totm nov 2023 SpaceX Discussion Thread

[tater]

If sea states matter enough to allow SpaceX to scrub for booster landing (because band sea states for that are bad sea states for capsule aborts—they would scrub nominally for the capsule, just in case, not the booster), then wouldn't they also have to scrub for the same sea states all the way until "abort to orbit?"

 

Wonder where that is on the ground track...

[tater]

So if that's the ISS track, the sea state needs to be good until whatever point abort to orbit is on that line. Interesting that this one closely follows the US coast, making the most likely aborts really close to land...

[Spaceception]

A bit more minor, but SpaceX got a website redesign. https://www.spacex.com/

[sevenperforce]

18 hours ago, CatastrophicFailure said:

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

Here you go. Made a few tweaks.

https://drive.google.com/file/d/1wLD3sPMQ6aY8F-w4xywW2l5vNzVMv4Ak/view?usp=sharing

Should be downloadable by anyone. Readme in spoiler.

Spoiler

Highly recommend setting cheats menu to unbreakable joints as well as no crash damage, at least during launch. Once you are only dealing with the Crew Dragon it's not as bad. You'll obviously have to create your own crew.

Hack gravity to 0.01 during the vehicle lift. Wait for oscillations to damp, then turn gravity back to 1.0 to "settle" it on the pad. Even at the lowest possible traverse rate, you may want to raise incrementally to damp oscillations.

I forgot to change the traverse rate on the crew access arm. Right now if the crew climbs onto the crew access arm and you tell it to extend all the way, it slingshots them off the crew access tower. So do that slowly. There are no stairs so if you fall off the crew access tower you'll need to hack gravity and jetpack up.

Action group 1 to release the clamps at the top of Falcon 9 and initiate raise. As I said above, raise with caution.

Manually get the crew out of their observation room and onto the crew access arm and then extend it to board Crew Dragon. Manually fill all the tanks. Each of the large reservoirs in the crew access tower has enough props to fully fill four of the tank segments. I suggest going from the bottom up...both to match the real thing, and to keep oscillations to a minimum.

Spacebar to fire all engines; action group 2 to release launch clamps, open the payload arms, and tilt the TEL back. If you want to recover the first stage, hold radial-out until about 100 m/s and then start to tilt toward the east; once you are just barely tilted over then hold prograde.

Action group 8 to toggle RCS on the Crew Dragon, then R to turn on RCS, then action group 7 to cut S1 engines and stage. Spacebar to fire the engine once clear. Hold prograde, and switch back to your first stage. 

Action group 6 to turn three engines back on and deploy the grid fins. Get to retrograde and do your boostback burn. Once deployed, grid fins will automatically start providing control authority. They do not rotate as a whole (I was unable to tie the servo to pitch, yaw, and roll control) but the individual blades do turn.

G to deploy gear and click the Brakes icon (don't just tap B) to lock gear in place.  

Once target orbit is reached, spacebar to decouple Dragon 2 and action group 8 to toggle Crew Dragon's RCS. Action group 9 and 0 to open and close the nosecone.

The upper stage has tons of battery power and a fixed antenna, so it will survive on orbit on its own. Use RCS to turn it prograde and then use the propulsive vents around the engine to deorbit.

EDIT: I think I accidentally put the upper-stage engine with the lower stage when staging. You might wanna fix that.

Edited May 22, 2020 by sevenperforce

[sevenperforce]

15 hours ago, mikegarrison said:

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.

I am assuming Skylab would have been heavier if they'd had more margin. Who doesn't want extra payload?

If there is any indication of the Saturn V's max monolithic lift to LEO then I will adjust.

Actually it looks like the monolithic lift capability of Saturn V was 118 tonnes, so I made the adjustment.

14 hours ago, wumpus said:

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

If we were launching Hubble today and intended it to be serviceable with additional missions, it could launch with an IDA and a simple airlock. Then Starliner or Crew Dragon can do the work. Why launch an airlock and orbiting laboratory every single time if the airlock can just stay with the satellite?

14 hours ago, tater said:

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).

