totm dec 2023 Artemis Discussion Thread

[tater]

4 minutes ago, sevenperforce said:

This veers OT but I think there is still a societal expectation for a female displaying a suit to "model" it in a way that wouldn't be expected of a man. Not a NASA-specific thing or even something specific to Kristine; just how society functions.

It could also be a choice of behavior. I can buy as many clothes, shoes, whatever as I like... which is not very much. My wife, OTOH (who slices people up for a living, and is no shrinking violet), has more shoes right now than I have owned in my entire life, combined, including all those I will own in the future. She'd likely "model" stuff differently than I would, too. I don't now how much is nurture, and how much is nature.

Spoiler

I bought my daughter a wooden train when she was a baby (Brio), and she made the engines talk to each other (like Thomas, though having never seen that book or show). My son ended up with the Brio, plus Thomas, and having been read the books, and seen the show---he made the trains make train noises. <shrug> Got daughter nerd stuff, she liked prinsesses (then later, nerd stuff, so it worked out eventually )

 

Sort of related, because there will be an RS-25 there:

@sevenperforce, you're DC area, right?

[jinnantonix]

8 hours ago, sevenperforce said:

To be fair, it is confusing. The older mission specs have the transfer vehicle returning independently to LOP-G to be refueled by a logistics launch, while the newer mission specs have it smash itself into the moon. But it certainly will not stay in LLO. As he points out in the video, it would need to do a hella plane change, which it won't have the dV for.

Reusing the tug just doesn't make sense to me. Why send a refueling mission with tanks and an engine when you could just send a new tug?

In my simulation I assumed re-usable AV and TV (all the literature points to this as NASA's preferred option) and redocking in LLO with refuelling only at LOP-G using the ESPRIT module to allow multiple lunar landings with only the DV being expendable (remains on the lunar surface ala Apollo).  Technically it works, plane changing was not a big issue, although the craft did need a few days in flight to reach LOP-G, (I don’t have access to a super computer to time launches to the second to allow a minimal rendezvous time).  Also I have assumed a very small and probably unrealistic lightweight 2-man AV. 

I think it makes sense to have a re-usable AV that can travel from lunar surface to LOP-G, and an expendable descent vehicle with a drop tank.  The problem I am finding is that for a realistic AV mass, the whole craft requires 5 heavy launches (including SLS/Orion) for each lunar landing.  I don't think that is going to be commercially viable.

Edited October 15, 2019 by jinnantonix

[sevenperforce]

1 hour ago, tater said:

Sort of related, because there will be an RS-25 there:

@sevenperforce, you're DC area, right?

Sure am. Can't swing that though, unfortunately -- prior engagement.

14 minutes ago, jinnantonix said:

I think it makes sense to have a re-usable AV that can travel from lunar surface to LOP-G, and an expendable descent vehicle with a drop tank.  The problem I am finding is that for a realistic AV mass, the whole craft requires 5 heavy launches (including SLS/Orion) for each lunar landing.  I don't think that is going to be commercially viable.

This is why I propose using a reusable crew module that makes the trip from LLO to Gateway under RCS, and having a single-stage lander/ascender with drop tanks for the landing itself. I think I can get it down to one SLS launch and two commercial launches.

[jinnantonix]

17 minutes ago, sevenperforce said:

This is why I propose using a reusable crew module that makes the trip from LLO to Gateway under RCS, and having a single-stage lander/ascender with drop tanks for the landing itself. I think I can get it down to one SLS launch and two commercial launches.

I think this option would favour the exclusive use of lower cost SuperDRACO engines (expendable) and DRACO RCS thrusters (re-usable on the AV).

Perhaps for pressure vessel - a smaller lighter orbital/non-re-entry version of the Orion capsule, otherwise using identical electronics and facilities?

