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Aura to Aqua Re-phasing

Aura to Aqua Re-phasing. Prepared by: Brian Robinson, a.i. solutions, Inc Joshua Levi , a.i. solutions, Inc October 2 nd , 2007. Introduction. Aura Flight Dynamics Team (FDT) was requested to analyze a change in Aura’s position with respect to Aqua.

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Aura to Aqua Re-phasing

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  1. Aura to Aqua Re-phasing Prepared by: Brian Robinson, a.i. solutions, Inc Joshua Levi , a.i. solutions, Inc October 2nd, 2007

  2. Introduction • Aura Flight Dynamics Team (FDT) was requested to analyze a change in Aura’s position with respect to Aqua. • Phase change would decrease the amount of time between Aqua and Aura instrument measurements. • Current phasing with respect to Aqua was determined based on requirements from Aura-MLS. • Met with Mark Schoeberl to present the initial results in June ’07.

  3. Analysis Requirements/Requests • Requirements: • Maintain current orbital requirements except for ground track control and along track separation. • Requests: • OMI: • Maintain a solar beta angle of 18.3 to 31.2 degrees (9/13/07). • Maintain Aura MLTAN between 13:40 and 13:45 (9/13/07). • MLS • ? • TES • ? • HIRDLS • ?

  4. Assumptions • To bound the problem, move Aura forward to a location where MLS and the MODIS/AIRS instruments view the same location at the same time. • Maintain current Mean Local Time of the Ascending Node (MLTAN) requirements. • Changes to the Aura location will be made via a change in the along-track separation. • Only orbit raising maneuvers and inclination adjust maneuvers (for orbit lowering purposes) can be utilized.

  5. Current Aura Orbit Requirements • Maintain MLTAN between 13:30 and 14:00 • Due to current MLTAN phasing with Aqua and timing of inclination maneuvers, MLTAN has been maintained between 13:40 and 13:45. • Current MLTAN is 13:44 and is trending to a minimum of ~13:42. • Orbit +/- 20Km of the WRS-2 ground path that is 1 path + 25 Km West of Aqua at the descending node. • Phasing of 15-22 minutes in along-track separation, but as close to 15 minutes as possible due in part to COMM requirements. • Current phasing is ~16 minutes in along-track separation, trending towards a minimum of ~15 in the next two years. • Solar beta angle requirement is 16 – 36 degrees.

  6. Current Aqua Orbit Requirements • Maintain MLTAN between 13:30 and 13:45 • The current Aqua MLTAN is ~13:35 trending toward a minimum of ~13:33. • Orbit +/- 10Km of the WRS-2 ground path at the descending node.

  7. Current Phasing

  8. Current Phasing

  9. Analysis • Calculate minimum Aqua-Aura along-track separation • MLS views ground location ~7 minutes ahead of Aura sub-satellite location. • Based on a circular orbit with a period of ~98.2 minutes, Aura orbits at a rate of 0.0611 deg/sec. • Assuming a ~7 minute along-track separation, the minimum separation is ~3200Km. • Only method for achieving this goal is to reduce the Semi-Major Axis (SMA) in order to increase the relative velocity between the two satellites. • An orbit raising maneuver after re-phasing is achieved would decrease the relative velocity to zero, establishing the new orbit.

  10. Proposed Phasing

  11. Effects • MLS views atmosphere nearly the same time as Aqua. • MLS views atmosphere offset from Aqua’s nadir point. • Viewing the Aqua nadir point is not compatible with the OMI MLTAN request of 13:40 – 13:45. • As Aura orbits, the MLS viewing location will switch sides at the poles. • On the ascending node, MLS will view East of Aqua • On the descending node, MLS will view West of Aqua. • TES/HIRDLS view ground location closer to Aqua’s nadir point track. • OMI will have increased coverage of the AIRS/MODIS swath.

  12. Options • Option I – Drag Option • Use atmospheric drag to reduce SMA and drift closer to Aqua. • Option II – Inclination Maneuver Option • Use 2 inclination maneuvers to reduce SMA and drift closer to Aqua.

  13. Option I – Drag Option • Use atmospheric drag to reduce the SMA and initiate the forward drift. • Drag Make-Up (DMU) maneuvers would be halted until desired separation is attained • Once the correct phasing is reached an orbit raising maneuver would stop the drift and establish a new ground-track control box. • There would be no change to the current MLTAN profile.

  14. Pre and Post-DMU locations within the WRS Error Box WRS Error without DMU Pre-DMU Post-DMU -5 km -45 km Feb ‘08 Nov ‘07 **Based on HP75 drag environment

  15. Option I – Drag Option Evaluation The duration of the re-phasing will be dictated by Aura’s position within the ground-track cycle. Pre- and Post-DMU results are reported to indicate the additional time required to drift through the ground-track cycles of each drag environment.

