SpaceX Falcon 9 FT - ORBCOMM-2 - Dec. 21, 2015 (Return To Flight) DISCUSSION

[leaflion]

The fact that the landing probability changed by 10% overnight makes me worry about their reusability business model.  A 10% change implys that an average probability of successful landing is somewhere <90% (lets say 80, becuase 100% is not an option)  I was under the impression that the business case for RTLS requires >95% recovery success to justify the increased vehicle costs and payload hit.

Maybe it will increase with practice?  Usually if your monte carlo is predicting less than 99% success you make changes to bring it up, since Monte Carlo runs typically over predict reliability. (You'll learn things you never knew you never knew -Pocahontas)  Something like what took down CRS-7 would never show up in a Monte-carlo run, since nobody expected it could fail.

Wonder how Orbcomm feels about this...

[mme]

Elon Musk ‏@elonmusk  2m2 minutes ago
Just reviewed mission params w SpaceX team. Monte Carlo runs show tmrw night has a 10% higher chance of a good landing. Punting 24 hrs.

Not sure what 'punting' means...

It's a term from American Football.  It's when you choose to kick the ball down field rather than try to keep possession of the ball.  Basically it's a way to try to improve your field position on your next possession, so it's a fairly apt analogy.  Ironically it's one of the few times we use our feet in football.

I'm surprised at this decision.  I guess it's in the contract, I wonder how Orbcomm feels about this.

[Chris Bergin]

Wonder how Orbcomm feels about this...

I've got a sneaky feeling they got a very, very cheap ride (relatively speaking) to go as RTF and ride along with what is a validation flight of the upgraded F9 and a landing attempt.

[Rocket Science]

I'ts the wind gusts tonight 22-24 kts... Better tomorrow night 12-15 kts.

http://graphical.weather.gov/sectors/mlb.php

[adriankemp]

December 20, 2015 (4:00 pm ET)
We have an update regarding tonight’s target launch for ORBCOMM’s OG2 Mission 2. Upon further review of the static fire data, SpaceX has determined that an additional day prior to launch will allow for more analysis and time to further chill the liquid oxygen in preparation for launch. Please note that we will now be targeting launch for tomorrow, Monday, December 21 at 8:34 pm ET.

From ORBCOMM -- which seems to indicate more probability of launch success, not just landing.

[mme]

Wonder how Orbcomm feels about this...

I've got a sneaky feeling they got a very, very cheap ride (relatively speaking) to go as RTF and ride along with what is a validation flight of the upgraded F9 and a landing attempt.

That's my assumption too even though I asked the same question.  I believe that both SES and Orbcomm are very supportive of SpaceX achieving reusability.  I think they see it as an investment in lower cost spaceflight in the long run (and cheaper, possibly delayed, rides in the meantime.)  It's got to be nerve racking on everyone though.  It sure is to me.

[Mapperuo]

and time to further chill the liquid oxygen in preparation for launch

So could they not chill it properly tonight?

[Chris Bergin]

December 20, 2015 (4:00 pm ET)
We have an update regarding tonight’s target launch for ORBCOMM’s OG2 Mission 2. Upon further review of the static fire data, SpaceX has determined that an additional day prior to launch will allow for more analysis and time to further chill the liquid oxygen in preparation for launch. Please note that we will now be targeting launch for tomorrow, Monday, December 21 at 8:34 pm ET.

From ORBCOMM -- which seems to indicate more probability of launch success, not just landing.

Well that would make a "bit" more sense, but they passed the data and the LRR, then not happy again. Bit confusing

[mzietzke]

A 10% better chance for landing, with a 10% lower chance of launching seems to indicate that they're sensitive to the added cost of a missile exploding on their landing pad as opposed to merely pushing back the launch. There is no damage to clean up after a weather delay.

[TrueBlueWitt]

December 20, 2015 (4:00 pm ET)
We have an update regarding tonight’s target launch for ORBCOMM’s OG2 Mission 2. Upon further review of the static fire data, SpaceX has determined that an additional day prior to launch will allow for more analysis and time to further chill the liquid oxygen in preparation for launch. Please note that we will now be targeting launch for tomorrow, Monday, December 21 at 8:34 pm ET.

