totm dec 2023 Artemis Discussion Thread

[sevenperforce]

2 minutes ago, Ultimate Steve said:

Except after you leave leo you can't really use the upper stage any more due to boiling and freezing of the propellants. A few hours after, yes, but not the multiple days that are likely for transit to gateway.

Paint the kerosene tank with black stripes and barrel-roll the stage during transit. Kerosene will be kept warm by solar heating. You'll lose about 0.2% of your LOX per day to boil-off, according to NASA's GR&As for lunar mission planning, but that's not terrible (especially since the majority of the burn happens within a few hours of launch). The stage would need a few of the same modifications that the first FH launch had (extra nitrogen tanks, extra helium tanks) but again, pretty minimal.

2 minutes ago, Ultimate Steve said:

But this is still big. As long as the distributed launch payload can dock itself, which an Artemis lander would almost definitely be able to do, the only real modification you need to do to fhus is adding a docking port under the fairing, and modify the adapter/docking port to be able to deal with the high g forces at burnout. The fhus has rcs so it can hold orientation while it is docked to.

Exactly.

2 minutes ago, Ultimate Steve said:

Europa clipper, however, would need to be given a docking port or some form of attachment system, and the necessary rcs and instruments to dock. Or you could modify the fhus for that.

Cheaper than a whole freaking SLS for sure.

[jinnantonix]

5 hours ago, tater said:

I never said it could not be done, I said it will not be done by these early Artemis landings

Actually, you didn't say that.  But perhaps we can agree on that.

As I have already suggested it is likely the first landing will not be to a crater floor for many of the good reasons you state.  Yes, a lower risk landing makes sense.  Yes, with solar power make sense.  Yes, they will need a lot more info to execute a safe landing in the crater.  Yes, they need good photos.  However I maintain the long term goal is the floor of Shackleton Crater, because that's where the ore is.  We have the technology.

Quote

Right now we're not even seeing proposals for surface infrastructure.

Maybe they find viable ore on the crater rim, and don't need nuclear power.  We don't have enough info yet.   

I would argue though that identifying the delivery of the "Lunar Asset" on Artemis 8 is a loose plan for surface infrastructure (I think mining equipment and/or ISRU), without being specific about design and where and how it will be deployed.

 

[tater]

6 minutes ago, jinnantonix said:

I would argue though that identifying the delivery of the "Lunar Asset" on Artemis 8 is a loose plan for surface infrastructure (I think mining equipment and/or ISRU), without being specific about design and where and how it will be deployed.

"Lunar Asset" isn't even a powerpoint facility.

By "not a thing" I mean very specifically "doesn't exist" or "is not funded to exist at some point in the future."

When a lunar asset is tasked with doing whatever work on the bottom of a dark crater, and they are bending metal, then we can talk about it more realistically.

[jinnantonix]

8 hours ago, sevenperforce said:

However...and here's the ridiculous part...if you launched a 3.5 tonne Pluto payload on an expendable Falcon Heavy and dropped it at staging, you would hit LEO with 81.3 tonnes of residuals.

If my math is right...holy crap. That's enough to throw up to 47.8 tonnes of distributed-launch payload to TLI. It's enough to deliver 38.3 tonnes of distributed-launch payload direct to LOP-G. It's enough to deliver a 26.9 tonne two-stage lunar lander to LOP-G, load it up with astronauts, and then drop it off in LLO.

Ok, so in KSP I launched a FHe (removed all the landing and guidance gear) with about 70kg of payload.  Resultant FH upper stage in LEO, wet mass = 78.8t, dry mass  = 10.0t (includes 1.1 t Merlin 1D Vac, 8.5t tanks, 0.4t upper decoupler).   

This excludes any losses needed to align with an existing crafts orbit to secure a rendezvous in LEO, which I am finding is typically about 300m/s, although I am sure the boffins could da better job.

