TRAJECTORY PREDICTIONS FOR HIGH ECCENTRICITY ORBITS OF SPACE DEBRIS OBJECTS D. Kruzynska, R. Pospieszynski, M. Kruzynski, J. Golebiewska, and E. Wnuk Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Sloneczna 36, 60-286 Poznan, Poland, email: [email protected] ABSTRACT solar effects, solar radiation pressure and influence of Earth’s atmosphere. For satellites with altitude of perigee higher than 1000 km perturbations from the atmosphere Since 1957 the number of space debris has been increas- are negligible. However, for objects reaching very low ing and it cause threat of collision. To calculate precisely perigee altitude atmosphere is the most important per- space debris orbit we used several perturbations in our turbation. We used NRMLMSISE-00 empirical atmo- force model: geopotential, luni-solar effects, solar radi- spheric model in our calculations. Besides date and exact ation pressure and influence of Earth’s atmosphere. For place we have to include all necessary solar activity data satellites with altitude of perigee higher than 1000 km like local apparent solar time, 81 day average of F10.7 so- perturbations from the atmosphere is negligible. How- lar flux, daily F10.7 solar flux for previous day and daily ever for objects which reaches its lower parts is one of magnetic index. One of¡ the most influential parameter is S the most important perturbation. For the last perturbation area-to-mass ratio m . Small changes in the parame- we used NRMLMSISE-00 empirical model to calculate ter cause significant changes in satellite orbit prediction. precise parameters for the atmosphere. For large amount In this paper we have examined the influence on satellites of objects using numerical integration there appears to be orbits by using different value of this parameter. Also, for a problem with time of calculations. For this reason, we some objects’ population, with real data from TLE Cat- decided to use analytical model, which is much faster and alogue we have calculated some short and medium-term more convenient. Due to highly elliptical orbit we had to orbits using both analytical and numerical integration. exchange the eccentricity function by the Hansen coeffi- cients. 2. HEO OBJECTS IN TLE SATELLITE CATA- Key words: HEO, Highly Elliptical Orbit, Space debris, LOGUE Orbit Propagation. On 19 April 2013, there are 14941 objects in the 1. INTRODUCTION Two/Three Line Element Set (TLE) Satellite Catalogue and 16859 objects in the Satellite Situation Raport (SSR) which are still on Earth orbit. This includes 2526 objects Highly Elliptical Orbit (HEO) is an orbit with a low alti- with e > 0:4. Furthermore, 653 objects have altitude tude of perigee and high altitude of apogee. The HEO of perigee higher than 1000 km and 1873 lower. Fig. orbit usually crosses the Low Earth Orbit (LEO) and 1 shows the distribution of the orbital elements for 520 reaches regions even higher than Geostationary Earth Or- HEO objects with the eccentricity e > 0:4, perigee alti- bit (GEO). This kind of orbit has high eccentricity which tude q > 800 km and apogee altitude Q < 52000 km. can reach 0:7 0:8 value. The number of objects on HEO Semi-major axis definitely concentrates on value around orbits is high and increases. HEO objects could cause 26500 km. The majority of objects have the eccentricity hazard while in perigee due to their extremely high ve- around 0.55 and 0.72. The number of objects have the locity. In such case the most threatened objects are LEO inclination from 0 to 30, but most of them concentrate satellites. To predict and avoid a collision we have to de- around the critical inclination. terminate the orbit of a satellite precisely. In such case, long-term orbit propagation is useless. In our work we performed only short and medium-term predictions. For short-term propagation trajectories are calculated only for 3. FORCE MODEL FOR HEO ORBITS a few revolutions with high accuracy and medium-term predictions up to several weeks with less precision. To calculate precisely space debris orbits we used the force Space debris objects moving in the HEO region are model including perturbations from: geopotential, luni- strongly perturbed by geopotential and atmospheric drag _____________________________________ Proc. ‘6th European Conference on Space Debris’ Darmstadt, Germany, 22–25 April 2013 (ESA SP-723, August 2013) when they are close to their perigee, and by luni-solar ef- fects and solar radiation pressure in apogee. Precise mod- TLE Satellite orbits