
SpaceX Isn't Planning to Reuse the Falcon 9 Rocket's second stage - rbanffy
https://www.bloomberg.com/news/articles/2018-11-17/musk-spacex-not-planning-to-reuse-falcon-9-aims-to-speed-bfr
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martythemaniak
I think this is just confirmation of something that's been true for a while.
Stage 2 reusability went from "we're working on it" to "yeah, that's
interesting, we'll take a look at it when we have time".

I think they were a little burned by the Falcon Heavy we well. It's an awesome
rocket, but it'll take a while for them to even break even on its R&D, as it
looks like it won't ever fly more than 2 times per year and then it'll be
quickly supplanted by the BFR.

And so, while we won't see a reusable Falcon Stage 2, we will see some kind of
weird test hybrid / mini BFS build around the falcon stage 2. I imagine it's
just a Stage 2 with the shape and control surfaces of BFS to test their re-
entry procedures.

[https://spacenews.com/spacex-to-modify-falcon-9-upper-
stage-...](https://spacenews.com/spacex-to-modify-falcon-9-upper-stage-to-
test-bfr-technologies/)

~~~
exabrial
I read somewhere that the Falcon Heavy will find a new niche in direct-to-
Geosynchronous launches. Currently, most launches take you to a transfer
orbit, then you have to use your satellite's fuel to position yourself in
synchronous orbit, a maneuver that can take months. The Falcon Heavy skips the
second step and you save your satellite's fuel. Can't seem to find the article
at the moment though.

~~~
wolf550e
1\. It only takes months if your satellite uses only ion engines. If it has
regular hypergolic propellant engines it only takes hours.

2\. ULA's (Lockheed Martin and Boeing) Atlas V and Delta IV can make direct-
to-GEO insertion, and basically only the DoD wants that. SpaceX plans to use
FH to get DoD contracts, but it's not a very large market. It used to be very
lucrative for ULA, but SpaceX will lower prices so it won't be as lucrative
for them.

~~~
jryle70
Months going to GEO are months of revenue lost, and mass for propellant is
less mass for payload. That's the tradeoffs that may not be compelling for
some customers.

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bufferoverflow
It makes sense. If BFR works, it will make all the rockets obsolete, by simply
being fully reusable. Hence the only sensible thing to do is to concentrate
100% of the efforts on it.

~~~
cma
What all is different about the BFR heat shield compared to the shuttle? I
assume there is much newer tech since the 70s, is it easier to refurbish?

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bufferoverflow
The shuttle didn't do any re-entry engine burns. It fully relied on the
friction.

~~~
Retric
It's not really friction that's slows stuff on reentry. The heat is from
compressing the air. Which is why the heat spikes away from the vehicle.

Anyway, the rocket equation means if you wanted to slow down before reentry
you would effectively need to accelerate to twice the final speed 0 to X then
X to 0. That's simply not going to happen.

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LeifCarrotson
It takes much, much less energy to slow down a nearly-empty shell than one
that was full of fuel and oxidizer.

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manicdee
You have to take the slowing-down fuel with you on the speeding-up part of the
trip though, which means it takes much more energy to speed up in the first
place.

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twtw
Yes. SpaceX surely knows this, and reckons that the cost is worth full
reusability with reduced refurbishment cost.

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Retric
No, they are using a heat shield which is unnecessary if you slow down before
reentry.

What confuses people is you need to bleed off a little energy to start decent,
and another tiny amount to land. But, between those points 99% of the energy
is bleed off via air.

~~~
manicdee
You can compare the weight of the heat shield required for atmospheric reentry
braking to the weight of the fuel you need for propulsive reentry braking: if
the fuel weighs more, use the heat shield instead. This could be the
difference, for example, between 100t of fuel versus 15t of heatshield.

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lostmsu
Not directly related to the topic, but I wonder if there's a way to at least
partially recover energy, spent on lifting stuff to the orbit, from kinetic
energy rockets have on reentry.

This question also applies to the heat generated from atmospheric friction
during liftoff and landing. And also to payloads.

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Nzen
When I want those kinds of perspectives, I usually check out the 'Isaac
Arthur' channel [0].

[0]
[https://www.youtube.com/channel/UCZFipeZtQM5CKUjx6grh54g/vid...](https://www.youtube.com/channel/UCZFipeZtQM5CKUjx6grh54g/videos)

Guessing as my uninformed self, I suspect we could recover energy by building
a tower that acts as the opposite of a rail cannon. If the craft is emitting a
magnetic field as it descends, it could create an electric current in the
tower. Of course, it would need to nearly touch the tower or emit a very
strong magnetic field, so the conditions probably contrive against this
scenario.

<edit adds succeeding> Or, descend through a tower and let the escaping air
drive a turbine.

I think the problem is that the energy has high intensity and low duration. It
would be similar to asking if we can get _some_ residential power with a
military grenade.

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ben_w
I’ve seen a suggestion that magnetic breaking of the form you suggest is a
better way to generate power from mining the moon than He3 — difference in
gravitational potential and extremely low concentrations of the latter in the
lunar surface.

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CamperBob2
What's the status of their efforts to recover and recycle the payload fairing?
I remember reading that they expected to save $1M or more per launch by doing
that.

~~~
wolf550e
No success yet. They are going to move the fairing catching boat "Mr Steven"
from the west coast to the east coast to then try again. And the fairing is
~$6M so they can save ~$5M per launch if it works.

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cagenut
I have no information other than the timing but it seems like that spate of
firing he did enabled both the starlink redesign and the focus switch to bfr.

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regnerba
Were there firings at more than the Starlink office?

