suivi des satellites artificiels

08 mars 2009

BOOK : "Chasseurs de satellites"

L'ensemble du site a été retraduit en français et fait l'objet d'un livre intitulé "chasseurs de satellites"
Droits réservés ISBN 978-2-7466-0651-7

Pour les commandes s'adresser à :
Guy LAFFAY 15 rue de la Toucharderie 78610 AUFFARGIS France
+33 (0)
Email :

Posté par revosat à 17:42 - Commentaires [1] - Permalien [#]

07 juin 2008

List of Satellite observed

OKEAN O rocket
COSMOS 807, 1025, 1220...
HELIOS 1A Rocket
TERRA (NASA environment)
LACROSSE 2, 3, 4, 5...
SATXX (not identified)

See all list here :


Posté par revosat à 10:17 - How to - Commentaires [0] - Permalien [#]

01 juin 2008

Summary of 2005-2008 Revosat activity


Revosat has gathered all the photographied satellites over AUFFARGIS (France).With these photos, their trajectories have been determined ie height, inclination orbit, ascending node.
We have reported the results on a diagram x axis=inclination of orbit and y axis= frequency.

ORBIT 49/53 °.Many observations have been carried out about docking ISS/SHUTTLE.Shuttle with Columbus (ESA) and docking of ATV jules Verne/ISS. Abrixas and Rosat two satellites operating in X rays have been well observed. They were at the end of their life so they were more luminous every month.

ORBIT 57°.Parameters of Uars , Lacrosse 3 and 5 have been well determined. Be careful of Uars changing rapidly of perigee.(Solar or NASA effect).The decaying of USA 193 has been observed till the rocket hit.

ORBIT 68°.Lacrosse 2 and 4 (Lacrosse 4 roc too) had been observed.

ORBIT 71°. These satellites are Spy Russian one. They are very high in the sky ie 850 kms and are the last to be seen before the full night.

ORBIT 82°.These satellites are spy Russian too. They are typically 500 kms high and some are interesting because they are decaying very rapidly from 400 kms. (See Revosat oct 2005 Cosmos 807 roc and Meteor 1-7).

ORBIT 86. All observations are IRIDIUM flares. These observations are very interesting because they allowed to compare time and location of the flares from the photos Revosat with Heavens above data.

ORBIT 98°.These satellites are environmental one.(heliosynchronous) They are numerous and mainly observed on summer because they photograph Earth with the light of the Sun so their transit take place two or three hours before midnight so 21/22 h TU over France consequently 9/10 h on the other side of earth Antipode to get photos with good contrast. Twilight took place at 21/22 hours only on summer and its duration is maximum on this season.

Envisat, Metop and Terra are perfectly heliosynchronous. But Okean O roc, Resurs 1-4 roc, Helios 1A roc are quasi heliosynchronous ie their transit are sooner every month concerning Okean O roc and Resurs 1-4 roc and later concerning Helios 1A roc. Evening satellite, Okean O roc will be seen on morning from 2009.

Cosmos 1484 and Cosmos 1484 roc are well visible and their respective precession are interesting because at the beginning (launching 1983) they were transiting together. Their transits are later every month.

ORBIT 108°.This orbit is SEASAT one and is particular because the shift is retro. It is the first oceano satellite before Topex Poseidon and so on. No explication about the choice of 108 degrees inclination. Its orbit shifts slowly retro with respect of sun. All is linked with Moon movement ie tides.

Posté par revosat à 23:24 - Observation - Commentaires [3] - Permalien [#]

07 mai 2008



On march 2008, we computed the spells of visibility and the unusual movement of perigee of USA 193(the argument of perigee had been kept ~100° to destroy more easily that satellite).
On April, with the last two line elements, we computed the last positions of the satellite.
The last TLE epoch are 12.4 H TU on 21 February 2008.
RAAN 26.1°
Arg perigee 100.08°

Mean anomaly 260.14. So (100+260=360°), the satellite is on the ascending node ie latitude=0°
The sidereal time of Greenwich at that epoch is 339° so the longitude is
360-339+26.1=47.1 east  or 313°.
We see too that, during that spell of visibility, the transits are ascending.
With that point of reference we computed the time of the first  transit near the latitude of Auffargis ~50°.
We found .25 hour after 12.4H and we computed  the positions two orbits after two orbits (~3 hours).
Finally we got that USA 193 transited over Dunkerque in FRANCE (lat 51.2/lo. 358°) at 6.24+12.4=18.64 TU on 21 February 08 and over Hawai at 15.05+12.4=27.45=3.45 or 3h 27mn TU.
It has been destroyed 6 revolutions after its transit over FRANCE. The debris may have been seen from CANADA. Their height are over 400 Kms and could transit around Earth over a year with the same inclination 58/59°.

