SpaceX Falcon 9 v1.1 - CASSIOPE - September, 2013 - GENERAL DISCUSSION THREAD

[pippin]

RazakSat wasn't launched on F9. And the various secondary payloads all had a pretty short design-TTL IIRC. The one secondary payload that was supposed to go to a stable orbit would have required a secondary burn and was lost due to the lack of it (Orbcom)

[douglas100]

As far as the possibility of there being any kind of Mars payload on this flight in concerned, I think the chances of that are essentially zero, for reasons given by a number of previous posters. But if they do a depletion burn to solar orbit, it's possible that those looking for cool pictures of the Earth from a distance might get them from upper stage cameras. If the batteries last long enough, of course.

[Antares]

Is this going to be a week-by-week "secret-timeline" slip?  I guess the USAF wants that vehicle pretty badly.

Non-sequitur.  I don't understand what you're trying to say.

[tobi453]

My comment was meant to say that for an accurate TMI burn you need a guidance cutoff at a precise delta-V which cannot be guaranteed with a burn to depletion. If your margins are healthy, you would invariably overburn by using up all propellant and missing the Mars flyby by a large margin.

Actually it is possible to do a burn to depletion during TMI if you hava a good guidance system. If you overburn you simply have to adjust your trajectory by pointing the thrust vector of your engine in a different direction. That way you will arrive at mars faster.

[Jim]

Actually it is possible to do a burn to depletion during TMI if you hava a good guidance system. If you overburn you simply have to adjust your trajectory by pointing the thrust vector of your engine in a different direction. That way you will arrive at mars faster.

Not really, it isn't because the time of depletion is unknown.

[smoliarm]

[...] it seems to me it's impossible to do TLI from polar orbit with one burn - just like it's impossible for TMI.

Mathematically, it's *always* possible to go from any point in any orbit to any future target with just one burn.  In fact, there is an infinity of such burns, getting there in one day, two days, one month, two months, etc.

Of course most of these will require an impractically large delta-V, for example if you start by heading in the wrong direction.  Others have practical disadvantages such as passing through planets. 

That being said, TLI from a polar orbit seems very little different from TLI from an equatorial orbit.  In either case, you want to fire when you are roughly opposite to the moon, changing your orbit to an ellipse with the perigee still near earth but the apogee where the moon will be when you get there.  The delta-v needed should be very similar.

Going to Mars takes a little more care.  First you need a dawn-dusk polar orbit.  Then your orbital velocity and the earth's velocity around the sun add directly at some point in your orbit, making it just about as good as any other parking orbit.  Of course you still have the problem that if you are not in a good Mars launch window, the delta-V required will be very high.  But since Maven is launching to Mars in just a month or two, we are quite close to the minimum delta-v needed.

Overall, the main disadvantage of a polar parking orbit would seem to be that it requires more delta-V in the first place, since the launch can't take advantage of earth's rotation.

Thanks a lot for clarification! Indeed, I forgot a lot of Orbital Mechanics.

[Arthree]

Actually it is possible to do a burn to depletion during TMI if you hava a good guidance system. If you overburn you simply have to adjust your trajectory by pointing the thrust vector of your engine in a different direction. That way you will arrive at mars faster.

Not really, it isn't because the time of depletion is unknown.

Yes really, the time of depletion is irrelevant as long as it comes after a transfer orbit that intercepts Mars is achieved.  After that, you can just burn in a direction that maintains the intercept until depletion.

Anyways, a TMI burn is not only off topic but way past the point of being impossible for various reasons already posted.

[tobi453]

Actually it is possible to do a burn to depletion during TMI if you hava a good guidance system. If you overburn you simply have to adjust your trajectory by pointing the thrust vector of your engine in a different direction. That way you will arrive at mars faster.

Not really, it isn't because the time of depletion is unknown.

You can fly a trajectory where it doesnt matter where you cut off as your are changing the trajectory/thrust vector acording to your speed increase.

Just look at military rockets. They chase a moving target and they still hit.

[mr. mark]

According to Robotbeat, the 9v1.1 was verticle today.

[mr. mark]

Something tells me there is more to this "blackout" than just customer satisfaction. Can't put a finger on it though.......

[Robotbeat]

Something tells me there is more to this "blackout" than just customer satisfaction. Can't put a finger on it though.......

