SpaceX COTS Demo 2/3 Updates (THREAD 2)

[ugordan]

Why wouldn't they try a night launch?  I much prefer daylight (especially twilight/dawn) launches from a visuals perspective, but why would a night launch be a holdup?

[Apollo-phill]

No reason why shouldn't launch at night .

Do they want good visual tracking to high altitude with this being early demo flight in which case  daylight preferable ?

|Do we know what is max azimuth on a NE to SW track for SpaceX from CCAF ?

AP

[ugordan]

Do they want good visual tracking to high altitude with this being early demo flight in which case  daylight preferable ?

They didn't seem to require that on Delta III's maiden flight...

Also, H-IIB maiden flight with the first HTV was a night launch.

[Apollo-phill]

OOps !!

Do we know what is max azimuth on a NE to SW track for SpaceX from CCAF ?
 
 should read 

Do we know what is max azimuth on a NW to SE track for SpaceX from CCAF ?

AP

[Rocket Guy]

They cannot launch to the ISS to the southeast from CCAFS. Obviously, otherwise the shuttle would have.

[ugordan]

Obviously, otherwise the shuttle would have.

And the shuttle didn't have other (abort) constraints?

[Rocket Guy]

And the shuttle didn't have other (abort) constraints?

Not sure what you're asking. He gave a launch time for the southeast trajectory. They only launch to the northeast to the ISS, as they always have and always will. The Bahamas are to the Southeast, and that is the main reason.

[Rocket Guy]

My own calculations (noted on L2 yesterday) suggest probably 7-9pm as well for February 7th, but the orbital data I have is a few months old.

[ugordan]

And the shuttle didn't have other (abort) constraints?

Not sure what you're asking.

You said if a southeast trajectory was allowed from CCAFS, the shuttle would obviously have used it. I'm asking whether that's really the case, for example what about TAL abort etc?

[Rocket Guy]

That I don't know. I'm sure it was looked into. Perhaps Benin was reachable.

[Apollo-phill]

I wondered anyway what the max azimuth is for a SpaceX Falcon9 launch from CCAFS on a NW to SE track for say , a  satellite launch, as opposed to an ISS cargo/crew launch - avoiding the Bahamas .


AP

[Rocket Guy]

All Cape launches, including spy satellites, that are headed directly into high inclinations (edited to note that some, like GPS, are done differently) head northeast.

[Comga]

Dragon more than likely isn't going to do a standard launch and rendezvous and therefore the launch time isn't as predictable.  Dragon will launch and do some standalone maneuvering and ops away from the ISS.

Please help me here.  My understanding was that launch has to occur when the orbit is overhead, so that no plane change is needed.  The location of the ISS in the orbit is not critical, as approach orbits with different altitudes have different periods, allowing the visiting vehicle to either catch up when below the ISS or "drop back" to it when above.

The attached image is captured from Heavens-Above today.  By drawing a red line east from near CCAFS, we see that the orbit crosses that latitude just after sunset.  (The instantaneous horizontal location in the image of the continents is  irrelevant as they are, of course, rotating with respect to the  terminator.)
 
A quick calculation of the precession of the ISS orbit (51.6 deg at 395 km mean altitude) is 5.03 deg/day.  With 58 days until the scheduled launch, that's 292 degrees shift West, which is equivalent to 68 degrees East.  This is indicated with the orange line.  Centering between sunrise and sunset on the Equator indicates where solar midnight is, which is illustrated with the yellow line.  Scaling the gap shows a little less than an hour. 

So, give or take a few minutes, doesn't launch have to occur around 11 PM local time?

[Space Pete]

From ISS On-Orbit Status Report for 11/12/2011.

CUCU Testing:
Ground-commanded loopback testing of CUCU (COTS UHF Communications Unit), to be used for the first SpaceX Dragon Demo in February next year, took place via S-band on 12/09 & 12/10 between 11:00 PM GMT and 3:00 AM GMT, performing transmit/receive tests between CUCU 1a and CUCU 1b. The goals of these tests were (a) to prove communications functionality over combinations of CUCU strings and ISS antennas as proved through demonstrating very low (<1e-05) BER (Bit Error Rate) in at least one transmit power setting, (b) to gather data that could potentially distinguish whether behaviours observed in the prior day's tests are indicative of CUCU-internal issues or issues with cabling or connectors downstream of CUCU transmitters, and (c) to characterize CUCU performance as a function of transmit power.

[ugordan]

So, give or take a few minutes, doesn't launch have to occur around 11 PM local time?

I don't think you're looking at this properly. During 2 months, Earth moves 60 deg around its orbit. So if you fixed ISS orbit w/respect to the sky, it would appear to shift (west, I think) 60 degrees with respect to the current midnight line. You need to take that into account as well as nodal regression.

Conversely, those 60 deg is a 4 hour shift so 11 PM - 4 = 7 PM, as already suggested.

[Rocket Guy]

Too inaccurate to use a map and approximate degree calculations. Have to either go by TLE projections, or you can take a known in-plane time recently (as I've done), go roughly 24 minutes a day on average, and get something between 8 and 9pm Feb. 7, give or take, more likely take.

It would surprise me if it isn't 7-9pm or close to it.

[Orbiter]

My own calculations (noted on L2 yesterday) suggest probably 7-9pm as well for February 7th, but the orbital data I have is a few months old.

Using my own logic, and this is by no means correct or ''official''

I ended up with a launch time of ~7:40pm EST on February 7th, 2012.

Sunset is 6:06 pm that day, so if we do get a launch, it would not only be a night launch but the very first night launch in SpaceX history.

Orbiter

[Comga]

So, give or take a few minutes, doesn't launch have to occur around 11 PM local time?

I don't think you're looking at this properly. During 2 months, Earth moves 60 deg around its orbit. So if you fixed ISS orbit w/respect to the sky, it would appear to shift (west, I think) 60 degrees with respect to the current midnight line. You need to take that into account as well as nodal regression.

Conversely, those 60 deg is a 4 hour shift so 11 PM - 4 = 7 PM, as already suggested.

You are correct.  That important element was left out of my approximations.  That would move the midnight line to the right (East  I believe) 58 degrees around the globe, bringing the crossing time back to 7PM, as you said.

So, RocketGuy, the graphical method is not all that inaccurate, even for those of us who haven't learned how to propagate orbits. :-)

But my main question remains:  Is it correct that the launch time is when the ascending orbit passes over the launch site?

[Rocket Guy]

Yes on the ascending orbit (node). You don't have to know how to propagate. If you have a known time for it one day you can just multiple 24 minutes x (number of days to date you want) and get the time to within a few minutes if it isn't too far. The further you go the more orbital decay or raising you might have, but the difference isn't all that much.

[Jim]

  The location of the ISS in the orbit is not critical,

Yes, it is critical.