From the curve speed versus anomaly we saw that V of the satellite was ~27900 kms/H compared to V missile~ 8000 kms/H. To hit successfully that satellite has really been a feat though the trajectory was well known before.

Posté par revosat à 01:18 - Observation - Commentaires [3] - Permalien [#]

02 avril 2008






During march ATV jules Verne(ESA) has been launched to be docked to ISS. (Inclination 51.6°)
See photo of ISS. The dashed trajectory on the photo allowed to get the time elapsed between two points (one period =1.6 second) then to compute the inclination, height and ascending node according to fast Kepler.
The docking is effective usually after two days, when it is Shuttle (NASA) or Progress but with ATV many experiments have been carried out so the docking has been effective only ~one month later.
We collected the RAAN of the two satellites to observe the different precessions and the argument of perigee to observe the use of their motors during the month.
We can see on the diagrams that the variation of the RAAN is –5.16 degrees/day relative to ISS and –5,207° /day relative to ATV.
ISS being always higher than ATV so more distant from the equatorial bulge  explains that ISS precession is smaller.
As for the perigee of ISS, it must have been regularly increasing because inclination is 51,6>63,4°( inclination inducing no movement of perigee).It is not the case .ISS manoeuvred to avoid debris of USA 193 recently destroyed with an inclination ~58° not very far from 51.6°.We can see the manoeuvres of ATV whenever perigee argument changed.

Posté par revosat à 23:27 - Observation - Commentaires [1] - Permalien [#]

07 mars 2008



The elements of Molniya typical are 40000kms*500kms*63.4°.Those of 11474 15642*433*62.7°. Molniya typical is very elliptic . Molniya 11474 is intermediate. Those two cases allow us to see the evolution of the distortion of the ground track near to the apogee.
We chose 200° as argument of perigee to obtain an apogee equal to 20° (200-180) whose slow movement could be visible over South of France.
1)Speed on orbit. The computed constant area of Molniya typical is 249*10^6.
The parameter of the ellipse 11979 kms, eccentricity=.7417
So Rho=11979/(1+.7417*cos((traj-200)*3.14/180))
As for Molniya 11474 Rho=10404/(1+.5275*cos((traj-200)*3.14/180)) .
2)V ground =Speed orbit*6378/Rho
3)SpinEarth. Earth spins 2*pi*6378 kms on equator in 24 hours so equal 2*pi*6378*cos(lat)/24 in kmh.
4)The Inclination (tan) without spinEarth is cos(lat)^2*tan(i)*(1-tan(lat)^2/tan(i)^2)^.5 see Revosat 2007.

We see that at latitude~ 45°,Earth spin and V ground of the satellite are close. (1260kmh) . di of Molniya typical can reach 89° .di of Molniya 11474 can reach 31°.Molniya typical can appear ~fix in the sky. Molniya 11474 apogee height is too low compared to that of Molniya typical(40000 and 15642kms). Russians used this possibility by adjusting over a town the argument of perigee .The inclinations of the orbit being ~63.4°, the configurations were stable. See comments of NASA and ESA.

Posté par revosat à 10:26 - Observation - Commentaires [1] - Permalien [#]

07 février 2008




We got photos of that satellite on 30 October 2007.19h18(1). Then we computed orbital elements with fast Kepler soft. and drew the last two spells of visibility on evening on February and March 2008.

The period of visibility is the time elapsed by the ascending node to precess 360°or 24 hours.

This period is 66 days dispatched in 49,25days and 16,75 days.

On the diagram, we see that there a first spell of ascending transits between 19 and 25 February and a second spell of descending transits between 4 and 10 March. Later the satellite will be decayed.

It appeared ,on the other hand, that inclination of orbit were 58.5° instead of 57° (Military satellites ex: Lacrosse 3 and 5) then we registered the precession of the argument of perigee to identify if that satellite was moving normally.

What a surprise! The argument of perigee is every ~20 days corrected to be ~100°.

On the scheme, perigee versus time, we reported the normal Keplerian movement of perigee (+1.55°/day) and the observed one.

The elements of the orbit were frozen to be a quasi circular one (eccentricity ~0)by using hydrazine rocket on board.

Why?. It is probably to control the decay till burning when entering high atmosphere.

A satellite with a frozen orbit is easier to be crashed into pacific ocean than with a changing one. It is quite the same , if US marine has to shoot it down with a missile .(NASA –Bush’s speech).

