totm nov 2023 SpaceX Discussion Thread

[tater]

 

[CatastrophicFailure]

3 hours ago, sevenperforce said:

The decoupler is attached directly to the base of the upper-stage tank and translated down; it has zero-force decoupling and is autostrutted to the Crew Dragon for stability. Staged decoupling is off.

Do you have the craft file posted anywhere? I need to pick it apart and discover it’s secrets. 

[tater]

 

[sevenperforce]

2 hours ago, magnemoe said:

This is a bit confusing, I tough Saturn 5 was more than 100 ton to LEO, yes part of this was 3rd stage use for lunar injection burn, 3rd stage also did the circulation burn into LEO.
It also launched Skylab. 

Often a vehicle's LEO payload is a matter of structural limitations and TWR. Skylab was 77 tonnes, which is what I have listed since it was the largest thing launched by Saturn V. As @tater pointed out, you can get a better idea of gross lift by including the final stage mass to LEO.

2 hours ago, magnemoe said:

Shuttle itself was not cargo although it was used as an short term space station for many missions but the dry mass for return should not count for it or starship. 

Hence the various column breakout.

 

2 hours ago, CatastrophicFailure said:

Do you have the craft file posted anywhere? I need to pick it apart and discover it’s secrets. 

I will post it tomorrow.

[CatastrophicFailure]

Quote

Rumors of my demise have been greatly exaggerated ...

—SN4, probably 

23 minutes ago, sevenperforce said:

will post it tomorrow.

Spoiler

 

[mikegarrison]

10 minutes ago, sevenperforce said:

Often a vehicle's LEO payload is a matter of structural limitations and TWR. Skylab was 77 tonnes, which is what I have listed since it was the largest thing launched by Saturn V. As @tater pointed out, you can get a better idea of gross lift by including the final stage mass to LEO.

It's almost like you guys are trying to work out whether a train or a ship is better for bringing cargo to Los Angeles. If the cargo is coming from Denver, then the ship isn't going to help you much, but if it's coming from Tokyo, the train is the one that won't work. Needs differ, and so the parameters of the problem are different.

If you just want to bring seven people to the ISS, Dragon or Starliner will be much cheaper than the Shuttle. If you want to send a crew to somewhere else in LEO and have them stay there for while they replace some instruments in a satellite, the Shuttle was your best choice. Saturn V was never used to launch anything other than Apollo and Skylab because there were no other missions that actually made much sense for it.

[wumpus]

15 minutes ago, mikegarrison said:

It's almost like you guys are trying to work out whether a train or a ship is better for bringing cargo to Los Angeles. If the cargo is coming from Denver, then the ship isn't going to help you much, but if it's coming from Tokyo, the train is the one that won't work. Needs differ, and so the parameters of the problem are different.

If you just want to bring seven people to the ISS, Dragon or Starliner will be much cheaper than the Shuttle. If you want to send a crew to somewhere else in LEO and have them stay there for while they replace some instruments in a satellite, the Shuttle was your best choice. Saturn V was never used to launch anything other than Apollo and Skylab because there were no other missions that actually made much sense for it.

While "If you want to send a crew to somewhere else in LEO and have them stay there for while they replace some instruments in a satellite, the Shuttle was your best choice" seems cut and pasted from a shuttle mission, it also seems reasonably similar to Gemini missions.  I suspect that even if the Shuttle was still available, NASA (or more likely Congress) would consider using commercial crew vehicles (although the Shuttle would still be vastly superior while in orbit).

That and it would probably require heavy modification to allow an airlock to let an astronaut out while wearing a modern space suit designed for satellite work.  Getting the cost of the modifications below a Shuttle launch may well be impossible (assuming one and only one mission.  Which is how way too many government contracts work).

[tater]

I’d say if you are in a parking orbit in LEO, your engines are off, and you have props left, the entire mass is one payload to LEO value, or arguably the entire mass minus the stage dry mass. I would call Apollo mass to orbit the mass of the SIVB, and everything on top (minus any spent props).

[tater]

45 minutes ago, mikegarrison said:

It's almost like you guys are trying to work out whether a train or a ship is better for bringing cargo to Los Angeles. If the cargo is coming from Denver, then the ship isn't going to help you much, but if it's coming from Tokyo, the train is the one that won't work. Needs differ, and so the parameters of the problem are different.

