Astrobotic PM-1 mission, CLPS mission with NASA and commercial payloads Options

[mcaplinger]

...3) pressure regulator failure leading to overpressurization.

Astrobotic is now saying

Astrobotic’s current hypothesis about the Peregrine spacecraft’s propulsion anomaly is that a valve between the helium pressurant and the oxidizer failed to reseal after actuation during initialization. This led to a rush of high pressure helium that spiked the pressure in the oxidizer tank beyond its operating limit and subsequently ruptured the tank.

This seems odd to me, since usually such a valve would open just once and then a downstream regulator would maintain system pressure at the desired safe level. But it sounds like they tried to avoid needing a regulator by just burping the valve open briefly (in hindsight maybe not such a good idea.)

[Explorer1]

https://www.astrobotic.com/update-10-for-pe...ne-mission-one/

Peregrine has been operational in space for 55 hours. We are at an approximate distance of 192,000 miles from Earth, which is 80% of the way to lunar distance. Although we are approaching lunar distance, the Moon won’t be there. We remain on our nominal trajectory for the mission, which includes a phasing loop around Earth. This loop goes out to lunar distance, swings back around the Earth, and then cruises out to meet the Moon. This trajectory reaches the Moon in about 15 days post-launch.

Peregrine continues to leak propellant but remains operationally stable and continues to gather valuable data. We estimate that we will run out of propellant in about 35 hours, an improvement on yesterday’s update. The team is working around the clock to generate options to extend the spacecraft’s life.

[Phil Stooke]

https://twitter.com/tony873004/status/1745274757417931128

This tweet (or whatever you call it these days) predicts a lunar impact on the second apogee.

Phil

[Thorsten Denk]

> This tweet (or whatever you call it these days)
I call it "TwiX"
Thorsten

[marsbug]

Jeff Foust reports that nine of the payloads are powered, and data is being collected - relating to how they operate in the space environment, not regarding the Moon, obviously - but that's still valuable for the payload teams. Article here: <a href="https://spacenews.com/astrobotic-gets-payloads-working-on-ailing-peregrine-lander/" target="_blank">https://spacenews.com/astrobotic-gets-paylo...regrine-lander/</a>

[Explorer1]

Great to see transparency from Astrobotic; Update #13 shows even another rover is functional.

They must all be glad that the other systems seem to be working perfectly, even though it's a pity the best they will be is impact probes (if that is in fact the trajectory). Would be an interesting target for LRO and yet another mark (or marks) on Phil's maps...

[Thorsten Denk]

I wonder if they still have enough control to do minor trajectory corrections.
Because in this case, maybe they could "choose" if the probe impacts the Moon, falls back on Earth, remains in a high orbit around Earth, or enters into orbit around the Sun.
I'm also not sure which one of these options would be the most desirable. (Thinking in particular what should happen to the ash they have on board.)

Thorsten

[HSchirmer]

This seems odd to me, since usually such a valve would open just once and then a downstream regulator would maintain system pressure at the desired safe level. But it sounds like they tried to avoid needing a regulator by just burping the valve open briefly (in hindsight maybe not such a good idea.)

That valve trouble sounds similar to Apollo 6, which was damaged due to valves opening and causing \'pogo\' shockwaves / water hammer effects in the piping.

I wonder if they still have enough control to do minor trajectory corrections.

I wonder if the rover\'s battery capacity could be tapped to extend the mission\'s data collection, ala Apollo 13?

If there rover battery is isolated, then try and deploy the rover, perhaps the existing spin could launch the rover into a slightly different trajectory?
You wouldn\'t change the distance much, but perhaps get enough separation to generate \'stereo impacts\' for seismic monitoring?

PostScript- looks like the lander is exposed to space and could be let loose?

[Explorer1]

Well, there's no functioning seismometers on the moon at the moment to benefit, so that's a bit of an issue.
I do agree that the payloads that can be released, may as well be. There is nothing to lose, is there?

[HSchirmer]

Well, there's no functioning seismometers on the moon at the moment to benefit, so that's a bit of an issue.

Yep, that's a problem.
Hmm, I thought somebody had gotten seismic data in recent years using the old Apollo laser retroflector array (LRA)... or perhaps I'm misremembering, and it was just modern re-analysis of old Apollo data.

