P3D Launch Sequence Study (Part II)

Started: December 5, 1996 -- Last Update: February 12, 1997

Viktor Kudielka (ÖVSV P3D Mission Analysis Project)

Introduction

This document is intended as a base for discussion of alternative launch sequences of P3D.

Since the start date of ARIANE 502 with P3D was due for a change, guessing from previous experience (AO-10: June 16, 1983; AO-13: June 15, 1988; P3D: June 14, 1997 ??? ) was obviously too optimistic. Part II contains two scenarios for the start dates June 21 and August 21, 1997 and consequently for different initial RAAN of the GTO (RAAN=260°, 320°). These two scenarios are more or less characteristic for the newly (December 17) announced schedule of early July. With these assumptions the situation for the final drift phase is deteriorating, compared to a start mid of April.

Alternatives for achieving a more favorable RAAN are presented in scenarios F, F1, and G.

Finally an outline for a more detailed analysis of arc-jet operation is given, including data requirements.

Scenario C1

This scenario is a modification of scenario C for a start date of June 21, 1997.

Initial Drift Phase

Orbit period changes are assumed to start with orbit #45 (day 21). The 16 hour period will be reached already on day 234.

Major Inclination Change

The major inclination change is done in five steps like scenario C. The direction of the impulses is assumed to have an along-track and an out-of-plane component only.
Orbit ArgP sma ecc inc HeightPer HeightApo VPer VApo deltaV
# deg km deg km km m/s m/s m/s
461 330.00 32269 0.7821 06.87 652 51130 10052 1229 000
462 330.33 32269 0.7821 09.87 654 51129 10051 1229 095
464 330.94 32269 0.7819 24.88 659 51124 10047 1229 466
466 331.41 32269 0.7817 39.88 665 51118 10037 1231 462
468 331.69 32269 0.7816 54.87 671 51112 10037 1231 459
470 331.78 32269 0.7814 61.00 675 51107 10034 1231 188

Total deltaV = 1670 m/s

Figures C1.2A and C1.2B show orbital and S/C parameters till day 253 (orbit # 470).

Final Drift Phase

The final drift phase is shown in figures C1.3A and C1.3B. ArgP will drift first to about 345° and then continuously decrease. 270° will be reached after about 14 years and the apogee footprint will even cross the equator after 25 years.

Summary -- Scenario C1

Scenario C2

This scenario is a modification of scenario C for a start date of August 21, 1997.

Initial Drift Phase

Orbit period changes are assumed to start with orbit #45 (day 21). The 16 hour period will be reached already on day 234.

Major Inclination Change

The major inclination change is done in five steps like scenario C. The direction of the impulses is assumed to have an along-track and an out-of-plane component only. The changes in eccentricity are much less than in scenario C.
Orbit ArgP sma ecc inc HeightPer HeightApo VPer VApo deltaV
# deg km deg km km m/s m/s m/s
486 330.18 32265 0.7823 06.63 645 51128 10058 1228 000
487 330.46 32265 0.7823 09.63 647 51126 10056 1228 094
489 331.03 32265 0.7822 24.62 648 51125 10055 1229 465
491 331.49 32265 0.7822 39.62 648 51125 10056 1229 461
493 331.78 32265 0.7823 54.63 646 51127 10057 1228 458
495 331.89 32265 0.7823 62.50 646 51128 10057 1228 240

Total deltaV = 1718 m/s

Figures C2.2A and C2.2B show orbital and S/C parameters till day 270 (orbit #495).

Final Drift Phase

The final drift phase is shown in figures C2.3A and C2.3B. ArgP will drift first to about 345° and then continuously decrease. 270° will be reached after about 16 years and the apogee footprint will cross the equator after 30 years.

Summary -- Scenario C2

Scenario F

This scenario for a start date of July 7, 1997 presents a new approach to achieve a more favorable RAAN in order to keep the ArgP within the wanted range for a longer period. ArgP will go through more than a full circle in order to allow RAAN to drift to near 0°, a much more favorable position.

Initial Drift Phase

Orbit period changes are assumed to start with orbit #1150 (day 515). Figures F.1A and F.1B show orbital and S/C parameters until day 790 (orbit #1600).

Major Inclination Change

The major inclination change is done (around day 790) in five steps like scenario C. The direction of the impulses is assumed to have an along-track and an out-of-plane component only.
Orbit ArgP sma ecc inc HeightPer HeightApo VPer VApo deltaV
# deg km deg km km m/s m/s m/s
1600 325.10 32277 0.7823 07.32 649 51149 10055 1228 000
1601 325.39 32277 0.7823 10.32 649 51149 10054 1228 105
1603 325.98 32277 0.7822 25.32 652 51146 10053 1228 518
1605 326.46 32277 0.7821 40.32 656 51142 10049 1229 513
1607 326.74 32277 0.7819 55.32 662 51136 10044 1229 510
1609 326.83 32277 0.7817 62.50 667 51131 10041 1230 244

Total deltaV = 1890 m/s

Final Drift Phase

The final drift phase is shown in figures F.3A and F.3B. ArgP will drift first to about 335° and then continuously decrease. 270° will be reached after about 16 years and the apogee footprint will stay on the northern hemisphere longer than the evaluated period of 35 years. These favorable conditions can be achieved by the delay of the major inclination change to more than two years after the start.