If you just want to bring seven people to the ISS, Dragon or Starliner will be much cheaper than the Shuttle. If you want to send a crew to somewhere else in LEO and have them stay there for while they replace some instruments in a satellite, the Shuttle was your best choice. Saturn V was never used to launch anything other than Apollo and Skylab because there were no other missions that actually made much sense for it.

We have a few possible missions going forward. ISS, cislunar, and I suppose satellite servicing could be a thing at some point if EVA from the commercial crew vehicles was a thing (or maybe a crew version of Dream Chaser at some point).

[YNM]

10 hours ago, lolkekov said:

Age is only a number

It can also be somewhat intentional - John Glenn, one of the Mercury astronauts, was later re-flown on the Space Shuttle in 1998.

3 hours ago, mikegarrison said:

If you want to send a crew to somewhere else in LEO and have them stay there for while they replace some instruments in a satellite, the Shuttle was your best choice.

I'm actually wondering how they'd launch new station modules into space for stuff like Artemis - will there be a common tug of sorts, in the same way Pirs/Poisk utilizing Progress, or like Zarya and Zvezda (being able to fly autonomously) ?

(Merged by Mod upon request)

Edited May 22, 2020 by YNM
thanks for the merge

[mikegarrison]

2 hours ago, wumpus said:

it would probably require heavy modification to allow an airlock to let an astronaut out while wearing a modern space suit designed for satellite work

Exactly. I had considered the airlock and MMU issues before I wrote that. The Canadarm was also an important tool for the shuttle when doing work like that.

[tater]

25 minutes ago, YNM said:

I'm actually wondering how they'd launch new station modules into space for stuff like Artemis - will there be a common tug of sorts, in the same way Pirs/Poisk utilizing Progress, or like Zarya and Zvezda (being able to fly autonomously) ?

They are going to announce the LV for the first 2 Gateway elements pretty soon. There are not too many possible choices. It's a direct launch with the PPE ding some of the work, no tug.

23 minutes ago, mikegarrison said:

Exactly. I had considered the airlock and MMU issues before I wrote that. The Canadarm was also an important tool for the shuttle when doing work like that.

The LV for that role might be New Glenn. It's supposed to be crew rated like Vulcan from the start.It has a huge mass to LEO, 45t. Seems like they could integrate a Starliner with a comanifested repair module. Module could have airlock and arm, plus power and propulsion (ion). Visit sat. Repair it. Change orbit. Leave repair module as a free floating station (it has power, etc), return to Earth. Maybe it can transition to a better orbit slowly to meet the next repair crew?

 

[YNM]

51 minutes ago, tater said:

It's a direct launch with the PPE ding some of the work, no tug.

Yeah, one thing sure is that an autonomous module would generally require connections that allows docking or at least berthing. Most of the USOS connectors doesn't allow this - hence they need to send it up in a shuttle and then do manual work for connecting the modules up. However I have to note that none of the currently available berthing and docking ports are anywhere as large as the fixed connectors they have on the USOS. There's also no way so far for one to dock / berth a truss structure, so stations built from autonomous modules definitely have to be of lower profile.

51 minutes ago, tater said:

Module could have airlock and arm, plus power and propulsion (ion). Visit sat. Repair it. Change orbit. Leave repair module as a free floating station (it has power, etc), return to Earth.

One thing that's been missing since the Shuttle is the capability to return whole crafts (modules / sats) back, although I wonder if such capabilities are ever required again...

Edited May 22, 2020 by YNM

[tater]

1 minute ago, YNM said:

One thing that's been missing since the Shuttle is the capability to return whole crafts (modules / sats) back, although I wonder if such capabilities are ever required again...

Well, we could probably use something to deorbit them...

[YNM]

Just now, tater said:

Well, we could probably use something to deorbit them...

Yeah but they wouldn't be in one piece...

[magnemoe]

4 hours ago, sevenperforce said:

Often a vehicle's LEO payload is a matter of structural limitations and TWR. Skylab was 77 tonnes, which is what I have listed since it was the largest thing launched by Saturn V. As @tater pointed out, you can get a better idea of gross lift by including the final stage mass to LEO.

This is true, has been questions about Falcon heavy could carry its theoretical expendable payload to LEO, a bit theoretical as its no planned missions for this. FH missions tend to be GTO or higher. 
Saturn 5 used 3rd stage for the last leg into LEO, think skylab used second stage to circulate this would reduce payload capasity.