That's what I used in my table, which gives the Saturn V a gross mass to LEO of 154 tonnes, dwarfing SLS Block 1B and the Shuttle at 115 tonnes each. Note that SLS Block 1B and the Shuttle both have the same gross mass to orbit, if the Shuttle is launched fully loaded. It's amazing how inefficient SLS is.

Note that the Atlas that launched John Glenn actually has a mass-to-orbit lower than the gross mass of the capsule, since the capsule had to provide the final circularization burn. It is tricky to figure out what mass to use for the capsules/vehicles.

Dragon 2 will be the only vehicle capable of comanifesting cargo until Block 1B.

14 hours ago, tater said:

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).

Incidentally this is one area where Starliner is more capable than Dragon 2. Starliner can, theoretically, dock to a mobile airlock and move it somewhere since it has aft thrusters. Crew Dragon's only aft thrusters have major cosine losses.

5 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?

That was for the Shuttle-C configuration. It's italicized since it was never actually used.

Edited May 22, 2020 by sevenperforce

[magnemoe]

1 hour ago, tater said:

If sea states matter enough to allow SpaceX to scrub for booster landing (because band sea states for that are bad sea states for capsule aborts—they would scrub nominally for the capsule, just in case, not the booster), then wouldn't they also have to scrub for the same sea states all the way until "abort to orbit?"

 

Wonder where that is on the ground track...

As other pointed out, acceptable sea state for first stage landing is not very different from capsule parachuting down and is recovered. 
SpaceX has done high risk missions before as in never recovered an FH core. 

[tater]

28 minutes ago, sevenperforce said:

Incidentally this is one area where Starliner is more capable than Dragon 2. Starliner can, theoretically, dock to a mobile airlock and move it somewhere since it has aft thrusters. Crew Dragon's only aft thrusters have major cosine losses.

Yeah, this is true. I suppose a downside of the Starliner abort system is that as part of the SM, any rescale of the SM is non-trivial. Otherwise, creating an enhanced Starliner might be easier as most of increasing duration capability is just tankage. As it is, to improve the SM (say they could bump up TPS for cislunar), they would also have to increase the abort motors.

28 minutes ago, sevenperforce said:

Dragon 2 will be the only vehicle capable of comanifesting cargo until Block 1B.

Does anyone know if the abort system pulls the trunk with cargo off the stack, or is the attachment to trunk cargo severed upon abort?

This has implications for ever making the trunk into a SM. If abort can pull full cargo mass off the stack in addition to the capsule, then the whole truck can be used. Otherwise any SM would be self-contained within the trunk (and left behind on abort). Either way, Crew Dragon is easier to modify than Starliner in this regard.

Edited May 22, 2020 by tater

[sevenperforce]

10 minutes ago, tater said:

Yeah, this is true. I suppose a downside of the Starliner abort system is that as part of the SM, any rescale of the SM is non-trivial. Otherwise, creating an enhanced Starliner might be easier as most of increasing duration capability is just tankage. As it is, to improve the SM (say they could bump up TPS for cislunar), they would also have to increase the abort motors.

Does anyone know if the abort system pulls the trunk with cargo off the stack, or is the attachment to trunk cargo severed upon abort?

This has implications for ever making the trunk into a SM. If abort can pull full cargo mass off the stack in addition to the capsule, then the whole truck can be used. Otherwise any SM would be self-contained within the trunk (and left behind on abort). Either way, Crew Dragon is easier to modify than Starliner in this regard.

I had wondered that a long time ago and I looked around to figure it out but came up empty. I imagine they jettison. 

Abort can push something like 6 gees but it is limited to 3 or 4 gees in most aborts.

[tater]

4 minutes ago, sevenperforce said:

I had wondered that a long time ago and I looked around to figure it out but came up empty. I imagine they jettison.

Seems likely. So any BLEO Crew Dragon would need a SM that is effectively a stage unto itself, inside the trunk.

