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From: karn@faline.bellcore.com (Phil R. Karn)
Newsgroups: sci.space,sci.space.shuttle
Subject: Re: space news from Aug 24 AW&ST
Message-ID: <1480@faline.bellcore.com>
Date: Thu, 15-Oct-87 15:20:09 EDT
Article-I.D.: faline.1480
Posted: Thu Oct 15 15:20:09 1987
Date-Received: Sat, 17-Oct-87 09:25:16 EDT
References: <8760@utzoo.UUCP> <311@idacrd.UUCP>
Organization: Bell Communications Research, Inc
Lines: 43
Summary: Actually, it's a Molniya approximation
Xref: mnetor sci.space:3451 sci.space.shuttle:394

> Phase III-C, another in the oscar
> series will go up on the first Ariane 4 in the early part of next year.
> It is also scheduled for Molniya orbit.

Actually, while we would *like* a true Molniya orbit, what we get is
actually just a close approximation. In a true Molniya orbit the
inclination is 63.5 degrees. At this value, the secular perturbation on
the argument of perigee vanishes. This means that the positions of
apogee and perigee remain fixed in the orbit plane instead of slowly
rotating.  The argument of perigee is usually chosen to be near 270
degrees, so apogee occurs at maximum latitude (i.e., high over the
Soviet Union).

While the Soviets launch lots of stuff directly into this orbit, it is
not used by the primary missions flying on the only launch vehicle
available to us (Ariane). We must therefore make use of the Ariane's
most common destination, geostationary transfer orbit (GTO).  An Ariane
GTO is typically 35800 km apogee by 200-250 km perigee, inclination 6 to
8 deg, and argument of perigee 180 degrees. This is designed to make it
easy to get to a geostationary orbit with a single apogee kick motor
firing.

Unfortunately for us, it is difficult to get into a Molniya orbit from
GTO. Most of our propellant is required just to raise inclination, and
rotating the argument of perigee at the same time by 90 degrees is not
possible. What we instead planned to do on Oscar 10 (and plan again for
Phase 3-C) is to raise inclination to just a few degrees short of 63.5.
Over the next several years, perturbations will slowly increase the
satellite's argument of perigee, bringing the latitude of apogee higher
into the Northern hemisphere over the lifetime of the satellite.  Of
course, once the arg of perigee gets to 270 degrees we would love to
hold it there. Inclination changes must be done at the equator, however,
and the burn would then have to occur at much lower altitude and higher
velocity, making the fuel requirement unreasonable.

On the other hand, it's entirely possible that we've overlooked some
really clever trick. If anybody knows how to get from Ariane GTO into a
*true* Molniya orbit with only 1500 m/sec or so of delta-V, please let
Bob or me know!

Ah, if we only had a dedicated launcher...

Phil