Three firms selected for Artemis Lunar Landers

Oldfart1939 · 2020-05-02 09:07:57

NASA announced yesterday that three different contractors have been selected for design work on lunar landers.

https://spacenews.com/nasa-selects-thre … em-awards/

SpaceX was surprisingly one of them with a new version of the Starship with altered descent engine geometry/configuration to minimize regolith displacement from exhaust.

GW Johnson · 2020-05-02 16:48:28

Hi Oldfart1939 from another old fart:

I saw that news item, too. The required engine change is minimal: just don't put the exit plane so close to the surface. Easiest way to do that is reduce your vacuum expansion ratio a tad. Performance suffers a bit, but if a disaster gets prevented, it's worth it.

They'll change more than rocket blast digging craters, before they actually go into production. The landing legs they currently show will only work on a very thick, steel-reinforced, concrete landing pad. The moon is more like soft, dry, fine sand. Even at 1/6th gee, what they have will not work on the moon. The numbers are quite easy to run. Limit your total contact pressure under 1 MPa, the allowable bearing strength for soft, fine, dry sand .

Stay well.

GW

Last edited by GW Johnson (2020-05-02 17:13:05)

Oldfart1939 · 2020-05-02 18:36:25

Since this particular vehicle will probably never return to Earth, and a reentry through atmosphere is unlikely, large folding external legs are in order. Maybe not so "cool looking, but effective on the moon.

kbd512 · 2020-05-02 19:13:01

Oldfart1939,

Yes, those were my thoughts exactly. This isn't about "looking cool", it's about "practical aerospace vehicle design". If it "looks cool", that's a very subjective added bonus. Pilots tend to think things are "cool" when they actually work as advertised.

Oldfart1939 · 2020-05-02 19:47:09

The SpaceX solution was well thought out; they haven't had experience in supporting large masses on unstable and soft regolith. That will come when doing additional testing on beach sand.

GW Johnson · 2020-05-03 16:03:30

OK, assume the landing pads on the 6 landing legs they currently show are a generous 0.5 meter dia. That's about 0.2 sq.m per pad, for at most 1.2 sq.m area on 6 such legs.

Now assume a landed Starship massing about 250 metric tons (150 tons inert mass and 100 tons cargo). On earth, that would be about 2400 KN of weight, and on the moon, about 400 KN of weight. The lunar surface bearing stress is weight/area which is roughly 330 KN/sq.m = 0.33 MPa. You could possibly land, on a one-way trip!

You'd need some propellant still on board to come home. That raises the landing weight on the moon. Delete all the cargo, but add at least a factor of 2 worth of propellant relative to inert mass: at least some 300 tons. Total to take off is now 450+ metric tons, and the total to land (assuming NO propellant production on the moon) is now about 550+ metric tons.

If you can make propellant on the moon (which I seriously doubt), the earth weight of 450 metric tons to take off is about 4400 KN. If you cannot, the earth weight of the mass to be landed of some 550 metric tons is around 5400 KN. On the moon, these weights are nearer 750 and 900 MN. On 1.2 sq.m, these are 0.620 and 0.750 MPa.

At 1 MPa bearing strength, you might get away with this on the face of it, but for the transient factor-2 increase during the landing dynamics. Raise those static pressures to about 1.5 to 1.8 MPa for the landing transients.

Greater than the 1 MPa allowable, for soft, dry, fine sand. It simply will not work! Your landing legs will stab deep into the lunar surface. And when they do, it will happen unevenly. That's Murphy's Law.

Now, you have landing pads about 9 or 10 m apart. You have a center of gravity roughly 50 m above grade. Tangent of the angle is about 0.18-to-0.2. That's about 10 degrees out of plumb. Just math.

Beyond that, the ship topples (and explodes) upon landing. Some of that is the uneven "stab" of landing legs into the soil. The rest is surface roughness out-of-level. So how much can you tolerate?

Not very bloody much in this design!

Remember, Neil Armstrong came within 15 seconds of aborting his landing for surface roughness exceeding what the Apollo LM could tolerate. Which based on leg span to center of gravity height was closer to 45 degrees!

I told you these numbers were easy to run! But most of you will not like the results! Spacex simply has a very LONG WAY TO GO before they EVER land a Starship off-world. And THAT'S just the uncomfortable truth of the matter!

