totm nov 2023 SpaceX Discussion Thread

[JoeSchmuckatelli]

2 hours ago, sevenperforce said:

using a small ullage burn to nudge the props from one tank to the other

Wait, what? 

 

I've not been following along... The plan is to use inertia to shift the fuel? 

Isn't slosh a problem? 

[JoeSchmuckatelli]

8 hours ago, RCgothic said:

keeping SLS going

...is actually worth it if for no other reason than keeping players in the game. 

MA Bell was cutting edge at one point, and then fully functional for years... But monopoly ultimately kills innovation.  (I know, so does pork) 

... 

Is the main frustration with SLS is that it's diverting funds from other players?  B/c SX is currently the only domestic rocket producer at any volume.  Unless BO suddenly starts to pump out working engines.  Whoops, sorry SLS has launched more big rockets than BO has to date - but you get what I mean.  There's other players trying to get in the game, but aside from SLS NASA doesn't have a lot of choices *right now*

[StrandedonEarth]

25 minutes ago, JoeSchmuckatelli said:

Is the main frustration with SLS is that it's diverting funds from other players?

I think the main frustration with SLS is that it doesn’t have the payload to do a truly useful lunar mission, hence the current architecture. The obscene amounts charged by the contractors just adds insult to injury, especially when it could be spent on other things. The lander should have been included for that price 

[tater]

1 hour ago, JoeSchmuckatelli said:

Is the main frustration with SLS is that it's diverting funds from other players? 

As @StrandedonEarth said, it's because it was not designed to do any particular mission. It is as I usually put it, a "rocket to nowhere."

A Jack-of-all-trades would be fine—but SLS is not that, it's a Jack-of-no-trades. Thee is simply no useful mission t can accomplish. If it was grossly overbuiolt, so it was not optimized for cislunar, but could do cislunar, and could maybe do weaksauce Mars missions, but not ideal, then who cares how much it costs? It;s that it's crazy expensive, and is useless. Shuttle was expensive, but at least it was a LEO vehicle that could do useful LEO stuff.

[tater]

SpaceX is targeting Thursday, December 7 for a Falcon 9 launch of 23 Starlink satellites to low-Earth orbit from Space Launch Complex 40 (SLC-40) at Cape Canaveral Space Force Station in Florida. Liftoff is targeted for 12:07 a.m. ET, with backup opportunities available until 2:59 a.m. ET. If needed, additional opportunities are also available on Thursday, December 7 starting at 11:01 p.m. ET.

[tater]

2 min

 

[tater]

Another routine flight to space

[sevenperforce]

4 hours ago, JoeSchmuckatelli said:

7 hours ago, sevenperforce said:

using a small ullage burn to nudge the props from one tank to the other

Wait, what? 

I've not been following along... The plan is to use inertia to shift the fuel? 

Isn't slosh a problem? 

Well that kind of gets at the root of the issue: there is no straightforward way to transfer propellants in microgravity.

Think about it. You've got two tanks, and you've got them connected somehow, and you've got a mix of gases and liquid in one tank but only gas in the other tank, and you need to transfer the liquid. How do you do it without using gravity?

Even if you have a way to increase the pressure in one tank and decrease the pressure in the other tank, you're just going to be pushing gas, because gas pressure waves move at the speed of sound while liquids move...well, slowly. Pumps won't work unless you can get the liquids into the inlets to begin with.

Prior mechanisms to transfer propellant have been extremely volume- and mass-limited and have typically used stable hypergolics. Russian vehicle prop transfers typically use a feeder tank in a disposable refueling vehicle, where the propellant is held inside a bladder that can be compressed by gas pressure to physically push the propellant into the destination tank:

But that's a small-scale solution. You can't very well fit every Starship tanker with inflatable bladders holding all of their propellant -- it would be so heavy that the damn thing would never get to orbit. 

Propellant settling is one big problem here. That's been tackled in a number of ways; most upper stages use solid ullage motors or cold-gas thrusters for settling, while the Space Shuttle and most capsules used a complex engine feed inlet with a structure that holds fluid inside it by surface tension. Once settled, the subsequent propellant burn provides the acceleration needed to keep the propellant flowing into the inlets. Starship currently uses propulsive vents (basically cold-gas thrusters) for settling before restart, although it may switch to hot-gas thrusters eventually. So if they provide settling with gas thrusters, they'll create an impulse that will get the propellant flowing (or, technically, an impulse that will move the tanks in one direction while the propellant is stationary relative to the original trajectory).

