SpaceX Falcon 9/Dragon COTS Demo (C2+) PRE LAUNCH UPDATES

[northanger]

forgot to mention:
it's the same illustration here
http://forum.nasaspaceflight.com/index.php?topic=28586.msg884934#msg884934
that says: Demonstration Mission Key Objectives

[AnalogMan]

forgot to mention:
it's the same illustration here
http://forum.nasaspaceflight.com/index.php?topic=28586.msg884934#msg884934
that says: Demonstration Mission Key Objectives

By the way, in case anyone missed it, the full set of slides presented during yesterday's post NASA FRR briefing can be found here:
http://www.nasa.gov/exploration/commercial/cargo/graphics_041612.html

And the videos are here:
http://www.nasa.gov/multimedia/videogallery/index.html?collection_id=80591

[northanger]

big thanks:
http://www.nasa.gov/exploration/commercial/cargo/graphics_041612.html
looking all over for those comparing them with the status report and what's new/different.

[manboy]

NASA asked us to rename the threads C2+ (as opposed to C2/C3 or D2/D3) so will rename all associated threads today.

So what's the new official "long name"?

[LegendCJS]

I had a question, not sure if this is the correct place to ask it.  Why is this launch window "instantaneous"? 

If even a few seconds of time delay would render the mission unable to even reach the ISS it seems like it the one instant of time where reaching the ISS is possible must by definition be so close to the edge of the mission's performance envelope that it would be a bad idea to launch in the first place.

Or is this just a matter of picking the best launch instant to maximize the RCS fuel available for in orbit maneuver testing?

[JBF]

I had a question, not sure if this is the correct place to ask it.  Why is this launch window "instantaneous"? 

If even a few seconds of time delay would render the mission unable to even reach the ISS it seems like it the one instant of time where reaching the ISS is possible must by definition be so close to the edge of the mission's performance envelope that it would be a bad idea to launch in the first place.

Or is this just a matter of picking the best launch instant to maximize the RCS fuel available for in orbit maneuver testing?

According to the FFR, you are correct, they want to maximize the fuel available.

[Robotbeat]

They have to do a bunch of abort tests for this mission. If any glitches happen, they'll have to do even more. More propellant thus pretty directly translates into greater possibility of mission success, in this case. Same thing in case the upper stage under-performs (or perhaps even an engine-out on the first stage?).

[corrodedNut]

noticed yesterday, in the COTS Status Report for Feb 23:

Demo C2+ Key Mission Objectives
http://www.nasa.gov/pdf/627984main_4-Status%20of%20COTS_508.pdf


Godspeed Falcon & Dragon!

So is that the "brain-in-a-tub" at the bottom of page 5?

[northanger]

So is that the "brain-in-a-tub" at the bottom of page 5?

have no idea... 
http://forum.nasaspaceflight.com/index.php?topic=28586.msg885026#msg885026
but now i'm curiouser! brb

[Jim]

I would say yes.  That looks like a system/avionics integration laboratory

[Comga]

forgot to mention:
it's the same illustration here
http://forum.nasaspaceflight.com/index.php?topic=28586.msg884934#msg884934
that says: Demonstration Mission Key Objectives

By the way, in case anyone missed it, the full set of slides presented during yesterday's post NASA FRR briefing can be found here:
http://www.nasa.gov/exploration/commercial/cargo/graphics_041612.html

And the videos are here:
http://www.nasa.gov/multimedia/videogallery/index.html?collection_id=80591

That last slide (Dragon departure) reminds me how little orbital mechanics I remember.  Those arcs don't look balistic to me, even for the odd world of small pertubations to orbits.  (Clohessy-Wiltshire and all that) 

What fraction of an orbit is each arc supposed to take? 
Is there continuous or intermittant thrusting involved?

Is that a pulse thrusting the capsule in the -Vbar direction, with it drifiting back and then down, followed by pulses in the +Vbar and -Rbar direction after the capsule falls "behind" the ISS, followed by a pulse in the +Rbar when the capsule reaches the RBar again, completing the first arc in half an orbit?

[peter-b]

Stuff

Interesting question, but do you think it might be more appropriately placed in the discussion thread?

[yg1968]

I had a question, not sure if this is the correct place to ask it.  Why is this launch window "instantaneous"? 

If even a few seconds of time delay would render the mission unable to even reach the ISS it seems like it the one instant of time where reaching the ISS is possible must by definition be so close to the edge of the mission's performance envelope that it would be a bad idea to launch in the first place.

Or is this just a matter of picking the best launch instant to maximize the RCS fuel available for in orbit maneuver testing?

According to the FFR, you are correct, they want to maximize the fuel available.

That was a question that was asked by Philipp (psloss) from this website (NSF). It was nice to get an official answer on that question especially given the fact that some posters had (wrongly) speculated that it was related to under performance of the Falcon 9.   

[ugordan]

It was nice to get an official answer on that question especially given the fact that some posters had (wrongly) speculated that it was related to under performance of the Falcon 9.   

You have no way of concluding from the official answer that it wasn't related to F9 performance. What if they need to drop off Dragon in a lower orbit than desired, causing the spacecraft in turn to expend more propellant on unnecessary orbit raising maneuvers? It's not a black and white situation.

[yg1968]

It was nice to get an official answer on that question especially given the fact that some posters had (wrongly) speculated that it was related to under performance of the Falcon 9.   

You have no way of concluding from the official answer that it wasn't related to F9 performance. What if they need to drop off Dragon in a lower orbit than desired, causing the spacecraft in turn to expend more propellant on unnecessary orbit raising maneuvers? It's not a black and white situation.

I wasn't the one doing the speculation. But it does provide an official answer as to why an instantaneous window was required for this flight (other than speculation on the F9 performance).

[Jim]

That was a question that was asked by Philipp (psloss) from this website (NSF). It was nice to get an official answer on that question especially given the fact that some posters had (wrongly) speculated that it was related to under performance of the Falcon 9.   

It isn't wrong.  Dragon isn't carrying a full load of cargo.

[yg1968]

That was a question that was asked by Philipp (psloss) from this website (NSF). It was nice to get an official answer on that question especially given the fact that some posters had (wrongly) speculated that it was related to under performance of the Falcon 9.   

It isn't wrong.  Dragon isn't carrying a full load of cargo.

Probably to maximize propellant. Right? Is SpaceX being paid extra for delivering the cargo? This is not part of the CRS contract. It's a test flight.

[ugordan]

Probably to maximize propellant. Right?

Come on. The propellant tanks can only hold so much propellant and are by default full. They haven't offloaded cargo just so they can cram more prop into an already finite volume of tanks.

[yg1968]

Probably to maximize propellant. Right?

Come on. The propellant tanks can only hold so much propellant and are by default full. They haven't offloaded cargo just so they can cram more prop into an already finite volume of tanks.

You need more propellant for more cargo weight. Right? So less cargo equals more margin in case of unexepected problems.

[e of pi]

Probably to maximize propellant. Right?

Come on. The propellant tanks can only hold so much propellant and are by default full. They haven't offloaded cargo just so they can cram more prop into an already finite volume of tanks.

Pehaps the better question for what yg1968 appears to be asking is if there is some possibility that they are short-loading the cargo to get more delta-v (and thus more margin for the various orbital demo manuevers) out of the same fixed quantity of fuel. If you can't increase the mass ratio by increasing fuel, do it by cutting dry mass. Since cargo delivered is not critical on this flight, but sufficient margin for the various demo manuevers is, it makes sense to me that they might be doing that.