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

[meberbs]

As for how quickly SpaceX can retarget the first stage to a different destination, recall that on an earlier flight, when the sea state was too rough to attempt a landing on the ASDS, the stage was re-targeted late in the count to land something like 10 km from the barge, onto the sea and away from the ASDS "flotilla".

So, I imagine they can retarget from the RTLS trajectory to one that targets the ASDS fairly late in the count, if weather or other conditions call for it.

I thought they had moved the ASDS away from the landing site that time, not moved the landing site.

Due to the complexity of optimization problems, I expect that the flight pattern is pre-loaded on the stage (in some form that allows the stage to do corrections for wind, etc e.g. get to altitude x, with velocity y, not fire at x power for y seconds). It seems like it wouldn't be too hard to have 2 different plans loaded for the boost back and landing. They are in communication with the stage, so they should be able to switch as much as they want before stage separation. After separation they start the boost back and that probably locks in the destination.

This is just guesswork on my part though.

[Kabloona]

They are in communication with the stage, so they should be able to switch as much as they want before stage separation.

The stage has no uplink capability. It tries to land at whatever coordinates are stored in it before launch.

Uplink would be risky because you cannot guarantee the stage will receive the uplink command, so there's chance the stage goes where you don't want it to, or vice versa. Safer and simpler to have 100% certainty ahead of time by loading/selecting the desired landing coordinates in the flight computer just before launch.

And if you don't know in the last few minutes of the count where you want to land, you have bigger problems. There's no way weather conditions are going to change so drastically in 10 minutes of flight time that you decide in-flight to land elsewhere.

[OxCartMark]

As for how quickly SpaceX can retarget the first stage to a different destination, recall that on an earlier flight, when the sea state was too rough to attempt a landing on the ASDS, the stage was re-targeted late in the count to land something like 10 km from the barge, onto the sea and away from the ASDS "flotilla".

So, I imagine they can retarget from the RTLS trajectory to one that targets the ASDS fairly late in the count, if weather or other conditions call for it.

It was definitely not a retargeting of the F9 but rather the ASDS being off the designated spot.  But my strong recollection from that time was that the ASDS being intentionally moved was revisionist history which was stated by SpaceX shortly after but which was not supported by the circumstantial evidence and timeline that was available at the time.  I am of the belief that the ASDS wasn't capable of holding its position due to being in a powerful storm which (in some combination) overpowered the stationkeeping thrusters and heavily damaged the stationkeeping thrusters.  If it had been tasked with moving to a new location it would have been there.  In actuality it was so far out of position that the SpaceX and the two ships tending the ASDS took (IIRC) ~4 days to determine where it had drifted to (IIRC, more than a hundred miles south).  The wave damage to the equipment at the bow was extensive and much of it had to be replaced when they got to port.  I think this is the video that shows the damage but I'm unable to view it on this primitive computer to confirm it -

[Hankelow8]

So if SX decides they want to blow it up in a spectacular way, who cares? It's no more of a loss than every other rocket delivery system ever.

Sure they could.  But SpaceX has shown that they never waste an opportunity to learn.  Which is why they have "landed" many stages in the ocean, even though they had no plan to recover them - real data to feed back into their simulations.  And all it costs is a little extra fuel.

And no doubt SpaceX employees will be dancing in the aisles if they successfully deliver their customer payloads, yet fail to recover the 1st stage.  They know what it takes to be allowed to continue experimenting...

I think the land landing has no real danger provided the self destruct can still be activated.

I am certain they will be monitoring the stage as it descends towards its landing point, if at anytime it deviates from its decent trajectory it can be destroyed over the sea, it's not until the last few seconds it will be over tera firma,  even if it crashes then there is a least a mile of clear space to absorb the explosion.

[vulture4]

I agree. With only the booster stage and almost all fuel expended, the potential for damage is far less than it would be during the launch. The challenge is getting range approval, but apparently this has been accomplished.

[meberbs]

They are in communication with the stage, so they should be able to switch as much as they want before stage separation.

The stage has no uplink capability. It tries to land at whatever coordinates are stored in it before launch.

Uplink would be risky because you cannot guarantee the stage will receive the uplink command, so there's chance the stage goes where you don't want it to, or vice versa. Safer and simpler to have 100% certainty ahead of time by loading/selecting the desired landing coordinates in the flight computer just before launch.

And if you don't know in the last few minutes of the count where you want to land, you have bigger problems. There's no way weather conditions are going to change so drastically in 10 minutes of flight time that you decide in-flight to land elsewhere.