They will finally have to face this issue when they are forced to face-up to off-site abort landings with Starship, while doing nothing more than trips to LEO at most, or even suborbital flights. They aren't there yet.

The version of Starship that does finally become an LEO transport, will look NOTHING like these early flight test prototypes! The version that flies beyond LEO will look NOTHING like the orbital transport version!

You might as well steel yourselves for those massive changes to the design. Spacex is good, but they simply do NOT KNOW what they don't know yet. And it shows, rather egregiously.

GW

Oldfart1939 · 2020-05-03 17:13:47

GW-
I hope the artist conceptions get a bit more refined to reality in near future. The topple-over issue is one that most concerns me after weight-bearing area. After all, the center of mass must fall within the entire footprint defined by the landing legs; otherwise....

Oldfart1939 · 2020-05-04 08:36:52

NASA evaluation sees SpaceX lander innovative but Risky! They obviously tossed SpaceX a bone to keep them in the game, as a fallback in case none of the other contractors can perform.

https://spacenews.com/nasa-evaluation-s … but-risky/

Void · 2020-05-04 11:33:27

I know I am intruding, but how about a variation on Falcon 9 landing legs?
https://www.spacex.com/news/2013/03/26/landing-leg

I think they could be offset from the triplet, triple canted landing thrusters.

They would only have to be deployed once. You would be able to go back to Lunar orbit without folding them back up again.

A well understood technology, (By SpaceX). And you might have some special permissions in Lunar gravity to reduce the mass of them, provided your landing thrusters could put it down gently.

---

By the way I have seen some suggestions that this rocket might also go to LEO from the Moons surface and back again. But I really do understand that that consumes a lot of propellant without an Aero-burn. Still maybe they can eject the sea level engines at some point to partially compensate for that, since it is not intended to ever land on Earth.

Pardon the intrusion please.

Last edited by Void (2020-05-04 11:36:58)

Oldfart1939 · 2020-05-04 16:25:04

Void-

That was my idea for landing in first place. Probably need more than just 3; probably a set of 6 for stability and weight distribution. Not sure about discarding engines, though.

Void · 2020-05-04 16:43:35

O.F. 1939
Quote:

Void-
That was my idea for landing in first place. Probably need more than just 3; probably a set of 6 for stability and weight distribution. Not sure about discarding engines, though.

Well, good then I guessed a solution after you and it might be a good guess.

Yes, the engine removal would produce marginal performance improvements perhaps, but then perhaps requires a spacewalk to remove the engines you don't want. But I do seem to recall that Vulcan is planed to drop engines and re-enter them to atmosphere.

Still I do agree that SpaceX will want to get to the deed any way they can, and then perhaps later if multiple Moon-Starships are built and sent, maybe tune the process up a bit more.

If they get it running it could be a fantastic machine. As I see it, it could push a whole palate of propellants and hardware to the Moon and drop it down.

The question would be who wants to do what on the Moon. Scientific outpost? Re-fueling station. Massive industrial production, such as Oxygen for Mars bound Starships?

I think the machine(s) if they get it working, could move a massive amount of materials to the Moon. Question will be does someone want to do that.

And I will see if I can refrain from further intrusion into this thread.

Last edited by Void (2020-05-04 16:49:23)

Oldfart1939 · 2020-05-04 16:55:42

No. Intrusions are welcome, because we are brainstorming here, most of the time. Old fogeys tend to become too narrow in ideas and applications.

kbd512 · 2020-05-04 19:15:37

I really want to test the assertion that we can land a truly massive rocket on the surface of another planet, perform little to no refurbishment of the engines prior to subsequent runs, refuel it there using whatever propellant precursor chemicals happen to be available, and then take off again months later without any rapid unscheduled deconstruction of the turbo machinery sections of the engine or propellant tank welds failing. If we can manage those three things, then I think our transportation is reliable enough for a Mars mission. We'll need to do that at least several times prior to major overhaul of the engines to determine the design's suitability for colonization purposes.

Oldfart1939 · 2020-05-04 19:31:13

kbd512-
I suspect that Musk has the same idea as you put forth here. SpaceX is big on testing to destruction; build it; test it; break it; fix it; build it again. Just watching the Boca Chica construction and testing is exactly that model.

Void · 2020-05-05 09:58:16

O.F. 1939,

Very decent of you.

