SpaceX Falcon 9 v1.1 - Dragon - CRS-5/SpX-5 -Jan. 10, 2015 - DISCUSSION

[hrissan]

You're making this too easy!

The first four Saturn I launches were suborbital.  (...etc)

I'm not examining the flight results, or the presence of an upper stage.  I'm comparing the launch campaign results.  This comparison shows that SpaceX is still experiencing problems that were solved at this stage of an earlier, largely comparable program.  And it isn't just about two days on this campaign.  It is about the recurring issues during multiple campaigns.

 - Ed Kyle

I have a strange feeling if they had as many instruments assessing health of the stage in 1960s, they would scrub more often, not less...

If you have a sensor telling you that some value in some point of engine is slightly out of the family, you scrub and inspect.

If you have no sensor at that point or have sensor, but no sophisticated data collecting and processing, well, you launch and it might not blow up.

I may be wrong...

Summary: less actual issues now, but more issues detected, hence more scrubs.

[CJ]

WRT Falcon and valves, minor Google-fu reveals numerous Atlas V and Delta IV issues and scrubs due to valves as well - including EFT-1.

Yes but ULA folks quickly fix the issues, and launch.   It's doesn't take ULA weeks of downtime to fix the recurring problems.

The SpaceX problem was fixable in a day or two.  It only got pushed to January because of NASA's constraints on when they could visit the ISS combined with the Christmas holiday.  The delay before that was at NASA's request so NASA could scramble to get new cargo after Orbital blew up their vehicle.  I guess you missed that.

I guess you also missed over the last summer the way SpaceX did three commercial launches in a row from the same pad with well under a month in between -- far faster turn-around time than ULA ever does.

You raise a very good point on the ISS scheduling issue. Two, in fact; that the first delay was at NASA's request (due to one of the Antares' engines experiencing a performance anomaly which resulted in the Cignus vehicle achieving a sub-optimal trajectory), and secondly, the launch window constraints of ISS missions.

Regarding the later, I wonder how many ULA launches experience short countdown delays that would result in a scrub if going to ISS? (Especially back when their current launchers were as new as F9 1.1.) ULA doesn't fly missions to ISS, so they don't have to deal with launch windows that are that tight (around 2 seconds, I think).

I'm personally glad that SpaceX is very cautious and prone to delays as opposed to getting "go fever". I'd much, much rather see CRX-5 (and all other launches) launch late as opposed to an on time RUD.

[deruch]

I read and compared the Mission Overview section of the CRS-4 (http://www.spacex.com/sites/spacex/files/spacex_presskit.pdf) and CRS-5 (http://www.nasa.gov/sites/default/files/files/SpaceX_NASA_CRS-5_PressKit.pdf) press kits.  There were a few small differences (highlighted in colors):

Note- the CRS-3 and CRS-4 press kits are identical in this section.

Approximately 161 seconds into flight, the first-stage engines are shut down, an event known as Main-engine cutoff, or MECO. At this point, Falcon 9 is 80 kilometers (50 miles) high, traveling at 10 times the speed of sound. Three seconds after MECO, the first and second stages will separate. Eight seconds later, the second stage’s single Merlin vacuum engine ignites to begin a seven-minute burn that brings Falcon 9 and Dragon into low-Earth orbit. 

Forty seconds after second-stage ignition, Dragon’s protective nose cone, which covers Dragon’s berthing mechanism, will be jettisoned. Nine minutes and 40 seconds after launch, the second-stage engine cuts off (SECO). Thirty-five seconds later, Dragon separates from Falcon 9’s second stage and achieves its preliminary orbit. It then deploys its solar arrays, and begins a carefully choreographed series of Draco thruster firings to reach the space station.

Approximately 157 seconds into flight, the first-stage engines are shut down, an event known as main-engine cutoff, or MECO.  At this point, Falcon 9 is 80 kilometers (50 miles) high, traveling at 10 times the speed of sound.  Four seconds after MECO, the first and second stages will separate.  Eight seconds later, the second stage’s single Merlin vacuum engine ignites to begin a seven-minute burn that brings Falcon 9 and Dragon into low-Earth orbit.

Forty seconds after second-stage ignition, Dragon’s protective nose cone, which covers Dragon’s berthing mechanism, will be jettisoned.  Nine minutes and 27 seconds after launch, the second-stage engine cuts off (SECO). Thirty-five seconds later, Dragon separates from Falcon 9’s second stage and achieves its preliminary orbit. It then deploys its solar arrays, and begins a carefully choreographed series of Draco thruster firings to reach the space station.

