totm nov 2023 SpaceX Discussion Thread

[sh1pman]

3 hours ago, sevenperforce said:

Not enough space or capability to really do anything other than go and return

So just like Orion then.

[RCgothic]

Apollo's command module had a pressurised volume of 10.4m3.

Crew dragon has a pressurised volume of 9.3m3.

That's only a 10% difference. With a proper service module it could get to the moon and back.

 

 

[zolotiyeruki]

A 10% reduction in pressurized volume represents a much larger reduction in *crew* space, though, since a bunch of the pressurized volume is occupied by equipment.

[mikegarrison]

Apollo's command module was already a really tight space to spend a week living in.

[zolotiyeruki]

Given technological advancements over the last half century, I imagine the equipment in Crew Dragon takes up a lot less space than Apollo's did

[kerbiloid]

6 minutes ago, zolotiyeruki said:

Given technological advancements over the last half century, I imagine the equipment in Crew Dragon takes up a lot less space than Apollo's did

Which equipment?

https://www.hq.nasa.gov/alsj/CSM06_Command_Module_Overview_pp39-52.pdf

Edited October 17, 2019 by kerbiloid

[tater]

Yeah, the usable volume is likely larger in Crew Dragon.

[Xd the great]

54 minutes ago, kerbiloid said:

Which equipment?

https://www.hq.nasa.gov/alsj/CSM06_Command_Module_Overview_pp39-52.pdf

Maybe a control panel?

[kerbiloid]

3 minutes ago, Xd the great said:

Maybe a control panel?

10 cm of thickness is gained...

Though, if have a watch at CST-100 cabin video... Not that it's much thinner. (from 03:00).

Spoiler

 

 

Edited October 17, 2019 by kerbiloid

[Thor Wotansen]

Well, if you do design a separate service module for Dragon to dock to to go around the Moon, you could always add in a cabin, I mean, you're already docking to it.  That way you wouldn't have to jeopardize the abort capabilities of the Dragon by loading the trunk with a full service module.

[sevenperforce]

47 minutes ago, Thor Wotansen said:

Well, if you do design a separate service module for Dragon to dock to to go around the Moon, you could always add in a cabin, I mean, you're already docking to it.  That way you wouldn't have to jeopardize the abort capabilities of the Dragon by loading the trunk with a full service module.

If you want the mission to DO anything other than just being in what is essentially a really really high elliptical orbit, you'd need it to be able to dock at the destination. You'd either have to have the cabin feature a docking port on the other end (requiring inline thrusters) or dispense with the cabin entirely and use a service module that docks inside the Dragon's trunk.

[CatastrophicFailure]

21 minutes ago, sevenperforce said:

If you want the mission to DO anything other than just being in what is essentially a really really high elliptical orbit, you'd need it to be able to dock at the destination. You'd either have to have the cabin feature a docking port on the other end (requiring inline thrusters) or dispense with the cabin entirely and use a service module that docks inside the Dragon's trunk.

Not that difficult to engineer, the Russians have done that for years ever since TKS. Maybe repurpose/rebuild a spare US station node. 
 

Actually, Dreamchaser uses exactly this design for its cargo module, contract them to build the SM/hab. Doesn’t need to be very large, after all.

 

[Nothalogh]

14 hours ago, RCgothic said:

That's only a 10% difference. With a proper service module it could get to the moon and back.

 

31 minutes ago, sevenperforce said:

You'd either have to have the cabin feature a docking port on the other end (requiring inline thrusters) or dispense with the cabin entirely and use a service module that docks inside the Dragon's trunk

Why not both?

Soyuz basically does this, and is a proven architecture

[sevenperforce]

3 minutes ago, Nothalogh said:

Why not both?

Soyuz basically does this, and is a proven architecture

If you do both then you have two different dockings, which is unpleasant in a sense but I suppose not fatal.

[Nothalogh]

1 minute ago, sevenperforce said:

two different dockings

The plug-in SM dock would not be any more of a dock than the one between the capsule and the trunk, as for the forward hab module you just dock to whatever you need to with it just like the Soyuz does

[magnemoe]

17 minutes ago, Nothalogh said:

 

Why not both?

