Post by Lynn McGuire Post by Thomas Koenig Post by Lynn McGuire
Landing on the tail with fire coming out is oh so cool !
It is also an _extremely_ arrogant maneuver that they managed to
pull off, time and time again.
So how would you have the first stage rocket land for reuse ?
Landing on the tail with a rocket engine isn't the arrogant part, it's
even been done before. Landing using a *Suicide Burn* (though SpaceX
tries to promote "hover slam" instead...) because your engine is far
to powerful to allow a normal landing WAS/IS considered arrogant.
IE, the hard part about the landing a Falcon 9 first stage is that
even with just a single rocket running at the lowest possible setting
they have a T/W of way above 1. Depending on assumptions the lowest
possible T/W is somewhere in the 1.8 to 2.05 range for an nearly empty
Falcon 9 first stage (SpaceX doesn't publish the data needed to
compute it exactly).
Given that they can't shut it down and then restart the engine either
at this point this means they get exactly one attempt and has to nail
it (nearly) perfectly, if they missed low they've crashed, if they
missed high they have to cut power anyway and fall the rest of the way
because not doing so will make things worse (due to T/W>1).
It may SOUND simple (not!) but AFAIK it resulted in several new
peer-review mathematical papers plus a lot of experimenting to get it
Post by Lynn McGuire
The rocket used for the 60 Starlink satellites Wednesday was on its 6th
The Starlink-8 mission was B1049's 5th launch (second one) and landing
(first), not 6th.
B1048 was the first booster to do a 5th launch, it didn't land due to
an earlier engine failure late in the ascent, it had to burn the other
engines for longer to compensate and thus ended up with too little
fuel left. The root cause was found to be an issue with the
cleaning/refurbishing procedures that has been corrected.
That extra resilience is one of the beauties with SpaceX approach of
using using 9 engines and using "extra" capacity when available to
enable reuse, during most of the first stage ascent the rocket can
automatically compensate for one failing engines (and late enough even
if two fails) by using that reserve which is so much better loosing
the payload (which often cost many times the rocket launch).
Other than to NASA or the US Military SpaceX are basically not
offering non-reusable Falcon 9 launches any longer, if you want that
much performance they'll sell you a reusable Falcon Heavy launch for
less than the non-reusable Falcon 9 used to cost - this is for the
cheapeast FH variant, with both side core landing on land and the
center core on a drone-ship (there are other more powerful variants).
Post by Lynn McGuire
Landing on the tail is all about reuse. Don't you care about recycling
our tools and materials ?
There are other ways to reuse, IE things like SSTO, the current Skylon
schema (and the very different earlier ones!), "parachutes", "grabbed
by helicopter" (being tested on Elektron), "eject engine/avionics and
grab by helicopter" (being studied for Vulcan) or "separate
engine/avionics and put propellers on it" (being studied for possible
future version of Ariane 6).
The method SpaceX uses work FOR THEM because their design is is built
explicitly for it, having a fairly early stage separation and
oversized/owerpowered second stage - this helps them with reuse of the
first stage but hurt them a bit for GTO or any launch further out
(but not having a LH2 engine is a bigger handicap for high C3 launches
anyway but... FH's cheap brute force still makes it often doesn't matter).
Starship+SuperHeavy follows a similar template, it too stages
comparatively early and has a powerful second stage but since they use
methalox instead it doesn't hurt them quite as much for high-C3
mission - and methalox allows ISRU for Mars which is massive plus for
Musks stated long term goals.
Pretty much ALL other large rockets go way faster at stage separation
(need way heavier heat shield) and have comparatively puny second
stage engines which makes it much harder to use the approach SpaceX
uses, basically they'd need to throw away everything they have and
start from scratch to use it and they have way too much invested to do
As such it should come as no surprise the only other real actors that
is going for a similarish approach is Blue Origin's New Glenn, no old
hardware to bog them down. I'm explicitly ignoring various "lets copy
Falcon 9 and launch it in 2025 or more likely 2028+" proposals
For smaller rockets (like Elektron) I think parachutes or more likely
grabbed by helicopter is the mostly likely ways forward IF the payload
penalty is doable for smaller rockets.