totm dec 2023 Artemis Discussion Thread

[jadebenn]

On 11/11/2019 at 4:13 PM, jinnantonix said:

Anything else, and the craft won't fit in the FH standard fairing.  Which is the whole problem with the Boeing lander.

Pardon me for the confusion, but why are you trying to fit the Boeing lander in a FH fairing anyway?

[sevenperforce]

1 hour ago, tater said:

Bottom left is interesting. Stacked vertically in fairing, lands horizontally.

I just realized that possibility.

There are some really, really cool ways to try and do that. Particularly if two engines are used for descent but only one for ascent.

19 minutes ago, jadebenn said:

Pardon me for the confusion, but why are you trying to fit the Boeing lander in a FH fairing anyway?

The Boeing solution is to use a cargo SLS launch, which is inestimably stupid and generally regrettable. The Boeing lander could be easily sent to TLI using distributed launch -- send it up on Vulcan or Atlas V or New Glenn or Falcon Heavy; boost it to TLI with a naked FHe -- but it won't fit in any commercial fairing.

[sh1pman]

43 minutes ago, sevenperforce said:

The Boeing solution is to use a cargo SLS launch, which is inestimably stupid and generally regrettable. The Boeing lander could be easily sent to TLI using distributed launch -- send it up on Vulcan or Atlas V or New Glenn or Falcon Heavy; boost it to TLI with a naked FHe -- but it won't fit in any commercial fairing.

Even in New Glenn fairing? if not, then surely paying Blue Origin to make a bigger fairing must be a cheaper option compared to, well, the SLS option.

[jinnantonix]

20 hours ago, sevenperforce said:

Progress can transfer nitrogen tetroxide, UMDH, and pressurant into Zvezda via connectors in its non-androgynous SSVP docking ring. The US's NDS is planned to someday have this capability, though it does not at present. In any case, this type of transfer capability is likely not high-flow enough to enable the kind of architecture we're discussing. On the other hand, what we need is simpler than the SSVP, in a sense, because we do not need to transfer pressurant independent of propellant. The tank that would couple to the crew module would contain its own pressurant and simply force fuel and oxidizer at high back pressure through one-way ports into the RCS piping of the crew module.

It would only make sense to have the connector also serve as the structural mating point for the tank. The tank itself can be very "dumb" with all the valves controlled within the capsule's RCS. 

High flow isn't really a problem in my view.  The capsule has it's own propellant tank.  The external drop tank need only trickle feed the internal tank, which then provides the high flow propellent.  And how "high flow" are these thrusters anyway? 

Quote

The Altair lander solved this by having a separate airlock module mounted offset, parallel to the ascent module, to be left on the surface. Of course that was only enabled by the prodigious 10-meter fairing on Ares V, which is out of the question here.

Remember that the crew module does not necessarily need to go in the fairing. It's fine to launch it separately. We might have to eschew plans to include a Cygnus, but that's okay.

  I am reluctant to exclude the capsule and the Cygnus because they can provide a single solution for the avionics and communications equipment.  Launching without adds more problems than this airlock design solves.  But lets just say we were to exclude - the problem is that the lander ends up being really tall, and this creates stability issues.

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What about using an off-axis docking port? I am envisioning a docking port that mates to the ascent stage, but also includes an access tunnel to a lower-stage airlock that sits next to the engine. That tunnel is severed with electric bolts (frangible as backup) before ascent. Balance the weight of the airlock on one side with downmass capability on the other, and mount the ascent tanks perpendicular.

Tried that, it gets in the way of the drop tanks and lander legs.  Also adds a stupid amount of complexity and risk of catastrophic failure.  

Spoiler

Extremely noisy catastrophe on Mars

 

And noting we don't need a huge 6-man airlock, as they seem to think is necessary in Hollywood.   We just need enough room for two EVA suits, and some wriggle room for the crew to get in and out of the suits and exit/enter the hatch (one at a time).  I am sure this can be built (and thoroughly tested) best as an internal airlock.  OK, it's going to be a tight fit for the crew, but this is not a joy ride.  

And then there is the option of depressurising the whole capsule, and removing the airlock issue entirely.  The Apollo missions all did it successfully, though not sure it's ideal for a 2 week surface mission.

Quote

You don't have to do all the modeling. Just post the wet and dry masses of the ascent stage and the drop tanks and I will do the math to figure out what it could reasonably drop onto the surface from TLI.

