LIVE: SpaceX - Falcon I (Mk.II) NET March 20 (Attempt 2)

[Jim]

kevin-rf - 27/3/2007  2:56 PM
 Since both stages use the same flight computers and electronics is it fair to lump it into the cost of the second stage?.

There is only avionics/guidance package in the upperstages.  The booster has minimal avioinics, just enough to convert signals from the upperstage to  commands to the hardware and to sent measurements back.  The first stage can't fly by itself

[Danderman]

kevin-rf - 27/3/2007  11:56 AM    Based on Mr. Musks coment why did the second stage try to burn through the roll/slosh problem instead of giving up the ghost? A safer approach would be to shutdown the stage when control is lost instead of risking a random flight where ever it wants to go. Imagine the uproar if it had landed on Chavez's diner table... Makes you wonder again about the whole thrust terminated flight termination system. On the eastern range isn't one of the jobs for the antigua and bermuda tracking stations to make sure the rocket is flying high and fast enough to clear Africa? If not, snip snip...

An interesting point.  There are two choices here:

 1) Shut down the upper stage engine whenever flight parameters are excessive, and hope that the stage with its unburned propellant do not land anywhere important; or

2) Burn as long as possible, to drain propellant and to gain velocity to ensure that the stage burns up on re-entry.

Since this is an upper stage, presumably reaching 80 or 90 percent of orbital velocity and returning via a ballistic path, would pretty much ensure that a nearly empty stage would turn into vapor, mostly.

 

[kevin-rf]

Jim - 27/3/2007  2:17 PM

kevin-rf - 27/3/2007  2:56 PM
 Since both stages use the same flight computers and electronics is it fair to lump it into the cost of the second stage?.

There is only avionics/guidance package in the upperstages.  The booster has minimal avioinics, just enough to convert signals from the upperstage to  commands to the hardware and to sent measurements back.  The first stage can't fly by itself

Thats my point, the there is only one avionics/guidance package (Just bad wording on my part) so it is unfair to count it as part of the upper stage. Both stages use it and is really does not belong to either stage... All your stages belong to it

Does the higher pressure of a pressurized upper stage reduce pogo to a point where it is not a major concern? Did the Delta pressure fed upper stages ever have issues with pogo? I don't recall spacex ever mentioning the word. Sounds like slosh and not pogo where the problem with the second flight.

[rpspeck]

“HUH? GPS is harder to use when the item you're trying to control is traveling at near orbital velocities. The consumer-grade gyros in camcorders (and even in tactical weapons) have much too high a drift rate for use in a 20 minute launch vehicle ascent if you want any kind of acceptable orbit insertion precision. You might want to get your technical story straight.”

The GPS software is different and the RF sections must accommodate larger Doppler effects.  These are BIG problems only if you expect to use $99 GPS receivers.  Since both simple and differential GPS have been used on the ISS, this is a “done deal”.

I actually understand that if you are getting GPS data once per second, the drift rate of the gyros is not a big issue.  Simple gyros serve for attitude rate feedback (<1 second time requirement), bridge possible GPS glitches and serve to smooth the attitude data for multi-second intervals.  A series of +/- 50 foot, 3 dimensional positions, strung out along a 1000 mile path, is a pretty good initial orbit estimate!

(Incidentally, I have independently developed and successfully flown gyro referenced, near hover guided rockets, thus I do understand something of guidance requirements.)
   
I stand corrected on the pressure fed Delta second stage.   I understood that there was some technical doubt about pressure fed “Big Dumb Boosters” as proposed by Andrew Beal.  You all have made it completely clear that only political issues stood in the way.  Granting that the second stage is harder than the first stage, Beal’s 800 thousand pound thrust operational motor (and his planned, much larger version) would have made “Heavy Lift” a reality years ago

[stockman]

Anyone have any ideas when we might start to see some summary of the terabyte of data they are going through? I am especially interested in seeing the FULL video they claim to have. I think that would be spectacular. Anyone here any information on WHEN we might see some of this?

thanks

[aero313]

kevin-rf - 27/3/2007  2:56 PM
By definition the falcon I second stage needs to operate at a higher tank pressure than the pump fed first stage and will have more complex plumbing.

I'm curious as to why you think this.  Pressure fed stages typically have very little plumbing, especially as compared to a pump-fed stage.  Yes, the plumbing must be designed and proofed to a higher pressure, but that doesn't make it more complex, just thicker-walled.

I am very curious what the second stage costs in relation to the first stage. Since both stages use the same flight computers and electronics is it fair to lump it into the cost of the second stage? Nasa had a payload bolted to the second stage, it still counts as a payload and not just part of the second stage. Just because the electronics are bolted to the second stage why should the cost be lumped on the second stage?

