totm nov 2023 SpaceX Discussion Thread

[Bill Phil]

37 minutes ago, llanthas said:

Kinda surprised that nobody's talking about the fact that those boosters reversed from 1,000 mph, back towards Canaveral.  And THEN had power left to land.  How can they possibly be so much more efficient than anything flown before? 

 

That's basically 2.5 full launches worth of fuel for each of them..

Rocket equation is exponential. With no upper stage/core/payload that needs to be lifted, the dry mass is reduced, increasing the mass ratio to a decent amount. Stages are very light compared to their max propellant loads. Even with just a little propellant left, you can get a lot of Dv. It's not pushing anything but itself.

[mikegarrison]

The real breakthrough that is allowing SpaceX and Blue Origin to make these propulsive landings is not a boost in their rocket's fuel efficiency. It is the increased capacity and speed of the computers onboard the stage to handle controlling the return flight and landing.

Another important breakthrough compared to older rockets is reliable restarting and the ability to deeply throttle-down the engines.

[tater]

 

[YNM]

4 hours ago, llanthas said:

Kinda surprised that nobody's talking about the fact that those boosters reversed from 1,000 mph, back towards Canaveral.  And THEN had power left to land.

... That's basically 2.5 full launches worth of fuel for each of them..

You know that an empty truck is likely to be more efficient than a fully loaded truck right ? Same goes to a fully loaded stage with stuff on it vs. an empty shell.

3 hours ago, mikegarrison said:

It is the increased capacity and speed of the computers onboard the stage to handle controlling the return flight and landing.

Another important breakthrough compared to older rockets is reliable restarting and the ability to deeply throttle-down the engines.

And as long as the price of the hardware exeeds the propellant price, the fact that the hardware price is spread over more flights.

Edited February 10, 2018 by YNM

[Northstar1989]

Just found time and energy to watch the launch (working as an EMT is demanding!)  Very cool!

Now they've just gotta start looking at more things they can do with all that payload.  Developing a system of Propulsive Fluid Accumulators and orbital fuel depots would make it possible to refuel the upper stage in orbit (by launching it with surplus kerosene and getting LOX from the PFA's) to enable upper stage recovery, and go a long way towards bringing down the cost of interplanetary space travel by allowing mission designers to leverage the fuel mass they bring to Low Earth Orbit (so 1 ton of Kerosene becomes as good as more than 3 tons of Kero/LOX in Low Earth Orbit, as Kero/LOX is more than 2/3rd's Oxygen by mass...) for instance...

https://en.m.wikipedia.org/wiki/Propulsive_fluid_accumulator

http://www.alnaspaceprogram.org/blog/?p=25

Maybe somebody could also talk Musk into seriously looking into use of Microwave Thermal Rockets for use in Earth Departure Stages (ideally, a reusable one that could be added to the BFR as an optional second stage between the booster and final stage to increase its payload capacity, and would seperate from the BFR before leaving Earth's SOI and do a boostback/recapture burn+aerobraking to eventually land back on Earth for refurbishing...) while they're at it.  Because Musk's original field of study was Physics, he should be well aware of the potential benefits of using energy beamed from outside a spacecraft, rather than just onboard fuel, for propulsion- particularly as this would allow you to propel a spacecraft with just pure Hydrogen (for great ISP) or Nitrogen (which would be available in nearly-unlimited quantities from Propulsive Fluid Accumulators), and the same beamed power technology could be used to supercharge a fleet of Propulsive Fluid Accumulators (which otherwise would have to run off solar panels and only manage a small propellant surplus each month...) either with power from Earth's surface or from solar collection satellites in higher (and therefore lower-drag and more stable) orbits...  And, of course, such technology could be used to provide a Moon Base or orbiting space station with extra electrical power as well...

 

Just some ideas on breakthrough technologies that Musk could work on next if Congress/Senate still isn't biting on a manned Mars mission at Falcon Heavy prices and the BFR doesn't work out.

Because Musk's background *was* in Physics and the main thing holding Microwave Thermal Rocketry back is actually the development of cheaper and more robust Gyrotrons... (the aiming and relay-systems to shoot those microwaves at a rocket during launch or while it's in orbit overhead, or to bounce and refocus those microwaves off a relay satellite in low orbit if the target isn't in direct Line of Sight are actually relatively easily achieved- it's the Gyrotrons and power-sources of batteries or capacitors which drive up the costs and prevent research into this field...  Interestingly when Musk started his PhD in Physics, he initially wanted to work on developing better high-energy capacitors- so this would give him the opportunity to revisit that old love with a much larger team...) this isn't so far-fetched as it seems.

