EXP-TESS-RQMT-0001
Rev #Pre-Release 20131212
Mission Requirements Document
Transiting Exoplanet Survey Satellite (TESS)
Mission Requirements Document (MRD)
Effective Date: TBD: Pre-Release 20131212
Expiration Date: TBD: Pre-Release 20131212
Goddard Space Flight Center
Greenbelt, Maryland
National Aeronautics and
Space Administration
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Mission Requirements Document
CM FOREWORD
This document is a TESS controlled document. Changes to this document require prior approval
from the TESS Program Office. Proposed changes shall be submitted to the TESS Configuration
Management Office (CMO), along with supportive material justifying the proposed change.
Questions or comments concerning this document should be addressed to:
EHPD Configuration Management Office
Mail Stop 460
Goddard Space Flight Center
Greenbelt, Maryland 20771
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Mission Requirements Document
REVIEW/APPROVAL PAGE
Prepared by:
/electronic signature on file/
Benjamin Cichy
TESS Systems Engineer
Code 599
_______
Date
Reviewed by:
/electronic signature on file/
George Ricker
TESS Principle Investigator
MKI
_______
Date
/electronic signature on file/
TBD
TESS Project Scientist
Code TBD
_______
Date
/electronic signature on file/
TBD
TBD: SMA
TBD
_______
Date
/electronic signature on file/
TBD
TBD: OSC
TBD
_______
Date
/electronic signature on file/
TBD
TBD: MKI/LL
TBD
_______
Date
/electronic signature on file/
TBD
TBD: FDF
TBD
_______
Date
Approved by:
/electronic signature on file/
Jeff Volosin
TESS Project Manager
Code 401
_______
Date
All reviews and approvals are electronic via the TESS MIS at:
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DOCUMENT CHANGE RECORD
Rev/Version
Description of Change
Level
2013/12/12 -Added back requirements on mission life
and extended mission consumables that
were erroneously deleted.
-Expanded GND allocation to be one of
MOC,SOC,FD,TSO
-Added inertial frame requirement
-Updated science requirements to reflect
changes to L1 requirements
-Removed requirements on pointing and
stability that will be covered in the
Allocations Requirements Document
Approved By
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Date
Approved
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Mission Requirements Document
LIST OF TBDs AND TBRs
REQ ID
MRD_13
MRD_16
MRD_17
MRD_26
MRD_49,
MRD_53
MRD_82,
MRD_83
MRD_86
MRD_98
MRD_4
MRD_71
Description
Instrument availability. Updated this requirement
to allocate to instrument 6+ days of lost observations
per observation period.
Measurement time tag precision. TBR on value
required by science.
Measurement time tag accuracy. TBR on value
required by science.
Instrument Solar Heat Flux. TBD req
Orbital Debris. TBD as to whether TESS must
comply with GEO orbital debris requirements.
Range Safety. Review whether these requirements
can be tailored to match OSC design.
Instrument Robustness. Discuss if we need this req.
Observatory LAHO Sun Angle. Do we need to add
an epsilon to the 90 degrees.
Contamination Control. Need to add requirement
from instrument at this level.
Downlink Performance. Review margin.
Owner
Cichy
Due Date
12/20/13
Vanderspek
12/20/13
Vanderspek
12/20/13
Hynes
Hynes
12/20/13
12/20/13
Hynes
12/20/13
Cichy
Cichy
12/20/13
12/20/13
Cichy
12/20/13
Cichy
12/20/13
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Mission Requirements Document
Table of Contents
1.0
Introduction ................................................................................................................................. 1
2.0
Mission Description ................................................................................................................... 2
3.0
Requirements .............................................................................................................................. 2
4.0
Appendix A Definitions ............................................................................................................. 2
5.0
Appendix B Requirements Verification Matrix ................................................................ 3
6.0
Appendix C Requirements Linkage Audit .......................................................................... 4
1.1
1.2
Mission Overview................................................................................................................................... 1
Requirements Architecture ............................................................................................................... 1
3.1 General Requirements ......................................................................................................................... 2
3.2 Science Requirements .......................................................................................................................... 2
3.3 Mission Phase Requirements ............................................................................................................ 1
3.3.1 Prelaunch .......................................................................................................................................................... 1
3.3.2 Launch ................................................................................................................................................................ 1
3.3.3 Ascent and Commissioning........................................................................................................................ 1
3.3.4 Science Operations ........................................................................................................................................ 1
3.3.5 Decommissioning .......................................................................................................................................... 2
3.4 Mission Design and Navigation Requirements ........................................................................... 2
3.5 Mission Operations Requirements .................................................................................................. 2
3.6 Mission Robustness and Safety Requirement ............................................................................. 2
3.7 Data Handling Processing and Archiving ...................................................................................... 2
3.8 Project Interfaces................................................................................................................................... 2
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1.0
Introduction
This document contains the mission-level requirements for the Transiting
Expolanet Survey Satellite (TESS).
