SpaceX Falcon 9 v1.1 - Jason 3 - SLC-4E Vandenberg - Jan 17, 2016 - DISCUSSION

[Herb Schaltegger]

Again, analysis is expensive. Verification of procedures is expensive. Training is expensive. Lost vehicles and upset customers is even more expensive.

Either you understand that or you don't. Carry on ...

[abaddon]

Again, analysis is expensive. Verification of procedures is expensive. Training is expensive. Lost vehicles and upset customers is even more expensive.

Reasonable points, to be sure sure, although unproven that this specific tactic is so terrible.  SpaceX appears to be doing it, despite your concerns.

Either you understand that or you don't. Carry on ...

That doesn't help your argument, it just come off as condescending.  If you don't want to continue the conversation, there are less offensive ways to make your point and end your participation.

[JamesH]

Again, analysis is expensive. Verification of procedures is expensive. Training is expensive. Lost vehicles and upset customers is even more expensive.

Either you understand that or you don't. Carry on ...

Building rockets is expensive. SpaceX are trying to make it cheaper. If the savings > (analysis + verification + training + loss) then they would do it, surely? I understand that, that's math that is.

[Herb Schaltegger]

Again, analysis is expensive. Verification of procedures is expensive. Training is expensive. Lost vehicles and upset customers is even more expensive.

Reasonable points, to be sure sure, although unproven that this specific tactic is so terrible.  SpaceX appears to be doing it, despite your concerns.

Either you understand that or you don't. Carry on ...

That doesn't help your argument, it just come off as condescending.  If you don't want to continue the conversation, there are less offensive ways to make your point and end your participation.

It's not meant to be condescending so much as indicate weariness at these repeated off topic arguments, usually started by someone arguing with Jim about why things work the way they do in the launch business. The point is, procedures matter. Following them is a good way to avoid on-the-fly accidents and errors. Remember what started this - discussing why cryogenic rockets aren't generally launched under-loaded.

[abaddon]

It's not meant to be condescending so much as indicate weariness at these repeated off topic arguments, usually started by someone arguing with Jim about why things work the way they do in the launch business.

And yet, apparently(?) Jim was wrong about what SpaceX is doing.  If we just list out the things Jim says and keep a scorecard, I am sure it would be 99.9% of the time correct.  And I know there's a tremendous amount of time wasted with people posting crazy and horribly naive stuff, especially in the SpaceX forums.

However, SpaceX is doing it, which means "the way it has always been done" (in this case) isn't "the only reasonable way to do it", or SpaceX is making a mistake.  Either way, it's relevant and worthwhile to discuss it in those terms on a space-obsessed forum, in my opinion.

I've lost track of whether it is in fact thread appropriate at this point, however, so I'll leave it at that myself.

[RoboGoofers]

Would G loads be too high if the 2nd stage was underfilled? I can imagine that without the ballast of a full fuel load, a small payload could experience excessive G loading.

[WHAP]

Ive seen less than full propellant loads on both stages.

Define less.  90%, 80%?

You're challenging my memory Jim.  IIRC, most were in the low 90% range, but I want to say that one of the upper stages has been loaded below 90%, at least in one of the tanks.

[macpacheco]

Would G loads be too high if the 2nd stage was underfilled? I can imagine that without the ballast of a full fuel load, a small payload could experience excessive G loading.

Underfilling the 2nd stage is an even worse idea. Each ton of 2nd stage fuel/lox does far more useful work than each ton of 1st stage fuel/lox.
I agree with Jim. Both tanks must be filled to max capacity. Hopefully SX will never loose an engine again, but if it does, leaving fuel on the ground isn't a good idea.
One old pilot's adage, the only time you have too much fuel is if you're on fire. It applies just the same for space.

[cscott]

I could stand to hear less pontificating about what are "bad ideas" and more discussion about what launch providers *actually do*.

[manoweb]

Question: why is it important to have *more* fuel if an engine goes out? The same amount of energy delivery can be made by burning less engines a little more no?

It is true that fuel is "cheap" relatively speaking, but if there is no need to load the max capacity for a lighter launch, why waste tens of thousands of dollars? There might be thresholds were even the worst case scenario will not benefit by having more fuel onboard.

[Stan-1967]

Question: why is it important to have *more* fuel if an engine goes out? The same amount of energy delivery can be made by burning less engines a little more no?

It is true that fuel is "cheap" relatively speaking, but if there is no need to load the max capacity for a lighter launch, why waste tens of thousands of dollars? There might be thresholds were even the worst case scenario will not benefit by having more fuel onboard.

In the case of your upper stage with only a single engine, losing that one engine is a very bad day.  In the case of the first stage, yes, you can burn longer with the other engines, but you will also have more gravity losses because you will not have as much thrust to weight accelerating you to orbit.

[manoweb]

Oh I see. In any case, for some missions there might be an upper limit that is lower than full capacity where even considering the reduced efficiency, it makes no difference to load more fuel (that, if not used, means lower efficiency anyway)

[Steven Pietrobon]

I agree with Jim. Both tanks must be filled to max capacity. Hopefully SX will never loose an engine again, but if it does, leaving fuel on the ground isn't a good idea.

That may actually cause a large reduction in payload performance. For example, say you design your vehicle for maximum payload to LEO. You will get a certain size upper stage. For a GTO payload, you increase the size of the upper stage, reducing the payload mass. That gets you the largest mass into GTO. If you used this larger stage for LEO missions, you need to reduce the upper stage propellant mass in order to get the maximum payload mass into LEO.