I have a bunch of questions, but as yet am not knowledgeable enough to do my own analysis (sorry):  Do these alterations represent "real" changes to the flight profile?  or just clarifications and improved accuracy of information distributed?  or Is this normal adjusting to deal with the slightly different orbits of ISS? or Different weights of each mission?  Could the 4 second difference in the 1st stage burn time be related to the recovery attempt/boost-back being performed on this flight?  If that was so, I would have expected the second stage to burn longer on CRS-5.  Instead it's 13 second shorter.  Improved engine performance? 


edit: Comga linked this comment to begin a more general discussion of the delays between MECO and stage separation in the General Falcon/Dragon discussion thread.  I went back, tabulated, and posted the various combinations of delays that SpaceX has had planned between MECO and second stage ignition (from press kit info, not necessarily accurate to flight data).  The table is in my reply to the linked comment. 

[cscott]

So, now we see what I presume is the full reusable core configuration. Is this the shape of the future?

No, legs will change.

To elaborate a little, @cambrianera is referring to Elon's tweet on Nov 22:

Using legs as air brakes to drop terminal velocity in half requires slight redesign & more data. Maybe flight 21.

There is a heated discussion over in the "legs" thread over whether "slight redesign" means the changes will be small, or whether Elon will finally bow to the majesty of @cambrianera's original leg design and adopt that.

But regardless, @cambrianera's point is that the legs will be modified some before we see the "final" full reusable core configuration.  Doesn't mean that this might not be the "initial" full reusable core configuration, though.  It would just take a payload hit compared to the future final configuration.

[Prober]

pleased everyone is being respectful of each other in this thread, and a real conversation is taking place.

 

[Avron]

So, now we see what I presume is the full reusable core configuration. Is this the shape of the future?

No, legs will change.

To elaborate a little, @cambrianera is referring to Elon's tweet on Nov 22:

Using legs as air brakes to drop terminal velocity in half requires slight redesign & more data. Maybe flight 21.

There is a heated discussion over in the "legs" thread over whether "slight redesign" means the changes will be small, or whether Elon will finally bow to the majesty of @cambrianera's original leg design and adopt that.

But regardless, @cambrianera's point is that the legs will be modified some before we see the "final" full reusable core configuration.  Doesn't mean that this might not be the "initial" full reusable core configuration, though.  It would just take a payload hit compared to the future final configuration.

I would expect some rework in the legs, not only for breaking but for guidance . They will also need to change to allow for easier logistics

[douglas100]

I don't think the redesigned legs will be used for guidance.  The grid fins and engines already do that.

[Coastal Ron]

I don't think the redesigned legs will be used for guidance.  The grid fins and engines already do that.

I would think so too.  At most the legs provide wind resistance during various stages of deployment.

[guckyfan]

I don't think the redesigned legs will be used for guidance.  The grid fins and engines already do that.

I would think so too.  At most the legs provide wind resistance during various stages of deployment.

I fully agree that they would not be used for guidance in Grid Fin style. However I think it may be possible they will be deployed in two steps. First in a position of an arrow head, helping provide stability and only before touchdown, when the landing burn already started, into its landing leg position. Though, if the Grid Fins can provide sufficient stability, full deployment from the beginning is easier and preferable.

[douglas100]

I don't think the redesigned legs will be used for guidance.  The grid fins and engines already do that.

I would think so too.  At most the legs provide wind resistance during various stages of deployment.

I fully agree that they would not be used for guidance in Grid Fin style. However I think it may be possible they will be deployed in two steps. First in a position of an arrow head, helping provide stability and only before touchdown, when the landing burn already started, into its landing leg position. Though, if the Grid Fins can provide sufficient stability, full deployment from the beginning is easier and preferable.

Yes, two stage deployment is a possibility (perhaps also to reduce the aerodynamic forces on the legs) but I agree that single step deployment makes more sense.

[rpapo]

A couple of questions about early deployment:

(1) How would you start the initial full or half deployment without deceleration forces?  Perhaps by deploying during the boostback or reentry burn? 

(2) Deploying half-way at first would be far better, aerodynamically.  Less turbulence, and a higher chance of keeping the aerodynamic center of drag above the center of gravity.  But, especially while it is supersonic, will the legs disturb the slipstream enough to affect the ability of the grid fins to maintain the stage on a stable and accurate course?

(3) With the legs extended, even half-way, will the rocket still go supersonic in descent before the thickening air reduces terminal velocity to subsonic?

(4) If the legs are extended, even partially, during the boostback and/or the reentry burns, then will they need an ablative coating like was used for F9R-Dev1?  It is possible that if the partial extension is small enough, then the underside of the legs will not receive enough radiative heating to matter.  Conductive heating (from impinging exhaust) is quite another matter.  Especially if you envision it as Okan just did over on L2.