I very much agree that at least for human interplanetary transfers, the SpaceX interplanetary transfer every ~2 years, is the way to go.

We would like humans to be in the interplanetary environment for as short a period of time as possible.

But now, SpaceX has begun to contemplate a variant without a heat shield and aerobrake flaps, for now for the Moon. I love it.

For the Moon, it may work. And eventually Oxygen might come from the Moon, to assist spacecraft returning to Earth or LEO, and also for Spacecraft going to Mars. So, for me that is worth a look. But also could there be low hanging fruit of another kind to get from the Moon, that could assist space development elsewhere. Just easy to manufacture stuff of some kind, you would want to take to Mars, or to LEO of places between LEO and the Moon?

If such easy to make things can be sourced from the Moon, then they do not have to be sourced from elsewhere, such as the surface of the Earth.

So, I am looking at the complementary relationship which I believe could exist between the two main types of "Starship" that could go to Mars.

You could send a Lunar Starship to Mars. No heat shield, no braking flaps, you cannot enter the atmosphere with it. So, that is almost entirely out of the question. But there may be a way to profit immensely from a different method of entry to the Hill Sphere of Mars, outside of the atmosphere. Particularly if you do have a Mars type Starship that can go through the atmosphere.

Lets change the name of the "Lunar Starship" to the "Vacuum Only Starship". It only experiences atmosphere of significance once, and that is at it's birth. Once it is launched to LEO, on the Super Heavy, it is a creature of Vacuum for the rest of it's life.

So then to make best use of it, I see it as a barge tug in the American variation.

An example:
https://www.britannica.com/video/22281/ … ippi-River
Please pardon the commercials.

If you were going to send a barge assemble to Mars, with a Vacuum Starship as the "Tug", and if you were going to use the ~2 year interval method, you could, but each "Barge" would or would not have means to land on Mars itself, a heat shield, etc. as necessary. The Hohmann transfer. In such a situation you could sacrifice the "Tug", since it is not equipped, to enter the Martian atmosphere and land.

But you also might, if you had enough propellant for the Vacuum Starship, be able to have the Starship unhook after it got the various self landing elements unhooked from itself to have it enter the Martian Hill Sphere, by propulsion. Very mass and energy expensive. Or, it might do a propulsive burn to swing back out of the Martian Hill sphere, back towards Earth, where of course it would need propellant to break into orbit by propulsion, very expensive. I am just be as complete about options as I can. I do not at this time particularly favor the above.

I would modify the above options with the use of Ballistic Capture. Pretty much any of the options above in some variation could be done using Ballistic capture I venture, or speculate. It is worth thinking about in my opinion.

https://en.wikipedia.org/wiki/Ballistic_capture

Ballistic capture is most likely not the preferred method to transfer people, at least until we also can include into it synthetic gravity and very good radiation shielding.

But, if I understand it correctly, you can do ballistic capture, where your launch windows are very much expanded, (You are not restricted to the ~2 year intervals), and you may go to orbit in the Martian Hill Sphere, without needing to Aerobrake.

You could use individual one time landers to aerobrake themselves and land themselves as an option, but I say that in passing.

If you have an Atmosphere Capable Starship, and you have done a Ballistic capture of a "Barge Assembly" into Mars orbit, then you may sequentially do an up and down from the Martian Surface with the Atmosphere Capable Starship, to get the materials you want down to the Martian surface.

So, rather than a Atmosphere Capable Starship sitting idle for two years on the Martian surface, you could use until it breaks. This particular Atmospheric Capable Starship would not be one you were counting on for sending people back to Earth. It would be a Cargo Transport.

And with Ballistic capture, you can make several barge deliveries to the Martian Hill Sphere, during the ~Two Year interval that is mandated by the use of Hohmann Transfer, for Atmospheric Starships intended for human transfers.

While we struggle with the concept of how to make enough propellant to send a Starship back to Earth, this Ballistic capture method could deliver GiggaTons of stuff to Mars, that was for the purpose of generating more propellants.

So, where Robert Zubrin has expressed useful criticisms, that need a solution, SpaceX has appeared to have chances to solve the landing problems for the Moon. I say also his concern about a Starship being idle on the surface of Mars can in part be solved by using them to bring GigaTons of stuff down to the Martian surface from mass items delivered to the Martian Hill Sphere by the Ballistic Capture Barge Method.

