totm nov 2023 SpaceX Discussion Thread

[tater]

2 hours ago, NFUN said:

Amazon was getting sued for violating fiduciary responsibilities for not buying SpaceX launches for Kuiper, so Bezos wouldn't've'd much of a say either way

Buying a few SpaceX launches is win-win for AMZN. They accelerate their progress (and they have a timer ticking with FCC), and get the regulators off their backs.

[sevenperforce]

On 12/3/2023 at 8:44 AM, darthgently said:

It would be interesting to have a fuel barge near the landing barge, put in just enough fuel into the landed booster to hop it back to Canaveral.  Super fast turnaround, bay-bee.

Hmm.

Sea level thrust of a single Merlin 1D is 845 kN, and only one row of three engines is restartable. Max thrust for liftoff is therefore 2.54 MN. They could add more TEA-TEB to accomplish more restarts, at a minor weight penalty. Assuming the need for a T/W ratio of at least 1.3, the landed stage could have a liftoff mass no greater than 199 tonnes. Assuming 24 tonnes for an empty booster, that allows 175 tonnes of propellant. However, thrust will be lower since the fuel barge won't be able to effectively subcool the propellants, so let's say it gets 150 tonnes.  That's a total Δv of 5.48 km/s, so definitely doable.

What would be more difficult would be strengthening the legs to increase their load-bearing capability by a factor of more than seven and redesigning them so they can fold back up on their own at liftoff.

Kinda pointless when you have to send the landing ship out and bring it back between launches anyway.

[darthgently]

2 hours ago, sevenperforce said:

Kinda pointless when you have to send the landing ship out and bring it back between launches anyway.

My first thought was an island landing pad with refuel support in the Caribbean area located in the most useful location for most launches.  But is is probably less expensive in fuel (considering chill overhead etc) to barge it back, so, yeah

[tater]

37 minutes ago, darthgently said:

My first thought was an island landing pad with refuel support in the Caribbean area located in the most useful location for most launches.  But is is probably less expensive in fuel (considering chill overhead etc) to barge it back, so, yeah

And what's the savings other than time (and that is assuming zero refurb)?

Hopping back has all the issues @sevenperforce mentioned, plus it requires possible check/refurb costs—and time. Maybe installation of a nose cone? Then more refurb back at the pad.

Also, wear and tear. Each such flight adds 2 flights to the total number of uses, with only half of the flights sending a payload. So if they turn out to be good for... 30 flights, you'd be burning half of them on hops.

[darthgently]

1 hour ago, tater said:

And what's the savings other than time (and that is assuming zero refurb)?

Hopping back has all the issues @sevenperforce mentioned, plus it requires possible check/refurb costs—and time. Maybe installation of a nose cone? Then more refurb back at the pad.

Also, wear and tear. Each such flight adds 2 flights to the total number of uses, with only half of the flights sending a payload. So if they turn out to be good for... 30 flights, you'd be burning half of them on hops.

Mostly it would be schweeet PR and internet video fodder

[tater]

2 minutes ago, darthgently said:

Mostly it would be schweeet PR and internet video fodder

It would need a payload on top as well to move the CM forward. if it were to fly grasshopper style it could not travel 100s of km.

[darthgently]

Another reason to hope IFT-3 makes orbit

 

... actually, careful reading of the slide in the post doesn't support the post's assertion that the attempt will necessarily occur during IFT-3.  But m going to hope anyway, because why not?

Edited December 5, 2023 by darthgently

[Spaceception]

IFT-3 will be a pretty big test, if they're going to attempt to complete a major milestone during the flight. Does it technically make it the first contracted flight of Starship, at least indirectly?

[Nuke]

you still need to get it to orbit without exploding. 

[magnemoe]

42 minutes ago, Nuke said:

you still need to get it to orbit without exploding. 

Yes, I would wait with that test until reaching orbit. 

[darthgently]

5 minutes ago, magnemoe said:

Yes, I would wait with that test until reaching orbit. 

It is amusing that mere orbit wasn't highlighted as the obvious milestone IFT-3 is straining toward before any other

[RCgothic]

1 hour ago, Spaceception said:

IFT-3 will be a pretty big test, if they're going to attempt to complete a major milestone during the flight. Does it technically make it the first contracted flight of Starship, at least indirectly?

Propellant transfer is a milestone, true, a really important one.

But demonstrating RVac apparently was a milestone as well, got there first on IFT-2.

[Spaceception]

1 hour ago, RCgothic said:

Propellant transfer is a milestone, true, a really important one.