Soyuz basically does this, and is a proven architecture

Soyuz is optimized for low weight, they have orbital module with an docking port. The orbital module can be ejected but then they can not dock. Soyuz also has an standard service module. 
Dragon is optimized to reuse. so it integrates all the expensive parts including the service module and abort system who shares fuel with the maneuver system into the craft. The trunk only hold solar panels, radiators and unpressurized cargo.
An standard idea is to put fuel tanks and an hypergolic vacum engine in the trunk for deep space missions. This can also draw from dragons internal tanks. 
 

[sevenperforce]

19 hours ago, Nothalogh said:

The plug-in SM dock would not be any more of a dock than the one between the capsule and the trunk, as for the forward hab module you just dock to whatever you need to with it just like the Soyuz does

You know, I was going to say that there is not enough volume to fit sufficient propellant into the trunk, but after doing a little digging it looks like there is a shocking amount of volume. Even if only half the quoted volume of the Dragon 2 trunk (37 cubic meters) was utilized, due to tank wall volume, helium COPVs, and potential added thrusters (it is easier to add additional Dracos than redesign the dragon claw to allow propellant transfer; right now it only provides electrical power and coolant), the high bulk density of NTO/MMH would permit 22 tonnes of added propellant. Assume 4 tonnes of additional dry mass for tankage, etc., and you end up with a whopping 2100 m/s of dV in the "service module" tanks alone.

Of course T/W would be lousy. With four forward Dracos, Dragon 2 had something like a fifteen-minute deorbit burn. You would need a vacuum-expanded SuperDraco, which would bump you up to 2200 m/s and get you to a T/W ratio of at least 0.25 gees (more as prop is expended; less if you downthrottle). That's more than enough dV to deliver significant cargo to the Gateway and return; not enough to enter and leave lunar orbit, though. And with a wet mass of 43 tonnes, you would need an expended-center-core Falcon Heavy just to get to LEO.

You could, however, expend a Falcon Heavy with a small orbital module a la Soyuz, dock it to the Dragon 2 with the FHUS still attached, then fire the FHUS once more for TLI.

Edited October 18, 2019 by sevenperforce

[tater]

 

[kerbiloid]

They should follow my old advice in the Contares mod thread and make a bicapsule ship, say Twin Dragon.
I prefer this way for multiseat capsule ships in KSP, so why they shouldn't?

Remove Superdracos, they are a heresy.

Make a reusable propulsion-instrumentation module out of the Dragon capsule.
Nozzles backwards (i.e. upwards on aerobraking), solar panels, antennas and sensors inside the former engine nacelles.

Then remove engines from the crew capsule. Except atmospheric RCS.

Only the crew capsule should be saved on abort. So, let it stay on top as is.

LES requires ~300 m/s.
Deorbiting from ISS/Mir altitude requires ~250 m/s.
I.e. both LES and deorbit engine require 300 m/s of delta-V.
You anyway need either LES or deorbit every flight.
So, combine LES with deorbit into LES/Deorbit engine.
Don't do like CST-100, use proper solid motor. It's less effective but more reliable.

So, put the crew capsule onto a solid LES/deorbit motor. It's ~3 t heavy for Dragon, so ~3 m³ of volume.
For the given capsule diameter 3.5 m, it would be less than a meter high ring below the capsule, with several powder charges and several nozzles along the ring.
Let the LES/deorbit nozzles stick out so when they ignite, they do this outside, not right under.

(They may even make a tunnel through the heatshields and LES to pass into the rear part of the ship, if they want. Like in Gemini for MOL, Soyuz-VI, TKS.
But this is not necessary, while anyway good. Because in this case they may have a room inside the service capsule, too.)

Put the rear, service capsule below the ship, heatshield up.
Put main fuel fuel tanks in the rear capsule.

Connect the "overturned" rear capsule with LES with an interstage truss.
Maybe cover the interstage with lightweight local shroud. Maybe put additional expendable fuel and/or water tanks inside the interstage, between the rear capsule and the LES/deorbit unit.

