Author Topic: SpaceX Falcon 9 / Dragon 2 : SpX-DM1 : March 2, 2019 : DISCUSSION  (Read 403186 times)

Offline lrk

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I'm surprised that trunk jettison was prior to the de-orbit burn.  Was that due to concerns over potential impacts with it during re-entry?  And is that going to remain the standard timeline for return operations going forward?  Should there be some unexpected issue with the deorbit burn, not having the solar panels and radiators would, I imagine, seriously limit the amount of time the capsule can remain healthy while a fix is worked on.

On the other hand, the trunk failing to seperate after de-orbit would present an even more critical problem, as the capsule would try to enter nose-first.   I would guess that the risk of a thruster failure between separation and de-orbit is smaller than the risk of a separation failure, since the thruster performance would be monitored throughout the flight. 

Offline lonestriker

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I'm surprised that trunk jettison was prior to the de-orbit burn.  Was that due to concerns over potential impacts with it during re-entry?  And is that going to remain the standard timeline for return operations going forward?  Should there be some unexpected issue with the deorbit burn, not having the solar panels and radiators would, I imagine, seriously limit the amount of time the capsule can remain healthy while a fix is worked on.

On the other hand, the trunk failing to seperate after de-orbit would present an even more critical problem, as the capsule would try to enter nose-first.   I would guess that the risk of a thruster failure between separation and de-orbit is smaller than the risk of a separation failure, since the thruster performance would be monitored throughout the flight.

Someone mentioned in the forums or Twitter that Dragon 2 could survive on batteries alone from launch until docking. So there's a lot more battery capacity than you think. People really should approach issues from the standpoint that they don't understand the choice that SpaceX made, rather than "there's a problem with the choice SpaceX made." It is rocket science and they are really good at it.
« Last Edit: 03/08/2019 07:21 pm by lonestriker »

Online CorvusCorax

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IMHO the choice is perfectly right. If you deorbit first and then detach the trunk - and detaching fails - the capsule enters in a very stable aerodynamic nose first orientation and will burn through nosecone, front hatch, parachutes, pressure vessel, crew and finally propellant tanks first while the trunk remains protected by the capsules heat shield.

However I am surprised they detached the trunk in such a high, almost circular orbit. It could take many months if not years for reentry, in the exact same plane of the station where it's gonna be an obstacle any future visiting vehicle will have to navigate around. At least its mass to area ratio isn't high, being a hollow cylinder.

IMHO a weird choice. Obviously you don't "deorbit" with the trunk attached, but lowering perigee to something under 200 km so it reenters more quickly would have made more sense intuitively. That of course is a procedure choice they might still make in the future.

Offline Rocket Science

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Not to rain on what is a great day however all the monkey motion under the chutes and the bobbing in the swells that folks have been commenting on would not exist with a crew Dream Chaser... Just sayin'... ;)
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Online John Alan

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IMHO
Leaving the trunk in such a high circular orbit was unwise....
Many of you know I'm in the "clean up you mess today" camp on rocket hardware left in orbit...  >:(

However...  ???
IF the "fluffy" nature of the truck results in the now tracked object coming down and then deorbiting faster then seems obvious to myself anyway... then we will have learned something of note.

Maybe they were hedging keeping as much prop available for this first reentry, and ditched the trunk to save as much as possible... in case Dragon uses RCS more then calculated during re-entry...  ???
« Last Edit: 03/08/2019 09:24 pm by John Alan »

Offline RDMM2081

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The trunk exterior is like 50% solar panels right? Can anything interesting be done with a flying mass of solar panels in a relatively stable orbit?  My imagination is already getting the better of me here.

Offline Eerie

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Can anything interesting be done with a flying mass of solar panels in a relatively stable orbit?

It's uncontrollable, so no.

Offline VoodooForce

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Does anyone know if EM was in the Hawthorne control centre to the left of Gwynne Shotwelll? My stream was fairly pixelated at that point.

Can anything interesting be done with a flying mass of solar panels in a relatively stable orbit?

It's uncontrollable, so no.

I assumed he meant in the future. Using leftover Dragon 2 truck in a way sort of similar to the shuttle ET wet workshop proposals would be really neat if doable.

Offline RobW

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If Musk is successful with Starship / Super Heavy, it only has to work minimally (no crew, no refuelling) and it would (with a small arm) be capable of returning trunks for re-use.

Maybe leaving the trunk in a high orbit is just Musk backing his work on Starship, and planning to take advantage of it.
Science fiction writer, spaceflight blogger, and unrepentant technological optimist.

