totm nov 2023 SpaceX Discussion Thread

[Ultimate Steve]

32 minutes ago, magnemoe said:

Why is half of the height of the trunk off limit and coned, yes they have stuff like radiators who I suspect its the cutoff on the lower overhead view. 

Might be the dome of the upper stage.

[Cuky]

5 hours ago, Rutabaga22 said:

What is the difference between the draco engine and the superdraco? Is one for abort and one for another thing?

SuperDraco are those 8 engines used for abort which were originally intended to be used for landing as well. Draco engines are all those RCS thrusters

Edited October 1, 2022 by Cuky

[magnemoe]

11 hours ago, Ultimate Steve said:

Might be the dome of the upper stage.

Obvious answer is obvious. 

[RCgothic]

11 hours ago, Rutabaga22 said:

What is the difference between the draco engine and the superdraco? Is one for abort and one for another thing?

They use the same fuel tanks, but Superdraco is *way* more powerful, isn't restartable, and the ISP isn't as good as Draco.

Superdraco: 71kN, 235s ISP 

Draco: 0.4kN, 300s ISP

[tater]

 

 

 

[wumpus]

7 hours ago, RCgothic said:

They use the same fuel tanks, but Superdraco is *way* more powerful, isn't restartable, and the ISP isn't as good as Draco.

Superdraco: 71kN, 235s ISP 

Draco: 0.4kN, 300s ISP

Note that Draco is optimized for vacuum, Superdraco  needs to operate in the atmosphere (and at low pressures as well), this may be a big reason in the difference in Isp.  No idea about superdraco not being restartable: being hypergolic, most of the issues are moot.  I'm guessing that it has turbopumps (couldn't find data), as it appears considerably more complicated than you would expect from a pressure fed engine.  Certainly it is designed to be reusable, the only reason they'd only bring enough fuel to start the turbopumps once is that it only fires for aborts: no need to fire it again.

[RCgothic]

The restartableness of Superdraco was connected to the valve that exploded I believe. IIRC the solution to that issue removed its ability to restart in flight.

[mikegarrison]

3 hours ago, RCgothic said:

The restartableness of Superdraco was connected to the valve that exploded I believe. IIRC the solution to that issue removed its ability to restart in flight.

It's nearly the same problem that the Starliner had. That dinitrogen tetroxide is nasty stuff and corrosive AF. It doesn't play nicely with valves.

SpaceX eventually got rid of the check valves by putting in burst panels, IIRC, so that really I think they have no way of shutting off the SuperDracos, much less restarting them. They are kind of one-time-use items.

Edited October 2, 2022 by mikegarrison

[tater]

 

[mikegarrison]

What they really need is to just put a ladder on the side of the Dragon and have one of the astronauts climb it while bumping their head on something. That's an infallible drive system that doesn't even require any fuel.

[tater]

 

[magnemoe]

5 hours ago, wumpus said:

Note that Draco is optimized for vacuum, Superdraco  needs to operate in the atmosphere (and at low pressures as well), this may be a big reason in the difference in Isp.  No idea about superdraco not being restartable: being hypergolic, most of the issues are moot.  I'm guessing that it has turbopumps (couldn't find data), as it appears considerably more complicated than you would expect from a pressure fed engine.  Certainly it is designed to be reusable, the only reason they'd only bring enough fuel to start the turbopumps once is that it only fires for aborts: no need to fire it again.

Superdraco is also optimized for trust, I find it very likely its nozzle is under size for the engine simply as an larger nozzle take up too much space inside the capsule. 
Engines are pressure feed and as other say they was intended to be restarable but this has been removed. 

[Elthy]

8 hours ago, tater said:

 

Do you have a tl:dw?

[Beccab]

Some info from Jared:

So, no additional fuel needed for the mission but the one in the Dragon tanks and the docking will happen backwards, with the tank. This allows the deorbit thrusters to be used to boost it and the crew of the capsule to come out of it from the usual docking hatch instead of modifying the ingress hatch for it. Also, in case anyone's curious, a possible working name for it is "Polaris Rising"

 

[Beccab]

How it should look probably (not my account, the Dragon hatch should be probably open while the Hubble cover should be closed)

Edited October 2, 2022 by Beccab

[CatastrophicFailure]

16 hours ago, mikegarrison said:

What they really need is to just put a ladder on the side of the Dragon and have one of the astronauts climb it while bumping their head on something. That's an infallible drive system that doesn't even require any fuel.

Do you want to summon the Kraken? Because that’s literally how you summon the Kraken…

maybe if it brings a Giant Meteor along too…

3 hours ago, Beccab said:

Also, in case anyone's curious, a possible working name for it is "Polaris Rising"

Better name: 

20 hours ago, RCgothic said:

The restartableness of Superdraco was connected to the valve that exploded I believe. IIRC the solution to that issue removed its ability to restart in flight.

I… don’t think so. And I don’t have much to back that up, but I could swear I saw a thing in the lead up to Demo 2 detailing the 8 or so abort modes that said otherwise. Some of the late-flight modes call for multiple SuperDrake burns, both prograde and retrograde to hit the right target. I think maybe that burst disc is just a replacement for the “master valve” that allows fuel into the system, there’s other valve down the line for actually controlling the engines. The aborts call for some pretty specific targeting, so they’ve gotta at least be able to stop the engines under control even if they can’t re-light them.  Anyways, here’s the best I could find. It does mention a “series” of SuperDrake burns during Mode 2a:

https://www.nasaspaceflight.com/2020/05/examining-crew-dragons-launch-abort-modes-and-splashdown-locations/

[magnemoe]

Hubble has an docking adapter, not sure its compatible with the dragon one, as in did not understood, but the docking adapter can be swapped out. 
Now you might put one inside the trunk but it has to telescope out so clear the trunk and you need to set it up to be able to dock. 
I say it might be easier to add extra detachable drako thrusters. If they have fuel lines into the trunk this gives an much easier option. 