Edited October 15, 2019 by jinnantonix

[tater]

The LockMart lander designs I think all reuse the Orion pressure vessel and related ECLSS stuff. Of course that also makes whatever design it is incredibly expensive. I can't imagine a LockMart lander (all stages) coming in at any less than 2X the cost of Orion (marginal, not dev cost). Note that the 900 M$ Orion price tag doesn't include the SM at all, which is an in-kind contribution from ESA. 2B$/lander would probably be a bargain from LockMart, frankly.

That's where this all falls apart. I can't see the money happening.

[sevenperforce]

24 minutes ago, jinnantonix said:

I think this option would favour the exclusive use of lower cost SuperDRACO engines (expendable) and DRACO RCS thrusters (re-usable on the AV).

Perhaps for pressure vessel - a smaller lighter orbital/non-re-entry version of the Orion capsule, otherwise using identical electronics and facilities?

Yes, but the SuperDraco is rather thrusty. SuperDraco's 100% thrust is 71 kN, but that's highly underexpanded. With a proper engine bell, which is essential for efficiency, the SuperDraco would push at least 95 kN if not substantially higher. You probably can't downthrottle as far if the engine is properly expanded, but even if you could, SuperDraco's 20% minimum throttle would still be 18 kN.

If you have just a single SuperDraco directly under your CoM, then you can hover if you are landing above 11 tonnes, which is easy enough. But if you are doing balanced engines on the sides, you need to be landing at least 22 tonnes, which may be a bit much (remember that the landing stage is empty at touchdown). Hover is essential for hazard avoidance on landing. 

I wish we had a good idea about the mass of the thermal backshell and the main heat shield on Orion.

[jinnantonix]

1 hour ago, sevenperforce said:

Yes, but the SuperDraco is rather thrusty. SuperDraco's 100% thrust is 71 kN, but that's highly underexpanded. With a proper engine bell, which is essential for efficiency, the SuperDraco would push at least 95 kN if not substantially higher. You probably can't downthrottle as far if the engine is properly expanded, but even if you could, SuperDraco's 20% minimum throttle would still be 18 kN.

If you have just a single SuperDraco directly under your CoM, then you can hover if you are landing above 11 tonnes, which is easy enough. But if you are doing balanced engines on the sides, you need to be landing at least 22 tonnes, which may be a bit much (remember that the landing stage is empty at touchdown). Hover is essential for hazard avoidance on landing. 

I wish we had a good idea about the mass of the thermal backshell and the main heat shield on Orion.

I would suggest then 3 x SuperDRACOs inline.  The engines will be fired for LLO insertion (x3), then again for descent from LLO to surface.  At landing the outer engines are cut, and only the central engine is fired at 20% thrust with DRACO thrusters providing fine adjustment.  If the central engine fails or there is a problem with landing, aborting will involve firing the two outer engines to return directly to LLO. If either of the 2 outer engines fail, the central engine is used at full thrust to return to LLO.  These engines are ejected during ascent, just prior to reaching LLO so they will quickly degrade in orbit and impact lunar surface.  DRACO thrusters engines are used to complete LLO and go to NRHO for rendezvous with the LOP-G.  A new SuperDRACO engine set is delivered with each new descent stage, and replacement of any failed DRACO thrusters deployed by Canadarm at the LOP-G.

@tater obviously there is a reason the Orion is so expensive - it has a lot of redundant features for extended space flight for a relatively large crew.  Anything with a human rating is going to be tested and proved by R&D to the nth degree.  So a suitable human rated lander for 2 weeks deployment on the lunar surface, with all the necessary features, is going to be a costly beast regardless of who builds it.  Leveraging features already designed and tested for Orion is only going to help the bottom line.  Re-usability of the module will also assist.

SSTU Labs model of the Orion capsule estimates that a heavy heat shield with ablator = 796 sufficient for re-entry from lunar orbit, has a mass of 2.9 tons.  Their model for an Orion orbital craft (no chutes or heat shield) has a dry mass of 3.4 tons.