At the minimum, they have uplink capability for the FTS. With all of the downlink capability (multiple video streams, telemetry, etc.) They definitely would be able to include a confirmation that commands are received. It is easy enough to keep resending until it is received correctly. It is possible that the FTS is too isolated to use its uplink antenna for this purpose. I would be a little surprised if they didn't have some other uplinks they send, but it is possible they don't.

I agree that there should be no reason to change the landing site after T-0, so they may not have bothered implementing this. On the other hand, they never expected a cargo dragon to be free flying during a launch failure, so they didn't give it parachute deploy option in that case. Using lessons learned, they might include a "switch landing site" command as a backup in case things go wrong (engine out leaves insufficient fuel for RTLS?).

I was mostly just stating the absolute last time it might be possible to perform the landing site decision.

[JamesH]

They are in communication with the stage, so they should be able to switch as much as they want before stage separation.

The stage has no uplink capability. It tries to land at whatever coordinates are stored in it before launch.

Uplink would be risky because you cannot guarantee the stage will receive the uplink command, so there's chance the stage goes where you don't want it to, or vice versa. Safer and simpler to have 100% certainty ahead of time by loading/selecting the desired landing coordinates in the flight computer just before launch.

And if you don't know in the last few minutes of the count where you want to land, you have bigger problems. There's no way weather conditions are going to change so drastically in 10 minutes of flight time that you decide in-flight to land elsewhere.

There has been some argument from the 'older' rocket people about this. My thought is that even though current designs have no uplink to rearrange landing site. it will be useful as time goes by. There are reasons why you might want to change the landing site even up to stage separation, or even later. Perhaps an F9H, landing all three first stage cores at landing site, one core lands by crashes and upsets the second landing pad - you might want to tell subsequent cores to land further away, either on emergency pads, or perhaps even on a barge. Or perhaps a reentry burn isn't as good as expected, and you need to reassign the landing to somewhere it can actually reach, like an offshore barge.

As always, FTS is there in case the reassignment goes wrong.

[cscott]

I was deliberately vague about "last minute" to try to avoid this sort of wheel spinning about what exactly that means.  We don't have definitive information from SpaceX (although it would be a great question to ask at the next pre launch briefing), so it's all guesses.  I think the reasonable range of options is "before fueling is complete" (as Coastal Ron proposed) to "just before the boost back burn occurs".  I think later than that would be dicey, and it's probably not worth squandering engineering resources on low-probability contingencies with a low probability of favorable outcome.  (Although sometimes those decisions change after a failure demonstrates that the scenario was not quite as unlikely as was hoped.)

Personally I'd split the difference and guess that landing point selection is fixed sometime around the T-15min hold.

[Kaputnik]

There barge will in all likelihood be deployed for this flight.  They can divert to the barge "at the last minute" (for a suitable definition of last).

The barge story does not end with a land landing.  There are still plans to land F9 and FH stages far out to sea on performance-critical missions. Even if spurned this month, they will return.  We'll see a sea landing at some point.

Answers my question! Thanks! I wasn't aware that the landing site could be switched "at the last minute," suitably defined. Fascinating! The vehicle it has, apparently, a lot of built-in guidance flexibility for targeting its landing location. I wonder to what extent different mission profiles (based on the mass of satellite(s), LEO or GTO) determines which platform to target. (But that's off topic for this thread.)

Isn't this all conjecture? Is there any independent verification that the ASDS might be deployed for this launch?

[Kabloona]

There barge will in all likelihood be deployed for this flight.  They can divert to the barge "at the last minute" (for a suitable definition of last).

The barge story does not end with a land landing.  There are still plans to land F9 and FH stages far out to sea on performance-critical missions. Even if spurned this month, they will return.  We'll see a sea landing at some point.

Answers my question! Thanks! I wasn't aware that the landing site could be switched "at the last minute," suitably defined. Fascinating! The vehicle it has, apparently, a lot of built-in guidance flexibility for targeting its landing location. I wonder to what extent different mission profiles (based on the mass of satellite(s), LEO or GTO) determines which platform to target. (But that's off topic for this thread.)

Isn't this all conjecture? Is there any independent verification that the ASDS might be deployed for this launch?

Yes, it's conjecture, but based on logic. It will take 1-2 days for the ASDS and support ship to get to the landing zone. If FAA approval for RTLS hasn't been received by that time, SpaceX will have to assume that an ocean landing will be their only option and send the ships out. And that window (FAA aporoval before the deadline for sending ships out) is now only about a week long.

Plus, SpaceX will likely want a backup recovery option in case they DO receive FAA approval for RTLS but some other last-minute issue prevents an RTLS attempt and they need to land at sea instead. In which case a golden opportunity would be missed if the ships are sitting at the dock.