Assuming deltaV for LEO to LOP-G = 3.55km/s, then this craft with ISP=348 can get about 28.5t of payload from LEO to LOP-G.  

What am I missing?

Edited November 8, 2019 by jinnantonix

[sevenperforce]

12 hours ago, jinnantonix said:

Ok, so in KSP I launched a FHe (removed all the landing and guidance gear) with about 70kg of payload.  Resultant FH upper stage in LEO, wet mass = 78.8t, dry mass  = 10.0t (includes 1.1 t Merlin 1D Vac, 8.5t tanks, 0.4t upper decoupler).

Your upper stage has double the dry mass it should. The Merlin 1D masses 470 kg and the extended reinforced carbon-carbon nozzle is heavy, but not greater than the mass of the engine itself. I would estimate the MVac at 550 kg tops. Tankage is under 4 tonnes. A good dry mass estimate for the upper stage is 4.5 tonnes...maybe 4.7 if you go with a longer-duration "Frankenstage" for BLEO ops. 

12 hours ago, jinnantonix said:

Assuming deltaV for LEO to LOP-G = 3.55km/s, then this craft with ISP=348 can get about 28.5t of payload from LEO to LOP-G.  

What am I missing?

dV from LEO to LOP-G is actually 3.63 km/s. But yeah, your dry mass is messing you up.

[tater]

The cold gas thrusters on F9 S2 would need improvement, I think.

Also, can Vac Merlin throttle?

934kN engine. Our mass per @sevenperforce is 81.3t props, 47.8t payload, plus the dry mass of S2, say 4t. So at the start of the burn... that's not bad at all.

~7m/s² at the beginning of the burn, and under 2 g (~18m/s²) at the end when it's just the payload.

 

[.50calBMG]

I believe the current MVac can throttle, but not quite as deeply as the SL versions, ~40% IIRC.

[tater]

@sevenperforce, how low did you have to throttle the core to get the staging velocity so high? Did you simply shut down FH core stage engines?

Kooky idea...

Take a Dragon pressure vessel.

Take a F9 fairing shape. Make the fairing out of something strong that can hold propellants. Say, steel.

Put dragon in the top. Bottom is tanks, some engines, solar panels, etc. And legs.

Could that actually use the volume in a way to maximize the payload mass and get ~47t "under the fairing?"

[tater]

Not counting the PAF part at the bottom, the volume of the F9 fairing is about 160 cubic meters.

Interestingly, this is almost the same volume as F9 stage 2 itself.

Edited November 8, 2019 by tater

[sevenperforce]

57 minutes ago, tater said:

The cold gas thrusters on F9 S2 would need improvement, I think.

Also, can Vac Merlin throttle?

934kN engine. Our mass per @sevenperforce is 81.3t props, 47.8t payload, plus the dry mass of S2, say 4t. So at the start of the burn... that's not bad at all.

~7m/s² at the beginning of the burn, and under 2 g (~18m/s²) at the end when it's just the payload.

The cold gas thrusters have sufficient placement authority for roll control and ullage, so that will be enough for holding position. I would imagine that the docking sequence could potentially involve a slight "spin-up" once the vehicles were perfectly aligned, before final close. The upper stage would need more bottled nitrogen, of course, as well as more helium. Hence the same Frankenstage design as the FH demo.

Merlin Vac can downthrottle to 39% of max thrust. Dry mass of S2 is 4.5 tonnes...let's say 5 tonnes after Frankenstage mods. Reduce payload to 44 tonnes (the same TLI throw as Saturn V) to ensure sufficient residuals and account for increased dry mass and possible boil-off during rendezvous. At minimum throttle that's just 7.4 m/s².

Not that it would be a problem anyway...we have routinely seen S2 burnout with much smaller payloads.

57 minutes ago, tater said:

@sevenperforce, how low did you have to throttle the core to get the staging velocity so high? Did you simply shut down FH core stage engines?