[tater]

9 minutes ago, jinnantonix said:

@tater obviously there is a reason the Orion is so expensive - it has a lot of redundant features for extended space flight for a relatively large crew.  Anything with a human rating is going to be tested and proved by R&D to the nth degree.  So a suitable human rated lander for 2 weeks deployment on the lunar surface, with all the necessary features, is going to be a costly beast regardless of who builds it.  Leveraging features already designed and tested for Orion is only going to help the bottom line.  Re-usability of the module will also assist.

It's expensive because of how is has been procured, plain and simple. LockMart would be doing a disservice to their shareholders if they didn't milk Congress for every penny then can possibly wring out of them. Any lander not procured on a fixed price contract will be a rip off.

[jinnantonix]

13 minutes ago, tater said:

It's expensive because of how is has been procured, plain and simple. LockMart would be doing a disservice to their shareholders if they didn't milk Congress for every penny then can possibly wring out of them. Any lander not procured on a fixed price contract will be a rip off.

Anything human rated is going to be expensive, obviously.  Fixed price is usually the most expensive means of procurement because the risk is entirely borne by the supplier, so there needs to be contingency built into the price.  Lockheed Martin designed their 100% re-usable lunar lander with an Orion pressure vessel for a reason - they must be thinking it will be overall commercially competitive compared to a craft with a brand new, purpose-built AV.  Consider the issue of testing, Orion with all its features is already nearly fully tested for human rating.  How much would it cost to build an alternative, and test it?  Using Orion would appear to be a no-brainer from a commercial perspective.  But is it too heavy?

[mikegarrison]

7 minutes ago, jinnantonix said:

Fixed price is usually the most expensive means of procurement because the risk is entirely borne by the supplier

Well....

Yeah, but in a competitive bidding situation that's taken care of. Suppliers who won't accept enough risk won't get the job.

It's not 100% simple either way, but fixed price is probably a better deal for the government than cost-plus.

[tater]

26 minutes ago, jinnantonix said:

Anything human rated is going to be expensive, obviously.  Fixed price is usually the most expensive means of procurement because the risk is entirely borne by the supplier, so there needs to be contingency built into the price.  Lockheed Martin designed their 100% re-usable lunar lander with an Orion pressure vessel for a reason - they must be thinking it will be overall commercially competitive compared to a craft with a brand new, purpose-built AV.  Consider the issue of testing, Orion with all its features is already nearly fully tested for human rating.  How much would it cost to build an alternative, and test it?  Using Orion would appear to be a no-brainer from a commercial perspective.  But is it too heavy?

Reusable is not a thing where propellants are supplied by expendable LVs (look up the thread). The LM reusable lander is hydrolox. That means a huge LV (just because volume for H₂). You then need to get props from LEO to the lander. Even the largest LV will take multiple flights with a great upper stage tanker (ACES?) just to fill the lander. All those stages are complete spacecraft that must be thrown away. They could try and refill one of those stages in LEO, in which case they might take fewer tanker flights to the Moon, but just as many LEO launches to refill the tanker. Fully reusable lunar landers make a lot of sense under two conditions:

1. They can be refilled locally, on the Moon from ISRU.

2. They can be refilled by a 100% reusable tanker system from where the propellants come (Earth).

3. Something like 2 for LEO, then a dedicated tanker of large capability that moves props to the Moon from LEO.

1 is a long time off, I think, and 2 is Starship (assuming it works) or any other 100% reusable LV. 3 is a combo of 2, and something more akin to a giant ACES.

[sevenperforce]

9 hours ago, jinnantonix said:

I would suggest then 3 x SuperDRACOs inline.  The engines will be fired for LLO insertion (x3), then again for descent from LLO to surface.  At landing the outer engines are cut, and only the central engine is fired at 20% thrust with DRACO thrusters providing fine adjustment.  If the central engine fails or there is a problem with landing, aborting will involve firing the two outer engines to return directly to LLO. If either of the 2 outer engines fail, the central engine is used at full thrust to return to LLO.

Placing them inline was my thought as well. Great redundancy, and with sufficient gimbal even a single surviving outer engine could thrust through the CoM. However, it clashes with the need for an airlock that is jettisoned on the surface. I'm not sure about sizing the engines, though. The sea level SuperDracos barely have any nozzle at all so they will be underexpanded and easily downthrottled. I wonder how big a proper nozzle would be.