[Lars-J]

I agree with Jim. Both tanks must be filled to max capacity. Hopefully SX will never loose an engine again, but if it does, leaving fuel on the ground isn't a good idea.

That may actually cause a large reduction in payload performance. For example, say you design your vehicle for maximum payload to LEO. You will get a certain size upper stage. For a GTO payload, you increase the size of the upper stage, reducing the payload mass. That gets you the largest mass into GTO. If you used this larger stage for LEO missions, you need to reduce the upper stage propellant mass in order to get the maximum payload mass into LEO.

That should be less of an issue for the F9 upper stage compared to most upper stages, since it has higher thrust to weight ratio than most upper stages. (like Centaur)

[Semmel]

I agree with Jim. Both tanks must be filled to max capacity. Hopefully SX will never loose an engine again, but if it does, leaving fuel on the ground isn't a good idea.

That may actually cause a large reduction in payload performance. For example, say you design your vehicle for maximum payload to LEO. You will get a certain size upper stage. For a GTO payload, you increase the size of the upper stage, reducing the payload mass. That gets you the largest mass into GTO. If you used this larger stage for LEO missions, you need to reduce the upper stage propellant mass in order to get the maximum payload mass into LEO.

But only if the thrust of the first stage at liftoff has so little margin that it cant lift a full first stage plus full larger second stage plus heavy LEO satellite. Or in other words, the thrust must be such that it is possible to lift large rocket + GTO sat but not  large rocket + LEO sat. The difference is pretty small, not sure how you would end up with a rocket like that.

[woods170]

Again, analysis is expensive. Verification of procedures is expensive. Training is expensive. Lost vehicles and upset customers is even more expensive.

Either you understand that or you don't. Carry on ...

Like Jim you are unable to understand that SpaceX is willing to pay the cost for additional analysis, test and verification of non-usual ways of building, operating and flying spaceships and rockets. SpaceX is even prepared to lose experimental vehicles in the process. For example, they fully expected Grasshopper to eventually make a crater. It didn't, but it's successor eventually did on an especially challenging flight profile. By the time this happened SpaceX already had all the data they needed for pulling of a first stage landing, yet they still kept pushing with F9R-Dev1, despite there being no obvious reason to do so.
On the risk of being blunt: get this into your head: SpaceX does not do all things rationally. They are directly controlled and governed by someone who is willing to take exceptional risk in shifting aerospace frontiers.

Edit: and SpaceX Elon Musk just proved my point. They changed the plans for F9-21 stage 1 (Orbcomm-2). It has now moved to LC-40 for a static fire and has been placed on the TE using an ordinary crane because there is no second stage present. And if the scuttlebutt I'm hearing is correct than the same stage will still be used for LC-39A LSORR, meaning that SpaceX intends to hotfire that stage twice, on two different launchpads. Not exactly SOP for old-space is it? But then again, this IS SpaceX we're talking about.

[Alastor]

One old pilot's adage, the only time you have too much fuel is if you're on fire. It applies just the same for space.

I think I missed your point.
Isn't being on fire the whole point of rockets using boosters ? 

[modemeagle]

I agree with Jim. Both tanks must be filled to max capacity. Hopefully SX will never loose an engine again, but if it does, leaving fuel on the ground isn't a good idea.

That may actually cause a large reduction in payload performance. For example, say you design your vehicle for maximum payload to LEO. You will get a certain size upper stage. For a GTO payload, you increase the size of the upper stage, reducing the payload mass. That gets you the largest mass into GTO. If you used this larger stage for LEO missions, you need to reduce the upper stage propellant mass in order to get the maximum payload mass into LEO.

When I originally ran simulations on V1.1 and FH I found that my simulation showed that the upper stage was build more for FH than the single stick.  My simulation showed the maximum payload to a 200X200X28 orbit for the single stick was to launch with a less than full SII tanks.  I believe it was close to 60% but don't remember the exact number.  This, of course, was just a simulation but I feel it was close.

[Robotbeat]

Question: why is it important to have *more* fuel if an engine goes out? The same amount of energy delivery can be made by burning less engines a little more no?...

Much higher gravity losses if you lose an engine early on.

[WHAP]

Again, analysis is expensive. Verification of procedures is expensive. Training is expensive. Lost vehicles and upset customers is even more expensive.

Either you understand that or you don't. Carry on ...

Like Jim you are unable to understand that SpaceX is willing to pay the cost for additional analysis, test and verification of non-usual ways of building, operating and flying spaceships and rockets. SpaceX is even prepared to lose experimental vehicles in the process. For example, they fully expected Grasshopper to eventually make a crater. It didn't, but it's successor eventually did on an especially challenging flight profile. By the time this happened SpaceX already had all the data they needed for pulling of a first stage landing, yet they still kept pushing with F9R-Dev1, despite there being no obvious reason to do so.
On the risk of being blunt: get this into your head: SpaceX does not do all things rationally. They are directly controlled and governed by someone who is willing to take exceptional risk in shifting aerospace frontiers.

Edit: and SpaceX Elon Musk just proved my point. They changed the plans for F9-21 stage 1 (Orbcomm-2). It has now moved to LC-40 for a static fire and has been placed on the TE using an ordinary crane because there is no second stage present. And if the scuttlebutt I'm hearing is correct than the same stage will still be used for LC-39A LSORR, meaning that SpaceX intends to hotfire that stage twice, on two different launchpads. Not exactly SOP for old-space is it? But then again, this IS SpaceX we're talking about.

SpaceX is not breaking new ground by offloading stages.  It's old-Space (gasp)!  In fact, SpaceX is doing things the way old-old-Space use to do it - test, fail, repeat, push the envelope.  New-old-Space is boring.