No idea. SpaceX advertises 3.5 tonnes direct to Pluto, so I assume it can get 3.5 tonnes direct to Pluto. You need 8.2 km/s, with the Oberth effect to get a Hohmann transfer to Pluto. The only way to get that much dV out of the upper stage is if it has nearly 75% of its propellant remaining at LEO SECO-1; the only way to get to LEO while burning only 25% of S2 propellant is to stage at around 1,031 m/s short of LEO. How SpaceX achieves that is up to them.

[tater]

Crappy picture:

Idea is that instead of trying to jam something inside of the fairing, you make the fairing the craft.

If the dry mass of the whole thing could be 7 tons, it ^^^ has 6000m/s dv if it is 47.8t wet. A direct ascent lander from Gateway. Getting the 47.8t to LEO is doable without expending an entire FH, right? Maybe just expend the core?

 

[tater]

Naked FH S2 could push Orion and a Gateway module that is substantially larger than SLS Block 1b allows to Gateway, too.

Send Orion to LEO on whatever other vehicle can get it to LEO. DIVH?

350M$+150M$ and you get more than is possible with 1 2+ B$ SLS launch (and they can stop bothering with EUS dev, saving billions). Course then SLS has no use... spend the cores under dev with ICPS as huge C3 launchers for space probes (something it's actually good for!)?

[Retro Starship]

Love this topic! Being somewhat knew, both with KSP and getting back into rocketry, I found this cool PFD from Nasa about gateway and some interesting stuff about it and lunar module Ideas. fwiw

https://www.nasa.gov/sites/default/files/atoms/files/20181206-crusan-gateway-reduced-v4.pdf

[sevenperforce]

1 hour ago, tater said:

Idea is that instead of trying to jam something inside of the fairing, you make the fairing the craft.

If the dry mass of the whole thing could be 7 tons, it ^^^ has 6000m/s dv if it is 47.8t wet. A direct ascent lander from Gateway. Getting the 47.8t to LEO is doable without expending an entire FH, right? Maybe just expend the core?

You run into some problems with the structural and aerodynamic limits of the stage during ascent, here. The PAF simply cannot handle very heavy, tall payloads, Starlink notwithstanding. The fairing support is independent of the payload support. 

And that is a lot of hypergols.

Also, where would the engines go?

[tater]

I was using the mold line as the guide, not the actual fairing or PAF attachments. The idea here would be to dump the PAF, and they'd need a new attachment to S2. Engine(s) (Super Dracos with a better bell) on bottom. Use the entire stage diameter for the stage sep.

You're right on the current PAF, of course, the max payload is ~11t according to the User guide. Starlink was over 13t though. Crew dragon with max trunk cargo is almost 17t I think. Dunno if that is attachment limited (really, use something like the trunk separator).

[sevenperforce]

16 minutes ago, tater said:

I was using the mold line as the guide, not the actual fairing or PAF attachments. The idea here would be to dump the PAF, and they'd need a new attachment to S2. Engine(s) (Super Dracos with a better bell) on bottom. Use the entire stage diameter for the stage sep.

I confess I am very fond of Boeing's lander design. Putting the airlock on the descent stage and the engines on the sides allows it to comanifest flatpacked cargo to the lunar surface or act as an independent cargo lander that doubles as a surface asset (showers, anyone?). It also permits the ascent stage to be limited just to what is needed for return.

16 minutes ago, tater said:

You're right on the current PAF, of course, the max payload is ~11t according to the User guide. Starlink was over 13t though. Crew dragon with max trunk cargo is almost 17t I think. Dunno if that is attachment limited (really, use something like the trunk separator).

Dragon 1 and 2 both use the trunk to mate to the tank structure that the PAF bolts to. With Starlink I think they may have braced the sats against the payload fairing. 

[tater]

6 minutes ago, sevenperforce said:

I confess I am very fond of Boeing's lander design. Putting the airlock on the descent stage and the engines on the sides allows it to comanifest flatpacked cargo to the lunar surface or act as an independent cargo lander that doubles as a surface asset (showers, anyone?). It also permits the ascent stage to be limited just to what is needed for return.

