Author Topic: SpaceX Falcon 9 v1.1 - CASSIOPE - September, 2013 - GENERAL DISCUSSION THREAD  (Read 375602 times)

Online guckyfan

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They won't do the braking burn right away anyway.

You think? If I were planning the manuvers, I'd make it as close to realistic, back to the pad, as is safely practical. Maybe landing in the water a few dozen miles off the coast of Vandenburg. What would the range safety issues be there, considering that they just launched maybe 10 minutes before landing or splash down? Proving that they can get the S1 back to the area of the landing pad comes only second to proving that it doesn't break up on the way back.

If they are going to do it, they may as well do as much as they can. JMO.

This is the Cassiope thread. The first launch. Elon said explicitly that it will fly along its elliptic trajectory. No boostback for the first try.

Offline krytek

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They won't do the braking burn right away anyway.

You think? If I were planning the manuvers, I'd make it as close to realistic, back to the pad, as is safely practical. Maybe landing in the water a few dozen miles off the coast of Vandenburg. What would the range safety issues be there, considering that they just launched maybe 10 minutes before landing or splash down? Proving that they can get the S1 back to the area of the landing pad comes only second to proving that it doesn't break up on the way back.

If they are going to do it, they may as well do as much as they can. JMO.

This is the Cassiope thread. The first launch. Elon said explicitly that it will fly along its elliptic trajectory. No boostback for the first try.
Anyone care to guess where along the elliptic trajectory? close to apogee?

Offline meekGee

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They won't do the braking burn right away anyway.

You think? If I were planning the manuvers, I'd make it as close to realistic, back to the pad, as is safely practical. Maybe landing in the water a few dozen miles off the coast of Vandenburg. What would the range safety issues be there, considering that they just launched maybe 10 minutes before landing or splash down? Proving that they can get the S1 back to the area of the landing pad comes only second to proving that it doesn't break up on the way back.

If they are going to do it, they may as well do as much as they can. JMO.

What they are testing is the slow-down burn and the "how fast is too fast" question.  Any burn that's too early is just wasted, since the stage speeds up as it falls back down
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Offline Lars_J

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They won't do the braking burn right away anyway.

You think? If I were planning the manuvers, I'd make it as close to realistic, back to the pad, as is safely practical. Maybe landing in the water a few dozen miles off the coast of Vandenburg. What would the range safety issues be there, considering that they just launched maybe 10 minutes before landing or splash down? Proving that they can get the S1 back to the area of the landing pad comes only second to proving that it doesn't break up on the way back.

If they are going to do it, they may as well do as much as they can. JMO.

This is the Cassiope thread. The first launch. Elon said explicitly that it will fly along its elliptic trajectory. No boostback for the first try.
Anyone care to guess where along the elliptic trajectory? close to apogee?

No, presumably close to atmospheric entry.

Offline krytek

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They won't do the braking burn right away anyway.

You think? If I were planning the manuvers, I'd make it as close to realistic, back to the pad, as is safely practical. Maybe landing in the water a few dozen miles off the coast of Vandenburg. What would the range safety issues be there, considering that they just launched maybe 10 minutes before landing or splash down? Proving that they can get the S1 back to the area of the landing pad comes only second to proving that it doesn't break up on the way back.

If they are going to do it, they may as well do as much as they can. JMO.

This is the Cassiope thread. The first launch. Elon said explicitly that it will fly along its elliptic trajectory. No boostback for the first try.
Anyone care to guess where along the elliptic trajectory? close to apogee?

No, presumably close to atmospheric entry.
why?

Offline iamlucky13

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No, presumably close to atmospheric entry.
why?

At apogee, speed is at its minimum. You can drop the speed to zero, but it will still gain significant velocity again before atmospheric drag becomes significant.

At entry-interface, velocity is at a maximum. At that point, you retroburn enough to keep the drag and thermal loads within survivable limits and then drag will keep you at terminal velocity the rest of the way.

Offline kevin-rf

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.
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Offline mr. mark

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Thanks for the answers. Hope SpaceX provides split screen video. One with the second stage and satellite release and the other on first stage reentry.

Offline oiorionsbelt

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This launch of CASSIOPE will be a first, in as much as, there will be as much or more attention on the first stage after it's done it's job, as during.

Offline Lars_J

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.

Offline MP99

Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.

Disagree.

Re-entry is the really hard part, and will include a slow-down burn. If they can prove that OK, then there's nothing difficult about also doing a boost-back burn in later tests.

Once they survive re-entry (possibly not on the first attempt), they can prove out the landing process.

Adding a boost-back burn would just be unnecessary complication on early tests - certainly the first one.

cheers, Martin

Offline cambrianera

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.
Why?
1) Testing attitude control of first stage after staging;
2) Testing engine restart and performance;
3) Testing first stage reentry with the same parameters (only direction is different);
4) Testing attitude control for landing;
5) Testing low altitude-backward motion engine restart;
6) Testing landing software.
Something missing?
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Offline MP99

3) Testing first stage reentry with the same parameters (only direction is different);

I'm wondering about that.

