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

[Robotbeat]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Interesting.  Why not?

a.  it limits the amount of analysis that has to be done
b.  There are only empty and full sensors on the tanks
c.  hard to determine load by head pressure accurately due to prop boil off.

Just easier to launch full and deal the excess on orbit

Also allows lower peak acceleration vs partial tanks, which is easier on the payload. And if there's a performance problem (say, engine-out), there's extra margin to achieve the correct orbit.

[ZachS09]

I was guessing 8 seconds as the duration of the Static Fire, but I guess I was one second too long.

[Lars-J]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Interesting.  Why not?

a.  it limits the amount of analysis that has to be done
b.  There are only empty and full sensors on the tanks
c.  hard to determine load by head pressure accurately due to prop boil off.

Just easier to launch full and deal the excess on orbit

And propellant is cheap.

[WHAP]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Interesting.  Why not?

a.  it limits the amount of analysis that has to be done
b.  There are only empty and full sensors on the tanks
c.  hard to determine load by head pressure accurately due to prop boil off.

Just easier to launch full and deal the excess on orbit

And propellant is cheap.

Wow - normally I'm one to agree with Jim, but when so many others are on board, I'm going to say - WRONG!  And I mean that in the nicest way  .
a. True.  But sometimes that extra work isn't too hard if you're comfortable with and confident in your processes.
b. Not true. 
c. Depends on how you define "accurately". 
d. No, this could be a performance hit.
e. Sure, but not relevant if you can't get where you want to go otherwise.

I've seen less than full propellant loads on both stages.

[Semmel]

Comparing the fuel load with orbcomm doesn't make sense, it's not the same vehicle. Different second stage, different thrust at lift off different fuel density.

Also it makes sense to land on the drone ship even if they could return to launch site. It's the last 1.1 and loosing it is not as bad as loosing a F9 FT that tries a barge landing. So in case there are any residual systematic problems with barge landing, better find out on a 1.1 rather than on a FT version.

[guckyfan]

Also it makes sense to land on the drone ship even if they could return to launch site. It's the last 1.1 and loosing it is not as bad as loosing a F9 FT that tries a barge landing. So in case there are any residual systematic problems with barge landing, better find out on a 1.1 rather than on a FT version.

Right, especially as the next barge landing will be without any margins.

[macpacheco]

Right, especially as the next barge landing will be without any margins.

Is that because the mission requires substantial 2nd stage margins ?
How can a 600kg satellite take that much performance if DSCOVR was 750kg and went into solar orbit ?
That doesn't seem to compute.

Edit: Apologies... I just now understood Musk's tweet means they need to perfect ASDS for high energy missions (but doesn't mean this one IS a high energy mission)... Actually just how I predicted a couple weeks ago.

[andrewsdanj]

Right, especially as the next barge landing will be without any margins.

Is that because the mission requires substantial 2nd stage margins ?
How can a 600kg satellite take that much performance if DSCOVR was 750kg and went into solar orbit ?
That doesn't seem to compute.

I think 'next launch' refers to the subsequent SES-9?

[guckyfan]

I think 'next launch' refers to the subsequent SES-9?

Yes, maybe I wasn't clear enough. I should have mentioned SES-9.

[meberbs]

d. No, this could be a performance hit.
e. Sure, but not relevant if you can't get where you want to go otherwise.

I've seen less than full propellant loads on both stages.

I can understand a less than full second stage, but a less than full first stage doesn't make sense to me from a performance perspective. As long as the payload is not so heavy that thrust < weight, any bit higher or faster you can be when you run your fuel down to match the alternative starting fuel level should only mean that much better performance.

Am I making a mistake in my logic somehow? (Technically, the logic wouldn't work for a RTLS Falcon 9, since the stage could end up further down range and need more residual fuel for boost back , causing it to hit MECO earlier.)

[woods170]

don't need to.  Cryogenic launch vehicles aren't launched with partial propellant loads.

You projecting the old-space 'way-of-doing-things' on SpaceX again. Not advisable.

[Jim]

Ive seen less than full propellant loads on both stages.

Define less.  90%, 80%?

[Herb Schaltegger]

don't need to.  Cryogenic launch vehicles aren't launched with partial propellant loads.

You projecting the old-space 'way-of-doing-things' on SpaceX again. Not advisable.

You generalizing just to criticize Jim is not advisable either. Regularly launching vehicles with only partial prop loads simply means your vehicle is over-designed from the start. Prop is cheap. Analysis and control logic verification isn't. Do it once for a full vehicle and be done with it.

[LouScheffer]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Sure they are.  Remember the Russian DM-03 that failed due to too much LOX being loaded?   From the Wikipedia article (which is backed by the more authoritative sources) https://en.wikipedia.org/wiki/Blok_DM-03

During preparations for launch, the Blok DM-03 was fuelled using instructions intended for the Blok DM-2, which included an instruction to fill the tanks to 90% capacity.[3] Owing to the DM-03's larger tanks, this was more propellant than needed for the mission, and left the rocket too heavy to achieve orbit.

So whatever the desired loading was, it was well short of 90%.

[Herb Schaltegger]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Sure they are.  Remember the Russian DM-03 that failed due to too much LOX being loaded?   From the Wikipedia article (which is backed by the more authoritative sources) https://en.wikipedia.org/wiki/Blok_DM-03

During preparations for launch, the Blok DM-03 was fuelled using instructions intended for the Blok DM-2, which included an instruction to fill the tanks to 90% capacity.[3] Owing to the DM-03's larger tanks, this was more propellant than needed for the mission, and left the rocket too heavy to achieve orbit.