That's the starting point for my modelling.  I am working on it now.  According to my numbers, this design and with single OMS and drop tanks is more efficient than I originally thought.  The below calculations assume 2.7 tonne crew re-usable capsule. 

EDIT: There is 1.0 t of down mass capability.

Stage	Req dV	Wet mass	Dry mass	ISP	dV	Comment
NRHO-LLO	730	31.187	23.159	319	930.4	Tanks are emptied before drop +
LLO-Surf	1620	21.936	13.072	319	1618.3	Drop at 2km altitude
LLO-Surf	250	12.972	11.987	319	246.9	Final 2km descent, incl 1.0t downmass
Surf-LLO	1870	8.905	4.841	319	1905.4	Drop legs and downmass *
LLO-NRHO	730	4.012	2.982	260	756.0

+ Includes normal burn for aligning with landing zone

* Prior to circularising into LLO, the AV will need to do a normal burn to align with the orbital plane of the LOP-G

Note:  Modelling this in KSP is difficult because of the low thrust of the OMS engine.  It is very difficult to calculate the lunar landing.  

Edited November 13, 2019 by jinnantonix

[sevenperforce]

13 hours ago, sh1pman said:

Even in New Glenn fairing? if not, then surely paying Blue Origin to make a bigger fairing must be a cheaper option compared to, well, the SLS option.

The Boeing lander appears to fill out the whole volume of the SLS Block 1b payload fairing pretty thoroughly.

9 hours ago, jinnantonix said:

High flow isn't really a problem in my view.  The capsule has it's own propellant tank.  The external drop tank need only trickle feed the internal tank, which then provides the high flow propellent.  And how "high flow" are these thrusters anyway? 

Ah, see, this is a critical difference. I was going to have the capsule without any internal propellant reserves, fed only from the pressed drop tank.

The trouble with pressure-fed thrusters is the pressurant. The SSVP docking port that Progress uses to mate with Zvezda has three different lines to allow transfer of fuel, oxidizer, and pressurant, because the propellant won't move without the pressurant to push it. But that makes things quite complex, because you have to have two liquid lines and one gas line, all at different pressures, and you have to have an internal system on the receiving tankage to vent existing pressurant in the propellant tanks and valve off the pressurant while it is being filled, and so forth. You probably need a separate nitrogen tank to purge. If you run your pressurant through a regenerative cooling loop, that adds more complication. I don't even know how ullage is handled.

I thought it would be simpler, all things being equal, to dispense with the internal tank altogether and simply plumb the reaction control system thrusters to a two-line port for the drop tank to mate with. That way the pressurant never has to transfer; it's merely used to push the fuel and oxidizer out of the drop tank and into those lines through the port. One-way flow, no ullage problems.

If we do trickle propellant transfer into internal tanks, however, a lot of things change. There is no inline drop tank. The crew capsule's fuel, oxidizer, and pressurant tanks would be refilled from excess capacity in the transfer drop tanks while still connected to LOP-G. 

10 hours ago, jinnantonix said:

And noting we don't need a huge 6-man airlock, as they seem to think is necessary in Hollywood.   We just need enough room for two EVA suits, and some wriggle room for the crew to get in and out of the suits and exit/enter the hatch (one at a time).  I am sure this can be built (and thoroughly tested) best as an internal airlock.  OK, it's going to be a tight fit for the crew, but this is not a joy ride.  

And then there is the option of depressurising the whole capsule, and removing the airlock issue entirely.  The Apollo missions all did it successfully, though not sure it's ideal for a 2 week surface mission.

Depressurizing the whole capsule is definitely not a good option.

What we most need is extra volume. Volume is not always heavy. This is another reason why doing the crew capsule launch independent of the lander is helpful. You can launch a very lightweight but very large (4+ m diameter, 6+ m long) module vertically on Falcon 9 to TLI, but then have it mate to LOP-G and to the lander horizontally. 

11 hours ago, jinnantonix said:

According to my numbers, this design and with single OMS and drop tanks is more efficient than I originally thought.  The below calculations assume 2.7 tonne crew re-usable capsule. 

EDIT: There is 1.0 t of down mass capability.

Stage	Req dV	Wet mass	Dry mass	ISP	dV	Comment
NRHO-LLO	730	31.187	23.159	319	930.4	Tanks are emptied before drop +
LLO-Surf	1620	21.936	13.072	319	1618.3	Drop at 2km altitude
LLO-Surf	250	12.972	11.987	319	246.9	Final 2km descent, incl 1.0t downmass
Surf-LLO	1870	8.905	4.841	319	1905.4	Drop legs and downmass *
LLO-NRHO	730	4.012	2.982	260	756.0

I will try to run some numbers and see how it works. One note -- if the capsule is being used for significant dV, the R4-D is a better choice for the RCS thrusters, and they get 312 s. Also, I would propose giving 100-300 m/s of dV to the capsule so that it circularizes while the lander crashes; that will help with the overall efficiency as well.

