Author Topic: SpaceX Falcon 9 v1.1 - CASSIOPE - September, 2013 - GENERAL DISCUSSION THREAD  (Read 507447 times)

Offline kevin-rf

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Elon's twitter feed could be a good indication on how well the vacuum chamber testing goes. If a week or two goes by without anything, then it might be time to worry about the schedule.
That might be true in a world without ITAR. But we're not living in such a world.

Bragging about a successful test is not prohibited by ITAR.

It is if you include measurements with unit's like inches ;)
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Offline MP99

Elon's twitter feed could be a good indication on how well the vacuum chamber testing goes. If a week or two goes by without anything, then it might be time to worry about the schedule.
That might be true in a world without ITAR. But we're not living in such a world.

Bragging about a successful test is not prohibited by ITAR.

It is if you include measurements with unit's like inches ;)

Since us doesn't understand millimetres, those should be safe!

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Offline Garrett

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Elon's twitter feed could be a good indication on how well the vacuum chamber testing goes. If a week or two goes by without anything, then it might be time to worry about the schedule.
That might be true in a world without ITAR. But we're not living in such a world.

Bragging about a successful test is not prohibited by ITAR.
Maybe I was pushing it with ITAR. What I should have tried to emphasize is that the delay it takes for Elon to tweet about something should not be used to worry about anything. There are a variety of other factors that could delay a billionaire CEO of two big corporations from tweeting about a fairing sep test.
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Offline deltaV

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I guess there are three options:-
1) start low, and ramp up the re-entry speed until they find a problem - either break-ups or in post-flight analysis.
2) start high, and ramp down the re-entry speed until one survives. [Edit: least likely, I think.]
3) target the expected re-entry speed and see how it copes, then adjust as required.

Binary search / bisection, which is similar to your #3, is much more efficient in terms of number of tests needed than #1 or #2.

Offline aero

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Does anyone know what the staging altitude and velocity will be? What they may be? Are we expecting it to flip end for end immediately on separation and do the retro-burn, or do we expect some other flight profile?
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Offline FutureSpaceTourist

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Elon has previously said that for their reusability approach to work staging has to occur rather earlier than currently (IIRC Mach 6 rather than current Mach 10?). I believe this is to avoid the need for a heat shield on the first stage. May also be related to ease of reovery at the launch site?
« Last Edit: 04/07/2013 07:43 pm by FutureSpaceTourist »

Offline Kabloona

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Does anyone know what the staging altitude and velocity will be? What they may be? Are we expecting it to flip end for end immediately on separation and do the retro-burn, or do we expect some other flight profile?

I think we're expecting first retro-burn just before entry interface, and then the stage free-falls at terminal velocity until a second burn just before hitting the water.

Doing the first burn immediately after staging would not accomplish much, since the stage will gain velocity as it falls and would need another burn before entry interface. It would, I guess, alter the ballistic trajectory to make the impact point closer to the launch site, but the downside is needing three restarts instead of two. For that reason, I imagine they'll try to keep it simple and go with two burns only.

There's also the factor of needing some finite amount of time after staging to reorient the stage for the retro burn. If they're using small cold gas thrusters to do a 180, more or less, it'll take some time to do that re-orientation.

 There's also the question of propellant settling before the first burn. Has anyone heard anything on that subject?
« Last Edit: 04/07/2013 09:14 pm by Kabloona »

Offline aero

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At what altitude is the entry interface?
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Offline Kabloona

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At what altitude is the entry interface?

Was 400kft for Shuttle. Don't know if it's different for F9.

Offline Nomadd

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 Speaking of propellant settling, how does that work anyhow? Would they wait till they encounter some drag to settle the propellant to the bottom of the tanks?
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Offline aero

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At what altitude is the entry interface?

Was 400kft for Shuttle. Don't know if it's different for F9.

400kft is 122 km. I think it will be lower for the F9 because, when staging at mach 6, there is only enough kinetic energy to coast upward against gravity for an additional 30 to 35 km above the staging altitude. I don't know the staging altitude of the F9 but I think it is lower than 90 km. My atmospheric calculator table runs out at 86 km altitude, and the atmosphere is pretty thin that high up.
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Offline aero

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Yes, entry interface is not the term to use in describing a recovering S1. Entry Interface has a specific meaning and seems to be defined as 400,000 feet altitude on the trajectory of vehicles passing from space to earth. SpaceX S1 and boosters don't reach that altitude so I can't use that term to describe any phase of their flight.

Re. Falcon 9 v1.1, the S1 does reach altitudes and speeds where total temperature and pressure are negligible, the apex of the trajectory for example. The term I seek is one to identify the altitude along the decending arc of the trajectory where total temperature and pressure can no longer be ignored. The S1 engines will need to slow the descent at or above that point. I'll name this the critical total pressure altitude as I believe it is total pressure and associated total temperature within the engine fairing that will frustrate re-use.