Calculations suggest that the SuperDracos have an expansion ratio of 4.2 and an exit pressure of around three atmospheres, for a vacuum thrust of 73 kN and a sea level Isp of 235 s. Vacuum Isp is 242 s. With a chamber pressure of 1000 psi, SuperDraco should be good for up to 330 s if it had a proper engine bell (compare the RD-843, pressure-fed at 300 psi with a vacuum Isp of 315.5 s; AJ10, pressure-fed at up to 131 psi with a vacuum Isp of up to 319 s; peak theoretical propellant Isp of 341 s). Increasing Mach number by 37% with a propellant specific heat ratio of 1.225 requires a nozzle with just 10.9% greater area or an exit diameter of about 8.4 inches. Not nearly as large as I would have expected...I guess the ridiculously high chamber pressure helps with that.

With 15 degrees of gimbal, the engine cluster would fit in a 1.07 m x 0.43 m x 0.5 m box (L x W x H). Way more compact than I would have predicted.

Just trying to think, now, of an architecture where the airlock and landing legs can be jettisoned on the surface. Then again, if the airlock is sufficiently lightweight it's not a terrible burden.

Quote

These engines are ejected during ascent, just prior to reaching LLO so they will quickly degrade in orbit and impact lunar surface.  DRACO thrusters engines are used to complete LLO and go to NRHO for rendezvous with the LOP-G.  A new SuperDRACO engine set is delivered with each new descent stage, and replacement of any failed DRACO thrusters deployed by Canadarm at the LOP-G.

I agree on using Dracos to circularize in LLO, but I would say to drop the entire descent/ascent stage as a monolith (think dropping the external tank off the Shuttle). Replacing thrusters via Canadarm is not feasible, however. Any problems with the crew capsule would result in needing a new crew capsule.

Quote

SSTU Labs model of the Orion capsule estimates that a heavy heat shield with ablator = 796 sufficient for re-entry from lunar orbit, has a mass of 2.9 tons.  Their model for an Orion orbital craft (no chutes or heat shield) has a dry mass of 3.4 tons.

Orion also has a thermal backshell with a titanium honeycomb body, fiber tiles, and aluminum plating. No idea how much that weighs.

8 hours ago, jinnantonix said:

Consider the issue of testing, Orion with all its features is already nearly fully tested for human rating.  How much would it cost to build an alternative, and test it?  Using Orion would appear to be a no-brainer from a commercial perspective.  But is it too heavy?

Dragon 2 is lighter and is already plumbed with Dracos...just saying.

7 hours ago, tater said:

The LM reusable lander is hydrolox. That means a huge LV (just because volume for H₂). You then need to get props from LEO to the lander. Even the largest LV will take multiple flights with a great upper stage tanker (ACES?) just to fill the lander. All those stages are complete spacecraft that must be thrown away.

It is very telling that LM's reusable lander design assumes the creation of a solar-electric hydrolox-electrolysis depot to make their lander feasible.

But yes. Replaceable drop tanks are the only real reuse enabler at this point.

Edited October 16, 2019 by sevenperforce

[tater]

 

[sevenperforce]

11 hours ago, jinnantonix said:

I would suggest then 3 x SuperDRACOs inline.  The engines will be fired for LLO insertion (x3), then again for descent from LLO to surface.  At landing the outer engines are cut, and only the central engine is fired at 20% thrust with DRACO thrusters providing fine adjustment. 

It just occurred to me -- another advantage here is that you can give the central engine a shorter nozzle if needed to allow downthrottling without flow separation combustion instabilities, since you can use the other two engines for the high-efficiency burns.

Edited October 16, 2019 by sevenperforce
Fixed that -- thanks Ultimate

[Ultimate Steve]

1 minute ago, sevenperforce said:

It just occurred to me -- another advantage here is that you can give the central engine a shorter nozzle if needed to allow downthrottling without flow separation, since you can use the other two engines for the high-efficiency burns.

