Sea Launch performance

Anyone know offhand why the recent Sea Launch performance was less
than the previous ones?

The most recent launch was:
4737 kg, 760 km perigee, 35768 apogee, 0 inclination.

The first launch on their previous launch page was Thuraya,
5108 kg, 1200 km perigee, 35768 apogee, 6.3 degree inclination

So the recent launch put a lighter satellite into a lower orbit. Does
Sea Launch come in variants?

Lou Scheffer

"Lou Scheffer" wrote in message
om...
Anyone know offhand why the recent Sea Launch performance was less
than the previous ones?

The most recent launch was:
4737 kg, 760 km perigee, 35768 apogee, 0 inclination.

The first launch on their previous launch page was Thuraya,
5108 kg, 1200 km perigee, 35768 apogee, 6.3 degree inclination

So the recent launch put a lighter satellite into a lower orbit. Does
Sea Launch come in variants?

Lou Scheffer

As far as I can tell Sea Launch only uses one of two Zenit configurations.

(Lou Scheffer) wrote in message . com...
Anyone know offhand why the recent Sea Launch performance was less
than the previous ones?

The most recent launch was:
4737 kg, 760 km perigee, 35768 apogee, 0 inclination.

The first launch on their previous launch page was Thuraya,
5108 kg, 1200 km perigee, 35768 apogee, 6.3 degree inclination

So the recent launch put a lighter satellite into a lower orbit. Does
Sea Launch come in variants?


Sea Launch Zenit 3SL comes in only one flavor to date - a two
stage Ukranian Zenit topped by a Russian Blok DM-SL restartable
third stage. I suspect the difference in the two missions
you've listed was that the most recent launch used energy to
reduce inclination while the Thuraya launch used the same energy
to raise perigee.

- Ed Kyle

(ed kyle) wrote in message . com...
Sea Launch Zenit 3SL comes in only one flavor to date - a two
stage Ukranian Zenit topped by a Russian Blok DM-SL restartable
third stage. I suspect the difference in the two missions
you've listed was that the most recent launch used energy to
reduce inclination while the Thuraya launch used the same energy
to raise perigee.

- Ed Kyle

Not really, being launched from the equator, Zenit doesn't have to
reduce inclination. In fact, flying East and fully exploiting the
Earth rotation should give it a slightly better lift.

So it is a mistery why their "high perigee" is not twice as high.

(Lou Scheffer) wrote in message . com...
(ed kyle) wrote in message . com...
(Lou Scheffer) wrote in message . com...
Anyone know offhand why the recent Sea Launch performance was less
than the previous ones? [...]
I suspect the difference was that the most recent launch used
energy to reduce inclination while the Thuraya launch used the
same energy to raise perigee.

This is backwards for a launch from the equator, I think. It takes
*more* energy to put a satellite into a non-zero inclination ...


You're right. I booted this one. If all other things were equal,
it would have taken Zenit 3SL slightly *more* energy to put Thuraya 2
into it's 6.3 deg orbit from an equatorial launch site than it did to
put Echostar 9 into it's 0.03 degree orbit.

Which begs your question, why was the heavier (5,177 kg) Thuraya 2
injected into a higher energy orbit (35,797 x 1,200 km x 6.3 deg) than
4,737 kg Echostar 9 (35,806 x 760 km x 0 deg)? After reviewing all of
the Sea Launch results I could get my hands on, I have one or two
plausible reasons. Echostar 9, a Space Systems Loral 1300 design,
was the first non-Hughes (Boeing Satellite Systems) satellite to be
orbited by Sea Launch. Either the SS/Loral spacecraft adapter
hardware was a bit heavier than the Boeing/SS adapters (possibly due
to the provision of more instrumentation for such an inaugural flight),
or the spacecraft used a more benign (lower g-load) flight profile
for this initial flight. (On the first Sea Launch/Thuraya flight, the
5,108 kg spacecraft was injected into a 35,823 x 214 km x 6.3 deg
orbit.)

Does Sea Launch come in variants?

Sea Launch Zenit 3SL comes in only one flavor to date [...]

