Author Topic: LIVE: Electron 2nd Test Flight "Still Testing" - 3 Cubesats - January 21, 2018  (Read 185743 times)

Offline Ictogan

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Could a SpaceX like boost back burn followed by a grid fin controlled reentry make parachute or mid-air recovery viable for something like the Electron? (Of course maybe SpaceX has patented it so they’d need to pay a license fee?, or find some other method like an enormous streamer or foldout helicopter blades?)
If you are already using grid fins and in-air relight capability, it would save on complexity and possibly weight to just soft land using the engines - assuming that the engines can be throttled within a decent range.

Offline pb2000

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Speaking as an electrical engineer, I can tell you that the "hot swap" was a very big deal.  There's a reason they were applauding in the control room...

72 KW ~ 9 electric sauna stoves, doesn't sound so bad.

(Ok if you need put a considerable amount of kerosene and LOX thought those stoves in mach 13, then it can bit tricky)
I picture the electric pumps as being roughly equivalent to an electric drivetrain in a car. Power should be roughly similar.

I'm not an electrical engineer, but what strikes me as difficult is that battery voltage will fall as it discharges, meaning cutting in the other battery is tricky since it will be at its fully charged open circuit voltage. Connecting batteries with different voltages in parallel is usually to be avoided. DC-DC voltage conversion to allow different batteries at different voltages is possible but doing it at probably 100+ KW would have significant dry mass penalty.

So it seems like they figured out a way to manage the transition with the engine running at high power, without disrupting propellant flow. Gotta agree with Ed, that caught my attention as well. Not obvious to me what they even did. Just had them connected simultaneously for a couple milliseconds?
There are probably a thousand was of doing it, the only trick is keeping the weight down. I doubt the switching would even need to be that fast given the momentum in the system.
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Offline pb2000

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Could a SpaceX like boost back burn followed by a grid fin controlled reentry make parachute or mid-air recovery viable for something like the Electron? (Of course maybe SpaceX has patented it so they’d need to pay a license fee?, or find some other method like an enormous streamer or foldout helicopter blades?)
If you are already using grid fins and in-air relight capability, it would save on complexity and possibly weight to just soft land using the engines - assuming that the engines can be throttled within a decent range.
Rocket Lab has stated that they have no plans to make Electron recoverable.
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Offline Space Ghost 1962

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A small, recoverable vehicle can be done by a completely different strategy than RL and Vector use with expendables.

RL is about concise execution of minimal LV propulsion/frame/tanks with very narrow manufacturing/materials, so watching them bring it off was like that of an extremely narrow program that was brought in over time to hit the numbers *exactly*.

(Vector seems to be about stretching a marginal approach (pressure fed polypropylene lox props/tank/structure) to barely meet minimums.) Perhaps top down vs bottom up.

If you were to do a small recoverable vehicle, you'd have a combined bottom up and top down approach, where you'd be reusing the same CF airframe, but replacing portions to extend the dynamic range of the vehicle after each recovery. This would be the long way round the barn to prove systems to reach orbit, but highly economical at each step (due to reuse).

You'd worry about never getting there. (Although everyone, including ULA and SX does that with new/next vehicles.)

The key to it would be a highly dynamic risk regime, especially WRT props/materials/engine, because you'd need significant propulsion margin to get somewhere significant soon enough to matter. Likely a lot of "booms" at the beginning.

SX had most of their booms in the middle of the program. ULA will likely have no booms.

So this would be more like Armadillo or Masten. They all have considerably different approaches.

Offline Lar

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Could a SpaceX like boost back burn followed by a grid fin controlled reentry make parachute or mid-air recovery viable for something like the Electron? (Of course maybe SpaceX has patented it so they’d need to pay a license fee?, or find some other method like an enormous streamer or foldout helicopter blades?)
SpaceX doesn't patent things. So others can copy. If they can solve the problems without knowing the details. They have an existence proof to guide them though.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline gin455res

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...