And, by providing mass-leveraging (PFA's powered by microwaves), or much better ISP (Microwave Thermal Rockets using LH2) for the Earth Departure Burn they could really bring down the cost-per-kg of BFR by a lot... (by reducing relative mission mass-requirements to orbit.  For example a detachable second stage could allow for a much larger portion of the BFR final stage to be dedicated to payload- since less Delta-V would be required of it to get to Mars- and improve overall mass efficiency by increasing the number of stages.  Getting back to Earth from Mars would then require a little more effort with a reduced final stage fuel capacity though: probably a longer/slower return-trip at least...)

 

Anyhow, I look forward to seeing what Musk does next.  Sadly, I fear the Falcon Heavy, while a big step in the right direction, won't be quite enough to really push politicians to return to the Moon or go to Mars (flag-and-footprints style) on its own.  For that, more work on orbital-refueling (needed for the BFR anyways) and technologies like orbital fuel-depots and Propulsive Fluid Accumulators (to mass-leverage the fuel we launch to LEO) to bring down the costs even further will probably be needed...  Falcon Heavy will probably prove useful for bigger satellites, probes, and space stations though...

Edited February 10, 2018 by Northstar1989

[YNM]

A good step would be if SpX have branches in every state or so (subcontractors works too).

[magnemoe]

7 hours ago, mikegarrison said:

The real breakthrough that is allowing SpaceX and Blue Origin to make these propulsive landings is not a boost in their rocket's fuel efficiency. It is the increased capacity and speed of the computers onboard the stage to handle controlling the return flight and landing.

Another important breakthrough compared to older rockets is reliable restarting and the ability to deeply throttle-down the engines.

More as in thinking out of the box, we soft landed probes on the moon 50 years ago, most upper stages has restart capabilities, probably not the first ones but saturn 5 3rd stage could be restarted probably others before that too. Nor it lots of computer power needed, you could done lots of it by remote to, stage would be on its own during reentry and touchdown would be best done by it self as we tend to loose connection. 

The problem was that all thought they needed wings and probably even atmospheric engines on stage for reuse. 
This adds lots of weight and increases complexity a lot, last increases development costs a lot so nobody did it with the exception of the space shuttles. 

Merlin is not very deep throttleable, raptor will be. 

Lesson learned is also older than mud: the enemy of an good working and cheap system is an perfect one. 

Interesting delta clipper was on the right track, main issue was trying for SSTO or pure fantasy as I call it. 

[Delay]

How much unburned fuel is inside a landed Falcon 9, by the way? Of course they probably burn as much as possible (and too much at least once), but how close do they actually get to "empty"?

[PB666]

10 hours ago, mikegarrison said:

The real breakthrough that is allowing SpaceX and Blue Origin to make these propulsive landings is not a boost in their rocket's fuel efficiency. It is the increased capacity and speed of the computers onboard the stage to handle controlling the return flight and landing.

Another important breakthrough compared to older rockets is reliable restarting and the ability to deeply throttle-down the engines.

You mean the trial and error that companies went through.

Its more than just solving the equations for X (whatever the coordinated of the launch pad are), Vx = 0 (relative to the surface of the earth at X), and thrust as a function of altitude, friction as a function of altitude axis relative velocities. There are many other factors.
1. How much gas pressures you need to re-fire an engine experiencing certain dynamic pressures (things like mock test firing models under different pressures)
2. How much friction you generated traveling backward with the grid fins facing a certain direction. This equation gets really hair when the space craft goes transonic. A computer will not likely get this correct on the first pass, it requires some in the field modeling. You have 9 rocket engines coming across the sound barrier and they are shaped the exact opposite of a Sears-Haack shape, you have grid fins sticking out . . . .
3. Grid fins: what are they and how do they behave, this is not trivial . .once deployed.. .deep in space the grid fins act as a particle deflectors, as the hit the peak of dynamic forces and under the boundary layer they are doing far less breaking than the engines(off), after they go trans-sonic they begin increasing huge amounts of drag again.
4. Throttle up times while under huge dynamic pressures.
5. Initial ISP when under huge dynamic pressures.
6. How to factor in estimated and actual atmospheric conditions on the descent.

