Jonathan's Space Report
No. 361 1998 May 24 Cambridge, MA
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Shuttle and Mir
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Launch of the Station seems to be slipping further, with a probable
delay of STS-88 to December according to news reports. This would push
STS-93 to January according to the AP report.
Progress M-39 remains docked to the Mir orbital complex, and the crew
are unloading it. STS-91 is on the pad, ready for the final US trip to
Mir. In addition to Andrew Thomas, much of the US scientific equipment
aboard Mir will also be brought home.
For mission STS-91, Discovery's payload bay has a new configuration.
Forward in the bay is the external airlock and docking system. Behind
this is the tunnel adapter, which on most earlier missions was between
the docking system and the main cabin. Behind the tunnel adapter is the
Spacehab tunnel, followed by a single Spacehab module. The Spacehab
module carries water, food, and equipment for Mir. Further aft in the
payload bay is the Alpha Magnetic Spectrometer. This particle physics
experiment uses a new cross-bay carrier, containing a large (3000 kg)
magnet and scintillator detectors which will be used in a search for
antiprotons and antinuclei in cosmic rays.
Eight GAS canisters are also installed in the payload bay. Bay 6 port
has SEM-3, with high school experiments, and an inert canister
containing commemorative flags. Bay 6 starboard has G-648 (Canadian
space agency organic thin films experiment) and another canister of
flags. Bay 13 port has G-765 (Canadian space agency fluids experiment)
and SEM-5 (high school passive experiments). Bay 13 starboard has two
small size (2.5-cubic foot) containers, G-090 and G-743.
Recent Launches
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HGS-1 completed its first lunar flyby on May 13, and returned to a
perigee of about 36000 km at about 0300 UTC on May 17. HGS has decided
to send the satellite on a second lunar flyby on Jun 6 to further
improve the orbit. Current orbit is 35646 km x 475763 km x 18.2 deg.
Galaxy 4H, a Hughes HS-601 satellite, failed on May 19, disrupting pager
services across the United States. A computer failure resulted in loss
of attitude control. Ku-band traffic is being transferred to Galaxy 3R,
while Galaxy 6 is being moved to the Galaxy 4H orbital position to
replace its C-band coverage.
Echostar 4 has reportedly had problems deploying its solar panels.
Orbits
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The following discussion is for technically oriented pedants only.
There's been a lot of discussion lately about the exact definitions of
varous kinds of orbit: what is the difference between Low Earth Orbit
(LEO) and Medium Earth Orbit (MEO)? There's no right answer, since these
names are arbitrary. I have my own definitions, which I give below. The
boundaries I use are motivated by the physical boundaries in the
atmosphere and by historical practice.
My proposed definitions:
(1) Atmospheric (ATM): suborbital trajectory with apogee less than
80 km (mean height of the mesopause, and same as old USAF definition of
50 miles for astronaut wings)
(2) Suborbital spaceflight (SO): suborbital trajectory with apogee more
than 80 km.
(3) Transatmospheric orbit (TAO): orbital flight with perigee less than
80 km but more than zero. Potentially used by aerobraking missions and
transatmospheric vehicles, also in some temporary phases of orbital
flight (e.g. STS pre OMS-2, some failures when no apogee restart)
(4) LEO: Low Earth Orbit. Orbits with perigee above 80 km and apogee
less than L km. It's not clear what the value of L should be. A
histogram of apogee heights for objects currently in orbit shows a big
peak from 100 km to about 2500 km, followed by an almost empty region,
followed by a small peak at 19000 km (GLONASS and GPS) and another peak
at 36000 km (GEO). Why are there so few satellites in the 3000 - 19000
km range? It's because of the radiation belts. Of course polar orbit
satellites pass through the radiation belts even at low altitude (the
magnetosphere dips into the auroral circle). But at 3000 km and up you
pass through the belts at all latitudes. What is the lower level of the
radiation belts? I'm still researching this. However, if you look at the
apogee histogram in more detail, you see that the lower orbit satellites
have two broad peaks: one from 300 km to 1300km peaking at 800-1000 km;
and another at 1300-2200 km peaking at 1500 km. This analysis is
compromised by the fact that the histogram may be dominated by debris
objects from a small number of explosions; it would be better to plot
payloads only. Redoing the analysis with only international designations
"A" and "B" (e.g. 1997-04B, but not 1997-04F) gives a similar result
but with narrower peaks. In particular, there are very few payloads or
rocket stages with apogees in the 1100 to 1400 km or 1600 to 2000 km
ranges. I therefore suggest that the LEO/MEO boundary value L should be
set at either:
apogee 1000 km, a round number definition which would exclude the large
number of satellites in the 1000-1100 km range including Parus/Tsikada and
Transit navsats. I think 1000 km is a little too low to exclude.
apogee 1100 km, a strict definition of LEO
apogee 1600 km, a definition including Globalstar and Strela/Gonets and older ESSA/NOAA
polar satellites
apogee 2000 km, a safe 'round number' definition including all LEO
payloads and debris objects.
period 120 minutes ( 2 hours ). Another 'round number'.