Speaking as an electrical engineer, I can tell you that the "hot swap" was a very big deal.  There's a reason they were applauding in the control room...

72 KW ~ 9 electric sauna stoves, doesn't sound so bad.

(Ok if you need put a considerable amount of kerosene and LOX thought those stoves in mach 13, then it can bit tricky)
I picture the electric pumps as being roughly equivalent to an electric drivetrain in a car. Power should be roughly similar.

I'm not an electrical engineer, but what strikes me as difficult is that battery voltage will fall as it discharges, meaning cutting in the other battery is tricky since it will be at its fully charged open circuit voltage. Connecting batteries with different voltages in parallel is usually to be avoided. DC-DC voltage conversion to allow different batteries at different voltages is possible but doing it at probably 100+ KW would have significant dry mass penalty.

So it seems like they figured out a way to manage the transition with the engine running at high power, without disrupting propellant flow. Gotta agree with Ed, that caught my attention as well. Not obvious to me what they even did. Just had them connected simultaneously for a couple milliseconds?

I imagine the smaller fuel pump slowing down quicker than the oxidizer pump. Could the inertia of the oxidiser pump bridge the gap and also act as a generator briefly to keep the fuel pump slowing at the same rate as the oxidizer?

Offline Patchouli

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WRT reuse: Isn't Vector planning to do mid air recovery of the first stage as it descends by parachute? That doesn't sound like it would add a lot of mass to the launcher.

I think parachutes would be lighter for a small vehicle than a fuel reserve for powered landing as they work better at small scales while for larger vehicle the square cube law helps with propellant volume.


Rocket Lab has stated that they have no plans to make Electron recoverable.
Not really enough margin for recovery systems who knows maybe they might consider playing recovery on the next vehicle.
But the Rutherford would be a lot cheaper to manufacture than a turbo pump engine as it would have no hot side turbo machinery.
« Last Edit: 01/23/2018 12:06 am by Patchouli »

Offline Space Ghost 1962

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DC motors typically stop near instantly. Gas generator / expander driven turbines spool down slowly with a tail-off of thrust.

Closed cycle engines shutdown very precisely on a ramp down, otherwise they go boom.

(Observing with a telescope the shutdown of US engines during twilight launches allows you to see this detail - likewise start-up, when props flood a downrange ebbing plume of the booster.)

One likely benefit of an electric pump engine is short tail-off, which means greater precision on avoiding overburn, as the software can better estimate the resultant. 

Online abaddon

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I know I’m (very) LTTP but - Congratulations Rocket Lab!  Well done!  She’s a beaut.

Offline sewebster

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FYI, there is a more general RocketLab Electron thread here:

http://forum.nasaspaceflight.com/index.php?topic=35300.0

Offline catdlr

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Quote
Limited edition "I never want to hold again" tees available for pre-order now. 48 hours only. 
https://twitter.com/RocketLab

Way to capitalize on a (probably) iconic moment.

Quote from: RocketLab
Transcript from Rocket Lab 'Still Testing' attempt
"Flight VMS, mission coord..."
"Go ahead, VMS"
"Do you want any hold points?"
"Say again"
"Do you want any hold points?"
"I... didn't get'cha. One more time."
"Do you want any hold points? As in, do you want to hold again at T-... 18, or 20?"
"I never want to hold again."
I'd buy that shirt immediately if Rocketlab was shipping to Europe :(.

Now the video...

Rocket Lab - Still Testing Launch Attempt "I NEVER WANT TO HOLD AGAIN"


Rocket Lab
Published on Jan 22, 2018


Transcript from Rocket Lab 'Still Testing' attempt 20.01.2018
"Flight VMS, mission coord..."
"Go ahead, VMS"
"Do you want any hold points?"
"Say again"
"Do you want any hold points?"
"I... didn't get'cha. One more time."
"Do you want any hold points? As in, do you want to hold again at T-... 18, or 20?"
"I never want to hold again."