Programmer X writes a program according to all the laws of physics that he is aware of.
Programmer X watches boosters crash in ocean . . . . .telemetry data reveals parameters (X, Y, Z . . .he is not exactly sure which one) is off. Meaning actual f(x,y,z) at dT=q had an elevation of minus something (meaning its intercepts the water) when it was expected that velocity would be -1 m/s. (This could also be rotational or surface relative horizontal velocity)
Programmer X as of yet does not have enough data to determine how to fix the f(X,Y,Z) but he just creates a constant that tells the engines to fire a quarter of second earlier than it would have. 

If you are using radiotelemetry or GPS and you are traveling at very high speed, your data is old by the time the data reaches the flight computer. At some point as the flight closes in on a target at high speed it has to actually be processing its reference frame and applying fudge factors relative to its reference frame.

F9 has 9 engines at its disposal, based on symmetry it has 4 pairs + 1 engine, each engine can be throttled down to 40%. This means relative to initial full thrust it can operate from 4.4% up to 11.111% on one engine 8.88% to 22.222% on two engines, 13.3333% to 33.33% on three engines (meaning 33.33% to 4.444% if you on 3 engines and off two engines during the descent). Given the fact that it is experiencing a >> 10 m/s² in the second prior to landing its got more than enough variability.

What probably has the most meaning, if you don't want to was alot of weight and money on very fancy engines that can down-throttle to 5%, just use a bunch of cheaper, lighter engines. The problem is with kerosene, which has a low vapor pressure, you need enough head gas to fire them multiple times, this is not required with cryogenic fuels. Why they lost the core?

I am very critical, and I was very critical of space X designs in the beginning . . . .kerosene on the first stage I see as part of the problem. I don't know if methane is the solution, propane might be a better solution, there is a trade-off, if you must fire a rocket many times some type of cryogenic gas is the way to go, plus you get that ISP if done right. RS25 however tries to get too much thrust from a small engine (making it expensive and prone more complex and failure prone) . .so you don't want to go that way. The 9-engine craft seems to be a good compromise because you don't need complexity. But they use the FH  boosters to build altitude (18 engines back to surface) the core to build momentum (9 engines back to surface) and once the S2 has got a good vertical momentum and 3000 m/s (about 3/8ths of what it needs to orbit) it has enough thrust and momentum (i.e. time) to accelerate the rest.

BTW, as per an earlier argument . . . . . .we should consider one of the limiting factors on other launch systems in the heavy category . . .repeating . . the RL10-b2 is rather limited in its thrust and difficult to pack multiple engines. So if you want to get something heavy into orbit with hydrolox fuels, a single RL10b-2 is not the way to go unless you want the RL10b-2 stage to fire from 5000 m/s, this is effectively a 3rd stage. Something is going to have to change in the hydrolox engine usage if the traditional players hope to compete with space X. RL10b-2 is too small and bulky. 

 

[tater]

DC-X tested most everything space X is doing in terms of propulsive landings, except the actual reentry parts. They even did the horizontal to vertical transitions for BFS.

[sevenperforce]

14 hours ago, tater said:

You'll notice that it actually returns with some significant angle of attack, hence the kerosene soot even on the nose (and the flow along the fuselage would bring some past the nose, anyway.

I could be wrong (_{probably not}), but I think the soot on one side of the nose is the result of plume impingement from the core engines. If you watch the webcast through separation, you can see very clearly the sudden glow from the Merlin plume washing over the nose cones. The soot deposits are on the same side as the attachment manifold.

13 hours ago, llanthas said:

Kinda surprised that nobody's talking about the fact that those boosters reversed from 1,000 mph, back towards Canaveral.  And THEN had power left to land.  How can they possibly be so much more efficient than anything flown before?

That's basically 2.5 full launches worth of fuel for each of them..

I believe they only need to reserve about 15-20% of their fuel load for boostback, entry, and landing.

SpaceX did the "test as you fly" dev mode, using a strong (but not terribly strong) first stage in a normal two-stage-to-orbit launch system. So dry mass is pretty low. Of course, this means they need to do an entry burn. New Glenn won't need a boostback or entry burn, because it will be designed as reusable from the start, so its dry mass will be much higher. But it will need to reserve more propellant for its landing burn, because, high dry mass.

New Glenn won't be able to gain significantly more margin by flying expendable, while SpaceX has a big advantage in that area.

