Atlas Centaur Rockets

Jason Hatton (jason.hatton@etss.u-strasbg.fr)
Sat, 04 Apr 1998 13:46:37 +0000

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Dear All,
		There have been a number of recent posts to SeeSat about observations
of flashing Centaur rockets, so I decided to do some research &
determine how many of these are potentially observable. I've observed
several of these recently & they are IMHO some of the easiest objects to
observe in high eccentricity orbits.

Atlas Centaurs are relatively large upper stage rockets, most of which
are initially in geostationary type transfer orbits (ie. an apogee of
36000km & a perigee of a few hundred km). What is of interest to visual
satellite observers is that many flash & so can easily observed at
ranges of 10,000km or more in binoculars or small telescopes often
flashing at mag +6 or brighter. For people lucky enough to see these
objects at perigee (100 - 600km) they can be very bright indeed (mag
+1). The Atlas Centaur & Atlas-I Centaurs are cylindrical 10m x 3m
rockets with a bare metal surface, whilst Atlas-II Centaurs are 15m x 3m
& covered with an orange foam. If this is anything like the material
covering Shuttle external tanks it may darken with exposure to sunlight
& so could alter the flash pattern of the rocket. Centaurs have also
been launched on by Titan rockets, those on Titan-IIIE rockets are
fairly similar to Atlas Centaurs, whilst those launched on Titan-IV's
have a larger (5m) diameter.

I used the Atlas Centaur launch record, Jonathan's space report,
alldat.tle & the PPAS flash measurement database to draw up a list of
potentially observable Atlas Centaurs (no time yet to do the same thing
for Titan-Centaurs). This list is given below. There are several things
of interest;
(i) Most of the Atlas Centaurs which have been observed flash
(ii) Most pre 1978 launched Centaurs are in stable GTO orbits
(600x36000km)
(iii) Most of the recently launched Centaurs have been put into transfer
orbits which decay rapidly (ie. perigee's of 100-200km) despite very
high apogee's (some up to 80,000km)
(iv) There are several Centaurs in LEO. Starting later this year some
Atlas Centaur launches will be made in to Polar LEO from Vandenberg, so
we may well be treated some nice easily observable flashing satellites!

There are elements for 57 Atlas Centaurs (& several Titan Centaurs) in
alldat.tle, obtained from Mike McKant's web site. Several of these are
likely to decay in the next couple of years & two (Goes 10r & DBS 2r)
are predicted to decay this month. If your planning on observe these &
other Centaurs with low perigee's it's probably a good idea to get fresh
elements, since the orbital period can decrease quite rapidly.  

I hope this is of interest / use for observing

Best wishes & clear skies,

Jason

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Potentially observable Atlas Centaur Rockets (3-Apr-98)
Table best viewed with "word wrap" turned off.				

(a) Atlas Centaurs								
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Norad			Common				Flash	Year	2yr	
ID	Intl. Desn.	Name (r)	incl.	period	Period	Meas.	Decay?	Notes
-------------------------------------------------------------------------------------
694	1963-47A	Atlas Centaur 2	30.4	104	42.6	1997	N	
698	1963-47D	AC-2 deb	29.9	106	0.5	1997	N	Deb
700	1963-47F	AC-2 deb	30.5	108	67	1995	N	Deb
701	1963-47G	AC-2 deb	30.0	105	1.88	1995	N	Deb
739	1963-47H	AC-2 deb				No obs.	N	Deb
3598	1968-110B	OAO-A2r		30.5	99.5	5	1993	N	
4069	1969-69B	ATS-5r		17.2	703	8.77	1997	N	
4882	1971-06B	Intelsat-4-2r	28.2	650	5.6	1997	N	
6779	1967-001X*	Intelsat-4-3r	28	650	9	1997	N	
5816	1972-03B	Intelsat-4-4r	28	650	1.5	1994	N	
6058	1972-41B	Intelsat 4-5r	27.5	650	25.4	1997	N	
6155	1972-65B	OAO-3(C)r	35	98.6	S	1993	N	
6797	1973-58B	Intelsat-4-7r	28	650	3.19	1998	N	
7545	1974-93B	Intelsat-4-8r	26	650	?	1994	N	
7902	1975-42B	Intelsat-4-1r	26	650	lp	1982	N	
8331	1975-91B	Intelsat4A-1r	21.6	651	7.3	1983	N	
8621	1976-10B	Intelsat4A-2r	21.8	650	lp 	1983	N	
8840	1976-42B	Comstar-1 (1A)r	21.2	650	4.7	1997	N	
9329	1976-73B	Comstar-2 (1B)r	21.3	650	19.75	1991	N	
10025	1977-41B	Intelsat4A-4r	21.3	650	4.56	1983	N	
10722	1978-02B	Intelsat4A-3r	21.5	650	lp	1991	N	
12908	1978-16C	FLTSATCOM F1Deb	26.4	170	18.5	1996	?	Deb
10779	1978-35B	Intelsat4A-6r	21.8	650		?	N	
10976	1978-68B	Comstar-3 (1C)r	21.4	650			N	
12069	1980-87B	FLTSATCOM F4r	26.1	162	7.37	1996	?	
12445	1980-98B	Intelsat-5-2r	23.7	225	12.62	1998	?	
12363	1981-18B	Comstar-4 (1D)r	20.7	650	2.99	1997	N	
12497	1981-50B	Intelsat-5-1r	23.6	210	4.96	1996	?	
13007	1981-119B	Intelsat-5-3r	23.6	210	6.02	1997	?	
15631	1985-25B	Intelsat5A-10r					Decayed?		
15874	1985-55B	Intelsat5A-11r	23	530	17.82	1997	?	
16102	1985-87B	Intelsat5A-12r	23	465.6	3.89	1996	?	
								
