NASA Human Landing System

[tater]

8 minutes ago, sevenperforce said:

Does anyone know the upper limit of discrete payloads for LEO by most commercial vehicles? Because if we know that number then we can start sizing accordingly.

I was just looking at things like extant and planned upper stages, and eyeballing it. I want to say that one of the ACES stages talked about was something like 35 tonnes, and won't fit in a Falcon fairing volume (including the fairing).

That was the trouble with Zubrin's proposal to use FH for "Moon Direct." He used the figure to LEO, without actually thinking about what it can actually loft. The possibility exists to use S2 props to put the payload in an eccentric orbit (like the GTO one yesterday, for example, or even higher), then phase any other, distributed launches to rendezvous. This is in fact the supposed plan for any Starship to the Moon (landing) refilling ops, since it doesn't have the dv to do the return trip itself from LEO, but it does from higher up.

I suppose once refilling is a thing, it doesn't matter. Where they rendezvous, though phasing and launch delays are substantially complicated by elliptical orbits.

[sevenperforce]

Just now, tater said:

I was just looking at things like extant and planned upper stages, and eyeballing it. I want to say that one of the ACES stages talked about was something like 35 tonnes, and won't fit in a Falcon fairing volume (including the fairing).

That was the trouble with Zubrin's proposal to use FH for "Moon Direct." He used the figure to LEO, without actually thinking about what it can actually loft. The possibility exists to use S2 props to put the payload in an eccentric orbit (like the GTO one yesterday, for example, or even higher), then phase any other, distributed launches to rendezvous. This is in fact the supposed plan for any Starship to the Moon (landing) refilling ops, since it doesn't have the dv to do the return trip itself from LEO, but it does from higher up.

I suppose once refilling is a thing, it doesn't matter. Where they rendezvous, though phasing and launch delays are substantially complicated by elliptical orbits.

Refueling isn't a magic fix for issues like boiloff and ullage. Starship gets around it by having such a massive square-cube advantage that boiloff and generous RCS use are inconsequential, but something like Centaur can't manage nearly so easily. IIRC, Centaur has to actively vent hydrogen boil-off throughout its entire coast just to maintain ullage and prevent the tanks from popping.

The Falcon 9 user's guide suggests the current payload adapter is limited to 11 tonnes for center of mass reasons, but says that higher-mass payloads can be accommodated as a special service. I believe the problem is not so much with structural loads on the upper stage (and certainly not for the lower stage) as it is the bending moment on the payload adapter during pitchover under power. If the payload's center of mass is too high above the payload adapter then it will not be able to stay secure. The largest payloads launched in a fairing to date have been the Iridium NEXT clusters at over nine tonnes.

But all you need to remedy that is to design a custom PAF, which isn't so bad. Structural limitations on the vehicle itself are probably much higher.

[sevenperforce]

Looking at the Delta IV user guide, ULA offers about a dozen different Delta IV PAFs with suggested maximum load limits ranging between 5.0 for the flimsiest ones and 9.1 tonnes for the heaviest ones.

The Atlas V has eight different PAFs with maximum loads ranging from 6.3 tonnes to 9 tonnes.

The New Glenn user guide released two months ago and cited explicitly that they could do at least 20 tonnes in a dual-manifested launch, which makes that the lower bound of structural limitations on the upper stage (though I do not know if their PAF can handle 20 tonnes in a single-payload mission). The 45-tonne reference orbit was, naturally, inclusive of residuals.

In terms of pure upper-stage structural limits, we know that Delta IV Heavy took the 21-tonne Orion EFT to LEO. So its stage structural limits are more than 230% of its biggest PAF.

[tater]

30 minutes ago, sevenperforce said:

Refueling isn't a magic fix for issues like boiloff and ullage. Starship gets around it by having such a massive square-cube advantage that boiloff and generous RCS use are inconsequential, but something like Centaur can't manage nearly so easily. IIRC, Centaur has to actively vent hydrogen boil-off throughout its entire coast just to maintain ullage and prevent the tanks from popping.

No, boiloff is huge. And as rendezvous orbits become elliptical, it's worse because the phasing is harder, and the time for each orbit is longer, so the dead time to refill (I'm sticking with the SpaceX term here, since refuel seems like it leaves out oxidizer ) results in even more boiloff. The ACES solution certainly helps, and seems like a useful tech for many upper stages with cryos to think about doing (making power with the vented gas).

None the less, with common docking/refilling hardware, it seems like distributed, commercial launch can do a lot.

