by Jason Hatton , SeeSat subscriber
There had been a number of posts in April 1998 to SeeSat about observations of flashing Centaur rockets, so I decided to do some research and determine how many of these are potentially observable. I've observed several of these recently and they are IMHO some of the easiest objects to observe in the high eccentricity orbits.
Atlas Centaurs are relatively large upper stage rockets, most of which are initially in geostationary type transfer orbits (i.e., an apogee of 36000 km and a perigee of a few hundred kilometers). What is of interest to visual satellite observers is that many flash, and so, can easily be observed at ranges of 10,000 km or more in binoculars or small telescope, often flashing at magnitude +6 or brighter. For people lucky enough to see these objects at perigee (100-600 km), they can be very bright indeed (mag +1).The original Atlas Centaur and Atlas I Centaur rockets are cylindrical 9m x 3m rockets with a bare metal surface (an insulating fiberglass covering is jettisoned before reaching orbit), with twin engines.
Atlas II Centaurs are 10m x 3m, covered with an orange PVC foam. If this is anything like the material covering shuttle external tanks, it may darken with exposure to sunlight and so could alter the flash pattern of the rocket. Additionally, the tank surface is often decorated with mission logos/art work which may also alter the reflective properties of the surface.
The Atlas IIIA Centaur (formerly IIAR), scheduled to launch in 1999, is similar to the Atlas II Centaur rocket, except only a single engine is mounted on the centerline of the booster.
The Atlas IIIB Centaur (formerly IIARC), scheduled for 2002, has a two engine stretched tank booster.
Centaurs have also been launched on Titan rockets. Those on Titan-IIE rockets are fairly similar to Atlas Centaurs, whilst those launched on Titan-IVs have a larger (5m) diameter. You can see a Titan IV Centaur leaving earth orbit on a planetary journey to Saturn here .The possible image of a Titan IV Centaur venting fuel launched on May 9, 1998 at 01:38 UT from a classified US ORION signal intelligence mission (USA 139) to a geosynchronous orbit can be found here (171k) . Photo was taken by Charles Cornwell. Specifics are found in photo.
Jonathan's Space Report and the PPAS flash measurement database were used to draw up a list of potentially observable Atlas Centaurs. This list is given below.
There are elements for 50 plus Atlas Centaurs (and several Titan Centaurs) in the "alldat.tle" file obtained from Mike McCants' web site. Several of these are likely to decay in the next couple of years. If you are planning on observing Centaurs with low perigees, it's probably a good idea to get fresh elements since the orbital period can decrease quite rapidly.
Atlas Centaur's
_____________________________________________________________________________________________________________
Norad Common Target Flash Year Decay in Notes
ID Intl. Desn. Name (r) Orbit incl. period Period Meas. Accel? 2 years?
_____________________________________________________________________________________________________________
694 1963-47A None GTO 30.4 104 44.9 1997 D N
698 1963-47D Fragment 0.5 1997 A?
700 1963-47F Fragment 65.5 1997 D
701 1963-47G Fragment 2.09 1995 D
739 1963-47H Fragment No obs.
3598 1968-110B OAO-A2 LEO 30.5 99.5 S 1993 D N
4069 1969-69B ATS-5 GTO 17.2 703 8.885 1998 S N
4882 1971-06B Intelsat-4-2 GTO 28.2 650 5.64 1998 D N
6779 1971-116B Intelsat-4-3 GTO 28 650 9.36 1998 D N
5816 1972-03B Intelsat-4-4 GTO 28 650 1.531 1998 D N
6058 1972-41B Intelsat 4-5 GTO 27.5 650 25.391 1997 A/var? N
6155 1972-65B OAO-3(C) LEO 35 98.6 S 1997 S N
6797 1973-58B Intelsat-4-7 GTO 28 650 3.19 1998 D? N
545 1974-93B Intelsat-4-8 GTO 26 650 lp 1998 ? N
7902 1975-42B Intelsat-4-1 GTO 26 650 ~200 1998 D N
8331 1975-91B Intelsat4A-1 GTO 21.6 651 7.97 1998 A/var? N
8621 1976-10B Intelsat4A-2 GTO 21.8 650 lp 1983 A N
8840 1976-42B Comstar-1 (1A) GTO 21.2 650 4.917 1998 S/var? N
9329 1976-73B Comstar-2 (1B) GTO 21.3 650 21.22 1999 D N
10025 1977-41B Intelsat4A-4 GTO 21.3 650 5.38 1998 D N
10722 1978-02B Intelsat4A-3 GTO 21.5 650 lp 1991 D? N
12908 1978-16C FLTSATCOM F1deb GTO 26.4 170 17.86 1998 A
10779 1978-35B Intelsat4A-6 GTO 21.8 650 4.495 1998 D N
10976 1978-68B Comstar-3 (1C) GTO 21.4 650 4.915 1998 D N
12069 1980-87B FLTSATCOM F4 GTO 26.1 162 8.626 1998 D ?
12445 1980-98B Intelsat-5-2 GTO 23.7 225 14.285 1998 D ?
