1. Low Thrust Transfer to Sun-Earth L 1 and L 2 Points with a Constraint on the Thrust Direction LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 Alexander A. Sukhanov Natan A. Eismont Space Research Institute (IKI) of Russian Academy of Sciences Moscow, Russia Space Research Institute (IKI) of Russian Academy of Sciences Moscow, Russia

2. An experimental low-thrust mission to the Sun-Earth L1 and L2 points is considered (Module-M mission) MISSION GOALS Solar wind exploration Magnetic storm prediction Testing new technologies MISSION STEPS Delivery of the spacecraft component to the International Space Station (ISS) by Progress cargo spaceship Assembling the spacecraft at ISS Launch from ISS and transfer to L 1 using Solar Electric Propulsion Transfer to the L 1 point and insertion into a halo orbit Launch from the halo orbit, transfer to L 2 point, and insertion into a halo orbit LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 2

3. SPACECRAFT CONCEPT Spacecraft is spin-stabilized with spin axis orthogonal to the Sun Solar arrays form a cylindrical surface coaxial to the spin axis Thrusters are directed along the spin axis in both directions LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 3

4. THRUSTER PARAMETERS NameD-38 TypeTAL Power750 W Specific impulse2200 s Efficiency (including loss in PPU)0.5 Thrust force0.035 N Mass flow rate1.6  10 -6 kg/s Resource3000 hours Propellantxenon LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 4

5. SPACECRAFT PARAMETERS Wet initial mass290 kg Xenon mass85 kg Characteristic velocity7.5 km/s Solar panel area110 m 2 Effective solar array area30 m 2 Electric power3 kW Number of thrusters8 Number of simultaneously running thrusters2 Maximum time of the low thrust run7340 hr LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 5

6. SPIRAL TRANSFER LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 6

7. ORBIT SHADOWING Launch in June-July or December-January minimizes the orbit shadowing down to 7.5 percent of the spiral transfer time These optimal launch dates lead to a high (> 50°) inclination to the ecliptic plane Launch in May or November was selected for the further analysis: the shadowing is 8.5 percent, inclination to the ecliptic plane is 35° LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 7

8. PARAMETERS OF THE SPIRAL TRANSFER Time of flight280 days Number of orbits1330 Consumed characteristic velocity6850 m/s Propellant consumption78.9 kg Spacecraft mass211.1 kg LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 8

9. TRANSFER TO L 1 AND INSERTION INTO A HALO ORBIT Time of flight (after the spiral)140 days Characteristic velocity of the insertion into halo290 m/s Propellant consumption2.8 kg Spacecraft mass in halo208.3 kg Amplitude A y of the halo orbit62,000 km LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 9

10. L 1 TO L 2 TRANSFER WITH ZERO COMPLETE ORBITS 10 LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002

11. L 1 TO L 2 TRANSFER WITH ZERO COMPLETE ORBITS Consumed characteristic velocity306 m/s  v 1 50 m/s  v 2 196 m/s  v 3 60 m/s Time between  v 1 and  v 2 70 days The transfer duration181 days Propellant consumption2.9 kg Final spacecraft mass205.4 kg A y amplitude of the L 2 halo800,000 km LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 11

12. L 1 TO L 2 TRANSFER WITH ONE COMPLETE ORBIT 12 LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002

13. LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 13 L 1 TO L 2 TRANSFER WITH ONE COMPLETE ORBIT Consumed characteristic velocity224 m/s  v 1 65 m/s  v 2 18 m/s  v 3 141 m/s Time between  v 1 and  v 2 82 days The transfer duration259 days Propellant consumption2.2 kg Final spacecraft mass206.1 kg A y amplitude of the L 2 halo300,000 km

14. 14 L 1 TO L 2 TRANSFER WITH TWO COMPLETE ORBITS LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002

15. L 1 TO L 2 TRANSFER WITH TWO COMPLETE ORBITS Consumed characteristic velocity70 m/s  v 1 35 m/s  v 2 2 m/s  v 3 33 m/s Time between  v 1 and  v 2 70 days The transfer duration319 days Propellant consumption0.7 kg Final spacecraft mass207.6 kg A y amplitude of the L 2 halo150,000 km LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 15

16. SYMMETRIC TWO-IMPULSE L 1 TO L 2 TRANSFER LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 16

17. SYMMETRIC TWO-IMPULSE L 1 TO L 2 TRANSFER Consumed characteristic velocity86 m/s  v 1 43 m/s  v 2 43 m/s The transfer duration307 days Propellant consumption0.8 kg Final spacecraft mass207.5 kg A y amplitude of the L 2 halo62,000 km LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 17

18. SUMMARY OF THE TRANSFERS LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 18

19. CONCLUSIONS The low thrust orthogonal to the Sun allows performing: – transfer to L 1 or L 2 Sun-Earth point; – insertion into a halo orbit; – halo-to-halo transfer. This makes it possible to simplify the spacecraft design and control Duration of both the Earth-to-halo and halo-to-halo transfers can be shortened by means of a higher propellant consumption Propellant consumption can be reduced by means of the duration increase for both the Earth-to-halo and halo-to-halo transfers LIBRATION POINT ORBITS AND APPLICATIONS Parador d'Aiguablava, Girona, Spain 10 – 14 June, 2002 19