The cost-benefit tradeoff is the marginal cost of fuel and manpower to send the ships out versus the benefit of increased probability of recovering a $20 million stage intact. Seems like that's a no-brainer, but we'll see.

[cscott]

The FCC permit includes the barge and its location.  In the barge tracking thread there has been some recent activity, moving jacks aboard & etc.  But yes, there's some amount of speculation, which is why I said, "in all likelihood".  And of course plans could change: the barge could spring a leak or blow a thruster or something.  But I think I'm safe in saying that careful watchers expect the ASDS to be deployed... and rather soon, too: it takes a few days to get on station.  So shortly after the static fire you'd expect to see it leave port.

[Jim]

At the minimum, they have uplink capability for the FTS. With all of the downlink capability (multiple video streams, telemetry, etc.) They definitely would be able to include a confirmation that commands are received. It is easy enough to keep resending until it is received correctly. It is possible that the FTS is too isolated to use its uplink antenna for this purpose. I would be a little surprised if they didn't have some other uplinks they send, but it is possible they don't.

I agree that there should be no reason to change the landing site after T-0, so they may not have bothered implementing this. On the other hand, they never expected a cargo dragon to be free flying during a launch failure, so they didn't give it parachute deploy option in that case. Using lessons learned, they might include a "switch landing site" command as a backup in case things go wrong (engine out leaves insufficient fuel for RTLS?).

I was mostly just stating the absolute last time it might be possible to perform the landing site decision.

FTS is a separate and isolated system.  It is not tied in with the launch vehicle avionics. The range is the only one that can send the signals.   Other than FTS, there are no other transmitters.

Launch vehicles are autonomous and do receive any uplinks.  The FTS is moving to an autonomous system and it won't use receivers.

[Jim]

There has been some argument from the 'older' rocket people about this. My thought is that even though current designs have no uplink to rearrange landing site. it will be useful as time goes by. There are reasons why you might want to change the landing site even up to stage separation, or even later. Perhaps an F9H, landing all three first stage cores at landing site, one core lands by crashes and upsets the second landing pad - you might want to tell subsequent cores to land further away, either on emergency pads, or perhaps even on a barge. Or perhaps a reentry burn isn't as good as expected, and you need to reassign the landing to somewhere it can actually reach, like an offshore barge.

No, none are valid reasons. 
a. If the weather isn't good enough to launch, it isn't good enough to land.
b.  There isn't going to be multiple pads to reassign inflight for FH mission.
c.  They aren't going to send out the barge on missions not needing it.

[Johnnyhinbos]

There has been some argument from the 'older' rocket people about this. My thought is that even though current designs have no uplink to rearrange landing site. it will be useful as time goes by. There are reasons why you might want to change the landing site even up to stage separation, or even later. Perhaps an F9H, landing all three first stage cores at landing site, one core lands by crashes and upsets the second landing pad - you might want to tell subsequent cores to land further away, either on emergency pads, or perhaps even on a barge. Or perhaps a reentry burn isn't as good as expected, and you need to reassign the landing to somewhere it can actually reach, like an offshore barge.

No, none are valid reasons. 
a. If the weather isn't good enough to launch, it isn't good enough to land.
b.  There isn't going to be multiple pads to reassign inflight for FH mission.
c.  They aren't going to send out the barge on missions not needing it.

Can you provide your backup for point #3? I'm not saying you're wrong, it's just that such definitive statements must come from hard facts.

[JamesH]

There has been some argument from the 'older' rocket people about this. My thought is that even though current designs have no uplink to rearrange landing site. it will be useful as time goes by. There are reasons why you might want to change the landing site even up to stage separation, or even later. Perhaps an F9H, landing all three first stage cores at landing site, one core lands by crashes and upsets the second landing pad - you might want to tell subsequent cores to land further away, either on emergency pads, or perhaps even on a barge. Or perhaps a reentry burn isn't as good as expected, and you need to reassign the landing to somewhere it can actually reach, like an offshore barge.

No, none are valid reasons. 
a. If the weather isn't good enough to launch, it isn't good enough to land.
b.  There isn't going to be multiple pads to reassign inflight for FH mission.
c.  They aren't going to send out the barge on missions not needing it.

a. I didn't mention weather. I agree with ' not fit to launch, not fit to land at LS', but there are other reasons why you might have to abort a landing at LS but still be able to land offshore.
b. Why not? High launch rates and possible  damage to pads will mean there likely will need to be more than 3 at LS. Long term anyway.
c. Why not? It's cheap as a backup  compared to the loss of a 1st stage.

