20b - 1NASA’s Goddard Space Flight Center

Flight Dynamics

Mark Beckman

NASA/GSFC Code 595

August 16-17, 2005

20b - 2NASA’s Goddard Space Flight Center

Document Tree

• Primary:– Flight Dynamics Specification 431-SPEC-000063

• Parent:– LRO Mission Requirements Document 431-RQMT-000004

• Two-Way:– LRO Mission Concept of Operations 431-OPS-000042– LRO Propulsion Subsystem Statement of Work and Specification 431-

SOW-000017– Detailed Mission Requirements for the LRO Ground System 431-

RQMT-000048– LRO Ground System Interface Control Document 431-ICD-000049– ACS Pointing Document TBD– LRO ACS Spec TBD

20b - 3NASA’s Goddard Space Flight Center

Lighting constraint at spacecraft separation.

The LRO launch window shall be constrained such that the nominal spin direction at separation is within 15 deg of either the Sun or anti-Sun.

FDS-2.2.2MRD-4

May add northern insertion if analysis shows dV improvement or additional daily launch opportunity required.

LRO shall insert into lunar orbit over the lunar southern pole and have an initial southern argument of periselene. (TBR)

FDS-2.4MRD-11

Daily opportunities further reduced with lighting constraint.

LRO shall have one daily launch opportunity that consists of a short coast minimum energy direct transfer to the moon.

FDS-2.2.1MRD-24

MRD-3

Short coast northern TTIs may require coast time up to 68 min.

LRO shall be launched on a 7925H-9.5 launch vehicle with a coast time of up to 68 (TBD) minutes.

FDS-2.1MRD-24

MRD-3

RequirementParagraph

Concept/ComplianceLevel 3: RequirementsLevel 2 Req.

Lunar Reconnaissance Orbiter (LRO)

Flight Dynamics Level 2 Flow DownKey Requirements

20b - 4NASA’s Goddard Space Flight Center

Additional dV saved by performing earlier.

LRO shall perform an MCC1 maneuver prior to L+24 (TBD) hours to correct for LV dispersions.

FDS-2.2.2MRD-3

MRD-25

MRD-10

Minimizes finite burn loses.LRO shall perform up to eight (TBD) LOI maneuvers to insert the spacecraft into the commissioning orbit.

FDS-2.4.2MRD-146

MRD-10

MRD-11

Consistent with frozen orbit for commissioning.

LRO shall maintain a periselene of greater than 200 km (TBD) after LOI1.

FDS-2.4.1MRD-146

Safe altitude.LRO shall maintain a minimum altitude of 100 km (TBD) during LOI phase.

FDS-2.4MRD-146

RequirementParagraph

Concept/ComplianceLevel 3: RequirementsLevel 2 Req.

Lunar Reconnaissance Orbiter (LRO)

Flight Dynamics Level 2 Flow DownKey Requirements

20b - 5NASA’s Goddard Space Flight Center

Altitude control band dictates frequency of stationkeeping maneuvers.

The primary mission shall be conducted in a circular mapping orbit with a nominal altitude of 50 +/- 20 km (altitude is measured to mean lunar surface).

FDS-4.1.2MRD-12

Stationkeeping strategy C complies.

LRO's stationkeeping shall target periselene in the southern hemisphere 50% of the time.

FDS-4.1.3MRD-146

MRD-12

Eccentricity, argument of periapsis and longitude repeat every month within the separation between consecutive groundtracks.

LRO shall perform a stationkeeping cycle approximately every 27.4 days.

FDS-4.0MRD-146

MRD-12

No stationkeeping dV required.

The commissioning orbit shall be a frozen orbit at 30x216 km altitude and a 270 deg argument of periapsis.

FDS-5.0MRD-11

RequirementParagraph

Concept/ComplianceLevel 3: RequirementsLevel 2 Req.

Lunar Reconnaissance Orbiter (LRO)

Flight Dynamics Level 2 Flow DownKey Requirements

20b - 6NASA’s Goddard Space Flight Center

Consistent with existing S-band measurements and current lunar gravity model.

LRO shall have a minimum Orbit Determination Accuracy of 500/18 m (total position RMS/radial RMS, 1-sigma, post-processed).

FDS-3.1.4MRD-41

May not be possible for all of LOI1

LRO maneuvers shall be performed in view of S-band tracking stations.

FDS-3.1.6MRD-147

RequirementParagraph

Concept/ComplianceLevel 3: RequirementsLevel 2 Req.

Lunar Reconnaissance Orbiter (LRO)

Flight Dynamics Level 2 Flow DownKey Requirements

20b - 7NASA’s Goddard Space Flight Center

Transfer Trajectory

Solar Rotating Coordinates

Earth

Moon at encounter

Cis-lunar transfer4 day transferLaunch C3: –2 km2/s2

1-day

Lunar Orbit

Sun direction

Nominal Cis-lunar Trajectory

20b - 8NASA’s Goddard Space Flight Center

Mission Orbit

20b - 9NASA’s Goddard Space Flight Center

Verification

• Ground station tracking certification– One new antenna (18m at White Sands)

– Four antennas (Australia, Belgium, Hawaii, Sweden)

– Flight Dynamics Facility (FDF) certifies tracking station measurement accuracy

• End-to-End tests• Flight Dynamics Simulations

– Contingency plans

– Anomalies

20b - 10NASA’s Goddard Space Flight Center

Summary

• Only a few key Level 2 driving requirements– All well understood

• Many derived Level 3 requirements– Some in flux as spacecraft design/con ops solidify

• Flight Dynamics Specification details all mission design and navigation– References to all analysis documents

• Flight Dynamics is ready to proceed to PDR