Isn't flow separation only really a thing in the atmosphere or have I misunderstood it the whole time?

[sevenperforce]

1 hour ago, Ultimate Steve said:

Isn't flow separation only really a thing in the atmosphere or have I misunderstood it the whole time?

Good catch. Not flow separation so much as combustion instabilities.

Flow separation and combustion instabilities can both happen if you downthrottle too low, but outside of atmo it is only combustion instabilities.

[mikegarrison]

2 hours ago, Ultimate Steve said:

Isn't flow separation only really a thing in the atmosphere or have I misunderstood it the whole time?

No, actually. Take an extreme case of a "nozzle" that is a flat disk, so the angle of the nozzle is 180 degrees. The flow will separate from this nozzle even in vacuum. It just has too much momentum to allow it to turn the corner and stay attached to the wall. (The Coanda effect comes in to play here and will help some of the flow reattach to the wall.)

For a nozzle with a reasonable angle of divergence, then the situation changes and the flow will stay attached until the adverse pressure gradient gets to be too large for the flow momentum to sustain. This is where the ambient pressure comes in to play, because it the case of a diverging nozzle the ambient pressure is part of the adverse pressure gradient.

 

[Mitchz95]

This was already posted in the SpaceX thread, but it's relevant here...

 

[Ultimate Steve]

 

*Loud sigh*

They likely wouldn't have made the 2024 date but I would rather have them try for an aggressive date and miss it than try for a realistic date and have the risk of it having to pass through another presidential administration.

I'm pretty sure that this isn't for sure though. It might just be talking at this point.

 

I swear, though... If I have to wait 9 years for this to happen...

[Retro Starship]

Wow great topic about Artemis!  Excellent utubes, pics and info! I hope this happens very soon as well! Will follow this one, very interesting.

[jinnantonix]

10 hours ago, sevenperforce said:

Just trying to think, now, of an architecture where the airlock and landing legs can be jettisoned on the surface. Then again, if the airlock is sufficiently lightweight it's not a terrible burden.

I would have thought that building a lightweight airlock internal to the Orion made sense, since it is very roomy and likely there will be only 2 crew for lunar landings.

 

Quote

I agree on using Dracos to circularize in LLO, but I would say to drop the entire descent/ascent stage as a monolith (think dropping the external tank off the Shuttle). 

I have been thinking that for greatest efficiency, the craft would leave behind the fuel tanks associated with the descent phase on the surface (like Apollo).  Unlike Apollo it would jettison the engines and fuel tank prior to reaching LLO, and have one remaining integrated fuel tank for feeding the thrusters with enough fuel to reach NRHO.

Quote

Orion also has a thermal backshell with a titanium honeycomb body, fiber tiles, and aluminum plating. No idea how much that weighs.D

Interesting.  If it is feasible to reduce the mass by removing re-entry components, each kg saved makes a big difference to the size of the completed craft.  I am proceeding with an assumed lander mass of 4.0 tons.

 

Quote

Dragon 2 is lighter and is already plumbed with Dracos...just saying.

Good point.  However my understanding is the Dragon2 is more massive even than Orion.  Not sure what the mass is with all the re-entry components stripped away.

 

Quote

It is very telling that LM's reusable lander design assumes the creation of a solar-electric hydrolox-electrolysis depot to make their lander feasible.

It's obvious that the big cost is getting (I calculate) over 26 tons of propellant to the LOP-G per mission.  In the absence of ZBO, delivering storable fuels is expensive.

 

Edited October 17, 2019 by jinnantonix

[jinnantonix]

Here is the suggested lunar lander model, including 3 inline Super DRACO engines, Orion pressure vessel with ladder and RTG and additional DRACO thrusters for improved acceleration and redundancy.

Ascent vehicle.  The Orion pressure vessel upper stage is re-usable and is able to transit from LLO to NRHO using only DRACO thrusters.  The upper stage has a wet mass of 4.6 tons (excluding crew and logistics) so could be launched on a Falcon 9 or Vulcan, and transit autonomously to the LOP-G utilising its DRACO thrusters.  Since it is re-usable, only one launch is required across the Artemis program.

