totm dec 2023 Artemis Discussion Thread

[GuessingEveryDay]

7 hours ago, Beccab said:

God, yes please

It looks like the old Astrovan, but for offroading!

[sevenperforce]

Question. I know there are 16 booster separation motors that fire to pull the boosters away from the core, but are there any core separation motors to pull the core away from ICPS? Or does ICPS use propulsive hydrogen venting to separate itself?

ICPS doesn't fire its RL10-B2 at all until the coast to apogee.

[tater]

https://www.nasa.gov/sites/default/files/atoms/files/artemisi_missionavailability_may2022.pdf

 

[tater]

 

[Beccab]

What

[steve58]

Not sure if this has been posted anywhere (did a quick search, but came up zilch), but you can have your name included (for free) on a flash drive that will fly aboard Artemis I.

https://www.nasa.gov/send-your-name-with-artemis/

Edited May 17, 2022 by steve58

[Minmus Taster]

On 5/17/2022 at 10:30 AM, Beccab said:

What

Starship:

[SunlitZelkova]

 

[tater]

On 5/19/2022 at 3:20 PM, SunlitZelkova said:

 

"LOW LUNAR ORBITS
Circular or elliptical orbits close to the
surface; excellent for remote sensing,
difficult to maintain in gravity well.
» Orbit period: 2 hours"

Also excellent for SENDING HUMANS TO THE SURFACE THEN RENDEZVOUS AND DOCKING WHEN THEY RETURN.

For some inexplicable reason they leave that out. Oh, yeah, their garbage capsule can't do that.

There are legit reasons for using Lagrange orbits, but it's disingenuous to list pros and cons of orbits and have no cons to the orbit they were forced to choose due to dv constraints—which were entirely self-inflicted by not specifying what mass was needed to TLI to accomplish some minimum range of useful mission parameters.

 

Cons of NRHO:

1. More dv required for nominal surface operations

2. More mission complexity for surface operations

3. More complex abort contingencies due to phasing

 

Edited May 23, 2022 by tater

[Minmus Taster]

On 5/16/2022 at 3:39 PM, tater said:

https://www.nasa.gov/sites/default/files/atoms/files/artemisi_missionavailability_may2022.pdf

 

2023...

Edited May 19, 2022 by Minmus Taster

[steve9728]

Wait... 2023?????

Spoiler

 

[Piscator]

Just figuring out all the launch windows until 2023 doesn't mean they intend to launch in 2023.

[JoeSchmuckatelli]

6 hours ago, Piscator said:

Just figuring out all the launch windows until 2023 doesn't mean they intend to launch in 2023.

This is SLS we are talking about. 

The PDF likely shows all the dates SLS won't fly. 

[tater]

7 hours ago, Piscator said:

Just figuring out all the launch windows until 2023 doesn't mean they intend to launch in 2023.

True, the point is that it gives some idea of when opportunities exist. And it's more than the green dates on the calendar. SLS has to have the FTS installed, then it has 20 days to launch, or it must roll back to the VAB. Not sure how much time it takes upon rollout to get the vehicle ready at the pad—a day? Two? I would assume they roll out in advance of a launch window, then they have 20 days, after which back to the barn, the repeat.

A lot will depend on weather I think.

[Autochrome]

I'm just hoping that Artemis I launches sometime in the summer break so I can view it live instead of having to watch it as a recorded video after school.

Edited May 23, 2022 by Autochrome

[sevenperforce]

On 5/19/2022 at 5:20 PM, SunlitZelkova said:

 

NRHO is best described as the lunar equivalent of a sun-synchronous orbit (since precession keeps it oriented perpendicular to Earth, like the precession of a sun-synch orbit keeps it oriented perpendicular to Sol), but elliptical.

It does have the advantage of permitting very low-cost phase changes, which makes it useful as a gateway back to Earth entry interface or to deep space -- except that if you were already in a polar LLO, you could achieve the same utility by using an optimal three-burn maneuver: apoapsis raise burn, phase change burn at apoapsis, and Oberth ejection burn. Plus the Oberth savings from staging deep space missions from NRHO are not nearly as much as the Oberth savings from simply burning direct out of LEO.