Limited edition "I never want to hold again" tees available for pre-order now. 48 hours only - https://shop.rocketlabusa.com/collections/men/products/48-hr-pre-order-mens-i-never-want-to-hold-again-t-shirt-black

https://www.youtube.com/watch?v=Fon8RmP9Qew?t=001

« Last Edit: 01/23/2018 04:41 am by catdlr »
Tony De La Rosa, ...I'm no Feline Dealer!! I move mountains.  but I'm better known for "I think it's highly sexual." Japanese to English Translation.

Offline Req

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I'm not an electrical engineer, but why wouldn't you just have the pumps running off of capacitors to solve any voltage drop or hot swap complications?

Edit: Batteries->capacitors->pumps
« Last Edit: 01/23/2018 07:21 am by Req »

Offline Steven Pietrobon

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Capacitors could do it, though they'd probably need to be big though and designed for high voltage.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline chewi

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Rocket Lab Reveals Secret Engine and "Kick Stage" for the Electron Rocket
http://www.popularmechanics.com/space/rockets/a15854376/rocket-lab-engine-kick-stage-electron-rocket/

Offline Ronsmytheiii

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Quote
RocketLab: We successfully tested a previously unannounced kick stage on the "Still Testing" Electron launch, using it to circularize the orbits of the two Spire Lemur-2 CubeSats on board.

https://twitter.com/nova_road/status/955863191686402048
« Last Edit: 01/23/2018 05:12 pm by Ronsmytheiii »

Offline jcm

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Rocket Lab Reveals Secret Engine and "Kick Stage" for the Electron Rocket
http://www.popularmechanics.com/space/rockets/a15854376/rocket-lab-engine-kick-stage-electron-rocket/

Interesting. This explains the three high orbit objects and two of the three low orbit objects. We still have one
object unaccounted for (could just be a small piece of debris)
-----------------------------

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Offline yg1968

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Offline acsawdey

Capacitors could do it, though they'd probably need to be big though and designed for high voltage.

These are multiphase brushless DC motors which typically have a controller driving each phase connection either to ground or the DC supply with a H-bridge driver. You'd generally have some capacitance right by the drivers anyway. Hot-swap is just using probably some kind of high reliability relay to switch the dc supply. Probably the motor controller won't notice or will compensate as long as the logic power supply to it is clean. The motor speed and power are closed-loop controlled, the motor will either have a hall effect sensor to see the position of the rotor, or the controller may just use a sensorless scheme where it uses the back-emf to see what the rotor is doing.

Online gongora

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The kick stage has avionics and RCS on board.  I wonder if that is the guidance for the entire Electron vehicle, and if that is also the RCS used during second stage flight. 

That would certainly be the cheapest way to do it.

Offline Comga

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The kick stage has avionics and RCS on board.  I wonder if that is the guidance for the entire Electron vehicle, and if that is also the RCS used during second stage flight. 

A mean trick Rocket Lab pulled there, I think, making us all think it was a successful launch while the actual flight with 2/3rds of the payloads continued for another 40 minutes.  I wonder if they would have told us if a failure had occurred during that black-out phase.

I wonder, too, how this kick stage affects the claimed performance (150 kg to a 500 km sun synchronous orbit).  This flight only carried 13 kg of payload.  Perhaps much of the payload capability was used up by having the kick stage on board.

 - Ed Kyle

What did you mean by  "mean"?
 
The advantage of private enterprise.  They don't have to tell us a thing.
We, on the other hand, have to give them kudos and respect.

This explains the "third stage" or "stage 3" callout heard during the countdown.
Putting all of the avionics in the kick stage could have several advantages.

NASA's Green Propellant Infusion Mission has yet to fly, and has only ACS sized engines.
GPIM seems OBE after this.

Edit/Lar: Soften.
« Last Edit: 01/23/2018 11:16 pm by Lar »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

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