30 minutes ago, sevenperforce said:

The Falcon 9 user's guide suggests the current payload adapter is limited to 11 tonnes for center of mass reasons, but says that higher-mass payloads can be accommodated as a special service. I believe the problem is not so much with structural loads on the upper stage (and certainly not for the lower stage) as it is the bending moment on the payload adapter during pitchover under power. If the payload's center of mass is too high above the payload adapter then it will not be able to stay secure. The largest payloads launched in a fairing to date have been the Iridium NEXT clusters at over nine tonnes.

But all you need to remedy that is to design a custom PAF, which isn't so bad. Structural limitations on the vehicle itself are probably much higher.

I wasn't thinking load/stress, I was just thinking payload density. Take the extreme case of expendable core FH. What could you put in LEO that fits in the fairing volume (assume a fairing shaped payload, with no fairing) that gets close to the stated mass to LEO? The closest would probably be a fairing shaped tank of propellant.

[sevenperforce]

1 hour ago, tater said:

None the less, with common docking/refilling hardware, it seems like distributed, commercial launch can do a lot.

I wasn't thinking load/stress, I was just thinking payload density. Take the extreme case of expendable core FH. What could you put in LEO that fits in the fairing volume (assume a fairing shaped payload, with no fairing) that gets close to the stated mass to LEO? The closest would probably be a fairing shaped tank of propellant.

The usable volume in a Falcon 9 fairing over 216 cubic meters. If you poured water into the fairing's usable volume, you'd only be 1/3 of the way full before you'd hit Falcon Heavy expendable's 63.8 tonne limit. For reusable configurations you'd use even less of the volume before you'd be mass limited.

Now, if you're trying to loft hydrolox in bulk, then yes, you're going to run into problems filling up Falcon Heavy expendable's mass budget. A fairing-sized hydrolox tank would mass just about exactly 62 tonnes. But, again, we aren't flying Falcon Heavy expendable, and we aren't lifting pure hydrolox.

Common bulk densities for reference:

• Water: 1 g/mL
• Hydrolox: 0.32 g/mL
• Methalox: 0.83 g/mL
• Kerolox: 1.03 g/mL
• Hypergolics: 1.2 g/mL

[tater]

I tend to think of hydrolox as the useful deep space propellant, so I was comparing to ACES.  I suppose the losses are worth looking at vs the 80 seconds of specific impulse. I don't see NASA as going to Methane, though, with ULA and BO both as hydrolox upper stage players. I suppose they could use solar to crack water in orbit, then just loft the water...

[tater]

A quick look shows there have been some papers on using water in propellant depots, then cracking it to LOX/Hydrogen as needed. This solves many issues.

[sevenperforce]

4 minutes ago, tater said:

I tend to think of hydrolox as the useful deep space propellant, so I was comparing to ACES.  I suppose the losses are worth looking at vs the 80 seconds of specific impulse. I don't see NASA as going to Methane, though, with ULA and BO both as hydrolox upper stage players. I suppose they could use solar to crack water in orbit, then just loft the water...

There's an idea. What's the value per gallon of water in orbit?

And hey, that's something that would be enabling even without LOP-G. Go grab about a billion in venture capital, buy a reusable electric-pump-cycle hydrolox engine with accompanying thrusters, and build a solar-electrolysis propellant depot to be lofted into LEO by Falcon 9, then buy Falcon Heavy launches to send as much water as you can to the station, as frequently as it will launch. Use your hydrolox engine and thrusters to build a tug with a metallic heat shield for aerobraking, then offer direct-to-GEO services from basically any orbit.

 

Masten has done a lot with small methalox thrusters that would be usable for a lander engine under the right circumstances.

[tater]

Solar thermal is possible to move it as well. The I_sp for water as propellant stinks in that use case (under 200), but for hydrogen I have seen numbers that look a lot like NTRs (up to 1000). Ot could be a tug/depot, I suppose. Depends on the logistics. How long to crack water. Do you dock the craft to be refilled, then crack props, or does it need a (huge) hydrogen tank, because it takes forever to crack. Then there is boiloff while you crack the props (you need to make hydrogen a lot faster than you lose it). Something like ACES could use boiloff to crack more H, however.

[sevenperforce]

2 hours ago, tater said:

Solar thermal is possible to move it as well. The I_sp for water as propellant stinks in that use case (under 200), but for hydrogen I have seen numbers that look a lot like NTRs (up to 1000). Ot could be a tug/depot, I suppose. Depends on the logistics. How long to crack water. Do you dock the craft to be refilled, then crack props, or does it need a (huge) hydrogen tank, because it takes forever to crack. Then there is boiloff while you crack the props (you need to make hydrogen a lot faster than you lose it). Something like ACES could use boiloff to crack more H, however.