At that point they could try to use some sort of pump, but it's a more mass-efficient solution to just keep the gas thrusters thrusting and let the propellant drain "down" relative to the thrust vector, just as it would under the influence of gravity. In particular, the flow from the donor tank in to the recipient tank is going to lower the pressure in the donor tank and increase the pressure in the recipient tank, so the pressure increase in the recipient tank can be used to continuously feed gas thrusters on that tank, keeping the whole stack settled:

Of course you'd need COPVs or maybe a resistance heater in the donor tank to keep it at equal or higher pressure than the recipient tank, but that's really no big deal.

Edited December 7, 2023 by sevenperforce

[Elthy]

2 hours ago, sevenperforce said:

but it's a more mass-efficient solution to just keep the gas thrusters thrusting and let the propellant drain "down" relative to the thrust vector

Is it realy? The volumes they want to transfer at some point are huge, hundrets of cubic meters. Even with some big fuel connectors this will take some time, requiring lots of delta-v to provide the acceleration. I could only imagine a hybrid solution, ullage to provide e.g. 0.01g so the propelant is settled during the transfer while the actual transfer happens with strong pumps, keeping the time under acceleration to a minimum.

[CBase]

3 hours ago, sevenperforce said:

Prior mechanisms to transfer propellant have been extremely volume- and mass-limited

Several medias like arstechnica meanwhile provided information that the tank to tank demonstration should amount 10 metric tons ! Small compared to starship scale, but definetly breaking grounds in microgravity.

 

[Meecrob]

On 11/24/2023 at 4:58 PM, mikegarrison said:

Water deluge has been used for 50 years, at least. The question is not "how did SpaceX design a water deluge system so quickly?", but rather "why did they think they didn't need one before?"

Good point, I'm guessing they erred too much on the side of "lets see if this works, and if it doesn't, we will add the deluge system." I totally agree, they kinda looked silly with the whole concrete tornado thing they had going on for IFT-1. My point was more specifically aimed at the fact that I think they already had the design down, they did not fabricate and install it because they were trying to get away with the least amount of infrastructure as possible. I think this time it was a misstep. they could have looked totally on the ball if they had've implemented their deluge system for IFT-1.

[sevenperforce]

5 hours ago, Elthy said:

8 hours ago, sevenperforce said:

it's a more mass-efficient solution to just keep the gas thrusters thrusting and let the propellant drain "down" relative to the thrust vector

Is it realy? The volumes they want to transfer at some point are huge, hundrets of cubic meters. Even with some big fuel connectors this will take some time, requiring lots of delta-v to provide the acceleration. I could only imagine a hybrid solution, ullage to provide e.g. 0.01g so the propelant is settled during the transfer while the actual transfer happens with strong pumps, keeping the time under acceleration to a minimum.

To be clear, you would definitely need continuous acceleration for settling regardless of whether you used a pump. The weight of a pump that can move tens of tonnes of liquid quickly is non-negligible, and neither is the weight of a sufficient power source.

In contrast, if you're transferring by constant ullage acceleration then you're only losing gas -- gas that would have to be displaced anyway as the destination tank is filled.

[tater]

3 hours ago, Meecrob said:

Good point, I'm guessing they erred too much on the side of "lets see if this works, and if it doesn't, we will add the deluge system." I totally agree, they kinda looked silly with the whole concrete tornado thing they had going on for IFT-1. My point was more specifically aimed at the fact that I think they already had the design down, they did not fabricate and install it because they were trying to get away with the least amount of infrastructure as possible. I think this time it was a misstep. they could have looked totally on the ball if they had've implemented their deluge system for IFT-1.

To be fair, they had the water deluge components on site at the time of IFT-1. I think you are right they figured they could just do it and sustain some damage, then they'd rip it apart and add the stuff already on site, but they underestimated the damage.