[Jim]

a. I didn't mention weather. I agree with ' not fit to launch, not fit to land at LS', but there are other reasons why you might have to abort a landing at LS but still be able to land offshore.
b. Why not? High launch rates and possible  damage to pads will mean there likely will need to be more than 3 at LS. Long term anyway.
c. Why not? It's cheap as a backup  compared to the loss of a 1st stage.

a.  Not really.  There is nothing that requires a change between launch and boost back that requires an uplink.  It can be done before launch. 
b.  What high launch rates?  Even long term, still will be days between landings.  And for FH, there isn't time to react for one booster to the other.
c.  Not cheap.  It takes resources and manpower.  The factory has the manpower already.  Anyways, resuse is not proven.

Hence, still no valid reasons.   Not going to win this one either.

Also, the range is not going to want a change in mid-flight.

[Lee Jay]

Also, the range is not going to want a change in mid-flight.

At one point, they must have been able to handle it, because isn't that exactly what a TAL or RTLS abort would have been?

[JasonAW3]

a. I didn't mention weather. I agree with ' not fit to launch, not fit to land at LS', but there are other reasons why you might have to abort a landing at LS but still be able to land offshore.
b. Why not? High launch rates and possible  damage to pads will mean there likely will need to be more than 3 at LS. Long term anyway.
c. Why not? It's cheap as a backup  compared to the loss of a 1st stage.

a.  Not really.  There is nothing that requires a change between launch and boost back that requires an uplink.  It can be done before launch. 
b.  What high launch rates?  Even long term, still will be days between landings.  And for FH, there isn't time to react for one booster to the other.
c.  Not cheap.  It takes resources and manpower.  The factory has the manpower already.  Anyways, resuse is not proven.

Hence, still no valid reasons.   Not going to win this one either.

Also, the range is not going to want a change in mid-flight.

Jim, 

      You know as well as I do how fast the weather can change in Florida.  It's going to take about a half hour for that stage to boost back to the Cape, and the winds at various high and mid range altitudes can change from fairly calm to howling fast in minutes.
      Down in Ft. Lauderdale, which is, admittedly, a few hundred miles south of the Cape, there were more times than I like to remember, when I went outside for a bit, under only slightly cloudy skys, and within less than half an hour, we had thunderstorms and waterspouts.
      Truthfully, the odds are against such a weather change, but it can and has happened in the past.

      As to the booster switching, I'm not totally sure what you're saying about FH, but, trying to land two or three first stages on a barge, is just plain out.
      I agree with you, if this is what you're referring to.  Software changeouts, eh, I'd be REALLY uncomfortable doing that mid descent, in fact,unless the system is set up to allow instant change out of software mid flight, it'd be a damned foolish thing to do.
      Likely manual control of each stage on seperate telemetry channels would be the only realistic choice for trying to redesignate a landing site for each rocket, and even then, we're talking very high risk.

     As to the barge being sent out, as a safety net, maybe, but only if the cost of sending it out with crew, cordoning of the area as a saftey zone, and the general expendatures of fuel, food, etc, were less than or equal to, half of what a new stage would cost.  Otherwise, if it's too much danger to land on land, splash it.
     Right now, they're trying to perfect landings in general.  Sudden gusts of wind, combined with the top heavy nature of the beast, makes for some tricky landing maneuvers, regardless if it is on land or sea.

[JasonAW3]

Also, the range is not going to want a change in mid-flight.

At one point, they must have been able to handle it, because isn't that exactly what a TAL or RTLS abort would have been?

Lee Jay, I'm going to have to go with Jim on this one.

     The difference between the Space Shuttle and the Falcon 9 first stage are pretty substantial, not the least being that the Shuttle was manned and could, in a pinch, be manually flown.

     The Falcon 9 first stage, as I understand it, hasn't been configured to be flown either manually or by remote.

[eriblo]

Also, the range is not going to want a change in mid-flight.

At one point, they must have been able to handle it, because isn't that exactly what a TAL or RTLS abort would have been?

Lee Jay, I'm going to have to go with Jim on this one.

     The difference between the Space Shuttle and the Falcon 9 first stage are pretty substantial, not the least being that the Shuttle was manned and could, in a pinch, be manually flown.

     The Falcon 9 first stage, as I understand it, hasn't been configured to be flown either manually or by remote.

The range will know exactly how to handle a course change - that's their job. The Shuttle is irrelevant for the reasons given by Jason and also lacked FTS on the Orbiters (which is all that would have returned) for the same reasons.