1.1
Mission Overview
TESS will discover thousands of exoplanets in orbit around the brightest stars in
the sky. In a two-year survey, TESS will monitor 500,000 stars for tem- porary drops in
brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey
will identify planets ranging from Earth-sized to gas giants, around a wide range of stellar
types and or- bital distances. No ground-based survey can achieve this feat. TESS stars
will be 30-100 times brighter than those in the relatively narrow field-of-view of the
Kepler satellite, and therefore TESS planets will be orders-of-magnitude easier to
characterize with follow-up observations. At last it will be possible to study the masses,
sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a
sample of rocky worlds in the habitable zones of their host stars. TESS will provide
prime targets for observation with the James Webb Space Telescope (JWST), as well as
other large ground-based and space-based telescopes of the future. TESS data will be
made public 6 months after downlink, inviting immediate community-wide efforts to
study the new planets. The TESS legacy will be a catalog of the nearest and brightest
main-sequence stars hosting transiting exoplanets, which will forever be among the most
favorable targets for detailed investigations.
Figure 1: Observatory Overview and Coordinate Frames
1.2
Requirements Architecture
The TESS MRD responds to the Program Level Requirements (L1) levied in the
Appendix to the Explorers Program Plan.
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2.0
Mission Description
A detailed mission description can be found in the Operations Concept Document
(EXP-TESS-TBD).
3.0
Requirements
3.1
General Requirements
MRD_2 Mission Life
The TESS Project shall be designed to operate for a 2 year mission after a 2 month postlaunch commissioning phase.
Rationale: Programmatic constrains from HQ.
Allocation: SC, INSTR, MOC, FD, SOC, TSO
MRD_102 Extended Mission Consumables
The TESS Project shall launch with sufficient propellant to operate for 4 years in the
science orbit.
Rationale: Enables the possibility of an extended mission.
Allocation: SC
MRD_3 Environmental Requirements
The TESS Project shall meet the requirements in the Environmental Requirements
Document (ERD).
Rationale: Levy requirements from LV environments and on-orbit environments. ERD
will include LV and transportation mechanical & thermal environments, as well as
radiation on-orbit thermal requirements
Allocation: SC, INSTR
MRD_4 Contamination Control
The TESS Project shall deliver an Observatory with contamination levels consistent with
the objectives of the mission. (TBD)
Rationale: Parent for contamination requirements at L3 and L4. The TESS Project
Contamination Control Plan outlines the processes that will be followed to achieve these
requirements.
Allocation: SC, INSTR
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MRD_5 Orbital Debris
The TESS Project shall prevent the release of any orbital debris during nominal
Observatory deployment, operations, and disposal.
Rationale: Elminates need for TESS to demonstrate mitigations to released debris per
NASA Standard Process for Limiting Orbital Debris (NASA-STD-8719.14).
Allocation: SC, INSTR, LV
MRD_6 Probability of Accidental Explosion
The TESS Project shall have an integrated probability of explosion for all credible failure
modes of the Observatory and Launch Vehicle less than 0.001 (excluding small particle
impacts).
Rationale: Required per NASA Standard Process for Limiting Orbital Debris (NASASTD-8719.14). Requirement 4.4.2.1.1.
Allocation: SC, LV
MRD_7 Common Reference Frames
The TESS Project shall comply with the reference frames in Figure 1.