11 hours ago, jinnantonix said:

+ Includes normal burn for aligning with landing zone

* Prior to circularising into LLO, the AV will need to do a normal burn to align with the orbital plane of the LOP-G

I don't think either of these are necessary. The departure burns from NRHO are optimized for proper planar insertion, and the ascent burn is timed to coincide with return to NRHO. That's the nice thing about polar landing sites.

[tater]

https://oig.nasa.gov/docs/MC-2019.pdf

Pretty general doc about NASA projects and issues. 34 B$ so far on Orion/SLS, expected to exceed 50 B$ by 2024.

[sh1pman]

2 hours ago, tater said:

https://oig.nasa.gov/docs/MC-2019.pdf

Pretty general doc about NASA projects and issues. 34 B$ so far on Orion/SLS, expected to exceed 50 B$ by 2024

50 billion, jeez. And I thought Vostochny cosmodrome was the greatest monument of bloated government spending of public funds in space industry.

So what was the point of using Shuttle-based parts for it, then?

[tater]

1 minute ago, sh1pman said:

So what was the point of using Shuttle-based parts for it, then?

Saved loads of money (only cost 9 billion!), and it flew in just a few years (end of 2016!).

Oh, wait...

[jinnantonix]

12 hours ago, sevenperforce said:

I will try to run some numbers and see how it works. One note -- if the capsule is being used for significant dV, the R4-D is a better choice for the RCS thrusters, and they get 312 s. Also, I would propose giving 100-300 m/s of dV to the capsule so that it circularizes while the lander crashes; that will help with the overall efficiency as well.

OK, I am just modelling with the SSTU Labs RCS thruster blocks, since unmodded KSP does not support hypergolic fuels.  Good to know a better Isp values is available, I will tweak the part configuration file accordingly.  This will give the capsule a bit more dV.  

Stage	Req dV	Wet mass	Dry mass	ISP	dV
LLO-NRHO	730	4.012	2.982	312	907.2

On another note, I am really having a lot of trouble with a successful landing.  The OMS is just so wimpy with regard to thrust.  I am finding that using the thrusters as well as the OMS at full thrust, I am getting better results.  In this mode, KSP just can't automate a calculation of the most efficient landing, let alone land at a predefined LZ.  So at this stage I am just trusting that NASA has the ability to make the theoretical numbers work IRL.

 

Quote

I don't think either of these are necessary. The departure burns from NRHO are optimized for proper planar insertion, and the ascent burn is timed to coincide with return to NRHO. That's the nice thing about polar landing sites.

When doing the tests these normal corrections turned up because I don't have a team of geeks calculating every manoeuvre to 3 decimal places accuracy.  The corrections weren't onerous about 20-30 m/s dV only.

Edited November 14, 2019 by jinnantonix

[jinnantonix]

15 hours ago, sevenperforce said:

What we most need is extra volume. Volume is not always heavy. This is another reason why doing the crew capsule launch independent of the lander is helpful. You can launch a very lightweight but very large (4+ m diameter, 6+ m long) module vertically on Falcon 9 to TLI, but then have it mate to LOP-G and to the lander horizontally. 

I think this is the best solution, although 6m long is not ideal for craft stability when landing. 

The Orion space craft is designed for 4 crew on 3 week missions, so should be OK for 2 crew with part of the volume consumed by an internal airlock.  The stresses on the lander capsule is way less than on the Orion, so I am thinking it should be possible create a full scale Orion pressure vessel, 3.3m x 5m diameter and with just minor structural enhancements, and it should be very light.  This can be modeled by tweaking the mass of the SSTU Labs SC-C-CX Orion Orbital craft (with no heat shield) reducing the mass to 2.7 tonnes.  It fits inside a FH standard fairing with room for an additional logistics container for the LOP-G ~5 t maximum mass (not shown) - his could be a small pressurised container mounted with docking ports on the top of the craft.  A Cygnus is not required, as the Lander capsule supports avionics and communications, and only needs a small amount of fuel to complete the docking at LOP-G.

. 