That is, unless aerodynamic drag slows the descent enough that temperature and pressure never become a problem. Drag will slow the stage to less than what the upward velocity was at equal altitudes, (excepting near the surface) but I think the SpaceX attempts to recover stages with parachutes shows that drag alone is not enough. So maybe the S1 engines need to run from just above the critical total pressure altitude until the stage slows to  terminal velocity at lower altitude where this terminal velocity does not result in exceeding the critical total pressure at the stagnation points within the engine environment. Such engine controls should be programmable I would hope.
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Offline Okie_Steve

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As has been mentioned before up-thread, it's not the vertical velocity component that's the problem, it's the horizontal moving like a bat-out-of-hell part that will cause most of the trouble. Straight vertical drop should reach reasonably slow terminal velocity all by itself, just like Felix Baumgartner when he jumped out of the Red Bull capsule - without a rocket burn to slow him down.

Offline Robotbeat

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As has been mentioned before up-thread, it's not the vertical velocity component that's the problem, it's the horizontal moving like a bat-out-of-hell part that will cause most of the trouble. Straight vertical drop should reach reasonably slow terminal velocity all by itself, just like Felix Baumgartner when he jumped out of the Red Bull capsule - without a rocket burn to slow him down.
It wouldn't be that different if you shot it at an angle or straight up. In fact, the one straight up would have significantly higher reentry forces (and, I believe, heat load).
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Offline Soralin

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I guess there are three options:-
1) start low, and ramp up the re-entry speed until they find a problem - either break-ups or in post-flight analysis.
2) start high, and ramp down the re-entry speed until one survives. [Edit: least likely, I think.]
3) target the expected re-entry speed and see how it copes, then adjust as required.

Binary search / bisection, which is similar to your #3, is much more efficient in terms of number of tests needed than #1 or #2.
Or another (partial) option, or at least something to consider, that testing might depend on what fits the payload it's carrying.  Small payload, lots of margin - slow it down a lot.  Big payload, not much margin - I guess we're testing coming in fast this time.
« Last Edit: 04/08/2013 06:30 am by Soralin »

Offline ArbitraryConstant

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Speaking of propellant settling, how does that work anyhow? Would they wait till they encounter some drag to settle the propellant to the bottom of the tanks?
That's a very interesting thought. If they have cold gas for attitude control, they can avoid the destructive belly flop and use the atmosphere. Maybe even at the staging altitude for burn back.

Offline Kabloona

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At what altitude is the entry interface?

Was 400kft for Shuttle. Don't know if it's different for F9.

400kft is 122 km. I think it will be lower for the F9 because, when staging at mach 6, there is only enough kinetic energy to coast upward against gravity for an additional 30 to 35 km above the staging altitude. I don't know the staging altitude of the F9 but I think it is lower than 90 km. My atmospheric calculator table runs out at 86 km altitude, and the atmosphere is pretty thin that high up.

Just for comparison, Antares A-ONE ascent profile shows S2 coasting up to 189 km before ignition, so presumably S1 will coast up to an apogee in that neighborhood, well above entry interface...

But we know the deltaV split for F9 is more balanced, with less dV in S1 and more in S2, so F9 S1 apogee will obviously be lower.
« Last Edit: 04/09/2013 01:42 am by Kabloona »

Online Galactic Penguin SST

Well, well, well......

SFN now lists this flight at July 9 at 9-11 am PDT (16:00-18:00 GMT). Surely not three F9's in July!? (or heck five F9-1.1 between July and November?)

Edit: Thaicom 6 launch date now listed in August, so at most only 2 F9s in July. (but the second possibility still stands!)
« Last Edit: 04/09/2013 09:12 pm by Galactic Penguin SST »
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Offline Herb Schaltegger

Quote from: Robotbeat link=topic=31429.msg1036088#msg1036088 date=1365401150
[/quote
It wouldn't be that different if you shot it at an angle or straight up. In fact, the one straight up would have significantly higher reentry forces (and, I believe, heat load).

It might have a higher peak heat flux but the total heat load would likely be greater for a flatter entry trajectory due to the longer time spent traveling through thicker atmosphere.
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Offline mlindner

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Well, well, well......

SFN now lists this flight at July 9 at 9-11 am PDT (16:00-18:00 GMT). Surely not three F9's in July!? (or heck five F9-1.1 between July and November?)

Edit: Thaicom 6 launch date now listed in August, so at most only 2 F9s in July. (but the second possibility still stands!)

Hmm unfortunate, but its only a half-month slip. Things still look more or less on schedule. Do we have a more direct source than SFN? I'd be curious where they learned of it.
« Last Edit: 04/10/2013 12:57 am by mlindner »
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