of Antarctica (Requirement
56627).
4.7-1 c) NOT APPLICABLE. For controlled reentries, the product of the probability of
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SHERPA Orbital Debris Assessment Report (ODAR)

failure of the reentry burn (from Requirement 4.6-4.b) and the risk of human casualty
assuming uncontrolled reentry shall not exceed 0.0001 (1:10,000) (Requirement 56628).

ODAR Section 8: Assessment for Tether Missions
Not applicable. There are no tethers in the SHERPA mission.

END of ODAR for SHERPA

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Document Created: 2015-11-02 14:46:52
Document Modified: 2015-11-02 14:46:52

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