Rationale: Good practice that all elements use the same reference frames
Allocation: SC, INSTR, MOC, FD, SOC, TSO
MRD_100 Inertial Reference Frame
The TESS Project shall use J2000 as the inertial reference frame for all interfaces.
Rationale: Standardize inertial reference frame across the project
Allocation: SC, INSTR, MOC, FD, SOC, TSO
MRD_99 Technical Allocations
The TESS Project shall meet the requirements in the Technical Allocations Requirements
Document (ARD)
Rationale: Allocates project-level resources between project elements.
Allocation: SC, INSTR
3.2
Science Requirements
MRD_9 Instrument Accommodation
The TESS Project shall accommodate a wide field imaging photometer (the Instrument).
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Rationale: Parent for L3 accommodation requirements.
Allocation: SC, INSTR
MRD_10 Observation Period
The TESS Project shall have a High Altitude Science Observation (HASO) period of at
least 25 days.
Rationale: Requirement on orbit so that instrument has the opportunity to observe target
stars for a minimum of 25 days.
Allocation: FD
MRD_11 Instrument FOV
The TESS Project Instrument field of view (FOV) shall be at least 23 deg x 90 deg
oriented from ecliptic plane to ecliptic pole.
Rationale: L1-BSR1 requires distribution of targets over celestial sphere. This
requirement ensures that during the 2 year mission TESS will be able to observe a large
fraction of the sky by observing 26 sectors each for 2 orbits. L1-BSR2 requires the FOV
to cover the ecliptic poles.
Allocation: INSTR
MRD_12 Targets per Observation Period
The TESS Project shall be capable of observing 15000 target stars per orbit distributed
over the Instrument FOV.
Rationale: Level 1 BSR1 requires 200,000 stars over the course of the mission. In order
to account for variation in stellar density this number is scaled by a factor of sqrt(3).
Dividing the scaled number by the 26 observation periods of the mission and rounding
and adding some margin yields 15000 target stars per period.
Allocation: INSTR
MRD_13 Instrument Availability
The TESS Project shall collect data from each target star for at least [20 TBR] days
during each 2 orbit observing period. (TBD)
Rationale: This accounts for loss due to LAHO, Earth/Moon interference, eclipses, etc…
Allocation: INSTR
MRD_15 Postage Stamp Photometric Measurements
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The TESS Project shall generate a series of continuous "Postage Stamp" photometric
measurements centered on each target star with integration times less than or equal to 64
seconds.
Rationale: Primary science product with sufficient resolution to detect planetary transits
and perform astroseismology.
Allocation: INSTR
MRD_16 Measurement Time Precision
The TESS Project shall align Postage Stamps made of a target star on adjacent orbits with
a relative precision of +/- [5 TBR] sec.
Rationale: Roland to provide (TBD)
Allocation: SC, INSTR
MRD_17 Measurement Time Tag Accuracy
The TESS Project shall timetag Postage Stamps with an accuracy of +/- [500 TBR] ms
relative to UTC.
Rationale: Roland to provide (TBD)
Allocation: SC, INSTR, MOC
MRD_18 Full Frame Images
The TESS Project shall be capable of generating and collecting Full Frame Images from
the Instrument every 2 hours.
Rationale: Primarily for diagnostic purposes. CSR specifies 12 per day, however
frequency will be specified in operations.
Allocation: INSTR
MRD_19 Measurement Sensitivity
The TESS Instrument shall have an instrumental effictive area, defined as the product of
the geometric area of the entrance pupil, the CCD QE over the 0.6-1.0 um bandpass, the
transmissivity of the optics, and the transmissivity of the bandpass filter, of at least 50
cm^2.
Rationale:
Allocation: INSTR
MRD_20 Coarse Pointing Control
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The Observatory shall point the Instrument boresight to within 120 arc-sec 3-sigma
without the use of the Instrument.
Rationale: The Instrument does not support a lost-in-space attitude solution. Coarse
pointing is required to get the instrument on to the correct guide stars. Includes thermomechanical misalignment between Instrument and Spacecraft.
