CLPS Mission Design Trade-Offs

[Zed_Noir]

So how silly would it be to put an Estes-E sized solid (Burn Time: 2.4 sec; Total Impulse: 27.2 N-sec; Mass: 59.9 g) on each leg and auto-fire it just before contact? Soyuz capsules (and New Shepard?) sort-of kind-of do this.... It softens the blow, so to speak, reducing 'jerk.' They would also help pitch the lander to match the slope. Once they've all fired the total imposed torque would be zero. Retail cost is less than $12 per motor, and if you agree to slap an Estes decal on your lander I bet you get them for free....

What could possibly go wrong?

they don't fire at the same time

Plus what to use as proximity sensor to initiated ignition of each motor along with power and control issues.

Also how would the Estes motors fared in vacuum and zero-G conditions along with possible thermal issues from being in sunlight and in the shade.

Until the Estes motors have demonstrated to work nominally in near Lunar surface environment after transit from LEO. They shouldn't be considered for use on a Moon lander. Someone will have to do kamikaze lithobraking with maybe a cubesat Estes motor test rig over the Lunar regolith first.

[edzieba]

So how silly would it be to put an Estes-E sized solid (Burn Time: 2.4 sec; Total Impulse: 27.2 N-sec; Mass: 59.9 g) on each leg and auto-fire it just before contact? Soyuz capsules (and New Shepard?) sort-of kind-of do this.... It softens the blow, so to speak, reducing 'jerk.' They would also help pitch the lander to match the slope. Once they've all fired the total imposed torque would be zero. Retail cost is less than $12 per motor, and if you agree to slap an Estes decal on your lander I bet you get them for free....

What could possibly go wrong?

I assume you mean firing up, unlike the Soyuz and Shenzhou landing motors?
Rather than on the legs, a single upward-firing thruster triggered by any leg contact may work to settle the lander and null horizontal and rotation residuals through constraint (friction against the ground) as long as the legs are beefy enough that the maximum impact force from landing plus hold-down thrust does not snap one - at which point your settling thruster has just made things worse.

However, any extra thrusters/giant wide legs/harpoons/sticky goop/other-ACME-catalogue-sourced-mechanisms all need to trade against 'land without the residuals in the first place'. We have existence proof that tall spindly objects can reliably land vertically after descent from high velocities, even with the added problems of wind and the ground bouncing up and down and rolling about. This is not an intractable problem that needs more hardware thrown at it, it just takes a few tries to debug.

[sdsds]

I assume you mean firing up, unlike the Soyuz and Shenzhou landing motors?
[...]

Hadn't thought of that option! Currently knowing nothing about the failure mode a certain six-legged lander experienced, it's tough to guess if hold-down thrust would have helped.

Plus what to use as proximity sensor to initiated ignition of each motor along with power and control issues. [...]

Yes, in truth it's hard to envision any actively controlled solution that wins over purely passive, mechanical, one-time-use 'crush zone' shock absorbers.

[Jim]

Plus what to use as proximity sensor to initiated ignition of each motor along with power and control issues.

Also how would the Estes motors fared in vacuum and zero-G conditions along with possible thermal issues from being in sunlight and in the shade.

Until the Estes motors have demonstrated to work nominally in near Lunar surface environment after transit from LEO. They shouldn't be considered for use on a Moon lander. Someone will have to do kamikaze lithobraking with maybe a cubesat Estes motor test rig over the Lunar regolith first.

Use Aerotech motors

[Zed_Noir]

Plus what to use as proximity sensor to initiated ignition of each motor along with power and control issues.

Also how would the Estes motors fared in vacuum and zero-G conditions along with possible thermal issues from being in sunlight and in the shade.

Until the Estes motors have demonstrated to work nominally in near Lunar surface environment after transit from LEO. They shouldn't be considered for use on a Moon lander. Someone will have to do kamikaze lithobraking with maybe a cubesat Estes motor test rig over the Lunar regolith first.

Use Aerotech motors

@Jim, you are no fun.
Would really want to see someone try to test fire an Estes motor over the Lunar regolith.

Are there solid Aerotech motors as puny as an Estees motor?

[sdsds]

[...]
b) their choice to contain the propellants rather than allow boil-off meant temperature/pressure were rising and they risked loss of tank structural integrity?