But, "if you knew the impact time in advance, could the existing array of Apollo laser retroreflectors be used to obtain usable seismic data, extracted from the jitter of the laser signal?" seems like an interesting nerdy question, (or homework for a graduate physics course).
But to GET that level of precision on impact time, you'd have to get precise measurements of Peregrine's trajectory. Probably, the range & orbit can be roughly calculated based on loss of signal going behind the moon / reacquisition of signal upon emergence?
Fortunately, IIRC Peregrine does have a next-gen laser retroreflector mounted on its deck, so perhaps it would be possible to use the retroreflector to get more precise distance and angle measurements over time? Then use that prediction of impact time to turn on ranging lasers and see if the Apollo LRA shows any jiggle.

Who knows, perhaps the Psyche laser communication cat-video could be reused to paint the lunar LRA during predicted impact? (Quick review) as a rough guess, a 267 megabit per second laser signal SEEMS like it should contain enough information to identify signal jitter caused by from siesmic events shaking the LRA?

[Phil Stooke]

Scott Tilley has an impact prediction:

https://twitter.com/coastal8049/status/1745668952754389197

The current estimated location is near Luna 13 in Oceanus Procellarum.

Phil

[Explorer1]

Some (marginally) better news.

Peregrine has now been operational in space for more than 4 days. The spacecraft remains stable and operational, and is currently in a planned loss-of-signal period for about another hour and a half. The leak rate on Peregrine has continued to slow, and the spacecraft is estimated to now have 52 hours of propellant remaining. Our engineers continue to work on solutions to extend life expectancy and there is growing optimism that Peregrine could survive much longer than the current estimate.

EDIT Dec 13:

Lunar distance achieved, teleconference with NASA set for Thursday.
Some more optimism about extending the life of the lander, and certainly a major milestone just to get this far. I am reminded of Philae's many difficulties 10(!) years ago, and the sudden imposition of a time limit. If the various payloads can be tested as much as possible regardless of the impossibility of soft landing, that is still quite an achievement. Perhaps the rovers can be released, even if it's futile....

[Greenish]

Been thinking about ways to visualize the evolving fuel situation, and whether it was converging towards anything or otherwise showing trends. I thought of two ways.

• First version plots the projected zero-fuel time vs the update time, alongside a reference "out of time" line (where y=x). Some linear trendlines indicate that initially they weren't improving faster than the leak. But eventually have caught up and overall each improvement was been greater than the proportional loss during the time between updates (dy/dx > 1). But that should probably be interpreted in light of a presumably ~exponential decay...
• Second illustration tries to show that a little more directly. At each update timestamp I draw a line* to zero after the stated number of hours. Initial "fuel" value at time of anomaly report (update #1) arbitrarily set to 100, projecting backwards using slope from following update (#6, which was the first one with a time estimate). *N.B: may make more sense to think of y-axis like log(remaining fuel)? Not sure if that distinction makes a difference anymore...

And of course, between the time I started plotting and when I post this, now they're projecting to hit the Earth. Ah well.

[Greenish]

In case anyone cares to not re-do the tabulation, here's the values I used.

CODE

Update #, Update Timestamp, Stated Remaining Hrs, Est Zero Fuel Time
14    2024-01-12 11:52    52    2024-01-14 15:52
13    2024-01-11 19:01    48    2024-01-13 19:01
11    2024-01-10 18:35    36    2024-01-12 06:35
10    2024-01-10 10:56    35    2024-01-11 21:56
7     2024-01-09 12:17    40    2024-01-11 04:17
6     2024-01-08 21:16    40    2024-01-10 13:16
1     2024-01-08 09:37    n/a

[HSchirmer]

eventually have caught up and overall each improvement was been greater than the proportional loss during the time between updates

Well, I'd suspect that a stuck valve works both ways. Which suggests that there is now a helium & NO/NO4 froth filling the oxidizer and pressurant tanks. Which might not be so bad, having some liquid in the pressure tank might have helped to close the wonky valve.

The analogy I think of is just cracking open a warm 2 litre bottle of soda- you get an initial blast of carbonated water, but that quickly subsides and what mostly escapes the opening (here the cracked tank) is the gas, not so much the liquid.

Perhaps the trick here would be figuring out a way for 'ullage thrust' to push the "flat soda" oxidizer (and fuel) into the engine for a burn attempt?