Allocation: SC
MRD_26 Instrument Solar Heat Flux
The Observatory shall limit the solar flux on the Camera Structure Assembly to [6 TBR]
W/m^2 during nominal operations. (TBD)
Rationale: To maintain a stable thermal environment for the instrument during science
operations, and limit thermal transients during LAHO. Does not apply during fault
conditions. Parent for sunshade on Observatory, and also constrains slew design during
LAHO.
Allocation: SC, MOC, FD
MRD_27 Noise Floor
The Observatory shall have a photometric noise floor of 60 ppm or better on a timescale
of 1 hour during High Altitude Science Operations (HASO).
Rationale: Flowdown of L1 to allow for detection of Earth sized planet transits.
Allocation to SC and INSTR at L3 tracked in ARD.
Allocation: SC, INSTR
MRD_28 Science Context Data
The TESS Project shall collect, transmit, and archive Ancillary Spacecraft data and
Instrument Housekeeping data to support science analysis.
Rationale: Ancillary data allows ground post-processing of science data.
Allocation: SC, INSTR, MOC, SOC
MRD_30 Follow-Up Direct Imaging
The TESS Project shall be capable of performing direct imaging and follow-up
observations for 5000 targets.
Rationale: Identify sufficient number of targets for spectroscopic follow-up observations
Allocation: TSO
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MRD_31 Follow-Up Reconnaissance Spectroscopy
The TESS Project shall be capable of performing spectroscopic follow-up observations
for 2000 targets.
Rationale: Identify sufficient number of targets for high s/n transit photometery
Allocation: TSO
MRD_97 Follow-Up Transit Photometry
The TESS Project shall be capable of performing high S/N transit photometry follow-up
observations for 100 targets.
Rationale: Identify sufficient number of targets for radial velocity measurements
Allocation: TSO
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MRD_32 Follow-Up Radial Velocity
The TESS Project shall be capable of performing radial velocity follow-up measurement
of 100 targets.
Rationale: Peform a sufficient number of radial velocity measurements to achieve the L1
of 50 measured masses
Allocation: TSO
3.3
Mission Phase Requirements
3.3.1 Prelaunch
MRD_35 Integration and Test
The TESS Project shall be designed to support Observatory Integration, Test, and Launch
Site operations.
Rationale: The project must design for test, integration, and launch in addition to on orbit
operations. Hardware and software design must account for safe operations in all
environments.
Allocation: SC, INSTR, MOC, FD, SOC, LV
3.3.2 Launch
MRD_38 Initial Acquisition
The TESS Project shall acquire telemetry from the Observatory no later than separation +
2 minutes.
Rationale: Spacecraft transmitter must be powered OFF during launch due to LV
constraints. This requirement sets the time at which first contact with the spacecraft can
be established. 2 minutes chosen to minimize telemetry outage duration around LV sep
critical event, and provide time for SC to turn on transmitter and ground to acquire signal.
Allocation: SC, MOC, FD
MRD_39 Post Launch Autonomy
The Spacecraft shall autonomously achieve a thermally stable and power positive state
after separation from the Launch Vehicle.
Rationale: Any critical deployments must happen autonomously so that the health of the
vehicle does not depend on the ability of the ground to command the vehicle.
Allocation: SC
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3.3.3 Ascent and Commissioning
MRD_41 Commissioning
The TESS Project shall characterize the health and performance of the Observatory
within 2 months after launch.
Rationale: Enables project to evaluate end-to-end system operation, and troubleshoot any
issues early in operations.
Allocation: SC, INSTR, MOC, SOC
MRD_42 Operational Orbit
The TESS Project shall achieve the operational science orbit within 2 months after
launch.
Rationale: Allows for a full 2 year science mission
Allocation: FD
3.3.4 Science Operations
MRD_46 LAHO
The TESS Project shall be capable of performing all required Observatory housekeeping
and data downlink during Low Altitude Housekeeping Operations (LAHO) spanning
Perigee +/- 8 hours.
Rationale: Bounds the time that the observatory will be down for communication and
engineering activities each orbit. Also sets time range where s/c must be able to support
high-rate communication passes.