The less coverage, the less negative fallout if they fail. And this is a very risky mission, what with being the first F9 v1.1 flight.

[mr. mark]

No more riskier than the Falcon 1 Flight 4 launch. They launched that mission live, had some assembly pics and they betted the farm on that one. 

[malu5531]

The C3 for Mars flyby if we're talking about departure on September 9th is about 53 km2/s2, or as "low" as C3=18 towards the end of October.  It might be an empty stage but I doubt it can give itself that much of a boost.

Source: Trajectory Optimization Tool.

I have now concluded a TMI will not be possible.

I've never used/known about C3, but after some googling and updating my calculations, the delta-v necessary for TMI from a 300x300 orbit using C3=53 km2/s2 (TMI on September 9), is 5403 m/s. Available Delta-v in LEO is 3731 m/s, 2248 m/s is used to lift apogee to 300x1500 for payload, then an additional 3155 m/s would be needed for TMI (next orbit), but there is only remaining fuel for 1483 m/s => TMI is not possible, so I guess I must put this idea to rest.. :/

However, my calculations show escape trajectory with C3 < 11 km2/s2 might be possible.
(Calculations; http://tinyurl.com/CassiopeMars - disclaimer; IANARS, BOTE, guesstimates, etc)

[ugordan]

Something tells me there is more to this "blackout" than just customer satisfaction. Can't put a finger on it though.......

I'm sure if the WDR is successful they'll put out a press release announcing the activation of the VAFB pad, with a picture of the vehicle that happens to hide anything above 2nd stage.

[Robotbeat]

No more riskier than the Falcon 1 Flight 4 launch. They launched that mission live, had some assembly pics and they betted the farm on that one. 

Actually, I'm not sure about that. F1 had lots of test flights beforehand (unsuccessful, but a lot was learned), and flight 3 was nearly successful. Now, SpaceX has already proved they can get a big rocket into space, so they don't have a ton to gain from a lot of publicity right now, but they have plenty to lose.

I'm sure when it's successful (I give it a 80% chance, at least... they have a ton of margin on this flight, so even an engine out /at lift-off/ and another higher up could be survivable), especially if the reentry of the second stage works well, we'll see plenty of footage.

[Jason1701]

Something tells me there is more to this "blackout" than just customer satisfaction. Can't put a finger on it though.......

I'm sure if the WDR is successful they'll put out a press release announcing the activation of the VAFB pad, with a picture of the vehicle that happens to hide anything above 2nd stage.

WDR is performed with nothing significant above the second stage.

[Robotbeat]

Something tells me there is more to this "blackout" than just customer satisfaction. Can't put a finger on it though.......

I'm sure if the WDR is successful they'll put out a press release announcing the activation of the VAFB pad, with a picture of the vehicle that happens to hide anything above 2nd stage.

WDR is performed with nothing significant above the second stage.

Sure, but they'll probably still show pictures without showing that the rocket is "headless." Last time, they cropped out the top of the rocket during the WDR.

[ugordan]

Something tells me there is more to this "blackout" than just customer satisfaction. Can't put a finger on it though.......

I'm sure if the WDR is successful they'll put out a press release announcing the activation of the VAFB pad, with a picture of the vehicle that happens to hide anything above 2nd stage.

WDR is performed with nothing significant above the second stage.

I know. And still, at least two times in the past they hid that part of the vehicle from view.

[Jim]

You can fly a trajectory where it doesnt matter where you cut off as your are changing the trajectory/thrust vector acording to your speed increase.

Just look at military rockets. They chase a moving target and they still hit.

Not the same analogy nor applicable.  The military missiles are still thrusting and have excess energy.   Doesn't work for orbital transfers where you don't know what your actual energy gain will be

[meekGee]

My comment was meant to say that for an accurate TMI burn you need a guidance cutoff at a precise delta-V which cannot be guaranteed with a burn to depletion. If your margins are healthy, you would invariably overburn by using up all propellant and missing the Mars flyby by a large margin.

Actually it is possible to do a burn to depletion during TMI if you hava a good guidance system. If you overburn you simply have to adjust your trajectory by pointing the thrust vector of your engine in a different direction. That way you will arrive at mars faster.

yup - you simply no longer will be doing a "minimum energy" transfer.

But, I vote for a GTO "WDR" as the likely intent.