Ascent vehicle launching from the lunar surface after separation from the descent stage.

 

Lander stage 2 is full expendable.  Comprises:

• 4 x drop tanks which are jettisoned after the LOP-G to LLO transit
• 4 x fuel tanks with lander legs for the descent from LLO to lunar surface
• 1 x Ascent vehicle tank with 3 x SuperDRACO engines  

This craft has a wet mass of 31 tons but may be launched (partially fueled) comanifested with the crewed Orion on the SLS, docking directly with the Ascent Vehicle upper stage at the LOP-G

 

Modified Cygnus type refueller able to transit autonomously to the LOP-G, dock and utilise the ESPRIT module to deliver up to 10 tons of payload, including logistics and hypergolic propellant.  Two refuelling / reprovisioning missions using a Falcon Heavy LV  is required per lunar landing mission.

Edited October 17, 2019 by jinnantonix

[jinnantonix]

On 10/16/2019 at 10:44 AM, sevenperforce said:

Yes, but the SuperDraco is rather thrusty. SuperDraco's 100% thrust is 71 kN, but that's highly underexpanded. With a proper engine bell, which is essential for efficiency, the SuperDraco would push at least 95 kN if not substantially higher. You probably can't downthrottle as far if the engine is properly expanded, but even if you could, SuperDraco's 20% minimum throttle would still be 18 kN.

I tested the model above landing from LLO.  The descent stage mass is about 17 tons at touchdown, so the single central SuperDRACO at about 80% thrust hovers nicely, and allows the thrusters to be used to maintain altitude, and adjust laterally to avoid obstacles at the LZ.  I reckon the 80% thrust limiter could be preset prior to launch from Earth.

[jinnantonix]

On 10/17/2019 at 12:17 AM, sevenperforce said:

Orion also has a thermal backshell with a titanium honeycomb body, fiber tiles, and aluminum plating. No idea how much that weighs.

Some details around manufacturing here:  http://spaceflight101.com/spacecraft/orion/

"Installed around the pressure vessel and its various external systems are composite backshell panels with titanium honeycomb cores that provide primary thermal control to the spacecraft as well as micro-meteoroid orbital debris (MMOD) protection using laminate panels. A total of 49 composite panels make up Orion’s outer shell with additional thermal protection layers installed on top. A total of 970 TUFI coated AETB-8 thermal tiles with Space Shuttle heritage are installed on Orion’s backshell to protect the internal equipment from heating during re-entry. These tiles consist of silica glass fibers and have excellent thermal characteristics.

The forward bay is protected by a dedicated cover also using composite materials (see section on Orion’s parachutes). In the aft section, Orion’s core structure interfaces with the Heat Shield Support Structure consisting of a titanium skeleton that holds the heat shield.

To withstand re-entry heating of up to 2,800 degrees Celsius when returning from Mars, the Orion spacecraft is equipped with the world’s most powerful heat shield which also is the largest ever built with a diameter of just over five meters.

The heat shield uses a titanium skeleton that provides the interface points with the crew module and adds strength to the heat shield required for it to withstand the impact with the water at splashdown. The skeleton is held in place by six brackets on the CM aft bulkhead. Fitted atop the skeleton is a carbon fiber skin that provides additional strength and acts as mounting surface for the AVCOAT ablative heat shield material. This structure consists of one center, 18 gore and 18 shoulder panels."

 

Seems to me there is a lot of room for reducing the lander capsule mass by redesigning the outer shell minus the load bearing and heat resistant components.  THere is no requirement for chutes nor any of the associated systems.  Items like seats could be removed entirely, like Apollo the crew remain in an upright "standing" position during landing, ascent and craft acceleration. 

Some mass is added for the airlock and RTG and perhaps additional materials for sleeping in lunar gravity.

 

Edited October 20, 2019 by jinnantonix

[tater]