Sea Launch Orbital Geometry

We've probably discussed this before, but the
upcoming Sea Launch mission (set to begin once
the seas die down) has reintroduced an unanswered
question to my attention.

On this mission, the DMSL upper stage will perform
two burns to put 4.7 metric ton XM-3 into GTO.
The first burn will put the payload into a
180 x 9452 km x 0 deg parking orbit. The second
burn will begin 47 minutes after liftoff, at an
altitude of 4682 km, and will last three minutes.
The final planned orbit is 2466 x 35830 km x 0 deg.

Other commercial launchers typically perform upper
stage burns at either perigee or apogee. What is
different about Zenit 3/DMSL?

- Ed Kyle

Ed Kyle wrote:

Other commercial launchers typically perform upper
stage burns at either perigee or apogee. What is
different about Zenit 3/DMSL?

If they launch from the equator they don't have the plane changes
to worry about. Just a guess.

Jim Davis

"Ed Kyle" writes:

On this mission, the DMSL upper stage will perform
two burns to put 4.7 metric ton XM-3 into GTO.
The first burn will put the payload into a
180 x 9452 km x 0 deg parking orbit. The second
burn will begin 47 minutes after liftoff, at an
altitude of 4682 km, and will last three minutes.
The final planned orbit is 2466 x 35830 km x 0 deg.

Other commercial launchers typically perform upper
stage burns at either perigee or apogee. What is
different about Zenit 3/DMSL?


Perhaps some secondary consideration, such as keeping the second burn or first target
apogee within sight of specific ground stations. Or maybe limiting the time between
the two engine firings. Making the parking orbit apogee 2400 km, and doing the
second burn at apogee, would be slightly more efficient, I think, but would require a
longer coast and end up with the second burn, and target apogee, over the indian ocean.

Lou Scheffer

In article .com,
Ed Kyle wrote:
Other commercial launchers typically perform upper
stage burns at either perigee or apogee. What is
different about Zenit 3/DMSL?

This isn't the first time Sea Launch has used a somewhat puzzling mission
plan. My suspicion is that there are some obscure constraints on the
third stage which somehow dictate this. (There are some constraints on
fuel mass -- e.g., there has to be at least 2t left in the tanks for the
final restart, for some reason -- but they don't explain this.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

On 22 Feb 2005 17:06:05 GMT, in a place far, far away, Jim Davis
made the phosphor on my monitor glow in such
a way as to indicate that:

Ed Kyle wrote:

Other commercial launchers typically perform upper
stage burns at either perigee or apogee. What is
different about Zenit 3/DMSL?

If they launch from the equator they don't have the plane changes
to worry about. Just a guess.

Shouldn't make any difference, since the plane change maneuver is
combined with the transfer maneuver.