Offline Roy_H

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Although I too thought they would leave the trunk in a lower orbit, I would like to know the expected time before it re-enters and burns up. 2 to 3 years? It certainly won't be over 5.
"If we don't achieve re-usability, I will consider SpaceX to be a failure." - Elon Musk

Online Herb Schaltegger

However I am surprised they detached the trunk in such a high, almost circular orbit. It could take many months if not years for reentry, in the exact same plane of the station where it's gonna be an obstacle any future visiting vehicle will have to navigate around. At least its mass to area ratio isn't high, being a hollow cylinder.

The trunk is very "fluffy" ballistically speaking. It will deorbit itself relatively quickly.
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Offline ppb

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Not to rain on what is a great day however all the monkey motion under the chutes and the bobbing in the swells that folks have been commenting on would not exist with a crew Dream Chaser... Just sayin'... ;)
Those things also wouldn't exist with Dragon propulsive landing---also just sayin'  ;-)
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Online obi-wan

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I'm surprised that trunk jettison was prior to the de-orbit burn.  Was that due to concerns over potential impacts with it during re-entry?  And is that going to remain the standard timeline for return operations going forward?  Should there be some unexpected issue with the deorbit burn, not having the solar panels and radiators would, I imagine, seriously limit the amount of time the capsule can remain healthy while a fix is worked on.

The trunk by itself has a much lower ballistic coefficient than the crew capsule. Take a look at the ground track across the U.S. - if it deorbits with the capsule aiming at landing just offshore, the trunk is going to land somewhere in the U.S. mainland. There was something a while back about landing on an ascending node so the capsule lands in the Atlantic and the trunk lands in the Gulf of Mexico - but that's pretty congested with boats and oil platforms. At space station inclination, you have a higher chance of landing in an ocean or empty land on an uncontrolled entry.

Offline andylander

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Not to rain on what is a great day however all the monkey motion under the chutes and

Not sure what monkey motion is but I saw the capsule being EXTREMELY stable under the chutes - no pendulum motion and no spin at all. In general more chutes make the capsule more stable and I think the lateral sliding that the canopies were doing was by design - canopies drift around, capsule remains stable.

I agree about the bobbing in the ocean though, that doesn't look like much fun. The relatively tall Dragon looks like it is pitching over a lot more with each wave than the much more squat Apollo capsules, because of it's relative height. I wonder if hey considered an inflatable donut for Dragon like the Apollo capsule had?

Offline Rocket Science

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Not to rain on what is a great day however all the monkey motion under the chutes and the bobbing in the swells that folks have been commenting on would not exist with a crew Dream Chaser... Just sayin'... ;)
Those things also wouldn't exist with Dragon propulsive landing---also just sayin'  ;-)
Agreed, but that was SpaceX's task to prove unequivocally to NASA... I never commented on what we saw (others did) down to splashdown as it performed as expected for a capsule vehicle. I'm pleased with the outstanding results of the mission!
"The laws of physics are unforgiving"
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Offline freddo411

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Anyone got a link to the video of the sea recovery ops?   The vids I watched show the fast boats approaching ; then it cuts off.   I'm wondering if it takes 2 minutes or 10 minutes to get to the capsule.
Also, I'd like to see what things are done during the recovery.

Interesting to note that 5 of the apollo capsules ended up inverted in the water:
https://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm?fbclid=IwAR1JAzUIgqBnEpZwS68P8dJfTj3Gg45ODznkcLtPhdWv6AL8BYaUhURs0Es

I'm disappointed that NASA wouldn't let SpaceX develop its preferred landing methodology ... which would not have any of these complications and potential dangers.    That being said, it appears to be no more or less troublesome than mercury, gemini, and apollo.

Online abaddon

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Not to rain on what is a great day however all the monkey motion under the chutes and the bobbing in the swells that folks have been commenting on would not exist with a crew Dream Chaser... Just sayin'... ;)
One can always imagine how much superior something that doesn't exist is to something that does.

Offline Rocket Science

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Not to rain on what is a great day however all the monkey motion under the chutes and the bobbing in the swells that folks have been commenting on would not exist with a crew Dream Chaser... Just sayin'... ;)
One can always imagine how much superior something that doesn't exist is to something that does.
And if man were meant to fly he'd have wings... Failure of imagination...
« Last Edit: 03/09/2019 10:06 pm by Rocket Science »
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline Grandpa to Two

I'm a bit amazed that people think that a parachute covering the capsule is a critical flaw. That's just the luck of the draw when dealing with parachutes like this. For any round parachute there is a wind direction that could push it on top of the capsule or jumper.
Soyuz runs into the same problem occasionally. Of course thatís on the ground, not water.  This event has been planned for, it will be studied and changes may or may not be made. Looked exactly like I thought it would, similar to Apollo. Well done Elon and all involved, a mostly perfect first attempt. Brilliant!
"All truths are easy to understand once they are discovered; the point is to discover them" Galileo Galilei

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