What's the diameter of that Boeing lander... it's 37t or less for sure (SLS)... so naked FH can easily send (or indeed take directly as you mentioned) the Boeing lander to Gateway.

Just need to get it to LEO.

Course NG could do that (take lander to LEO) as well (spreading the $$$$ around).

NG takes Boeing lander to LEO. FH sends it to Gateway (and has enough margin that maybe it can comanifest something with the lander).

Edited November 8, 2019 by tater

[sevenperforce]

1 hour ago, tater said:

What's the diameter of that Boeing lander... it's 37t or less for sure (SLS)... so naked FH can easily send (or indeed take directly as you mentioned) the Boeing lander to Gateway.

Just need to get it to LEO.

Course NG could do that (take lander to LEO) as well (spreading the $$$$ around).

NG takes Boeing lander to LEO. FH sends it to Gateway (and has enough margin that maybe it can comanifest something with the lander).

Sounds good to me. Two launches plus SLS+Orion. Might even be able to land the side boosters, particularly if New Glenn can throw it into an eccentric orbit. The SLS fairing is 8.4 meters to New Glenn's 7 meters...hopefully the Boeing lander isn't too big.

Of course once New Glenn is flying, its hydrolox upper stage would also have very good performance as a naked tug.

Making the Boeing lander's ascent stage stage reusable would also be very mass-efficient.

Edited November 8, 2019 by sevenperforce

[sevenperforce]

For reusing an Artemis component like Boeing's ascent module, there are four basic possibilities.

Capsule Reuse. In this approach, the only thing that is carried over between missions is the actual pressure vessel, backup power, LS, and associated hardware. All propulsion, propellant tankage, propellant, and primary power elements are delivered to Gateway and mated to the capsule at the start of the sortie; this carries the capsule down to the lunar surface (with or without any number of additional stages) and returns it to LOP-G before being jettisoned and discarded. The advantage here is that you have the safety assurance of a brand new propulsion unit for every launch and you do not need to develop any new docking systems or propellant transfer; the disadvantage is that it is the least mass-efficient approach.

Capsule and Propulsion Reuse. Here, the capsule includes reusable propulsion and RCS, but the tanks are discarded at the end of every mission. This requires the development of dockable/mateable tanks which can expend their propellant and then be jettisoned. It is advantageous because you do not need to develop propellant transfer and you do not throw away perfectly good engines after every mission so you save mass. It is also the most mass-efficient approach, in a way. The difficulty in developing such tanks is the primary disadvantage here, though end-of-life considerations for the engines are another concern.

Descent Module Refilling. In this version, the entire capsule is reused, along with propulsion system and tanks, and the ascent module's tanks are refilled from excess capacity on the descent module. This has the advantage of only requiring a single connection event during mission construction (structural and for prop transfer) but does require full-scale propellant transfer development. It also is less mass-efficient with respect to the descent module, which is then required to carry the weight of empty tanks. If the descent module is multistage (e.g., if there is a transfer stage as well), then using the transfer stage props is ideal because that is jettisoned before descent.

Logistics Module Refilling. This seems to be the version that NASA favors, though I don't know why.

 

 

[tater]

The issue with saving components like the crew cabin, cabin and RCS, etc. is that they also have consumables to consider.

The idea of total refilling  (your LMR, above) can work, but the idea of putting it at the Moon itself is bizarre, IMO.

Wonder if a fairing-looking lander could function as a sort of Zubrin-like "mini-Starship"--but one that never leaves space. Send it to TEI, have it aerobrake (as many passes as needed, it's uncrewed) and circularize in LEO. Refill it there, reattach it to naked FH, and send it back to Gateway? Maybe it has krypton thrusters from starlinks for this purpose?

