1. PROBA 2 orbits and conditions of EUV observations V. Slemzin P. N
PROBA 2 orbits and conditions of EUV observations V. Slemzin P.N. Lebedev Physical Institute, Moscow

2. Preliminary parameters of the Proba 2 orbit (from ESA Science Management Plan, 27/04/06)
“Eurokot” launch opportunity, co-passenger of the SMOS satellite
Sun-synchronous, stabilized at 06:00 LT
Inclination:
<H> = 755 km
14.5 orbits/day with a period of 99.2 min
Launch date: 1 Feb > 1 Sept 2007
Mission duration: > 1 year
284 days without visible eclipses, 80 days with eclipses <18 min/orbit

3. Tools for evaluation and data sources:
STK - Satellite Tool Kit (universal) – stand alone package
TRAKSTAR code (T.S. Kelso, (Position and Velocity, Latitude, Longitude, and Altitude, look angles, right ascension and declination, etc.)
SPIRIT software (based on TRAKSTAR code)

4. Calculation of orbital parameters
Two-Line Element (TLE) files are produced from orbital measurements by the NASA Orbital Information Group (
PROBA2-755
Sat. N year,doy U
#orb incl.an. RAAN Eccentr orb/day #orbit
H=700 km Period= 98.5 min
H=755 km Period= 99.2 min
H=800 km Period=100.6 min

5. EUV occultations by absorption in the Earth’s atmosphere
Averaged data for quiet atmosphere
Transmission of the Earth’s atmosphere (based on SPIRIT measurements):
Hlos, km A A EUV occultation
450 km penumbra
350 km
250 km
<200 km < umbra

6. UV and VIS Eclipse periods and their duration
Sun-Synchronous Non-Sun-Synchronous
PROBA2
H=755km
TRACE
H=600 km
CORONAS-F
H=500km
VIS eclipses: 14/05-30/07 (77 d)
UV eclipses: 12/04-30/08 (141 d)
Period without UV eclipses: <2 month/year
Period without UV eclipses: 3 weeks/year

7. First day on orbit (1Feb 07) No eclipses
Beginning of UV eclipse period (~2 weeks before VIS eclipse)
UV eclipse: from 450 to 50 km – 10,5 min
Total - 24% of all time in eclipse

8. End of UV eclipse period
01 Aug 2007
(-35.5, 85.6)
(-34.6,-127.8)
(-71.5,170.6)

9. 20 km

10. Precession of the orbit
Sun-synchronous orbit: max of time is available for observations of the Sun. Stabilized at 6:00 LT - the orbital plane is near normal to the Sun direction.
Precession of the orbit : non-sphericity of the Earth
Variation of beta-angle between the orbital plane and direction to the Sun (H=755 km)
The curves for Hlos are similar!

11. Optimization of total time of UV eclipses
The orbit can be optimized on total UV eclipse time by variation of the RAAN angle
The angle from the inertial X-axis to the ascending node.
The ascending node is the point where the satellite passes through the inertial equator moving from south to north.
Right ascension is measured as a right-handed rotation about the inertial Z-axis.
RAAN(t1)  RAAN(t0)+10· (t1-t0,days)
Launch 1 Feb RAAN=32.50
1 Sep
Each 1% = 3.65 days!

12. RAAN=41.50
RAAN=51.50