totm nov 2023 SpaceX Discussion Thread

[tater]

It's important to remember SpaceX only paid $3.5M each for them, and at the time they did, both SS and SH had legs.

Literally less than the retail price of a single Be-4 engine for 2 platforms.

[JoeSchmuckatelli]

1 minute ago, tater said:

It's important to remember SpaceX only paid $3.5M each for them, and at the time they did, both SS and SH had legs.

Literally less than the retail price of a single Be-4 engine for 2 platforms.

Ouch 

[Nuke]

flip is only $600k so its probibly not expensive enough for spacex.

[darthgently]

6 hours ago, mikegarrison said:

Have you considered that maybe it was just a bad idea that they finally got around to accepting as a bad idea?

I remember they bought them back when they thought they'd be landing without stage 0 with catching arms.  That is a lot more stuff to put that high on a rig that small

[Beccab]

5 hours ago, tater said:

It's important to remember SpaceX only paid $3.5M each for them, and at the time they did, both SS and SH had legs.

Literally less than the retail price of a single Be-4 engine for 2 platforms.

And on top of that, their hoists have found a new life as the Mechazilla hoists of the Cape and Boca launch towers - while I'm not sure if that adds up to 7 millions, it's definitely a large part of it

[CBase]

8 hours ago, darthgently said:

When the eventual goal is thousands of launches per year to Mars and elsewhere  with an additional suborbital hop industry (I'm skeptical on that last, but not the first)  that infrastructure isn't that far out. 

I imagine by that point it would be more an international project with lots of  nations having skin in the game than merely an Elon project.  I mean not even the Wright Bros imagined the current worldwide airport infrastructure and ATC network

Current downrange placement of the barge is ~300km from launch site. Even if it can be spread significant with a different profile, a ring around earth would require 20 or even more launch sites, some located far out on the ocean.

I didn't think so far ahead, but you are right, once we are a spacefaring civilization a closed network of launchsites makes sense. But for the next 5 or even 10 years Elon will need an intermediate solution to drive up space business with SS/SH.

[Exoscientist]

 Interesting article:

Quote

SpaceX rolls naked Starship prototype to test site. 

SHIP 26 JOINS SHIP 25 FOR PROOF TESTING. (NASASPACEFLIGHT - STARBASE LIVE)

By Eric Ralph

Posted on February 12, 2023

https://www.teslarati.com/spacex-rolls-naked-starship-prototype-to-test-site/

 

  Much web discussion is going on on space forums about the Starship version Ship 26. This surprised everyone in being a completely expendable format. It has no top or bottom flaps, heat shield, or legs. Since it is to be expendable it likely also has no ballast tanks. The most frequent speculation is its a test vehicle for orbital refueling. But it has no visible external connections for linking up to another Starship.

 The key clue is it’s moved to the suborbital launch pad. This means it can launch without the SuperHeavy booster. With 6 Raptor 2 engines it can launch fully fueled unlike the previous Starship test flights meant just to test landing.

 The key question: what is the dry mass of this expendable version without flaps, legs, heat shield, or ballast tanks? If you know that you can calculate how much payload it can lift to orbit in a single stage.

 Elon said the expendable version with only 3 engines might mass only 40 tons:

https://twitter.com/elonmusk/status/1111798912141017089?s=61&t=A46qVnS2GH4VVA-pQSUlkg

 Add another 5 tons for 3 more engines and this version might mass 45 tons. However, the increased thrust may require strengthening of the tanks which would increase the dry mass. On the other hand, this version would have to support far less payload atop it than the max 250 tons of the full two-stage so would need reduced tank strengthening.

  The argument can be made that just being moved to the suborbital launch pad does not mean it is going to be launched. It might be just used for pressure testing for example.

 However, the “Angry Astronaut” did a video from Boca Chica showing the Raptor work station being moved towards Ship 26:

https://www.youtube.com/live/MmUwHVji9b4

 He says that’s only done if you are installing engines on the Starship. You don’t do that if you are only doing pressure testing. He notes though that it could be putting engines either on S26 or S25. Probably we’ll know by the end of today which ship is having engines installed.

  Robert Clark

Edited February 15, 2023 by Exoscientist

[Beccab]

4 minutes ago, Exoscientist said:

The key clue is it’s moved to the suborbital launch pad. This means it can launch without the SuperHeavy booster. With 6 Raptor 2 engines it can launch fully fueled unlike the previous Starship test flights meant just to test landing.

Every ship was moved to the suborbital launchpads - S24 went there four times I believe, for instance. It's where they do cryo tests (before the cryo station was available) and static fires

[RCgothic]

I suspect S26 has multiple internal tanks.

