SpaceX Starship : First Flight : Starbase, TX : 20 April 2023 - DISCUSSION

[dgkimpton]

Proof?
"...the hit has version"?
And what, specifically is that "unnecessary complication"?
RCS engines burning "methalox", which would actually be gaseous methane and oxygen?
And what is that complex bit of plumbing photographed by Kenniston?

Proof being the photo shows the Hot Gas version (which is what Manley was asking about) mounted to a SuperHeavy, and we now have confirmation from Elon that it will be unmounted and ordinary Nitrogen thrusters will be used instead. So clearly they are working on two different reaction control systems in parallel. Presumably, they hoped the Hot Gas version would be ready in time, but it has some kinks or unexpected complexity that makes it too much risk to fly with.

[jpo234]

SpaceX aims to launch first orbital Starship flight in July, company president says

[IntoTheVoid]

The unnecessary complication Elon is referring to are the hot gas thrusters. Cold gas thrusters are a lot more simple and have been used on Starship so far. So after initially pushing for a first test of the hot gas thrusters during the first orbital attempt, it seems like they have now decided to play it safe and use cold gas thrusters instead, eliminating one unknown.

Yeah, the hot gas thrusters are often called methalox, even though that doesn't make much sense if they are indeed using gaseous oxygen. That said, I don't know if it's actually confirmed that they'll be using gaseous methane and oxygen. Cryogenic pressure-fed hot gas thrusters are a thing too.

The picture shows a SH forward dome, and the complex plumbing attached to it is an assembly of three hot gas RCS thrusters, one nozzle pointing left, one right, one towards the camera.

Proof being the photo shows the Hot Gas version (which is what Manley was asking about) mounted to a SuperHeavy, and we now have confirmation from Elon that it will be unmounted and ordinary Nitrogen thrusters will be used instead. So clearly they are working on two different reaction control systems in parallel. Presumably, they hoped the Hot Gas version would be ready in time, but it has some kinks or unexpected complexity that makes it too much risk to fly with.

I think people are failing to take into account other recent info and making the wrong conclusions.

Aside from the comment about the Hot Gas Thrusters, he also recently said that BN3 aka 'Booster 2' would be going to the Pad A test stand and that the next one would be the orbital booster. Thus, the actual implication, is not necessarily that the new thruster isn't ready for orbital flight. It is that the new thruster is an "unnecessary complication" on a ground test (hop test?) booster. Unstated, but also not unreasonable to consider, that perhaps they don't have enough of them to risk them before the orbital flight. But there is not (yet?) any implication that the hot gas thrusters will not be ready for the first orbital booster. It's just that this is not that booster, in spite of the common expectation that it was.

[OTV Booster]

The unnecessary complication Elon is referring to are the hot gas thrusters. Cold gas thrusters are a lot more simple and have been used on Starship so far. So after initially pushing for a first test of the hot gas thrusters during the first orbital attempt, it seems like they have now decided to play it safe and use cold gas thrusters instead, eliminating one unknown.

Yeah, the hot gas thrusters are often called methalox, even though that doesn't make much sense if they are indeed using gaseous oxygen. That said, I don't know if it's actually confirmed that they'll be using gaseous methane and oxygen. Cryogenic pressure-fed hot gas thrusters are a thing too.

The picture shows a SH forward dome, and the complex plumbing attached to it is an assembly of three hot gas RCS thrusters, one nozzle pointing left, one right, one towards the camera.

Proof being the photo shows the Hot Gas version (which is what Manley was asking about) mounted to a SuperHeavy, and we now have confirmation from Elon that it will be unmounted and ordinary Nitrogen thrusters will be used instead. So clearly they are working on two different reaction control systems in parallel. Presumably, they hoped the Hot Gas version would be ready in time, but it has some kinks or unexpected complexity that makes it too much risk to fly with.

I think people are failing to take into account other recent info and making the wrong conclusions.