Allocation: SC, INSTR, MOC, FD
MRD_45 HASO Telemetry
The TESS Project shall be designed to receive Observatory Houskeeping Data during
HASO.
Rationale: Allows for ground operations team to evaluate and respond to onboard
anomalies without waiting up to 13 days for the next LAHO communications
opportunity.
Allocation: SC, MOC
MRD_47 Target Specification
The Observatory shall point the Instrument at a ground specified inertial target.
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Rationale: Observing strategy will be based on pointing the instrument boresight at 26
different inertial targets to define observation sectors.
Allocation: SC, SOC
3.3.5 Decommissioning
MRD_49 Decommissioning
The TESS Project shall be designed to decommission and passivate the Observatory at
the end of the mission. (TBD)
Rationale: Required per NASA Standard Process for Limiting Orbital Debris (NASASTD-8719.14)
Allocation: SC, MOC, FD
3.4
Mission Design and Navigation Requirements
MRD_51 Mission Orbit
The TESS Project shall achieve an operational orbit that is a 2:1 lunar resonance High
Earth Orbit.
Rationale: This orbit provides long science view periods, periods that are close to the
earth for downlink & is, to first order, stable with respect to lunar perturbations.
Allocation: FD, LV
MRD_52 Mission Orbit Max Perigee
The TESS Project shall operate the Observatory in orbits with perigee less than 22 Re for
the mission life.
Rationale: Allows for balance of Transmitter power, downlink rate & pass duration using
standard DSN 34m dishes
Allocation: SC, FD
MRD_101 Mission Orbit Max Apogee
The TESS Project shall operate the Observatory in orbits with apogee less than 90 Re for
the mission life.
Rationale: Bounds communication requirements during HASO. The semimajor axis of
the TESS science orbit is close to 38 Re. With perigee at its lowest allowed, 7 Re, the
apogee would be at its highest possible, 2*38 – 7 = 69 Re. However these are all bounded
by the post-lunar encounter apogee which is 90 Re.
Allocation: SC, FD
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MRD_53 Avoidance of Geosynchronous Orbit
The TESS Project shall achieve an operational orbit that does not intersect the GEO band
for a period of at least 100 years after end of mission. (TBD)
Rationale: Required per NASA Standard Process for Limiting Orbital Debris (NASASTD-8719.14). Requirement 4.6.2.2 specifies disposal at EOM to be above GEO for at
least 100 years. Requirement 4.6.2.4 specifies a probability of success of 0.9 for disposal
operations. The latter is satisfied by operating the mission during nominal ops in the
desired disposal orbit (dispose in place).
Allocation: FD, LV
MRD_54 Launch Period
The TESS Project shall have launch opportunities on 25 days of any given Lunar cycle.
Rationale: Maximize the probability of launch within a given lunar cycle. 25 days ~=
90% of lunar cycle.
Allocation: FD, LV
MRD_55 Launch Window
The TESS Project shall provide for launch windows of at least 20 minutes during each
day of the launch period.
Rationale: Allow for minor delays in launch countdown (e.g. weather or clearing of
range).
Allocation: FD, LV
MRD_56 Eclipse Frequency and Duration
The TESS Project shall limit the total number of eclipses during the nominal mission to
16 with one eclipse that has a max duration of 6 hours, and the remainder having max
durations of 4 hours.
Rationale: Allows power system sizing for reasonable battery size while providing
adequate flexibility in mission design targeting of lunar fly-by and launch day of year
constraints.
Allocation: SC, FD, LV
MRD_57 Observatory HASO Sun Angle
The TESS Project shall collect science data over the range +/-15° between the Spacecraft
z-axis projected onto the ecliptic plane and the anti-sun vector.
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Rationale: Constrains science operations to allow for thermal and power limits. Mission
design requires 13.5 degrees. 15 degrees provides approximately 10 percent margin over
requirement for variations in orbital period.
Allocation: SC, INSTR, FD
MRD_98 Observatory LAHO Sun Angle
The TESS Project shall operate across a range of sun angles less than [90 TBR] degrees
during LAHO.
Rationale: Sets performance spec for solar arrays and thermal design.