This has an average height of 1680 km and a maximum apogee of 3280 km.
With the 2000 km or 2 hr definitions, MEO (Medium Earth Orbit) would be the relatively
unpopulated region between LEO and the geosynch corridor, which contains
the Glonass and GPS satellites and the old Midas early warning sats,
and not much else. I have decided to use the 2 hr definition, but I suspect
that the industry may end up using something toward the lower end, say
the 1100 km definition.
I consider several subcategories of LEO sorted by inclination. The physically
motivated one is LEO/S or SSO: Sun Synchronous orbit, when the orbital plane
precesses to keep the same sun angle. This requires a period (hh:min) of
T = 3:47 * ( - cos i )** (3/7) +/- 0:10, for i = 97.0 - 103.0 degrees.
It's probably good enough to use a less strict but simpler definition of SSO:
LEO/S Sun Synch T = 1:26 - 2:00, i = 95.0 - 104.0
One might also usefully define
LEO/R Retrograde: T = 1:26 - 2:00, i = 104.0 - 180.0
LEO/P Polar: T = 1:26 - 2:00, i = 85.0 - 95.0
LEO/E Equatorial T = 1:26 - 2:00, i = 0.0 - 20.0
Of course technically `retrograde' is anything with i more than 90.0 degrees,
but one is more likely to refer to orbits with i below 104 deg as polar or
sun-synchronous.
The next boundary of interest is between MEO and the 'geosynchronous
corridor'. To study the geosynchronous corridor, it's most helpful to
work in orbital period and consider drift rates. For a pure equatorial
orbit, non-Keplerian perturbations introduce drifts of order 0.05
degrees per day. These dominate Keplerian drift in longitude if the
period is roughly between 23h 55.5m and 23h 56.5 min. I call this
'geostationary orbit'. Satellites which are still operational but are
being moved from one slot to another usually are drifting at between 0.1
and 10 degrees per day. I find the 10 degree per day drift rate one
convenient boundary, corresponding to periods from 23h 17m to 24h 37m
(that's what I used to use in my geo.log file). An alternative criterion
is to make a period cut from 23h to 25h: 1 hour either side of the
geosynch period.
MEO is then everything vaguely circular below 23 hours and above LEO.
Objects which are in elliptical orbits and with MEO-type orbital
periods, I call HEO (highly elliptical orbits). A special case of HEO is
the Molniya orbit, with inclination 63 degrees and period 12 hours,
giving zero perigee precession and an apogee stabilized in longitude
every other orbit. Another special case is geostationary transfer orbit
(GTO), subclasses of which I defined in JSR 310 back in Jan 1997
(included in the summary table below).
I now use personal definitions as follows:
Period (hh:mm) Inc (deg) Ecc
Three with the synchronous period:
GEO/S Stationary 23:55.5 - 23:56.5 0.0 - 2.0 0.00 - 0.01
(the good stuff, circular and equatorial)
GEO/I Inclined GEO 23:55.5 - 23.56.5 0.0 - 2.0 0.01-0.05
and 23:55.5 - 23.56.5 2.0 - 20.0 0.00-0.05
(still circular and somewhat equatorial)
GEO/T Synchronous 23:55.5 - 23.56.5 0 - 20.0 0.05 - 0.85
and 23:55.5 - 23.56.5 20.0-180.0 0.00 - 0.85
(synchronous but not circular equatorial)
The corresponding three cases with periods not equal to the magic one:
GEO/D Drift GEO 23:00 - 25:00 0.0 - 2.0 0.00 - 0.05
GEO/ID Inc. Drift GEO 23:00 - 25:00 2.0 - 20.0 0.00 - 0.05
GEO/NS Near-Sync 23:00 - 25:00 0 - 180 0.05 - 0.85
and 23:00 - 25:00 20 - 180 0.00 - 0.85
Rather than High Earth Orbit (too easily confused with Highly Elliptical
Orbit) I use Deep Space Orbit (DSO), for anything circular above GEO,
and Deep Highly Eccentric Orbit (DHEO) for elliptical deep orbits.
Finally, I summarize the categories I am suggesting in the table below.
If you would like to propose alternative definitions, please forward
them to me.
