Author Topic: Sierra Space: General Company and Development Updates and Discussions (Read 51140 times)

Robotbeat · « **Reply #60 on:** 04/11/2025 03:13 am »

Regenerative fuel cells don’t really outperform lithium batteries for the most part. Not for daily cycling, at least.

JEF_300 · « **Reply #61 on:** 04/27/2025 05:40 am »

Quote from: Robotbeat on 04/11/2025 03:13 am

Regenerative fuel cells don’t really outperform lithium batteries for the most part. Not for daily cycling, at least.

What do you mean by perform here? Cause it would seem to me there are a lot of metrics to judge by.

Robotbeat · « **Reply #62 on:** 04/28/2025 04:58 pm »

Quote from: JEF_300 on 04/27/2025 05:40 am

Quote from: Robotbeat on 04/11/2025 03:13 am
Regenerative fuel cells don’t really outperform lithium batteries for the most part. Not for daily cycling, at least.

What do you mean by perform here? Cause it would seem to me there are a lot of metrics to judge by.

total system mass for earth or mars.

For the moon, it can potentially go the other way, but it’s still close.

JEF_300 · « **Reply #63 on:** 04/28/2025 07:47 pm »

Quote from: Robotbeat on 04/28/2025 04:58 pm

Quote from: JEF_300 on 04/27/2025 05:40 am
Quote from: Robotbeat on 04/11/2025 03:13 am
Regenerative fuel cells don’t really outperform lithium batteries for the most part. Not for daily cycling, at least.

What do you mean by perform here? Cause it would seem to me there are a lot of metrics to judge by.
total system mass for earth or mars.

For the moon, it can potentially go the other way, but it’s still close.

Ok. That's what I guessed you'd meant, but I'm glad we clarified. And regenerative fuel cells performing similar or worse than lithium batteries in daily use, in terms of overall mass, makes sense to me with my limited knowledge.

So my intuition is that regenerative fuel cells might do better than lithium ion batteries for long term (ISS-like, multi-decade) deployments, especially in a thermal environment as extreme as the surface of the Moon. And since the vast majority of the imagery in this video is of a Moon base...

Does this make any sense? I'm not well plugged into the power systems world.

Robotbeat · « **Reply #64 on:** 04/29/2025 07:59 pm »

No, on the contrary, the regenerative fuel cells are more complicated with more moving parts (valves, etc), and so likely will last less long (note that the actual fuel cells themselves are electrochemical devices with degradation over time much like lithium cells, on top of the moving parts & pressure vessels).

I was referring to energy storage period and cycle time. For the Moon, you’re storing enough for 14 days of darkness instead of like half a day or so on Mars or Earth.

TrevorMonty · « **Reply #65 on:** 05/01/2025 06:23 pm »

When used as part of a fuel cell, 1 kg of hydrogen can produce up to 23 kWh of electrical energy.

https://ahdb.org.uk/knowledge-library/hydrogen-electrolysis#:~:text=When%20used%20as%20part%20of,lower%20with%20an%20older%20battery.

Typical Li Ion battery is 250WH per kg.

To increase storage just need to add more LH and LOX tanks which are lot lighter and simpler than batteries.
Producing LH and LOX from water exhaust during lunar day shouldn't be issue given amount of solar available.

Robotbeat · « **Reply #66 on:** 05/03/2025 12:59 pm »

Okay, so now you also need water tanks.

Lithium batteries are available at up to 500Wh/kg.

AndrewM · « **Reply #67 on:** 05/08/2025 11:19 pm »

Full Press Release

https://twitter.com/SierraSpaceCo/status/1920448680483586190 [May 8]

Quote

We have had another successful demonstration of our Resilient GPS (R-GPS) technology for the U.S. Space Force (USSF). In this third milestone, our team demonstrated an early integration of the R-GPS satellite technology through FlatSat flight software and hardware subsystem testing, in addition to successful communication with ground software.

Press Release: https://sierraspace.com/press-releases/sierra-space-marks-third-testing-milestone-with-space-force-r-gps-satellite-program