Feel free to enlarge the crew capsule inner volume by removing the nacelles and expanding the cabin (it anyway has proportions closer to Soyuz/Zarya rather than to CST-100/Orion), and anyway splashes.

Now you have an almost reusable bicapsule ship with greater volume, looking like a bee.

The LES/deorbit solid motor is expendable. It's used either to eject the crew capsule, or to deorbit.
So, it is not lost like on Apollo, Orion, Soyuz, etc, and doesn't carry additional liquid engines like in CST-100. It's always spent on purpose.
Also you don't have hypergolic fuel on landing anymore (that idea looks just insane, though rather spectacular, as we could see).

And it gives several deorbit options:

• deorbit whole ship with main engines, separate, jettison LES;
• deorbit whole ship with LES (you remember, the nozzles are sticking out), separate the ship;
• separate the ship, deorbit every capsule with available motors;

So, you splash two absolutely similar capsules per flight and save almost everything except the interstage truss and additinal low-pressure tank if any.

Of course, the ship gets for a couple of tonnes heavier, but is it a problem when the rocket is reusable?

To avoid high accelerations on deorbiting by LES, make it a toroidal pipe/gas chamber with several powder charges attached, between the nozzles.
In LES mode ignite them all at once, in deorbit mode one by one.

***

Additionally.
Make the capsule heatshield separable. Place the aerobraking RCS inside the heatshield, with nozzles up.
Separate the lower part of the capsule after aerobraking, like you separate heatshields in KSP.
Let the heatshield + RCS engines + RCS fuel tank land away from the capsule on a small parachute.

Let the landing legs (six of course, not 3 or 4) be under the capsule, and extend after the heatshieldpad is separated.
Don't pierce the heatshield with the legs. If you like piercing, better pierce it with a bottom hatch to get into the rear capsule in flight.

***

Additionally 2.

Use combined landing.
Put three drogue chutes instead of big ones, let the capsule be descending at 20 m/s speed. The chutes get much smaller.

At several tens of meters above the ground ignite solid landing motor under the ship, between the legs, jettison the chutes, and make your total velocity zero at 2 meters altitude.
Then rotate nozzles up, slowly land, and burn out the rest of the powder.

So, it can land on land and not overturn.

If the engines fail, don't jettison the chutes. The legs and the seats will dampen these 20 m/s, they have to have less than a meter of pistons stroke in total.

Edited October 18, 2019 by kerbiloid

[Nothalogh]

15 hours ago, sevenperforce said:

then fire the FHUS once more for TLI.

Precisely what I was thinking.

A MethaLox FHUS would be a real winner in this scenario.

Edited October 19, 2019 by Nothalogh

[sevenperforce]

6 hours ago, Nothalogh said:

Precisely what I was thinking.

A MethaLox FHUS would be a real winner in this scenario.

A methalox FHUS would either need to be stretched (which would push fineness ratio too high) or swollen (which would mess with aero loading on the side boosters) to be optimal. You'd have more thrust and less weight.

[tater]

 

[tater]

He was asked about payload, and the questioner said 150t to LEO, and he was not corrected.

Says regarding TPS that they will iterate and change as needed, not tied to any particular system. The goal is that they are easy to apply, too. He even said that for very high velocity entries they could add ablative to tiles (return from mars, as his example). He said in that case reuse (implying the tiles here) was not important if that's what it takes.

 

 

Other than Q&A fairly standard talk.

At 32:23 there is a pic of Starship on the Moon with how cargo is deployed, that's new.

[Terwin]

3 hours ago, tater said:

He was asked about payload, and the questioner said 150t to LEO, and he was not corrected.

There were also graphics early on that specifically said 150t as well as multiple statements about 150t to orbit, then refuel so you can take the same 150t to moon/mars

[tater]

20 minutes ago, Terwin said:

There were also graphics early on that specifically said 150t as well as multiple statements about 150t to orbit, then refuel so you can take the same 150t to moon/mars

They've also said "over 100t" (Elon), and the ship mass on the charts is too low (sort of by the difference). Ie: 150t+85t is 235t. 235-120t is 115t.

Dunno what it is.