Boiloff wouldn't be an issue for a solar-electrolysis prop depot; you'd already need a massive array of radiators to liquefy everything in the first place.

[sevenperforce]

Just occurred to me that the Draco develops 300 s in vacuum. Clustering Dracos wouldn't be enough for a lander, but would they be enough to perform an LOI burn at the gateway? Because that would both save mass and make everything ridiculously simple. 

[Cunjo Carl]

NASA's Administrator Jim Bridenstine hopped on a soap box to talk about NASA's aspirations for the Moon at the end of a 3AM talk with SpaceX & NASA about commercial crew.

It's a high level overview about the politics, goals and hopeful benefits of NASA's recent commercial programs. There's no real new information, but everything I've read so far has been fairly scattered, so it was nice to get this informal rundown ' right from the horse's mouth ' as it were. He's also surprisingly eloquent for 3AM!

The other similar presentation I'd seen was a much stiffer request from industry, and included many more.... aspirational items. https://youtu.be/JN0OWlfGWhw?t=439

 

[tater]

Bridenstine has honestly been just great. I'm not a fan of the current plans, but they have to make lemonade with the lemons they are given.

[Cunjo Carl]

Apparently NASA's poised to be getting bushels of funding. In a recent talk Bridenstine was talking about their budget, and he sounded downright rosy about it.

It's another high level talk about upcoming plans. A lot of it focuses on gateway, which has been talked about quite a bit in this thread, so I'll keep it going. If folks think I should do a new thread for this sort of stuff though, let me know.

And, the overview of what they talk about:

Beginning: We're goin' to the Moon!
6:30 We're getting lots of money (We hope)
7:00 Low boom flight demonstrator (X-59)
9:45 All electric plane (X-57)
11:00 Urban air mobility (flying delivery drones, flying cars)
12:30 Commercial crew
15:15 CLPS- Gotta go fast. Have 10 payloads ready to go.
16:15 Gateway
      Will be funded if the budget request goes through
      Gateway will use solar electric thrust for maneuvering
      Designed for access to all parts of the moon
18:45 Need SLS, Orion ESM, and reusability (tugs, etc)
      Want Orion to be mostly reusable by EM4
21:15 Funding for various projects
22:45 Tour of a full scale mockup of Orion
26:30 Announcing opening 3 pristine lunar samples
28:30 Gateway again
      Not crewed full time
      Canada will be helping with robotics (Canadarm returns?)
      ESA and JAXA are joining as well
32:15 Solar Electric Propulsion
      For moving gateway between orbits
      Hall thruster based (no surprise)
      Show and tell of their enormous vac chamber vf6
      Getting prototypes this month
38:45 'Space directive 1'
39:30 Mars
      Recently found complex organic compounds
      Still looking for life
      Budget request has funding for Mars 2020, sample return and the helicopter
43:45 Osiris Rex, New Horizons
44:45 Helio physics, solar flares and the Parker probe
46:15 Earth science: funding and goals
48:15 Astrophysics & James Webb Space Telescope
52:45 Gateway yet again
      Radio telescopes on the far side of the moon are a possibility
54:00 Recap & closing statements
      Use of NASA research in agriculture, industry and disaster relief
      Talk about us on social media, please.

[tater]

https://spacenews.com/nasa-tweaks-call-for-lunar-lander-concepts/

[Nightside]

20 minutes ago, tater said:

https://spacenews.com/nasa-tweaks-call-for-lunar-lander-concepts/

It sounds like this opens the acceptable designs up to more “space age” style ships like Starship or that Lockheed-Martin lander we saw last year.

