OHM Deep Space Crew Dragon

[Max-Q]

v2.0 is out.

• Added a HAB module in the trunk
• Minor MFD bugfix

 

[francisdrake]

I have to confess I missed out that the version v2.0 of the Deep Space Dragon was already based on the new DM2 (now Crew Dragon 2022) capsule. I flew some mission segments, including the Asteroid approach and it looks excellent!

This was also a test if the new Crew Dragon 2022 fully replaces its predecessor, and it does. No problems whatsoever.

When hovering close to the barren surface of the asteroid, two thoughts came to my mind:

• What the heck am I doing here? This is a pretty lonely place, far from home.
• I'd prefer to have more than one engine to rely on the return flight.

It might make sense to have more than one engine for deep space missions. Even airliners flying on long-range ETOPS routes must have two. Orion has a set of ATV-type thrusters as backup, if its AJ10 main engine fails.
Based on the organization of Dragons systems in quads, I would opt for 4 smaller engines for deep space propulsion.

 

[Max-Q]

I have to confess I missed out that the version v2.0 of the Deep Space Dragon was already based on the new DM2 (now Crew Dragon 2022) capsule. I flew some mission segments, including the Asteroid approach and it looks excellent!

This was also a test if the new Crew Dragon 2022 fully replaces its predecessor, and it does. No problems whatsoever.

Now I have a confession: I never tested if the Crew Dragon 2022 fully replaced the DM2 Dragon & Inspiration4 addons...
Glad to hear it works fine.
Did you find the VC viewpoint in the HAB? I labeled every storage locker down there by hand...

What the heck am I doing here? This is a pretty lonely place, far from home.

Exploration. That is what.

I'd prefer to have more than one engine to rely on the return flight.

It might make sense to have more than one engine for deep space missions. Even airliners flying on long-range ETOPS routes must have two. Orion has a set of ATV-type thrusters as backup, if its AJ10 main engine fails.
Based on the organization of Dragons systems in quads, I would opt for 4 smaller engines for deep space propulsion.

The trick here is that the trunk mounted SPS uses CTF as the oxidizer for this mission. CTF is a real beast to deal with, and any engine that uses the trunk fuel supply has to deal with it. It attacks anything remotely organic vigorously and runs at an extremely high chamber temperature.
I could look at adding 4 APS thrusters to the trunk like Orion has as a backup to the SPS, engineering challenges of dealing with 5 CTF thrusters instead of one aside. I will report back soon.
Something like this?

 

[francisdrake]

Hi, sorry for the late reply!
I think the Orion back-up thrusters use the same fuel source as the main engine. So if the main engine fails, nearly the same dV can be achieved, although at longer burn durations.

If the secondary propulsion system of a Deep Space Dragon uses different fuels, it might be difficult to come back to Earth in case the main thruster fails in mid-flight.

Thinking of options:

• The proposed 1 + 4 layout. May need to check the achievable dV with the back-up thrusters.
• Use Dragons nose thrusters as back-up. They are there anyhow, and might do the job.
• 2 or 4 smaller CTF engines. Smaller engines might be easier to design, and the loss of a single engine would not kill the mission.

 

[Max-Q]

I think the Orion back-up thrusters use the same fuel source as the main engine. So if the main engine fails, nearly the same dV can be achieved, although at longer burn durations.

If the secondary propulsion system of a Deep Space Dragon uses different fuels, it might be difficult to come back to Earth in case the main thruster fails in mid-flight.

The proposed 1 + 4 layout. May need to check the achievable dV with the back-up thrusters.

Exactly. Keep all the trunk prop system separate. The trunk uses CTF, while Dragon uses NTO. The 4 smaller APS thrusters would use the big fuel tanks in the trunk just like the main engine.
dV available from the APS would be basically the same, except maybe slightly less from lower ISP.

Use Dragons nose thrusters as back-up. They are there anyhow, and might do the job.

That would be great, except... The Dragon's prop system could never handle CTF, and even if it could, there are no prop lines from the trunk to the Dragon so a redesign of the umbilical would be in order. Even so, I don't really want CTF lines running anywhere close to the crew... Or to have CTF contaminated plumbing onboard for entry, splashdown, and recovery. Better to let all the CTF stuff burn up on entry.
If you've read the book "Ignition", I'm sure you understand why I don't want CTF anywhere close to much of anything!

2 or 4 smaller CTF engines. Smaller engines might be easier to design, and the loss of a single engine would not kill the mission.

That would be good except for the lunar lander mission, where I unfortunately need all that thrust for LOI with the lander docked.

I envision three thrust modes:

• SPS + 4 APS (for contingencies where a lot of thrust is needed fast)
• SPS only (large burns)
• 4 APS only (small burns or SPS failed)