Posté par revosat à 10:21 - Observation - Commentaires [1] - Permalien [#]

07 janvier 2008



The inclination of the trajectory of a satellite in the sky is sometimes quite different from that we expect, considering (i) inclination of  the orbit. Two cases.
I)Quasi circular satellite. by example Iridium (i)=86.4 °(on january 2008)
II)Elliptic satellite example Molniya 11474 (i)=62.70,Aureole-2roc,USA 129 (On february 2008),
I)Quasi circular.
We know the relations between latitude (lat) and longitude (lo) on an orbit inclined (i). TAN(i)=TAN(lat)/SIN(Lo)
then TAN(lat)=TAN(i)*SIN(lo) and  d(lat)/d(lo)=cos(lat)^2*tg(i)*cos(lo)
But cos(lo)^2=(1-Tan(lat)^2/Tan(i)^2)
1)So d(lat)/d(lo)=cos(lat)^2*tan(i)*(1-tan(lat)^2/tan(i)^2)^.5  or cos(lat)^2*(tan(i)^2-tan(lat)^2)^.5
If latitude =0° then d(lat)/d(lo)=1*Tan(i)*1=Tan(i) the ground inclination is i
If latitude =(i) then d(lat)/d(lo)=0 the ground inclination is 0 see here after the curves but these results don’t take into account the speed rotation of Earth.
In fact the ground inclination is the sum of the movement of the satellite Vsat and the spin of the Earth Vspin.

2)Vsat Vs is 40000kms/T  T is period (hour).(precession is negligible)

3)Spin Earth.SE The equatorial rotation of Earth is 40000 kms in 24 h. At latitude lat the spin is Vequatorial*cos(lat).

4)Ground speed GS. We use GS^2=VS^2+SE^2-2*SE*VS*cos(i)

5)To get di, the delta angle to add to (i) to have the true inclination, we use

6)Results. See curves. We see that the equatorial ground inclination of iridium is 90°.The inclination 86.4° of the orbit of iridium has specially been chosen by Motorola to be 90° at the equatorial ground track  with Earth spin. We observe that the inclination decreases regularly from equator to pole.( di) is always minor compared to (i). It will be quite different with elliptic orbit where (di) may be quite superior to (i).

Posté par revosat à 10:29 - Observation - Commentaires [3] - Permalien [#]

07 novembre 2007



The elements of typical Molniya are 40000/500 kms/63.4°.
Such elements give a semi major axis A=(40000+500)/2+6378=26628kms
C=26628-(6378+500)=19750 kms
Period T=26628^1.5/6028.9/60 =12.0120876 hours
Nb rev/day=24/12.012=1.99798 rev/day
Perigee rotation +4*10^-4°/day
Nodes precession –1.1338°/day
Among the series Molniya-3, we found a different one N°24640  in Heavens above base with such data.
Apogee=36544 kms**Perigee=94 kms**Inclination 63.6391°.
The perigee and apogee are very low compared to that of typical Molniya. (may be a problem of propulsion during the launch).
These data induce 2.236 revolutions every day instead of 2 and a precession of –1.17°/day of the ascending node and –3*10-3 °/day of the perigee instead of ~0° habitually.

1)The transits can take place over FRANCE during night and because of the shift of the perigee , on a height very inferior to 36000 kms.

2)The rotation of the perigee (-12°=-11*365*3*10^-3 since the launch on 1996) induce a change of the aspect of the north ground track because the speed of rotation of the earth can balance that of Molniya at a decreasing latitude and not only at 63.6 as it was the case generally.
Because the argument of perigee decrease and so about the apogee, the height of the satellite increase with years during the zenital ascending transits(ZAT) and decrease during the zenital descending transits(ZDT) over FRANCE.
If Molniya X (by ex 15738)has an argument of perigee increasing, the height of zenital ascending transits(ZAT)decrease and height of zenital descending transits(ZDT) increase over FRANCE.


We will tackle the aspect of loop of the ground track near apogee on REVOSAT 2008.

Posté par revosat à 16:10 - Observation - Commentaires [1] - Permalien [#]

07 octobre 2007

AUREOLE-2 rocket


On  the beginning of 2007, we studied the predictions of transits of aureole-2 roc. By now we computed the height versus anomaly and the main resonance 15/1 at first with low accuracy then with high accuracy by solving the equations with a short software.
We published a board with the NR/NP resonances of Aureole-2 roc and a board with resonances 14/1,15/1,16/1 of well known satellites considered as circular one.

Posté par revosat à 16:14 - Observation - Commentaires [1] - Permalien [#]