[...]
b.  They likely had vents

That was my assumption, until the media telecon where Altemus or Crain seemed to say they had zero boil-off. Any use of a pressure-relief vent counts as boil-off, yes?

So yes, Crain confirmed they used vents, making no statement about boil-off rates though.

[sdsds]

a) their supply of gaseous helium, used for both RCS and tank pressurization, was running low?

Crain or Altemus confirmed the lander ended up on the surface with no remaining consumables. Yet they showed the engine firing at the surface, so apparently ran dry immediately after propulsion was no longer necessary, i.e. near-zero margin.

[Jim]

Plus what to use as proximity sensor to initiated ignition of each motor along with power and control issues.

Also how would the Estes motors fared in vacuum and zero-G conditions along with possible thermal issues from being in sunlight and in the shade.

Until the Estes motors have demonstrated to work nominally in near Lunar surface environment after transit from LEO. They shouldn't be considered for use on a Moon lander. Someone will have to do kamikaze lithobraking with maybe a cubesat Estes motor test rig over the Lunar regolith first.

Use Aerotech motors

@Jim, you are no fun.
Would really want to see someone try to test fire an Estes motor over the Lunar regolith.

Are there solid Aerotech motors as puny as an Estees motor?

Don't think black powder would work

[Comga]

So how silly would it be to put an Estes-E sized solid (Burn Time: 2.4 sec; Total Impulse: 27.2 N-sec; Mass: 59.9 g) on each leg and auto-fire it just before contact? Soyuz capsules (and New Shepard?) sort-of kind-of do this.... It softens the blow, so to speak, reducing 'jerk.' They would also help pitch the lander to match the slope. Once they've all fired the total imposed torque would be zero. Retail cost is less than $12 per motor, and if you agree to slap an Estes decal on your lander I bet you get them for free....

What could possibly go wrong?

they don't fire at the same time

They are not supposed to fire at the same time in this (unlikely) scheme
Each pad has a contact probe that triggers the little motor
If one leg makes contact earlier than the others it fires earlier and the torque helps align the lander with the surface.

Of course, those of us who flew Estes rockets (Is there a weirdo here who didn’t?) know how long it takes for the electrical igniters to work. (I once built a giant model rocket with three engines side by side.  The third lit about 100 feet above the launch pad. Still flew straight!)


If all worked as conceived it would work almost as well as big balls of compressible aluminum sponge.

But that brings to mind another option for a future CLPS lander: a lunar version of the 1970’s Estes rocketcam, an Eaglecam from overhead.  Carry an Estes rocket with a rearward facing camera and a tiny transmitter.  Take context images of the lander. Get Estes to sponsor it.

[HMXHMX]

Or perhaps just build adequate gear?

[sdsds]

[...]
But that brings to mind another option for a future CLPS lander: a lunar version of the 1970’s Estes rocketcam, an Eaglecam from overhead.  Carry an Estes rocket with a rearward facing camera and a tiny transmitter.  Take context images of the lander. Get Estes to sponsor it.

This imaging from above scheme seems grand! I suppose as with any separation event someone would need to perform a re-contact analysis. Presumably that motivated sideways ejection of EagleCam.

[sdsds]

NASA (and previously the NACA) have a mandate to foster the aerospace sector of the US economy. Terms like commercial or private largely mean spaceflight conducted by 'for-profit' enterprises. CLPS markedly advances that approach.

For-profit enterprises bring to spaceflight a set of priorities different from those of academic research entities. CLPS providers care about lunar science only because customers might pay them to facilitate collection of science data. CLPS providers care about technology development either because customers will pay to facilitate it, or because their business plan calls for use of the technology to provide service to customers. CLPS providers care about prestige not out of nationalistic fervor but out of a desire to attract new customers to their brand.

Prestige has marketing value. Coca-cola is just flavored sugar water, and yet the brand is a major asset of the for-profit company that owns it. To succeed, CLPS providers need to establish awareness of their brands, and positive brand impressions. If doing that isn't part of a business plan the business won't thrive in a competitive marketplace.

The early CLPS missions have huge marketing potential. The EagleCam photo that wasn't obtained would have dramatically increased the value of the Nova-C and Intuitive Machines brands. It could have made front-page above-the-fold news in major media outlets. Those are  print-media phrases from days long past. Today still image photos are archaic, replaced by videos. So thus the marketing organization in a forward-thinking CLPS company should be strongly motivated to capture third-person perspective video of a lunar landing.