[RCgothic]

27 minutes ago, tater said:

Yeah, this is true. I suppose a downside of the Starliner abort system is that as part of the SM, any rescale of the SM is non-trivial. Otherwise, creating an enhanced Starliner might be easier as most of increasing duration capability is just tankage. As it is, to improve the SM (say they could bump up TPS for cislunar), they would also have to increase the abort motors.

Does anyone know if the abort system pulls the trunk with cargo off the stack, or is the attachment to trunk cargo severed upon abort?

This has implications for ever making the trunk into a SM. If abort can pull full cargo mass off the stack in addition to the capsule, then the whole truck can be used. Otherwise any SM would be self-contained within the trunk (and left behind on abort). Either way, Crew Dragon is easier to modify than Starliner in this regard.

Dragon2 pulls the entire trunk off. The fins on the trunk are for abort stability.

[tater]

5 minutes ago, RCgothic said:

Dragon2 pulls the entire trunk off. The fins on the trunk are for abort stability.

Yes. My question was about the cargo in the trunk, not the trunk itself.

trunk goes with capsule, does that include cargo attached to trunk, or is attachment severed.

[RCgothic]

1 minute ago, tater said:

Yes. My question was about the cargo in the trunk, not the trunk itself.

trunk goes with capsule, does that include cargo attached to trunk, or is attachment severed.

That doesn't sound likely. Effectively multiple auto-detatch operations and shifting cargo at the moment of abort. I'd be surprised.

Readiness review wrapping up. Suggestion is no showstoppers.

 

 

 

[sevenperforce]

17 minutes ago, tater said:

Seems likely. So any BLEO Crew Dragon would need a SM that is effectively a stage unto itself, inside the trunk.

It wouldn't be able to comanifest any sort of airlock or extended hab. I guess you could man-rate Falcon Heavy and put a hab on top, between the trunk and the top of S2, then do a transposition-and-docking a la Apollo, but that would mess with the OML.

4 minutes ago, RCgothic said:

7 minutes ago, tater said:

Yes. My question was about the cargo in the trunk, not the trunk itself.

trunk goes with capsule, does that include cargo attached to trunk, or is attachment severed.

That doesn't sound likely. Effectively multiple auto-detatch operations and shifting cargo at the moment of abort. I'd be surprised.

I think it likely depends on the release mechanism.

Ah, here's a pic:

Spoiler

Based on that, I reverse my original assessment. It looks like the release mechanism is specific to each individual piece of cargo. They wouldn't rely on the cargo to self-jettison. So cargo is likely pulled away with the trunk.

Of course SpaceX could easily enough design a trunk with a quick-release port inside.

[tater]

11 minutes ago, RCgothic said:

That doesn't sound likely. Effectively multiple auto-detatch operations and shifting cargo at the moment of abort. I'd be surprised.

Yeah, seems like increased complexity if the cargo was left behind. It's just been unclear, I never saw that testing included ballast to simulate cargo, for example. Also, few cargoes probably max out the capacity.

So if abort on Dragon can take the capsule and the total unpressurized cargo. Total cargo is 6000kg, so presumably some is inside (the crew/pressurized cargo), and that gives a sense of what a trunk as SM could be mass wise.

[RCgothic]

DM2 is certified for flight!

 

 

[tater]

8 minutes ago, sevenperforce said:

So cargo is likely pulled away with the trunk.

Agreed. Still, a "full" trunk as SM would use the full cargo capacity mass wise. It's not volume limited for hypergolics (~1075kg/m³ (based on Apollo LM propellant tank volumes)).

Wonder what volume of tanks you need for water, O₂, etc.? Trunk claims 37m³ total.

Here's a kooky idea (more distributed launch, and obviously assuming PICA-X can deal with EDL from the Moon):

Make a SM that is at the front of the trunk. Use as much mass as needed for everything not related to propulsion. FLy that on F9 to LEO.

At the back end of that ECLSS SM is a docking connector. Only needs to include electronic connections to the rest of the SM.

Take out old "naked" FH upper stage concept, and add a cargo to it. The cargo is a propulsion SM that docks to the back of the ECLSS SM inside the trunk. This loses some dv for the naked S2 since the residuals will be lower, but it allows more props in the SM. With ~12-13t of props (total mass ~25t?) Crew Dragon could have enough dv to do LOI, and TEI burns.