[Elthy]

1 hour ago, sevenperforce said:

In contrast, if you're transferring by constant ullage acceleration then you're only losing gas -- gas that would have to be displaced anyway as the destination tank is filled.

That would propably require a friction-less system. Its propable that the expended gas isnt enough to move the same volume of fuel through some more or less complex piping system.

[Nuke]

9 hours ago, sevenperforce said:

Well that kind of gets at the root of the issue: there is no straightforward way to transfer propellants in microgravity.

Think about it. You've got two tanks, and you've got them connected somehow, and you've got a mix of gases and liquid in one tank but only gas in the other tank, and you need to transfer the liquid. How do you do it without using gravity?

Even if you have a way to increase the pressure in one tank and decrease the pressure in the other tank, you're just going to be pushing gas, because gas pressure waves move at the speed of sound while liquids move...well, slowly. Pumps won't work unless you can get the liquids into the inlets to begin with.

Prior mechanisms to transfer propellant have been extremely volume- and mass-limited and have typically used stable hypergolics. Russian vehicle prop transfers typically use a feeder tank in a disposable refueling vehicle, where the propellant is held inside a bladder that can be compressed by gas pressure to physically push the propellant into the destination tank:

But that's a small-scale solution. You can't very well fit every Starship tanker with inflatable bladders holding all of their propellant -- it would be so heavy that the damn thing would never get to orbit. 

Propellant settling is one big problem here. That's been tackled in a number of ways; most upper stages use solid ullage motors or cold-gas thrusters for settling, while the Space Shuttle and most capsules used a complex engine feed inlet with a structure that holds fluid inside it by surface tension. Once settled, the subsequent propellant burn provides the acceleration needed to keep the propellant flowing into the inlets. Starship currently uses propulsive vents (basically cold-gas thrusters) for settling before restart, although it may switch to hot-gas thrusters eventually. So if they provide settling with gas thrusters, they'll create an impulse that will get the propellant flowing (or, technically, an impulse that will move the tanks in one direction while the propellant is stationary relative to the original trajectory).

At that point they could try to use some sort of pump, but it's a more mass-efficient solution to just keep the gas thrusters thrusting and let the propellant drain "down" relative to the thrust vector, just as it would under the influence of gravity. In particular, the flow from the donor tank in to the recipient tank is going to lower the pressure in the donor tank and increase the pressure in the recipient tank, so the pressure increase in the recipient tank can be used to continuously feed gas thrusters on that tank, keeping the whole stack settled:

Of course you'd need COPVs or maybe a resistance heater in the donor tank to keep it at equal or higher pressure than the recipient tank, but that's really no big deal.

for transfer i think the best approach is link up ports on the side, and put the linked ships into a roll. then conventional pumping can be used. you dont even need a very high rate of roll if you have a lot of time for settling. 

[CBase]

6 hours ago, Meecrob said:

they could have looked totally on the ball if they had've implemented their deluge system for IFT-1.

maybe, maybe not. CSI Starbase had a pretty good analysis that the ground shockwaves and breaking foundation caused stage 0 failure in first place.  The steel plate might have been strong enough to support the foundation, but might have failed as well. And failing after installation of the deluge system would have made foundation upgrades more difficult.

44 minutes ago, Nuke said:

for transfer i think the best approach is link up ports on the side, and put the linked ships into a roll.

rotational impulse was my first thought as well, as it is preserved. Actually the moving CoM betweent 2 ships might help as the donator tanks spins more the less fuel it has. For IFT-3 demonstration they could place 4 tanks in rotational symmetry with full tanks vis-a-vis and full and empty side by side. This way during ascent load is balanced and for the first attempt CoM stays at center.