The difference between a payload being bolted to the second stage and the LV avionics is that the avionics are required to get to orbit, the payload is not.  Also, the payload presumably changes every flight, the basic vehicle does not.  One can argue that propulsion costs should be bookkept separately from avionics, but the fact remains that upper stages are inherently more sensitive to weight than lower stages and from a cost/benefit standpoint  a launch vehicle company should spend it's money on reducing upper stage weight before lower stage weight.  Since the avionics usually must be carried to orbit, they become part of the effective upper stage weight.  Note that some launch vehicles (Vanguard as an example again) use spin-stabilized upper stages to allow the avionics weight to be jettisoned with a lower stage.  This changes the staging fraction for the avionics and thus the cost equation.  On the other hand, it also reduces injection accuracy.

Based on Mr. Musks coment why did the second stage try to burn through the roll/slosh problem instead of giving up the ghost?

A good launch vehicle control system will ALWAYS try to get to orbit.  An example of this is the second Pegasus mission.  A staging anomaly at the Stage 1 separation caused the upper stages to hinge around and actually face backwards at the time of Stage 2 ignition (this was seen on the IMU data).  The vehicle was able to correct this and actually achieved a stable but low orbit.  The payload was able to perform a degraded mission, but the alternative would have been no mission at all.

A safer approach would be to shutdown the stage when control is lost instead of risking a random flight where ever it wants to go. Imagine the uproar if it had landed on Chavez's diner table... Makes you wonder again about the whole thrust terminated flight termination system. On the eastern range isn't one of the jobs for the antigua and bermuda tracking stations to make sure the rocket is flying high and fast enough to clear Africa? If not, snip snip...

Every launch vehicle flown out of a US launch range must develop what are called impact limit lines.  This is the corridor where debris can safely fall if there is a mishap at any point during the flight.  In addition, during the flight the range safety organization tracks the vehicle and performs a continuous calculation of the instantaneous impact point (known as IIP).  This is the location where the debris would land if flight was terminated at that instant.  So long as the IIP does not cross the impact limit lines and travel outside this safe corridor, the vehicle is allowed to continue flight.  This allows the vehicle to try to right itself (as with Pegasus F2) or, at a minimum, provides additional flight data that might help uncover the cause of the anomaly.

[nacnud]

Er... when we get full video from the first failure?

[Jim]

rpspeck - 27/3/2007  4:11 PM
   I understood that there was some technical doubt about pressure fed “Big Dumb Boosters” as proposed by Andrew Beal.  You all have made it completely clear that only political issues stood in the way.  Granting that the second stage is harder than the first stage, Beal’s 800 thousand pound thrust operational motor (and his planned, much larger version) would have made “Heavy Lift” a reality years ago

That doubt still remains and there is no proof that Beal's big one would have worked.  I know that from some of his workers, that they had doubts.  They wished that Beal would have done the small one first justl like spacex.  There were still technical, assembly and logistical issues with the big one that weren't solved.

[Jim]

rpspeck - 27/3/2007  4:11 PM
The GPS software is different and the RF sections must accommodate larger Doppler effects.  These are BIG problems only if you expect to use $99 GPS receivers.  Since both simple and differential GPS have been used on the ISS, this is a “done deal”.

ISS and spacecraft use is much different that an LV.

[Jim]

stockman - 27/3/2007  4:28 PM

Anyone have any ideas when we might start to see some summary of the terabyte of data they are going through? I am especially interested in seeing the FULL video they claim to have. I think that would be spectacular. Anyone here any information on WHEN we might see some of this?

thanks

Maybe never, just like the first launch

[Jim]

kevin-rf - 27/3/2007  3:55 PM

Does the higher pressure of a pressurized upper stage reduce pogo to a point where it is not a major concern? Did the Delta pressure fed upper stages ever have issues with pogo? I don't recall spacex ever mentioning the word. Sounds like slosh and not pogo where the problem with the second flight.

I don't believe it was POGO

[rpspeck]

“ISS and spacecraft use [of GPS] is much different that an LV.”

So what?  My use of a GPS while hiking is very different from its use in a “Smart Bomb”.  The GPS primarily produces position data, with velocity vector calculated from incremental positions.  

If the GPS can be programmed to work at Earth surface velocity and at Earth orbit velocity (ISS), then it can be programmed to work at any intermediate speed.  A Consumer GPS will normally work up to about 1000 fps ground velocity, which provides a 2000 fps window as inertial velocity.  Weapons systems greatly increase this window.  A specialized system could certainly handle all velocities up to orbital.  

I understand that Attitude is extracted from GPS information with difficulty.  However, over a period of several seconds, the increments in position provide a good measure of the velocity vector and a pretty good acceleration vector.  (50 ft position, 50 ft/t for velocity and 50 ft/t^2  for acceleration: for t = 10 seconds, 5 ft/sec velocity vector error – out of 20,000 ft/s, and 0.5 ft/s^2 for acceleration – out of 160 ft/s^2m (5 g).  This provides an acceptable 0.25 milliradian short term velocity vector error, and a modest 3 milliradian attitude and thrust vector error = 0.2 degree.  This equals the drift of the Analog Devices ADXRS401 integrated circuit gyro with excellent autozero procedures.  For less than ten seconds, the gyro data is used for instantaneous attitude and angular rates (with smaller drift).  Beyond ten seconds, the GPS data is used (with increasing acceleration vector and attitude accuracy).  Thus these are worst case error values.