[The Amazing Catstronaut]

I don't think the redesigned legs will be used for guidance.  The grid fins and engines already do that.

I would think so too.  At most the legs provide wind resistance during various stages of deployment.

Adding additional, massive control surfaces also near-guarantees potentially mission critical guidance issues if the leg becomes unresponsive in a certain orientation. It's not a required capacity - we all know what happens when you start installing functionally useless capacity into spacecraft design.

[JFARNS]

Could the grid fins provide enough deceleration to allow the legs to open prior to the landing burn?

[mme]

A couple of questions about early deployment:
...
(2) Deploying half-way at first would be far better, aerodynamically.  Less turbulence, and a higher chance of keeping the aerodynamic center of drag above the center of gravity.  But, especially while it is supersonic, will the legs disturb the slipstream enough to affect the ability of the grid fins to maintain the stage on a stable and accurate course?

(3) With the legs extended, even half-way, will the rocket still go supersonic in descent before the thickening air reduces terminal velocity to subsonic?

(4) If the legs are extended, even partially, during the boostback and/or the reentry burns, then will they need an ablative coating like was used for F9R-Dev1?  It is possible that if the partial extension is small enough, then the underside of the legs will not receive enough radiative heating to matter.  Conductive heating (from impinging exhaust) is quite another matter.  Especially if you envision it as Okan just did over on L2.

I'm not an aerospace engineer, but I don't think there is any need to extend the legs that early.  Decelerating too early means reduced boost back distance and additional forces on booster but I don't see the benefit.  Reducing the velocity that early in the flight won't reduce the ultimate terminal velocity any more than doing so closer to the actual landing.

I think "early" deployment is still close to landing to shave off some speed at the end.  Momentum is proportional to velocity squared, so shaving off speed at the end saves a lot of fuel but puts a lot less stress on the airframe.

edit: typo

[guckyfan]

I think "early" deployment is still close to landing to shave off some speed at the end.  Momentum is proportional to velocity squared, so shaving off speed at the end saves a lot of fuel but puts a lot less stress on the airframe.

I think the opposite. The legs could be deployed during the RTLS burn. At that time and for most of the flight after that the stage is in near vacuum and will not experience much deceleration. But when it comes down it may decelerate enough high up that a reentry burn may be much shorter or even unnecessary. That would save a lot of fuel, maybe even a whole burn. So it could be worth expendig a little fuel for a higher return trajectory. When the legs are deployed after the reentry burn, the stage is slower but the legs may still experience a quite high load because it is already in dense atmosphere.

But like you I am not an aerodynamics expert and may well be wrong.

[WindyCity]

I am puzzled why some people appear to be criticizing SpaceX for its cautious, conservative approach to launch preparedness. The company has delayed launches when it detected potentially dangerous anomalies during pre-launch tests. Isn’t that how it’s supposed to work? Knowing especially that the F9v1.1 is still an evolving vehicle and that its flight history is relatively immature, I feel that the company should be applauded for taking time to get it right before committing to launch. Presumably, as the company gains more experience, and its technology matures, incidences of launch delays will diminish. That’s normal for a large number of developing technologies. If I were a SpaceX customer, I’d have a higher degree of confidence in the eventual success of my mission, knowing that my launch provider always went the extra mile to guarantee that none of its rockets got green-lighted that hadn’t passed every pre-launch test successfully.

[Antares]

I agree mostly.  At some point, though, the hardware problems need to go away and timely launches commence.  Especially given the ethos created by SpaceX that its way is different and better.  The 9th launch of the 1.1 should be getting rid of such things, no?  What slipped through Hawthorne and McGregor and manifested itself at the major test before launch?  Why?

[mfck]

...The 9th launch of the 1.1 should be getting rid of such things, no?

Why? Because of the mythical properties of the number nine?

[rower2000]

I have a bunch of questions, but as yet am not knowledgeable enough to do my own analysis (sorry):  Do these alterations represent "real" changes to the flight profile?  or just clarifications and improved accuracy of information distributed?  or Is this normal adjusting to deal with the slightly different orbits of ISS? or Different weights of each mission?

I would rather guess it's down to orbit and payload adjustments. Of course, the amount of fuel left on board stage 1 at MECO has to be taken into account for the burn profiles. Otherwise, I cannot think of a reason why a first-stage boost-back should impact the burn profile of stage 2. Especially towards a lower value...

But then, that's just an educated guess on my side and I could just as well be wrong .

[luinil]

The 9th launch of the 1.1 should be getting rid of such things, no?  What slipped through Hawthorne and McGregor and manifested itself at the major test before launch?

I remember a rocket that for it's 28th flight (8th in the Heavy configuration) had some valve problems (among other non vehicle related problems on that day) that conducted to a one day slip.