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Orbit Classification Summary
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(A = apogee/km, P = perigee/km, T = period/hh:mm, i = inc/deg, e = eccentricity)
Main categories
ATM Atmospheric A < 80
SO Suborbital A >= 80, P < 0
TAO Trans-Atm A >= 80, P = 0 - 80
LEO Low T= 1:26 - 2:00 (P>80)
MEO Medium T= 2:00 - 23:00, e < 0.5
HEO Highly Ellip T= 4:03 - 23:00, e > 0.5 (implies A > 13000)
GEO Near-Synch T=23:00 - 25:00
DSO Deep Space T>25:00, e < 0.5
DHEO Deep Eccentric T>25:00, e > 0.5
HCO Heliocentric
PCO Planetocentric
SSE Solar System Escape
Subcategories
LEO/S Sun Synch T = 1:26 - 2:00, i= 95.0 - 104.0
LEO/R Retrograde: T = 1:26 - 2:00, i= 104.0 - 180.0
LEO/P Polar: T = 1:26 - 2:00, i= 85.0 - 95.0
LEO/E Equatorial T = 1:26 - 2:00, i= 0.0 - 20.0
HEO/M: Molniya orbit T = 11:30 - 12:30, i= 62.0 - 64.0, e= 0.50 - 0.77
GEO/S Stationary T= 23:55.5 - 23:56.5,i= 0.0 - 2.0 0.00 - 0.01
GEO/I Inclined GEO T= 23:55.5 - 23.56.5,i= 0.0 - 20.0 0.00 - 0.05
GEO/T Synchronous T= 23:55.5 - 23.56.5,i= 0 - 180 0.00 - 0.85
GEO/D Drift GEO T=23:00 - 25:00 i= 0.0 - 2.0, e= 0.00 - 0.05
GEO/ID Inc. Drift GEO T=23:00 - 25:00 i= 0.0 - 20.0, e= 0.00 - 0.05
GEO/NS Near-Sync T=23:00 - 25:00 i= 0 - 180, e= 0.00 - 0.85
GTO subclasses of HEO, from JSR 310
GTO/L Low GTO A = 13000 - 30000
GTO/S Sub-GTO A = 30000 - 41000
GTO Std GTO P = 150 - 700, A = 34000 - 41000,
GTO/HP High Peri. GTO P = 700- 4000, A = 34000 - 41000,
GTO/H High GTO A > 41000
(Super-GTO now superseded by GTO/H and DHEO as appropriate)
Table of Recent Launches
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Date UT Name Launch Vehicle Site Mission INTL.
DES.
Apr 2 0242 TRACE Pegasus XL Vandenberg RW30/15 Solar obs. 20A
Apr 7 0213 Iridium 62 Proton-K/DM2 Baykonur Comsat 21A
Iridium 63 Comsat 21B
Iridium 64 Comsat 21C
Iridium 65 Comsat 21D
Iridium 66 Comsat 21E
Iridium 67 Comsat 21F
Iridium 68 Comsat 21G
Apr 17 1819 Columbia ) Shuttle Kennedy LC39B Spaceship 22A
Neurolab )
Apr 24 2238 Globalstar FM6) Delta 7420 Canaveral SLC17A Comsat 23A
Globalstar FM8) 23B
Globalstar FM14) 23C
Globalstar FM15) 23D
Apr 28 2253 Nilesat 1 ) Ariane 44P Kourou ELA2 Comsat 24A
BSAT 1B ) Comsat 24B
Apr 29 0437 Kosmos-2350 Proton-K/DM-2 Baykonur Comsat? 25A
May 2 0916 Iridium 69 CZ-2C/SD Taiyuan Comsat 26A
Iridium 71 Comsat 26B
May 7 0853 Kosmos-2351 Molniya-M Plesetsk Early Warn 27A
May 7 2345 Echostar 4 Proton-K/DM3 Baykonur Comsat 28A
May 9 0138 USA 139 Titan Centaur Canaveral SLC40 Sigint 29A
May 13 1552 NOAA 15 Titan 2 Vandenberg SLC4W Weather 30A
May 14 2212 Progress M-39 Soyuz-U Baykonur LC1 Cargo 31A
May 17 2116 Iridium 70) Delta 7920 Vandenberg SLC2W Comsat 32A
Iridium 72) Comsat 32B
Iridium 73) Comsat 32C
Iridium 74) Comsat 32D
Iridium 75) Comsat 32E
Current Shuttle Processing Status
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Orbiters Location Mission Launch Due
OV-102 Columbia OPF Bay 3 STS-93 Jan ?
OV-103 Discovery LC39A STS-91 Jun 2
OV-104 Atlantis Palmdale OMDP
OV-105 Endeavour OPF Bay 1 STS-88 Dec 3
MLP/SRB/ET/OV stacks
MLP1/RSRM66/ET-96/OV-103 LC39A STS-91
MLP2/
MLP3/
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| Jonathan McDowell | phone : (617) 495-7176 |
| Harvard-Smithsonian Center for | |
| Astrophysics | |
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| Cambridge MA 02138 | inter : jcm@urania.harvard.edu |
| USA | jmcdowell@cfa.harvard.edu |
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