Space catches its nose shrouds

Not nearly as important as recovering the first stage, but still
recovering the nose cone reduces yet again launch costs for SpaceX.
Their fairing recovery ships caught both halves of the nose cone on
their launch Monday.

https://spaceflightnow.com/2020/07/2...fairing-catch/

Alain Fournier

On Jul/25/2020 at 19:37, JF Mezei wrote :
On 2020-07-25 14:49, Alain Fournier wrote:
Not nearly as important as recovering the first stage, but still
recovering the nose cone reduces yet again launch costs for SpaceX.
Their fairing recovery ships caught both halves of the nose cone on
their launch Monday.


How is this done?

is there logic on the fairing to control parachutes to steeer to the
location of ship with the net?

Or does the ship with the net have high speed capability to position
itself under the arriving fairing?

My understanding is that it is the latter, the ships are high speed and
go to where the fairing will fall.

In the first case, I assume the awaiting ships are pre-positioned to
area where the fairings are expected to drop based on wind etc.

From orbital mechanics point of view, was this a question of SpaceX
learning how long it takes for the fairings to tumble in space before
they "hit" atmosphere and start to fall? Or it is a calculated thing?


Alain Fournier

On 2020-07-26 5:03, Alain Fournier wrote:
On Jul/25/2020 at 19:37, JF Mezei wrote :
On 2020-07-25 14:49, Alain Fournier wrote:
Not nearly as important as recovering the first stage, but still
recovering the nose cone reduces yet again launch costs for SpaceX.
Their fairing recovery ships caught both halves of the nose cone on
their launch Monday.


How is this done?

is there logic on the fairing to control parachutes to steeer to the
location of ship with the net?

Or does the ship with the net have high speed capability to position
itself under the arriving fairing?

My understanding is that it is the latter, the ships are high speed and
go to where the fairing will fall.


A considerable time ago, there was a video of a failed catch of a
fairing dropped from a helicopter. It was evident that the yaw (azimuth)
stability of the fairing+parachute was poor, with sometimes rapid
deviations left or right, which the ship could not match, because the
ship would have had to go "sideways" -- the ship could not turn quickly
enough to match the new trajectory.

This yaw instability probably depends a lot on the amount of turbulence
-- gusts -- in the wind. The videos from the recent successful catches
suggest a very calm day, with stable, laminar wind flow. Even so, the
fairings were caught close to the side edges of the nets.

Unless SpaceX can improve the fairing+parachute yaw stability, it seems
to me that the catch rate will remain low, and catches will succeed only
on such calm days.

Possibly the ship itself, and its motion through the air, are causing
turbulence in the wind wake. An aerodynamic design of the ship
superstructure might help.

Or the final approach and catch could be secured by using a drone to
carry a towing wire from the ship to the fairing, when the fairing is
say 100 m up, and then using the wire to slowly pull the fairing down
and into the net.

--
Niklas Holsti
niklas holsti tidorum fi
. @ .

In message
Alain Fournier wrote:

On Jul/25/2020 at 19:37, JF Mezei wrote :

is there logic on the fairing to control parachutes to steeer to the
location of ship with the net?

Or does the ship with the net have high speed capability to position
itself under the arriving fairing?

My understanding is that it is the latter, the ships are high speed and
go to where the fairing will fall.

It's both. The parachutes are derivatives of military systems that use
active steering to deliver a drop to a relatively small area, the ships
are fast and manoeuverable with multiple bow and stern thrusters to try
and get in the right spot in the relatively small area.

Anthony

On 2020-07-26 2:51 AM, Niklas Holsti wrote:
[snip]
Or the final approach and catch could be secured by using a drone to
carry a towing wire from the ship to the fairing, when the fairing is
say 100 m up, and then using the wire to slowly pull the fairing down
and into the net.


That's an interesting approach. Could be interesting to see if SpaceX
does a follow-on plan to do that. Mid-air capture was a way to recover
film cartridges ejected and de-orbited from spy sats back in the 60s.

Dave

JF Mezei wrote:
On 2020-07-25 14:49, Alain Fournier wrote:
Not nearly as important as recovering the first stage, but still
recovering the nose cone reduces yet again launch costs for SpaceX.
Their fairing recovery ships caught both halves of the nose cone on
their launch Monday.
[...]

is there logic on the fairing to control parachutes to steeer to the
location of ship with the net?

Or does the ship with the net have high speed capability to position
itself under the arriving fairing?

AFAIK they do both, it's not exactly hard to find quite a bit of
details (though the exact details is obviously SpaceX confidential).

The fairings have attitude thrusters for correct orientation during
re-entry (firings can sometimes be seen on stage 2 camera footage) and
then deploy a steerable parachute.

The boats used are capable of both high speed and high maneuverability
and the videos make it obvious that it's moving and maneuvering to get
the fairing to land in the large catching net.


In the first case, I assume the awaiting ships are pre-positioned to
area where the fairings are expected to drop based on wind etc.

If they weren't pre-positioned no amount of steering and boat speed
would help, unless you posit super-sonic boats :-)

Obviously the boats leave their base early enough to at least cover as
much of the expected landing area as possible. I don't know if that
mean they start in the middle of the most likely zone (becaue they
can't cover it all) or whether the likely zone is small enough that
they can afford to start at an offset (don't need to leave the port as
early which saves slightly on man-hours).

If you care you about that aspect you may well be able to make an
educated guess on it based on crunching public data for all the
fairing recoveries attempted so far. But I'm not going to do your job
for you.


From orbital mechanics point of view, was this a question of SpaceX
learning how long it takes for the fairings to tumble in space before
they "hit" atmosphere and start to fall? Or it is a calculated thing?

As mentioned above they have control systems on the fairing assembly
for both before and after re-entry but it's a very large and light
item so even very light wind variations make significant

Skydivers with steerable parachutes can make very precise landings
but... they're probably at least one order of magnitude less
susceptible to wind deviations than this (if not more) and also SpaceX
can't use TOO heavy equipment on the fairing or it might not be worth
it any longer (or at least not all launches might have recoverable
fairings).

It's important to remember that like suicide burn this kind of fairing
recover was still fairly recently considered sheer lunacy...

I doubt the fairing recoveries required enough complicated math to
result in a Math paper published in prestigious journals (the
hoverslam/suicide burn did) but that doesn't mean it's easy.

In fact, a lot of observers though SpaceX was going to give up on "net
on a fast boat" fairing recover based on their success with recovering
fairings from the sea.

Yes, it obviously saves LESS money and time than a non-water recover
but it's still worthwhile and much cheaper/simpler and they've had
already proven that to work.

I suspect they might have been right in light of a planned future that
includes Starship+SuperHeavy if it hadn't been for the sheer NUMBER of
launches they're going to need for Starlink before S+SH will be
available. Still, Starlink launches have already used water recovered
fairings so it wasn't a silly guess.