Allocation: SC, INSTR, FD
MRD_58 Observatory Pitch Angle
The TESS Project shall collect science data at pitch angles from 45° to 67.5° measured
from the ecliptic plane
Rationale: Nominal operations will always be at 45 degrees. 67.5 degrees for off nominal
case where camera closest to celestial pole fails, and operations team must reorient the
Observatory in order to meet threshold coverage of long-duration targets.
Allocation: SC, INSTR, FD
MRD_59 Orbit Determination during ascent
The TESS Project shall determine the orbit ephemerides during ascent to less than 3 km
(X,Y, Z J2000, 3sigma)
Rationale: Allow for pointing of DSN antennas & dV maneuver planning
Allocation: SC, FD
MRD_60 Orbit Determination during science orbits
The TESS Project shall determine the orbit ephemerides during the science orbit to less
than 3 km (X,Y, Z J2000, 3sigma)
Rationale: Allow for pointing of DSN antennas and control of orbit
Allocation: SC, FD
MRD_61 Slew Performance
The Spacecraft shall be capable of slewing >0.3°/sec with a control accuracy of ≤5° (3
sigma, per axis).
Rationale: The requirement is driven by the operations duration concept and efficiency.
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Allocation: SC, MOC, FD
MRD_62 Delta-V Attitude Accuracy
The Spacecraft shall control the Observatory thrust axis during ∆V maneuvers to within
5° of the desired target.
Rationale: Provides proper pointing during all maneuvers.
Allocation: SC, FD
MRD_63 Delta-V Maneuver Accuracy
The Spacecraft shall perform ∆V maneuver with an accuracy of +/- 5%.
Rationale: Bounds uncertainty for maneuver design. 5% used based on rule of thumb.
Allocation: SC, FD
3.5
Mission Operations Requirements
MRD_66 Real time commands
The TESS Project shall generate, transmit, and execute real time commands to the
Observatory.
Rationale: Real time commands are required for testing, engineering operations, and to
diagnose and recover from anomalies on orbit.
Allocation: SC, INSTR, MOC
MRD_67 Stored commands
The TESS Project shall generate, transmit, store, and execute command sequences
constructed with either absolute or relative execution times.
Rationale: The Observatory will be out of ground contact for much of the science orbit.
Stored commands are required to manage operations during this time.
Allocation: SC, MOC, SOC
MRD_68 Telemetry
The TESS project shall provide Observatory Housekeeping data to determine Spacecraft
and Instrument health, support science operations, and diagnose anomalies during all
mission phases.
Rationale: Telemetry required from observatory to determine spacecraft health on orbit,
readiness to launch on the pad, etc…
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Allocation: SC, INSTR, MOC, SOC
MRD_69 Recorded Telemetry
The TESS Project shall be capable of downlinking real-time and recorded Observatory
Housekeeping data during all S-band contacts.
Rationale: Allows for operations team to debug spacecraft outside of LAHO, potentially
enabling recovery prior to the next LAHO and thereby minimizing lost science.
Allocation: SC
MRD_70 CCSDS Protocols
The TESS Project shall utilize Consultative Committee for Space Data Systems (CCSDS)
protocols for command and telemetry links.
Rationale: Provides interoperability for flight and ground systems.
Allocation: SC, INSTR, MOC, FD, SOC
MRD_29 Science Downlink Data Allocation
The Observatory shall process the Science, Ancillary Spacecraft data, and Instrument
Housekeeping data to limit the total data volume for downlink to 92 GB per orbit.
Rationale: Downlink constraints preclude downlinking all raw data. Data must be
reduced onboard to a volume that can be downlinked in a nominal DSN downlink pass.
92 GB selected from analysis in CSR.
Allocation: INSTR
MRD_71 Downlink Performance
The TESS Project shall be capable of downlinking [221 TBR] GB of Instrument Data and
2 GB of Spacecraft Data in a 5 hour LAHO communication pass.
Rationale: Allows for the collection of 2 orbits of Spacecraft and Instrument data in
single DSN pass. Includes 20% margin over Instrument allocation in MRD_29.