[tater]

New vid with some onboard camera shots (few):

 

[Nuke]

1 hour ago, CBase said:

rotational impulse was my first thought as well, as it is preserved. Actually the moving CoM betweent 2 ships might help as the donator tanks spins more the less fuel it has. For IFT-3 demonstration they could place 4 tanks in rotational symmetry with full tanks vis-a-vis and full and empty side by side. This way during ascent load is balanced and for the first attempt CoM stays at center.

side to side dock, with structural linkage in addition to fuel, possibly canted at an angle (a few degrees) to create a low spot to pump from in the base of the tank (you could use a blister but this would be on the tile side of the ship and that might mess up with your reentry dynamics on the delivery side). pump lo2 and lch4 simultaneously controlling the flow rate of the pumps to balance the tanks. if the tanker is intended to remain stationary, install the structural hardpoints and transfer pumps on that side, that way you can make it really robust and decrease fuel transfer times (i don't think that's really relevant as you would have time for low performance pumping).

pumping mechanics are deceptively complex. im not sure how much g-force is needed to keep the pump wet and i dont know how they will behave under very low g, with coriolis effects in play and under cryogenic conditions over a dynamically changing cg. so it makes sense why elon would just rather spend the fuel on ullage and let the tanks drain, as that system only requires a few valves (that you would need in either system). the philosophy is the best part is no part. so it comes down to how much fuel you save, how much weight you need for the transfer pumps and how reliable those systems are. would be nice to have both options for redundancy, in case you lose a thruster or a pump.  redundancy is nice if you are going to have an on-station tanker with a long service life. 

Edited December 7, 2023 by Nuke

[Meecrob]

1 hour ago, CBase said:

maybe, maybe not. CSI Starbase had a pretty good analysis that the ground shockwaves and breaking foundation caused stage 0 failure in first place.  The steel plate might have been strong enough to support the foundation, but might have failed as well. And failing after installation of the deluge system would have made foundation upgrades more difficult.

Ok, but the deluge system worked. Like we all saw the awesome shockwaves  from the video...I'm not sure what your point is? Mine is that SpaceX reasonably knew they needed a deluge system, but they tried to get away without one. They obviously learned their lesson, as IFT-2 showed the effectiveness of their system. No concrete chunks tossed at high velocity to the surrounding areas.

[Ricktoberfest]

I had an idea and it’s probably dumb but here goes. Instead of a bladder to hold the liquid fuel, what about a bladder that holds a harmless gas inside the tank. To force liquid out of the tank you inflate the bladder with gas. The gas is contained in the bladder so only liquid is forced out of the tank by the pressure of the gas. In the receiving tank there could also be a gas bladder that starts full, but when you want to receive gas you open it up and push the gas into the full tanks bladder to pressurize it.   The empty tank bladder deflates, creates volume and reduces pressure, while the full tank bladder inflates, decreases volume for the liquid, and pressurizes the tank as it empties so liquid is forced out. 
 

Just something stupid that popped into my head reading about the liquid bladders used currently for the ISS. 

[tater]

Pretty clear they knew they needed deluge (since they built the parts they finally installed, and those parts were on site for IFT-1, just not installed), and thought they'd get incremental damage relative to their static fires. What resulted was not incrementally worse, but a state change of worse.

Plus side is that they fixed it quickly, and per Metzger, there is now new understanding of plume-soil interactions as a result.

 

[Ricktoberfest]

21 hours ago, Nuke said:

. worst case scenario it bankrupts the company and we lose falcon.

I think if SpaceX went bankrupt to that extent there’s someone out there willing to buy the rights to falcon 9, at least for the foreseeable future until they all get on the reusable bandwagon. 

[Royalswissarmyknife]

2 hours ago, tater said:

New vid with some onboard camera shots (few):

 

Wallpapers but its a video.

Edited December 7, 2023 by Royalswissarmyknife

[Meecrob]

1 hour ago, Ricktoberfest said:

I think if SpaceX went bankrupt to that extent there’s someone out there willing to buy the rights to falcon 9, at least for the foreseeable future until they all get on the reusable bandwagon. 

There is no way SpaceX is going bankrupt. They as a single company, outpace all other launchers combined.

[darthgently]

1 hour ago, tater said:

Pretty clear they knew they needed deluge (since they built the parts they finally installed, and those parts were on site for IFT-1, just not installed), and thought they'd get incremental damage relative to their static fires. What resulted was not incrementally worse, but a state change of worse.

Plus side is that they fixed it quickly, and per Metzger, there is now new understanding of plume-soil interactions as a result.

 

"... We need to dig a big hole to install this deluge system.". 

(engineers turn to look at booster 7 with thoughtful looks on their faces).

Edited December 7, 2023 by darthgently