Edited November 14, 2019 by jinnantonix

[sevenperforce]

13 hours ago, jinnantonix said:

OK, I am just modelling with the SSTU Labs RCS thruster blocks, since unmodded KSP does not support hypergolic fuels.  Good to know a better Isp values is available, I will tweak the part configuration file accordingly.  This will give the capsule a bit more dV.  

Stage	Req dV	Wet mass	Dry mass	ISP	dV
LLO-NRHO	730	4.012	2.982	312	907.2

On another note, I am really having a lot of trouble with a successful landing.  The OMS is just so wimpy with regard to thrust.  I am finding that using the thrusters as well as the OMS at full thrust, I am getting better results.  In this mode, KSP just can't automate a calculation of the most efficient landing, let alone land at a predefined LZ.  So at this stage I am just trusting that NASA has the ability to make the theoretical numbers work IRL.

I am considering whether a dual-engine design is a better solution. The descent burn is extremely long in most of my evaluations...almost to the point that you'd be burning all the way from LLO continuously.

13 hours ago, jinnantonix said:

When doing the tests these normal corrections turned up because I don't have a team of geeks calculating every manoeuvre to 3 decimal places accuracy.  The corrections weren't onerous about 20-30 m/s dV only.

Oh, okay. No worries. I thought you were working in a whole plane change. 

7 hours ago, jinnantonix said:

22 hours ago, sevenperforce said:

What we most need is extra volume. Volume is not always heavy. This is another reason why doing the crew capsule launch independent of the lander is helpful. You can launch a very lightweight but very large (4+ m diameter, 6+ m long) module vertically on Falcon 9 to TLI, but then have it mate to LOP-G and to the lander horizontally. 

I think this is the best solution, although 6m long is not ideal for craft stability when landing. 

It is if you're landing horizontally.

I wish I had KSP on this computer because I think I have a really, really cool solution.

[tater]

There's a mod that controls horizontal landers (balances multi-engines for offset CMs). Dunno how it plays with RO in terms of realistic throttle values, however.

[sevenperforce]

11 minutes ago, tater said:

There's a mod that controls horizontal landers (balances multi-engines for offset CMs). Dunno how it plays with RO in terms of realistic throttle values, however.

If you balance the engines correctly to begin with it's not a problem.

[tater]

5 minutes ago, sevenperforce said:

If you balance the engines correctly to begin with it's not a problem.

Makes propellant tank positioning extremely critical, however. It also makes cargo positioning very specific to that one vehicle. Also, part of the vehicle is an ascent stage...

It's doable, but non-trivial.

[Ultimate Steve]

This is a bit off topic, but I have been going through that budget thing that was posted a while back (might have been in the SLS thread. I'm not sure if we have a NASA thread any more so I guess I'll put it here). I found this interesting tidbit:

Quote

The House added $125 million for the development of nuclear thermal propulsion, $25 million more than FY2019. The request was zero. The Senate provided $100 million, of which $70 million is for the design of the flight demonstration by 2024.

It probably won't stick, but a flight demonstration of a nuclear thermal rocket by 2024 would be huge if it happens.

[sevenperforce]

52 minutes ago, tater said:

Makes propellant tank positioning extremely critical, however. It also makes cargo positioning very specific to that one vehicle. Also, part of the vehicle is an ascent stage...

It's doable, but non-trivial.

If the engines are fixed it is very challenging. If they have some gimbal, it's a little easier, because you can compensate through both gimbal and differential throttling.

This is sort of where I'm thinking....

Top is the capsule. Roughly the same size as extended Cygnus. Internal tankage in bulkheads; airlock on one side, docking port on the other, berthing and propellant transfer port on the bottom. A few windows. 

At bottom is the capsule with the ascent module attached. Depicted is the ascent module structure, engines, and ascent propellant tankage. Drop tanks and landing platform not yet pictured (the drop tanks affix to the landing platform; the landing platform attaches to the central thrust column between the ascent tankage).  Independent RCS for the ascent module is also not pictured. The ascent module forms a "cradle" under the cylindrical crew capsule and the engines and ascent propellant tanks are all offset but parallel to the CoM<->CoT vector.

With drop tanks installed, the descent module almost exactly fills out the Falcon 9 fairing, horizontally. 

The landing platform would have deployable legs and mate primarily to the central thrust column under the ascent tankage. In compression, the corners of the ascent frame would rest on arms that would distribute the capsule's weight directly to the legs. It would also have frag shields for the engines, mounting points for the drop tanks, a ladder up to the airlock, and room for flatpacked cargo.