And the whole barge would set off from the Earth/Moon Hill Sphere, using perhaps just 3 Vacuum raptor engines in a single Vacuum Starship. Obviously the Vacuum Starship would be tapping into a massive propellant Depot that it was pushing along with the hardware to deliver.

So, unless I have misunderstood how all of this can work, this post represents what I think could greatly help our intentions to "Occupy Mars".

Done

Ummm…..The Vacuum Starships, could conceivably be used as orbital space stations, if that helped the Mars cause. For instance a set of two, three, four, five, six, could be hooked together to create orbital synthetic gravity habitats. Water from Mars and/or materials from the Martian moons, Phobos and/or Demos, to provide shielding methods. Perhaps down the road magnetic shielding as well.

Last edited by Void (2020-05-05 10:47:11)

Oldfart1939 · 2020-05-05 16:34:32

I would prefer something a bit sexier for the name: "Deep Space Starship," primarily as a big freight and transfer "tug," as you have succinctly phrased it. Technically, would/could be less complex to build, and without heat shielding or re entry fins and grid fins. Capable of landing on planetary surfaces without atmospheres, as well. Moon; asteroids; Ganeymede; Callisto. The ideal deep space mining vehicle?

Void · 2020-05-05 17:01:56

"Deep Space Starship"

Yes, I like that O.F. 1939

Last edited by Void (2020-05-05 17:40:37)

Void · 2020-05-05 17:41:42

Well of course other things have occurred to me from the stimulus of the name you provided, and the other possible objectives/destinations it might serve to get the human effort(s) to.

To me it makes sense that as "Deep Space Starship" will be intended to travel through atmosphere once and would not be likely to lift any cargo, just itself to the vacuum of space. We can tolerate hybrid engines (Hybrid of Sea Level and Vacuum engines), for this ship.

This then offers flexibility, justifying the retention of the hybrid engines that got it through the atmosphere.

We would then have a method to compensate for a price if one, or two, or indeed all three of the vacuum engines went kaput during the mission. The hybrids would not be efficient, so then it might be necessary to burn more fuel to reach the objective, or you could arrange to eject some of the payload to deep space, either of these options, in order to get the majority of the mass to it's objective.

I can't quite be sure of the need, but also if the hybrid engines were gimbaled as the sea level engines are supposed to be, (I believe), then some additional maneuvering options would exist. Not sure what the needs would be, but it might be retained for such a purpose.

And finally, a decision for Mars, Mercury, or the asteroid belt would be do you want solar panels that are destined for those locations to earn their keep, in flight, to power some kind of electrical propulsion, or to assist life support presuming you have crew.

Similarly, for deeper space objectives, the same question as per fission reactors. It would be nasty to bring an already operating fission reactor down to the surface of an outer solar system object, but by robotics, perhaps not impossible.

Done

Not Done.

Last edited by Void (2020-05-05 17:50:11)

Oldfart1939 · 2020-05-05 18:40:08

Void-
You may have noted that I listed several specific cases where the Deep Space Starship could be useful; the asteroid belt, including Ceres and Vesta, but specifically Callisto. I envision Callisto as the furthest objective accessible through current chemical propulsion technology. Realistically speaking, that's a real stretch due to transit time in years. Beyond the asteroids, we need to address nuclear thermal propulsion with much higher specific impulses. Solar energy also diminishes as inverse square of distance from the Sun, so we're looking at a whole new ballgame. Chemical propulsion, augmented with nuclear electric could reduce transit times, but the low thrust of electric propulsion isn't good enough yet to begin engineering a system.
All this said, this new innovative Starship variant shows the innate creativity of good engineers left unfettered by government bureaucrats and politicians.

Added it edit: Callisto is the only one of the 4 Galilean satellites of Jupiter with a reasonable Van Allen type radiation environment for humans to survive and accomplish work on the moon's surface. I predict Callisto will become future man's base camp and staging point for true deep space exploration to Saturn and Titan, and the Uranus-Neptune realm.

Last edited by Oldfart1939 (2020-05-05 18:44:59)

Void · 2020-05-05 20:42:39

O.F. 1939,

I regard your assessment as correct.

I also note that Callisto very likely has the chemical mix desired.