Summary -- Scenario F

Modified Final Drift Phase (scenario F1)

Figures F1.3A and F1.3B show a slightly modified final drift phase. The major inclination change is here to 62° instead of 62.5°, saving a deltaV of 17 m/s. ArgP increases to 350° after 11 years and decreases then to 270° after 30 years. The height of perigee increases continuously to over 16000 km.

Scenario G

Scenario G is an attempt to achieve also a favorable RAAN similar to scenarios F and F1 on a shorter schedule, at the expense of a substantial increase of deltaV.

Initial Drift Phase

A first drift phase will be required to get an ArgP = 360/0°. If the initial orbital period is not changed, this will take about 245 days. Most of this period could be used for operation in three-axis stabilised mode, but with restricted power supply (solar panels not expanded). At ArgP = 0° a negative inclination change (greater than the then current inclination) will flip over the whole orbital plane. RAAN as well as ArgP are changed by 180°.

Second Drift Phase

A second drift phase will be needed to get to an ArgP of 325° for the final inclination change. This period will be used to increase the orbital period to 16 hours. Figures G.1A and G.1B show orbital and S/C parameters of the two drift phases.

Inclination Changes

The following tables provide details of the necessary inclination changes.

Orbit ArgP sma ecc inc RAAN HPer HApo VPer VApo deltaV
# deg km deg deg km km m/s m/s m/s
0554 359.98 24648 0.7145 06.82 180.7 659 35882 09855 1641 000
0555 180.31 24648 0.7145 03.18 000.5 659 35882 09855 1641 286

Orbit ArgP sma ecc inc RAAN HPer HApo VPer VApo deltaV
# deg km deg deg km km m/s m/s m/s
1056 325.07 32243 0.7832 02.93 294.3 612 51117 10083 1226 000
1057 325.35 32243 0.7832 18.03 294.2 612 51118 10084 1226 529
1059 325.88 32243 0.7833 33.03 293.9 608 51121 10087 1226 519
1061 326.26 32243 0.7835 48.04 293.6 604 51126 10091 1225 515
1063 326.46 32243 0.7836 63.05 293.4 600 51130 10094 1225 513

Final Drift Phase

The final drift phase is shown in figures G.3A and G.3B. ArgP will increase to about 335° and then decrease to 270° after about 18 years. The decrease continues to 210°. Then the trend changes again. Perigee will stay over the northern hemisphere for the whole life time. After 34 years the height of perigee will decrease rapidly (already outside of figure G.3B) and the S/C will burn up even faster than AO-13.

Summary -- Scenario G

More fine-tuning would be necessary to get the deltaV requirements down to an acceptable level, for example by an increase of the orbital period before the first inclination change and probably also an increase of the orbital period beyond 16 hours before the second, major inclination change.

Missing Details of Analysis

The analysis of the scenarios so far investigated has been done with quite a lot of assumptions. Most probably these assumptions where too optimistic and more detailed analysis is necessary. More specific data of the mechanical and electrical properties of the S/C as well as other operational data are required.

Power Budget

The power supply by solar radiation dependent upon has to be evaluated together with and must balance the power requirements of the following units/operations as a minimum (no communication operations): It might turn out that arc-jet operation cannot be done for a full hour each orbit.

Accumulated Radiation

All scenarios presented so far assume an initial height of perigee in the range of 500 to 700 km. This has been done to allow an efficient magnetic torquers operation for fast changes of spin and attitude and also for minimum deltaV requirements for inclination changes. No estimates of accumulated radiation have been done yet. If it turns out that radiation becomes a major issue, a compromise between accumulated radiation, elapsed time for spin and attitude changes and propellant required for inclination changes has to be found.

Center of Gravity Movement

The center of gravity of the S/C will move due to the changing mechanical configuration of the solar panels and the change of the propellant masses in the order of a few centimeters. Consequently the misalignment of the direction of the propulsion units will cause a mechanical momentum. Dependent upon the spin rate a nutation motion will occur when operating the booster. This causes a reduction of the total efficiency of the booster. Whether this nutation motion can be compensated partially or completly by the momentum wheels should be analysed in more detail.

Required data:

Attitude and Spin Changes, Unloading Momentum Wheels

In order to compile a realistic simulation of all of the powered and drifting phases of orbit development, the number of required perigee passes for certain attitude and spin changes, dependent on the height of perigee, is required.

Orbit and Attitude Determination

Timing estimates for orbit and attitude determination are needed for a complete schedule of S/C manoeuvers.

Minimum Time for Orbit Adjustment

A final remark might be in place in order not to raise the expectations of the users beyond reality.

Assuming the full amount of arc-jet propellant is loaded, we get a total of about 550 hours of arc-jet operation. Even if we assume one hour burns per orbit, which might be optimistic concerning the power budget, we arrive roughly at one year for arc-jet operation only. If we distribute this operation over several periods, we have to add time for the changes between spin and three-axis stabilised mode. Whatever strategy we follow, the minimum time of orbital operations will be one year. Due to power requirements and S/C attitude, no user operations will be possible during this time.

Dr. Viktor Kudielka, OE1VKW
viktor.kudielka@ieee.org