[Ultimate Steve]

Not really a practical use for a shuttle like return vehicle, but an inspirational one. Return the ISS to Earth and reassemble it at a major museum or something. The Smithsonian comes to mind but that may be too america-centric.

[CatastrophicFailure]

This might have gotten buried back up-thread, but interesting read here about Crew Dragon’s abort modes. There’s actually eight of them, one on the pad and seven in flight, some of which involve retrograde burns of the SuperDracos in order to hit a certain splashdown target, and especially later in flight need the SD’s to be very precise for the same targets, it’s not all just “burn like hells til the tanks are empty.” And yes, there’s even a short abort-to-orbit window. That kind of control even in an abort is one advantage of liquid engines I suppose. 

[kerbiloid]

ISS would be assembled in a Space Biology Museum.
Micro. Biology.

Because it's probably already populated nearly like Mir was.

Edited May 22, 2020 by kerbiloid

[RealKerbal3x]

Completely random thought here, but I wonder if B1058 will be reused for an uncrewed CRS2 Dragon flight after DM-2, since NASA doesn't yet like the idea of crew flying on flight-proven boosters.

[magnemoe]

2 hours ago, CatastrophicFailure said:

This might have gotten buried back up-thread, but interesting read here about Crew Dragon’s abort modes. There’s actually eight of them, one on the pad and seven in flight, some of which involve retrograde burns of the SuperDracos in order to hit a certain splashdown target, and especially later in flight need the SD’s to be very precise for the same targets, it’s not all just “burn like hells til the tanks are empty.” And yes, there’s even a short abort-to-orbit window. That kind of control even in an abort is one advantage of liquid engines I suppose. 

Think the first stage aborts just burn the tanks dry but with second stage they are effectively in space and can do just a short burn to get away from the stage then orient to do an second burn to adjust the landing site so you don't splash down in the middle of Atlantic but at selected places. 
Lastly their ballistic trajectory will land them in Europe so they do an retro burn to land in sea. 
After this they burn to an low orbit and then deorbit. 

[sh1pman]

13 hours ago, sevenperforce said:

Here, I threw this together.

It’s still unclear to me how STS has more “Cargo to LEO (uncrewed)” than SLS Block1. Both drop the core stage before LEO, engines don’t count in both cases. Would SLS get more cargo to LEO if they removed upper stage completely?

Edited May 22, 2020 by sh1pman

[zolotiyeruki]

6 hours ago, Ultimate Steve said:

Not really a practical use for a shuttle like return vehicle, but an inspirational one. Return the ISS to Earth and reassemble it at a major museum or something. The Smithsonian comes to mind but that may be too america-centric.

Well, if SuperHeavy/Starship's launch costs get down to $2 million as Elon projects, I could certainly see using that for retrieving parts and pieces of the ISS.  It would make for one heck of a museum exhibit!

[tater]

2 hours ago, sh1pman said:

It’s still unclear to me how STS has more “Cargo to LEO (uncrewed)” than SLS Block1. Both drop the core stage before LEO, engines don’t count in both cases. Would SLS get more cargo to LEO if they removed upper stage completely?

There were proposed cargo variants of Shuttle (Shuttle C, Shuttle HLV) that made a cargo pod with SMRs on the back and put it where the Orbiter would go. The pod has fairings, and you can lift large cargoes on the order of 70-90t.

So for actual payloads, that's a better number. My point in general was that with a reusable vehicle, particularly a crew vehicle, the vehicle itself IS the payload. It was like @mikegarrison's point about satellite service, if that's the sort of thing you need to do, you need Shuttle (or something similarly capable). The Orbiter being a thing you need in LEO, that makes it a payload, not a container to take a payload. I suppose the other way would be a further deconstruction that calls the astronauts and their required gear to do some job the payload, and everything that keeps them alive, etc doesn't count. Food? Not payload, that's payload support, humans are the payload . Again, it's a tricky thing to compare, honestly.

So for comparing boosters or stage1/stage2 stacks, the total mass to LEO is a valuable tool for comparing them. If you have actual stand alone cargo, then the actual cargo capacity matters (what it can actually carry under the fairing or inside a cargo bay). Shuttle and SLS confuse things a little with the sustainer architecture since they burn the main engines virtually to orbit. Not always useful to compare them.

 

 

Edited May 22, 2020 by tater

[RCgothic]

Sensible. No potential for awkward headlines before DM2.