NRHO is supposed to be super duper great for access to the lunar poles, but it really isn't. If your command module is in a polar orbit and your lander is at one of the poles, you can literally launch into a matched-phase trajectory at any time and get a fast transit to your command module. In contrast, fast transits to NRHO are only possible once every few days, and the added dV requirement on your ascent vehicle far outweighs the meager additional station-keeping that a command module would need if it just loitered in a polar LLO.

[tater]

Just now, sevenperforce said:

NRHO is supposed to be super duper great for access to the lunar poles, but it really isn't. If your command module is in a polar orbit and your lander is at one of the poles, you can literally launch into a matched-phase trajectory at any time and get a fast transit to your command module. In contrast, fast transits to NRHO are only possible once every few days, and the added dV requirement on your ascent vehicle far outweighs the meager additional station-keeping that a command module would need if it just loitered in a polar LLO.

And like everything else that involves the tyranny of the rocket equation, there are other things that then add mass. Say the ascent vehicle has been on the surface for the nominal full mission duration, they go to leave and there is a problem. They sort it out, but now their ideal launch window is gone. They can wait another 6.5 days (whatever it is), then try again—but they then have to have consumables aboard for that contingency (mass). Alternately, they could leave right away havin sorted the issue, but then they have to have props for phasing, and that will also take time, so also consumables (yet more mass). For a descent abort, they at least have the supplies, since they were gonna be on the surface for XX days, so not an issue, but it matters for edge cases and has to be planned for.

 

[sevenperforce]

6 minutes ago, tater said:

And like everything else that involves the tyranny of the rocket equation, there are other things that then add mass. Say the ascent vehicle has been on the surface for the nominal full mission duration, they go to leave and there is a problem. They sort it out, but now their ideal launch window is gone. They can wait another 6.5 days (whatever it is), then try again—but they then have to have consumables aboard for that contingency (mass).

The Constellation architecture itself, for which Orion was designed, was not optimal. The propellant you use for your lunar orbit insertion burn requires tanks; carrying those tanks down into the gravity well requires more propellant than merely leaving them in LLO (going from LLO to the lunar surface costs 1.87 km/s while going from LLO to Earth entry interface costs just 0.9 km/s). Constellation used the lander to perform the LOI burn because (a) it used more efficient cryogenics, and (b) giving Orion enough props to perform LOI for the entire stack would have made it too heavy to launch on Ares I.

A more optimal approach, with a Constellation architecture, would have been cryogenic drop tanks on the lander to supply props for LOI. Then you get hydrolox efficiency for your LOI burn but you don't have to carry those oversized empty tanks through 1.87 km/s down to the lunar surface.

[tater]

So much holdover from Constellation. Once committed to EOR at some level, why not go all in? I suppose back in the day the launch costs were high, so minimize launches. Once you have an architecture that involves extensive EOR <cough> LSS </cough> why not go all in, and assemble your moon ship(s) in LEO?

[tater]

Artemis IV Service Module frame:

 

[sevenperforce]

On 5/17/2022 at 12:21 PM, steve58 said:

Not sure if this has been posted anywhere (did a quick search, but came up zilch), but you can have your name included (for free) on a flash drive that will fly aboard Artemis I.

https://www.nasa.gov/send-your-name-with-artemis/

Just slapped all five of my kids’ names on it. 

[tater]

 

[tater]

 

[RCgothic]

Ouch. Follow-up to Artemis III likely delayed to 2028.

If I were NASA I'd be ordering more ICPS to make use of ML-1.

[Beccab]

4 minutes ago, RCgothic said:

If I were NASA I'd be ordering more ICPS to make use of ML-1.

Seriously, why wasn't this the plan from the beginning? Who thought "nah we don't need another ICPS for redundancy, everything will be fine. Shut it off"?