I need to restate this a bit. During the first four launches,
Sea Launch Zenits were rated at 4,900 kg to GTO. Since the
fifth (Thuraya 1) flight, the rockets have been rated at 5,250 kg
to GTO. Sea Launch claims that the rocket will eventually be able
to haul 6,000 kg to GTO (the eye-opening Thuraya 2 result seems
to support this). It is not clear to me that the improved ratings
are because the rocket has been significantly upgraded in any way.
When you run the numbers with the rocket equation, it seems
possible that Sea Launch Zenit might simply have an unadvertised
reserve payload capacity!

- Ed Kyle

In article ,
ed kyle wrote:
I need to restate this a bit. During the first four launches,
Sea Launch Zenits were rated at 4,900 kg to GTO. Since the
fifth (Thuraya 1) flight, the rockets have been rated at 5,250 kg
to GTO...

One possible reason for this -- with the caveat that I haven't checked the
numbers to see whether this changed at the right time -- is that the early
launches deliberately launched slightly north of due east, so that the
ground track did not cross the Galapagos Islands (which are right on the
equator and are the first downrange land). This was to avoid any
possibility that debris from a launch failure would fall there. That
offset was eliminated once more confidence built up.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

(Lou Scheffer) wrote in message . com...
Anyone know offhand why the recent Sea Launch performance was less
than the previous ones?

The most recent launch was:
4737 kg, 760 km perigee, 35768 apogee, 0 inclination.

The first launch on their previous launch page was Thuraya,
5108 kg, 1200 km perigee, 35768 apogee, 6.3 degree inclination

So the recent launch put a lighter satellite into a lower orbit. Does
Sea Launch come in variants?

I wrote an email to Paula Korn, the contact listed on the Sea Launch
web site. She was very responsive and wrote back immediately. She
confirmed that there are no variants, and stated that they always
shoot for an orbit which is determined in negotiation with the
customer. Hence it must be, for some reason, that the satellite
vendor wanted an orbit that was lower than Sea Launch is capable of
providing.

She also stated (understandably enough) that she was not going to
bother the trajectory designers with random questions from non-paying
customers.

This is even more mysterious to me since the 1300 bus has a liquid
apogee engine, and has been used with higher perigees before. From:
http://www.astronautix.com/craft/fs1300.htm for a 1999 mission:

"The Block DM3 upper stage released Telstar 6 in a 6638 km x 35,756 km
x 17.4 degree geosynchronous transfer orbit."

And from the same site:

"The Intelsat 905 satellite used a new version of the venerable
General Dynamics R-4D bipropellant engine, the R-4D-15 HiPAT (High
Performance Apogee Thruster) with a thrust of 445N. The first two
HiPATs were built by Marquardt/Van Nuys, but new ones were built at
GD's Redmond site."

This leaves the "heavy adaptor" theory, but it's hard for me to
imagine an adaptor that heavy (it would need to be well over 500 kg)
to reduce the performance to less that that of Thuraya-2.

Any other ideas?????

Lou Scheffer

(Lou Scheffer) wrote in message . com...
(Lou Scheffer) wrote in message . com...
Anyone know offhand why the recent Sea Launch performance was less
than the previous ones?

[Launch vehicle variants and solid apogee motor refuted....]

This leaves the "heavy adaptor" theory, but it's hard for me to
imagine an adaptor that heavy (it would need to be well over 500 kg)
to reduce the performance to less that that of Thuraya-2.

Any other ideas?????

How about this one? If you are using Xenon for stationkeeping, then
you won't use the liquid propellants for this. You'll get better
lifetime from the Xenon if the satellite is less massive, so you want
to use up most of your liquid propellents. And maybe you don't want
to launch with half empty tanks because of sloshing, etc. So if you
want to start with full tanks, and use most of it up, then you cannot
start from a high perigee. So they request a lower perigee than Sea
Launch is capable of providing....

Theory number 2 is bureaucratic inertia. Perhaps they initially did
all the power, thermal, qualification testing, etc. assuming a (for
example) 200-800 km perigee. Then Sea launch became more powerful,
but using this power would require re-doing all the analysis and
qualification. If the initial plan had enough lifetime margin, then
maybe they would keep it rather than redo all the analytical and
qualification work to get a marginal benefit.

Lou Scheffer