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Rocket Labs is well known in our community for using electric turbopumps on it's Rutherford engines used in Electron. Back on September 18, 2023 Eectron's string of 20 consecutive successes ended when the 2nd stage battery
hotswap resulted in arcing rather than running. <URL:https://youtu.be/AfYFqsk_NGk?t=2961>
Beck's kids resumed launches on December 15 using a nitrogen gas environment to suppress flashes on the hotswap. This was the 42nd Electron launch. <URL:https://youtu.be/iLwTLqaCnQ8?t=881>
See the nitrogen bottle at the topleft at <URL:https://youtu.be/iLwTLqaCnQ8?t=2452>
and at about t=2500 you see the battery pack falling towards the clouds.
Today was the 52nd launch, and the second with an upgraded battery system. The mylar bag and nitrogen bottle are not visible in the camera view, and a bare box is jettisoned successfully. <URL:https://youtu.be/wFH0ZS2GHd8?t=1590>
Launch 51:
<URL:https://youtu.be/ZdikUDvKYmc?t=2138>
for Synspective, a Japanese earth obs company.
Both the failed launch and today's launch were for SAR satellites belonging to Capella Space. The return-to-flight launch was also a SAR, for Japan's IQPS, and #51 was yet more SAR satellites.
[I remember when SAR filled the shuttle payload bay, definitely not a small-sat technology then.]
It seems Rocket Lab will not be doing this battery swap on Neutron.
The Archimedes engine is a staged combustion methalox engine, used on
both stages.
Snidely <snidely.too@gmail.com> wrote:
It seems Rocket Lab will not be doing this battery swap on Neutron.
Not really surprising, one of the reasons that batteries makes sense
on Electron is because it's a small rocket and turbo-pumps doesn't
really scale down that well while electric motors and batteries do. It
also let them avoid having to design the turbo pump which is not a
trivial exercise which likely helped with time-to-market.
While there's other methods that can be used for small engines but
they all come with downside so it comes down to weighing (pun
intended) the downsides of the various approaches.
I believe it was the right call for both weight and complexity for a
rocket of Electron's size (and likely got them running earlier) but
note that the only other electric pump engine so far is only very
marginally larger (Astra's Delphin engine at 29kN sealevel thrust vs Rutherford's 25kN).
Rocketlab's Archimedes engine is supposed to have 730 kN sealevel
thrust and 890 kN vacuum thrust (vs 26kN), IE 29-34 times more
powerful - as I understand it the battery pack required would likely
weight many times more than the turbo pumps at this scale which could
easily eat into the payload.
As mentioned designing a turbo-pump definitely isn't trivial but... in
this size class it's probably not avoidable if you want a rocket that
can compete! And it seems Rocketlab came to a similar conclusion given
the likely time-to-market advantage of electric pumps.
Exactly how big a rocket engine can get before battery weight becomes
a BIG problem is hard to say for an outsider and will vary depending
on specific requirements (including development time) but I think
there's good reason to believe it currently is well below the size of Neutron/Archimedes and will stay that way for the foreseable future.
I am a bit surprised we haven't seen more electric pump based upper
stage engines yet, I think they could make more sense there than for
big lower stage engines (higher Isp than open cycle which is the usual
other alternative). They may well be coming, it takes a long time to
design new engines.
The Archimedes engine is a staged combustion methalox engine, used on
both stages.
If you're designing a new reusable rocket and new rocket engine it
probably makes sense to go for methalox even if SpaceX has shown that
it is in fact possible to do with kerolox though that is a
gas-generator engine which likely helps with that.
instead, and see how that works out.-- Katy Jennison