[sevenperforce]

3 minutes ago, tater said:

The issue with saving components like the crew cabin, cabin and RCS, etc. is that they also have consumables to consider.

The idea of total refilling  (your LMR, above) can work, but the idea of putting it at the Moon itself is bizarre, IMO.

The advantage of capsule-only reuse is that internal consumables can be replaced internally, and the external module has brand new versions of everything external that could ever wear out or go bad.

5 minutes ago, tater said:

Wonder if a fairing-looking lander could function as a sort of Zubrin-like "mini-Starship"--but one that never leaves space. Send it to TEI, have it aerobrake (as many passes as needed, it's uncrewed) and circularize in LEO. Refill it there, reattach it to naked FH, and send it back to Gateway?

I think wear and tear would become an issue. Rapidly.

All of this bellyaching is really because Orion is just so damn wimpy.

[Ultimate Steve]

15 minutes ago, sevenperforce said:

All of this bellyaching is really because Orion is just so damn wimpy.

Yeah. Give Orion a more beefy service module, enough to go to llo and back, and suddenly the lunar architecture becomes far simpler. No gateway. Lighter Landers.

I wonder what it would take to give Orion drop tanks or something.

[sevenperforce]

4 minutes ago, Ultimate Steve said:

Yeah. Give Orion a more beefy service module, enough to go to llo and back, and suddenly the lunar architecture becomes far simpler. No gateway. Lighter Landers.

I wonder what it would take to give Orion drop tanks or something.

Ten years and $5B probably.

[tater]

28 minutes ago, sevenperforce said:

I think wear and tear would become an issue. Rapidly.

Well, seems like a Starship-derived tug could be a thing doing this. No fins, no legs. The idea is shallow passes. Lose mass by dumping the nose cone (this is really to look like the old STS tug or ferry). 1 vac Raptor, no other engines. So we lose maybe 1/3 of the dry mass with no gear, fin-flaps, etc. Unsure if it needs TPS for this entry case, but assume them for now. So mass more like 80t vs 120t. Same 1200t prop load. This is an "easy" SS. It's a 1 time use if refilling doesn't work, reusable otherwise (can also be topped up and used to tank up a SS in an elliptical orbit). Has >10,000 m/s dv "naked" and full, has 7989 m/s dv if it is hauling a 50t cargo (a whole lander). Topped off, such a 80t tug model looks like it could take nearly 400t to Gateway, then come back to LEO with aerobraking.

In a no initial refilling configuration---fly it as SS/SH stage 2 from Earth with no refilling---it looks like it might be able to take 10-20 tons (1-2X what B1b can comanifest) directly to Gateway, and return to LEO (aerobraking required).

 

 

Edited November 8, 2019 by tater

[jinnantonix]

17 hours ago, sevenperforce said:

Your upper stage has double the dry mass it should. The Merlin 1D masses 470 kg and the extended reinforced carbon-carbon nozzle is heavy, but not greater than the mass of the engine itself. I would estimate the MVac at 550 kg tops. Tankage is under 4 tonnes. A good dry mass estimate for the upper stage is 4.5 tonnes...maybe 4.7 if you go with a longer-duration "Frankenstage" for BLEO ops. 

dV from LEO to LOP-G is actually 3.63 km/s. But yeah, your dry mass is messing you up.

I am using the Kerbalised SpaceX and SSTU Labs mods.  The assumed mass of the Merlin 1D engine is clearly wrong, it actually assumes 1.43t, as you say this should be 470kg (Merlin 1D engine wiki) plus nozzle (80kg estimated).   I have been assuming the Falcon Heavy has a Falcon 9 FT upper, stage and SSTU has this at 8.0t dry mass and 98t wet mass. According to wiki the upper stage (tank) should be 4.0t dry mass, 111.5t wet mass. plus a fairing base , let's say 500kg.  I will tweak the values in SSTU and expect now that I should be able to model boosting a 37t payload from LEO to NRHO.

 

Edited November 9, 2019 by jinnantonix