totm dec 2023 Artemis Discussion Thread

[jinnantonix]

9 hours ago, sevenperforce said:

But there's another solution. Use FH with triple-core-recovery to send only the lander and inboard tanks to LEO, then use FH with an expended center core to send the drop tanks to LEO. The lander can do transposition, docking & extraction with the first drop tank, then rotate and dock with the second drop tank, which can remain fixed to the FHUS for TLI, which it can do easily. 

I am pretty sure  NASA would pay a lot to avoid assembly of the Dynetics lander in orbit.  It's simple enough to do this in KSP, but IRL not so sure it is a mature process.  Any mistake that compromises the drop tank operation potentially threatens the lives of the astronauts during lunar descent.  NASA will prefer a solution that launches fully integrated.

Is a naked FH fully expendable to LEO insufficient to take a 27ton payload from LEO to NRHO?  I think it is based on my BOTE calcs, but I am no expert.

What about a FH side core reusable launching a lightweight transit vehicle to LEO? then partial TLI, with the transit vehicle completing the passage to NRHO.  That would be more fuel efficient.

Edited May 9, 2020 by jinnantonix

[RCgothic]

27t payload plus 4.5t F9US is 31.5t dry mass.

Wet mass is the above plus 64t propellant residuals, 95.5t.

At 311s that gets you 3380m/s.

TLI from 250km LEO is 3280m/s.

I'd call that extremely marginal.

[jinnantonix]

2 hours ago, RCgothic said:

27t payload plus 4.5t F9US is 31.5t dry mass.

Wet mass is the above plus 64t propellant residuals, 95.5t.

At 311s that gets you 3380m/s.

TLI from 250km LEO is 3280m/s.

I'd call that extremely marginal.

Thanks, but it is worse than marginal, it doesn't include the delta-V to get from TLI to NRHO.  It looks like assembly in orbit is the only option.

[RCgothic]

Even if F9 US had the DV to perform NRHO insertion it currently hasn't demonstrated the required 3 days endurance. Any margin beyond TLI would be wasted.

[jinnantonix]

1 minute ago, RCgothic said:

Even if F9 US had the DV to perform NRHO insertion it currently hasn't demonstrated the required 3 days endurance. Any margin beyond TLI would be wasted.

Yes, and the additional fuel needed to allow the Dynetics lander to execute TLI to NRHO is 5 tons, increasing the launch mass to 32 tons.

[RCgothic]

7 minutes ago, jinnantonix said:

Yes, and the additional fuel needed to allow the Dynetics lander to execute TLI to NRHO is 5 tons, increasing the launch mass to 32 tons.

However, LAUNCHED on a partially expendable FH, FH can boost a 32t payload into an elliptical orbit ~1350m/s past LEO. You'd require roughly 31t more fuel to go the remaining distance to TLI.

Good news! We've just demonstrated the ability to send 32t to that orbit. A second naked falcon heavy partially reusable would arrive at rendezvous with 32t of propellant. Just separate the lander and dock to the fresh upper stage. It can complete the burn.

Only 2 cores expended too!

Edited May 9, 2020 by RCgothic

[jinnantonix]

28 minutes ago, RCgothic said:

However, LAUNCHED on a partially expendable FH, FH can boost a 32t payload into an elliptical orbit ~1350m/s past LEO. You'd require roughly 31t more fuel to go the remaining distance to TLI.

Good news! We've just demonstrated the ability to send 32t to that orbit. A second naked falcon heavy partially reusable would arrive at rendezvous with 32t of propellant. Just separate the lander and dock to the fresh upper stage. It can complete the burn.

Only 2 cores expended too!

Hoorah for SpaceX.  ULA's Vulcan team must be wondering why they bother. 

 

[RCgothic]

The tricky bits are pad turnaround, launch window, endurance, and barge availability.

You can't launch two FHs in close succession:

There's only one TEL (although I'm sure SpaceX could solve that issue if there was need). So a day or two to re-mount the next FH.

Barges is harder. Assume at least a week to get the cores back and unloaded and out again.

Pad turnaround at 39A is probably a lesser limit than either of the above.

Launch window is a tricky one. You have to aim the elliptical orbit for where the moon will be at the time of the second TLI burn. If your second US only has the endurance for an immediate rendezvous and burn then if that second launch scrubs for any reason then you have to wait a month for the moon to come around again.