[tater]

3 minutes ago, magnemoe said:

Hubble has an docking adapter, not sure its compatible with the dragon one, as in did not understood, but the docking adapter can be swapped out. 
Now you might put one inside the trunk but it has to telescope out so clear the trunk and you need to set it up to be able to dock. 
I say it might be easier to add extra detachable drako thrusters. If they have fuel lines into the trunk this gives an much easier option. 

Adding a telescoping mount inside trunk would be pretty easy.

[Beccab]

26 minutes ago, magnemoe said:

Hubble has an docking adapter, not sure its compatible with the dragon one, as in did not understood, but the docking adapter can be swapped out. 
Now you might put one inside the trunk but it has to telescope out so clear the trunk and you need to set it up to be able to dock. 
I say it might be easier to add extra detachable drako thrusters. If they have fuel lines into the trunk this gives an much easier option.

Jared himself said the opposite as i linked above, and the thing would be even harder than you make it: there are no thrusters and fuel lines at all in the trunk, which means you basically need an entirely new propulsion module. On top of that, docking nose first means you can't EVA with even more mods, as currently the docking tunnel is the only way in and out of a Dragon; if you want to avoid that you need further changes, allowing the ingress door to be used in space and suited up in a vacuum

[tater]

Busy day tomorrow.

10 hours:

 

20 hours:

 

[tater]

Dunno why they have Crew-5 up today, when it's on Wednesday. I was not paying attention last night when I posted.

[darthgently]

17 hours ago, Beccab said:

Jared himself said the opposite as i linked above, and the thing would be even harder than you make it: there are no thrusters and fuel lines at all in the trunk, which means you basically need an entirely new propulsion module. On top of that, docking nose first means you can't EVA with even more mods, as currently the docking tunnel is the only way in and out of a Dragon; if you want to avoid that you need further changes, allowing the ingress door to be used in space and suited up in a vacuum

A lot this docking  /  EVA via trunk also seems to skip the part that the heat shield can't easily have a passthrough in it, as noted above for fuel lines, but much less crew.  A side dock port, or even just a Gemini-ish hatch, on the capsule would still be really complicated at this point

[Beccab]

1 hour ago, darthgently said:

A lot this docking  /  EVA via trunk also seems to skip the part that the heat shield can't easily have a passthrough in it, as noted above for fuel lines, but much less crew.  A side dock port, or even just a Gemini-ish hatch, on the capsule would still be really complicated at this point

I mean, yeah? You seem to be under the impression that the astronauts need to reach Hubble's docking port - that is not the case. The port that the last STS mission mounted on it is not an access point or even a hatch, it's only usable to attach a spacecraft and stabilize it; Hubble's instrumentation and gyros can only be accessed from the sides, while the bottom of the telescope is mostly just where a Canadian can grab it or a capsule dock with it.

A service mission with either Orion (original proposal), dream chaser (2017 proposal) or Dragon (current proposal) would happen this way: after the spacecraft has connected with Hubble's port, an astronaut would always make a tethered EVA from it (in Dragon's case from the docking tunnel in the front, not in the back like you're suggesting), move to Hubble's bays on the sides, open them and replace/add what's necessary.

From a hardware standpoint, the service mission seems very feasible: as the EVA systems will already be tested by Polaris Dawn the main system that needs to be added is the rear docking port and the associated sensors. The main question marks are the cost and the astronaut stabilization system for a safe gyro replacement

[darthgently]

52 minutes ago, Beccab said:

I mean, yeah? You seem to be under the impression that the astronauts need to reach Hubble's docking port - that is not the case. The port that the last STS mission mounted on it is not an access point or even a hatch, it's only usable to attach a spacecraft and stabilize it; Hubble's instrumentation and gyros can only be accessed from the sides, while the bottom of the telescope is mostly just where a Canadian can grab it or a capsule dock with it.

A service mission with either Orion (original proposal), dream chaser (2017 proposal) or Dragon (current proposal) would happen this way: after the spacecraft has connected with Hubble's port, an astronaut would always make a tethered EVA from it (in Dragon's case from the docking tunnel in the front, not in the back like you're suggesting), move to Hubble's bays on the sides, open them and replace/add what's necessary.

From a hardware standpoint, the service mission seems very feasible: as the EVA systems will already be tested by Polaris Dawn the main system that needs to be added is the rear docking port and the associated sensors. The main question marks are the cost and the astronaut stabilization system for a safe gyro replacement

I thought I read previously in the thread about why not have an airlock in the trunk.  That is what I was referring to wrt crew passable.  I was lumping a lot into a relatively short post.  Mes culpa.  I'm very optimistic about possible solutions making Dragon do all kinds of duties.  The trunk offers a lot of possibilities

[Beccab]

5 minutes ago, darthgently said:

I thought I read previously in the thread about why not have an airlock in the trunk.  That is what I was referring to wrt crew passable.  I was lumping a lot into a relatively short post.  Mes culpa.  I'm very optimistic about possible solutions making Dragon do all kinds of duties.  The trunk offers a lot of possibilities

Oh, with "airlock in the trunk" you shouldn't think it as something like Spacelab with shuttle, but more as the Apollo Soyuz docking tunnel: Dragon would deploy it from the trunk, make a 180 degrees rotation and dock it with the docking port in the nose where it can be accessed. A problem with this is that the weight constraints in the trunk are much more severe in crew missions due to the aerodynamic forces during abort, but that is something that could be solved by attaching the payload to the ascent stage instead of the trunk (again like Apollo Soyuz and every crewed Saturn V launch)