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

[go4mars]

What if SpaceX will perform a TMI with a small payload with the upper stage? Something containing a simple camera, solar panels, cold gas thrusters and high gain antenna? I believe the performance should be enough to do this... a possible fly-by in case Mars "happens" to be close enough to use residual delta-v in upper stage to "take aim" early in flight, which might be possible considering the time is almost right for optimal TMI.

I don't think they would even need to announce it.  Would they? 

At the least, they could take some cool pictures of Earth as it recedes, and if the alignment is wrong for Mars, aim to crash it into some other celestial body.  There may be a few comm elements, or materials tests pertinent to Red Dragon or other future plans that would be worth trying when excess upmass allows. 

[baldusi]

Is Mars and Earth aligned correctly right now for a Mars flyby trajectory?

I don't think the planes are aligned now. Unless you do a very expensive plane change maneuver when you intersect the Mars orbital plane, I don't believe can't really reach Mars right now with a single impulse at LEO.

[DaveH62]

Is Mars and Earth aligned correctly right now for a Mars flyby trajectory?

I don't think the planes are aligned now. Unless you do a very expensive plane change maneuver when you intersect the Mars orbital plane, I don't believe can't really reach Mars right now with a single impulse at LEO.

Could anyone be ready for an X-Prize shot to the moon?

[edkyle99]

Is Mars and Earth aligned correctly right now for a Mars flyby trajectory?

The next minimum energy Mars trajectory window opens during November of this year.  I'm not sure how much extra energy would be needed for a, say, mid-September launch, but we are talking about a stage with almost zero payload.  There must be a calculator out there somewhere.

 - Ed Kyle

[Arthree]

Is Mars and Earth aligned correctly right now for a Mars flyby trajectory?

The next minimum energy Mars trajectory window opens during November of this year.  I'm not sure how much extra energy would be needed for a, say, mid-September launch, but we are talking about a stage with almost zero payload.  There must be a calculator out there somewhere.

 - Ed Kyle

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.

[Soralin]

Well, wild speculation is always fun.

Let's see, two things:  One, you could boost to a Mars transfer orbit anytime you like, for the same cost.  It's just that if you do it at the wrong time, you arrive at Mars-distance from the sun when Mars doesn't happen to be nearby.  Now, if it's just for a test, with a second stage that wouldn't be useful for much else, that could be fine in itself.

Secondly, what if you don't mind not reaching Mars right away?  I mean, if you boost into a Mars transfer orbit, and Mars isn't at the far end when you get there, you'll just find yourself in an elliptical orbit that goes between Earth-distance from the sun, and Mars-distance from the sun.  You won't reach Mars the first time you get out to Mars-orbital distance, but what if you plan to reach it on your 2nd or 3rd or 4th time around?  You could possibly make the launch timing work without needing much extra fuel, if you're willing to loop around multiple times in your orbit before reaching your destination.  Although any such plan would mean a travel time of multiple years at a minimum.

[ugordan]

Why are we still talking about Mars injections? Burn to depletion and TMI are mutually exclusive.

[smoliarm]

Why are we still talking about Mars injections? Burn to depletion and TMI are mutually exclusive.

From what I remember from the course of Orbital Mechanics (18 years ago) - this exactly the truth.
And to be honest, I don't remember much from Orbital Mechanics, but here is one more constraint on wild speculations:
CASSIOPE has near-polar orbit; and it seems to me it's impossible to do TLI from polar orbit with one burn - just like it's impossible for TMI.

[ugordan]

CASSIOPE has near-polar orbit; and it seems to me it's impossible to do TLI from polar orbit with one burn - just like it's impossible for TMI.

If by one burn you mean the first burn of the 2nd stage, then I agree. If you mean one restart after already in LEO, I disagree. You can do TLI and TMI, in case of the Moon it may affect your approach trajectory groundtrack (lunatrack?), in case of Mars it makes no difference as you're injecting into a hyperbolic trajectory away from Earth.

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.

People should stop contemplating such PR stunts and just be happy if the launch vehicle makes the planned orbit and deploys its primary payload successfully, IMHO.

[Chris Bergin]

CASSIOPE's going to Mars?

Let's keep this thread on this mission guys.

[Galactic Penguin SST]

CASSIOPE's going to Mars?

Let's keep this thread on this mission guys.

Nope, someone is speculating whether the empty second stage is capable of being sent on a Martian fly-by trajectory. 

[edkyle99]

CASSIOPE has near-polar orbit; and it seems to me it's impossible to do TLI from polar orbit with one burn - just like it's impossible for TMI.

An upper stage restart is needed for maximum performance to LEO, but it is not always necessary for lighter payloads, depending on orbit.  CASSIOPE is a very light payload for this rocket.

 - Ed Kyle

[Prober]

CASSIOPE's going to Mars?

Let's keep this thread on this mission guys.

someone was mistaken, and thought this was the party thread 

[LouScheffer]

CASSIOPE has near-polar orbit; and it seems to me it's impossible to do TLI from polar orbit with one burn - just like it's impossible for TMI.

An upper stage restart is needed for maximum performance to LEO, but it is not always necessary for lighter payloads, depending on orbit.  CASSIOPE is a very light payload for this rocket.

 - Ed Kyle

This depends more on the orbit desired than the weight.  The heaviest payloads ever orbited, the Apollo missions, did not use a restart to get into LEO.  This was OK since they used *very* low LEO orbits, stable for only a day or so IIRC.  This in turn was OK since within a few hours they would either go to the moon or return home.

[mr. mark]

I think that WDR was scheduled today. Guess we will see if SpaceX offers up a picture. Want to get my first glimpse of the 9V1.1 on the pad.

[PattiM]

I think that WDR was scheduled today. Guess we will see if SpaceX offers up a picture. Want to get my first glimpse of the 9V1.1 on the pad.

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

[LouScheffer]

[...] 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.

[Lars_J]

CASSIOPE has near-polar orbit; and it seems to me it's impossible to do TLI from polar orbit with one burn - just like it's impossible for TMI.

An upper stage restart is needed for maximum performance to LEO, but it is not always necessary for lighter payloads, depending on orbit.  CASSIOPE is a very light payload for this rocket.

 - Ed Kyle

Upper stage restart for LEO injection seems to be the exception rather than the rule for most LVs. All SpaceX missions so far have used direct injection.

[pippin]

All SpaceX F9 missions so far have launched self-propelled spacecraft.

[Lars_J]

All SpaceX F9 missions so far have launched self-propelled spacecraft.

Does RazakSat qualify as that, and the various secondary payloads carried on some F9 flights?