  16. Option I – Drag Option WRS-2 Error (Km) Solar Beta Angle (Deg) Date Date Mean Local Time Separation (Min) Along-Track Separation (Km) Date Date **Based on HP75 drag environment

  17. Option I – Drag Option Relative Phasing **Based on HP75 drag environment

  18. Option I – Drag Option Pro’s/Con’s

  19. Option II – Inclination Maneuver Option • Execute inclination maneuver that would lower the orbit in order to initiate a drift forward. • DMUs would be halted until desired separation is attained. • Once the correct phasing is reached an orbit raising maneuver would stop the drift and establish a new ground-track control box. • A small change to the MLTAN would be incurred due to the use of inclination maneuvers • The MLTAN is not expected to drift below 13:40 • If the maneuvers are not executed in concert with Aqua, a slow along-track drift will occur towards Aqua

  20. Option II – Inclination Maneuver OptionExpanded Description • Option II can be executed in two ways with significantly different results. • IIa – Pre 2009 • Two Inclination maneuvers are executed prior to the 2009 inclination series. • Two maneuvers would be executed because our maximum duration is 550 seconds and two maneuvers would induce a larger drift rate to the target separation. • The initially targeted Aura-Aqua separation would be ~4700Km*. • An orbit raise maneuver would reduce the drift rate, but due to the difference in Aqua and Aura MLT drift rates, Aura will continue to drift towards Aqua. • During the 2009 inclination series, the MLT drift rates will be synchronized and Aura will maintain a separation of > 3200Km. • IIb - 2009 • Nominal operations until 2009 inclination series. • Two of the TBD burns in the series will be executed at a larger than nominal yaw angle to induce a drift. • Once the targeted separation of ~3200Km is achieved, an orbit raising maneuver will be executed.

  21. Option II – Inclination Maneuver Option Evaluation ** Burn duration for Ground Track control only; does not include any needed inclination maneuvers.

  22. Option IIa – Inclination Maneuver Option WRS-2 Error (Km) Solar Beta Angle (Deg) Date Date Mean Local Time Separation (Min) Along-Track Separation (Km) Date Date Note: Additional analysis is required to determine the initial target along-track separation so that the drift to the final separation meets requirements.

  23. Option IIa – Inclination Maneuver Option Date

  24. Option IIa – Inclination Maneuver Option Relative Phasing

  25. Option IIa – Inclination Maneuver Option Pro’s/Con’s

  26. Option IIb – Inclination Maneuver Option Solar Beta Angle (Deg) WRS-2 Error (Km) Date Date Mean Local Time Separation (Min) Along-Track Separation (Km) Date Date Note: Additional analysis is required to reduce MLTAN separation rate, along-track separation rate and violations of the desired beta angle

  27. Option IIb – Inclination Maneuver Option Relative Phasing

  28. Option IIb – Inclination Maneuver Option Pro’s/Con’s

  29. Pro’s/Con’s 1 – Best, 2 – Medium, 3 – Worst

  30. Constellation Safety • Proposed Glory orbit location is 225 sec behind Aqua with a control box of +/-43 sec. • With a 10 second buffer the minimum separation between Aqua and Aura should be 278 sec (~2100 Km). • Aqua-Aura target separation is ~420 sec (~3200 Km). • Expect a 142 sec (~1100 Km) separation from Glory. • No missions will be affected by the change in Aqua-Aura separation.

  31. Recommendations • Based on information provided to the Aura FDT • Option I is the most logical choice to have the re-phasing operation completed as soon as possible. • If the project wishes to wait until 2009, Option IIb provides the quickest change in phasing. • The FDT recommends that Option IIa not be considered due to the high complexity and extended drift duration.

  32. Additional Questions • Does MLS want to view the same ground location as Aqua at the same time? • Is there a desired Aura location relative to Aqua? • Are there additional science constraints (i.e. beta angle) that should be addressed? • Are there any COMM issues?

  33. Additional Slides

  34. Historical Aura Solar Beta Angle

  35. Nominal Aura Beta Angle ~2 week violation Oct/Nov ’08 Max - ~31.32 Beta Angle (Degrees) Date

  36. Historical Aura MLTAN

  37. Nominal Aqua/Aura MLTAN Mean Local Time @ Ascending Node (Hours) Date

  38. Nominal MLTAN Separation MLTAN Separation (Minutes) Date

  39. Nominal Along-Track Separation Along-Track Separation (Km) Date

  40. Historical Aura Inclination

  41. Historical Aura Fuel Mass

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