What were the residuals on naked FH again?

 

[RCgothic]

1 minute ago, tater said:

What were the residuals on naked FH again?

 

Estimated 64t expendable, 57.5t centre core expended side cores ASDS.

[tater]

 

32 minutes ago, RCgothic said:

Estimated 64t expendable, 57.5t centre core expended side cores ASDS.

So Crew Dragon with an add on SM can be sent to LLO FHe. D2+SM can do LOI, and TEI from there. Might be able to do it expending the side boosters, and landing the core.

(not that I think they will, but it's an interesting possibility)

Edited May 22, 2020 by tater

[kerbiloid]

Spoiler

If Canadarm grabs that canadarmian triple handle on the photo, it can wear the Dragon as a guignol puppet.

 

[tater]

 

[tater]

 

[sevenperforce]

43 minutes ago, tater said:

Here's a kooky idea (more distributed launch, and obviously assuming PICA-X can deal with EDL from the Moon):

Make a SM that is at the front of the trunk. Use as much mass as needed for everything not related to propulsion. FLy that on F9 to LEO.

At the back end of that ECLSS SM is a docking connector. Only needs to include electronic connections to the rest of the SM.

Take out old "naked" FH upper stage concept, and add a cargo to it. The cargo is a propulsion SM that docks to the back of the ECLSS SM inside the trunk. This loses some dv for the naked S2 since the residuals will be lower, but it allows more props in the SM. With ~12-13t of props (total mass ~25t?) Crew Dragon could have enough dv to do LOI, and TEI burns.

What were the residuals on naked FH again?

Crew Dragon already has enough onboard dV to do a return from NRHO though not from LLO.

Trouble is there's no way to get anything from the trunk into Dragon 2. Connection between the trunk and the capsule only transfers electricity and coolant, no water or ECLSS expendables. So it's not very useful.

I wonder if you could use a Dragon XL on FH. It can carry up to 5 tonnes of pressurized cargo to NRHO. If we suppose it carries the same propulsion unit as Dragon 2 minus the SuperDracos, that's 1.4 tonnes of propellant, which corresponds to 8.9 tonnes total mass (assuming 500 m/s of dV at 300 s) and therefore a dry mass of 2.5 tonnes, just slightly more than half the mass of Dragon 1 (which makes sense if you strip off the aeroshell, chutes, and heat shield). Sent up empty on a center-core-expended FH, Dragon XL would reach LEO with about 54 tonnes of residuals in the upper stage. Let's call it 50 for margin and boiloff. Send up a Dragon 2 outfitted for a lunar mission (packed internals and extra ECLSS), and dock the two in LEO, nose to nose. Total mass is 23.4 tonnes plus residuals. FH upper stage has nearly 4 km/s of dV, more than enough to push to TLI with an eyeballs-out burn.

Once on TLI, Dragon XL separates from FHUS. Total mass is 18.9 tonnes. Dragon XL provides extra living space for the coast to cislunar space and some insertion dV. Probably not enough though. I wonder if they could build a Dragon XXL with extra props.

[CatastrophicFailure]

3 hours ago, sevenperforce said:

Note that the Atlas that launched John Glenn actually has a mass-to-orbit lower than the gross mass of the capsule, since the capsule had to provide the final circularization burn. It is tricky to figure out what mass to use for the capsules/vehicles.

Wait, what? I thought the whole Atlas booster wound up in orbit, as Mercury capsules had no way of adjusting their own orbit (other than solid retros for deorbiting), only attitude control?

[sevenperforce]

Just now, CatastrophicFailure said:

Wait, what? I thought the whole Atlas booster wound up in orbit, as Mercury capsules had no way of adjusting their own orbit (other than solid retros for deorbiting), only attitude control?

The Atlas booster made it to orbit but rapidly decayed. The Mercury capsule had two solid motor packages, one for circularization and one for deorbit. The deorbit module had three different motors in case one failed.

[tater]