SpaceX has a tech award from NASA for demonstrating the transfer of cryogenic propellant between tanks on a starship vehicle in orbit.

https://spaceflightnow.com/2020/10/16/nasa-selects-companies-to-demonstrate-in-space-refueling-and-propellant-depot-tech/#:~:text=An award to SpaceX worth,cargo to low Earth orbit.

S26 would be a logical tech demonstrator.

I believe it may also be an HLS milestone to do so.

In any case, SpaceX get a cheque from NASA if they send S26 to LEO and move some propellant around.

[Exoscientist]

21 minutes ago, Beccab said:

Every ship was moved to the suborbital launchpads - S24 went there four times I believe, for instance. It's where they do cryo tests (before the cryo station was available) and static fires

Thanks for that. I didn’t know you could do static fires there, which would need hold down clamps for example. I’ll be interested to find out if they’ll be installing 6 engines on it, as that is the current plan for an operational Starship. If yes, then it can do a launch fully fueled.

  Robert Clark

[Geonovast]

Overlapping threads have been merged.

[darthgently]

10 hours ago, CBase said:

Current downrange placement of the barge is ~300km from launch site. Even if it can be spread significant with a different profile, a ring around earth would require 20 or even more launch sites, some located far out on the ocean.

I didn't think so far ahead, but you are right, once we are a spacefaring civilization a closed network of launchsites makes sense. But for the next 5 or even 10 years Elon will need an intermediate solution to drive up space business with SS/SH.

Still, given what Shotwell states, the will be building bigger ocean platforms and that the goal is many of them as well as many landed.  Equatorial seems to follow

https://spacenews.com/spacex-drops-plans-to-covert-oil-rigs-into-launch-platforms/

[Nuke]

could the starship get to orbit with 4 vacuum engines when launched with superheavy? i keep getting this idea to replace the 3 sea level engines with a single vacuum engine. this configuration makes more sense for one way orbital insertions. say disposable starship, on orbit fuel depots, etc. 

[tater]

 

[sevenperforce]

8 hours ago, Exoscientist said:

The key clue is it’s moved to the suborbital launch pad. This means it can launch without the SuperHeavy booster. With 6 Raptor 2 engines it can launch fully fueled unlike the previous Starship test flights meant just to test landing.

Even with six engines, the T/W ratio of a fully-fueled Starship is barely more than 1:1 at sea level. There are 1200 tonnes of propellant plus 40 tonnes dry mass plus 5 tonnes for the three extra engines is 1245 tonnes. Each Raptor 2 can lift 230 tonnes, with the vacuum-optimized Raptors being overexpanded (and thus under-thrusty, around 213 tonnes thrust) at sea level, so 1329 tonnes of thrust, or a T/W ratio of just 1.06:1. Gravity drag will be huge. And that's without a fairing (which Ship 26 has) or payload. Also, keep in mind that what you say about lower tank mass probably already applies; Elon's 40 tonne number was aspirational

1 hour ago, Nuke said:

could the starship get to orbit with 4 vacuum engines when launched with superheavy? i keep getting this idea to replace the 3 sea level engines with a single vacuum engine. this configuration makes more sense for one way orbital insertions. say disposable starship, on orbit fuel depots, etc. 

I'm sure it could get to orbit, although unclear whether it would get to orbit with more or less payload.

A one-way or disposable Starship would have lower dry mass already because you don't need wings or a heat shield. Let's say 55 tonnes dry mass for the sake of this thought experiment. Let's say that a Starship with all six engines will fire all six together for the first half of the ascent and then fire only the vacuum engines for the second half of the ascent, leading to an average specific impulse of 372 seconds and a thrust at separation of 15.28 MN. Let's further say that your putative four-vacuum-engine Starship will fire all its engines for the whole ascent, leading to a constant specific impulse of 375 seconds and a constant thrust of 10.35 MN. In addition, the vacuum-engine Starship will have the same first stage characteristics but will have a second stage dry mass that is 3.2 tonnes lighter (52.8 tonnes).

Let's say that the dry mass of Superheavy is 300 tonnes and needs to reserve 25% of its propellant in order to do a RTLS boostback and landing. Even if these numbers aren't quite right, it won't matter because we're doing a comparative analysis.

Using these numbers, the Silverbird Astronautics calculator gives an estimated payload of 111 tonnes for the 4-engine Starship and a payload of 115 tonnes for the 6-engine Starship. So it looks like the gravity drag from not having all six engines would likely outweigh the advantage of lower dry mass and higher specific impulse. Slightly different booster numbers or dry mass numbers might reverse this, but in either case it's not going to be a very significant difference.