Allocation: SC, INSTR, MOC, FD, SOC
MRD_72 Data Retransmit
The TESS Project shall transmit the current and prior orbit's Instrument Data in each
comm pass.
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Rationale: L1 requires 95% of data collected by the spacecraft to be returned to the
ground. This approach allows for >97.5% of data to be returned in the presence of DSN
outages and weather.
Allocation: INSTR, MOC, SOC
MRD_73 Unattended operation
The TESS Project shall be capable of operating the Observatory, including collecting
science data, without ground intervention for 2 orbits.
Rationale: Communication passes may be lost due to ground station issues or weather.
Under the scenario where we are unable to communicate with the Observatory during an
individual LAHO, we do not want to sit idle for the subsequent orbit.
Allocation: SC, INSTR, MOC, FD, SOC
MRD_74 Common Time Format
The TESS project shall utilize the CCSDS Time code format.
Rationale: Consistent time code format across elements minimizes confusion
Allocation: SC, INSTR, MOC, SOC
MRD_75 Mission Critical Telemetry and Commanding
The TESS Project shall maintain continuous telemetry and command coverage during all
mission-critical events.
Rationale: Gold Rule 1.14. Continuous telemetry coverage shall be maintained during all
mission-critical events. Mission-critical events shall be defined to include separation
from the launch vehicle; power-up of major components or subsystems; deployment of
mechanisms and/or mission-critical appendages; and all planned propulsive maneuvers
required to establish mission orbit and/or achieve safe attitude. After separation from the
launch vehicle, continuous command coverage shall be maintained during all following
mission-critical events.
With continuous telemetry and command capability, operators can prevent anomalous
events from propagating to mission loss. Also, flight data will be available for anomaly
investigations.
Allocation: SC, MOC, FD
MRD_76 Commandability
The Observatory shall be capable of receiving and executing real-time commands at all
times after launch vehicle separation subject to RF constraints identified in the Spacecraft
to Ground ICD.
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Rationale: To support anomaly recovery, the ground should always have the capability to
command the spacecraft.
Allocation: SC, INSTR
MRD_77 Modification of flight software
The TESS Project shall allow for modification of all flight computer flight software
images.
Rationale: On-orbit modification of software provides the mission some robustness to
unanticipated operational conditions and scenarios.
Allocation: SC, INSTR, MOC, SOC
3.6
Mission Robustness and Safety Requirements
MRD_79 Fault Tolerance
The TESS Project shall mitigate credible single point failures that would prevent the
Project from achieving minimum mission success.
Rationale: Even though TESS is a single-string mission, critical single point failures that
prevent the project from achieving minimum mission success must be mitigated through
the use of high reliability parts, selective redundancy, graceful degradation, etc…
The project will maintain a SPF list that accepts single point failures through a waiver
process that evaluates the proposed mitigation.
Allocation: SC, INSTR
MRD_80 Safe Hold Mode
The Observatory shall detect anomalous conditions that threaten the health or
consumables of the Observatory and autonomously enter a minimum safe operating state
(Safe Hold) that maintains the health, consumables, and commandability of the
Observatory.
Rationale: Gold Rule 1.17. Safe mode provides a state that requires fewer resources and
is more robust than operational mode
Allocation: SC
MRD_81 Safe Hold Duration
The Observatory shall autonomously maintain Safe Hold mode indefinitely, or until all
propellant resources have been expended.
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Rationale: It may take multiple orbits for the ground to diagnose and recover the
spacecraft from an onboard anomaly. During this time commandability may be limited,
thus the spacecraft must autonomously maintain vehicle health. This includes performing
momentum management, which requires propellant.
Allocation: SC
MRD_82 Catastrophic Hazards
The TESS project shall mitigate any failure which leads to a Catastrophic Hazard with
three independent verifiable inhibits. (TBD)
Rationale: Gold Rule 1.24. Catastrophic Hazard A condition that may cause death or
permanently disabling injury, major system or facility destruction on the ground, or
vehicle during the mission.