Is that actually difficult? I suggest a micro-sat payload released after descent initiation could use a telescopic camera to capture a video of the landing from a location in orbit just past perilune. Pointing could perhaps be done solely by tracking the telemetry transmissions of the lander. On the first perilune pass the micro-sat would be radio-silent; on a subsequent pass it would transmit the video to the lander for relay to Earth. Sure, lander telemetry gives more technology development data, but the video would have much more marketing value.

[Steven Pietrobon]

Did the Apollo LM contact probes actually extend as far as shown in this diagram?

Yes they did. For Apollo 11, they removed the front probe to prevent it interfering with the astronauts exiting the lander. Each probe was 1.7 m long.

https://space1.com/Artifacts/Lunar_Module_Artifacts/Surface_Sensing_Probe/surface_sensing_probe.html
https://www.nasa.gov/history/alsj/a11/a11.landing.html

And ... are contact probes still a thing?

I'm not aware of them being used on recent landers.

[Steven Pietrobon]

So how silly would it be to put an Estes-E sized solid (Burn Time: 2.4 sec; Total Impulse: 27.2 N-sec; Mass: 59.9 g) on each leg and auto-fire it just before contact?

Well, perhaps using Estes motors might be bit a silly, but the Russian LK crewed Lunar lander was going to use four upward firing motors to settle the vehicle on landing!

https://nick-stevens.com/2016/02/20/soviet-lk-moon-lander/

[Steven Pietrobon]

So thus the marketing organization in a forward-thinking CLPS company should be strongly motivated to capture third-person perspective video of a lunar landing. Is that actually difficult?

Yes! Transmitting live video from 400,000 km away is not trivial. You a need a steerable high gain antenna with a few watts behind it to get the required link margin.

[sdsds]

So thus the marketing organization in a forward-thinking CLPS company should be strongly motivated to capture third-person perspective video of a lunar landing. Is that actually difficult?

Yes! Transmitting live video from 400,000 km away is not trivial. You a need a steerable high gain antenna with a few watts behind it to get the required link margin.

Live video would be really challenging, but once landed the lander could relay to Earth cached video received from the still-orbiting camera?

[chopsticks]

So thus the marketing organization in a forward-thinking CLPS company should be strongly motivated to capture third-person perspective video of a lunar landing. Is that actually difficult?

Yes! Transmitting live video from 400,000 km away is not trivial. You a need a steerable high gain antenna with a few watts behind it to get the required link margin.

Yet they did it on Apollo (TV camera).

[Bunsen]

So thus the marketing organization in a forward-thinking CLPS company should be strongly motivated to capture third-person perspective video of a lunar landing. Is that actually difficult?

Yes! Transmitting live video from 400,000 km away is not trivial. You a need a steerable high gain antenna with a few watts behind it to get the required link margin.

Yet they did it on Apollo (TV camera).

Apollo needed 20 watts of RF into a 20.5 dB gain¹ steerable antenna on the LM and the 70 m DSN antennas receiving.  Technology has improved since then, of course, so you might be able to do it with around 20 dB less in the link budget depending on desired video quality.  That would let you ditch either the high power amp and need for the 70 m dishes or the steerable antenna on the lander.  That's a significant burden -- 20 W of radiated RF probably means 100-200 W of power consumption, a steerable antenna is heavy and bulky (and relies on correct attitude knowledge and body motion staying in bounds and below its maximum slew rate), time on the big DSN dishes is scarce and expensive, and you need at least one of those or some combination of all three.  It's entirely doable, but plenty costly.

[1] I think this is dBi, but the technical note I'm reading isn't explicit.

[edzieba]

Apollo also sent slow-scan TV (200 TV lines, 10 FPS, colour frame sequential). By today's standards, that would be 'not even potato'. It was also not sent live during descent. Apollo also had the advantage of a much more extensive network of fixed and mobile ground stations than the DSN has available today (as well as having access to the DSN at the time, too).

[sdsds]

On the topic of physical contact sensors and other 'old school' ways of doing things, what's the status of radar for range detection during terminal descent? Given the ... technical difficulties ... with lidar lasers, not to mention their cost, is lidar really a design solution superior to radar?