For a fuel depot, it doesn't really matter, because the depot isn't going to be moving around enough for its dry mass or average specific impulse to make a difference. For an ultra-high-dV one-way mission (like a flagship payload to the outer planets), gravity drag won't really be an issue because you're going to be refilling in LEO anyway. So you'll probably want to only use a three-engine or even a two-engine version in that event.

[tater]

29 minutes ago, sevenperforce said:

Let's say 55 tonnes dry mass for the sake of this thought experiment.

I had used 85 up thread. But using the claimed 250t payload with SH expended (which btw mirrors F9 numbers with a ~40% payload loss for RTLS) we'd have a 55t vehicle in LEO with 250t of residual props.

That's 6349 m/s dv. Lunar landing from LEO is nominally ballparked at 6300 m/s.

 

[sevenperforce]

11 minutes ago, tater said:

45 minutes ago, sevenperforce said:

Let's say 55 tonnes dry mass for the sake of this thought experiment.

I had used 85 up thread. But using the claimed 250t payload with SH expended (which btw mirrors F9 numbers with a ~40% payload loss for RTLS) we'd have a 55t vehicle in LEO with 250t of residual props.

That's 6349 m/s dv. Lunar landing from LEO is nominally ballparked at 6300 m/s.

85-90 tonnes is the generally-accepted figure for the bones-dry mass of the fully-reusable Starship. With reservation of deorbit and landing props the effective dry mass goes up to 115-120 tonnes. 

I was going with 55 tonnes in order to account for a chomper fairing (for an expendable version) or for insulation and extra tanks/systems (for a depot).

I tend to think that Elon's aspirational 40 tonne version would basically be balloon tanks. Not realistic for most applications.

[tater]

6 minutes ago, sevenperforce said:

85-90 tonnes is the generally-accepted figure for the bones-dry mass of the fully-reusable Starship. With reservation of deorbit and landing props the effective dry mass goes up to 115-120 tonnes. 

I was going with 55 tonnes in order to account for a chomper fairing (for an expendable version) or for insulation and extra tanks/systems (for a depot).

I tend to think that Elon's aspirational 40 tonne version would basically be balloon tanks. Not realistic for most applications.

But a non-reusable vehicle could test things all-up in 1 flight possibly.

[sevenperforce]

10 hours ago, Exoscientist said:

Much web discussion is going on on space forums about the Starship version Ship 26. This surprised everyone in being a completely expendable format. It has no top or bottom flaps, heat shield, or legs. Since it is to be expendable it likely also has no ballast tanks. The most frequent speculation is its a test vehicle for orbital refueling. But it has no visible external connections for linking up to another Starship.

 The key clue is it’s moved to the suborbital launch pad. This means it can launch without the SuperHeavy booster. With 6 Raptor 2 engines it can launch fully fueled unlike the previous Starship test flights meant just to test landing.

 The key question: what is the dry mass of this expendable version without flaps, legs, heat shield, or ballast tanks? If you know that you can calculate how much payload it can lift to orbit in a single stage.

One other note -- Ship 27 has no heat shield and has a functioning Starlink Pez dispenser, so it is generally expected to function as an expendable Starlink 2 demonstrator.

It will not, however, be launched as a single stage.

Also, no Starship has ballast tanks.

[tater]

 

[sevenperforce]

6 hours ago, tater said:

 

Here's what the current lift points look like:

No way they can insert a catch rod into that upper load point using the grabber arms precisely enough while it's hovering. They've gotta have some plan for a pop-out catch pin of some kind.

[magnemoe]

46 minutes ago, sevenperforce said:

Here's what the current lift points look like:

No way they can insert a catch rod into that upper load point using the grabber arms precisely enough while it's hovering. They've gotta have some plan for a pop-out catch pin of some kind.

I assume they will add an structure who is extended  or fold out to catch on, first plan was to use the upper flaps or flaps hinge but that will damage the tiles and might damage the  structure, the flaps will also move off center of later ships. 
 

[tater]

10 minutes ago, magnemoe said:

I assume they will add an structure who is extended  or fold out to catch on, first plan was to use the upper flaps or flaps hinge but that will damage the tiles and might damage the  structure, the flaps will also move off center of later ships. 

Yeah... I suppose if they can ever manage to catch a SH, they can catch a ship with the right added hardware, but it seems pretty nontrivial in either case.

[sevenperforce]

50 minutes ago, magnemoe said:

I assume they will add an structure who is extended  or fold out to catch on, first plan was to use the upper flaps or flaps hinge but that will damage the tiles and might damage the  structure, the flaps will also move off center of later ships. 

As long as the structure can be in a recessed position (like the current lift points) then presumably it will be safe enough from the re-entry plasma. The trick will be constructing a pop-out load structure that will give enough clearance between the tiles and the catching arms.

[tater]

 

Didn't realize there were 2 tomorrow.