Allocation: SC, INSTR, MOC
MRD_83 Critical Hazards
The TESS Project shall mitigate any failure which leads to a Critical Hazard with two
independent verifiable inhibits. (TBD)
Rationale: Gold Rule 1.24. Critical Hazard A condition that may cause severe injury or
occupational illness, or major property damage to facilities, systems, or flight hardware.
Allocation: SC, INSTR, MOC
MRD_84 Inadvertent Commanding
The TESS Project shall protect against the inadvertent generation, transmission, and
execution of commands that may result in damage to the Observatory or loss of mission.
Rationale: Protects against a single operations team mistake causing damage to the
spacecraft. Also satisfies Gold Rule 1.23 where In a single string Spacecraft no single
command shall result in Spacecraft "OFF."
Allocation: SC, INSTR, MOC
MRD_85 Instrument Sun/Earth Sensitivity
The Instrument shall be capable of pointing at any target, including the Sun and the
Earth, indefinitely with no damage or permanent impact to performance.
Rationale: Allows for flexibility in mission design and spacecraft safing responses. No
expectation that the instrument will be able to collect science data when pointed at the
Sun - see requirement on Sun Angle for science operating range.
Allocation: INSTR
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MRD_86 Non Volatile Science Data Storage
The Instrument shall have the capability to store Science Data such that it will persist
across a power cycle of the instrument. (TBD)
Rationale: In certain fault conditions the Spacecraft may remove power from the
instrument. In these cases we do not want to lose the 2 orbits of science data that has been
collected onboard.
Allocation: INSTR
MRD_64 Missed Maneuver
The TESS Project shall be able to achieve the operational orbit and threshold mission in
the presence of any single missed or aborted maneuver.
Rationale: Allows the maneuvers to be handled as nominal operations rather than mission
critical events. Reduces the availability requirements on the ground and flight system.
Allocation: SC, MOC, FD
3.7
Data Handling Processing and Archiving
MRD_88 Science Data Retention
The TESS Project shall deliver >= 95% of Instrument data collected to the SOC.
Rationale: In this requirement, collected refers to data that has been successfully stored
within the Instrument onboard the spacecraft. This allocation allows for potential loss of
data in transmission and handling.
Allocation: SC, INSTR, SOC
MRD_89 Science Data Delivery Latency
The TESS Project shall deliver raw and calibrated Instrument data to the project archive
within 6 months of downlink.
Rationale: Allows for public access to TESS data during mission operations.
Allocation: SOC, TSO
MRD_90 Final Science Data Archive
The TESS Project shall deliver the final fully-calibrated set of science data products to
the project archive within 12 months following the end of mission.
Rationale: Allows the public access to TESS data after the mission has been completed.
Allocation: SOC, TSO
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3.8
Project Interfaces
MRD_92 Launch Vehicle Interface
The Observatory shall comply with the LV Interface Requirements Document (LVIRD).
Rationale: LV IRD creates requirements on the interface between the LV & spacecraft
Allocation: SC, MOC, LV
MRD_93 DSN S-Band Uplink and Downlink
The TESS Project shall use S-band through the Deep Space Network for nominal
command and telemetry.
Rationale: Need large dishes to communicate efficiently with TESS
Allocation: SC, MOC
MRD_94 DSN Ka-Band Science Downlink
The TESS Project shall use Ka-band through the Deep Space Network for nominal
Instrument Data transmission.
Rationale: Bandwidth is too large for X-band, rate is too high for S-band hence Ka-band
Allocation: SC, SOC
MRD_95 Space Network S-Band Uplink and Downlink
The TESS Project shall use S-band through the Space Network TDRS constellation for
contingency commanding and telemetry.
Rationale: TDRS provides contact for phasing orbits at perigee and for critical burns.
Critical operations may not match DSN coverage.
Allocation: SC, MOC
MRD_96 Mission Data Archive
The TESS Project shall use the Mikulski Archive for Space Telescopes (MAST) as the
project archive.
Rationale:
Allocation: SOC, TSO
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Appendix A Definitions
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Appendix B Requirements Verification Matrix
This section will be completed at a later date.
ID
Short Title
Requirement
Rationale
Allocation
Verification
Method
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Appendix C Requirements Linkage Audit
This section will be completed at a later date.
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