I also suggest that solar power is possible also for Callisto, because you might carve concave cavities in the materials of Callisto, probably linear around the equator. Aluminum foil then used to surface these cavities. Then you may arrange to have thermal and/or photoelectric receptors elevated above that. They should only need slight adjustment to stay in the slightly moving focus. I believe that Callisto does not have much of an axis tilt.

Some tricks similar to that as well. I have been thinking on that solar power one for some time.

Oldfart1939 · 2020-05-05 21:03:53

I don't want to take credit for the touting of Callisto as a human outpost; Robert Zubrin, in his book "Entering Space," discusses Callisto as a potentially habitable way station on the journey to the outer Solar System. Ganymede is also a possibility, but has a higher Van Allen background radiation issue to deal with. Callisto actually has a very thin CO2 atmosphere, and has water ice on the surface or below surface, which can provide refueling capacity for outward or Mars bound traffic. Combination of water ice and nuclear power will allow production of both Oxygen and Hydrogen by electrolysis, in addition to methane via Sabatier reaction of CO2 with Hydrogen.

Oldfart1939 · 2020-05-05 21:17:38

I wasn't certain, but after checking--Callisto is tidally locked with Jupiter. The solar power solution would be extremely limited in availability, and probably not worth the enormous engineering project you suggest. Beyond the asteroid belt, either nuclear or fusion energy comes into play as the power source. The orbital period of Callisto is 16.7 days, which means an outpost would be illuminated to some degree for 8.35 Earth days per orbit around the mother planet (father planet??) Jupiter. Given the temperatures on the surface, a powerful energy source would be required for sustaining a human presence.

Void · 2020-05-06 08:24:20

O.F. 1939,

Yes solar would be some trouble, but it is an available energy source if you use concentrating mirrors.

Fission may be possible. Unlike the other moons of Jupiter, Callisto is only partially differentiated. Also fragments of asteroid cores may have been impacting there for billions of years. It is possible that there may be materials near the surface to support fission. A similar argument may possibly be made for Mars. I will make the case that the Jupiter probe "Juno" actually uses solar panels for power in the orbit of Jupiter at this time. And it does not used concentrating mirrors.

https://en.wikipedia.org/wiki/Juno_(spacecraft)

The inner parts of the Jupiter system are far to hostile for our abilities at this time.

However, as you and others have pointed out Callisto is tolerable as a object of interest.

You might want to investigate the Trojan asteroids. About as many of them in association with Jupiter as there are in the actual asteroid belt.
Probably they have a lot of lighter materials, hopefully some metals.
https://en.wikipedia.org/wiki/Jupiter_trojan

Other resources of the Jupiter system could be it's magnetic field. Whereas Callisto is just outside of a main radiation belt, I would also like to look "Higher" in that field, to see if there is an ideal radiation environment. That is protection from GCR, and solar flairs. If so it could be a place to build synthetic gravitation habitats, from Callisto, Jupiter Trojan, and perhaps Main Belt Asteroids. And for those concentrating mirror should not be such a problem. They would be in microgravity, and could be of a very low mass construction.

Other Energy sources:
-On Callisto, you could extend energy generating tethers, and feed off of the differential motion between Callisto and Jupiters rotating magnetic field. Tethers might tend to be broken by impactors, so instead you might put the tether just under a layer of surface ice on the surface of the moon Callisto.
-In the Jupiter Trojans themselves, it may be possible to devise a method to harvest energy from the passing solar wind. Jupiter has them gravitationally locked into place, which would help.
https://science.nasa.gov/science-news/s … solarwind/
Now this one proposing to power the Earth, is, I think quite out of reach. But, if you had synthetic gravity habitats in the Jupiter Trojan "L4" and "L5" locations, I think the notion might be practical.

So, that about sums up what I am aware of as feasible resources for humans to try to use in the Jupiter system in the relatively near future. Relatively near, to me means 50-100 years, presuming a constant speed of progress of technology and intentions towards the solar system.

Last edited by Void (2020-05-06 08:40:37)

Oldfart1939 · 2020-05-06 08:55:19

Void-
Only reason the Juno probe is able to use solar is the constant irradiation using panels which are sun tracking configuration. The probe also uses Radioisotope Thermal generators to keep key components warm.

Void · 2020-05-06 09:02:02

A good thing for me to learn O.F. 1939.

Still while I will agree that solar for the Jupiter system is at the margins of utility, it is still a thing to look at if you have no Fission materials.
Hopefully Fission is a viable option.

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