 

[jinnantonix]

30 minutes ago, RCgothic said:

The tricky bits are pad turnaround, launch window, endurance, and barge availability.

You can't launch two FHs in close succession:

There's only one TEL (although I'm sure SpaceX could solve that issue if there was need). So a day or two to re-mount the next FH.

Barges is harder. Assume at least a week to get the cores back and unloaded and out again.

Pad turnaround at 39A is probably a lesser limit than either of the above.

Launch window is a tricky one. You have to aim the elliptical orbit for where the moon will be at the time of the second TLI burn. If your second US only has the endurance for an immediate rendezvous and burn then if that second launch scrubs for any reason then you have to wait a month for the moon to come around again.

 

I think the initial launch can be 1 or 2 months ahead of the second.  

[tater]

Dunno what the impact is on cadence from FL, but the reason that SX got tapped for some of these was the extended fairing—which is combined with vertical payload integration in the SpaceX proposal. So they are making some other facilities at the launch site(s).

[sevenperforce]

14 hours ago, jinnantonix said:

I am pretty sure  NASA would pay a lot to avoid assembly of the Dynetics lander in orbit.  It's simple enough to do this in KSP, but IRL not so sure it is a mature process.  Any mistake that compromises the drop tank operation potentially threatens the lives of the astronauts during lunar descent.  NASA will prefer a solution that launches fully integrated.

I'm sure they would, but I think this is one of the things about the Dynetics lander that they said is a challenge. I am anticipating sacrificial elements if they do docked assembly. Basically, imagine mounting the docking port on top of a radial decoupler in the VAB, so the LOCV-critical bit is not the bit that is actually assembled on orbit. Doesn't matter if the docking connection is janky or gets stuck, because it is a one-way mate.

I haven't re-run all the maths but I am pretty sure you can do this with full reuse on the first mission and an expended core on the second. So only one expended core and no elliptical staging orbit. Possible as long as the lander has storables. 

Quote

Is a naked FH fully expendable to LEO insufficient to take a 27ton payload from LEO to NRHO?  I think it is based on my BOTE calcs, but I am no expert.

Definitely insufficient. Fully-expendable, Falcon Heavy can throw 26.7 tonnes to GTO (2.27 km/s past LEO). TLI is 3.2 km/s and NRHO is another 430 m/s. You can do some very low-dV three-body trajectories with multiple swingbys for 100 m/s but only if you use storables. It's just not possible.

Wait, I misread what you said. Yes, yes, 100% yes. A naked FHUS can do this without sneezing. You only need 61 tonnes of props to get from LEO to NRHO with a 27-tonne payload, and FHe can deliver a nearly 65-tonne monolith to LEO, so it can definitely reach LEO with more than 65 tonnes of residuals. @tater will snap at me for saying it can deliver a monolith but he hasn't shown maths and I have.

It probably could pull it off with side-core recovery.

14 hours ago, RCgothic said:

27t payload plus 4.5t F9US is 31.5t dry mass.

Wet mass is the above plus 64t propellant residuals, 95.5t.

At 311s that gets you 3380m/s.

TLI from 250km LEO is 3280m/s.

311s is the isp of the underexpanded SL Merlin 1D  burning in vac. The vac-optimized Merlin 1D pushes 348 seconds.

12 hours ago, jinnantonix said:

Thanks, but it is worse than marginal, it doesn't include the delta-V to get from TLI to NRHO.  It looks like assembly in orbit is the only option.

If the lander has storables it is easier to give it extra dV and let it do a long transit.

But yes, unless SLS is used, it will take SOME kind of orbital assembly.

4 hours ago, RCgothic said:

Even if F9 US had the DV to perform NRHO insertion it currently hasn't demonstrated the required 3 days endurance. Any margin beyond TLI would be wasted.

USSF-44 late this year will provide direct GEO insertion for a 4-tonne classified USAF payload, demonstrating operational endurance (they already did a delayed restart on the very first test flight). If they can do half a day they can do three days.

2 hours ago, RCgothic said:

Launch window is a tricky one. You have to aim the elliptical orbit for where the moon will be at the time of the second TLI burn. If your second US only has the endurance for an immediate rendezvous and burn then if that second launch scrubs for any reason then you have to wait a month for the moon to come around again.

Agreed. I think that we will not see elliptical staging orbits until Starship.