12363 1981-18B Comstar-4 (1D) GTO 20.7 650 3.02 1998 D N
12497 1981-50B Intelsat-5-1 GTO 23.6 210 10.87 1998 D ? Double Maxima
12778 1981-73B FLTSATCOM F5 GTO 1981 S/var?
13007 1981-119B Intelsat-5-3 GTO 23.6 210 6.02 1997 D ?
13087 1982-17B Intelsat-5-4 GTO 17.21 1983 D
13599 1982-97B Intelsat-5-5 GTO 3.31 1990 D
14081 1983-47B Intelsat-5-6 GTO 2.93 1983 1
15874 1985-55B Intelsat5A-11 GTO 23 530 9.046 1998 D ?
16102 1985-87B Intelsat5A-12 GTO 23 465.6 3.89 1996 D ?
(b) Atlas I Centaurs
_____________________________________________________________________________________________________________
Norad Common Target Flash Year Decay in Notes
ID Intl. Desn. Name (r) Orbit incl. period Period Meas. Accel? 2 years?
_____________________________________________________________________________________________________________
20713 1990-65B CRRES Ellip 17 575 lp 1999 1 ?
21907 1992-13B Galaxy 5 GTO 19.7 640 18.21 1998 D N
22564 1993-015B UHF-F1 Sub 27.2 137.3 ~20 1998 Var 12/1999
22788 1993-56B UHF-F2 Sub 26.9 219 6.83 1997 Var
23133 1994-35B UHF-F3 Sub 26.9 250 23.9 1998 A? ?
23858 1996-27B SAX LEO 4 94.9 No obs 09/2000
(c) Atlas II Centaurs (Atlas II, IIA, IIAS)
_____________________________________________________________________________________________________________
Norad Common Target Flash Year Decay in Notes
ID Intl. Desn. Name (r) Orbit incl. period Period Meas. Accel? 2 years?
_____________________________________________________________________________________________________________
21804 1991-83B Eutelsat-II-F3 Super 17.5 753 40 1995 1 N (a)
21990 1992-32B Intelsat-K GTO 26.3 434 70 1994 1 ?
22010 1992-37B DSCS-III-B10 GTO No obs
22916 1993-074B DSCS-III GTO No obs
23414 1994-79B Orion Atlant.F1 Super 30.56 2880 No obs N
23468 1995-03B EHF-F4 Sub 26.8 470.3 lp 1998 A? ?
23554 1995-19B AMSC-1 Super 26.1 510 ~30 1998 1 ?
23590 1995-27B EHF-F5 Sub 26.9 450 25.4 1995 1 ?
23629 1995-38B DSCS-III-B5 GTO No obs
23658 1995-43B JCSAT3 Super 22.8 1640 No obs ? (b)
23697 1995-57B EHF-F6 Sub 26.7 470 lp 1998 D ?
23742 1995-69B Galaxy 3R Sub 26.7 470 2.93 1998 Var ?
23780 1996-06B Palapa C1 Super 21.7 1916 No obs ? (b)
23840 1996-20B Inmarsat-3-F1 GTO 21.5 640 No obs N
23968 1996-42B UHF-F/O-F7 Sub 26.9 471 No obs ?
24675 1996-70B Inmarsat-3-F3 GTO 22.2 650 23 1997 N
24733 1997-07B JCSAT-4 Super 23.4 349 No obs ? (b)
24881 1997-36B Superbird C Super 25.6 1664 No obs ? (b)
24937 1997-50B GE-3 Super 18.7 790 No obs N
1998-05B Capricorn Eccen No obs
25240 1998-014B INTELSAT 806 GTO 22.6 282.9 No obs 09/2000
25259 1998-016B UHF-F8 Sub 27 388.5 110 1998 1 ?
25372 1998-037B INTELSAT 805 GTO 22.9 520.4 No obs ?
25502 1998-058B UHF-F9 Sub 26.9 444.5 No obs ?
25631 1999-006B JCSAT-6 Super 25.6 2122 No obs ?
25674 1999-018B Eutelsat W3 Super 20.2 811 No obs ?
________________________________________________________________________________________________________________________________
Key: Target orbit GTO = Geostationary Transfer Orbit
Sub = Subsynchronous Geostationary Transfer Orbit
Super = Supersynchronous Geostationary Transfer Orbit
Ellip = Elliptical orbitincl. = orbital inclination Period = orbital period Flash period = measured flash period in seconds from PPAS 8 database lp = long period
Year Meas. = year of most recent flash period measurement, No obs. = no observations reported 2yr decay = SATEVO predicted date of decay in next two years
N = decay unlikely in near future ? = perigee less than 400km, so decay possible in next few years Decayed? = no elements in alldat.tle, so probably decayed in last 9 months Notes: (a) = listed as "Ariane rocket" (b) = old elements, possibly decayed or "lost" Deb = Debris or fragment (or reclassification????) Flash measurement - accelerating? A = accelerating
D = Decelerating
S = Stable, little or no change in period"
Var = variable flash period
1 = only one measurement
* Original Intl. Desn. = 1971-116B ** The Capricorn rocket is in an approx. 45 deg incl. high eccentricity orbit.
Return to VSO Home Page