distribution eling of the HEO orbits is therefore very complicated task for e>0.4 altitude of perigee >800 km in the semi-major axis both in the case of analytical and numerical prediction 140 method applied. To keep an appropriate accuracy level of 120 trajectory prediction, all perturbing forces have to be in- cluded and modeled with very high precision. Prediction 100 algorithms for HEO have to be used in a specific way. 80 In the case of analytical methods, one of the most diffi- 60 cult cases is the calculation of the eccentricity function Glpq(e) values, for e = 0:7 0:8 and for high indices. Number of objects 40 20 0 10000 15000 20000 25000 30000 35000 Semi-major axis [km] 4. THE APPLIED ORBITAL MODEL TLE Satellite orbits distribution for e>0.4 altitude of perigee >800 km in the eccentricity 25 Predicted HEO orbits were calculated with the use of or- bital software tool developed in the Astronomical Obser- 20 vatory of the Adam Mickiewicz University in Poznan, Poland [3]. The tool works both in analytical and nu- 15 merical modes and includes influence of the following perturbing forces: 10 Number of objects 5 ~ ~ ~ ~ ~ ~ 0 ~r = (F0 + FG + FM + FS + FSR + FA)=m; (1) 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 Eccentricity TLE Satellite orbits distribution for e>0.4 altitude of perigee >800 km where : in the inclination 70 60 50 ~ F0 is the keplerian term; 40 ~ FG 30 is the perturbation force due to ; 20 the geopotential Number of objects ~ 10 FM is the perturbation force due to 0 the Moon gravity; 0 10 20 30 40 50 60 70 80 90 100 o ~ Inclination [ ] FS is the perturbation force due to ; TLE Satellite orbits distribution the Sun gravity for e>0.4 altitude of perigee >800 km ~ in the perigee FSR is the perturbation force due to 80 the solar radiation pressure; 70 ~ 60 FA is the perturbation force due to 50 the atmospheric drag: 40 30 Number of objects 20 10 To get high precision of calculations we used the 0 NRLMSISE-00 atmosphere model. Unfortunately in so- 0 2000 4000 6000 8000 10000 12000 lar radiation pressure we didn’t use the shadow function. Perigee [km] Presented results have been obtained for the orbit of ob- Figure 1. Distribution of the semi-major axis, inclination, ject No. 23840 - ATLAS 2A CENTAUR R/B. The epoch eccentricity and altitude of perigee for 520 HEO objects of initial orbital elements was 2013/4/8.4214020700. We e > 0:4 with the eccentricity and with the perigee altitude used exact values of orbital elements from TLE Satellite q > 800 Q < 52000 km and apogee altitude km. Catalogue, which are shown in Tab. 1. As we can see the eccentricity of this object is really high, therefore, we have applied the value of index q = 50. Atmospheric perturbations Table 1. Set of initial input orbital elements. 0.12 S/m=0.02 a (km) 24656.4396648861 S/m=0.05 e 0.7008709 0.1 S/m=0.10 i (deg) 21.0075 ! (deg) 89.2578 0.08 (deg) 175.2247 0.06 M (deg) 5.5452 n (rev/day) 2.24209852 0.04 0.02 Changes in position vector r [km] 4.1. The eccentricity function 0 0 0.5 1 1.5 2 time [days] To calculate precisely orbital elements of the HEO ob- Solar radiation pressure perturbations 1.4 jects we have to use the Hansen coefficients instead of S/m=0.02 G (e) S/m=0.05 Kaula’s eccentricity function lpq which is related to 1.2 S/m=0.10 the Hansen function by the following relation: 1 0.8 (l 1);(l 2p) Glpq(e) = X (e) (2) l 2p+q 0.6 0.4 We calculated the Hansen function using the following formula [1] [2]: Changes in position vector r [km] 0.2 0 0 0.5 1 1.5 2 1 X1 time [days] X(k) = En;mJ (ke); n;m (1 + 2)n+1 k l l (3) l= 1 Figure 2. Changes in position vector due to the at- mospheric drag and solar radiation pressure perturba- tions which are dependent on S/m parameter. Each color where: presents different S/m parameter value. e Sun gravity perturbations = p ; (4) 35 1 + 1 e2 30 and 25 20 X1 15 n;m k l m k l m+s s 2s Ek l = ( ) Cn m+1 Cn+m+1 ; (5) 10 s=0 Changes in position vector r [km] 5 0 0.5 1 1.5 2 and Jl(ke) are the Bessel functions of the first kind. The time [days] Bessel function J0(ke) is calculated directly from the Moon gravity perturbations definition for small values of ke (ke < 20), and from Ja- 35 cobi asymptotic formula for the higher values. All other 30 Bessel functions Jl(ke); l > 0 are calculated by succes- 25 sive multiplication of J0(ke) by ps factors, that are deter- mined from the following recursive relation: 20 15 1 10 ps = : (6) 2s=ke ps+1 Changes in position vector r [km] 5 0 Then, 0 0.5 1 1.5 2 time [days] Figure 3.