Aside from the comment about the Hot Gas Thrusters, he also recently said that BN3 aka 'Booster 2' would be going to the Pad A test stand and that the next one would be the orbital booster. Thus, the actual implication, is not necessarily that the new thruster isn't ready for orbital flight. It is that the new thruster is an "unnecessary complication" on a ground test (hop test?) booster. Unstated, but also not unreasonable to consider, that perhaps they don't have enough of them to risk them before the orbital flight. But there is not (yet?) any implication that the hot gas thrusters will not be ready for the first orbital booster. It's just that this is not that booster, in spite of the common expectation that it was.

One complication is that the hot gas units seen are externally mounted. Production units will most likely be internal, especially if intended for orbit. Even if the basic design doesn't change the plumbing will probably be highly customized like the crazy wild plumbing under the hood of a late 1990's car.

[GHogan]

I first thought that the thrusters would go inside too. Then one of the renders showed the thrusters need to fire tangent to the hull. So they have to go outside.

[OTV Booster]

I first thought that the thrusters would go inside too. Then one of the renders showed the thrusters need to fire tangent to the hull. So they have to go outside.

That would work on SH. F9 has external pods. How would that work on SS?  It would be bad enough on the windward side but the side units would be really bad. They would be at exactly the place where the stagnation layer is thinnest and at its highest velocity.

[Lars-J]

I first thought that the thrusters would go inside too. Then one of the renders showed the thrusters need to fire tangent to the hull. So they have to go outside.

Don’t take the renders as gospel at this point. And there is absolutely no requirement that thrusters need to be able to fire tangent to the hull. It may be the most efficient thruster placement in theory, but in practice there will be trade-offs to make, such as how to protect the thrusters from the re-entry heat.

Look at the Shuttle RCS, it had plenty of thrusters that did not fire tangentially to the hull due to the need for TPS on the bottom side.

[OTV Booster]

I first thought that the thrusters would go inside too. Then one of the renders showed the thrusters need to fire tangent to the hull. So they have to go outside.

Don’t take the renders as gospel at this point. And there is absolutely no requirement that thrusters need to be able to fire tangent to the hull. It may be the most efficient thruster placement in theory, but in practice there will be trade-offs to make, such as how to protect the thrusters from the re-entry heat.

Look at the Shuttle RCS, it had plenty of thrusters that did not fire tangentially to the hull due to the need for TPS on the bottom side.

The differences in shape of the shuttle and SS means that the RCS placement doesnt easily carry over, and the difference in aerodynamic control authority points up a (maybe) greater need for RCS authority.


Looking at the shuttle nose, the side thrusters pierce a side that is tilted back slightly beyond vertical. They also pierce through the heatshield and call for custom tile shapes. There is some cosine loss because of their angle. They are also out of the shockwave and and the stagnation boundary layer which ITSM is the most important design parameter.


Moving this over to the SS (SH is not a problem) We're faced with a different airframe cross section. The midline of the cross section, or maybe slightly higher on the nose area, is where The shockwave is closest and the stagnation boundary layer is highest velocity. The closer the RCS engines are mounted behind this line, the shallower there firing angle can be or they risk exhaust impingement ripping tiles off. As they move back from the centerline the firing angle can get steeper, cosine losses less, and the cutout hole eclipse elongates.


This is some tight restraints. ISTM co-sign losses will be high.

[Jim]

No cosine losses since the other side fires at the same time


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[envy887]

No cosine losses since the other side fires at the same time


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Unless the thruster on the other side is firing exactly parallel to the one on this side, there will be cosine losses. The losses aren't large, though. At 15 degrees off centerline, nearly 97% of the thrust is going in the desired direction.

[Jansen]

Starship orbital flight information with Starlink

[meekGee]

No cosine losses since the other side fires at the same time


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Unless the thruster on the other side is firing exactly parallel to the one on this side, there will be cosine losses. The losses aren't large, though. At 15 degrees off centerline, nearly 97% of the thrust is going in the desired direction.

And the one on the other side is rotated in the opposite way, so not parallel.