But demonstrating RVac apparently was a milestone as well, got there first on IFT-2.

Oh, I meant something directly applicable to Artemis. Starship working (e.g. RVacs working) is more of a given for general operations. 

[sevenperforce]

41 minutes ago, Spaceception said:

Oh, I meant something directly applicable to Artemis. Starship working (e.g. RVacs working) is more of a given for general operations. 

Yeah, but also firing an RVac on a modern launch vehicle was definitely something. I don't believe we've clustered more than two engines of any appreciable size on an upper stage since the Saturn V, and the whole concept of a fixed-mount (that is, non-gimbaling) vacuum engine on an upper stage with separate full-size engines providing attitude control is pretty unique. We also haven't used vacuum-expanded regeneratively-cooled-nozzle engines in a vacuum...like, ever.

[Nuke]

im also not sure we have ever had a rocket explode twice in the same lauch before (excluding not missing the ground or secondary explosions on the ground). 

[Exoscientist]

25 minutes ago, Nuke said:

im also not sure we have ever had a rocket explode twice in the same lauch before (excluding not missing the ground or secondary explosions on the ground). 

 SpaceX still has not demonstrated the Raptor can be restarted in flight. In an attempt to restart the booster engines on the 2nd test flight, multiple engines failed with fires or explosions in the engine section:

 

But getting the Raptors to relight reliably in flight is essential  for their plans for reusability.

  Robert Clark

[Geonovast]

4 minutes ago, Exoscientist said:

SpaceX still has not demonstrated the Raptor can be restarted in flight

What did SN8, SN9, SN10, SN11, and SN15 use for their landing attempts, then?

[darthgently]

8 minutes ago, Exoscientist said:

 SpaceX still has not demonstrated the Raptor can be restarted in flight. In an attempt to restart the booster engines on the 2nd test flight, multiple engines failed with fires or explosions in the engine section:

 

But getting the Raptors to relight reliably in flight is essential  for their plans for reusability.

  Robert Clark

IFT-2 Raptor engines did relight successfully then failed quite a bit later (in rocket time scales) during extreme maneuvering after relighting.  You are kind of stuck on this for no logical reason I can grok

Edited December 5, 2023 by darthgently

[Exoscientist]

16 minutes ago, Geonovast said:

What did SN8, SN9, SN10, SN11, and SN15 use for their landing attempts, then?

 If you review the Starship landing tests, it has happened multiple times a Raptor engine has leaked fuel and caught fire. This was  only with one or at most 3 engines. Imagine this with 33 engines.

 

 I’m positing the Raptor is no more reliable now than on those landing tests on relights.

    Robert Clark

[Ultimate Steve]

All 33 don't need to restart, though, I think it is just the ring of 10. Current slightly educated speculation points to an issue with the dynamics of the fuel feed system and not with raptor itself. Some of the support for this is that one of the engines that stayed lit the whole time also failed. A review of the video shows that 9 of the 10 did reignite successfully, just something catastrophic happened over the next 20 seconds.

[darthgently]

11 minutes ago, Exoscientist said:

I’m positing the Raptor is no more reliable now than on those landing tests on relights.

You may want to figure in 33 raptors igniting fine and burning bright at near full throttle, under maximum load, for the entire stage 1 IFT-2 booster burn until shutdown at stage separation.  All evidence points to fuel supply issues, not engine issues, at this point

[Ultimate Steve]

3 minutes ago, darthgently said:

You may want to figure in 33 raptors igniting fine and burning bright at near full throttle, under maximum load, for the entire stage 1 IFT-2 booster burn until shutdown at stage separation.  All evidence points to fuel supply issues, not engine issues, at this point

The 33 don't count for this analysis, this is just about restarting in flight, which is a significantly different environment than ground start.

[darthgently]

8 minutes ago, Ultimate Steve said:

just something catastrophic happened over the next 20 seconds.

Like maybe a turbo pump centrifugally disintegrating when over-spinning in gas instead of liquid.  I'm even wondering if all that fuel sloshing forward couldn't have pulled a vacuum  at the pumps relative to the tank gas pressure.  Also imagine the impact and cavitation destruction when those over-spinning blades got into liquid again.  Like hitting a brick wall.

Edited December 5, 2023 by darthgently

[tater]

2 hours ago, Exoscientist said:

If you review the Starship landing tests

This is like pointing out failures of some version of Soyuz multiple versions back using engines that are no longer used.

[tater]

SpaceX will test relighting engines in flight by relighting engines in flight.