Re: Leasat 2 R/B

Philip Chien (
Sat, 13 Mar 1999 22:45:19 -0500

Ed Cannon <> said:

>] Was wondering if anyone has observed Leasat 2 R/B (#15244)....

>on STS-16 (41-D, or Discovery F1), he gives an "Orbus 7S" with
>"Syncom-4 2" (a.k.a. Leasat 2), and it seems Orbus is a type of
>There's a photo of an IUS (IUS-1, IUS-2, or both?) on these
>Maybe both sources are correct...?

No.  Orbus is a registered tradmark of UTC for their solid rocket motors.
The number indicates the thousands of pounds of propellant (thousands of
.454 kgs. for the rest of the world).

The Orbus 21 and Orbus 6 are used in the IUS.  In that application they're
known as the IUS-1 and IUS-2 stages respectively.  Orbus 21 also has
several other applications including the OSC Transfer Orbit Stage, the
Intelsat VI PKM when it's launched from a Titan III (including the infamous
case where it wasn't used), and the upper stage of the Lockheed-Martin
Athena launch vehicle.

Orbus 7S (S for spin stabilized) is basically a Minuteman III ICMB third
stage in use as an upper stage.  Besides Syncom IV the Orbus 7S is used as
the perigee kick motor for the JCSAT 2 launch on a Titan III commercial
rocket and I'm quite certain is used for the SDS-2 satellites (USA 40, USA
89, and USA 125).

The UTC catalog lists the following dimensions for the Orbus 7S -

Length 227.3 cm (89.5 in.)
Diameter 132.1 cm (52 in.)
Exit plane diameter 84.76 cm (33.37 in.)
throat diameter 17.47 cm (6.876 in.)
Nozzle expansion ratio 23.55

Philip Chien, KC4YER
Earth News
world (in)famous writer, science fiction fan, ham radio operator,
all-around nice guy, etc.