EDIT: If needed, the airlock could be moved to the top of the capsule and the capsule itself could be shortened so as to allow the drop tanks to protrude upward on either side. The capsule itself doesn't even need to have the vertical-launch/horizontal-integration approach. But the enabling feature is to use vertical launch and horizontal integration for the lander module.

Edited November 14, 2019 by sevenperforce
Addition

[tater]

6 minutes ago, sevenperforce said:

through both gimbal and differential throttling.

This is where a mod that does that is nice. It;s not like a real lander will have someone micromanaging the engines, the computer will do it. Maybe mechjeb/etc does that? (oddly enough, I never seem to install those mods since I enjoy manually flying spacecraft, even though in RL I think it's a job that should be entirely done by computers, lol.

[sevenperforce]

13 minutes ago, tater said:

This is where a mod that does that is nice. It;s not like a real lander will have someone micromanaging the engines, the computer will do it. Maybe mechjeb/etc does that? (oddly enough, I never seem to install those mods since I enjoy manually flying spacecraft, even though in RL I think it's a job that should be entirely done by computers, lol.

Yeah -- KSP can automatically use gimbal to adjust pitch, roll, and tilt, but not to correct for CoM. The Shuttle's OMS engines are a good example of this -- they could gimbal parallel if they were being fired simultaneously, or they could gimbal outward to thrust through the CoM if they were being fired one at a time. The only way to model this in KSP is to position them gimbaled-out by default and add angled docking ports so you can "control from here" when using only one engine. And even then you get cosine losses when firing both. 

To the ongoing horizontal-lander structure debate...it's possible (and perhaps easier) to do the horizontal landing module with only a single engine, but having two allows the combustion chambers to be higher than the base of the capsule, which decreases ground clearance. Having the two offset allows the entire lander module to be substantially narrower than twice the engine bell diameter, which is especially helpful when you need to fit frag shields somewhere.

[kerbiloid]

1 hour ago, tater said:

This is where a mod that does that is nice. It;s not like a real lander will have someone micromanaging the engines, the computer will do it. Maybe mechjeb/etc does that?

They should hire @allista and implement his Throttle Controlled Avionics (now for 1.8) as firmware.

 

[jadebenn]

I found this old presentation about what appears to be a precursor to the current Boeing lander design:

https://imgur.com/a/N6jgfBo

Here's the slide that summarizes its capabilities:

IMO, that two-week capability (if it exists in the current design, which I think is a safe assumption) is going to be a killer selling point. I doubt the National Team's lander will be able to do more than one since it lacks a dedicated habitat.

Edited November 15, 2019 by jadebenn
Imgur albums don't embed :(

[tater]

Yeah, I posted that design in the SSTU forum shortly after the presentation, actually. It's pretty cool looking.

[jadebenn]

2 minutes ago, tater said:

Yeah, I posted that design in the SSTU forum shortly after the presentation, actually. It's pretty cool looking.

Ah, were you the source of those pics? I found them in my pictures folder and I couldn't remember where they'd originated from.

[tater]

1 minute ago, jadebenn said:

Ah, were you the source of those pics? I found them in my pictures folder and I couldn't remember where they'd originated from.

Probably, I was posting them as a reference for future lander additions to SSTU, because it was a legit design, and really cool looking. There's a link to the paper at AIAA in there, too...

I reposted it here I think a few pages up.

 

Crud, AIAA paper had been free at the time.

[jadebenn]

3 minutes ago, tater said:

Probably, I was posting them as a reference for future lander additions to SSTU, because it was a legit design, and really cool looking. There's a link to the paper at AIAA in there, too...

I reposted it here I think a few pages up.

Doing some reading on it, it looks like the original design has the ascent module co-manifested with the descent module given its own cargo launch. However, that co-manifesting capability relied on an early transition to composite BOLE SRBs to gain enough mass margin to fit the AE and Orion on the same SLS, and gave the descent module an entire cargo launch to itself.

If the current Boeing proposal is to launch ascent and descent on a Block 1B, they must have downsized the lander quite considerably, meaning that the two-week ECLSS capability may have been lost.

[jinnantonix]

12 hours ago, Ultimate Steve said:

It probably won't stick, but a flight demonstration of a nuclear thermal rocket by 2024 would be huge if it happens.

I think nuclear propulsion is unlikely to be included within Artemis.  However, if Artemis demonstrates that ISRU on the moon is viable, nuclear propulsion would be a very efficient technology for building and managing the ISRU capability, and for future deep space transfers.