 Attitude errors ten times larger than this have little effect on the achievable Delta V, and no cumulative errors exist because position is directly measured by GPS and not derived from inertial “dead reckoning”.

Richard P. Speck,  Micro-Space, inc.

[Danderman]

Has anyone considered that the staging problem during the last flight may have been caused by uneven operation of the springs? If a spring locked up, wouldn't that cause the first stage to exhibit some yawing or pitching during the jettison process?

[yinzer]

If it was a spring issue, you'd expect to see first and second stages rotating in opposite directions.  If it's excessive angular rates at staging, you'll see them rotating in the same direction.  I think the video showed the latter.

[aero313]

rpspeck - 27/3/2007  8:06 PM
So what?  My use of a GPS while hiking is very different from its use in a “Smart Bomb”.  The GPS primarily produces position data, with velocity vector calculated from incremental positions...

Richard P. Speck,  Micro-Space, inc.

I don't think anyone here is disagreeing with you that GPS aided-nav can be used in conjunction with a lower-cost INS to achieve ascent to orbit.  It's been done before.  It also isn't quite as simple as you've made it out to be, by the way.

The point of contention, however, is your assertion that the upper stage of the vehicle isn't the more expensive/more complex one.

I'm afraid I also fail to understand why some people here seem to have the impression that the established launch providers blindly pick the most expensive method possible to achieve a task.   The reality is that the selection process must balance performance and reliability with cost.  

Just remember that Yugo no longer sells cars in the US for a reason.

[rpspeck]

Nothing is as simple as its description in these short notes.  Remember, I have built and flown several near hover, gimbaled motor, guided rockets.  The control loop modeling and development for these was “interesting”, but successful.  

My primary point is that radically lower cost technology is available to replace more expensive historic systems.  This may (as will be seen in the next few years) make markedly lower cost launch vehicles possible.   Richard P. Speck,  Micro-Space, Inc.

[Danderman]

Media reports indicate that Elon Musk has spent over $100 million of his own money to develop a lower cost launch vehicle.

[Jim]

rpspeck - 27/3/2007  10:15 PM

Nothing is as simple as its description in these short notes.  Remember, I have built and flown several near hover, gimbaled motor, guided rockets.  The control loop modeling and development for these was “interesting”, but successful.  

My primary point is that radically lower cost technology is available to replace more expensive historic systems.  This may (as will be seen in the next few years) make markedly lower cost launch vehicles possible.   Richard P. Speck,  Micro-Space, Inc.

Proof is in the pudding.  

Lower costs for 500kg to LEO isn't going to change anything

[Jeff Bingham]

Jim - 27/3/2007  10:56 PM

rpspeck - 27/3/2007  10:15 PM

Nothing is as simple as its description in these short notes.  Remember, I have built and flown several near hover, gimbaled motor, guided rockets.  The control loop modeling and development for these was “interesting”, but successful.  

My primary point is that radically lower cost technology is available to replace more expensive historic systems.  This may (as will be seen in the next few years) make markedly lower cost launch vehicles possible.   Richard P. Speck,  Micro-Space, Inc.

Proof is in the pudding.  

Lower costs for 500kg to LEO isn't going to change anything

Lower costs for 500kg to LEO is going to mean a WHOLE LOT to a growing market for and interest in small-sats, nanosats, and so on. It may not change much in the realm YOU are interested in, but it's a big world out there, and a LOT more in it than you may be aware of.

[Avron]

51D Mascot - 27/3/2007  11:21 PM

Jim - 27/3/2007  10:56 PM

rpspeck - 27/3/2007  10:15 PM

Nothing is as simple as its description in these short notes.  Remember, I have built and flown several near hover, gimbaled motor, guided rockets.  The control loop modeling and development for these was “interesting”, but successful.  

My primary point is that radically lower cost technology is available to replace more expensive historic systems.  This may (as will be seen in the next few years) make markedly lower cost launch vehicles possible.   Richard P. Speck,  Micro-Space, Inc.

Proof is in the pudding.  

Lower costs for 500kg to LEO isn't going to change anything

Lower costs for 500kg to LEO is going to mean a WHOLE LOT to a growing market for and interest in small-sats, nanosats, and so on. It may not change much in the realm YOU are interested in, but it's a big world out there, and a LOT more in it than you may be aware of.

Yip, it starts with a trickle, not very noticable at first, then it grows, feeding on success.. who knows, SpaceX is not limited by anything yet, and they have not gone to the Public for funding.. imagine what they could do with a few $100 million more?