[tater]

 

Quote

The awardees, from eight states across the country, are:

 

• Aerojet Rocketdyne – Canoga Park, California
  • One transfer vehicle study
• Blue Origin – Kent, Washington
  • One descent element study, one transfer vehicle study, and one transfer vehicle prototype
• Boeing – Houston
  • One descent element study, two descent element prototypes, one transfer vehicle study, one transfer vehicle prototype, one refueling element study, and one refueling element prototype
• Dynetics – Huntsville, Alabama
  • One descent element study and five descent element prototypes
• Lockheed Martin – Littleton, Colorado
  • One descent element study, four descent element prototypes, one transfer vehicle study, and one refueling element study
• Masten Space Systems – Mojave, California
  • One descent element prototype
• Northrop Grumman Innovation Systems – Dulles, Virginia
  • One descent element study, four descent element prototypes, one refueling element study, and one refueling element prototype
• OrbitBeyond – Edison, New Jersey
  • Two refueling element prototypes
• Sierra Nevada Corporation, Louisville, Colorado, and Madison, Wisconsin
  • One descent element study, one descent element prototype, one transfer vehicle study, one transfer vehicle prototype, and one refueling element study
• SpaceX – Hawthorne, California
  • One descent element study
• SSL – Palo Alto, California
  • One refueling element study and one refueling element prototype

 

[Ultimate Steve]

I notice that SpaceX has a descent element study in there. I wonder is that's Starship and it didn't fit in any other category...

Does the six month timeframe apply to the prototypes as well?

[tater]

Need to update this with the Boeing crew lander, and the BO/LM one.

[magnemoe]

On 2/22/2019 at 9:43 PM, sevenperforce said:

Refueling isn't a magic fix for issues like boiloff and ullage. Starship gets around it by having such a massive square-cube advantage that boiloff and generous RCS use are inconsequential, but something like Centaur can't manage nearly so easily. IIRC, Centaur has to actively vent hydrogen boil-off throughout its entire coast just to maintain ullage and prevent the tanks from popping.

The Falcon 9 user's guide suggests the current payload adapter is limited to 11 tonnes for center of mass reasons, but says that higher-mass payloads can be accommodated as a special service. I believe the problem is not so much with structural loads on the upper stage (and certainly not for the lower stage) as it is the bending moment on the payload adapter during pitchover under power. If the payload's center of mass is too high above the payload adapter then it will not be able to stay secure. The largest payloads launched in a fairing to date have been the Iridium NEXT clusters at over nine tonnes.

But all you need to remedy that is to design a custom PAF, which isn't so bad. Structural limitations on the vehicle itself are probably much higher.

Starship also uses methane who will get far less boiloff than hydrogen, more like oxygen I assume. The heatshield will also help here, pretty sure the header tanks need additional insulation because heat during reentry. Long duration missions especially manned will definitely require this here I assume they will fly with engines towards the sun. 

[tater]

The new Boeing crew lander is also using methane it looks like.

[wumpus]

5 hours ago, tater said:

The new Boeing crew lander is also using methane it looks like.

Any idea how much boiloff you get from just the LOX?  I'm fairly surprised they didn't just go straight to hypergolics, but zero-boiloff for LOX probably isn't that hard (especially if the work for Weber is available).

[sevenperforce]

16 minutes ago, wumpus said:

Any idea how much boiloff you get from just the LOX?  I'm fairly surprised they didn't just go straight to hypergolics, but zero-boiloff for LOX probably isn't that hard (especially if the work for Weber is available).

NASA's current Ground Rules and Assumptions for cislunar activities presume total propellant mass boiloff, per day, as follows:

• 0.35% for hydrolox
• 0.20% for methalox
• 0.20% for kerolox

We know kerolox does not boil off at all -- rather, it is more likely to freeze -- and so the LOX is the limiting factor for both kerolox and methalox. O/F ratio is higher for methalox than kerolox, anyway.

[jadebenn]

On 11/19/2019 at 8:04 AM, tater said:

The new Boeing crew lander is also using methane it looks like.

They're at the very least considering it. Though I've heard some talk that they may have to default to an all-storables design if they can't mitigate the boiloff. Considering a lot of the assumptions baked into the architecture, that'll be no easy feat.

I don't think the final decision has been made either way yet.

[tater]

4 minutes ago, jadebenn said:

They're at the very least considering it. Though I've heard some talk that they may have to default to an all-storables design if they can't mitigate the boiloff. Considering a lot of the assumptions baked into the architecture, that'll be no easy feat.

I don't think the final decision has been made either way yet.

Storables make far more sense, as the idea of 2 SLS launches anything like close together in time seems fully absurd, and on top of that long pole, I tend to think that distributed launch really needs to demonstrate rapid launch cadence first, then there can be talk of non-storable props, otherwise it makes sense to design architectures that are not as schedule-critical.

The issue of course is that any SLS-based architecture also needs the lander to do LOI (low at Gateway), and transfer to LLO (basically making it similar to direct LLO LOI) so the dv requirements for the vehicle are higher than they would be otherwise.

Edited November 20, 2019 by tater