(b) Atlas I								
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Norad			Common				Flash	Year	2yr	
ID	Intl. Desn.	Name (r)	incl.	period	Period	Meas.	Decay?	Notes
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20713	1990-65B	CRRESr		17	575		No obs	?	
21907	1992-13B	Galaxy 5r	19.7	640		No obs	N	
22564	1993-015B	UHF-F1r		27.2	137.3			2/2000	
22788	1993-56B	UHF-F2r				6.83	1997	Decayed?	
23133	1994-35B	UHF-F3r		26.9	250	34.2	1996	?	
23858	1996-27B	SAXr		4	94.9		No obs	5/2000	
24787	1997-19B	GEOS-K(10)r	27.4	417		No obs	4/1998	
								
(c) Atlas II								
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Norad			Common				Flash	Year	2yr	
ID	Intl. Desn.	Name (r)	incl.	period	Period	Meas.	Decay?	Notes	
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21804	1991-83B	Eutelsat-II-F3r	17.5	753		No obs	N	(a)
21874	1992-06B	DSCS-III-B01r				No obs	Decayed?	
21990	1992-32B	Intelsat-K r	26.3	434		No obs	?	
22010	1992-37B	DSCS-III-B10 r				No obs	Decayed?	
22928	1993-77B	Telstar-401r	23.6	335		No obs	2/2000	
23193	1994-047B	Direct TV D2 r	26	109	6.6	1998	4/1998	
23414	1994-79B	Orion Atlan.F1r	30.6	2880		No obs	N	
23468	1995-03B	EHF-F4r		26.8	470.3	150	1995	?	
23529	1995-13B	Intelsat 705r	26.7	274.1		No obs	10/2000	
23554	1995-19B	AMSC-1 r	26.1	510		No obs	?	
23590	1995-27B	EHF-F5 r	26.9	450	25.4	No obs	?	
23629	1995-38B	DSCS-III-B5 r				No obs	Decayed?	
23658	1995-43B	JCSAT3r		22.8	1640		No obs	?	(b)
23697	1995-57B	EHF-F6r		26.7	470	6	1995	?	
23742	1995-69B	Galaxy 3R r	26.7	470		No obs	?	
23780	1996-06B	Palapa C1 r	21.7	1916		No obs	?	(b)
23840	1996-20B	Inmarsat-3-F1 r	21.5	640		No obs	N	
23968	1996-42B	UHF-F/O-F7 r	26.9	471		No obs	?	
24316	1996-54B	GE-1 r					No obs	Decayed?	
24666	1996-67B	Hot Bird 2 r				No obs	Decayed?	
24675	1996-70B	Inmarsat-3-F3 r	22.2	650		No obs	N	
24773	1997-07B	JCSAT-4r				No obs	Decayed?	
24881	1997-36B	Superbird C r	25.6	1664		No obs	?	(b)
24937	1997-50B	GE-3 r		18.7	790		No obs	N	
25005	1997-59B	Echostar-F3 r	25.9	101		No obs	?	(c)
25020	1997-65B	IABS/DSC-III r	26.1	550		No obs	7/1999	
25087	1997-78B	Galaxy 8i r	26.1	811		No obs	11/2000	
?	1998-05B	"Capricorn" r	Classified elements**	No obs	?	

Key:
incl. = orbital inclination
Period = orbital period
Flash period = measured flash period in seconds from PPAS 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"
(c) = probably decayed in last 2-3 weeks
Deb = Debris or fragment

* Origonal Intl. Desn. = 1971-116B
** The "Capricorn" rocket is in an approx. 45 deg incl. high eccentricity orbit. 
What a shame that the elements are classified!

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