But agree cosine losses even for moderate angles are small and don't really matter here

[edzieba]

Starship orbital flight information with Starlink

Ah, SpaceX fuelling the Booster fate debate further. In addition to the "booster landing / Starship soft-landing" verbiage, there is now:

SpaceX intends demonstrate high data rate communications with Starship and the Super Heavy Booster on the ground at the launch site in Starbase, TX during launch, during booster recovery, in flight, and during reentry

[steveleach]

Starship orbital flight information with Starlink

Ah, SpaceX fuelling the Booster fate debate further. In addition to the "booster landing / Starship soft-landing" verbiage, there is now:

SpaceX intends demonstrate high data rate communications with Starship and the Super Heavy Booster on the ground at the launch site in Starbase, TX during launch, during booster recovery, in flight, and during reentry

Yep, another almost meaningless snippet that we will probably argue over in these forums for days, with all sides claiming it is evidence for their point of view.

It clearly means that the Starlink comms will be active for the entire time they are recovering the booster, therefore the booster must be intact the whole time, therefore it requires landing on a platform, therefore it requires legs.

Also, the fact that they specifically said "recovery" and not "landing" clearly indicates that it will be fished out of the water rather than landing on a platform, so it won't have any legs.

[OTV Booster]

No cosine losses since the other side fires at the same time


Sent from my iPhone using Tapatalk

Jim, help me out here. I don't have the math but I work pretty well conceptually. Here's what I see with a simple model that ignores all issues discussed except thrust angle. If the thrusters are parallel their thrust adds together. No cosine loss. If they are both pointed outward and opposite each other, they null each other out. Cosine loss is 100%. If they are at 45 deg (cos 45deg=.707) They get ~30% cosine loss.


I know you don't like being questioned, but what am I missing?

[FutureSpaceTourist]

twitter.com/infographictony/status/1411217106062823424

UPDATE: As we learn more about @SpaceX’s plans for its first Superheavy launch, I’ll keep you updated to any design & mission updates/changes. What’s different with this infographic? This one goes to eleven. Plus some fin mods & no entry burn for the booster as stated by Elon.

https://twitter.com/infographictony/status/1411217349223469056

Also a version with less text.

[Greg Hullender]

I'll be very disappointed if SpaceX doesn't at least try to recover the upper and lower stages from this launch. If nothing else, I'm sure they learn a lot more from actual recovered stages than they do from telemetry.

[alugobi]

I'm sure they learn a lot more from actual recovered stages than they do from telemetry.

First, they learn how to fly them and land them, telemetry teaching them that.  Then, once they can regularly recover the booster and ship, then can learn from the hardware what to tweak going forward. 

There are two phases to the development of the system.  Some might occur simultaneously, but the flying and reentering part has to predominate in the early stages.  I think that this how they're looking at it right now.  The willingness to sacrifice Raptors to the deep suggests this approach, I believe.

Edit: clarity

[OTV Booster]

I'll be very disappointed if SpaceX doesn't at least try to recover the upper and lower stages from this launch. If nothing else, I'm sure they learn a lot more from actual recovered stages than they do from telemetry.

If one of the platforms is ready MAYBE they'll try to land the booster on it. IF it has actual landing legs. Otherwise, just land on the water like the early F9 landing tests.


For the SS, well, I will be gobsmacked if it makes it through the fireball. The heatshield is IMO the most difficult technical challenge and they've not even laid out an entire tile suite, even as a mock-up.


The most cost effective move would be to try to get some StarLink telemetry out before it disintegrated. That would be an extremely useful tool if they can make it work. That and some ships with good optics and maybe some good high frequency radar with enough resolution to maybe identify the pieces as they shed.

[FutureSpaceTourist]

twitter.com/planet4589/status/1411781300063813648

I took a look at what's know for the proposed marginal-orbit trajectory for the Starship/Super Heavy test flight. I came up with an OK fit with an orbit that is about 70 x 860 km x 26.4 deg. The relatively high apogee is needed to accomodate a low perigee and the range to HI

https://twitter.com/planet4589/status/1411781527869046785

Here's some plots of the assumed trajectory superimposed on GoogleEarth:

twitter.com/planet4589/status/1411781897261355013

And here is my fake TLE:

https://twitter.com/planet4589/status/1411782265525485569

(Launch date of 0000 UTC Aug 1 is obviously arbitrary. Doubt it will be that soon!)