New Release "Artemis 8" using Dragon

[francisdrake]

In 2020 Robert Zubrin made a proposal to use a Dragon capsule and the upper stage of an empty FalconHeavy, dock them in Earth orbit and send them to the Moon. TheSpaceReview

An unloaded FalconHeavy upper stage has ~3 ton of fuel remaining,. Enough the send the stack to the Moon, capture into Lunar orbit and finally perform the Trans Earth Injection, with the Dragon docked to it. Some improvements will be needed - adding a docking port the FalconHeavy, coping with Oxygen boil-off during the flight, strengthen the Dragon's heat shield - but it seems possible and might provide an easy space taxi to the Moon.
Will it work?

Installation:
Before trying this scenario, these addons shall be installed:
Falcon9 and FalconHeavy by BrianJ, Dragon DM-2 by Donamy, Felix24 and BrianJ.

Note: The cfg-file of the FalconHeavy f9h_star48 will be overwritten by adding a docking port to it. No other changes.

Flying:
When starting the scenario, the Falcon9 is the focus vessel, while the FalconHeavy is in the background.
Press 'V' to startup the Falcon9. Note: The countdown already displayed is for the FalconHeavy.

The FalconHeavy will launch a minute later, but will overtake the Falcon9 as it has much more power and carries no payload.
When in orbit, align the orbital planes and synchronize with the FalconHeavy upper stage for docking.
Then jettison the Dragon with 'J', switch to it and dock to the FalconHeavy within 3-4 orbits.

After docking, switch to the FalconHeavy. Perform the Lunar Orbit Insertion when reaching the dashed node line at the top of the orbit MFD.
Burn until the apoapsis is a little farther out than the Moon's orbit.

When approaching the Moon, perform a Lunar capture maneuver. Keep the Dragon attached. After enjoying the view for some orbits around the Moon, burn for the Trans Earth Injection. Switch to the Dragon, separate from the spent FalconHeavy upper stage and fine-tune the return trajectory with the Dragon's thrusters.

Thanks to BrianJ, Donamy and Felix24 for providing such great addons!
Have fun flying!

 

[Pioneer]

Makes too much sense. Will never be done. But otherwise a fun mission to fly!

 

[francisdrake]

By the way, as shown in the top left picture my 39B launchpad position is not quite correct. The access arm is floating in mid-air. Could someone point me to correct position?
I calculated it with POS -80.6208892 28.626934, but obviously, this is a little offset..

 

[BrianJ]

Hi,
cool Really nice to see interesting stuff being done with the Dragon and Falcons!
EDIT: I thought I had an answer for you, but I don't yet!
There's a "double launch" scenario in the FalconHeavy add-on, but that uses LC-39A and SLC-40.
I'll see what I can do for LC-39B ;-)

EDIT2: OK, here's my best shot at putting the FalconHeavy Strongback on the unmodified LC-39B pad.
Note: If you use the "ARMVIS 1" line, it hides the crew access arm.

Strongback:FalconHeavy/lc39a_strongback_h
  STATUS Landed Earth
  POS -80.6208650 28.6272240
  HEADING 0.00
  ALT 33.200
  AROT 61.696 4.478 8.249
  AFCMODE 7
  PRPLEVEL 0:1.000000
  THLEVEL 0:1.000000
  NAVFREQ 0 0
  ANM 0.0000 0.0000 0.0000 0.0000 1.0000
  STTS 0 0 2
  ARMVIS 1

 

[BrianJ]

Also...if you use the "LC39A SpaceX" add-on, and launch the Dragon from LC-39A, it'll probably look nicer.

 

[francisdrake]

Thank you Brian! The launcher on 39B is much better centered now.
I will also have look into the Double Launch scenario that comes with the FalconHeavy.

B.t.w.: Is there documentation available on the secrets of the scenario file of the Falcon?
(like SOPR -0.5061 200000.0 200000.0 65000.0 39559.0 NULL NULL NULL NULL)
I appreciate the launch control dialog, but would like to understand the parameters as well.