12 hours ago, mikegarrison said:

The real breakthrough that is allowing SpaceX and Blue Origin to make these propulsive landings is not a boost in their rocket's fuel efficiency. It is the increased capacity and speed of the computers onboard the stage to handle controlling the return flight and landing.

Another important breakthrough compared to older rockets is reliable restarting and the ability to deeply throttle-down the engines.

Not only deep throttling, but deep throttling without significant isp losses. Early throttleable engines usually had huge isp loss because throttling was achieved by wasting thrust and propellant in some way. Really high chamber pressure, made possible by more modern construction methods, helps make engines more deeply throttleable without combustion instability.

Modern computers allow for accurate suicide burns, which allows propulsive landings without needing to hover first. That means you can get landings with a TWR over 1.

SpaceX built its own space program from the ground up, so they did things to save money, like clustering matching engines. This gave them a single engine to land on, unlike their pork-funded predecessors that picked different engines for each stage.

8 hours ago, Northstar1989 said:

Anyhow, I look forward to seeing what Musk does next.  Sadly, I fear the Falcon Heavy, while a big step in the right direction, won't be quite enough to really push politicians to return to the Moon or go to Mars (flag-and-footprints style) on its own.  For that, more work on orbital-refueling (needed for the BFR anyways) and technologies like orbital fuel-depots and Propulsive Fluid Accumulators (to mass-leverage the fuel we launch to LEO) to bring down the costs even further will probably be needed...  Falcon Heavy will probably prove useful for bigger satellites, probes, and space stations though...

Falcon Heavy can do moon missions easily enough but it's not going to get us on our way to Mars.

2 hours ago, Delay said:

How much unburned fuel is inside a landed Falcon 9, by the way? Of course they probably burn as much as possible (and too much at least once), but how close do they actually get to "empty"?

Every landing is very nearly a minimum residual shutdown.

38 minutes ago, tater said:

DC-X tested most everything space X is doing in terms of propulsive landings, except the actual reentry parts. They even did the horizontal to vertical transitions for BFS.

I'm still skeptical about this, by the way.

[tater]

I forgot entirely about the fact that the side boosters had the center core flying by, lol. That makes more sense.

As for the transition from biconic sorts of entry to tail landing... yeah, that's gonna be fun to watch, lol.

[YNM]

28 minutes ago, sevenperforce said:

... So dry mass is pretty low. Of course, this means they need to do an entry burn.

New Glenn won't need a boostback or entry burn, because it will be designed as reusable from the start, so its dry mass will be much higher ...

Why would it affect it ? It's not like MSL needed a reentry burn...

I think the bigger reason is to change the trajectories. Just straight no extra burn means a very shallow angle which is not easy to work with. Not easy to keep barges on deep water either.

I bet you my tenner New Glenn will do some extra burns, unless Bezos is extra ballsy for the barges.

Edited February 10, 2018 by YNM

[sevenperforce]

16 minutes ago, tater said:

I forgot entirely about the fact that the side boosters had the center core flying by, lol. That makes more sense.

As for the transition from biconic sorts of entry to tail landing... yeah, that's gonna be fun to watch, lol.

The impingement glow looks very similar to what precedes the Korolev cross on the Soyuz.

4 minutes ago, YNM said:

Why would it affect it ? It's not like MSL needed a reentry burn...

I think the bigger reason is to change the trajectories. Just straight no extra burn means a very shallow angle which is not easy to work with.

MSL? I'm lost.

Without an entry burn, the Falcon 9 first stages would burn up. Too fast, too much stress on the engines, too much heating. New Glenn will be reinforced and have TPS around the engines.

[magnemoe]

55 minutes ago, tater said:

DC-X tested most everything space X is doing in terms of propulsive landings, except the actual reentry parts. They even did the horizontal to vertical transitions for BFS.

This, I thought of an two stage version of it. I also belived the base had to be pretty thick for powered landing, think LEM and robot landers and dc-x scored there. 

[YNM]

5 minutes ago, sevenperforce said:

MSL? I'm lost.

Mars Science Laboratory, a.k.a Car on Mars with RTGs.

5 minutes ago, sevenperforce said:

Without an entry burn, the Falcon 9 first stages would burn up. Too fast, too much stress on the engines, too much heating. New Glenn will be reinforced and have TPS around the engines.

New Glenn will be as fast too. I guess that just means they prep up more if it is that way.

TPS on engines ? Wut ?? You mean ablatives like they probably already have ?