So whatever the desired loading was, it was well short of 90%.

You realize that just furthers Jim's point, right? Just because you CAN do something doesn't mean it's a good idea.

[Kabloona]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Sure they are.  Remember the Russian DM-03 that failed due to too much LOX being loaded?   From the Wikipedia article (which is backed by the more authoritative sources) https://en.wikipedia.org/wiki/Blok_DM-03

During preparations for launch, the Blok DM-03 was fuelled using instructions intended for the Blok DM-2, which included an instruction to fill the tanks to 90% capacity.[3] Owing to the DM-03's larger tanks, this was more propellant than needed for the mission, and left the rocket too heavy to achieve orbit.

So whatever the desired loading was, it was well short of 90%.

Let's be clear about the difference between a "full propellant load" and a "full tank." Of course you cannot fill a tank completely, you have to leave ullage. So a 100% propellant load may use only 90% tank volume.

The Zak article says the tanks were filled "90% full," one metric ton over the planned load. So let's say the planned load was 85% full. That "85% full" point may have represented the desired nominal "full load" of LOX, and anything beyond may have been using tank volume reserved for ullage.

http://www.russianspaceweb.com/proton_2010.html#glonass43

Also, the Zak article says the Blok DM-03 was developed to improve Zenit performance, but the in the case of this failure it was flying on Proton. So the propellant load was being adjusted for a different vehicle, which is why it didn't need to be as full as perhaps needed for Zenit.

So that's a rather unusual case, an upper stage flying on different vehicles and therefore needing different propellant loads.

In the case of SpaceX, where the upper stage is always flying on the same vehicle, I don't see why you'd ever fly with less than 100% prop load for margin, at least on stage 1 in case of engine out. What good is engine out capacity if you don't carry enough props to overcome resultant gravity loss?

[LouScheffer]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Sure they are.  Remember the Russian DM-03 that failed due to too much LOX being loaded?   From the Wikipedia article (which is backed by the more authoritative sources) https://en.wikipedia.org/wiki/Blok_DM-03

During preparations for launch, the Blok DM-03 was fuelled using instructions intended for the Blok DM-2, which included an instruction to fill the tanks to 90% capacity.[3] Owing to the DM-03's larger tanks, this was more propellant than needed for the mission, and left the rocket too heavy to achieve orbit.

So whatever the desired loading was, it was well short of 90%.

You realize that just furthers Jim's point, right? Just because you CAN do something doesn't mean it's a good idea.

Of course you can always make a mistake, but Jim's statement was that procedures would always call for a full tank.  In this case they increased the tank size by 25%, but for this mission they wanted the same mass of fuel.  So they meant to,  wanted to, and should have loaded it to 90% * 0.8 = 72% full, on purpose.  That was the desired launch state - a non-full tank, and was the correct fuel loading for a successful mission.  Then they mistakenly filled it, and it was too heavy for the lower stages to place into the desired orbit.   This demonstrates precisely *why* it is sometimes desirable to launch with partially full tanks.

[Jim]

Cryogenic launch vehicles aren't launched with partial propellant loads.

Sure they are.  Remember the Russian DM-03 that failed due to too much LOX being loaded?   From the Wikipedia article (which is backed by the more authoritative sources) https://en.wikipedia.org/wiki/Blok_DM-03

During preparations for launch, the Blok DM-03 was fuelled using instructions intended for the Blok DM-2, which included an instruction to fill the tanks to 90% capacity.[3] Owing to the DM-03's larger tanks, this was more propellant than needed for the mission, and left the rocket too heavy to achieve orbit.

So whatever the desired loading was, it was well short of 90%.

Cryogenic launch vehicles aren't launched with partial propellant loads.

Sure they are.  Remember the Russian DM-03 that failed due to too much LOX being loaded?   From the Wikipedia article (which is backed by the more authoritative sources) https://en.wikipedia.org/wiki/Blok_DM-03

During preparations for launch, the Blok DM-03 was fuelled using instructions intended for the Blok DM-2, which included an instruction to fill the tanks to 90% capacity.[3] Owing to the DM-03's larger tanks, this was more propellant than needed for the mission, and left the rocket too heavy to achieve orbit.

So whatever the desired loading was, it was well short of 90%.

I don't count the DM as part of a launch vehicle.  It may be a stage much like IUS on Titan IV, but it is treated like a payload as far as the main booster goes.  It isn't really part of the "integrated" launch vehicle.

[Prober]

Comparing the fuel load with orbcomm doesn't make sense, it's not the same vehicle. Different second stage, different thrust at lift off different fuel density.

 FT version.

careful, you slipped off the "promoted SX position" stating new model F9FT is the same as the old 1.1 with some small modifications.
 
Update: guess now the F9FT is no longer its been renamed to the F9
http://forum.nasaspaceflight.com/index.php?topic=37550.msg1473090#msg1473090

Edit: add update

[abaddon]

You realize that just furthers Jim's point, right? Just because you CAN do something doesn't mean it's a good idea.

You're absolutely correct; launching rockets into space is a bad idea.

More fairly; just because someone messes up doing something one time doesn't mean you should never do it.