 

[BrianJ]

B.t.w.: Is there documentation available on the secrets of the scenario file of the Falcon?
(like SOPR -0.5061 200000.0 200000.0 65000.0 39559.0 NULL NULL NULL NULL)
I appreciate the launch control dialog, but would like to understand the parameters as well.

I really should include that, shouldn't I ;-)
Here's the FH scenario parameters, I'll have to do the boosters/core and Falcon9 another time:

FAIRS:
Fairing jettisoned 0,1
Booster/Core connection arms animation 0-1
EDL-Only mode(core) 0,1
EDL-Only mode(boosters) 0,1

SOST:
Boosters,Core jettisoned 0,1,2
Core Ascent Autopilot on/off 0,1
Core Ascent Autopilot function 0,1,2,3,4,5
Upper Stage Autopilot on/off 0,1
Upper Stage ignition switch 0,1
Timer (various uses) 0-infinity
Core Flyback-EDL Autopilot enabled/disabled 0,1
Boosters Flyback-EDL Autopilot enabled/disabled 0,1
Ascent Autopilot timed throttle control function 0,1,2,3

SOPR:
Target Orbit inc(radians);
Target Orbit Perigee (m)
Target Orbit Apogee (m)
Core Flyback Fuel Reserve (kg)
Boosters Flyback Fuel Reserve (kg)
Core MECO Apogee Target(m)
Core Flyback Target (name)
Port Booster Flyback Target (name)
Starboard Booster Flyback Target (name)

LTMR:
Target Orbit Insertion Alt.(m)
Core Fuel level (kg)
LiftOff Timer HH 00-23
LiftOff Timer MM 00-59
LiftOff Timer SS 00-59
LiftOff Timer function 0,1,2,3
Forward Light on/off 0,1
Acceleration Limiter (m/s)

TRTL:
Ascent Autopilot Core Throttle level 0-1
Ascent Autopilot Booster Throttle level 0-1

Cheers,
Brian

 

[francisdrake]

I really should include that, shouldn't I ;-)

Thank you for the scenario parameters! I agree, it wouldn't be too bad if they were included in the doc's of the FH and F9.

As a next step I will have look into the 'B' version of this concept, using a small propulsion stage (SPS), as proposed in the original story. This could be small hypergolic stage, relieving the Falcon upper stage from long-duty during coasting and orbiting the Moon.

Some time ago I made the attempt to integrate this propulsion stage into the Dragon's trunk, but this was quite complicated to do with the Dragon addon. The screenshot below shows it after jettison from the trunk. Still, for 'Artemis 8' I will rather use a conventional design, docked to the front docking port.

 

[francisdrake]

Made a simple SPS stage, but ran into a fundamental problem:
The SPS stage has an attachment point at the rear, and a docking point at the front.
But - it looks like - you cannot dock to an attached vessel ...
While it makes the docking sound, the docking wiggle and even marks the vessel as docked, it does not physically attach it to the parent vessel.
The Dragon keeps floating forward into the SPS and FH upperstage. This is an unexpected behavior.
-----
Edit: Added a zip-file called "Artemis 8-02" to the front post. It contains the SPS scenarios 1b and 2b.
For a quick tryout of the strange docking behavior use the 2b scenario.

 

[BrianJ]

Hi,
I'll give your SPS scenario a try BUT - I think this is a known Orbiter "bug".

Docking a vessel to a "child" vessel leads to strange behaviour.
I just verified this by attaching the ISS as a "child" of Carina, then docked a DeltaGlider to ISS - the DeltaGlider starts drifting through the docking port. I think the problem gets worse depending on location of docking port and rotation speed.