Still, the barge will be ballsy. You know how bad F9 had it with barges...

Edited February 10, 2018 by YNM

[sevenperforce]

3 minutes ago, YNM said:

Mars Science Laboratory, a.k.a Car on Mars with RTGs.

Uh...MSL had a whole heat shield.

3 minutes ago, YNM said:

New Glenn will be as fast too. I guess that just means they prep up more if it is that way.

That's what I mean. NG is supposed to be full-up reusable from the first launch, so they are designing it with extra dry mass for TPS.

[YNM]

1 minute ago, sevenperforce said:

That's what I mean. NG is supposed to be full-up reusable from the first launch, so they are designing it with extra dry mass for TPS.

I don't see coating TPS on engines. After all, as with F9's sonic booms, the stress comes from aerodynamics and not heating.

And the barges... Unless he' dunkin' white hot insulator-coated engines on the sea...

Edited February 10, 2018 by YNM

[magnemoe]

Just now, YNM said:

Mars Science Laboratory, a.k.a Car on Mars with RTGs.

New Glenn will be as fast too. I guess that just means they prep up more if it is that way.

Still, the barge will be ballsy. You know how bad F9 had it with barges...

Block 5 and Glenn will have more thermal protection in the bottom, the engine bells them-self can take a lot, not so much for the delicate stuff on top of rocket engines.
On the same time you want to service this parts and you want it to be lightweight. 

[sevenperforce]

6 minutes ago, magnemoe said:

Block 5 and Glenn will have more thermal protection in the bottom, the engine bells them-self can take a lot, not so much for the delicate stuff on top of rocket engines.
On the same time you want to service this parts and you want it to be lightweight. 

Yeah, you want to watch plasma boundary layer flow around the engines. The bells themselves can handle a lot of heating, but the surround machinery will get toasty if you don't do something to redirect the plasma. The NG "sextoweb" will wrap down around the engines so that it produces effectively a blunt-body and plasma will flow around the outside.

SpaceX has opted to just reserve a little extra propellant and slow down with an entry burn.

[softweir]

3 hours ago, PB666 said:

You mean the trial and error that companies went through.

* snip *

A lot of good points. However, I feel I ought to point out that there has been a revolution in automation which has made SpaceX landings possible: Lossless Convexification of Nonconvex Control Bound. You can read about the technique SpaceX use HERE.

[CatastrophicFailure]

3 hours ago, tater said:

They even did the horizontal to vertical transitions for BFS.

 

2 hours ago, sevenperforce said:

I'm still skeptical about this, by the way.

Quite so.  I thought the DCX never got fully horizontal? It translated, sure, but pointing... up-ish. Source?

[sevenperforce]

In other news, the next SpaceX launch is only a week away! It will be the last flight of a Block 3 stage (this being the one from August 2017). The first Block 4 reflight will be a month later, in March. It doesn't look like we will get more than a single reflight per booster until Block 5...though I suppose they won't schedule any Block 4 re-reflights until they actually have reflown Block 4s handy.

So far, the fastest reflight has been booster 1036, at just under 5 months turnaround, for Iridium launches 2 and 4. No future scheduled reflights have a shorter turnaround time, though this will likely change as Block 4 reflights (and, later, Block 5) become standard.

What are the best numbers so far on FH and F9B5 performance in reusable configurations?

In the post-launch presser, Elon talked yet again about how FH could do a moon landing in one launch using orbital propellant transfer. I think this is a little dumb; the Falcon 9 upper stage CAN'T do orbital propellant transfer. Not even theoretically. It's not set up for it; the required modifications would mean a complete vehicle redesign. BFS will be designed for orbital prop transfer using the base prop loading system, but that's not something F9 can do, especially given the use of helium as pressurant.

However, there are other options. A little fun math: if an end-of-life F9B5 is used to launch ONLY an IDA (mass: 526 kg) mated to the PAF, it would reach orbit with around 25 tonnes of propellant remaining. That's enough to send up to 16 tonnes of payload to TLI, provided the payload can be docked to the IDA in LEO. No new tech or dev required.

[tater]

 

23 minutes ago, CatastrophicFailure said:

 

Quite so.  I thought the DCX never got fully horizontal? It translated, sure, but pointing... up-ish. Source?

 

[sevenperforce]

Swooping from nose-down to nose-first into a controlled stall, followed by engine ignition and vertical retropropulsive descent, seems like an unnatural act of physics comparable to an STS RTLS abort.