[RCgothic]

16 minutes ago, sevenperforce said:

311s is the isp of the underexpanded SL Merlin 1D  burning in vac. The vac-optimized Merlin 1D pushes 348 seconds.

Epic facepalm. Oops. Thanks for the correction.

[tater]

18 minutes ago, sevenperforce said:

Agreed. I think that we will not see elliptical staging orbits until Starship.

It was in their lunar SS proposal (now on topic in this thread to talk SS!) that they would have a tanker in LEO, right? Ie: 3 starships. One to LEO, top it off with a second, regular SS (fins/etc), lunar flies and is filled in one go from tanker.

Wonder if this is to avoid elliptical staging orbits? Phasing would be non-trivial for that.

From NASA:

Quote

Several Starships serve distinct purposes in enabling human landing missions, each based on the common Starship design. A propellant storage Starship will park in low-Earth orbit to be supplied by tanker Starships. The human-rated Starship will launch to the storage unit in Earth orbit, fuel up, and continue to lunar orbit.   

 

[RCgothic]

Decent article on the status of Artemis's constituent pieces. Praise for Bridenstine. His management of the lunar program has been deft.

I agree with one of the commentators - it seems like an actually competent person somehow managed to slip through an appointment process designed to weed such people out.

 

[jinnantonix]

On 5/10/2020 at 1:52 AM, sevenperforce said:

Definitely insufficient. Fully-expendable, Falcon Heavy can throw 26.7 tonnes to GTO (2.27 km/s past LEO). TLI is 3.2 km/s and NRHO is another 430 m/s. You can do some very low-dV three-body trajectories with multiple swingbys for 100 m/s but only if you use storables. It's just not possible.

Wait, I misread what you said. Yes, yes, 100% yes. A naked FHUS can do this without sneezing. You only need 61 tonnes of props to get from LEO to NRHO with a 27-tonne payload, and FHe can deliver a nearly 65-tonne monolith to LEO, so it can definitely reach LEO with more than 65 tonnes of residuals.

This is what I thought.  And it is great news, because it is a relatively low risk path, the ability to launch a fully integrated craft that can be deployed as an (initially) expendable lander at relatively low cost.

It is also interesting that the ULA Vulcan is (just) capable of launching the 27 ton Dynetics lander to LEO.  I am thinking that was was deliberate, to ensure ULA has a potential involvement in the launch.  NASA will love the competition for that initial launch.  

Quote

Praise for Bridenstine. His management of the lunar program has been deft.

Against all expectation it actually looks like the hardware for the lunar landing can be delivered.  The only issue I see that will prevent the 2024 human landing, is that the lander will not have been tested properly, and so will not be able to carry a human payload to the surface.  I would expect the first missions (Artemis 3 and 4) to be robotic, with humans remaining in orbit.

[tater]

 

[Barzon]

 

[RCgothic]

42 minutes ago, tater said:

 

Why this orbit?

[tater]

1 hour ago, RCgothic said:

Why this orbit?

Same reason as NRHO—it's someplace Orion can actually go to (and return from).

Also:

 

[sevenperforce]

10 minutes ago, RCgothic said:

Why this orbit?

Being only a very poor rocket scientist myself, I would nonetheless freely speculate that an elliptical coplanar posigrade orbit could be better because it lowers the dV requirements for the transfer, landing, and ascent stages between Orion and the poles. It's not a good spot for LOP-G because it has higher stationkeeping requirements than NRHO, but fine for a mission that only uses Orion.

[jinnantonix]

5 hours ago, tater said:

Same reason as NRHO—it's someplace Orion can actually go to (and return from).

Also:

 

So no transit vehicle.  The mission will rely on the LV's second stage for lunar orbit insertion.

[sevenperforce]

16 minutes ago, jinnantonix said:

So no transit vehicle.  The mission will rely on the LV's second stage for lunar orbit insertion.

It looks like it will rely on the PPE's SEP.

[jinnantonix]

2 minutes ago, sevenperforce said:

It looks like it will rely on the PPE's SEP.

Ah yes, I missed that.  270 days to "spiral out" to NRHO.  The minimal dV approach to NRHO.

[tater]

 

 

 

Part of what he said about that:

 

[sh1pman]

What "principles of safety in space" do these agreements establish? Safety from what, falling rocket stages?