From ORBCOMM -- which seems to indicate more probability of launch success, not just landing.

Well that would make a "bit" more sense, but they passed the data and the LRR, then not happy again. Bit confusing

Higher winds = higher convection  = harder to keep LOX at subcooled temp?

[Lee Jay]

The fact that the landing probability changed by 10% overnight makes me worry about their reusability business model.

You have to be careful when people are throwing around percentages.

Did he mean from 80% to 90%?

Or did he mean the probability of failure was reduced by 10% (from, say, 0.1% to 0.09%?  Or, maybe that's from 10% to 9%.

We can read his words but since percentages can be confusing when tossed around casually, we can't really know what he actually meant.

[butters]

Maybe the odds of a successful landing depend on how cold the LOX is at T-0. Higher temp = lighter LOX load = lower chance of nominal landing burn. This may reconcile the two comments.

[edkyle99]

This is a very light payload for this rocket.  If they are already worried about first stage return-to-launch-site margins, how is this design supposed to work with "real" payloads?

 - Ed Kyle

[a_langwich]

This is a very light payload for this rocket.  If they are already worried about first stage return-to-launch-site margins, how is this design supposed to work with "real" payloads?

 - Ed Kyle

It's probably a lot like the first Dragon flight to ISS:  the first attempt you want to sandbag as much as possible to give margin for all of the unknowns (which are swallowing everything). 

You don't judge how much a rocket will be able to lift based on the size of its first payload.

But I'm guessing you know all this, and this is just a light-hearted snark?

[Avron]

Not ready to launch - Marc Eisenberg ‏@Marc944Marc
@Marc944Marc I guess not ready enough.  We'll try for tomorrow.

[ugordan]

There is the question of just how much of the propellant margin they distributed between the stages. Is it possible that the 2nd stage is to carry much more margin than necessary because it needs to directly insert into a 620x660 km orbit?

There has to be some (near-)circular orbit altitude at which a continuous burn cannot directly get you to that state vector because you burn off your propellant too fast and accelerate too quickly. A heavier stage needs more time to accumulate the same delta-v from a given thrust engine so you have more coast time to play with. I'm wondering if that plays into it at all or if that point is way higher for F9.

[Fletch]

So I see the Garryowen has been punted to Monday, boring day at work for me then.  Guess I will chill like the LOX.

[Kim Keller]

   Is Falcon 9 still dependent on CCAFS radar for range tracking or have they switched over to a GPS system as Atlas and Delta have? They obviously have GPS on the first stage for landing at least. Not sure if this was covered somewhere in all the SpaceX discussion, but I couldn't find it, and I don't remember it being mentioned anywhere since a faulty radar held up a Falcon launch a while back.

They have GPS, but that does not eliminate the need for range radar (at least not yet); e.g., the Atlas V NROL-67 launch was also delayed due to range radar issues last year. edit: Just to be clear, the range still requires those radars, regardless of the LV's capabilities.  That may change in the future with autonomous FTS (among other things).

The F9 GPS is not used for range tracking purposes at this time; it's part of their GN&C. F9 still uses a C-band transponder for range tracking.

Also the range requires skin-track radar for ALL launches. So, even though ULA uses GPS-MTS for range tracking ( doing away with the requirement for a C-band interrogating radar), Atlas & Delta launches require the skin-track radar.

[ulm_atms]

I'm thinking a someone didn't order enough regular lox to cover the densification

You never know....They did use a lot with all the static fire issues.  Could you imagine if that really was the issue today?  Isn't SLS going to have that issue with the LH2 if they have to recycle/scrub until they get the bigger tank installed?  Or am I mis-remembering?

[meekGee]

What matters here is that Musk stated publicly that landing considerations factor into launch decisions*.

It's the change in thinking that goes with reusable vehicles.

Lots more changes like that are in line, I have no doubt. 

(*So in case of barge landings, it is straight forward to expect a launch delay if the weather at the barge location means a likely loss of the vehicle - though with time I expect barge locations to become more flexible)