Would they try a larger slow-down burn to give the stage a really easy time through re-entry on the first go, then ramp it down (ramp up re-entry speed) on subsequent tests?

There's value in recovering the stage and tearing it apart to see how it coped, as that could refine models of the optimal re-entry speed.


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.

cheers, Martin
« Last Edit: 03/30/2013 10:20 AM by MP99 »

Offline cambrianera

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@MP99
High altitude high speed test are something difficult to simulate/test outside real conditions.
I would expect SpaceX zeroing on this part after suffering some bruising on the parachute recovery attempt.
But the idea of a softer approach is reasonable.
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Offline meekGee

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The upside of starting with too much slow-down is that you have an article to recover, potentially, so can learn more.

Also, next flight as people noted has a large propellant margin.
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Offline mlindner

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I'm not sure how this test would differ from an actual boost back flight profile besides having a different flight direction. Why is there a claim that they will boost back, re-enter ballistically and the restart near the surface? If they need to slow down before entry interface then the mission will be a three burn re-entry not a two burn one. Burn to reverse trajectory, burn to slow down as it enters the atmosphere, and a third burn to slow down to zero velocity at zero altitude.

Edit: Grammar.

Also this is off topic here. We should talk in Falcon 9 v1.1 forum or in reusability forum.
« Last Edit: 03/30/2013 03:25 PM by mlindner »
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Offline Lars_J

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.
Why?
1) Testing attitude control of first stage after staging;
2) Testing engine restart and performance;
3) Testing first stage reentry with the same parameters (only direction is different);
4) Testing attitude control for landing;
5) Testing low altitude-backward motion engine restart;
6) Testing landing software.
Something missing?

Did I respond to YOU? (does kevin-rf post under multiple aliases?)

No. Just countering kevin-rf's 'claim' that boost-back was an essential point of this test, that it had to hit the atmosphere at the same speed that a boost-back flight would. I'm sure they will try to get somewhat close, but a ballistic trajectory will most likely have a larger horizontal velocity than a "lofted" boost-back one.

MY claim is that surviving reentry is the point of this test. Everything else is gravy.
« Last Edit: 03/30/2013 03:22 PM by Lars_J »

Offline aero

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.
Why?
1) Testing attitude control of first stage after staging;
2) Testing engine restart and performance;
3) Testing first stage reentry with the same parameters (only direction is different);
4) Testing attitude control for landing;
5) Testing low altitude-backward motion engine restart;
6) Testing landing software.
Something missing?

Since we seem to agree that they will not attempt a boost back of any form on this first test, then they should touch down with excess fuel. The amount of this excess fuel will give a rough estimate of the fuel available for boost back on subsequent test flights.
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Offline mlindner

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.
Why?
1) Testing attitude control of first stage after staging;
2) Testing engine restart and performance;
3) Testing first stage reentry with the same parameters (only direction is different);
4) Testing attitude control for landing;
5) Testing low altitude-backward motion engine restart;
6) Testing landing software.
Something missing?

Since we seem to agree that they will not attempt a boost back of any form on this first test, then they should touch down with excess fuel. The amount of this excess fuel will give a rough estimate of the fuel available for boost back on subsequent test flights.

No it will not. This mission is launching a 500kg satellite. There is a crazy amount of margin. This is also a test flight landing, anything done here is little evidence to how they actually plan to do things, just as early grasshopper tests had a different flight profile.
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Offline cambrianera

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Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.
Why?
1) Testing attitude control of first stage after staging;
2) Testing engine restart and performance;
3) Testing first stage reentry with the same parameters (only direction is different);
4) Testing attitude control for landing;
5) Testing low altitude-backward motion engine restart;
6) Testing landing software.
Something missing?

Did I respond to YOU? (does kevin-rf post under multiple aliases?)

No. Just countering kevin-rf's 'claim' that boost-back was an essential point of this test, that it had to hit the atmosphere at the same speed that a boost-back flight would. I'm sure they will try to get somewhat close, but a ballistic trajectory will most likely have a larger horizontal velocity than a "lofted" boost-back one.

MY claim is that surviving reentry is the point of this test. Everything else is gravy.

Did I something bad asking you what was wrong in kevin-rf's post?
By the way, I'm still not able to understand why kevin-rf's claims are wrong.
a) If you do a brake burn it will be made in the same attitude as a boostback burn (ie engine first, horizontal stage to kill horizontal speed).
b) When your horizontal speed will be equal (except for the direction) to the foreseen horizontal boostback speed, your stage will be in a ballistic trajectory mirrored to that foreseen for the boostback.

Seems simple  ???
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