So I'm not sure I can give you a solution - a workaround might be to give the FH a docking port in its .cfg, then you would have to jettison the SPS and dock the FH to it immediately after.
Cheers,
Brian

 

[BrianJ]

Here's a scenario to test the "Docked to Child" bug.
Also includes .cfg's for Carina and ISS with appropriate attachment points added.
ISS(child) is attached to Carina(parent). DeltaGlider is ready to dock to ISS.
Find the "DG dock to ISS child test" scenario in the list, give the DG a little Forwards RCS to dock, accelerate time 10x to see effect clearly.

 

[Kyle]

Interesting concept. I wonder how they'd keep the propellant cool enough to last a long duration lunar trip.

 

[ChrisRowland]

How do the Apollo scenarios manage this? The Saturn 5 has a LEM, then a service module and capsule. The SM and capsule undocks, then docks with the LEM to extract it from the Saturn third stage on the way to the moon. Some of that lot must be docked or at least atached to the third stage at some point.

As for keeping cryogenic propellants cool does it take more than a sunshield? The temperature of space is about 3K.

 

[BrianJ]

I gave the Artemis 2b scenario a try - using the Dragon, the bug is much worse. Maybe something else going on there as well! I don't know if there is much hope for fixing it given the existing Orbiter bug, as I mentioned above.
But a fairly usable workaround is to give the SPS.cfg another rear-facing docking port:

0 0 -0.5   0  0 -1  0 1  0  590

Then just jettison the SPS before you want to dock the Dragon to it, it'll find the docking port on the FH no problem.
Works well for me.

 

[BrianJ]

How do the Apollo scenarios manage this? The Saturn 5 has a LEM, then a service module and capsule. The SM and capsule undocks, then docks with the LEM to extract it from the Saturn third stage on the way to the moon. Some of that lot must be docked or at least atached to the third stage at some point.

Hi Chris,
I don't know how the Apollo add-on does it. Docked-to-docked vessels are fine, but docked-to-child(attached) will eventually cause a problem with drifting out of position.

 

[BrianJ]

@francisdrake
Here's a scenario using the DeltaGlider instead of the Dragon, docking with the SPS+FH stack.
Exactly the same problem, so no point me looking at the Dragon to try and fix.
See "Artemis DG dock test" scenario in the list, DG will dock with SPS - and then keep drifting!

 

[francisdrake]

But a fairly usable workaround is to give the SPS.cfg another rear-facing docking port:

Thanks for having a look into it. This is a good workaround! I updated the zip file in the first post, mentioning the jettison to re-dock procedure and adjusting the docking scenario file accordingly.

The SPS mass is sized according to the figures mentioned in Zubrin's article. It is a little heavy. The Falcon upper stage cannot quite complete the Trans Lunar Injection. The SPS is required to finish the burn after undocking.

Still I think to use a hypergolic propulsion stage is more realistic. As Kyle mentioned, oxygen boil-off is an issue. While it is simple to keep the Falcon upper stage alive for a few Earth orbits, it would be much harder to do this for long coast and Lunar orbit times.

 

[Sbb1413]

I often believe that human-rated Falcon Heavy is impossible because the rocket is too shaky to be safe for human. But anyway, nice add-on.

 

[N_Molson]

I often believe that human-rated Falcon Heavy is impossible because the rocket is too shaky to be safe for human. But anyway, nice add-on.

Shouldn't be a problem there, because it is an EOR scenario. The TLI stage and the spacecraft meet and dock in Earth Orbit (like Gemini/Agena, but with more Dv).

 

[francisdrake]

Glad if you like it! As N_Molson wrote, man-rating the FalconHeavy is not required, as the crew launch is on a Falcon 9. Only the upper stage will have contact to the Dragon, and this stage is technically - as far as I know - identical to the Falcon 9 upper stage.

Still a lot of teaking would be required. For example the Dragon's docking port need to withstand the acceleration load during the upper stage burns. The scenarios were made to see if Zubrin's theory is plausible. Orbiter is a great tool simulate such missions.